TIGIT and melanoma: Melanoma cells induce Tregs to overexpress various inhibitory checkpoint receptors, including programmed cell death protein 1 (PD-1), CTLA-4, T cell immunoglobulin and mucin domain-containing protein 3 (TIM-3), LAG-3, and T cell immunoglobulin and ITIM domain (TIGIT) [93–96].