HIV / AIDS
The scientific challenges of an HIV/AIDS vaccine
The development of a safe and effective AIDS vaccine is scientifically challenging on several fronts. An ideal vaccine must elicit immune responses capable of blocking infection by sexual, intravenous, and mother-to-child transmission. It may also need to be capable of stimulating immune responses such as antibodies that are effective in neutralizing free virus particles, as well as cellular immune responses, which destroy virus-infected cells. The induction of mucosal immunity is also being explored.
Meanwhile, the tremendous geographic diversity of HIV subtypes worldwide suggests that mixtures or “cocktails” of vaccines may be required for universal protective immunity. There is a lack of understanding of which anti-HIV immune responses are required to generate protective immunity against HIV and which components of the virus are necessary for an effective AIDS vaccine. Despite these challenges there is broad agreement within the scientific community that an effective AIDS vaccine is possible.
This optimism is based on the knowledge, firstly, that a small but growing number of people have been repeatedly exposed to HIV but have remained uninfected; they have elicited anti-HIV immune responses that could explain their resistance to infection. Secondly, there are now several candidate vaccines that have protected monkeys from infection and/or disease caused by the simian immunodeficiency virus (SIV) or the chimeric SIV/HIV (SHIV), carrying the HIV envelope; while most of these experimental vaccines did not provide complete protective immunity they were effective in significantly reducing viral loads and progression to disease in vaccinated monkeys. Thirdly, some candidate vaccines already in clinical trials have induced strong anti-HIV immune responses in human volunteers. Finally, vaccines have been successfully developed against several other viruses – measles, mumps, rubella, polio, hepatitis B and rotavirus, for example – with much less knowledge of their fundamental biology and pathogenic mechanisms than HIV.