[4-9] Hessell et al.[10] showed that an HIV-specific neutralizing R788 clinical trial antibody mutated in the Fc position was no longer able to elicit Fc-mediated functions, such as ADCC, and that the efficacy in preventing simian/human immunodeficiency virus (SHIV) infection of macaques was significantly decreased, suggesting that the ADCC function is important for the protection afforded by neutralizing antibodies. There is a more limited understanding of the role of ADCC in the small subset of HIV-infected subjects who naturally control chronic infection, although the role

of cytotoxic T lymphocytes and neutralizing antibodies has been extensively studied.[11-24] We previously detected ADCC-mediated NK-cell activation in a small cohort of six subjects with slow HIV progression, but found no clear correlation with the magnitude of the ADCC response and control of buy PD0325901 HIV. A recent study of 22 subjects indicated that elite controllers of HIV infection (subjects with consistent plasma HIV levels of < 50 copies/ml) have higher levels of ADCC antibodies than viraemic subjects, with an absence of correlation between cytotoxic T lymphocytes and neutralizing antibodies.[6] Whether these results are generalized across larger numbers of long-term slow-progressors

(LTSP) subjects is not clear. In addition, the HIV epitopes targeted by efficient ADCC are unknown but would logically be interesting vaccine targets. We analysed ADCC responses using an assay studying antibody-mediated interferon- γ (IFN-γ) and CD107a expression of NK cells. We

studied serum samples from 139 HIV-infected subjects not on anti-retroviral therapy; 65 subjects were LTSP who maintained a CD4 T-cell count of > 500/μl for at least 8 years after infection and the remaining 74 subjects were non-LTSP. We found that ADCC responses in LTSP subjects were broadly reactive against multiple HIV proteins and that LTSP subjects disproportionally targeted three specific ADCC epitopes within Vpu (viral protein U). The characteristics of the 139 subjects are shown in Table 1. All subjects were HIV-infected Atazanavir and not on anti-retroviral therapy at the time of sampling. Subjects enrolled in both cohorts provided written informed consent and the relevant human research ethics committees approved all studies. Subjects were recruited both through the Long-term non-progressor network co-ordinated by the Kirby Institute, Sydney, Australia and through the Melbourne Sexual Health Centre, Australia. Sixty-five of the subjects met the pre-defined criteria as LTSPs, being HIV-positive for more than 8 years without anti-retroviral therapy and maintaining a peripheral CD4+ T-cell count above 500 cells/μl. There were no viral load entry criteria. The remaining 74 subjects did not meet the criteria for LTSP (i.e. had not maintained CD4 T-cell counts > 500 cells/μl for 8 years). For both cohorts, serum for ADCC testing was derived from the earliest time-point available.