A study performed by Lindner et al. showed that IL-21-producing Tregs found in human breast, ovarian, cervical, colorectal, and prostate carcinomas, induce CD19+ B cells differentiation into Bregs (CD19+ CD38+ CD1d+ IgM+ CD147+) expressing IL‐10, indoleamine 2,3-dioxygenase 1 (IDO1), and granzyme B (GrB). Here, IDO1 is linked to prostate carcinoma.