A critical appraisal of a scientific paperVaccine against Dental Caries

: An Urgent Need

Presented by Ghada Elmasuri14-Nov-2013

Contents of the paper

Dental caries is still a major oral health problem. Affecting 60-90% of schoolchildren and the vast

majority of adults in most industrialized countries,. It is the most prevalent oral disease in several Asian

and Latin-American countries . More than 60% of the children aged 5 to 17 years in the

US have decayed, missing, or filled permanent teeth because of dental caries and 91% of dentate adults have caries experience.

Dental Caries Vaccine

Objective of this paper is supporting the development of vaccine to prevent and eliminate dental caries.Development of dental caries vaccine has been under investigation since1968.Three factors are assigned to the development of caries over timewide group of microorganisms can be isolated from carious lesionsS. mutans is the main microorganism involved in the initiation and development of carious lesions.

Antigenic components of S. mutans

Mutans streptococci

glucosyltransferases (GTFs)

N-catalytic sucrose-binding domain (CAT)

C- glucan-binding domain (GLU)

cell- surface protein PAc

Antigenic components of S. mutans targeted by vaccine

GTF-BGTF 1 GTF-CGTF

-S-1 GTF-DGTF-S

Glucosyltransferase (GTF) is the proteins components “ enzyme” that have been associated with virulence and the process of tooth surface colonization and adhesion.

In animal models, it was found; S. mutans that have lost the ability to produce GTF are unable to produce disease.

There 3 forms of glucotransferases and respective genes :

Vaccine hypothesisRecent studies suggest that oral immunization with GTF, has the potential to elicit a secretory IgA antibody response to interfere with accumulation and permanent colonization of S. mutans on tooth surfaces. This protein thus can be utilized for vaccine preparation.

Forms of vaccinehighly purified GTF from S. mutans

Whole killed cell of s.Mutans S. sobrinus cell

Vaccine hypothesis

Teeth

S.mutans

GTF enzym

es

GTF Antige

n

IgA Antibo

dy Associated with adhesion

Utilized as vaccine

Inhibit to produce

Mechanism of Action of Dental Vaccine- 1st mechanism

Saliva contains various immune component “antibodies ,immunoglobulins” like IgA, IgG and IgM in which IgA is the principal immune component.

The salivary IgA react with the bacterial surface receptors It inactivate surface glucosyltransferase (GTF) enzyme produced by streptococi resulting in preventing binding function so inhibiting colonization and subsequent caries formation.

Mechanism of Action of Dental Vaccine- 2nd

mechanism The second important mechanism involves the

migration of antigen IgA from Gut-Associated Lymphoid Tissues (GALT) “The digestive tract's immune system” to salivary glands.

The GALT, has many lymphoid nodules and particularly Peyer’s patches, are a rich source IgA that have the potential to migrate and populate distant lymphoid tissues and the salivary glands then inhibiting the activity of GTF.

Mechanism of Action of Dental Vaccine- 3rd mechanism

In addition to immunoglobulins” IgA, IgG and IgM , saliva also contains various cellular immune components like; lymphocytes, macrophages and neutrophils.On the basis of sufficient evidence, it was found that after a subcutaneous immunization with S. mutans, the organism is phagocytosed “ antigenic processing” by macrophages.

Experimental Studies- Animal trails

Experiments have been conducted by utilizing rodents and monkeys models.

Rodents are inexpensive and easy to maintain but the limitation is the short duration of the experiments compared with caries development time in humans. Therefore monkeys have been utilized for achieving the same results as with the rodents.

Experimental Studies- Animal trails

Immunization of monkeys utilizing a subcutaneous injection of a highly purified GTF from S. mutans or whole cells of S. mutans produced a reduction of about 70% in both smooth surface and fissure caries when compared with controls.

No increase in antibody titer was detected in saliva from monkeys orally immunized with enterically coated capsules containing viable S. mutans or uncoated capsules containing killed cells of the same organism.

Different Routes to ImmunizationHuman trials

Few human trials in adults have shown that it is possible to increase levels of salivary IgA antibodies to interfere with mutans streptococcal colonization .

Different Routes to Immunization

Active immunization -1- Oral route

by oral feeding “vaccine-containing capsules or liposomes”

gastric intubation, Oral immunization of 14 subjects with a coated

capsule containing S. sobrinus resulted in an increase in salivary IgA antibody response when combined with an aluminum based adjuvant “aluminum phosphate capsule” .

Oral immunization of 7 adult volunteers with a coated capsule containing 500 micrograms of GTF from S.mutans also resulted in elevating in elevating salivary IgA antibodies.

