Lindner et al. found that IL-21-induced human GrB+ Bregs inhibited CD4+ T-cell proliferation by transporting active GrB to T cells and degrading the T-cell receptor ζ-chain in vitro (30).Furthermore, these GrB+ Bregs were found to infiltrate numerous human solid tumors, including breast, ovarian, cervical, colorectal, and prostate carcinomas. Here, GZMB is linked to prostate carcinoma.