Aids Vaccine - Frequently Asked Questions

AIDS VACCINE - FREQUENTLY ASKED QUESTIONS

Dr Ira Shah
Editor – Pediatric Oncall
Pediatrician
Incharge, Pediatric HIV and TB Clinic, B.J.Wadia Hospital for Children

Is AIDS vaccine possible?
Yes, AIDS vaccine is possible. The neutralizing HIV antibodies have been identified thus vaccine that can lead to formation of these neutralizing antibodies can lead to protection. Also the mechanism and protection of simian immunodeficiency virus (SIV), (a virus similar to HIV in Chimpanzees) has been identified and one can apply same principle for Human immunodeficiency virus (HIV).

What are the drawbacks in preparing HIV vaccine?
Though several advances have been made in the goal towards AIDS vaccine, there are still hurdles that have to be overcome.

1.

HIV virus is of two types – Type 1 & 2. Also there are several subtypes for e.g., in India HIV-1 subtype C is prevalent whereas in Africa HIV-1 subtype B is prevalent. Thus the vaccine should provide protection against all types & subtypes of HIV virus.

2.

HIV virus mutates very rapidly. Thus vaccine should take care of mutated virus too.

3.

CD4 cells are the helper T cells that help for both cell mediated as well as humoral immunity. With a vaccine, the antigen is presented by skin dendritic cell and macrophages to the T lymphocytes that form neutralizing antibodies by stimulating B cells and memory cells by stimulating other T cells. Thus, on exposure to the HIV virus, the memory cells are activated and neutralizing antibodies are produced in large amount that destroy the virus. However in HIV infection, the virus affects the CD4 cells itself and thus vaccine induced memory cells may not function.

What are the goals of an HIV vaccine?

HIV vaccine should offer the following protective mechanisms.

	1.	Prevent infection with HIV virus.
	2.	In case infection still occurs, it should prevent progression of the disease.
	3.	In case infection still occurs, it should prevent transmission of the HIV virus from an infected person to a non-infected person.

What are the types of HIV vaccine under research?
There are several types of HIV vaccines that have been considered.

	a)	Live attenuated vaccine – This consists of inactivated HIV virus. However, since there is whole virus present, there is always a risk of activation of the virus and thus transmission of the disease. Thus live attenuated vaccine is never considered for HIV vaccine.
	b)	Subunit vaccine – This consists of a part of the protein of the HIV virus and that is injected to form neutralizing antibodies. Since only part of the virus is injected, there is no risk of transmission of the disease. However, this vaccine did not form neutralizing antibodies as expected.
	c)	Recombinant vaccine – This consists of part of the HIV gene that encodes for the protein that stimulates formation of the neutralizing antibody. Since only part of the gene is taken, there is no risk of transmission of the disease. This recombinant vaccine can also be given with a vector to enhance its efficacy. Presently all clinical trials of HIV vaccine are working on this principle and research is heading towards recombinant HIV vaccine.

Are HIV vaccine trials going on?
Currently AIDS vaccine trials are going on in over 30 centers in two dozen countries. The vaccine trial at present has successfully completed Phase 1 study in few centers.

What are various phases of HIV vaccine trial?
There are 3 phases through which the HIV vaccine trial will have to pass through before it can be implemented in general population.

Phase 1 trial – Is just to establish safety of the vaccine. Around 20-30 volunteers from a low risk population for HIV virus exposure are needed to establish this phase of the trial.

Phase 2 trial – Not only establishes the safety of the vaccine but also checks for formation of neutralizing antibody. Thus, it checks for both safety and efficacy of the vaccine. Over 200-400 volunteers are needed for this phase of the trial.

Phase 3 trial – It checks for the actual protection given by the vaccine by enrolling volunteers from high risk population of getting HIV in the trial. This phase needs around 1000 volunteers, successful completion of this phase of trial establishes the success of the vaccine and the vaccine can then be recommended for use in general population.

What are the reasons for slow progress in AIDS vaccine trial?
The major drawback in slow progress of HIV vaccine trial is the lack of volunteers for the trial. Also as vaccine trial requires lot of funding and resources. Currently the AIDS vaccine trial is being supported by IAVI (International AIDS Vaccine Initiative). However, resources are still lacking as needed and so progress is slow.

Last updated: 1^st December 2009
Advance Access: 1^st March 2009.

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	1.	HIV virus is of two types – Type 1 & 2. Also there are several subtypes for e.g., in India HIV-1 subtype C is prevalent whereas in Africa HIV-1 subtype B is prevalent. Thus the vaccine should provide protection against all types & subtypes of HIV virus.
	2.	HIV virus mutates very rapidly. Thus vaccine should take care of mutated virus too.
	3.	CD4 cells are the helper T cells that help for both cell mediated as well as humoral immunity. With a vaccine, the antigen is presented by skin dendritic cell and macrophages to the T lymphocytes that form neutralizing antibodies by stimulating B cells and memory cells by stimulating other T cells. Thus, on exposure to the HIV virus, the memory cells are activated and neutralizing antibodies are produced in large amount that destroy the virus. However in HIV infection, the virus affects the CD4 cells itself and thus vaccine induced memory cells may not function.