Immunological control of chronic HIV-1 infection: HLA-mediated immune function and viral evolution in adolescents

Abstract

Background: Differential protein targeting by HIV-specific CD8 T cells is associated with disparate plasma viral loads; however, it is unclear if the quality of these responses differs depending upon the specificity of the targeted epitopes.

Methods: We examined HIV-specific CD8 T-cell responses in HIV-infected adolescents carrying either an HLA class I allele associated with a favorable prognosis (HLA-B*57) or an allele associated with usual disease progression (HLA-B*35 or HLA-B*53) using interferon-gamma ELISpot and ICS assays.

Results: In an interferon-gamma ELISpot assay, p24 was the dominant protein targeted by B*57 carriers while responses to Nef dominated in B*35 or B*53 positive carriers. This differential protein targeting did not change during 4 years of follow-up. In these chronically infected adolescents, there were no significant differences in the quality of the immunodominant T-cell responses between the B*57 and B*35/B*53 carriers as measured by peptide avidity, degranulation, and immune memory markers. There was a trend towards higher expression of interleukin-2 from B*57-KF11 restricted CD8 T cells although this difference was not significant. Nevertheless both B*57 and B*35/53-restricted responses were relatively potent as reflected by the propensity of CD8 T cells to escape in p24 and Nef, respectively.

Conclusions: Differential protein targeting rather than the quality of T-cell responses appears to be a major distinguishing feature of HIV-specific CD8 T cells induced in B*57 carriers. These data suggest that viral fitness costs associated with CD8 T-cell pressure is an important factor determining differences in the viral load among HIV-infected patients.

Fig. 1. Comparison of T-cell responses with amino acid variability

REACH subjects were sorted into three groups on the basis of HLA class I, i.e. HLA B*57, B*35 and B*53 and others alleles. The average percentage of the total response to each protein in the three patient groups is shown in relation to the average entropy for each protein. All the T-cell responses at the 15–20-mer peptide level were pooled to represent each protein:**B*57 response compared with B*35/53 (P =0.005) or others (P =0.02); *B*35/53 compared with B*57 (P =0.03) or others (P =0.001) using Mann-Whitney U test.

Fig. 2. Longitudinal analysis of T-cell responses in B*57 and B*35/53 subjects

IFN-γ ELISpot T-cell responses in HLA-B*57 (n =7) and HLA-B*35/B*53 (n =11) subjects over a 4-year period are shown. The average percentage of the total response is shown for each targeted HIV-1 protein in (a) B*57 and (c) B*35/B*53. The median magnitude of response (SFC/10⁶ PBMC) to all the optimized HLA-B*57 restricted HIV-1 Gag and Nef epitopes (9-11-mer) is shown in (b). The B*57 restricted peptides tested were: Gag 162–172: KAFSPEVIPMF (KF 11); Gag 240–250: TSTLQEQIGWF (TF 11); Gag 147–155: ISPRTLNAW (IW 9); Gag 241–249: STLQEQIGW (SW 9); Gag 308–316: QASQEVKNW (QW 9); Nef 116–125: HTQGYFPDWQ (HQ 10) and Nef 120–128: YFPDWQNYT (YT 9). (d) B*35/B*53 restricted peptides that were tested: Nef 135–143: YPLTFGWCY (YY 9); Nef 74–81: VPLRPMTY (VY 8); Gag 36–44: WASRELERF (WF 9); Gag 124–142: NSSKVSQNY (NY 9); Gag 254–262: PPIPVGDIY (PY 9); Gag 327–334: NPDCKTIL (NL 8); Gag 180–188: TPQDLNTML; Gag 308–316: QASQEVKNW (QW 9) and Gag 203–212: DTINEEAAEW (DW10).

Fig. 3. Cytokine production, degranulation and memory phenotype of B*57–KF11 and B*35/B*53-YY9 restricted CD8 T-cell responses

PMBC were stimulated with peptides encompassing the KF11 peptide (B*57 subjects) or YY9 peptide (B*35/B*53 subjects) or SEB in an ICS assay as described. The production of IFN-γ, IL-2 and TNF-α by CD8 T-cells and the upregulation of CD127 and CD107 by CD3CD8 are shown. The top panel shows representative CD8 IFN-γ data from three subjects in each group. The bottom three panels show a representative data for CD8-IL2, CD8CD127 IFN-γ and CD8CD107 IFN-γ. The gates were drawn based upon density plots (not shown) using FlowJo software where a clear distinction was observed between CD8 positive and negative populations.

Fig. 4. Functional response patterns for KF11 and YY9 specific CD8 T-cells

T-cell responses specific for B*57-KF11 (a) or B*35/B*53-YY9 (b) expressed as a mean of the CD8 T-cell response in polychromatic flow cytometry are shown in a pie chart based on their functional capacity (single, dual, triple, and quadruple function). Boolean gating was performed to determine the contributions of one to four functions measured from CD3CD8 cells that produced IFN-γ, IL-2, TNF-α and/or CD107. The responder frequency (% mean) of each of the 15 functional subpopulations is shown for B*57-KF11 (c) and B*35/B*53-YY9 (d).