Conversely, PD-1 plays a crucial role in curtailing the activation of effector T cells and NK cells, while also promoting Treg formation in peripheral lymphoid tissues, including tumor locales.668 In the initial phase of the immune response, CTLA-4 restrains T cell proliferation, whereas PD-1 suppresses previously activated T cells in later stages. The gene discussed is CTLA4; the disease is neoplasm.