High frequency of CD4+FoxP3+ cells in HTLV-1 infection: inverse correlation with HTLV-1–specific CTL response

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Abstract
Evidence from population genetics, gene expression microarrays, and assays of ex vivo T-cell function indicates that the cytotoxic T lymphocyte (CTL) response to human T-lymphotropic virus type 1 (HTLV-1) controls the level of HTLV-1 expression and the proviral load. The rate at which CTLs kill autologous HTLV-1–infected lymphocytes differs significantly among infected people, but the reasons for such variation are unknown. Here, we demonstrate a strong negative cor-relation between the frequency of CD4+FoxP3+ Tax− regulatory T cells (Tregs) in the circulation and the rate of CTL-mediated lysis of autologous HTLV-1–infected cells ex vivo. We propose that the frequency of CD4+FoxP3+ Tax− Tregs is one of the chief determinants of the efficiency of T cell–mediated immune control of HTLV-1.