CD8A and neoplasm: Meanwhile, in TME, l-arginine is predominantly deficient or depleted, and immunosuppressive cells such as M2 macrophages, regulatory T cells, and MDSCs can compete with CD8+ T cells, which exert anti-tumor immunity, for l-arginine, while recent studies have found that supplementation with l-arginine along with knockdown of CAT-2 transporter promoted infiltration and activation of CD8+ T cells and suppressed tumor growth58.