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Thymosin Alpha-1 (TA-1)

Immunomodulatory peptide

Also known as Tα1, Zadaxin, Thymalfasin

An immunomodulatory peptide approved in some countries for hepatitis B and studied in sepsis and oncology. Genuinely contested: real trials exist and they disagree.

Guide updated Sep 2, 2026Literature checked Sep 2, 20262 curated studies42 literature recordsBaseline editorial
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Overview

In shortA peptide originally taken from thymus tissue. It is approved in about thirty countries for chronic hepatitis B, and not approved in the US or the EU. It sits in contested rather than unproven, and that distinction matters: real trials exist and they disagree with each other, which usually means any real effect is smaller or more situation-dependent than either side claims.

Thymosin alpha-1 is a 28-amino-acid peptide originally isolated from thymic tissue. It is approved in around thirty countries for chronic hepatitis B, and in some for hepatitis C and as a vaccine adjuvant, while remaining unapproved in the United States and the European Union.

It belongs in the "contested" category rather than the "unproven" one, and that is a meaningful distinction. Substantial randomised trials exist. They disagree. That is a different epistemic situation from having no trials, and it usually means the effect, if real, is smaller or more context-dependent than either side argues.

Mechanism

In shortIt adjusts immune function rather than simply turning it up or down. Reported effects include helping immune cells mature and improving how they detect threats. In sepsis the idea is to restore function in an immune system that has shut down, not to boost it generally, which is a claim the underlying work does not make.

Thymosin alpha-1 modulates immune function rather than suppressing or stimulating it uniformly. Described effects include promotion of T-cell maturation, enhancement of dendritic cell function, modulation of Toll-like receptor signalling, and increased natural killer cell activity.

Its proposed clinical rationale in sepsis is restoration of function in an immunoparalysed state rather than general immune stimulation. A subtle claim that is frequently flattened into "boosts the immune system", which is not what the mechanistic work describes and not a coherent therapeutic goal.

Evidence

In shortGenuinely contested. In chronic hepatitis B, pooled analyses report benefit, but the trials vary a lot in quality and there are concerns about which results got published. In sepsis the results split: one large trial reported fewer deaths at 28 days, others have not reproduced it, and the positive trials have been substantially criticised. Cancer work is early and mixed.

Contested, which here means genuinely so.

In chronic hepatitis B, meta-analyses of randomised trials report benefit on virological endpoints, with substantial heterogeneity and concerns about trial quality and publication bias in the underlying set.

In sepsis, results diverge. A multicentre Chinese randomised trial reported reduced 28-day mortality; other trials and subsequent analyses have not consistently reproduced it, and methodological criticism of the positive trials is substantial.

Oncology adjuvant work is early and mixed. The honest summary is that this is a compound where reasonable people read the same literature differently, which is rare in this catalogue and worth preserving as a distinct state from "no evidence".

Safety

In shortGenerally well tolerated in trials, with injection site reactions the most common complaint, and decades of approved use in some countries give a reasonable amount of real-world observation. The concern is theoretical rather than observed: what it does in autoimmune disease or in transplant patients is an obvious question that trials largely avoided by excluding them.

Generally well tolerated in trials, with injection site reactions the most common effect. Decades of approved use in some jurisdictions provides a reasonable amount of real-world safety observation.

The mechanistic concern is theoretical rather than observed: immunomodulation in autoimmune disease or in transplant recipients is an obvious question that trial populations largely excluded. It has not produced a notable safety signal in its approved indication.

Regulatory status

In shortApproved in around thirty countries for chronic hepatitis B, with extra uses in some. Not approved in the US or the EU. This is a good example of a compound whose legal status genuinely differs by country, which makes flat statements about legality meaningless.

Approved in around thirty countries for chronic hepatitis B, with additional indications in some. Not approved in the United States or the European Union; it has held orphan designation for some indications without completing approval.

This is a good example of a compound whose legal status genuinely differs by country in a way that makes unqualified statements about legality meaningless.

The literature

2 studies indexed. Findings and limitations get equal weight, on purpose.

Always check the primary source

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Everything above is free to read. What an account opens is the evidence underneath it: 2 studies with their limitations, and the regimen each trial actually reported.

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  • The dose each named trial administered, where recorded
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The wider literature

15 indexed papers and 27 registered trials mentioning Thymosin Alpha-1, straight from PubMed and ClinicalTrials.gov. 25 of 27 administer it; the rest measure it. These have not been read by us. Unlike the studies above, they carry no findings and no limitations written by anyone here, because writing either would mean claiming a reading nobody has done. They are a starting point for yours.

Registered trials (27)

  1. The Safety and Effectiveness of a Type of Interleukin-2 Plus Zidovudine Plus Thymosin in HIV-Positive Patients With and Without Symptoms of Infection

    National Institute of Allergy and Infectious Diseases (NIAID)NCT00001036

    interventionalphase1completedn=12

  2. Phase II Trial of Neoadjuvant Thymalfasin, PD-1 Inhibitor, and Chemoradiotherapy for cStage III GEJ Adenocarcinoma

    The First Affiliated Hospital with Nanjing Medical University2025NCT07277439

    interventionalphase2recruitingn=48

  3. "Thymalfasin Immunotherapy Study with Triple Regimen in Advanced MSS/pMMR Colorectal Cancer"

