Effect of CD4+CD25+ and CD4+CD25− T Regulatory Cells on the Generation of Cytolytic T Cell Response to a Self but Human Tumor-Associated Epitope In Vitro

CD4+ T cells naturally expressing CD25 molecules (natural T regulatory cells (Tregs)) have a role in maintaining self tolerance and in regulating responses to infectious agents, transplantation Ags, and tumor Ags. CD4+ Tregs induced from CD4+CD25- precursors (induced Tregs) also regulate immune responses in the periphery. However, which of these Tregs is a major impediment in generating antitumor CTL responses is not clear. We show that although the CD4+CD25+ subsets isolated from peripheral blood-derived lymphocytes do suppress the proliferation of CD4+CD25- effector T cells, they do not suppress the activation and expansion of the self but melanoma-associated, melanoma Ag-reactive T cell 1 (MART-1)27-35-specific CD8+ T cells stimulated by the respective peptide-loaded matured dendritic cells in vitro. The CD4+CD25- counterparts, in contrast, lead to the generation of CD25+ glucocorticoid-inducible TNFR+-Forkhead/winged helix transcription factor+ populations and efficiently suppress the activation and expansion of the MART-127-35 epitope-specific CTLs. Our data suggest that when CTL precursors are optimally stimulated, natural Tregs are not a formidable constraint toward generating a robust antitumor CTL response, but induced Tregs could be.