Thymosin α-1

Thymosin α-1 (Tα1) is a 28-amino-acid peptide derived from prothymosin α, naturally produced by thymic epithelial cells, that modulates innate and adaptive immunity by activating TLR signalling in dendritic cells and monocytes and promoting Th1-type T-cell responses. The thymus undergoes substantial involution from early adulthood, and declining thymic output with age contributes to T-cell senescence and immune ageing; Tα1 supplementation is proposed to partially compensate for this deficit. Thymalfasin (Zadaxin, SciClone Pharmaceuticals) is approved in over 35 countries — but not the United States — as an adjunct therapy for chronic hepatitis B and C and as an immunostimulant in patients with impaired immunity; it has been used off-label during COVID-19 outbreaks in several countries. Human evidence for anti-aging or longevity benefit is absent; trials in cancer and infection support immunomodulatory activity, but effect sizes and consistency vary. Tα1 is widely marketed by anti-aging clinics; its regulatory classification ranges from approved drug to unregulated peptide depending on jurisdiction.