MALARIA VACCINE

Deluxini SundralingamSaifuddin Syed

Malaria

Mosquito-borne disease

Transmitted by inoculation of plasmodium parasite sporozoite stage

Sporozoites invade hepatocytes, transform into liver stages

Subsequent liver-stage development leads to release of pathogenic merozoites

http://www.youtube.com/watch?v=VfxjJVLKWZw

Malaria Parasite

There are five species of Plasmodium protozoa which infect humans via mosquitos:

P. falciparum P. vivax P. malariae P. ovale P. knowelsi

Malaria Statistics

• 3 billion people are at risk of infection

• 225 - 300 million cases of malaria occurring annually

• 780,000 - 1 million attributable deaths worldwide

• Deaths occur in young children and pregnant women in developing countries

• Extraordinary cost in terms of human morbidity, mortality and economic burden

Geographic Distribution

Malaria Control Measures

3 major control measures exist and have been widely used in the last decade in an effort to reduce or control malaria

Artimisinin based Combination Therapy (ACT)

Long-lasting insecticidal nets (LLIN) or Insecticide Treated Nets (ITN)

Rapid diagnostic tests

Current Malaria Treatments

Quinine Chloroquine Amodiaquine Pyrimethamine Proguanil Sulfonamides Mefloquine Atovaquone Primaquine

Disadvantages

ACT has limiting factors: adopting policies, limited knowledge on safety in pregnancy, and the imbalance between demand and supply Recently WHO has recommended that a ban be placed on oral

artimisinin bases monotherapies due to emergence and spread of drug resistance.

LLIN/ITN There is also growing resistance to the insecticide used on nets;

45 countries have identified resistance to one of the four classes of insecticides used

Why Vaccines?

Shortfalls of control measures and continuing prevalence of malaria, the focus has shifted

WHO identified vaccines as a cost effective method to reduce the burden of this disease ▪ cost-effective analysis revealed the economic benefit of

reducing or eliminating malaria is enormous

▪ cost effectiveness of vaccines in public health indicated an economical return in improved health per dollar spent

Malaria Vaccine Rationale

Assumptions for Vaccines against Malaria

▪ Antibody-mediated protection ▪ Cell-mediated immune responses of the T-cells▪ Subsequent infections would recall both types of immune

responses

RTS,S

The focus of the presentation will be on RTS,S

Devloped in partnership by GSK, MVI-PATH, Bill and Melinda Gates Foundation, Academic Instituions and African Countries.

GSK announced that the eventual price of RTS,S will cover the cost of manufacturing, and a 5% return to be reinvested in R&D for second-generation malaria vaccines or vaccines against other neglected tropical diseases.

LifeCycle

Malaria parasite has a complex lifecycle; there are 3 areas of lifecycle development that are the focus of vaccine development research:

Pre-erythrocytic stage

Asexual erythrocytic stage (blood stage)

Sporogonic cycle (sexual stage)

Vaccines in Development

Development of RTS,S Circumsporozoite protein (CS)

A hybrid vaccine was created which combined an independent T-cell epitope along with the P. falciparum CS protein and hepatitis B surface antigen; hybrid was called R16HBsAg

R16HBsAg: included 16 tandem repeats of the epitope of the P. falciparum CS protein fused with the pre-S2 region of HBsAg

Aluminum salts (adjuvants) + R16HBsAg increased antibody response to the CS epitome in mice and rabbits

Clinical trials of R16HBsAg showed that R16HBsAg was safe and immunogenic

All the participants of the trial were given doses at monthly intervals; 20 displayed anti-CS antibody response, 17 displayed antibody titer of ≥ 1:1200, and 13 with anti- CS antibody response 10 months after vaccination

Development of RTS,S

R16HBsAg was later redesigned to include T- and B-cell epitopes from the C-terminus of the CS protein and was renamed to RTS,S

Novel particle was named RTS: ‘R’ for the CS repeats, ‘T’ for T-cell epitopes and ‘S’ for HBsAg. ‘S’ for genetically transformed yeast strain used to produce

these antigens, expressed two polypeptides, RTS and S, with a resulting 1:4 ratio

RTS,S and Adjuvants GSK developed and own the proprietary rights on the adjuvant systems (AS)

5 different types of adjuvants used in the formulation RTS,S AS01, AS02, AS03, AS04 and Alum

Alum and AS04 contain aluminum salts; which are safe and prolong immune stimulation via recruitment of antigenpresenting cells (APCs)

AS04, AS02 and AS01 also contain 3-deacylated monophosphoryl lipid A (MPL) MPL triggers immunity, humoral and cellular immune response by promoting the maturation of APCs by acting upon TLR-4

