AIDS Outlook

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The last time you had a cold, you prob-ably sniffled, coughed and stayed athome in bed for a couple of days.All the while, your immune system

fought a quick battle against the cause of thecold: a virus. It was a battle with a foregoneconclusion, as many of them tend to be. Inmost cases, the immune system is triumphant,

and mops the floor with the virus within acouple of weeks.

HIV is no ordinary virus, however. Aftera quick skirmish with the immune system what researchers call the acute phase ofinfection HIV escapes eradication, oftenliving on quietly for years and only much laterdragging the immune system to utter ruin.

In the past few years, researchers studyingthe long road from infection to AIDS have beenparticularly interested inimmune activation a state in which the immune system stays onhigh alert and prepared to fight.

In this condition, the immune system mar-

shals many types of cell into an active mode,ready to sense and attack pathogens. The bodyproduces abundant amounts of signalling

proteins, known as cytokines and chemokines,and a host of other proteins.

This ready and roused state is short lived inthe case of most viruses; however, HIV triggerschronic immune activation. Practically everyarm of the immune system that has been inves-tigated has been shown to be in a hyperactivestate, says Jason Brenchley, an investigator at

the US National Institutes of Health.As immune cells are activated, they become

targets for HIV, so an active immune systemparadoxically amounts to a higher viral load.Cells that constantly replicate when activatedeventually become depleted, causing a prema-ture ageing of the immune system. In a processthat is still mysterious, chronic immune acti-

vation seems to wreck the tissues that produceimmune cells1.

This set of effects has been linked to con-ditions ranging from heart disease to cancer.Even on its own, immune activation makesyou feel lousy, says Daniel Douek, chief of

human immunology atthe US National Instituteof Allergy and InfectiousDiseases Vaccine ResearchCenter.

Long roadThe basic outline of HIVpathogenesis is well chronicled. The virus entersthe body usually through mucosal tissue, suchas the lining of the vagina or anus. Once there,it encounters CD4 cells, which orchestrate theimmune response. The virus gains entry intothese cells, where it insinuates its DNA into host

nuclear DNA. For a day or less, each CD4 cellessentially becomes a factory for viruses, andthen it dies.

This is what allows HIV to persist whereother viruses beat a hasty retreat. Once theacute infection is past, HIV continues to rep-licate and diversify by mutating into many dif-ferent forms, each one a new challenge to theimmune system (see page S6).

Over years of infection, the average personsCD4 cells slowly decline. HIV takes up resi-dence in quiescent immune cells and possiblyin other hideouts (see page S11). The deple-tion of CD4 cells cripples the immune system,

leaving the host vulnerable to any attack, andturning HIV infection into full-blown AIDS.

A key element in this story is pace. Therate of disease progression varies enormouslybetween people, and some elite controllersnever reach the milestones that mark AIDS(see page S4). Scientists can roughly predictdisease course by looking at virus levels in theblood. As far back as 1993, however, research-ers found that elevated levels of CD38+ CD8+cells a subset of immune cells that correlatewith immune activation are a better harbin-ger of AIDS arrival2.

Immune activation is one ofthe oldest ideas in HIV research,notes Carl Dieffenbach, directorof the Division of AIDS at the USNational Institute of Allergy andInfectious Diseases. We have

just rediscovered this more timesthan I care to think about.

Recurring themeWhen researchers first began thinking aboutimmune activation, they saw it primarily as asymptom of the illness.

At the time before we had good drugs, or any

drugs at all, I think that most people thoughtthat [if] we got a good drug and knocked out thevirus, that immune activation would go away,says Susan Plaeger, director of basic research inDieffenbachs division. As therapies that controlthe virus became available, however, it was clearthat immune activation lingers even when viralnumbers are down.

Several new findings have brought immuneactivation back to centre stage, according toresearchers.

First, scientists discovered, about a dec-ade ago,that sooty mangabeys and Afri-can green monkeys, natural hosts of the

HIV-like simian immunodeficiency virus(SIV), do not show immune activation and do

On high alertHIV keeps the immune system in a hyperactive state,gradually leading to its ruin, reports Emma Marris.

HIV damages the gut and makes it leaky, allowing

other pathogens to enter and wreak havoc.

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15 July 2010OUTLOOKHIV/AIDS

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Practically every

arm of the immune

system has been

shown to be in a

hyperactive state.


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not get sick. Rhesus macaques, the experimen-tal model for HIV vaccines, do have immuneactivation, however, and develop AIDS (see

page S5).Second, researchersreported in 2008 that

elite controllers, despite their seemingly goodhealth and negligible viral loads, show someabnormal immune activation3. Finally, manyHIV-infected individuals taking antiretrovi-ral drugs have low viral loads but suffer frominflammation-related diseases of ageing heart disease, liver disease, cancer and per-haps even dementia earlier than do theiruninfected peers.

One trial, called Strategies for Manage-ment of Anti-Retroviral Therapy (SMART),which was designed to study drug scheduling

in HIV-positive people, found that proteinmarkers of inflammation were higher in thosewho died during the trial4. The implication isthat immune activation contributes to mortal-ity from conditions not typically classified asAIDS-related, says Douek.

Overall, evidence from natural host mon-keys and clinical observations suggest that

viral infection and immune activation are bothneeded for progression to AIDS.

Persistence of memoryWhat causes immune activation? Most obvi-ously, it is the virus. Like any invader, it causes

immune cells to wake up and gird their loinsfor battle. It is not clear, however, why the stateof activation should persist for decades.

It might be that the kind of cells that areinfected are so important to the immunesystem that the host has no choice but to tryto get rid of every last bit of the virus, suggestsGuido Silvestri, a pathologist at the Hospitalof the University of Pennsylvania in Phila-delphia.

In particular, the presence of virus in lymphnodes, where central memory CD4 cells live,could keep the immune system engaged infighting the virus, Silvestri suggests. These

cells specialize in retaining information abouta pathogens identity and creating armies ofrank-and-file effector memory cells for whenthe host re-encounters the threat. Tellingly,sooty mangabeys and African green monkeysdo not lose as many central memory cells orshow chronic immune activation.

It doesnt really matter how much virusyou produce in the body, but what kind ofcells are killed, says Silvestri. Not all CD4cells are created equal. Some are really quiteexpendable.

Evidence in the past seven years of a greatdecline of CD4 cells in the gut has prompted

two more theories about how HIV causeschronic immune activation.

In the acute phase, the virus depletes CD4cells in the mucosal tissue of the gut, and theirnumbers never bounce back5,6.In the process,the virus also destroys the gut mucosas struc-tural cells. The gut has holes, it is leaky, saysDouek.

Damage to the guts immunesystem allows other pathogensto make their way to lymphnodes and penetrate the body,where the rest of the immune

system must wake up and fendthem off, says Satya Dandekar,a microbiologist at the Univer-sity of California, Davis.

This immune activation persists even whendrugs knock the virus down to undetectablelevels because the gut has lost its ability torepair itself. Early treatment might preventthis damage, Dandekar says. A lot of benefitthat one sees in early treatment may reallystem from repair of the mucosal sites.

Another, potentially complementary, the-ory suggests that the weakened gut defenceallows pieces of the omnipresent and

generally benign gut bacteria to enter thebloodstream, where they activate the immunesystem7.

This microbial translocation has beenshown in HIV-infected people in severalstudies, mostly in the later stages of disease. InMay 2010, Douek, Brenchley and colleaguesreported in Science Translational Medicinethat HIV infection increases the numbers ofregulatory T cells a subtype of CD4cellsthat modifies the immune response andlowers the numbers of another immune cellthat helps defend the gut mucosa8. The result-ing imbalance might lead to a leaky gut and a

dysfunctional immune system, the research-ers suggest.

Some researchers argue that microbialtranslocation is the consequence, not cause, ofimmune activation, but Douek dismisses thecriticism. Its a circle immune activationcauses leaky gut which causes immune activa-

tion which causes leaky gut,he says. In a sense it doesntmatter [which came first].

Given that immune activa-tion is intricately tied to diseaseprogression, measuring viral

load or even the number ofCD4 cells might not be the bestway to chart the disease, Douek

adds. Doctors could instead count centralmemory CD4 cells or markers of immune acti-

vation and inflammation, and combine severalmeasurements into a standardized algorithmthat predicts the course of infection.

Meanwhile, some groups are trying tocalm the chronically alert immune systemby adapting therapies for other inf lamma-tory conditions some as basic as aspirinor vitamin D and designing drugs to stopmicrobial translocation.

Now that we are able, we believe, tosuppress virus for many, many years withantiretroviral drugs, says Douek, immuneactivation and inflammation in treated indi-viduals may become the greatest obstacle tolong-term health. Emma Marris writes for Nature from Columbia,

Missouri.

1. Sodora, D. L. & Silvestri, G.AIDS22,439446 (2008).

2. Giorgi, J. V.et al.J. Acquir. Immune Defic. Syndr.6,904912

(1993).

3. Hunt, P. W.et al. J. Infect. Dis.197, 126133 (2008).

4. Kuller, L. H. et al.PLoS Med.5, e203 (2008).

5. Guadalupe, M. et al.J. Virol.77, 1170811717 (2003).

6. Brenchley, J. M.et al.J. Exp. Med.200,749759 (2004).

7. Brenchley, J. M.et al.Nature Med.12, 13651371 (2006).8. Favre, D. et al.Sci. Transl. Med.2,32ra36 (2010).

In the acute phase of infection, HIV depletes the guts CD4 immune cells (seen in the bumps on left),

and their numbers never bounce back (right).

