CD39+ Activated Tregs in Cutaneous Squamous Cell Carcinoma: Insights From a Mendelian Randomization and Flow Cytometry Study

Cutaneous squamous cell carcinoma is a common keratinocyte-derived malignancy shaped by the immune microenvironment. Regulatory T cells are essential for maintaining immune balance, yet within tumors, they suppress protective immunity and promote cancer progression. The contribution of specific subsets of these cells to cutaneous squamous cell carcinoma remains unclear. In this study, we combined genetic causal inference with blood-based immune profiling to investigate the role of CD39-expressing regulatory T cells. Peripheral blood samples from patients and healthy controls were analyzed by flow cytometry, which revealed an increased frequency of activated regulatory T cells in patients. Using genome-wide association study data, Mendelian randomization analyses identified a causal relationship between genetically predicted CD39-positive regulatory T cells and risk of cutaneous squamous cell carcinoma. In an independent validation cohort, the proportion of CD39-expressing cells within the activated regulatory T cell population correlated with higher tumor stage and disease progression. These findings demonstrate that CD39-positive regulatory T cells constitute a distinct immunosuppressive subset with clinical relevance. By integrating immunophenotyping, genetic inference, and validation in patient samples, this study provides novel evidence for the role of CD39-positive regulatory T cells in cutaneous squamous cell carcinoma and supports their potential as selective targets for future immunotherapy.