AS03 and AS02 use oil (squalene)-in-water-based emulsion; the oil phase contains a unique substance DL-a-tocopherol. DL-a-tocopherol enhances antigen-specific response, early eosinophil and neutrophil migration, antigen loading in monocytes, and affect cytokine production

AS02 and AS01 contain the saponin QS21; QS21 stimulates antibody and CTL responses to antigens

RTS,S Trials in Adults Late 1990s the first RTS,S field trials were conducted in adults in Gambia

and Kenya. In the phase II trials RTS,S was combined with AS02A; RTS,S/AS02A,

was found to be safe, well tolerated and immunogenic. Before the third vaccination, test group had an increase of twenty fold

concentration of antibodies against the CS protein Maintained an increase of tenfold during the following year This combination provided heterogeneous protection against strains

other than its original strain Overall 34% vaccine efficacy versus parasitic infection, During peak malaria transmission season, a fourth round of

RTS,S/AS02A was administered; the result was higher antibody concentrations and a vaccine efficacy of 47%

RTS,S Trials in Adults

The combination of RTS,S/AS01B was found to be superior to RTS,S/AS02A in humans

The results found a higher level of antibodies against the CS protein in patients with RTS,S/AS01B when compared to patients with RTS,S/AS02A

It was also demonstrated that those participants administered with the vaccine had a higher blood concentration of antibodies then the participants in the control group with and efficacy rate of 30%

This gave further support for the superiority of the RTS,S/AS01B formulation and led a decision to evaluate in a paediatric population

RTS,S Trials in Paediatric Population

Starting in 2001, 2 separate phase I trials began in paediatric population at risk for sever malaria In the phase I trials RTS was combined with AS02A with different

vaccine doses tested for. The trials showed safety, immunogenicity, and the doses were well tolerated in all population

In 2003 phase II trials began in paediatric populations, At the 6 month interval, efficacy for first episode of disease was

30% and efficacy against sever malaria was 57.7% At 45 months the population was tested again to reveal efficacy for

first episode of disease was 30.5% and efficacy against sever malaria was 38.3% while also revealing 25% reduction in malarial disease

RTS,S Trials in Paediatric Population

Another 2 trials were setup afterwards to examine RTS,S/AS02D in infants After 3 months trial 1 showed vaccine efficacy of 65.9% and an overall

efficacy against infection at 35.5% After 3 months trial 2 showed vaccine efficacy of 65.2% and an overall

efficacy against infection at 41.8%

Another paediatric formulation was developed and tested for paediatric population due to its success in adults; RTS,S/AS01E In 2007, clinical trials conducted showed improved safety and

immunogenicity when compares to RTS,S/AS02D Over an 8 month period vaccine efficacy for first episode was reported at

53% and at 15 months was reported to be at 45.8%

Phase III Clinical Trial

Randomized, controlled and double-blinded 2 age categories : 6 to 12 weeks of age 5-17 months of age 3 study groups with children

who received all 3 doses of the vaccine administered at 1-month intervals and scheduled for a booster dose 18 months after the third dose

who received the primary vaccination series without a booster

control group who received a non-malaria comparator vaccine.

Efficacy of RTS,S/AS01

Reduced clinical episodes of malaria and severe malaria by half

Efficacy of RTS,S/AS01 in 2011 and 2012 during 12 months of follow-upAge Group Severe Malaria Clinical Malaria

6 to 12 weeks of age 36.6% 31.3%

5-17 months of age 47.3% 55.8%

Safety of RTS,S/AS01

Serious Adverse Events

Number of Deaths

Among the infants died, only 10 were due to diagnosis of malaria

Age Group RTS,S/AS01 Control Group

6-12 weeks 569/4358 293/2179

5-17 months 1048/5949 642/2974

Age Group RTS,S/AS01 Control Group

6-12 weeks 49 18

5-17 months 56 28

Safety of RTS,S/AS01

Other serious adverse events occurred after vaccination includes seizures, pyrexia, myositis and febrile convulsion

The most frequently reported symptoms were pain and fever. Overall, RTS,S/AS01 vaccine was more reactogenic than was control

Result of RTS,S/AS01 Phase 3 Trial

1 month after the administration of the third dose of a study vaccine, 99.9% of children and 99.7% of infants in the RTS,S/AS01 group were positive for anti–circumsporozoite antibodies

Other Vaccines for Malaria

SPf66 AdCh63/MVA MSP1 PfSPZ MSP3 GMZ2 AMA1-C1/Alhydrogel +CPG 7909 FMP1AS02A

Bibliography

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