Thymalin is a polypeptide complex extracted from calf thymus by mild acid extraction — a mixture of short thymic peptide fragments rather than a single defined molecule — developed by the Khavinson school in Russia as a bioregulator preparation, and proposed to restore age-related immune dysfunction associated with thymic involution by supplying thymic hormonal signals that support T-lymphocyte differentiation, immune homeostasis, and immunological reserve in elderly subjects. Its active substances include the dipeptides Lys-Glu (KE, the same dipeptide sold separately as vilon) and Glu-Trp (EW), the latter isolated from thymalin by reversed-phase HPLC and synthesized as the pharmaceutical Thymogen. As a thymic bioregulator, thymalin is proposed to modulate gene expression in aging lymphoid cells through peptide-chromatin interactions and to support thymopoiesis and T-cell maturation in subjects whose endogenous thymic output has declined with age-associated involution; in vitro it shifted human hematopoietic stem cells toward a mature T-lymphocyte marker profile (CD28 up, CD44 and CD117 down), and thymalin and its KE and EW dipeptides reduced IL-1β, IL-6 and TNF-α synthesis in stimulated human blood mononuclear cells. The Khavinson laboratory has reported that long-term courses of thymalin and related thymic and pineal peptides were associated with reduced all-cause mortality in elderly cohorts over extended follow-up — the 2003 Neuro Endocrinol Lett study and the 2002 Adv Gerontol review cited on this profile — and geroprotective effects in Russian geriatric research populations. Thymalin is not FDA-approved; in Russia it is marketed as an immunomodulatory drug — 'put into practice as an immunocorrector', in the Khavinson group's words — and has been used clinically there, including in elderly patients, but its evidence base derives from Russian-origin observational and preclinical studies whose elderly-cohort outcome data have not been independently replicated in Western trials. Thymalin is not the same substance as thymulin, the defined zinc-dependent nonapeptide thymic hormone, despite the similar names.
Research on thymalin has investigated immune-system restoration in aged subjects, T-lymphocyte counts and function, cytokine balance, and partial reversal of age-associated thymic involution. Khavinson-group reviews report lifespan extension in aged animal models, and observational work in elderly human cohorts using thymic peptide preparations has associated treatment with reduced all-cause mortality over multiyear follow-up — findings published in Russian medical literature and not yet replicated independently. As a thymic bioregulator, thymalin is proposed to work by restoring the hormonal output of the aging thymus rather than by immunosuppression or direct cytokine administration, which distinguishes it from synthetic immunomodulatory drugs. Research interest also covers age-related susceptibility to infection, autoimmune regulation, and immune resilience within longevity-focused bioregulator research.