In the treatment of malignant tumors such as renal cell carcinoma and prostate cancer, the FDA-approved immune checkpoint inhibitors Ipilimumab and Tremelimumab, which target CTLA-4 (cytotoxic T-lymphocyte-associated protein 4), have demonstrated potent anti-tumor effects by targeting Treg cells [25]. Here, CTLA4 is linked to prostate cancer.