CD4 and cancer: The results of the study by Xiao et al. reported that a rich environmental profile is an important factor in cancer risk and progression, the enhanced anticancer effect of the enriched environment is mediated in part by the regulation of immune responses, such as CD4 helper T cells and CD8 cytotoxic T lymphocyte; BDNF acts as a key brain mediator and synergizes with immunity to exert anticancer effects.37