Naturally arising memory-phenotype CD4+ T lymphocytes give rise to multiple helper subsets to contribute to tumor immunity while inhibiting GVHD

Abstract Memory-phenotype (MP) CD4+ T lymphocytes spontaneously develop in steady state from peripheral naïve precursors in a manner dependent on self-antigen recognition. While MP cells possess innate type 1 and 3 effector functions that can contribute to host defense and autoimmunity, their immunological functions in tumor immunity and graft-versus-host disease (GVHD), which results from therapeutic bone marrow transplantation (BMT) against hematological malignancies, remain unclear. Here we show that in mixed lymphocyte reactions, MP lymphocytes can generate T helper 1 (Th1), T helper 17 (Th17), and regulatory T (Treg) cell subsets, whereas naïve cells dominantly differentiate to Th1. Consistent with this, naïve lymphocytes mainly induce Th1 responses in the mouse EL4 model of malignant lymphoma and the B16 model of malignant melanoma, whereas MP cells efficiently give rise to Th1, Th17, and Treg subsets to exert mild, IFN--dependent antitumor activities in vivo. Moreover, we demonstrate using a mouse model of BMT that MP cells more efficiently differentiate into Treg cells to partially suppress GVHD as compared to naïve T lymphocytes. Furthermore, our data suggest that when used as donor T lymphocytes in BMT in tumor-bearing mice, MP cells give rise to Th1, Th17, and Treg cells to generate antitumor responses without inducing GVHD. Together these results identify MP cells as a unique T-cell population that has potential to generate multiple T helper subsets including Th1 and Treg cells, thereby contributing to tumor immunity while inhibiting development of BMT-associated GVHD.