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It doesnt really

matter how much

virus you produce in

the body, but what

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Bob Hoff has been HIV-positive since1984. He has never taken antiviraldrugs, yet his immune cells are numer-ous and healthy, and the virus is unde-

tectable in his blood.Hoff is an elite controller who can do what

big pharma and vaccine developers cannot:hold HIV in check and keep AIDS at baywithout medications.

More than 33 million individuals areinfected with HIV, and about 2.7 million join

those ranks each year. However, it is estimatedthat 1 in every 200 people infected never suc-cumbs to the virus1, whereas another 6 or solong-term non-progressors (LTNPs) controlHIV, albeit with a higher viral load, and remainsymptom-free for at least seven years.

Figuring out how these people controlHIV could inspire vaccines and therapiesthat mimic their immune systems. [When]you meet someone whos been infected for25 years, looks entirely healthy and has nevertaken any medications, you just feel like theanswer is standing there for us to just fish out,says Bruce Walker, director of the Ragon Insti-

tute in Charlestown, Massachusetts.Since 2003, the International HIV Control-lers Studyhas examined the factors that keepelite controllers and LTNPs healthy. Otherresearch groups are studying the few peoplewith natural immunity to HIV, who resistinfection even after multiple exposures.

An infected individual carries, on average,about 30,000 copies of HIV RNA per millilitreof blood. Those with AIDS have more than100,000 copies, LTNPs have between 50 and2,000, and elite controllers have fewer than 50,which is well below the detection limit of mostconventional tests.

Last year, Walker showed that the immunesystem in elite controllers cripples the virus,

forcing it to mutate and evolve in a way that

renders it less fit2. These people didnt getinfected with a wimpy virus they made theirviruses wimpy, he says.

Hints from the genomeTogether with researchers at the Broad Insti-tute in Cambridge, Massachusetts, Walker alsoled a genome-wide association study includingabout 1,000 elite controllers. Earlier this yearhis team announced, at a conference in Banff,Canada, that 350 single-nucleotide polymor-phisms (SNPs) clustered in the major histo-compatibility complex (MHC) a region onchromosome 6 rich with immune-response

genes seem to protect elitecontrollers from the effects ofthe virus.

One clue to the role of theseSNPs comes from a study pub-lished in Nature in May thisyear3. Walker and colleaguesreported that a variant of the human leukocyteantigen B (HLA-B) gene located in the MHCboosts the immune response by producingpowerful killer T cells, which recognize anddestroy infected cells. T cells from those whocarry the HLA-B57variant recognize manyparts of the HIV virus and more HIV mutants

than do T cells from controls.About 65% of elite controllers carry theHLA-B57allele, says Mark Connors, chiefof the HIV-Specific Immunity Section at theUS National Institute of Allergy and Infec-tious Diseases. The link between the alleleand T-cell function is an attractive idea, butthe computer models need to be backed upexperimentally, Connors notes.

Quiescent systemsRare individuals with natural immunity toHIV could also yield game-changing discov-eries. These people including sex workers,

haemophiliacs who have received contami-nated blood, and individuals with an infected

partner are repeatedly exposed to the virus,

but never get infected.Some women weve been studying for years

have been exposed hundreds of times to menwe know are HIV-positive. They werent usinga condom, despite counselling, and still theywerent infected, says microbiologist KeithFowke of the University of Manitoba whohas been studying a cohort of commercial sexworkers in Nairobi for more than 20 years.Thats well beyond the realm of luck itssomething really biological, he says.

HIV-resistant women appear to have quies-cent or resting immune systems, Fowke says.They show lower levels of cytokines, which are

signalling proteins that rampup the immune response,and the activity of many non-immune genes is also lowerthan in controls.

The women have moreregulatory T cells, which calm

the immune system, and fewer activated CD4immune cells. However, their ability to fight otherinfections and viruses is not compromised.

HIV infects and replicates better in activatedcells. Fewer targets allow greater opportunityfor the evolution of immune responses thatwould eliminate the virus, says Frank Plum-

mer, scientific director general of the NationalMicrobiology Laboratory at the Public HealthAgency of Canada. The idea that a quietimmune system could be the key is potentiallyparadigm shifting, Plummer adds.

Some reported data contradict this hypoth-esis. Plummer has proposed launching a globalconsortium to study individuals with naturalimmunity. He and others are also trying toidentify the genes that endow the Kenyanwomen with resistance to HIV. Bijal Trivedi is a freelance writer in Washington

DC.

1. Okulicz, J. F.et al.J. Infect. Dis.200, 17141723 (2009).

2. Miura, T. et al.J. Virol.83,27432755 (2009).3. Komrlj, A. et al.Nature465, 350354 (2010).

Learningfrom theeliteResearchers hope to unlock

the secrets of the select

few who rein in, or even

resist, HIV infection, says

Bijal Trivedi.

Some Kenyan sex workers, like Dorothy Mumbe (above), resist HIV infection even after being

exposed hundreds of times to HIV-positive men.

V O T R U N G D U N / C O R B I S S Y G M A

These people didnt

get infected with a

wimpy virus they

made their viruses

wimpy.

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M

ale African green monkeys arenotorious for their striking redpenis, bright-blue scrotal areaand white abdomen. To AIDS

researchers, however, these monkeys andanother African species, the sooty mangabey,are known for a less visible trait.

Both are natural hosts of the simian immu-nodeficiency virus (SIV), which is the primatecounterpart and ancestor of HIV.Althoughinfected monkeys have more than 100,000 cop-ies of SIV per millilitre of blood, they do notget sick or develop anything resembling AIDS.By contrast, Asian macaques infected with SIVmimic the trajectory of human HIV infection.

Understanding what allowsthe African monkeys to coex-ist with SIV could help develop

drugs or vaccines against HIVthat ape their response.

Comparative AIDS researchis essential to figure out what protects us fromtransmission, and what protects us frompathogenesis, says Guido Silvestri, professorof pathology at Emory University.

SIV infections in the natural host monkeysshare similarities with human HIV and macaqueSIV infections; however, it is the differencesthat intrigue researchers. For example, unlikehumans and macaques, female natural hostsrarely pass the virus on to their offspring.

In people, there is a general trend: the more

virus in the body, the faster the progressionto AIDS. This is probably why elite control-lers, whose immune systems can whittle down

viral loads to barely detectable levels, rarely getAIDS (see page S4). By contrast, sooty mang-abeys and African green monkeys with highviral loads remain healthy.

What is more, the natural hosts maintainrelatively healthy numbers of CD4 cells white blood cells that orchestrate the immuneresponse and are targets of HIV in both bloodand the mucus lining of the genital tract.

Evasive targets

One key to the monkeys resilience might bethat they have fewer cells that HIV can infect.

CD4 cells in sooty mangabeys have lower lev-els of the receptor CCR5, which HIV needsto enter the cell. African green monkeyshave fewer surface CD4 receptors, which are

required for HIV infection.Theyve chosen two different ways of

removing target cells of the virus, notes DanielDouek, who leads the Human ImmunologySection of the US National Institute of Allergyand Infectious Diseases Vaccine ResearchCenter. I really think that is the root of whythey dont progress [to AIDS].

Viral load is not the only factor influenc-ing progression. People with low levels ofHIV sometimes show seriousinflammation

and a slow decline in CD4cells. Some such cases slowlyprogress to AIDS, says Steven

Deeks, professor of medicine atthe University of California, SanFrancisco.

There are people who think it is only thevirus, others think it is only inflammation, andwe think it is a little of both, adds Deeks.

When the virus first infects the body, humans,macaques and natural hosts mount a dramaticimmune response. In sooty mangabeys andAfrican green monkeys,this reverts to base-line levels after aboutthree months, whereasit remains high in

humans and macaquesthroughout the chronicinfection.

It is amazing that[the natural hosts] areable to switch off thesepathways of immuneresponse even when

virus replication remainsconsistently high. And itseems that they benefitfrom doing this switchoff, says Silvestri.

One potential trig-

ger for chronic immuneactivation in humans

and macaques could be the loss of T-helper 17(TH17) cells a subset of CD4 cells that is keyfor antibacterial defence. Douek and others

have shown that SIV-infected sooty mangabeysand African green monkeys have healthy levelsof TH17 cells in the mucus lining of the gastroin-testinal tract. Loss of these cells is a hallmark ofprogressing infection in humans and macaques(see page S2).

Model monkeysIn their search for a surrogate for HIV inhumans, researchers use about 20 differ-ent SIV strains and modified SIVs, dubbedSHIVs, to infect different species of macaques.Each virushost combination has strengthsand limitations.

The main problem with the SIVmacaquemodel, says Paul Bieniasz, a virologist at theAaron Diamond AIDS Research Center, NewYork, is that the SIV genome differs by about50% from HIV-1, which is the most prevalentstrain worldwide.

To create a better model for vaccine tests,Bieniasz and colleagues are modifying HIV-1to grow in monkeys. So far, they have createda version that will infect pigtail macaques,initially causing virus levels to reach up toone million copies per millilitre of blood justlike in the initial stages of human infection.

