Natural immunity

We know an HIV vaccine must be possible. For example, on average ten years elapse from the time a person is infected with HIV to the time when the virus has done enough damage to warrant an AIDS diagnosis. This means that the immune system has some ability to control HIV, albeit temporarily. During this time a viral load which, in acute infection, peaks at several million copies/ml is typically contained to some tens of thousands of copies. The role of a vaccine could be to improve these defences to a point at which they would contain HIV replication more completely, and permanently.

Additionally, there are people who exhibit an exceptional ability to shrug off HIV infection, and analysing what is different about their immune systems yields ideas for vaccines. For example, some female sex workers and male partners of HIV-positive men have remained HIV uninfected, or infected but able to control infection so that it is harmless, for many years, despite repeated sex without condoms.

About 0.4% to 2% of people with HIV (the precise proportion depends on definition) are ‘long-term non-progressors’ who maintain high CD4 counts/ratios and still do not need medication after more than 20 years of infection. However studies show that many non-progressors do, in fact, have slow declines in CD4 counts and might better be called ‘slow progressors’.1

A slightly higher proportion are so-called ‘controllers’ who maintain undetectable or consistently low viral loads without antiretroviral therapy; although many of them do experience declining CD4 counts.2 A much smaller proportion – according to one scientist, no more than one in 300 people3 – are ‘elite controllers’ who maintain normal CD4 counts, normal CD4 ratios and an undetectable viral load.

So some people have immune responses that seem to be able to control HIV replication just as well as antiretroviral drugs. Moreover animals such as sooty mangabeys maintain high viral loads with simian immunodeficiency virus (SIV) without seeming to suffer any immune damage. Researchers are building and testing vaccines designed to stimulate the immune cells that are believed to be responsible for the apparent acquired immunity either to the virus or to its effect on the immune system.

Already experimental vaccines against SIV, a close cousin of HIV that infects monkeys, have been shown to prevent AIDS4 and even to show signs of eliminating infection, once acquired in monkeys.5

Before we look at the specific results, however, we need to look at exactly what an HIV vaccine would have to do, and which strategies have been tried so far.

References

  1. Mandalia S et al. Frequency and characteristics of long-term non-progressors and HIV controllers in the Chelsea and Westminster HIV cohort. 17th Annual BHIVA Conference, Bournemouth, abstract O28, 2011
  2. Thiébaut R et al. Long-term nonprogressors and elite controllers in the ANRS CO5 HIV-2 cohort. AIDS 25(6): 865-867, 2011
  3. Okulicz JF and Lambotte O Epidemiology and clinical characteristics of elite controllers. Current Opinion in HIV & AIDS 6(3): 163-168, 2011
  4. Shiver JW et al Replication-incompetent adenoviral vaccine vector elicits effective anti-immunodeficiency-virus immunity Nature 415: 331-335, 2002
  5. Hansen SG et al. Profound early control of highly pathogenic SIV by an effector memory T-cell vaccine. Nature, early online publication, doi:10.1038/nature10003, May 2011
This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.