CD4 and neoplasm: In research on NSCLC, exosomes from Rab27a-overexpressing tumor cells have been shown to promote the maturation of DCs by upregulating major histocompatibility complex class I molecules (MHC II) and the costimulatory molecules CD80 and CD86, significantly promoting the proliferation and response of CD4+ T cells in vitro and in vivo [32].