These monkeys do not become sick and,

after six months, their infection mimics thatseen in long-term non-progressors, whonaturally control HIV levels and slow theirprogression to AIDS (see page S4).

We basically have to find a way to make thevirus more robust in pig-tail macaques, saysBieniasz. We need it to trigger AIDS. Bijal Trivedi is a freelance writer in Washington

DC.

The primateconnectionStudies comparing HIV infection and its simian

counterpart in different monkey species are filling

gaps in knowledge, explains Bijal Trivedi.

African green monkeys (left) and sooty mangabeys (right) are natural

hosts of the HIV-like simian immunodeficiency virus, meaning that theynever develop anything resembling AIDS.

R O D W I L L I A M S / N A T U R E P L C O M

BIOSPHOTO/CORDIERSYLVAIN/BIOSP

HOTO/STILLPICTURES

It is amazing that

[the monkeys] are

able to switch offthese pathways.

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W

hen people talk about infec-tious disease, the host is oftendescribed as being at war withthe pathogen, which is an apt

metaphor. Look closely at HIV infection,however, and it also seems like a dance: thevirus and the immune system match eachother, step for step, in a performance as intri-cate as it is deadly.

Each persons immune system is unique anddances differently. Although HIV infection usu-ally leads to AIDS, the timing and course of pro-gression varies greatly from person to person.

In the past few years thanks to methodsthat detect HIV soon after infection research-ers have learnt that the immune response inthe first weeks often sets the long-term courseof the disease. They are also learning how the

body makes antibodies to HIV, and how thisimmune response evolves over time insightsthat might aid the search for a vaccine.

HIV becomes detectable in the bloodstreamabout ten days after the initial infection. Overthe next two to three weeks, it spreads through

the body, replicating wildly. At the same time,killer T cells which recognize and destroyinfected cells begin proliferating rapidly.

HIV levels in the bloodstream peak 21 to 28

days after infection, and T cells spike a week ortwo later. As T cells accumulate, they begin toreduce the amount of virus in the bloodstream.

With some viruses, this is where the danceends. There are many infections we havewhere T-cell immune responses control thevirus, says Sir Andrew McMichael, professorof immunology at Oxford Universitys Weath-erall Institute of Molecular Medicine. In thesecases chicken pox, for example the virusremains in the body, but usually does not causelong-term problems.

In most people infected with HIV, however,killer T cells become progressively less effective.

HIV has an almost limitless capacity to mutate,and in effect is constantly trying on new dis-guises turning the dance into a masquerade.

Because T cells respond to HIV, it is temptingto conclude that the virus leads the dance. Theimmune system also exerts a subtle influence,

however, shaping the evolution of the virus.When virus levels initially peak, HIV is rela-tively homogeneous, with millions of identical

copies of the infecting strain. Last year,researchers showed that the viral sequencelater evolves precisely in the parts to whichthe T cells respond1.

The mutants [are] being selected very rap-idly, within days, right in front of your eyes, saysMcMichael, who led the study. Within weeks,the body is teeming with escape mutants thatthe T cells must learn to recognize.

Handicapped defenceFrom the beginning, HIV selectively targetsand kills CD4 or helper T cells, the mastercoordinators of the host immune response,

notes John Moore, professor of immunologyand microbiology at Weill Cornell MedicalCollege in New York. So you have this holein the immune repertoire.

Eventually, the depletion of CD4 cells leavesthe body susceptible to pathogens, signallingthe progression to AIDS. Even early on, how-ever, the CD4 cells are dysfunctional, impair-ing the immune response to HIV. Withoutfunctioning helper T cells, newborn killerT cells fail to mature, or die prematurely, andso the body becomes progressively less able togenerate new ones as the virus evolves.

Three to six months after infection, the level

of HIV in the bloodstream stabilizes to a setpoint. This predicts the course of an individ-uals disease: a higher set point usually meansa quick progression to AIDS, and a lower setpoint means a slower sequence.

What defines the set point is not fullyunderstood, but theres some sort of bal-ance between the nature or virulence of thevirus and the immune response of the host,McMichael says. For example, a highly viru-lent strain of HIV is likely to result in a high setpoint even if the immune response is strong.

The varying strength of the immune responsecan be traced (see sidebar) in large part to

human leukocyte antigen (HLA) molecules.Three types of HLA class I molecule, HLA-A,HLA-B and HLA-C, are found on the surface ofevery host cell. These HLA molecules hold onto protein scraps from the virus and signal tothe killer T cells that the cell is infected.

The genes for these HLA molecules arethe most variable in the genome each hashundreds of different alleles. This variability,reshuffled each generation, allows the body torecognize a huge variety of pathogens.

TheHLA-B gene seems to have the strongestoverall effect on HIV, says Mary Carrington,head of the HLA Immunogenetics Section at

the US National Cancer Institute. Those whocarry some HLA-B alleles, such as B27, B57

Dancing with anescape artistSarah DeWeerdt describes the intricate relationship

between HIV and the host immune system, each

influencing the others next moves.

HIV (red) selectively targets and kills CD4 immune cells (pink), the master coordinators of theimmune response.

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andB58, tend to develop AIDS slowly. Otheralleles, such as B07and B35, are associatedwith a rapid progression.

Those alleles that offer protection bind tohighly conserved HIV proteins that are essen-tial to the virus function. If the virus mutatesin these proteins, it often does so at a cost,becoming less virulent and contributing toa lower set point. In contrast, less protectivealleles bind pieces of proteins that HIV can

mutate away and not have any effect on viralfitness, Carrington says.

Slow burnThe dance with HIV includesanother set of partners: anti-bodies that recognize and bindto viral proteins. Antibodiesappear early in HIV infec-tion, at a similar time to killerT cells. The early antibodies are not effective,however, and do not reduce virus levels in thebloodstream.

Antibodies that neutralize HIV and pre-

vent it from infecting cells are produced aboutthree months after exposure. This is relativelylate compared with the response to many viralinfections, and might be partly due to viraldamage to B cells and the germinal centreswhere they mature.

These problems have long been known tooccur in chronic HIV infection; however,researchers showed last year that they beginin the first weeks or even days of infection2.It was surprising to find that there was suchearly destruction and damage to germinalcentres, says lead investigator Barton Haynes,director of the National Institutes of Health-

funded Center for HIV/AIDS Vaccine Immu-nology (CHAVI).

When neutralizing antibodies finally areproduced, the virus mutates to evade them,the body fashions a new response, the virusescapes again, and so on, in an endlessto-ing and fro-ing between the antibodysystem and the virus, says Dennis Burton,professor of immunology and microbialscience at the Scripps Research Institute inLa Jolla, California. But there isnt any greatimpact [of the antibodies] as far as we can see

on the overall virus replication.Two to three years after

infection, about one in everyfour or fivepeople infectedwith HIV begins to makebroadly neutralizing antibod-ies, which inactivate manydifferent strains. Ironically,bythe time they make the anti-bodies, these people have too

much virus, too many flaws in the immuneresponse and too many reservoirs for the virusto benefit from them. What is more, HIV canmutate to evade these antibodies much faster

than the body can develop new ones.Still, broadly neutralizing antibodies aresomething of a holy grail for vaccine research-ers. Theyre the sorts of antibody responsesthat wed like to elicit or induce through vac-cination, says Burton.

Two large-scale efforts are under way, onecoordinated by CHAVI and the other by theInternational AIDS Vaccine Initiative, to under-stand better how these antibodies are made. Foreach effort, researchers took blood samplesfrom hundreds of people every few months,beginning a few weeks after HIV infection.

The researchers plan to isolate the broad-

est, most potentantibodies from the partici-pants, then retrace how the virus and antibody

response have evolved. The exciting thing forme is that more and more people are becom-ing interested in the host side of this, saysHaynes. Were going to have to understandthis area of biology before [an HIV] vaccineis going to be made. Sarah DeWeerdt is a freelance writer in Seattle.

1. Goonetilleke, N. et al.J. Exp. Med.206, 12531272 (2009).

2. Levesque, M. C.et al.PLoS Med.6, e1000107 (2009).3. Fellay, J. et al.Science317, 944947 (2007).

Immune cells (like the one above, in green) exert a subtle influence on the evolution of the HIV virus (red).

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For years, scientists have been trying to

understand why some people with HIV

quickly develop AIDS and others seem

more resistant. One method, genome-wide association, involves scanning

bits of DNA scattered throughout the

genome to look for variations more

common in the latter group.

A handful of studies have identified

several single-nucleotide polymor-

phisms (SNPs) associated with better

control of HIV. Most variants are in

human leukocyte antigen (HLA) mol-

ecules, which help the immune system

to recognize infected cells.

For example, the first genome-wide

association study of HIV linked a variant

of theHLA-C

gene to a stronger immuneresponse and slower progression to

AIDS3. Variations in HLA-B also seem to

delay disease course.

Results from an international study

of about 2,000 HIV-infected individu-

als, expected to be published later this

year, confirm the importance of the HLA

system, says Mary Carrington, head of

the HLA Immunogenetics Section at the

US National Cancer Institute.

These studies reliably pick up common

variations present in at least 4% of the

population. Rarer variants might also

affect HIV control, notes David Gold-

stein, director of the Center for HumanGenome Variation at Duke University.

