PBT significantly enhanced the antitumor efficacy of PD-1 blockade in both 4T1 mammary carcinoma and B16F10 melanoma tumors resistant to anti-PD-1 monotherapy, increasing tumor-specific cytotoxic T cells and survival of tumor-bearing animals beyond that with PBT or PD-1 blockade alone (99). Here, PDCD1 is linked to melanoma.