Specific antibody-dependent cellular cytotoxicity responses associated with slow progression of HIV infection

Abstract

Antibody-dependent cellular cytotoxicity (ADCC) is potentially an effective adaptive immune response to HIV infection. However, little is understood about the role of ADCC in controlling chronic infection in the small number of long-term slow-progressors (LTSP) who maintain a relatively normal immunological state for prolonged periods of time. We analysed HIV-specific ADCC responses in sera from 139 HIV(+) subjects not on antiretroviral therapy. Sixty-five subjects were LTSP, who maintained a CD4 T-cell count > 500/μl for over 8 years after infection without antiretroviral therapy and 74 were non-LTSP individuals. The ADCC responses were measured using an natural killer cell activation assay to overlapping HIV peptides that allowed us to map ADCC epitopes. We found that although the magnitude of ADCC responses in the LTSP cohort were not higher and did not correlate with CD4 T-cell depletion rates, the LTSP cohort had significantly broader ADCC responses compared with the non-LTSP cohort. Specifically, regulatory/accessory HIV-1 proteins were targeted more frequently by LTSP. Indeed, three particular ADCC epitopes within the Vpu protein of HIV were recognized only by LTSP individuals. Our study provides evidence that broader ADCC responses may play a role in long-term control of HIV progression and suggests novel vaccine targets.

Figure 1

Magnitude of antibody-dependent cellular cytotoxicity (ADCC) responses within the long-term slow-progressors (LTSP) cohort. (a) Gating strategy for the intracellular cytokine staining (ICS) ADCC assays. The gating strategy for the ICS assay first gates on lymphocytes in the forward/side scatter and then CD3⁻ CD2⁺ CD56⁺ natural killer (NK) lymphocytes analysed for dual intracellular interferon-γ (IFN-γ) and surface CD107a expression. (b) The magnitude of ADCC-mediated NK cell IFN-γ and CD107a expression across the LTSP cohort were measured for the various peptide pools. Every dot represents a subject and only subjects that induced an ADCC response above background levels (more than three times unstimulated sera and > 2 SD over HIV-negative controls) are depicted. (c) CD4 percentage changes over time in correlation with the magnitude of ADCC response within the LTSP cohort for the gp140 protein (left panel); and the RTV peptide pool (which spans the Rev, Tat and Vpu regulatory proteins; right panel).

Figure 2

Long-term slow-progressors (LTSP) show more and broader antibody-dependent cellular cytotoxicity (ADCC) responses against HIV peptide pools. (a) Comparison of the percentage of responders that introduce ADCC responses from both cohorts to HIV-1 peptide pools as measured by interferon-γ (IFN-γ) and CD107a expression from gated natural killer (NK) cells. Significant differences are indicated by asterisks (P < 0·02). (b) Comparison of the percentage of responders from both cohorts that produce ADCC responses to zero, one or several peptide pools. Differences between the LTSP cohort and the non-LTSP cohort were significant (P = 0·003) in a 4 × 2 Fischer's exact test.

Figure 3

Mapping of antibody-dependent cellular cytotoxicity (ADCC) epitopes in Vpu. Representative flow cytometry plots of ADCC-mediated natural killer (NK) cell activation [interferon-γ (IFN-γ) and CD107a expression] are shown for sera from long-term slow-progressors (LTSP) subjects responding to Vpu peptides. The top panel (a) shows a response to the RTV (Rev, Tat, Vpu) peptide pool which is mapped to the Vpu pool. The second row (b) shows the Vpu peptide pool response from (a) that is mapped to sub-pools of six or seven peptides each. The third row (c) shows the Vpu response from (a) and (b) that is mapped to individual overlapping peptides 10–12. The fourth row (d) shows another serum from another LTSP subject with Vpu epitopes mapped to two other overlapping peptide epitopes.