Immunodominant HIV-specific CD8+ T-cell responses are common to blood and gastrointestinal mucosa, and Gag-specific responses dominate in rectal mucosa of HIV controllers

Abstract

Previous studies have suggested that polyfunctional mucosal CD8(+) T-cell responses may be a correlate of protection in HIV controllers. Mucosal T-cell breadth and/or specificity may also contribute to defining protective responses. In this study, rectal CD8(+) T-cell responses to HIV Gag, Env, and Nef were mapped at the peptide level in four subject groups: elite controllers (n = 16; viral load [VL], <75 copies/ml), viremic controllers (n = 14; VL, 75 to 2,000 copies/ml), noncontrollers (n = 14; VL, >10,000 copies/ml), and antiretroviral-drug-treated subjects (n = 8; VL, <75 copies/ml). In all subject groups, immunodominant CD8(+) T-cell responses were generally shared by blood and mucosa, although there were exceptions. In HIV controllers, responses to HLA-B27- and HLA-B57-restricted epitopes were common to both tissues, and their magnitude (in spot-forming cells [SFC] per million) was significantly greater than those of responses restricted by other alleles. Furthermore, peptides recognized by T cells in both blood and rectal mucosa, termed "concordant," elicited higher median numbers of SFC than discordant responses. In magnitude as well as breadth, HIV Gag-specific responses, particularly those targeting p24 and p7, dominated in controllers. Responses in noncontrollers were more evenly distributed among epitopes in Gag, Env, and Nef. Viremic controllers showed significantly broader mucosal Gag-specific responses than other groups. Taken together, these findings demonstrate that (i) Gag-specific responses dominate in mucosal tissues of HIV controllers; (ii) there is extensive overlap between CD8(+) T cells in blood and mucosal tissues, with responses to immunodominant epitopes generally shared by both sites; and (iii) mucosal T-cell response breadth alone cannot account for immune control.

FIG. 1.

Concordant and discordant CD8⁺ T-cell responses in peripheral blood and rectal mucosa of controllers and noncontrollers. Concordant (shared between peripheral blood [PB] and rectal mucosa [RMC]) and discordant (unique to PB or RMC) responses for Gag (A), Env (B), and Nef (C) as determined by IFN-γ ELISPOT assay. All data are presented in spot-forming cells per million (SFC/million). Each data point represents the median response of all concordant or discordant epitopes in a single subject. Horizontal bars represent the median response for each group. *, P < 0.05; **, P < 0.01.

FIG. 2.

CD8⁺ T-cell targeting of HIV Gag and Nef. Peptide cluster maps were constructed to visualize the frequency of subjects targeting specific areas of Gag and Nef. (A) Gag p17, (B) Gag p24, (C) Gag p2, p7, p1, and p6, and (D) Nef. Each peptide numbered on the y axis is a 15-mer which overlaps by 11 amino acids with the next numbered peptide. The colored horizontal bars represent the frequency of controllers (left side) and noncontrollers (right side) with concordant (blue bars), discordant blood (red bars), or discordant mucosal (green bars) responses to a particular peptide. Vertical bars in the center of the map delineate important structural or functional features, and numbered boxes show the locations of well-characterized immunodominant epitopes.

FIG. 2.

CD8⁺ T-cell targeting of HIV Gag and Nef. Peptide cluster maps were constructed to visualize the frequency of subjects targeting specific areas of Gag and Nef. (A) Gag p17, (B) Gag p24, (C) Gag p2, p7, p1, and p6, and (D) Nef. Each peptide numbered on the y axis is a 15-mer which overlaps by 11 amino acids with the next numbered peptide. The colored horizontal bars represent the frequency of controllers (left side) and noncontrollers (right side) with concordant (blue bars), discordant blood (red bars), or discordant mucosal (green bars) responses to a particular peptide. Vertical bars in the center of the map delineate important structural or functional features, and numbered boxes show the locations of well-characterized immunodominant epitopes.

FIG. 3.

Strength of the IFN-γ response to HLA-B27- and HLA-B57-restricted Gag epitopes in HIV controllers. (A) IFN-γ response to five immunodominant HLA-B27- and HLA-B57-restricted Gag epitopes compared to that for an immunodominant HLA-A2-restricted Gag epitope as measured by ELISPOT assay. Each symbol represents the response to a particular epitope in a single subject as indicated by the figure legend in both rectal mucosa (RMC) and peripheral blood (PB). The vertical bar graph shows the median response for all non-HLA-B27 and HLA-B57 epitopes. (B) Magnitude of five HLA-B27 and HLA-B57 epitopes compared to those of non-HLA-B27 and HLA-B57 epitopes. All data are presented in spot-forming cells per million (SFC/million). Horizontal bars represent the median magnitude for each group. *, P < 0.05.

FIG. 4.

Strength of the IFN-γ response to HIV Gag, Env, and Nef in rectal mucosa and peripheral blood. Median IFN-γ response to Gag, Env, and Nef in rectal mucosa (A) and peripheral blood (B), as measured by ELISPOT assay. All data are presented in spot-forming cells per million (SFC/million). Each data point represents the median Gag, Env, or Nef response in a single subject. Horizontal bars represent the median response for each group. *, P < 0.05; ***, P < 0.001.

FIG. 5.

Breadth of the CD8⁺ T-cell response. The number of epitopes (breadth) recognized within Gag, Env, and Nef by CD8⁺ T cells in rectal mucosa (A) and peripheral blood (B), as measured by IFN-γ ELISPOT assay. Horizontal bars represent the median breadth of response for each group. *, P < 0.05; **, P < 0.01.

FIG. 6.

Proportion of the CD8⁺ T-cell response attributed to Gag, Env, or Nef. Each pie shows the proportion of the measured response magnitude (A) or breadth (B) attributed to Gag, Env, and Nef in either peripheral blood or rectal mucosa of controllers and noncontrollers. The numbers in the middle of the pies signify the median number of spot-forming cells/million (A) or the median number of epitopes targeted in each protein (B), followed by the percentage of the total response magnitude or breadth.