The goal of a therapeutic vaccine is to bolster immune responses against HIV in hopes of boosting the body's ability to control HIV replication. For most people, natural immune responses against HIV are not enough to control HIV disease for the long-term. It is hoped that by boosting immune responses artificially that HIV disease progression could be prevented or significantly delayed.
Studies of therapeutic vaccines focus on people with HIV who are healthy with relatively intact immune systems. Most studies have included people with CD4+ cell counts above 250 at study entry. Many studies require people to have even higher CD4+ cell counts at study entry, above 300 or 500, and also require that a person never had a CD4+ cell count below 250. Most studies of therapeutic HIV vaccines will require people to take anti-HIV medications while they are receiving the experimental vaccine.
People with lower CD4+ cell counts are generally not included in studies of therapeutic HIV vaccines because the effectiveness of a vaccine is dependent on immune function. If a person has poor immune status, vaccines are unable to induce new immune responses or bolster existing responses. Thus, therapeutic HIV vaccines will likely never prove useful for people with advanced-stage HIV disease and low CD4+ cell counts.
Many therapeutic HIV vaccine studies currently ongoing include some period of time off all therapy. Taking people off all therapy after they have received a therapeutic HIV vaccine might show if the new immune responses are able to prevent HIV from reproducing without the help of anti-HIV medicines.
Each product will carry its own unique risk of side effects. In general, however, side effects associated with experimental therapeutic HIV vaccines have been similar to side effects of commonly available vaccines. That is redness, swelling and/or pain at the site of the injection and sometimes mild flu-like symptoms.
Side effects could be more serious than mild pain or flu symptoms, however. They could include more severe pain and/or ulceration at the site of injection.
If the vaccine was made out of whole-killed or live-crippled HIV, it's possible that the virus in the vaccine could combine with a person's HIV and potentially become infectious. One therapeutic vaccine, HIV-Immunogen (Remune), is a whole-crippled form of HIV. In studies to date there is no evidence that it worsened anyone's HIV infection. There is also no evidence to date, however, that it has benefited anyone.
It is possible that an experimental therapeutic HIV vaccine could stimulate HIV replication and increase the risk of HIV disease progression. Vaccination stimulates and activates the immune system and this has been associated with increases in HIV replication. Also, immune responses brought about by vaccination could possibly enhance the ability of HIV to infect cells.
It is possible that people who receive an experimental therapeutic HIV vaccine that doesn't work will not benefit from an effective therapeutic HIV vaccine. It is very likely that people who participate in a study of a therapeutic HIV vaccine and receive the experimental vaccine (rather than the placebo) will not be eligible to participate in studies of other therapeutic HIV vaccines and other experimental anti-HIV and immune-based approaches.
It is possible, by participating in an experimental therapeutic HIV vaccine study, that the vaccine will be effective in slowing or preventing HIV disease progression. People who received the vaccine (rather than the placebo) will have gained earlier access to an effective therapy.
Ultimately the decision to participate in an experimental drug study is a very personal decision. Products tested so far have had relatively few side effects, but results from studies aren't very encouraging. New products that boost the immune system differently and/or more potently are constantly entering small studies. Currently most (if not all) studies of therapeutic vaccines require that people be on anti-HIV therapy, and most studies include some period of time off all therapy following vaccination.