HAVCR2 and neoplasm: T cell function can also be inhibited by other co-inhibitory “checkpoint” molecules, such as cytotoxic T lymphocyte-associated protein-4 (CTLA-4), T cell immunoglobulin and mucin domain containing-3 (Tim-3), lymphocyte activating gene 3 (Lag3) and T cell immunoreceptor with Ig and ITIM domains (TIGIT), which are upregulated on the surface of T cells after activation and remain highly expressed on T cells in the tumor microenvironment (TME) due to persistent activation signals.