Immune correlates of HIV control

The development of an effective HIV vaccine is still hampered by the lack of clearly defined immune correlates of HIV control. Although a number of immune markers have been associated over last years with relative viral control and slower HIV disease progression, these associations are oftentimes complicated by the causality dilemma that does not allow to directly assign cause or effect to the identified parameters. In addition, many of these immune markers may act in concert or represent surrogate makers for otherwise controlled HIV infection. This review will revisit the current knowledge of host genetic and immune markers and their associations with HIV control, particularly examining the roles of virus-specific T cells and humoral immune responses and testing their role as direct correlates of control.

HIV evolution: CTL escape mutation and reversion after transmission

Within-patient HIV evolution reflects the strong selection pressure driving viral escape from cytotoxic T-lymphocyte (CTL) recognition. Whether this intrapatient accumulation of escape mutations translates into HIV evolution at the population level has not been evaluated. We studied over 300 patients drawn from the B- and C-clade epidemics, focusing on human leukocyte antigen (HLA) alleles HLA-B57 and HLA-B5801, which are associated with long-term HIV control and are therefore likely to exert strong selection pressure on the virus. The CTL response dominating acute infection in HLA-B57/5801-positive subjects drove positive selection of an escape mutation that reverted to wild-type after transmission to HLA-B57/5801-negative individuals. A second escape mutation within the epitope, by contrast, was maintained after transmission. These data show that the process of accumulation of escape mutations within HIV is not inevitable. Complex epitope- and residue-specific selection forces, including CTL-mediated positive selection pressure and virus-mediated purifying selection, operate in tandem to shape HIV evolution at the population level.