Tumor-infiltrating lymphocytes (TILs) serve as representative markers for the predominant presence of CD8+ cytotoxic T lymphocytes (CTLs), CD3+ T cells, and CD4+/FoxP3+ regulatory T cells (Tregs) within the glioblastoma (GBM) tumor microenvironment (TME). The gene discussed is CD8A; the disease is glioblastoma.