Interleukin-7 enhances memory CD8(+) T-cell recall responses in health but its activity is impaired in human immunodeficiency virus infection

Abstract

Memory CD8(+) T cells regain function during a recall response, but the requirement of signals in addition to antigen during a secondary immune response is unknown. In this study, the ability of interleukin-7 (IL-7) to enhance memory CD8(+ ) CD45RA(- ) CD127(+) T-cell responses in health and in human immunodeficiency virus (HIV) infection was investigated. CD8(+) T-cell-depleted peripheral blood mononuclear cells (PBMCs) from HIV(-) and untreated HIV(+) donors were pulsed with a cytomegalovirus/Epstein-Barr virus/influenza (CEF) peptide pool, and co-cultured with autologous memory CD8(+) T cells in the presence of IL-7. Cell survival and the function of memory CD8(+) T-cell subsets were then evaluated. Memory CD8(+) T-cell proliferation and interferon-γ (IFN-γ) production was enhanced by the presence of antigen, and the addition of IL-7 further enhanced antigen-induced proliferation. In HIV(+) individuals, the presence of antigen enhanced IFN-γ production to a small degree but did not enhance proliferation. Lastly, IL-7 did not enhance antigen-mediated proliferation of memory CD8(+) T cells from HIV(+) individuals. IL-7 therefore appears to have a role in secondary immune responses and its activity is impaired in memory CD8(+) T cells from HIV(+) individuals. These results further our understanding of the signals involved in secondary immune responses, and provide new insight into the loss of CD8(+) T-cell function in HIV infection.

Figure 1

CD8⁺ T-cell subset distribution. Representative dot-plots are shown of bulk CD8⁺ T cells isolated from the peripheral blood mononuclear cells (PBMCs) of (a) human immunodeficiency virus-negative (HIV⁻) individuals and (c) human immunodeficiency virus-positive (HIV⁺) individuals, and CD45RA and CCR7 expression was analyzed to determine cell subset distribution. CD8⁺ CD45RA⁻ CD127⁺ T cells were isolated from bulk CD8⁺ T cells from (b) HIV⁻ individuals and (d) HIV⁺ individuals and stained for CD45RA and CCR7 to determine initial memory CD8⁺ T-cell subset distribution.

Figure 2

Antigen and interleukin-7 (IL-7) increased the proliferation of CD8⁺ CD45RA⁻ CD127⁺ T cells. CD8⁺ CD45RA⁻ CD127⁺ T cells were co-cultured with peptide-pulsed CD8⁺ T-cell-depleted peripheral blood mononuclear cells (PBMCs) for 6 days, and then carboxyfluorescein diacetate succinimidyl ester (CFSE) dilution, CD45RA expression and CCR7 expression were analyzed by flow cytometry and gated on CFSE⁺ cells. Proliferation was enhanced by the presence of antigen in (a) total memory CD8⁺ T cells (*P = 0·012, determined using the Student's t-test), as shown in a representative dot-plot summarized in a bar graph. (b) These effects occurred specifically in the central memory CD8⁺ T cell (T_CM) and effector memory CD8⁺ T cell (T_EM) subsets (**P = 0·022 and ***P = 0·033, respectively, determined using the Student's t-test). IL-7 enhanced antigen-mediated proliferation of (c) total memory CD8⁺ T cells [*P = 0·004, determined using analysis of variance (anova); and P < 0·05, determined using Dunnett's post-test] and (d) memory CD8⁺ T-cell subsets, specifically the T_CM (**P = 0·0001, determined using anova; and P < 0·01, determined using Dunnett's post-test) and T_EM (***P = 0·0005, determined using anova; and P < 0·01, determined using Dunnett's post-test) subsets (n = 6). T_EMRA, terminally differentiated effector memory CD8⁺ T-cell subset.

Figure 3

Antigen-induced interferon-γ (IFN-γ) production by CD8⁺ CD45RA⁻ CD127⁺ T cells. CD8⁺ CD45RA⁻ CD127⁺ T cells were co-cultured with peptide-pulsed CD8⁺ T-cell-depleted peripheral blood mononuclear cells (PBMCs) for 6 hr and then IFN-γ production, and CD8, CD45RA and CCR7 expression, were analyzed by flow cytometry. Representative dot-plots show antigen-enhanced IFN-γ production by (a) total memory CD8⁺ T cells (*P = 0·023, determined using the Student's t-test) and the data are summarized in bar graphs. (b) Antigen specifically induced IFN-γ expression in individual memory CD8⁺ T-cell subsets, specifically the effector memory CD8⁺ T cell (T_EM) and terminally differentiated effector memory CD8⁺ T cell (T_EMRA) subsets (**P = 0·0008 and ***P = 0·031, determined using the Student's t-test). Interleukin-7 (IL-7) did not enhance antigen-mediated IFN-γ production of (c) total memory CD8⁺ T cells or (d) memory CD8⁺ T-cell subsets (n = 6). T_CM, central memory CD8⁺ T-cell subset.

Figure 4

Neither antigen nor interleukin-7 (IL-7) induced CD107a/b expression on CD8⁺ CD45RA⁻ CD127⁺ T cells. CD8⁺ CD45RA⁻ CD127⁺ T cells were co-cultured with peptide-pulsed CD8⁺ T-cell-depleted peripheral blood mononuclear cells (PBMCs) for 6 hr, and then the expression of CD107a/b CD8, CD45RA and CCR7 were analyzed by flow cytometry. Representative dot-plots show how antigen did not induce CD107a/b expression on (a) total memory CD8⁺ T cells or (b) the memory CD8⁺ T-cell subsets, and data are summarized in bar graphs. IL-7 did not enhance antigen-mediated CD107a/b expression on (c) total memory CD8⁺ T cells or (d) memory CD8⁺ T-cell subsets (n = 6). T_CM, central memory CD8⁺ T-cell subset; T_EM, effector memory CD8⁺ T-cell subset; T_EMRA, terminally differentiated effector memory CD8⁺ T-cell subset.

Figure 5

Neither antigen nor interleukin-7 (IL-7) enhanced the function of CD8⁺ CD45RA⁻ CD127⁺ T cells from human immunodeficiency virus-positive (HIV⁺) individuals. CD8⁺ CD45RA⁻ CD127⁺ T cells from HIV⁺ individuals were co-cultured with peptide-pulsed CD8⁺ T-cell-depleted peripheral blood mononuclear cells (PBMCs) and analyzed for functional responses by flow cytometry. (a) Cells were cultured for 6 days with antigen alone or with antigen and IL-7 (10 ng/ml), and carboxyfluorescein diacetate succinimidyl ester (CFSE) dilution was analyzed by flow cytometry and gated on CFSE⁺ cells. CD8⁺ CD45RA⁻ CD127⁺ T cells were also co-cultured for 6 hr with antigen and it was found that (b) interferon-γ (IFN-γ) production was enhanced in total memory CD8⁺ T cells (*P = 0·030, determined using the Student's t-test), and (c) CD107a/b expression was not enhanced (n = 5).