To identify rare variants, he argues,

researchers should compare whole

genome sequences rather than looking at

markers for differences.

Goldstein is planning to sequence

the genomes of at least 50 people who

have been infected with HIV for years

but have not developed AIDS. He also

plans to compare the genomes of peo-

ple who progress relatively rapidly with

those who progress slowly.

Although the high cost and slow

speed make whole-genome sequencing

difficult, both limitations are rapidly

diminishing, Goldstein says. A lot of

this story is going to be told over the

next two or three years. S.D.

Geneticinvitation

Theres some sort of

balance between the

nature or virulence

of the virus and the

immune response of

the host.

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Last September, after more than 20 yearsof disheartening research, HIV vaccineresearchers had their first, albeit small,taste of success.

In a clinical trial of about 16,000 people in

Thailand, the candidate vaccine RV144 low-ered the rate of HIV infection by about 30%.

RV144 remains far from market, but thetrial gave the field a badly needed boost. AfterMercks much-hyped V520 failed in 2007,many researchers questioned whether a suc-cessful vaccine could be developed.

We showed for the first time that its pos-sible, says Jerome Kim, deputy director of sci-ence at the US Military HIV Research Programand a lead investigator onthe RV144 trial.

No one yet knows why RV144 worked orhow to improve on it; however, this glimmerof success, together with recent clues to other

ways to boost the immune response to HIV,has researchers feeling optimistic. This reallyis a renaissance, says Wayne Koff, chief scien-tific officer of the International AIDS VaccineInitiative (IAVI) in New York.

Thai mysteryVaccines generally rely on two tactics: trickingthe immune system into producing antibodies

that can bind to key parts of a virus and pre-vent it from infecting cells; and activating theimmune systems cellular response, which tar-gets and destroys infected cells.

The trouble is that HIV varies widely even

within an infected individual. HIV infectiontends to elicit antibodies and immune cellsthat are specific to one particular strain, andno help against others.

This variability defeated vaccine efforts untilRV144. In this combination formula, ALVAC(developed by Sanofi Pasteur) is designedto elicit a cellular immuneresponse, whereas AIDSVAX(made by Global Solutionsfor Infectious Diseases) isdesigned to induce produc-tion of antibodies1.

The odds were against this combination

from the beginning: ALVACs efficacy hadnever been tested alone, and AIDSVAX hadflopped in two previous trials. One group ofleading researchers was so sure of failure theycalled on the government to scrap the study.So why did the combination succeed?

Barton Haynes, head of the NationalInstitutes of Health (NIH)-funded Center forHIV/AIDS Vaccine Immunology, is prob-ing this mystery by analysing blood samplesfrom trial participants. We need to studythis trial to try and understand everythingwe possibly can about what happened andwhy, Haynes says.

Genetic diversityMeanwhile researchers are hunting forbroadly neutralizing antibodies, which canbind to numerous HIV strains and block themfrom infecting cells. A vaccine that could trickthe body into producing these antibodiesmight prevent infection.

In 2009, researchers from IAVI and TheScripps Research Institute in La Jolla, Cali-fornia, isolated two broadly neutralizingantibodies from the blood of an HIV-positiveindividual in Africa2. Last October, at a con-ference in Paris, NIH researchers announced

three more antibodies that bind to a new targeton the virus. Weve clearly broken through a

wall, says Gary Nabel, head of the NIHs Vac-cine Research Center.

Isolating the antibodies is only half the

challenge. How can the vaccine prompt thebody to produce them? Thats the $64,000question, says Dennis Burton, director ofIAVIs Neutralizing Antibody Consortium,and professor of immunology and microbialscience at Scripps.

Burton and others are trying reverse engi-neering techniques working backwardsfrom the antibody structure to buildmolecules that stimulate the body to producethem.

In March, at a meeting in Banff, Canada,Merck researchers announced that they havedesigned a molecule that elicits a neutralizing

antibody in guinea pigs and rabbits. It is thefirst time that this kind of reverse engineer-ing process has been validated on the biologicside, says Koff, so its a real advance.

Some groups are exploring strategies thatbypass the immune system. For example, ateam at the Childrens Hospital of Philadelphia

has devised a way to insert thegenes for these antibodies intocells using an engineered virus.These recombinant vectorsproduce enough antibodies toprotect monkeys from infec-

tion with an HIV-like virus3. The team plans

to test the concept in people.A good vaccine would also boost the cellular

immune response. To overcome HIVs diver-sity, researchers are testing artificial geneticsequences that mimic parts of its genomebut cover the widest possible array of strains.These sequences are not [ones] that are foundin their entirety in any naturally occurringvirus, says Dan Barouch, chief of vaccineresearch at Beth Israel Deaconess MedicalCenter in Boston, Massachusetts.

Injected into rhesus monkeys, these mosaicsequences incite an immune response broaderand deeper than with the natural virus4,5. A

clinical safety trial is planned, Haynes says.Although these studies seem promising,continuing obstacles make HIV research-ers loath to predict when a vaccine might beready.

What you can say is that it would be a majormiracle if we had one in less than ten years,Nabel says. On the other hand, were doingeverything we can to surprise ourselves. Cassandra Willyard is a freelance writer in New

York.

1. Rerks-Ngarm, S. et al.N. Engl. J. Med.361,22092220(2009).

2. Walker, L. M.et al.Science326,285289 (2009).3. Johnson, P. R. et al. Nature Med.15,901906 (2009).

4. Barouch, D. H. et al.Nature Med.16,319323 (2010).5. Santraand, S. et al.Nature Med.16,324328 (2010).

Tiny steps towardsan HIV vaccineRecent successes are reinvigorating research into a

vaccine for HIV, reports Cassandra Willyard.

Although no one yet knows why, a candidate vaccinecalled RV144 seems to prevent HIV infections.

APPHOTO/MHRP

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Were doing

everything we can to

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Developing a vaccine against HIVhas proven infinitely complex, butdesigning alternative methods ofprevention has not been any easier.

Of the handful of strategies tested in recentyears, only male circumcision has been anunequivocal success. Older strategies, such as

condoms and needle exchange, all soundedmore promising than they turned out to be.

After decades of disappointment, research-ers are turning to antiretroviral therapy theone tool proven to stop the virus in its tracks.Trials are under way to test whether oralantiretroviral pills or gels laced with the drugscan prevent infections. Researchers are alsotesting whether treating infected individualsearly can make them less infectious (see side-bar on page S12).

We are in a new antiretroviral-based pre-vention generation, says Mitchell Warren,director of the AIDS Vaccine Advocacy Coa-

lition, a New York-based non-profit organi-zation aimed at accelerating HIV-preventionresearch.

Scientists are also assessing combinationsof two or more of the strategies for examplecondoms, needle exchange, male circumci-sion and antiretroviral drugs.Because no new preventionintervention will be a silverbullet, we must understandthe optimal combinations ofinterventions, says StefanoBertozzi, HIV director for theBill & Melinda Gates Founda-

tions Global Health Program.The ideal prevention strategyis cheap, effective and easy to use. Althoughcondoms meet these requirements, many menare reluctant to use them. In the early 1990s,researchers began thinking about strategiesthat women could control. They estimated thata microbicide that is 60% effective at prevent-ing HIV infection could prevent 2.5 millioninfections in just three years1.

Unfortunately, the microbicide field hasbeen plagued by failures. Scientists havedeveloped dozens of candidates, and led atleast six into clinical trials. Despite promising

preclinical data, however, each has failed toprevent infection. Alarmingly, a couple even

appeared to increase womens risk of contract-ing the virus.

In December, researchers reported the mostrecent failure: a gel called PRO2000, which hadshown promise in a small study, but had noeffect on HIV transmission in a trial of 9,385African women.

Preventive pillsThese disappointing results were not a majorsetback, says Sharon Hillier, professor ofobstetrics, gynaecology and reproductive sci-ences at the University of Pittsburgh in Penn-sylvania. We had already moved on to thenext generation of products, which are muchmore potent.

The new generation of microbicides, twoof which are in clinical trials, are laced withpotent antiretroviral drugs. Results fromthe first trial, a 900-person test of a vaginalgel containing tenofovir, are expected to be

announced in July at the International AIDSConference in Vienna.

The preventive power of antiretroviral pillshas been harnessed before, to block transmis-sion of the virus from mother to unborn child.For example, a single dose of the antiretroviral

nevirapine, given to the motherduring labour and to the infantafter birth, cuts HIV transmis-sion by more than 40%.

Scientists reason that thepills might also prevent the virus from taking hold inuninfected adults. This pre-

exposure prophylaxis (PrEP)strategy is being tested in atleast five independent trials. The first resultsare expected later this year. We are goingto get our first glimpse at whether thesenew approaches with antiretrovirals work,Warren says.

For such methods to be effective, they mustbe used regularly daily or before every riskysexual encounter. That might be feasible in thecontrolled setting of a clinical trial, but imprac-tical in the real world, notes Robin Shattock,professor of cellular and molecular infectionat St Georges, University of London.

Some researchers are devising ways to makethese methods easier to use. For example, a

vaginal ring much like the ones used for

contraception could deliver low doses ofthe drug for a month or more. Researchers atWeill Cornell Medical College in New Yorkhave designed a ring that delivers both antiret-roviral drugs and contraceptives, although ithas not been tested outside the laboratory2.

