Transmission of HIV-1 CTL escape variants provides HLA-mismatched recipients with a survival advantage

One of the most important genetic factors known to affect the rate of disease progression in HIV-infected individuals is the genotype at the Class I Human Leukocyte Antigen (HLA) locus, which determines the HIV peptides targeted by cytotoxic T-lymphocytes (CTLs). Individuals with HLA-B*57 or B*5801 alleles, for example, target functionally important parts of the Gag protein. Mutants that escape these CTL responses may have lower fitness than the wild-type and can be associated with slower disease progression. Transmission of the escape variant to individuals without these HLA alleles is associated with rapid reversion to wild-type. However, the question of whether infection with an escape mutant offers an advantage to newly infected hosts has not been addressed. Here we investigate the relationship between the genotypes of transmitted viruses and prognostic markers of disease progression and show that infection with HLA-B*57/B*5801 escape mutants is associated with lower viral load and higher CD4+ counts.

Following infection with HIV, it is well established that a person's genetic makeup is a major determinant of how quickly they will progress to AIDS. Particularly important is the class I Human leukocyte antigen (HLA) gene that is responsible for alerting the immune system to HIV's presence. One of the reasons our immune systems are unable to beat HIV is that the virus can mutate to forms that our HLA genes no longer recognise. However, some people have versions of the HLA gene (for example HLA-B*57 and HLA-B*5801) that are known to force HIV to tolerate mutations that damage its ability to reproduce. Slower HIV reproduction is thought to be one reason that HLA-B*57 and HLA-B*5801 positive people progress to AIDS more slowly than most other HIV infected persons. We report here on a study of HLA-B*57 and HLA-B*5801 negative women in which better control of disease tended to be associated with their being infected with viruses carrying mutations that have been previously shown to reduce replication. These mutations characterise viruses found infecting HLA-B*57 and HLA-B*5801 positive people. This indicates for the first time that HLA-B*57 or HLA-B*5801 negative people that are infected by such reproductively compromised viruses may also experience better survival prospects.