Human CD4+ CD25+ regulatory T cells control T-cell responses to human immunodeficiency virus and cytomegalovirus antigens

Abstract

Regulatory T (T(R)) cells maintain tolerance to self-antigens and control immune responses to alloantigens after organ transplantation. Here, we show that CD4(+) CD25(+) human T(R) cells suppress virus-specific T-cell responses. Depletion of T(R) cells from peripheral blood mononuclear cells enhances T-cell responses to cytomegalovirus and human immunodeficiency virus antigens. We propose that chronic viral infections lead to induction of suppressive T(R) cells that inhibit the antiviral immune response.

FIG. 1.

T_R cells suppress superantigen-induced cytokine production. IFN-γ expression in T cells in PBMC was compared with that of T cells in PBMC depleted of CD25⁺ cells (a). The cultures were stimulated for 18 h with SEB. Brefeldin A was added for the last 5 h to promote cytokine accumulation. Means ± standard errors of the mean are shown (n = 3). (b) CD25⁺ T cells were added back into PBMC depleted of CD25⁺ cells at increasing ratios. The CD25⁺ T cells were stained with CFSE before being added back and were gated out of the analysis. (c) CD25⁺ T cells and sorted CD25⁺ CD4⁺ T cells (>99% pure) were added back into PBMC depleted of CD25⁺ cells. Means ± standard errors of the mean are shown (n = 2).

FIG. 2.

Suppressive CD25⁺ T cells can be induced from PBMC depleted of CD25⁺ T cells after activation with SEB. PBMC were depleted of CD25⁺ cells (a), labeled with CFSE, and cultured in the presence of SEB for 7 days (b). At day 7 (c), the CD25⁺ and CD25⁻ cell fractions were added into fresh PBMC cultures from the same donor. The cocultures were stimulated for 18 h with SEB. Brefeldin A was added for the last 5 h to promote cytokine accumulation. The CFSE-stained cells added into the fresh PBMC at day 7 were gated out of the analysis. Representative data are shown.

FIG. 3.

The frequency of T_R cells in HIV patients is unaltered. PBMC from HIV patients (n = 10) and healthy subjects (n = 10) were stained with fluorochrome-labeled monoclonal antibodies and analyzed for the frequencies of CD4⁺ CD25⁺ T cells and CD8⁺ CD38⁺ T cells. Means ± standard errors of the mean are shown.

FIG. 4.

T_R cells suppress antiviral immune responses. PBMC from a healthy CMV-infected individual were stained with a CMV pp65 tetramer and with cell surface markers (a). The frequency of tetramer-positive CD8⁺ T cells was compared with the frequency of IFN-γ-expressing T cells in PBMC, PBMC cultures depleted of CD25⁺ cells, and PBMC cultures depleted of CD25⁺ cells to which the depleted cells were added back in a 1:3 ratio. PBMC from an HIV-infected subject were stimulated with HIV antigens (b). The frequencies of IFN-γ- and TNF-α-expressing T cells in PMBC cultures and PBMC cultures depleted of CD25⁺ cells were compared. Representative data are shown.

FIG. 5.

Depletion of T_R cells enhances the antiviral immune response to HIV. PBMC from HIV-infected subjects (n = 6) were stimulated with HIV and CMV antigens. The frequencies of IFN-γ- and TNF-α-expressing T cells in PMBC cultures and PBMC cultures depleted of CD25⁺ cells were compared. The cells were gated on the CD3⁺ CD8⁻ and CD3⁺ CD8⁺ T cells. The shaded area in each graph represents the level of detection. Note: the scale on the y axis differs in the panels.