On the other hand, anti-PD-1 therapy of tumors infiltrated with sub-optimally primed T cells can lead to exhaustion of these T cells; optimal priming of these T cells by cancer vaccine treatment prior to anti-PD-1 therapy can overcome anti-PD-1-mediated T cell exhaustion and lead to tumor eradication [111] (Figure 1). The gene discussed is PDCD1; the disease is cancer.