Fully differentiated HIV-1 specific CD8+ T effector cells are more frequently detectable in controlled than in progressive HIV-1 infection

Abstract

Background: CD8+ T cells impact control of viral infections by direct elimination of infected cells and secretion of a number of soluble factors. In HIV-1 infection, persistent HIV-1 specific IFN-gamma+ CD8+ T cell responses are detected in the setting of disease progression, consistent with functional impairment in vivo. Recent data suggest that impaired maturation, as defined by the lineage markers CD45RA and CCR7, may contribute to a lack of immune control by these responses.

Methodology/principal findings: We investigated the maturation phenotype of epitope-specific CD8+ T cell responses directed against HIV-1 in 42 chronically infected, untreated individuals, 22 of whom were "Controllers" (median 1140 RNA copies/ml plasma, range<50 to 2520), and 20 "progressors" of whom had advanced disease and high viral loads (median 135,500 RNA copies/ml plasma, range 12100 to >750000). Evaluation of a mean of 5 epitopes per person revealed that terminally differentiated CD8+ T cells directed against HIV-1 are more often seen in HIV-1 Controllers (16/22; 73%) compared to HIV-1 progressors (7/20; 35%)(p = 0.015), but the maturation state of epitope-specific responses within a given individual was quite variable. Maturation phenotype was independent of the HLA restriction or the specificity of a given CD8+ T cell response and individual epitopes associated with slow disease progression were not more likely to be terminally differentiated.

Conclusions/significance: These data indicate that although full maturation of epitope-specific CD8+ T cell responses is associated with viral control, the maturation status of HIV-1 specific CD8+ T cell responses within a given individual are quite heterogeneous, suggesting epitope-specific influences on CD8+ T cell function.

Figure 1. T cell differentiation profile in bulk CD8+ T cells.

Based on the lineage markers, CD45RA and CCR7 bulk CD8+ T cells of HIV-1 Controllers (black bars) and HIV-1 progressors (hatched bars) were stratified into 4 subpopulations: effector (E), effector memory (EM), central memory (CM) and naïve (N) CD8+ T cells. Terminally differentiated (E) CD8+ T cells were of significantly higher frequency in HIV-1 Controllers (p = 0.017, Mann-Whitney), while Progressors had higher levels of CM cells (p = 0.02), indicated by asterisks (*).

Figure 2. The effector phenotype of an individual CD8+T cell response may not be adequately reflected in a peptide pool.

Panels A and C show IFN-γ production upon stimulation with the Pol peptide pool (A) and an individual Pol peptide (C). Panels B and D are gated on the IFN-γ producing cells and show differentiation phenotype of these HIV-1 specific cells as defined by CCR7 and CD45RA isoform. The terminally differentiated response to the Pol peptide 356–374 (31.9% CCR7−/CD45RA+ of gated cells) is diluted in the response to the entire Pol peptide pool (only 8.8% gated cells are CCR7−/CD45RA+).

Figure 3. Terminally differentiated HIV-1-speficic CD8+ T cells are more frequently detectable in HIV-1 Controllers compared to HIV-1 Progressors.

(A) Percentage of CD45RA+/CCR7−/CD8+ T cells for the 126 and 106 HIV-1-specific CD8+ T cell responses tested in HIV-1 Controllers and Progressors, respectively. Frequencies of effector phenotype T cell responses were significantly higher in HIV-1 Controllers (squares) compared to progressors (triangles). An HIV-1 specific CD8+ T cell response with >20% of CD45RA+/CCR7− cells was considered to be of terminally differentiated phenotype (dotted line) . (B) More HIV-1 Controllers had at least one terminally differentiated HIV-1 specific T cell response compared to HIV-1 Progressors (p = 0.015, Fisher's exact). (C) Of the CD8+ T cell responses against HIV-1 tested per individual a higher percentage of terminally differentiated responses were detectable in HIV-1 Controllers (p = 0.007, Mann Whitney). For 3 Controllers all investigated responses were of the terminally differentiated phenotype, while five Controllers had none.

Figure 4. Maturation phenotype of HIV-1 specific CD8+ T cells by HLA type and epitope specificity.

Panel A shows the percentage of CD45RA+/CCR7− CD8+ T cells of 46 HLA-A2, -A3, -B14, -B27 and -B57-restricted epitopes tested in the study cohort. Panel B depicts the percentage of CD45RA+/CCR7− CD8+ T cells specific for six specific HIV-1 epitopes tested (restricting HLA allele and peptide sequence are shown). Data reflective of a total of 21 study subjects, who had responses to the specific HLA-matched optimal epitopes tested (14 Controllers and 5 Progressors).