Immunomodulation of UVB-induced regulatory T cells prevents the establishment of squamous cell carcinoma.

BACKGROUND: Cutaneous squamous cell carcinoma (cSCC) is the second most common form of skin cancer in Asian, Caucasian, and Hispanic populations and its aggressive form contributes to significant morbidity and mortality. Chronic ultraviolet B (UVB) exposure is a major environmental carcinogen that drives cSCC initiation, progression, and immune evasion. Regulatory T cells (Tregs) are known mediators of UVB-induced immunosuppression; however, their direct involvement in the establishment of cSCC remains elusive. METHODS: Flow cytometry was employed to quantify Treg populations in the skin and draining lymph nodes of UVB-exposed and untreated mice. The functional role of Tregs following UVB exposure was examined using a contact hypersensitivity assay, where Treg activity was modulated by anti-cytotoxic T-lymphocyte-associated protein (CTLA)-4, anti-TIGIT, and anti-FR4 antibodies. The capacity of UVB to render mice susceptible to immunogenic cSCC tumor establishment was assessed under different UVB exposure regimens. Treg-modulating antibodies were administered following UVB treatment and prior to tumor implantation to explore whether UV-induced Treg manipulation can prevent cSCC tumor establishment. RESULTS: UVB irradiation for 5 consecutive days significantly increased the number of CD4+ Foxp3+ Tregs in both skin and skin-draining lymph nodes. These Tregs were shown to be suppressive in contact hypersensitivity assays. However, suppression was prevented following depletion of Tregs and/or avolition of their function using monoclonal antibodies. Consistently, chronic UVB exposure prior to tumor implantation permitted the establishment and growth of otherwise immunogenic cSCC tumors, which correlated with the expansion and recruitment of Tregs into the skin. Importantly, immunomodulation with anti-CTLA-4 or anti-FR4 after chronic UVB exposure effectively prevented cSCC establishment, indicating that the manipulation of UV-induced Tregs prevented the establishment and growth of immunogenic cSCC tumors. CONCLUSION: Our findings show that the manipulation of UV-induced Tregs prevents early cSCC establishment. Thus, strategies aimed at modulating Treg function or abundance in the skin may represent a feasible therapeutic avenue for the prevention of cSCC tumor emergence in patients.