Similarly, antiretroviral injections that lastfor several months, like the contraceptiveinjection Depo-Provera, might be prefer-able to a daily pill. The less you have to thinkabout it, the more likely it will be adopted,Shattock says.

Aggressive strategies

Scientists have known for more than a decadethat people who have low viral loads are lesslikely to pass on the virus. Some studies haveshown that treating HIV-infected individu-als early decreases their risk of infecting theirpartners. One research teamis testing thisapproach dubbed treatment as prevention in a clinical trial of 1,750 couples.

Last year, the World Health Organization(WHO) proposed that an aggressive globalstrategy of yearly universal HIV tests andimmediate antiretroviral treatment for thoseinfected could dramatically slow the spread ofHIV within a decade, and reduce prevalence

to 1% within 50 years3

.Many experts argue, however, that this testand treat approach will be difficult to imple-ment. I think it will be a challenge even inthe US, let alone in places with a much higherHIV burden, says Connie Celum, director ofthe University of Washingtons InternationalClinical Research Center in Seattle. How doyou think about test and treat when its sucha long way to go to even treat those who willdie in a few years if they dont get [antiretro-virals]?

The US National Institutes of Health (NIH)is planning to test a less-regimented strategy

in Washington DC and New York Citys Bronxneighbourhood. The three-year study, set to

Joining forcesNo single strategy alone is likely to thwart HIVs spread.Researchers are turning to prevention packages of two

or more approaches, Cassandra Willyard reports.

Because no

new prevention

intervention will be a

silver bullet, we must

understand the

optimal combinations

of interventions.

This Chinese device, a ShangRing, holds the

foreskin in place, allowing it to be snipped away

quickly with no stitches required.

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10/21

N

ot long ago, you would have beenhard-pressed to find an HIVresearcher who would utter the wordcure.

HIV has a remarkable ability to resist anti-viral drugs and hide in the body, so the idea oferadicating the virus seemed impossible. Sug-gesting otherwise, researchers feared, couldcreate false hope and complacency.

In the past few years, however, there areincreasingly loud whispers about a cure forHIV. The year 2007 saw the clinical debut ofintegrase inhibitors, which prevent HIV frominserting into the host genome. The followingyear, a bone-marrow transplant eliminated thevirus from the body of an infected Germanman (see sidebar, Interfering with genes). Lastyear, breakthroughs in cell-culture techniques

allowed researchers to screen for drugs thatcan lure HIV from its hiding places.

I was very pessimistic five years ago, butwe had to try, says Warner Greene, direc-tor of the Gladstone Institute of Virologyand Immunology in San Francisco. And asweve tried, Ive become much more optimis-tic that we might be able to achieve a drug-free remission.

His optimism is understandably tinged withcaution, however, as scientists promising erad-ication were proven wrong once before.

In the summer of 1996, researchers attend-ing the eleventh international AIDS meeting

in Vancouver trumpeted data showing thatcertain combinations of antiretroviral drugscan suppress HIV to undetectable levels inthe blood.

The buzz grew over the course of the fol-lowing year. In May 1997, David Hos groupat the Aaron Diamond AIDS Research Insti-tute in New York reported inNature that HIVlevels in eight people dropped by two ordersof magnitude within ten days of receiving aparticular three-drug combination and wereundetectable within eight weeks1.

Using a mathematical model, the research-ers estimated that, barring any complications,

the drugs could eradicate the virus from aninfected person in less than three years.

If that sounded too good to be true, it was.In the same issue of the journal, Bob Sili-cianos group from Johns Hopkins Univer-sity inspected the small number of dormant

immune cells that harbour HIV. Because thesecells do not replicate, they are impervious totreatment. Once activated, however, his teamfound that these cells can start pumping outthe virus into the blood and lymph nodes2.

Two other groups described these so-calledlatent reservoirs in 1997, and two years later Sili-cianos team estimated that it would take about60 years for drugs to flush out HIV from thesestores3. It was a real blow, I think, to people whowere interested in eradication, Siliciano says.

The field instead shifted focus to preventingresistance by using combinations of three ormore drugs dubbed highly active antiretro-

viral therapy (HAART) andto decreasing the side effects oftreatment.

These efforts were hugely suc-cessful: there are 32 approvedHIV drugs, and at least a dozenmore in the pipeline (Table 1),which, together, can suppressthe virus for decades.

Now that HAART works sowell, Siliciano says, were turning to the nextstep: can we actually cure anybody?

In the pipeline

Like most viruses, HIV hijacks its hosts cel-lular machinery to replicate. HIV is a memberof a particularly nefarious family of viruses,however, which insert their DNA into thehost genome. When the host cell replicates,its daughters make more virus.

Antiretroviral drugs target different stagesof this replication cycle, limiting the viral loadand allowing immune cells a chance to clearout infected cells. The most widely used drugsblock the enzymes that HIV needs to infectnew cells. The standard regimen includes twodrugs that block reverse transcriptase, whichHIV needs to convert its RNA genome into

DNA, and one protease inhibitor that preventsviral particles from maturing.

In 2007, Merck released raltegravir. Thiswas the first drug to target HIVs integraseenzyme, which stitches the viral DNA intothe host genome.

Clinicians welcomed drug cocktails spikedwith raltegravir after large clinical trials showedthey trounce drug-resistant strains of HIV, andsuppress virus levels significantly faster than dostandard combinations. Several other integraseinhibitors are in the pipeline, and early datasuggest that they are better than raltegravir.

The number of papers on HIV integraseinhibitors has just boomed over the last twoyears, notes Yves Pommier, chief of the Labo-

ratory of Molecular Phar-macology at the US NationalCancer Institute. Its marvel-lous that now we have veryeffective inhibitors for all thethree HIV enzymes it willbe very hard for the virus toescape them all.

Other HIV proteins mightalso make good targets. In 2002,

Michael Malim and colleagues fired up the fieldwith the discovery that one of these proteins,Vif, degrades a human enzyme, APOBEC3G,which evolved eons ago to damage viral DNA4.

Without Vif, APOBEC3G would block HIVreplication.That basic research is starting to pay off,

and many scientists are hunting for drugs thatblock Vif. In 2008, Greenes group at the Glad-stone Institute launched a collaboration withGilead Sciences to find Vif inhibitors.

Another tactic is to target the host cell,rather than the virus. HIV primarily attacksCD4 T cells, which normally help the immunesystem fend off invaders. A handful of newcompounds block CCR5, which is a receptoron the surface of CD4 cells that HIV must bindin order to penetrate the cell.

In 2007, Pfizer debuted the first CCR5blocker, maraviroc, which is effective at keeping

The outlookfor a cureThere is a formidable arsenal of drugs available to treat

HIV. Virginia Hughes finds that, for the first time in years,

there is also renewed hope of a cure.

Protease inhibitor drugs (spheres) bind to a

viral enzyme (yellow) and prevent HIV particles

from maturing.

P H A N T A T O M I X / S C I E N C

E P H O T O L I B R A R Y

Its marvellous that

now we have very

effective inhibitors

for all the three HIV

enzymes it will be

very hard for the virus

to escape them all.

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viral levels in check. However, people whohave been on HAART for long periods tend tocarry HIV strains that use the CXCR4 receptorinstead of CCR5. Drugs that block CXCR4 arealso being developed, but animal studies sug-gest the drugs are toxic.

Daily doseNo matter how effective the available drugs,the harsh reality is that they must be takenfor life although when to start them is anequivocal point (see sidebar, Perfect timing). Iftreatment is interrupted, HIV rapidly springs

back into action, rising to detectable levelswithin weeks.Partly to make taking the medications more

palatable, and partly to keep the HIV drugarsenal stocked with new compounds, manycompanies have invested in making pills thatcombine multiple drugs.

Taking one pill a day is much easier thantaking two or three, says Michael Mullen,acting chief of infectious diseases at MountSinai Medical Center in New York. Pharmais realizing that the most important challengein antiretroviral therapy is improving adher-ence by simplifying regimens.

So far, only the commercially available pillAtripla one of the most widely prescribed

HIV drugs in the United States combinesdrugs from different classes. More are on theway, however.

Last year, GlaxoSmithKline and Pfizertogether launched ViiV Healthcare, a com-pany that will focus on creating new antiret-roviral medicines, particularly combinationpills. In April, Gilead Sciences began phaseIII testing of its Quad pill, which combinestwo reverse transcriptase inhibitors and oneintegrase inhibitor.

These combinations might make taking thepills less cumbersome, but they will not be able

to alleviate the harsh side effects. Depending onwhen therapy is begun, the lifespan for thoseon HAART is 10 to 30 years shorter than aver-age. They also suffer from a host of conditionsincluding heart, kidney, liver and bone disease,cancers and serious cognitive problems.

Some studies suggest that these compli-cations are more the result of a sustainedinflammatory response to the virus than ofdrug toxicity. In either case, the chronic prob-lems are a natural consequence of long-terminfection.

The ideal HIV drugs would not just sup-press the virus, but would eliminate it from

the body something that is just beginningto look feasible.

In 2008, doctors in Germany made an

astounding announcement: they had

wiped out HIV from a middle-aged man

when they gave him a bone-marrow

transplant to treat his leukaemia.

