Tumor-infiltrating lymphocytes (TILs) in GIST are constituted predominantly of CD3+ T cells, including CD8+ cytotoxic T lymphocytes (CTLs), CD4+ T helper type 1 lymphocytes (Th1), CD4+ T helper type 2 lymphocytes (Th2), Forkhead box P3 protein (FoxP3) expressing T-regulatory cells (T-regs,) and IL-17+ T helper cells (Th17). The gene discussed is CD4; the disease is gastrointestinal stromal tumor.