Overview
Thymosin Alpha-1 (Tα1) is a 28-amino acid acetylated peptide originally isolated from calf thymus tissue as part of Thymosin Fraction 5, a mixture of thymic peptides studied from the 1960s onward for their role in immune system development. Tα1 corresponds to the N-terminal fragment of the precursor protein prothymosin alpha and is understood to be involved in T-lymphocyte maturation and broader modulation of innate and adaptive immune responses.
Unlike most peptides covered in this library, Thymosin Alpha-1 has an established international regulatory history: it is approved and marketed under the brand name Zadaxin in a number of countries, including China and several other Asian and Latin American markets, and has held approvals or been used under named-patient/compassionate frameworks in some European contexts, primarily as an adjunct in chronic hepatitis B and C management and as an immune adjuvant in immunocompromised patients. It is not approved as a medicine in Ireland or the EU under standard marketing authorisation. This guide is for educational and research purposes only. Not medical advice.
Clinical & Research Status
| Evidence Type |
Status |
| Human RCT |
✔ |
| Observational |
✔ |
| Animal Studies |
✔ |
| In Vitro |
✔ |
| Regulatory Approval |
✔ (outside Ireland/EU — e.g., China, marketed as Zadaxin) |
Mechanism of Action
Thymosin Alpha-1 is studied as an immunomodulatory peptide that acts on multiple components of the innate and adaptive immune system rather than through a single defined receptor mechanism. Research has identified interactions with Toll-like receptors (particularly TLR9 and TLR2) on dendritic cells and other innate immune cells, promoting dendritic cell maturation and cytokine production, including interferon-alpha and other type I interferons.
On the adaptive immune side, Tα1 has been studied for its role in promoting T-cell maturation and differentiation within the thymus and periphery, increasing the expression of T-cell surface markers, enhancing natural killer (NK) cell activity, and modulating the balance of T-helper cell subsets. Additional mechanistic research has explored Tα1's interaction with the enzyme prolyl hydroxylase (PHD) and effects on hypoxia-inducible factor (HIF) pathways, as well as antioxidant and anti-apoptotic properties observed in some preclinical models, positioning it as a broad immune "restorative" or "balancing" agent rather than a narrowly targeted immunostimulant.
Research Areas & Reported Effects
Chronic Viral Hepatitis (B and C)
The most extensively studied clinical application of Thymosin Alpha-1 is as an adjunct treatment in chronic hepatitis B and hepatitis C, historically often combined with interferon-alpha, and investigated for its effect on viral load reduction, ALT normalisation, and histological improvement in liver tissue in multiple randomised controlled trials and meta-analyses conducted primarily prior to the direct-acting antiviral era for hepatitis C.
Immune Adjuvant in Vaccination and Immunocompromised Populations
Research has examined Tα1 as an adjuvant to improve antibody response to vaccines (including influenza and hepatitis B vaccines) in populations with blunted immune responses, such as older adults, dialysis patients, and individuals with certain immunodeficiencies.
Sepsis and Critical Illness
A notable and more recent area of clinical trial research has investigated Thymosin Alpha-1 as an adjunctive immunomodulatory therapy in sepsis and septic shock, where dysregulated immune response contributes to mortality, including trials conducted in China examining survival and immune marker outcomes.
Oncology Adjunct Research
Thymosin Alpha-1 has been studied as an adjunct to chemotherapy and other cancer treatments in several tumour types, with research examining whether it can help offset chemotherapy-induced immunosuppression and improve markers of immune function during treatment, most commonly in trials conducted in Asia.
Research Data Summary
| Study / Model |
Reported Effect |
| Chronic Hepatitis B/C RCTs and Meta-Analyses |
Reported improved rates of viral response and ALT normalisation when combined with interferon-alpha versus interferon alone in several trials. |
| Sepsis Adjunctive Therapy RCTs (China) |
Reported reduced 28-day mortality and improved monocyte HLA-DR expression (an immune competence marker) in some trial populations receiving Tα1 alongside standard sepsis care. |
| Vaccine Adjuvant Studies (Older Adults/Dialysis Patients) |
Reported enhanced antibody titres following influenza or hepatitis B vaccination when co-administered with Tα1 compared with vaccine alone. |
| Preclinical Dendritic Cell / TLR Signalling Studies |
Reported promotion of dendritic cell maturation and type I interferon production via TLR9-dependent and TLR9-independent pathways in vitro. |
Stack Combinations Studied
- Thymosin Alpha-1 + Interferon-alpha → Research rationale: The most historically studied combination, investigated in chronic hepatitis B/C trials for synergistic antiviral and immunomodulatory effect predating widespread direct-acting antiviral therapy.
