While genetic loss of PD-L1 or inhibition of either PD-1 or CTLA-4 with a monoclonal antibody did not slow cyst progression, combination treatment of anti–PD-1 and anti–CTLA-4 significantly slowed PKD, suggesting, as seen in cancer clinical trials, that dual immune checkpoint blockade increases efficacy and response rate (20, 35). Here, PDCD1 is linked to cancer.