Human behavior, especially human sexual behavior, is extremely difficult to change. So, best modality for preventing the spread of HIV infection is the development of a safe and effective vaccine. Historically, vaccines have given us a safe, cost-effective, and efficient weapon for preventing disability, illness, and death from infectious diseases.
Successful vaccines for the most part are prepared on the basis of fact that the body can mount an adequate immune response to the microbe or virus in question during natural infection. Even with serious diseases such as smallpox, measles, poliomyelitis and other serious diseases, the body in the vast majority of cases clears the infectious agent and provides protection against future exposure. But unfortunately, this is not the case with HIV infection because the natural immune response to HIV infection is unable to clear the virus from the body. HIV is unique for the fact that it attacks the immunity of the body, which is responsible for the defense of the body.
Some of the factors that are responsible for the problematic nature of development of an effective HIV vaccine are the high mutability (undergoes frequent mutation and change its strain) of the virus, the fact that the infection can be transmitted by cell free or cell associated virus. There is a need for the development of effective mucosal immunity for HIV vaccine which is also a problematic area.
Some HIV infected individuals are long term non progressors, and a number of individuals have been exposed to HIV several times but remain uninfected; these facts suggest that there are elements of an HIV specific immune response that can be used to prepare effective vaccine.
Attempts to develop a vaccine with the envelope protein gp120 aimed at inducing neutralizing antibodies in humans were performed based on the induction of neutralizing antibodies in non human primates. These attempts were failure because elicited anti sera failed to neutralize primary isolates of HIV cultured and tested in fresh peripheral blood mononuclear cells. Two phase 3 trials were undertaken in the United States and Thailand using soluble gp120, and the vaccines failed to protect human volunteers from HIV infection.
The main goal of an HIV vaccine is to prevent infection and if given to an uninfected individual that significantly alters the course of disease or the infectivity of the individual, should that person become infected. A number of studies were done in monkeys using vaccines that induce predominantly cellular (T cell) immune responses have not protected the animals against infection but have lowered the initial burst of viremia following acute infection as well as decreased temporarily the viral set point. Most of the sexually transmitted HIV infections occur when the transmitting partner is experiencing high levels of viremia such as during the acute HIV syndrome or during the advanced stage of disease when the viral load is very high. This type of vaccine, which can limit the initial burst of viremia in primary infection and decrease the established viral set point, could have benefits for the individual as well as for their sexual partners.
Finally it is clear that it will take several years of clinical trials to establish the efficacy or lack thereof of a candidate vaccine for HIV that are under developmental stages at present.
