Thymosin Alpha-1

Tα1 modulates both innate and adaptive immune responses by stimulating the differentiation and maturation of T-cells, dendritic cells, and natural killer cells. It upregulates MHC class I and II expression, enhancing antigen presentation. It also promotes the production of key cytokines including interferon-γ and interleukin-2, which are central to immune surveillance.

Thymosin alpha-1 (thymalfasin; Zadaxin) is a 28-amino-acid synthetic peptide corresponding to the N-terminal sequence of prothymosin alpha, developed as a biological response modifier with established clinical use outside the United States for chronic viral hepatitis and as an immune adjuvant in cancer and immunocompromised patients. Thymalfasin modulates innate and adaptive immune responses by upregulating Toll-like receptor expression and dendritic cell maturation, enhancing T-helper 1 cytokine signaling, and potentiating antigen-specific T-cell responses in settings of impaired immune function. A prospective multicenter randomized controlled trial demonstrated that combination therapy with thymosin alpha-1 and entecavir improved serological outcomes in HBV-related compensated cirrhosis compared to entecavir alone, and cumulative RCT evidence supports its role as an immune adjuvant in hepatitis B and C treatment. Thymosin alpha-1 is approved in approximately 35 countries — including China, Italy, and other Asian and Eastern European markets — for hepatitis B and hepatitis C adjuvant therapy, but has not received FDA approval in the United States and is available in US-adjacent research contexts only as an investigational compound. Thymosin alpha-1 dosage: in approved clinical protocols (hepatitis B adjuvant therapy), thymalfasin is administered as 1.6 mg subcutaneously twice weekly for 26–52 weeks. This dosing schedule is derived from the pivotal trials conducted by SciClone Pharmaceuticals, which developed Zadaxin. In COVID-19 research during 2020–2021, Chinese clinical centers studied thymosin alpha-1 as an immune adjuvant in severe and critical COVID-19 patients, with published observational and small RCT data; this research context brought renewed attention to the peptide's immune-modulating properties outside the hepatitis indication. Within the recovery and immune-support peptide landscape, thymosin alpha-1 is most closely compared to thymosin beta-4 (TB-500) — the two peptides share the thymosin nomenclature but have distinct mechanisms and research profiles. Thymosin alpha-1 is an immune activator (TH1 upregulation); thymosin beta-4 is primarily studied for tissue repair and actin dynamics. Providers offering immune-modulating peptide compounds are listed in the PeptideBase directory.