CD4 and neoplasm: It is possible that CD4+ Th1 cells in the ACT provide a source of IL-2 to support CD8+ CTL survival and recruit tumour-specific CD8+ CTLs.32, 33, 34 CD4+ Th cells have also been shown to improve CD8+ CTL memory response by retained CD27 expression during lymphocytic choriomeningitis virus infection.35