CCR5-dependent homing of T regulatory cells to the tumor microenvironment contributes to skin squamous cell carcinoma development

Squamous cell carcinoma (SCC) is one of the most common human cancers worldwide. Recent studies show that regulatory T cells (Tregs) have a critical role in the modulation of an anti- tumor immune response, and consequently the SCC development. Since the accumulation of Tregs at the tumor site is, in part, due to selective recruitment through CCR5 and CCR5-associated chemokines, we investigated the role of CCR5 in the SCC development. Our findings showed that CCR5-deficient mice (CCR5KO) were efficient in controlling papilloma's incidence when compared with wild-type mice. Analysis of tumor lesions in wild-type (WT) and CCR5KO mice revealed that lack of CCR5 lead to significant reduction in frequency of Treg cells and increased of CD4 T cells into the tumors. Moreover, the adoptive transfer of naturally occurring Tregs CD4+CD25+CCR5+, CD4+CD25-CCR5+ or CD8+CCR5+ conventional T cells to CCR5KO mice resulted in an increased papilloma incidence. Interestingly, adoptive transfer of WT CD4+CD25+CCR5+ cells to CCR5KO mice induced more undifferentiated SCC lesions, characterized by higher infiltration of macrophages and dendritic cells. In the present study, we also demonstrated that Treg migration to the tumor microenvironment is mediated by CCR5, and these cells are promoting tumor growth via inhibition of anti-tumor cells such as cytotoxic CD8+ T cells. Our findings reinforce the therapeutic potential of CCR5 inhibition for cancer treatment, and indicate an attractive approach for SCC treatment.

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