Similarly, intracellular L-arginine concentrations enhance the differentiation of T SCM and T CM cells with longer persistence and stronger anti-tumor activity in murine models. One study used L-arginine supplementation in the cell medium to promote a switch from glycolysis to OXPHOS in CAR-T cells. The metabolic shift towards OXPHOS contributed to a higher proportion of memory cells with increased survival ability and stronger antitumor cytotoxicity . Moreover, adding 6-diazo-5-oxo-L-norleucine (DON) to the cell culture enhances OXPHOS and reduces glycolytic activity . This resulted in more T CM subsets and stronger anti-tumor activity in vivo . Furthermore, recent studies indicate that using PhysiologixTM xeno-free (XF) hGFC (Phx), a human growth factor, facilitates T cell proliferation and CAR-T cell expansion . CAR-T cells were compared to cells conditioned in Phx or HS to determine a difference in anti-tumor response in a murine xenograft model . T cells cultured in Phx had improved persistence in vivo and superior cytotoxic capabilities in vitro . Specifically, the dipeptide carnosine found in Phx augments the persistence of T cells and shifts them towards an oxidative state, thus enriching the T CM cell subset.