CD4 and neoplasm: Numerous studies have shown that cytotoxic CD8+ (killing tumor cells) and CD4+ (helper T cells promote tumor cell death and/or regulatory T cells) lymphocytes influence the prognosis and response to tumor therapy, and that the functional status of CD8+ and CD4+ determines the ability to kill tumor cells (Galon et al., 2006; Pagès et al., 2009; Wallis et al., 2015).