Thymosin alpha-1

Thymosin alpha-1 (also written Tα1, thymalfasin, or by the brand name Zadaxin) is a 28-amino-acid synthetic peptide derived from thymosin fraction 5, originally isolated from calf thymus by Allan Goldstein in the 1970s. The peptide is an immunomodulator approved in more than 35 countries (not including the United States) for the treatment of chronic hepatitis B and C and as an adjuvant in immune-compromised patients.

Peppudex card: see the mechanism + evidence-grade summary at [Peppudex / Thymosin alpha-1](https://peppudex.com/peptides/thymosin-alpha-1).

Overview

Thymosin alpha-1 is one of the most clinically validated immunomodulatory peptides on the global market, with FDA-approved status in many jurisdictions outside the US, including Italy, Brazil, Singapore, and across much of Asia. Brand name Zadaxin is marketed by SciClone Pharmaceuticals. The compound is on the WHO List of Essential Medicines in many countries.

The sequence is the N-terminal 28 amino acids of prothymosin alpha, Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN.

Mechanism

The compound is a toll-like receptor 9 (TLR9) agonist with additional indirect effects on dendritic-cell maturation and Th1/Th2 cytokine balance. Major effects observed in clinical and preclinical studies:

• Increased CD4+ and CD8+ T-cell function
• Enhanced natural killer cell activity
• Modulation of Th1/Th2 cytokine balance toward Th1
• Improved antibody response to vaccination

Evidence

Broad clinical evidence base across multiple indications:

• Chronic hepatitis B · Multiple Phase 3 trials in Asia showed virological response when combined with IFN-α or pegylated IFN.
• Chronic hepatitis C · Adjunct to standard antiviral therapy (now historical given DAA dominance).
• Sepsis · Phase 3 in China (Wu et al., Crit Care 2013) reported 28-day mortality reduction.
• COVID-19 · Multiple Chinese trials reported clinical benefit in severe COVID-19; results have not consistently met Western trial methodology.
• Vaccine adjuvant · Used to enhance influenza vaccine response in elderly populations.

Dosing literature

Approved dosing in non-US jurisdictions is subcutaneous 1.6 mg twice weekly for chronic hepatitis B/C, typically for 6-12 months. The wiki does not recommend any human dose; in the United States, thymosin alpha-1 is research-use only.

Storage

Lyophilized thymosin alpha-1 is stable at –20 °C for at least 24 months. Once reconstituted with bacteriostatic water, store at 2-8 °C and use within 28 days.

Regulatory status

• United States. Not FDA-approved. Research-use only.
• Italy / Brazil / Singapore / China / 30+ other countries. Approved as Zadaxin for chronic hepatitis B and C and as an immune-system adjuvant.
• WADA. Not listed on the 2024 Prohibited List.

See also

• Humanin · another endogenous peptide with immunomodulatory/protective effects
• Reconstitution · vial-prep math
• [Peppudex card · Thymosin alpha-1](https://peppudex.com/peptides/thymosin-alpha-1) · mechanism, evidence grades A-F, FAQs, peer-reviewed sources

References

• Goldstein AL, Goldstein AL. "From lab to bedside: emerging clinical applications of thymosin alpha 1." Expert Opin Biol Ther. 2009;9(5):593-608. PMID 19392576.
• Wu J, et al. "The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicentre, single-blind, randomized and controlled trial." Crit Care. 2013;17(1):R8. PMID 23327199.
• Liu Y, et al. "Thymosin Alpha 1 Reduces the Mortality of Severe Coronavirus Disease 2019 by Restoration of Lymphocytopenia and Reversion of Exhausted T Cells." Clin Infect Dis. 2020;71(16):2150-2157. PMID 32442287.