Active immunization -1- Oral route

Disadvantage: - Effects of stomach acidity on antigen Rapid breakdown “degredation” of antigenic

proteins “ not long sustained” Low absorption inductive sites were relatively distant. oral immunization with S. mutans is ineffective in

stimulating a secretory IgA response unless combined with an adjuvant.

Adjuvant for the Vaccine

Mucosal application of antigens by themselves rarely results in sustained IgA responses.

Considerable has been expended to develop immunomodulators (adjuvants) that enhance mucosal responses to dental caries vaccines.

Adjuvant is defined as any substance that acts to accelerate, prolong, or enhance antigen-specific immune responses when used in combination with specific vaccine antigens. “have been called the dirty little secret of vaccines”

Types of Adjuvant

1. Synthetic peptides: subcutaneous immunization with a synthetic peptide derived from the GTF “S. mutans” enzyme, induced higher levels of serum IgG antibody.

2. Liposomes : as carriers of small drug molecule and proteins.

Used in delivery of several drugs particularly anticancer, to target the cells where it should reach.

Improve mucosal immune responses by facilitating delivery of s. mutans antigen to lymphoid elements of inductive tissue.

Its efficacy has been found to increase two fold in a rat model.

An increase of IgA antibodies have been found in humans as well .

Adjuvant for the Vaccine

3. Recombinant vaccines: oral immunization with the recombinant Salmonella vaccine was effective in inducing protection against S. sobrinus in rats.

4. Coupling with Cholera and E. coli toxin subunits: It has been found that addition of small amounts of “nontoxin unit” of the Cholera Toxin (CT) or E. coli toxin (LT) can greatly enhance mucosal immune responses to intragastrically or intranasally applied s. mutans antigens and was effective in suppressing the its colonization.

Active immunization- 2- Intranasal route

To induce protective immunity in mucosal inductive sites that are in closer anatomical relationship to the oral cavity.

Targets the Nasal-Associated Lymphoid Tissue (NALT).

When a formula containing 500 micrograms of GTF from S.mutanswas administered intranasally to the tonsils, either in soluble form or incorporated in liposomes, salivary IgA antibodies were also increased.

Active immunization -3- Tonsillar route

The palatine tonsils and especially the nasopharyngeal tonsils, have been suggested as potent sites.

Various trials have shown that topical application of formalin-killed S. sobrinus cells in rabbits can can induce the appearance of IgA antibody in both the major and minor salivary glands and can significantly decrease the consequences of infection with cariogenic S. sobrinus.

Active immunization- 4. Minor salivary gland

Lips, cheeks and soft palate

Experiments in which S.sobrinus GTF was topically administered onto the lower lips of young adults showed that those who received labial application of GTF had significantly lower proportions mutans streptococci/total streptococcal flora in their whole saliva during a six-week period following a dental prophylaxis, compared with a placebo group

Active immunization -5. Rectal

Colo-rectal region has the highest concentration of lymphoid follicles “lower intestinal tract” so this region is an inductive location for mucosal immune responses in humans.

Preliminary studies indicated that rectal immunization with bacterial antigens such as Helicobacter pylori or Streptococcus pneumoniae have induced salivary IgA responses.

This route use can be an alternative for children who have a respiratory disorder that prevent intranasal application of vaccine.

Active immunization -6. Systemic route

Studies have shown that IgG antibodies are well maintained at titre, IgM progressively fall and IgA antibodies increase slowly in titre.

Protection against caries was highly associated with increased serum IgG antibodies.

After subcutaneous administration of S. mutans in monkeys; IgA, IgG and IgM antibodies were produced, find their way into the oral cavity via the gingival crevicular fluid and are protective against dental caries.

The development of serum IgG antibodies takes place within months of immunization.

Active gingivo-7. Salivary route

To limit the potential side effects associated with the other routes of vaccine administration, and to localize the immune response, gingival crevicular fluid has been used as the route of administration as follows:

Injecting lysozyme into rabbit gingiva: elicited local antibodies.

Brushing live S. mutans onto monkey`s gingiva : failed to induce antibody.

Using smaller molecular weight Streptococci antigen resulted in better performance probably due to better penetration.

Passive Immunization “oral application”

Is the transfer of active immunity in the form of ready-made antibodies. “naturally acquired”

Mouthrinses containing bovine milk or hen egg yolk, IgY antibody to S. mutans cells led to short-term decreases in mutans streptococci in saliva or dental plaque.

British scientists at Guys Hospital in London working on ways to inject a peptide that blocks S. mutans into fruits. They have already isolated a gene and the peptide that prevents the bacterium from sticking to the teeth. They are trying to find ways to deliver the peptide into the mouth through apples and strawberries.

