Human CD4+ T Cells Recognize an Epitope within α-Fetoprotein Sequence and Develop into TGF-β-Producing CD4+ T Cells

Abstract

There is limited information on the influence of tumor growth on the expansion of tumor-specific TGF-β-producing CD4+ T cells in humans. α-Fetoprotein (AFP) is an oncofetal Ag and has intrinsic immunoregulatory properties. In this study, we report the identification and characterization of subsets of CD4+ T cells that recognize an epitope within the AFP sequence (AFP46–55) and develop into TGF-β-producing CD4+ T cells. In a peptide-specific and dose-dependent manner, AFP46–55 CD4+ T cells produce TGF-β, GM-CSF, and IL-2 but not Th1-, Th2-, Th17-, or Tr1-type cytokines. These cells express CTLA-4 and glucocorticoid-induced TNR receptor and inhibit T cell proliferation in a contact-dependent manner. In this study, we show that the frequency of AFP46–55 CD4+ T cells is significantly higher (p = 001) in patients with hepatocellular carcinoma than in healthy donors, suggesting that these cells are expanded in response to tumor Ag. In contrast, tumor necrosis-inducing treatments that are shown to improve survival rate can shift the Th1/TGF-β-producing CD4+ T cell balance in favor of Th1 responses. Our data demonstrate that tumor Ags may contain epitopes which activate the expansion of inducible regulatory T cells, leading to evasion of tumor control.