Tumour infiltrating lymphocytes (TILs) constitute a subpopulation of immunocompetent mono- and polymorphonuclear lymphocytic cells, the most important of which includes a subset of CD3+CD4+ T helper type 1 (Th1) lymphocytes, cytotoxic CD3+CD8+ T cells (CTLs) and regulatory T lymphocytes (CD4+CD25+Foxp3+Tregs). The gene discussed is CD4; the disease is neoplasm.