Data from OX40⁺ Regulatory T Cells in Cutaneous Squamous Cell Carcinoma Suppress Effector T-Cell Responses and Associate with Metastatic Potential

Abstract

<div>Abstract<p><b>Purpose:</b> Cutaneous squamous cell carcinoma (cSCC) is the most common human cancer with metastatic potential. Despite T cells accumulating around cSCCs, these tumors continue to grow and persist. To investigate reasons for failure of T cells to mount a protective response in cSCC, we focused on regulatory T cells (Tregs) as this suppressive population is well represented among the infiltrating lymphocytes.</p><p><b>Experimental Design:</b> Flow cytometry was conducted on cSCC lymphocytes and <i>in vitro</i> functional assays were performed using sorted tumoral T cells. Lymphocyte subsets in primary cSCCs were quantified immunohistochemically.</p><p><b>Results:</b> FOXP3<sup>+</sup> Tregs were more frequent in cSCCs than in peripheral blood (<i>P</i> < 0.0001, <i>n</i> = 86 tumors). Tumoral Tregs suppressed proliferation of tumoral effector CD4<sup>+</sup> (<i>P</i> = 0.005, <i>n</i> = 10 tumors) and CD8<sup>+</sup> T cells (<i>P</i> = 0.043, <i>n</i> = 9 tumors) and inhibited IFNγ secretion by tumoral effector T cells (<i>P</i> = 0.0186, <i>n</i> = 11 tumors). The costimulatory molecule OX40 was expressed predominantly on tumoral Tregs (<i>P</i> < 0.0001, <i>n</i> = 15 tumors) and triggering OX40 with an agonist anti-OX40 antibody overcame the suppression exerted by Tregs, leading to increased tumoral effector CD4<sup>+</sup> lymphocyte proliferation (<i>P</i> = 0.0098, <i>n</i> = 10 tumors). Tregs and OX40<sup>+</sup> lymphocytes were more abundant in primary cSCCs that metastasized than in primary cSCCs that had not metastasized (<i>n</i> = 48 and <i>n</i> = 49 tumors, respectively).</p><p><b>Conclusions:</b> Tregs in cSCCs suppress effector T-cell responses and are associated with subsequent metastasis, suggesting a key role for Tregs in cSCC development and progression. OX40 agonism reversed the suppressive effects of Tregs <i>in vitro</i>, suggesting that targeting OX40 could benefit the subset of cSCC patients at high risk of metastasis. <i>Clin Cancer Res; 22(16); 4236–48. ©2016 AACR</i>.</p></div>