The doctors had replaced the bone

marrow with that of a donor who

carried a genetic variation that disrupts

the function of the CCR5 receptor in

T cells. When this molecular doorway

is broken, HIV cannot enter host cells.

To this day, despite having stopped all

antiretroviral therapy, the man has no

detectable HIV in his blood.

Bone-marrow transplants are not a

practical option for treating HIV

infection: upwards of one in three people

who receive them die, and they cost at

least US$150,000. Still, the case offers

hope for scientists using gene therapy

to tinker with CCR5, and perhaps other

genes involved in HIV replication.

For example, RNA interference, which

is a method of silencing genes, has been

shown to prevent the virus from repli-

cating and mutating in cultured T cells.

Researchers have also launched several

clinical trials using methods to modify the

CCR5 gene in host cells.

Carl June and his colleagues at the

University of Pennsylvania are harvest-ing T cells from HIV-infected individuals

and disrupting the CCR5 gene using

zinc fingers protein components that

recognize specific DNA sequences and

turn genes on or off. Preliminary results

from the 18-person trial are expected in

March 2011.

At a conference in January this year,

June reported that the gene therapy

has allowed one participant who is off

antiretroviral treatment to maintain

undetectable levels of virus for two

weeks longer than is typical.

Last year, the first randomized andplacebo-controlled test of a gene

therapy for HIV showed that a technique

that uses ribozymes RNAs that cut

other kinds of RNA to disrupt HIV

genes is safe, but does not reduce viral

load.

Although these methods have not yet

been proven effective, the potential

benefits have encouraged researchers.

Drugs have to be taken every day, but

gene therapy could do the same thing in a

one-time treatment, notes Ben Berkhout,

professor of virology at the University of

Amsterdam. V.H.

Interferingwith genes

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How early should someone infected with

HIV begin treatment? Doctors in the

developed world recommend drugs when

the number of an infected individuals

CD4 immune cells falls to less than 350

per cubic millimetre of blood. Many

doctors in the United States say

treatment should begin as soon as HIV

infection is diagnosed, even if CD4

counts are normal.

This very aggressive approach is

new, and its based on non-definitive

data, says Steven Deeks, professor of

medicine at the University of California,

San Francisco.

Still, Deeks supports early interven-

tion because research has shown that

lower CD4 levels pre-therapy lead to

more age-related problems. The longer

you wait, the more inflammation, the

more immunologic dysfunction and

perhaps more of these diseases will

occur, he says.

The longer you wait,

the more inflammation,

the more immunologic

dysfunction and perhaps

more of these diseases

will occur.

In April 2009, a report in the New

England Journal of Medicine found that

beginning therapy when CD4 levels are

less than 350 cells per cubic millimetre of

blood carries a 69% higher risk of death

compared with levels of 351 to 500 cells

per cubic millimetre.

This was an observational study,

however, so researchers could not deter-

mine whether certain characteristics of

people who get early treatment such

as better drug-adherence rates or less

recreational drug use explain why they

fare better.To resolve the debate, an international

research team last year launched a

randomized, prospective clinical trial,

called the Strategic Timing of Antiretro-

viral Treatment, which is projected to run

until 2015.

Even if early treatment is beneficial,

cautions Gregg Gonsalves, an AIDS

activist who has been on antiretroviral

therapy for 15 years, actual clinical

practice may play out entirely differently,

in terms of peoples ability to stay adher-

ent to medications and deal with side

effects.V.H.

Perfecttiming

Elusive targetTo eradicate the virus from the body, scientistsmust first pinpoint its hiding places. HIV isparticularly good at staying invisible. In 1997,three teams independently discovered oneHIV reservoir: resting memory T cells. Thesecells stay quiet for decades, and are activatedonly when the immune system encounters aninvader that it has seen before.

An HIV-infected individual carries about

one million infected resting memory cells.However, while in this state, these cells areinvisible to the immune system. The only wayto destroy the reservoir, scientists reason, isto stimulate the cells to begin making virus,thereby rendering them vulnerable to antiret-roviral drugs.

In the late 1990s, researchers used agentssuch as interleukin-2 growth factor, whichactivates all T cells, to prod the cells outof their resting state. Provoking a globalimmune response is dangerous, however,and can trigger massive leakage of fluids intotissues.

One alternative is to tickle the latent cells sothat they express HIV proteins without repli-cating themselves. For example, inhibitors ofhistone deacetylases enzymes that suppressHIV transcription could stimulate latentcells to produce HIV.

Screening for such drugs is technicallychallenging because resting T cells tend todie in culture. In the past year, however, sev-eral groups have genetically or chemicallyengineered the cells so that they can survivelonger in culture, allowing scientists to screenfor drugs that target the viral reservoirs.

Its actually fairly easy to find compounds

that turn on latent HIV without causing globalT-cell activation, says Siliciano. Weve already

found several. Although the compoundsidentified so far are probably too toxic for usein people, he notes, it is encouraging that thetechnique works on the small scale.

There might also be many other reservoirs inwhich HIV replicates at low levels. These couldbe blood stem cells, other immune cells such asmacrophages, or inaccessible caves such as thebrain or the gastrointestinal tract.

If were going to come up with an eradica-

tion strategy, its not going to be just as simpleas purging the virus from T cells, says MarioStevenson, professor of molecular medicine atthe University of Massachusetts.

Last year, several leading researchers calledfor a large collaboration involving academia,industry and the government to identify HIVshiding places and investigate ways to drag thevirus out of them5(see page S21).

The ultimate test for any treatment thatattempts to clear out the reservoirs is to takepatients off therapy and see whether theirviral loads stay in check which some deemunethical.

Even the most enthusiastic researchersadmit that the field is far from understand-ing latency, and is at least a decade away fromproducing compounds that could clear out theviral reservoirs. If history is any guide, how-ever, they will not stop trying.

Scientists are stubborn, Stevenson says.That persistence on the part of the scientificcommunity hopefully exceeds the persistentqualities of the virus. Virginia Hughes is a freelance writer in New

York City.

1. Perelson, A. S. et al. Nature387, 188191 (1997).2. Chun, T. K.et al. Nature387, 183188 (1997).3. Finzi, D. et al. Nature Med.5,512517 (1999).

4. Sheehy, A. M. et al. Nature418,646650 (2002).5. Richman, D. D.et al. Science323, 13041307 (2009).

Although antiretroviral drugs are effective, they must be taken for life, and can cause harsh side effects.

ROBERTOBOREA/APPHOTO

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Leadership Initiative, a five-year programmethat recruits established institutions to thefight against HIV. In February this year, theCDC also initiated the I Know campaign,which encourages young people to talk aboutHIV on social networking sites.

Prevention campaigns should also be tai-lored to specific high-risk groups, such as sexworkers at truck stops, homosexual men whouse crystal methamphetamine or older womenmarried to injecting drug users, experts say.

Health authorities have avoided publiclysingling out marginalized populations, notesBruno Spire, research director of the Marseille

branchof the Institut National de la Sant etde la Recherche Mdicale. The solution is to

empower these groups, so its not about preven-tion for these groups but prevention with thesegroups, says Spire, who is HIV-positive.

Peer educationSpire and colleagues are experimenting withpeer-to-peer outreach programmes, in whichhigh-risk community members educate oth-ers. In one preliminary project showing earlysuccess, MSM who are not medical profes-sionals were trained to administer diagnostictests to others in four French cities.

In 2006, the CDC recommended mak-ing HIV tests a part of routine medical care.

The following year, UNAIDS and the WHOproposed similar guidelines. A complex webof social, psychological, legal and financial fac-tors prevent many people at risk from gettingtested, however.

For example, lack of health insurance, cul-tural misconceptions and worries over immi-gration status deter many economic migrantsfrom learning their status. Laws that prosecuteindividuals who knowingly transmit HIV alsoprevent high-risk groups from seeking care.

Many perceive themselves often wrongly as being at low risk, says Christoforos Mal-louris, director of programmes at the Amster-

dam branch of the Global Network of PeopleLiving with HIV. For instance, few preventionor testing schemes target the elderly.

Even in 2010, the stigma associated withHIV cannot be underestimated, adds Mal-louris, who is HIV-positive.

[In the MSM community] I hear a lot ofrejection because of HIV status and see a lotof sero-sorting of partners according to sta-tus, so you see a lot of positivepositive andnegativenegative couples, he says. This isan indication of the ignorance of what is reallyrisk. Instead of learning about it, people try todeal with it by not dealing with it at all.

According to UNAIDS, an estimated 21% ofHIV-infected individuals in the United States

and 27% in Canada are unaware of their HIVstatus. In Europe, up to 38% of infected peopleare diagnosed after the virus has caused irrep-

arable damage to their immune systems.The problem is that when these patients

finally do enter care, most are at a very latestage of infection, says Jens Lundgren, direc-tor of the Copenhagen HIV Programme andprofessor of viral diseasesat the University ofCopenhagen. This late percentage situationhas not improved at all, and remains an abso-lutely unresolved problem in the developedworld.

Early diagnosis is important for several rea-sons. A growing body of research suggests thatearly and easy access to treatment and supportservices can limit the virus spread.

For example, a widely discussed 2008 analy-sis by the Swiss National AIDS Commissionfound that an HIV-positive person with anundetectable viral load after six months ofantiretroviral therapy who has no other sexu-ally transmitted infections carries a negligiblerisk of passing on the virus.

