Susceptibility to CD8 T-cell-mediated killing influences the reservoir of latently HIV-1-infected CD4 T cells

Abstract

Background: HIV-1 establishes a lifelong infection in the human body, but host factors that influence viral persistence remain poorly understood. Cell-intrinsic characteristics of CD4 T cells, the main target cells for HIV-1, may affect the composition of the latent viral reservoir by altering the susceptibility to CD8 T-cell-mediated killing.

Results: We observed that susceptibilities of CD4 T cells to CD8 T-cell-mediated killing, as determined in direct ex vivo assays, were significantly higher in persons with natural control of HIV-1 (elite controllers) than in individuals effectively treated with antiretroviral therapy. These differences were most pronounced in naive and in terminally differentiated CD4 T cells and corresponded to a reduced viral reservoir size in elite controllers. Interestingly, the highest susceptibility to CD8 T-cell-mediated killing and lowest reservoirs of cell-associated HIV-1 DNA was consistently observed in elite controllers expressing the protective HLA class I allele B57.

Conclusions: These data suggest that the functional responsiveness of host CD4 T cells to cytotoxic effects of HIV-1-specific CD8 T cells can contribute to shaping the structure and composition of the latently infected CD4 T-cell pool.

Figure 1. Increased susceptibility of CD4 T cells from elite controllers to CD8 T cell-mediated killing

(A) Representative dot plots reflecting the proportions of Annexin V-positive CD4 T cells following exposure to A2-SL9-specific CD8 T cells, with or without prior pulsing of target cells with the epitopic peptide. Data from bulk CD4 T cells and indicated CD4 T cells subsets are shown. (B–C) Proportions of Annexin V-positive CD4 T cells from HIV-1 negative persons (Neg), HAART-treated subjects (HAART) or elite controllers (EC) after co-culture with identical immunodominant HIV-1-specific CD8 T cell populations (B), or without exposure to HIV-1-specific CD8 T cell clones (C). Left panels reflect data from all individuals in each study cohort, right panels indicated data from subgroups of patients expressing HLA-B57 or HLA-A2/HLA-B8. Significance was tested using Mann-Whitney U tests.

Figure 2. CD4 T cell subset-specific susceptibility to cytotoxic effects of HIV-1-specific CD8 T cells

(A): Proportions of Annexin V-positive CD4 T cells with naïve (NA), terminally-differentiated (TE), central-memory (CM) and effector-memory (EM) phenotype, after exposure to four different HIV-1-specific CD8 T cells. Data from all three study cohorts are included. (B–E): Susceptibility of naïve (B), central-memory (C), effector-memory (D) or terminally-differentiated CD4 T cells from the three study cohorts to HIV-1-specific CD8 T cells. Left panels indicate data from all individuals within each study group, middle panels indicate data stratified by expression of HLA-B57 vs. HLA-A2/B8. Significance was tested using Mann-Whitney U tests. Right panels indicate Spearman’s correlations between susceptibilities to CD8 T cell mediated killing and corresponding levels of immune activation in indicated CD4 T cell subsets.

Figure 3. Latent viral reservoirs in CD4 T cell subsets from elite controllers and HAART-treated patients

(A–B): Cell-associated HIV-1 DNA in total, naïve and memory CD4 T cells from all HAART-treated persons and elite controllers (A) and following stratification according to expression of HLA-B57 or expression of HLA-A2 or B8 (B). (A–B): Data from each patient are shown as individual symbols. The lower limit of detection with minimum input DNA of 20,000 cell equivalents was 1 copy/1 million cells. Data are not shown for samples with insufficient DNA. Significance was calculated using Mann-Whitney U tests. Orange symbols=HAART treated patients, blue symbols=elite controllers.

Figure 4. Latent viral reservoirs in naïve CD4 T cells are associated with susceptibilities to CD8 T cell-mediated killing

(A): Data reflect Spearman’s Correlations between susceptibility of indicated CD4 T cell populations to CD8 T cell mediated killing, and corresponding levels of cell-associated HIV-1 DNA. (B–C): Spearman’s correlation between magnitude of total (B) or Gag-specific (C) interferon-γ secreting HIV-1-specific CD8 T cells and corresponding levels of cell-associated HIV-1 DNA.