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Antiretroviral treatment
An area of research which has become closely bound up with work on therapeutic immunisation is the use of antiviral drugs during ‘primary infection’ with HIV. It is hoped that this can modify the subsequent course of infection by preserving the ability of the immune system to control HIV. This is discussed in the HIV & AIDS Treatments Directory.
If antiviral treatment becomes the 'standard of care' for people newly infected with HIV, will it still be possible to evaluate the effect of AIDS vaccines? This question is related to concerns about the use of PEP, discussed earlier in this chapter. However, it might appear to be more serious where vaccines given prior to infection to modify the long-term course of infection are concerned. Will we be able to tell if it is the vaccine, or the early treatment, that has this effect?
Without preventing infection, a vaccine could alter the immune response so that viral load stays low, the disease progresses slowly or not at all, and onward transmission is restricted. Animal studies support the idea that such a vaccine is achievable, especially when strong cellular immune responses against HIV can be induced.
Primary infection with HIV is more likely to be picked up in people at high risk who are being closely monitored, as in a vaccine trial, than in the rest of the population. In fact, clinical trial participants for research on treating primary infection have often been recruited from vaccine feasibility studies.
It is argued here that many people who have not been seriously ill with HIV may reasonably decide not to undergo treatment with demanding and toxic antiviral drugs. Many would prefer to wait if they can for a time when a wider range of better and safer treatments is likely to be available. It is already clear that some people who start on such treatment will not be prepared or able to continue doing so on a lifelong basis. Indeed, it is that prospect which deters some people from commencing anti-HIV treatments.
Research on the interactions between antiviral treatment and vaccination inducing cellular immunity could be of particular value in identifying clinically relevant and protective immune responses; this is a research opportunity, not an obstacle.
A potentially more serious problem may emerge for vaccine research if the idea of 'pre-exposure prophylaxis' - the use of a low-dose continuous antiretroviral treatment, most probably with the drug tenofovir - proves successful as a method of HIV prevention in clinical trials. However, it remains to be seen what proportion of people at high risk of HIV will be able to adhere long-term to this or any other drug treatment and a vaccine is always likely to be more cost-effective than a treatment taken continuously.