Tuftsin is a tetrapeptide that binds the neuropilin-1 (Nrp1) receptor, modulating TGF-β, cGMP, and Ca2+ signaling. Tuftsin is derived from the Fc region of IgG. Tuftsin exhibits immunomodulatory activity, inducing leukocytes to become cytotoxic effector cells and stimulating phagocytosis in macrophages and microglia in cellular models. Tuftsin also displays anticancer chemotherapeutic benefit, enhancing the effects of co-administered chemotherapeutic compounds. In animal models, tuftsin also inhibits withdrawal-associated behaviors.