CD4 and neoplasm: A study in an ovalbumin (OVA)-expressing tumor model showed that when OVA-specific CD4 T cells were transferred into tumor-transplanted aged mice (20 months old) and young mice (≤ 6 months old) with OX40 agonist, the OX40 stimulation-induced effector T-cell differentiation of the transferred cells was reduced in aged mice [36].