Thymosin Alpha-1 (Zadaxin): Immune-Modulating Peptide
28-amino-acid peptide originally isolated from thymus. Approved in 30+ countries for hepatitis B; investigated for sepsis, cancer adjuvant and COVID-19.
✅ Approved
- Full name
- Thymalfasin / Thymosin alpha-1 (Tα1)
- Class
- Immunomodulatory peptide
- Half-life
- ~2 hours
- Route
- Subcutaneous
- Brand names
- Zadaxin (SciClone / Sigma-Tau)
- Regulatory status
- Approved in China, Italy and ~30 countries for HBV and immune adjunct; not FDA-approved
What it is
Thymosin alpha-1 is a 28-residue acetylated peptide originally isolated from bovine thymus fraction 5. Synthetic Tα1 is approved in many countries as an adjuvant for chronic hepatitis B and as an immune modulator in sepsis and vaccine response.
How it works
Tα1 promotes differentiation and function of T-helper cells, augments Th1 responses, and enhances dendritic-cell activity through TLR-2 and TLR-9 signalling. It restores immune function in immune-suppressed states.
In chronic HBV, Tα1 combined with pegylated interferon improves sustained virologic response rates. Mechanistic effects in cancer adjuvant settings rely on enhanced tumour antigen presentation.
What the research shows
Meta-analyses in hepatitis B and Phase 2 trials in sepsis/COVID-19 support immune-modulatory efficacy.
Chien RN et al. (1998) — HBV meta-analysis
Chien R.N. et al., Hepatology 1998;27:1383–1387 (+ subsequent meta-analyses). 👥 Human studies
Randomised trials of Tα1 monotherapy or combination with interferon in chronic HBV demonstrated higher HBV DNA-negativity and ALT normalisation rates than interferon alone.
Meta-analyses support approval in multiple jurisdictions.
Limitations: Effect sizes modest; newer nucleoside analogues largely supplanted first-line use.
Wu J. et al. (2020) — COVID-19 severe pneumonia
Wu J. et al., Clin Infect Dis 2020;71:e204–e211. 👥 Human studies
Retrospective analysis of 76 severe COVID-19 patients: Tα1 reduced mortality vs matched controls (11.8% vs 30%).
Prospective RCTs attempted during 2020–2022 produced mixed signals; no regulatory approval for COVID-19.
Limitations: Retrospective; small; confounding by indication.
Safety and limitations
Generally well tolerated: injection-site reactions, transient muscle pain, rare rashes. No major laboratory abnormalities have been consistently reported.
Not FDA-approved; evidence quality varies. Products purchased outside regulated markets may not meet pharmacopeia standards.