CD62Lhigh CD4+CD25+ Regulatory T cells primed in tumor-draining lymph nodes abrogate antitumor efficacy of effector T cells via B7-2 / CTLA-4 T-T interaction

Abstract

2653

Tumor cells possess altered antigens that can be recognized by T cells, however, lack of danger signals and antigenic similarity to self-somatic cells, which tumor cells are derived from, engage the self-tolerance mechanism. This is one of the major reasons why anti-tumor immunity is hardly acquired. Secondary lymphoid organs are the places where antigen information carried by antigen presenting cells is converted to adaptive immune responses. We reported that antitumor effector T cells, which can mediate antitumor reactivity to cure established tumor in vivo, in LNs draining a growing skin tumor exclusively belonged to the CD62Llow subpopulation. Moreover, it was suggested that CD62Lhigh T cells contained regulatory subpopulation, because of our observation that the elimination of CD62Lhigh cells promotes generation of highly potent antitumor T cells upon CD3 stimulation. Recent studies revealed CD4+ T cells that constitutively express CD25 are playing a critical role in maintaining peripheral tolerance in numerous systems examined, such as infection, transplantation, autoimmunity, and tumor immunity. However, CD25 is also up-regulated on effector T cells upon TCR engagement before clonal expansion. Thus, it is difficult to distinguish regulatory T cells by CD25 expression, especially in LNs where T cell priming is going on, and this difficulty make it impossible to analyze how regulatory T cell are primed in LNs. Here, we analyze CD4+ tumor-draining LN T cells based on CD62L and CD25 expression and demonstrate that both antitumor effector T cells and regulatory T cells are primed in the same LNs draining growing skin tumors with different kinetics. CD62Llow antitumor effector T cells increased early in TDLN but were quickly taken over by CD62Lhigh CD4+CD25+ regulatory T cells, which are capable of abrogating the antitumor reactivity of CD62Llow LN T cells. Either CD62Llow CD4+CD25+ or CD62Llow CD4+CD25- LN T cells were proven to be antitumor effector T cells since they mediated antitumor efficacy when tranfered to skin tumor bearing mice, while the functions and phenotype of CD62Lhigh CD4+CD25- T cells were compatible with naïve T cells. FoxP3 expression was found to be unique for CD62Lhigh CD4+CD25+ LN T cells. CD62Lhigh CD4+CD25+ T cells could not be distinguished from CD62Llow CD4+CD25+ T cells by GITR, CTLA-4, or LAG3 expression. CD62Lhigh CD4+CD25+ LN T cells abolished proliferation and IFNγ production of CD62Llow effector T cells in the presence of immobilized anti-CD3 mAb. Unexpectedly, CD62Lhigh CD4+CD25+ regulatory T cells expressed B7-2. Blockade of CTLA-4/B7-2 interactions resulted in loss of regulatory activities. Our results indicated that CD62Lhigh CD4+CD25+ regulatory T cells primed in tumor-draining LNs abrogated the antitumor effector T cell functions via B7-2/CTLA-4 T-T interaction.