We previously observed that the anti-tumor efficacy of combined anti-PD-L1 and anti-TIGIT blockade in mice is abrogated by a CD226-blocking mAb (Johnston et al., 2014), suggesting that costimulation by both CD226 and CD28 is required to overcome inhibition by PD-1 and TIGIT. The gene discussed is PDCD1; the disease is neoplasm.