Adverse prognostic impact of regulatory T‐cells in testicular diffuse large B‐cell lymphoma

Objectives Testicular diffuse large B‐cell lymphoma (T‐DLBCL) is a rare and aggressive extranodal lymphoma. We have previously shown that high content of tumor‐infiltrating lymphocytes (TILs) and PD‐1 expressing TILs associate with better survival in T‐DLBCL. In this study, we have further characterized distinct TIL subtypes and their proportions in association with patient demographics and survival. Methods We used multiplex immunohistochemistry to characterize TIL phenotypes, including cytotoxic T‐cells (CTLs; CD8+, OX40+, Granzyme B+, Ki‐67+, LAG‐3+, TIM‐3+, PD‐1+), CD4+ T‐cells (CD3+, CD4+, TIM‐3+, LAG‐3+), regulatory T‐cells (Tregs; CD3+, CD4+, FoxP3+), and T helper 1 cells (Th1; CD3+, CD4+, T‐bet+) in 79 T‐DLBCLs, and correlated the findings with patient demographics and outcome. Results We observed a substantial variation in TIL phenotypes between the patients. The most prominent CD8+ TILs were Ki‐67+ and TIM‐3+ CTLs, whereas the most prominent CD4+ TILs were FoxP3+ Tregs. Despite the overall favorable prognostic impact of high TIL content, we found a subpopulation of T‐bet+FoxP3+ Tregs that had a significant adverse impact on survival. Lower content of CTLs with activated or exhausted phenotypes correlated with aggressive clinical features. Conclusions Our results demonstrate significant variation in TIL phenotypes and emphasize the adverse prognostic impact of Tregs in T‐DLBCL.