CD4 and prostate cancer: One explanation for this unusual finding was that Treg expansion relied on IL-2 levels produced by specific antigen-activated effector lymphocytes either CD4 + or CD8 + T cells (Sojka et al. 2008; Romano et al. 2019) to weaken a potentially harmful overreactive immune response, although no significant increase in the level of IL-2 expression was observed in prostate cancer patients receiving CIRT in our study, indicating that other mechanisms like the binding of TNF to TNF receptor type 2 might contribute to expansion of Tregs (Salomon et al. 2018).