Passive Immunization

The latest research in the field of passive immunization is developing a caries vaccine by generating a hybrid immunoglobulin A-G heavy chain from four transgenic tree Nicotiana tabacum.

Itis colourless and tasteless, can be painted onto the teeth rather than injected.

Passive Immunization Advantage: Avoiding any risks that might arise from active

immunization. Cost and of acceptance. Disadvantage: The antibodies can persist in the mouth

for only a few hours at most or up to 3 days in plaque.

New Fusion Anti-caries DNA VaccineMutans

streptococci

glucosyltransferases (GTFs).

N-catalytic sucrose-

binding domain (CAT)

C- glucan-binding domain (GLU)

cell- surface protein PAc

anti-caries DNA

vaccine, pGJA-P/VAX

A fusion of antigenic domains, PAc & GLUaccelerated and increased antibody responses in rabbits saliva compared with nonfusion DNA vaccine.its protective effect against S. sobrinus infection proved to be weak.

Conclusion of the paper Dental caries is a major public health problems

worldwide that has a considerable impact on individuals and communities as a result of the pain and suffering, impairment of function and reduced quality of life.

Animal studies suggest that a great promise in targeting key elements in the molecular pathogenesis of S. mutans wither through active or passive immunization strategies.

Therefore, development of dental caries vaccine as effective prevention measures to integrate any based public health programs should be a main focus.

Paper CritiqueGeneral comments

1. Some information are represented in disarranged and jumbled pattern.

2. Problem in linking and connection between information.

3. Duplicating the information.

Paper Critique scientific comments

Author skewed toward caries vaccine Vaccine is not an urgent need. “ Title” Dental caries has been a problem for humans

since the beginning of time. The earliest recorded reference to dental caries is from a Sumerian text (5,000 B.C.)

The author had over looked the following limitations of dental caries vaccine :

1. The main target is infants & young children, immunization should take place prior to infection “in the second year of life”.

2. Most adults have already experienced dental caries so good response may not be seen.

3. Caries vaccine is mainly targeting S. Mutans.

S. Mutans is not the only cariogenic microorganism “Streptococcus sobrinus, Lactobacillus acidophilus”

Scardovia wiggsiae has been isolated in 2010 and thought to be the main cause of early childhood dental caries (Dewhirst et al.,2010)

Paper Critique scientific

comments

This new pathogen, was present in the mouths of children with severe early childhood caries when other known pathogens such as Streptococcus mutans were absent.

4. Dental caries is multi factorial disease that is highly related to living conditions, lifestyles and environmental factors.

5. The issue of safety. Some patients with rheumatic fever show cross reactivity between heart tissue antigens and certain Streptococci antigens.

6. Debate similar to fluoride “about its effectiveness and

number of vaccine received and ways of delivery

Funds to produce a licensed products and cost barrier for disadvantaged children, FDA approval?.

Paper Critique scientific

comments

Paper Critique scientific

comments Objective of the paper is unrealistic “elimination of caries”!? Its not mentioned number of papers reviewed The conclusion of the paper is not sound and doesn’t answer the main objective and purpose of the paper . The author only considered recommendation of by a ‘Panel on Caries Vaccine’ constituted by ‘National Institute of Dental and Craniofacial Research’ (NIDCR) in 2003.Most of studies results cited in the paper to support the paper objective are based on old studies. New supporting evidences was neglected.

References History of Dentistry: Ancient Origins, hosted on the

American Dental Association website. Page accessed 9 January 2007.

Dewhirst, F. E., Chen, T., Izard, J., Paster, B., Tanner, A. R., Yu, W., . . . Wade, W. (2010 October). The Human Oral Microbiome. Journal of Bacteriology, vol. 192 no. 19 5002-5017. doi: 10.1128/JB.00542-10

Downes, J., Mantzourani , M., Beighton , D., Hooper, S., Wilson, M. J., Nicholson, A., & Wade, W. G. (2011). Scardovia wiggsiae sp. nov., isolated from the human oral cavity and clinical material, and emended descriptions of the genus Scardovia and Scardovia inopinata. International Journal of Systeatic and Evolutionary Microbiology, 61(Pt 1):25-9. doi: 10.1099/ijs.0.019752-0. Epub 2010 Feb 5.

Gross, E. L., Beall, C. J., Kutsch, S. R., Firestone, N. D., Leys, E. J., & Griffen, A. L. (2012). Beyond Streptococcus mutans: Dental Caries Onset Linked to Multiple Species by 16S rRNA Community Analysis. PLoS One, 7(10): e47722. doi: 10.1371/journal.pone.0047722.

World Conference on Social Determinants of Health (2011). "Rio Political Declaration on Social Determinants of Health" (PDF). World Health Organization. Retrieved 2013-03-27.