The CD8+ T lymphocytes can be further divided into CD8+CD28+ T lymphocytes (CTL) and CD8+CD28− T lymphocytes based on the expression of CD28 on the surface of CD8+ T lymphocytes, of which CD8+CD28− T lymphocytes are a class of regulatory T cells that do not have tumor-killing functions. This evidence concerns the gene CD28 and neoplasm.