Correlates of spontaneous viral control among long-term survivors of perinatal HIV-1 infection expressing human leukocyte antigen-B57

Abstract

Objective: We sought to identify immunologic and virologic correlates of spontaneous viral control among long-term survivors of perinatal HIV infection expressing the protective human leukocyte antigen (HLA)-B57 allele.

Design: The frequency, epitope specificity, and functional attributes of HIV-specific T cells and sequence variation within B57-restricted epitopes were compared between 'spontaneous controllers' who maintained normal CD4 percentages and viral loads less than 3000 copies/ml without antiretroviral therapy, and 'treated progressors' who had initiated HAART.

Methods: Recognition of HIV optimal epitopes was assessed by interferon gamma (IFNgamma) enzyme-linked immunosorbent spot. Functional characterization of CD8 cells targeting B57 epitopes was performed by staining for cytokine production (intracellular IFNgamma, interleukin-2, tumor necrosis factor alpha) and degranulation. Sequencing of autologous RNA was performed to determine the prevalence of viral escape mutations within B57-restricted epitopes and associated compensatory mutations.

Results: HLA-B57 remained immunodominant during chronic infection in both controllers and progressors, but controllers recognized fewer epitopes and targeted epitopes within Gag and reverse transcriptase only, whereas progressors demonstrated a broader response targeting additional proteins. No individual epitope was targeted more frequently by spontaneous controllers. CD8 cytokine production patterns were heterogeneous among individuals and even among different epitopes in the same individual and did not correlate with spontaneous viral control. Extensive sequence variation within B57 epitopes was observed in both groups, but only progressors displayed additional capsid mutations that are known to offset the viral fitness cost of B57-driven immune escape.

Conclusion: Among HLA-B57-positive long-term survivors, spontaneous control of viremia is not associated with a qualitatively or quantitatively superior T-cell response, but with uncompensated fitness-attenuating mutations in the viral capsid.

Figure 1. Comparison of the HIV-specific T cell response in B57+ controllers and progressors by IFNγ Elispot

All responses are expressed as spot-forming cells per million PBMC (SFC/million). A. In both spontaneous controllers and treated progressors, a high proportion of HIV-specific T cells targeted B57-restricted epitopes (SFC/million recognizing B57 optimals divided by SFC/million recognizing all HLA-matched optimals; median plus interquartile range is shown). B. Both the breadth (upper panel) and the magnitude (lower panel) of response were higher among progressors, following stimulation with both B57 optimal epitopes (left half of each panel) and all HLA-matched optimals (right half of each panel). C. Among controllers, the B57-restricted optimal response exclusively targeted epitopes in Gag and RT, whereas progressors exhibited a broader response, which targeted Nef and other proteins in addition to Gag and RT. D. No individual B57-restricted epitope was targeted more frequently by controllers than progressors.

Figure 2. Recognition of autologous variant Gag peptides restricted by HLA-B57

Recognition of defined optimal epitopes (a) KF11, (b) QW9, and (c) ISW9 (solid lines) and peptides corresponding to the autologous viral variant present in each subject (dotted lines) were compared using progressive titrations of the peptides in an IFNγ Elispot assay. (Data regarding recognition of TW10 variants has been previously published[22]). Variants of KF11 were recognized with lower avidity than the wild-type epitope, but no consistent impact of sequence variation within ISW9 or QW9 was noted.

Figure 3. Functional assessment of CD8 T cells specific for B57-restricted HIV epitopes

Degranulation (assessed by CD107a staining) and production of 3 cytokines (IL-2, IFN-γ or TNF-α) by individual CD8 T cells was measured in a multiparameter flow assay. All flow plots are gated on CD8+ T cells; NA= CD28/49d-only negative control. A. Functional profiles of CD8+ T cells targeting distinct B57-restricted epitopes differ markedly within a single individual, as demonstrated by the response of CH-11, a representative HIV-infected progressor who recognized 5 B57-restricted epitopes. The flow plots highlight the divergent response pattern to epitopes KF11 and QW9. The pie charts depict the proportion of CD8 cells exhibiting each distinct functional profile in response to all 5 epitopes. B. Functional profiles of CD8 T cells targeting a single epitope (KF11-Gag) differed markedly among subjects, but did not correlate with disease control. Pie charts depict the proportion of KF11-specific CD8 T cells exhibiting 1, 2, 3, or 4 functions.