Prevention fatigueAs HIV/AIDS has matured into a chronicdisease, developed nations face a host of newconcerns, including the care of long-term sur-

vivors and the best time to initiate antiretrovi-ral treatment (see sidebar on page S13).

Long-term survivors can grow tired of prac-ticing safe sex, adhering to the demandingdrug regimens and informing new partners oftheir HIV status what experts call preven-tion fatigue notes Koen Block, executivedirector of the Belgium-based European AIDSTreatment Group.

They also struggle with depression, socialisolation and loneliness. One 2006 study of 914people in New York City found that two-thirdsshowed symptoms of depression. We also see

very fragile and inadequate social networks fora lot of these folks, says Mark Brennan, seniorresearch scientist at the New York-based AIDS

Community Research Initiative of America,which conducted the study.Medical problems associated with taking

antiretroviral drugs for many years are a sober-ing reminder that, despite all that scientistshave learnt, there is a long way to go beforeinfected people can live trouble-free lives.

Antiretroviral therapy is really one of thegreat advances of modern medicine peopleare getting decades of productive life out ofthese drugs, notes Steven Deeks, professorof medicine at the University of California,San Francisco. Theyre just not yet getting acomplete life. Paroma Basu is a freelance writer in Lausanne,

Switzerland.

Demonstrators outside the White House in Washington DC protest against declining funds for

HIV/AIDS prevention and cure.

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Mambo?The single Kiswahili word for How are

you? arrives in a weekly text message fromthe AIDS clinic in Nairobi.

From Kajiado, 200 miles away, the clinicspatients, mostly members of pastoral Maa-sai communities, respond with Sawa(OK)or Shida (problem). If, after two days, thepatient does not respond, a nurse followsup with a telephone call. This simple systemconfirms that patients remember to take theirdrugs and are feeling well.

The scheme, which began in May 2007,takes advantage of the fact that, even thoughthe roads between Kajiado and Nairobi arepoor, the mobile telephone service is inex-pensive and reliable.

The texting scheme is the brainchild of

researcher Richard Lester, who noticed thatabout one-half of his patients in Nairobiowned mobile telephones and about 90% hadaccess to a shared telephone.

With funds from the US Presidents Emer-gency Plan for AIDS Relief (PEPFAR),Lesterand the University of Nairobi in 2007 launcheda randomized trial to test whether mobiletelephones can help improve follow-up andoutcome in patients in remote rural areas. Pre-liminary analysis of the data suggests that thosewho participate have lower viral loads, making

them less likely to develop drug resistance ortransmit the infection.

This has huge implications, says Lester,assistant clinical professor at the University

of British Columbia. Hospitals and clinics inKenya and Ethiopia are planning to adopt thescheme, he says.

Mobile telephones are just thelatest strategy in the developingworlds fight against HIV/AIDS.In the past three decades, thesecountries have launched aware-ness campaigns, built testing and counsellingfacilities, expanded their research capacity, col-laborated in international trials and negotiatedfor better access to drugs. With no vaccine ormicrobicide in sight, governments are devisinginnovative approaches, including door-to-door

testing and social networking sites.

Innovative approachesIn April this year, South Africa, until recentlythe poster child for AIDS denialism, launchedthe countrys biggest HIV testing programme.President Jacob Zuma publicly disclosed hisHIV statusnegative to lessen the stigma.The government also announced free male-circumcision services as part of its preventionprogramme.

To those who have been on the front lines ofthe disease from the beginning, the landscapeis dramatically different.

When as a very young doctor I saw my firstHIV patient with Kaposis sarcoma, I thoughtit was something unique. I did not anticipatethe devastation that would unfold before me,says Salim Abdool Karim, director of the Cen-tre for the AIDS Programme of Research inSouth Africa (CAPRISA). Yet, [if] I have seenthe devastation, I have also seen the miracle ofhope offered by antiretrovirals, Karim says.

Despite undeniable gains, however, thecourse of the epidemic remains largelyunchanged. In sub-Saharan Africa, for everyperson who gains access to antiretroviraldrugs, two get infected with HIV, Karim says.

New complications arise all the time. HIVhas revived tuberculosis (TB; see page S18),

making room for deadlier, drug-resistantversions. As in richer nations (see page S14),doctors in some developing countries are see-

ing early heart attacks and kidney failure inHIV-positive individuals.

Its like we are running backwards on thetreadmill, Karim says. We are not stemmingthe tide of the epidemic.

Broken promisesPrevention programmes in most developingcountries rely largely on international funds,which are vulnerable to donor fatigue and theglobal economic downturn.

Despite lofty promises, many donor agencieshave not delivered. For example, the GlobalFund to Fight AIDS, Tuberculosis and Malaria

pledged US$10 billion a year when it was setup in 2001, but has delivered only US$3 billiona year so far.

In 2009, funds from US-basedcharities except from the Bill& Melinda Gates Foundation had decreased by 3% since2007/2008, and funds from

European charities had decreased by 7% since2006,according toan April 2010 report fromthe International Treatment PreparednessCoalition of HIV-infected people and theirsupporters.

Abandoning the AIDS response now will

inevitably lead to a return to headlines aboutpeople dying of AIDS that we read at thebeginning of the decade, the report warns.

PEPFAR is one of the few schemes to havemaintained funding. Launched in 2003 bythen-President George Bush, it was extendedfor a further five years in 2008. This legisla-This legisla-tion authorizes up to US$48 billion to combatglobal HIV/AIDS, TB and malaria.

In a time of tightening budgets and eco-nomic constraints, this request for the eighthyear of PEPFAR is the largest request to datein a presidents budget, says Eric Goosby,PEPFARs US global AIDS coordinator.

PEPFAR programmes continue to scaleup prevention, treatment and care forHIV/AIDS. According to a September 2009analysis, PEPFAR has directly supportedantiretroviral therapy for more than 2.4 millioninfected individuals.

As welcome as donor aid is, however, itcan skew national priorities. As an example,Karim points to South Africa, where HIVresearch infrastructure expanded impres-sively, with international studies on both basicand clinical research.

But much of the research agenda meetsinternational rather than domestic priori-

ties, Karim notes. For example, South Africais researching HIV vaccines, but not the high

DevelopingsolutionsThere is more to combating HIV in the developing world

than providing affordable drugs. T. V. Padma looks at the

innovative new strategies being employed.

Text messages sent to mobile telephones are

helping clinics in Nairobi follow up on patients in

remote villages.

TOMFOX/DALLASMORNINGNEWS/CORBIS

We are not

stemming the tide

of the epidemic.

HIV worldwide

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levels of infection among its young women orwhy a substantial increase in condom distribu-tion from 8 million in 1994 to 376 million in2006 has not reduced its rate of new infec-tions in high-risk groups.

National governments are no better at fund-ing their AIDS programmes. At an April 2001summit in Abuja, Nigeria, 52 African coun-tries pledged to allocate at least 15% of theirnational budgets for health. In 2007, only three(Botswana, Djibouti and Rwanda) were on

track, and three others (Burkina Faso, Liberiaand Malawi) had reached some targets.

These slow and bureaucratic governments areno match for the rapid shifts in the epidemic.

HIV/AIDS in Central and Southeast Asiahas spread from injecting drug users to theirsexual partners. In countries such as India andPakistan, the epidemic once spread mainlythrough commercial sex work and drug use, butis increasingly affecting heterosexual couples.

Affordable drugsDeveloping countries also need to sustain andexpand treatment programmes that depend

on cheap HIV drugs, the demand for whichcontinues to grow.Over past years, international charities have

taken the lead in providing cheap medicines tothe poor. For example, the Clinton Foundationhas negotiated lower prices with 8 firms on 40drug formulations and with 12 suppliers for test-ing kits. This has translated into cheaper drugsfor two million people, nearly one-half of theinfected population in developing countries.

Much credit also goes to India and Brazil,which thumbed their noses at drug companiesand encouraged other developing nations todo the same.

Before 2005, Indian laws recognized patentsonly for the process used to make a drug, not

for the drug itself. Indian companies used thisloophole to produce cheap generic versions ofexpensive antiretroviral drugs.

These days, 92% of those receiving treatmentin low- and middle-income countries takegeneric drugs made in India the pharmacyof the developing world.

In 2000, Brazil threatened to issue a com-pulsory license a clause in international pat-ent law that allows countries to waive patentsduring national health emergencies arguing

that its growing AIDS epidemic was a nationalemergency.

It carried out its threat in 2007, issuing acompulsory license to import efavirenz which prevents HIV from replicating froman Indian firm. In 2008, Brazils patent officealso rejected a patent for tenofovir.

Following in Brazils defiant footsteps, abouta dozen developing countries have issuedcompulsory licenses. Brazil revolutionizedglobal AIDS treatment and shaped globalAIDS treatment policy, says Amy Nunn,assistant professor of medicine at BrownUniversity in Rhode Island.

Things could go wrong again, however. In2005, India agreed to recognize internationalpatents, meaning its companies can produceonly generic drugs that are already on the mar-ket. In five or ten years, this is likely to create aserious shortfall in affordable drugs.

