CD4 and neoplasm: Therapeutic cancer vaccine effectiveness is often compromised by T cell exhaustion that can be driven by the suboptimal priming of CTLs (such as persistent antigenic stimulation, lack help signals from DCs and CD4+ T cells)[79, 80] or the existence of inhibitory signals from tumor or stromal cells.[81] Exhausted T cells display a dysfunctional state, losing their capability of producing cytokines and cytotoxic enzymes against tumor cells.