Within the thymus, cells are regulated by a complex mixture of cytokines and small peptides collectively known as thymic hormones. These peptides include thymosin, thymopoietin, thymic humoral factor, and thymulin. Thymulin is a zinc-containing peptide secreted by the thymic epithelial cells, and it can partially restore T cell function in thymectomized animals. Zinc is an essential mineral for the development of T cells. Consequently, zinc-deficient animals have defective cell-mediated immune responses.

Thymosin alpha-1 is an immunomodulatory polypeptide belonging to the group of thymic hormones. It is also produced endogenously by the thymus gland and increases T cell-mediated immune responses by several mechanisms, including stimulation of T-cell differentiation and/or maturation, activation of natural killer cells and dendritic cells, and stimulation of proinflammatory cytokine release. Pilot studies in patients with advanced melanoma have suggested that thymosin alpha-1 may improve the efficacy of dacarbazine-based regimens. Thymosin alpha-1 has had a very favorable adverse reactions even when used in cancer treatment studies.