It is a very complex issue, says MauroSchechter, professor of infectious diseases atthe University of Rio de Janeiro. We needmore innovation but at the same time, peopleshould have access to treatment, Schechtersays. How do you do both at the same time?We have not found the answer.

One potential solution is UNITAID, a

not-for-profit patent pool set up in March2010, in which drug companies forgo their

patent rights in selected countries, and allowlocal firms to make medicines with mutuallyagreeable licence fees.

Networks of hopeDeveloping countries are also coming up withinnovative solutions to their own, and others,problems in different arenas.

For example, in the late 1990s, the Boston-based non-profit group Partners in Healthfounded the HIV Equity Initiative to provide

treatment and care to infected people in Haiti.This small charity has grown into a network ofnine health centres that serve 1.2 million peo-ple under a national programme supported byHaitis health ministry.

In 2007, a doctor from Haiti set up a similarrural clinic with volunteers in the mountainsof Lesotho, an African country with no medi-cal school and about 80 doctors to attend to itstwo million people.

India, Brazil and South Africa are also col-laborating on research projects, including HIVvaccines, combating HIVTB and creatingmaps of viral diversity.

Brazil provides locally made HIV drugsto almost a dozen countries in Central andSouth America, and in Africa. In March thisyear, several Portuguese-speaking countriestogether set up a network on HIV and sexuallytransmitted diseases.

At an individual level, too, the urge to helpand support each other is obvious. In Kajiado,for example, those who receive the weeklyMambo? text forward it to relatives who arenot part of the Kenyan trial.

As people become more connected, theybecome more hopeful, says Lester. Hoperemoves stigma. T. V. Padma is a freelance writer in New Delhi

and South Asia editor of SciDev.net

Despite undeniable gains against the epidemic, in countries like India (pictured above) and Pakistan, the epidemic is spreading to heterosexual couples.

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S

ayoki Mfinanga calls it the monsterfor the way it wreaks havoc on a body.

Co-infection with HIV and tubercu-losis (TB) can be devastating, trigger-

ing rapid weight loss, severe pneumonia and,often, a quick death.

Treating both diseases simultaneously doesnot improve matters, and in fact can cause fatalkidney and brain damage. We dont under-stand what happens when you combine TBand AIDS drugs, says Mfinanga, director ofthe Muhimbili Medical Center at the NationalInstitute for Medical Research in Dar esSalaam, Tanzania.

With weakened immunity, HIV-positivepatients are highly susceptible to TB, and TBmakes HIV disease progress quicker. Accordingto a 2009 World Health Organization (WHO)

report, there were more than 1.4 million casesof TBHIV co-infection worldwide, resultingin about 0.5 million deaths in 2008. In sub-Saharan Africa, home to nearly 80% of thoseinfected with both diseases, TB is the leadingcause of death for HIV-infected individuals.

TB might be an important reason why HIVpatients in the developing world suffer higherrates of mortality after beginning antiretroviraltherapy, says Steve Lawn, asso-

ciate professor of infectiousdiseases and HIV medicine atthe Desmond Tutu HIV Cen-tre in Cape Town. Althoughthe probability of death afterthe first 12 months of antiret-roviral therapy is about 1.8%in developed countries1, Lawnand colleagues found that the rate is as high as26% in sub-Saharan Africa2.

In May 2010, the Center for Global HealthPolicy drew together leaders in US sciencepolicy and advocacy to discuss the alarmingincrease in TB fuelled by HIV in the develop-

ing world. In 2008, TB killed more peoplethan anytime in recorded history, said PeterCegielski, team leader for drug-resistant TB atthe US Centers for Disease Control and Pre-vention. In sub-Saharan Africa, thats purelybecause of HIV.

The deadly fallout of co-infection is forc-ing officials to take notice and revise theirpriorities. We consider co-morbidity of HIVand TB so prominent that it makes sense to useHIV money for TB research, says AnthonyFauci, director of the US National Instituteof Allergy and Infectious Diseases. In fact,Fauci says, what Im planning to do is to uti-

lize some of our clinical trial networks thatwere only for HIV to study TB alone and TBwith HIV.

Exacting its tollIn the past few years, access to HIV medi-cines in the developing world has improved.As more individuals have begun taking thedrugs, however, they have faced unexpectedcomplications. Interactions between drugsfor HIV and TB can cause nausea, allergicreactions and joint pain. Rifampin, which isthe mainstay of TB treatments, weakens theefficacy of antiretroviral drugs such as pro-

tease inhibitors and the non-nucleoside inhib-itors efavirenz and nevirapine. The Bacillus

Calmette-Gurin (BCG) TB vaccine can belethal in HIV-infected infants.

Many TB patients who were previously

improving with drugs relapse after startinga course of immune-boosting antiretroviraltherapy, with a paradoxical reaction calledimmune reconstitution inflammatory syn-drome (IRIS). It may be that as antiretroviraldrugs improve immunity, an inflammatoryreaction is directed at the mycobacterium caus-ing TB, and that reaction gives rise to the IRISsymptoms, says Graeme Meintjes, senior clini-cal researcher at the University of Cape Town.

IRIS typically occurs two weeks after TBpatients begin taking antiretroviral drugs. Thelymph nodes in the neck swell, high fevers hit

and dry coughing begins. Some

patients develop abscesses,stomach pain or kidney dam-age. About one person in everyten who develop IRIS has men-ingitis or inflammation of thebrain, and many of these peopledie. Because definitions of IRIS

vary and there are no diagnostictests, reports of its frequency range from 8% to43% of TB patients taking AIDS drugs3.

IRIS was first described in the mid-1990s,but has become more common since. Theresno question that the large-scale roll-out ofantiretroviral therapy has helped millions of

lives, but to be blind to the consequences ofmassive interventions, which are lifelong anddelivered to a large proportion of your popu-lation, is not helpful, says Robert Wilkinson,professor of infectious diseases at the Univer-sity of Cape Town.

In some cases, the immune-suppressingsteroid prednisone can mitigate IRIS. Becauseof the risk of side effects such as diabetes, highblood pressure and osteoporosis, however,prednisone should not be given for more thana few months. Worse, if prednisone is given topeople who have drug-resistant TB or anotherinfection that could be mistaken for IRIS, it

might exacerbate the condition.

Eye of the monsterOne way to prevent IRIS might be in the tim-ing of antiretroviral therapy. Some clinicianstry to avoid IRIS by delaying antiretroviraldrugs until after the patient has completedTB treatment, but a February 2010 reportof a controlled clinical trial in South Africacast doubt on this strategy. The researchersreported that twice as many people died inthe group that delayed taking antiretroviralsas in the group that treated both diseases atthe same time4.

This has stirred some controversy: in June2010, other researchers challenged the study

Fightingthe monsterCo-infection with HIV and tuberculosis is a potent

combination. Amy Maxmen investigates the impact

of this deadly duo.

Many tuberculosis patients on the mend relapse

after taking antiretroviral drugs, developingswollen neck glands and high fevers.

GRAEMEMEINTJES

We considerco-morbidity of HIV

and TB so prominent

that it makes sense to

use HIV money for TB

research.

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design5, and questioned the influence of drug-resistant TB6 and other factors that contributeto IRIS7. Three ongoing large trials are explor-ing the ideal time for those on TB treatment tobegin antiretroviral therapy.

Other researchers are testing various com-binations of antiretroviral and TB drugs.Forinstance, Wilkinsons team is assessing thesafety of combining HIV treatments with theTB drug isoniazid. The WHO recommends

isoniazid over rifampin for HIV-positive indi-viduals in areas of high TB prevalence who donot show signs of TB, although it has not beenrigorously tested in this setting.

Frustrated doctors say they hope that aseach new HIV or TB drug enters the market,they will not need to scramble to learn howco-infected patients react.

We quite often sit at meetings where phar-mas try to convince us to use their [HIV]drugs for South Africa, but unless the drugsare compatible with pregnancy and TB, unlessthey are compatible with rifampin, they arentvery useful for us, says Linda-Gail Bekker,

deputy director of the Desmond Tutu HIVCenter. They need to be tested in pregnantwomen and TB patients but that rarely hap-pens, and often thats an afterthought.

Some drug developers, however, are finallyrealizing the importance of developing TBsolutions that work for HIV-positive patients.You cant use a TB vaccine worldwide on amassive scale and screen everyone in advancefor HIV thats impractical, says GordonDouglas, executive chairman of the AerasGlobal TB Vaccine Foundation, a non-profitorganization that partners with companies todevelop TB vaccines.

The clinical trial for one of Aeras lead can-didates, AERAS-402, includes HIV-infected

adults in South Africa. Animal data sug-gest that it will be safe for infants with HIV,Douglas says. Thus far, there have been noserious adverse reactions in adults. DavidMcMurray, an immunologist at Texas A&MCollege of Medicine who is not affiliated withAeras, says the vaccine ought to be perfectlysafe in HIV-positive individuals. Results areexpected before 2013.

Clinical trials for HIV vaccines have not yet

been designed with TB patients in mind, how-ever. A fundamental issue is that if someonehas an episode of TB and develops immunedysfunction, will that affect the ability of thatindividual to mount a response when theyregiven an HIV vaccine? asks Clive Gray,department head of HIV immunology at theNational Institute for Communicable Diseasesin Johannesburg. The way to answer that isto do an HIV vaccine trial in people withimmune memory to TB, but its not really onthe agen

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