- Thymosin Alpha-1 + standard sepsis critical care protocols → Research rationale: Studied as an adjunct to conventional intensive care sepsis management to assess whether restoring immune competence markers improves survival outcomes.
- Thymosin Alpha-1 + seasonal/hepatitis vaccination → Research rationale: Investigated as a vaccine adjuvant to enhance antibody response in populations with reduced immunogenicity to standard vaccination.
⚠️ Stack combinations listed for research reference only. Not safety or efficacy guidance.
Research Protocol Reference
experimental research protocols only — not dosing recommendations.
| Protocol |
Dose (experimental model only) |
Duration (experimental model only) |
Frequency (experimental model only) |
Research Context |
| Published Hepatitis B/C Trial Protocol |
1.6 mg (fixed dose typically used in published Zadaxin trials) |
6-12 months |
Twice weekly (subcutaneous, per published trial designs) |
Chronic viral hepatitis, often combined with interferon-alpha. |
| Published Sepsis Adjunct Trial Protocol |
1.6 mg, occasionally twice daily in some trial arms |
7-10 days |
Once or twice daily (subcutaneous, per published critical care trial designs) |
Adjunctive immunomodulation in septic shock/sepsis. |
| Vaccine Adjuvant Study Protocol |
1.6 mg per published studies |
Single course around vaccination window |
Single or short-course dosing around time of vaccination |
Enhancing vaccine antibody response in reduced-immunogenicity populations. |
Observed Side Effects in Research
- Injection site reactions (redness, mild pain)
- Rare reports of mild fever or flu-like symptoms
- Generally reported as well tolerated across published trials, including in combination with interferon-alpha
- Long-term surveillance data is more limited outside markets where Zadaxin has extended approved clinical use
Thymosin Alpha-1 has one of the more established human safety records among peptides in this library given its approved clinical use as Zadaxin in several countries, though it remains unapproved for use in Ireland and the EU, and published trials vary in size, design quality, and geographic origin.
Compound Data
- CAS Number
- 62304-98-7
- Molecular Formula
- C129H215N33O55
- Molecular Weight
- Approximately 3108 g/mol
- Half-Life
- Approximately 2 hours in circulation following subcutaneous administration (varies by study)
- Synonyms
- Tα1, Zadaxin (brand name), Thymalfasin, prothymosin alpha (1-28) fragment
- Research Classification
- Thymic peptide, Immunomodulator, Approved medicine (select countries, not Ireland/EU)
Scientific References
- [Goldstein AL, Low TL, McAdoo M et al. 1977] — Thymosin alpha1: isolation and sequence analysis of an immunologically active thymic polypeptide. — Proceedings of the National Academy of Sciences — [In vitro / Animal]
- [Garaci E et al. 2000] — Thymosin alpha 1 in combination with cytokines and chemotherapy for the treatment of cancer. — International Immunopharmacology — [Human / Review]
- [Romani L et al. 2004] — Thymosin alpha1 activates dendritic cells for antifungal Th1 resistance through toll-like receptor signaling. — Blood — [Animal / In vitro]
- [Wei Y et al. 2013] — Thymosin alpha-1 reduces the mortality of severe sepsis by increasing peripheral blood lymphocytes and monocyte HLA-DR expression. — Critical Care Medicine / related sepsis literature — [Human RCT]
- [Sherman KE et al. 2005] — Combination therapy with thymosin alpha1 and interferon for the treatment of chronic hepatitis C infection: a randomized, placebo-controlled trial. — Hepatology — [Human RCT]
- [Camerini R, Garaci E 2015] — Historical review of thymosin alpha 1 in infectious diseases. — Expert Opinion on Biological Therapy — [Review]
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