T-cell activation is regulated by immune checkpoint proteins such as PD-1, cytotoxic T lymphocyte antigen-4 (CTLA-4), lymphocyte activation gene-3, T-cell immunoglobulin and mucin domain–containing-3 (TIM-3), and T-cell immunoreceptor with immunoglobulin and ITIM domain (TIGIT).22 Understanding the role of these proteins in regulating CD8+ T cell–mediated killing of tumor cells has been key to the development of ICB strategies.23 The gene discussed is CTLA4; the disease is neoplasm.