Subset- and Antigen-Specific Effects of Treg on CD8+ T Cell Responses in Chronic HIV Infection

We, and others, have reported that in the HIV-negative settings, regulatory CD4+CD25highFoxP3+ T cells (Treg) exert differential effects on CD8 subsets, and maintain the memory / effector CD8+ T cells balance, at least in part through the PD-1/PD-L1 pathway. Here we investigated Treg–mediated effects on CD8 responses in chronic HIV infection. As compared to Treg from HIV negative controls (Treg/HIV-), we show that Treg from HIV infected patients (Treg/HIV+) did not significantly inhibit polyclonal autologous CD8+ T cell function indicating either a defect in the suppressive capacity of Treg/HIV+ or a lack of sensitivity of effector T cells in HIV infection. Results showed that Treg/HIV+ inhibited significantly the IFN-γ expression of autologous CD8+ T cells stimulated with recall CMV/EBV/Flu (CEF) antigens, but did not inhibit HIV-Gag–specific CD8+ T cells. In cross-over cultures, we show that Treg/HIV- inhibited significantly the differentiation of either CEF- or Gag-specific CD8+ T cells from HIV infected patients. The expression of PD-1 and PD-L1 was higher on Gag-specific CD8+ T cells as compared to CEF-specific CD8+ T cells, and the expression of these markers did not change significantly after Treg depletion or co-culture with Treg/HIV-, unlike on CEF-specific CD8+ T cells. In summary, we show a defect of Treg/HIV+ in modulating both the differentiation and the expression of PD-1/PD-L1 molecules on HIV-specific CD8 T cells. Our results strongly suggest that this particular defect of Treg might contribute to the exhaustion of HIV-specific T cell responses.我们及其他研究团队此前已有报道，在HIV阴性（HIV-negative）人群中，调节性CD4+CD25highFoxP3+ T细胞（Treg）对CD8+ T细胞亚群发挥差异化调控作用，并至少部分通过程序性死亡受体1（PD-1）/程序性死亡配体1（PD-L1）通路维持记忆性与效应性CD8+ T细胞的平衡。本研究旨在探讨慢性HIV感染状态下Treg对CD8+ T细胞应答的调控效应。相较于HIV阴性对照人群的Treg（Treg/HIV-），本研究发现HIV感染患者体内的Treg（Treg/HIV+）无法显著抑制多克隆自体CD8+ T细胞的功能，这提示Treg/HIV+的免疫抑制功能存在缺陷，或是HIV感染状态下效应T细胞对其敏感性降低。实验结果显示，Treg/HIV+可显著抑制经巨细胞病毒（Cytomegalovirus, CMV）、EB病毒（Epstein-Barr virus, EBV）及流感病毒（Influenza virus, Flu）组成的回忆抗原（CEF）刺激的自体CD8+ T细胞的干扰素-γ（IFN-γ）表达，但无法抑制HIV-Gag特异性CD8+ T细胞。在交叉培养实验中，我们证实Treg/HIV-可显著抑制HIV感染患者体内CEF特异性或Gag特异性CD8+ T细胞的分化。相较于CEF特异性CD8+ T细胞，Gag特异性CD8+ T细胞表面PD-1与PD-L1的表达水平更高；且与CEF特异性CD8+ T细胞不同，此类免疫检查点分子的表达在Treg耗竭或与Treg/HIV+共培养后无显著变化。综上，本研究证实Treg/HIV+在调控HIV特异性CD8+ T细胞的分化及PD-1/PD-L1分子表达方面存在功能缺陷。本研究结果强烈提示，Treg的这一特定功能缺陷可能加剧了HIV特异性T细胞应答的耗竭。