Regulatory T cells restrain IL-2- and Blimp-1-dependent acquisition of cytotoxic function by CD4+ T cells

In addition to helper and regulatory potential, CD4+T cells also acquire cytotoxic activity marked by granzyme B (GzmB) expression and the ability to promote rejection of established tumors. Here we examined the molecular and cellular mechanisms underpinning the differentiation of cytotoxic CD4+T cells following immunotherapy. CD4 transfer into lymphodepleted animals or regulatory T cell (Treg)depletion promoted GzmB expression by tumor-infiltrating CD4+which was prevented by IL-2 neutralization. Transcriptional analysis revealed a polyfunctional helper and cytotoxic phenotype characterized bythe expression of the transcription factors T-bet and Blimp-1. Whilst T-bet ablation restrictedIFN-gproduction, lossof Blimp-1preventedGzmB expressionin response to IL-2, suggesting these are two independent programs required forpolyfunctionality of tumor-reactive CD4+T cells. The data underscores the role of Treg, IL-2 and Blimp-1 controlling the differentiation of cytotoxic T cells and offers a pathway to enhancement of anti-tumor activity through their manipulation. To investigate gene expression of TCR-transgenic Trp1 CD4+ T cells in B16 melanoma, tumor-bearing mice were left untreated or treated at day 8 with total body irradiation (RT)+Trp1+aCTLA-4 (Trp1 Th-ctx), Trp1+GVAX+aCTLA-4 (Trp1 Th), or Trp1 cells in the absence of irradiation or vaccine as a control (Trp1 ctrl). Foxp3- cells were isolated from tumours of Th and Th-ctx treated mice and draining lymph nodes of ctrl treated mice 8 days after treatment initiation.