TIGIT and cancer: In addition to PD-1/PD-L1 and CTLA-4, other checkpoint molecules such as the T-cell immunoglobulin and mucin domain 3 (TIM-3), lymphocyte activation gene-3 (LAG3), T-cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif (ITIM) domain (TIGIT), and, more recently, V-domain immunoglobulin suppressor of T-cell activation (VISTA) have been explored as potential targets for the development of new agents for cancer immunotherapy (4).