    Beijing Friendship Hospital2025NCT06829355

    interventionalphase2recruitingn=52

  4. Immuno-effect of Tα1 for Stage I NSCLC

    Yousheng Mao2024NCT06598839

    interventionalnarecruitingn=40

  5. Neoadjuvant With Tα1 Plus Immuno-chemotherapy for Resectable NSCLC

    Xuanwu Hospital, Beijing2024NCT06607926

    interventionalnanot yet recruitingn=40

  6. Thymalfasin (Thymosin Alpha 1; Ta1) as an Enhancer of Vaccine Response Among Older Adults Receiving Booster Doses of COVID-19 Vaccine

    The Methodist Hospital Research Institute2024NCT06821100

    interventionalphase1recruitingn=75

  7. Thymalfasin-based PRaG Mode for Advanced Refractory Solid Tumors

    Second Affiliated Hospital of Soochow University2023NCT05790447

    interventionalphase2unknownn=60

  8. Neoadjuvant Chemoradiotherapy Combined With PD-1 Inhibitor and Thymalfasin for Locally Advanced Mid-low Rectal Cancer

    Beijing Friendship Hospital2023NCT06024356

    observationalcompletedn=47

  9. Thymosin Alpha-1 for irAE Secondary to ICIs

    Jun Wang2023NCT06178146

    interventionalphase4unknownn=40

  10. The Impact of Thymosin α-1 on the Efficacy of Concurrent Chemoradiotherapy Followed by Immunotherpay Consolidation for Locally Advanced NSCLC

    Sun Yat-sen University2023NCT06139419

    interventionalphase2completedn=114

  11. Thymosin Alpha 1 to Prevent COVID-19 Infection in Renal Dialysis Patients

    William B. Ershler, MD2021NCT04428008

    interventionalphase2completedn=189

  12. Thymosin-alpha 1 for Adjuvant Treatment After Radical Resection of High-risk Stage II and III Colorectal Cancer

    Fudan University2021NCT05086614

    interventionalphase3recruitingn=2500

  13. Thymalfasin (Thymosin Alpha 1) to Treat COVID-19 Infection

    Rhode Island Hospital2020NCT04487444

    interventionalphase2terminatedn=56

  14. Efficacy and Safety of Combination Therapy of Thymalfasin and Entecavir in HBeAg-positive ETV-experienced Patients

    Wen-hong Zhang2017NCT03448744

    interventionalphase4unknownn=240

  15. The Efficacy and Safety of Thymosin-α1 in Patients With HBV-related ACLF

    Sun Yat-sen University2017NCT03082885

    interventionalnacompletedn=120

  16. The Efficacy and Safety of Ta1 for Sepsis

    Sun Yat-sen University2016NCT02867267

    interventionalphase3completedn=1106

  17. SBRT Combined With Thymalfasin for Metastatic Esophageal Cancer

    Hangzhou Cancer Hospital2016NCT02545751

    interventionalphase2unknownn=29

  18. Thymosin Alpha 1 Plus Maintenance Therapy With the Standard of Care (SoC) in Patients With Metastatic Non-Small Cell Lung Cancer (NSCLC), EGFR Wild Type

    SciClone Pharmaceuticals2016NCT02906150

    interventionalphase2unknownn=140

  19. Radiotherapy Combined With Thymosin for Metastatic NSCLC Patients Who Showed Stable Disease After First Line TKI Therapy

    First People's Hospital of Hangzhou2016NCT02787447

    interventionalphase2unknownn=46

  20. SBRT Combination With rhGM-CSF and Tα1 for Stage IV NSCLC Patients Who Failed in Second-line Chemotherapy

    The First Affiliated Hospital of Xiamen University2016NCT02976740

    interventionalphase2unknownn=48

  21. Thymalfasin Adjuvant Therapy in Hepatitis B Virus (HBV)-Related Hepatocellular Carcinoma (HCC) After Curative Resection

    Jia Fan2015NCT02281266

    interventionalphase4unknownn=360

  22. Abscopal Effect for Metastatic Small Cell Lung Cancer

    Zhejiang Provincial People's Hospital2015NCT02542137

    interventionalphase2withdrawnn=0

  23. Optimized Treatment and Regression of HBV-induced Early Cirrhosis

    Beijing Friendship Hospital2013NCT01938820

    interventionalphase4completedn=82

  24. Optimized Treatment and Regression of HBV-induced Compensated Liver Cirrhosis

    Beijing Friendship Hospital2013NCT01943617

    interventionalphase4completedn=606

  25. Phase Ⅲ Trial for Combination Treatment of PEG-Tα1 and Adefovir for HBeAg-positive Chronic Hepatitis B

    Jiangsu Hansoh Pharmaceutical Co., Ltd.2013NCT02366247

    interventionalphase3unknownn=463

  26. Phase II Trial for Combination Treatment of PEG-Tα1 and Adefovir for HBeAg Positive Chronic Hepatitis B

    Jiangsu Hansoh Pharmaceutical Co., Ltd.2011NCT02366208

    interventionalphase2completedn=116

  27. Thymosin Alpha-1 in Combination With Peg-Interferon Alfa- 2a and Ribavirin for the Therapy of Chronic Hepatitis C Nonresponsive to the Combination of IFN and Ribavirin.

    sigma-tau i.f.r. S.p.A.2004NCT01178996

    interventionalphase3completedn=552

Papers (15)

  1. Thymosin α-1 in Cancer Therapy: Immunomodulatory Mechanisms, Clinical Applications, and Translational Perspectives.

    Chuang SC, et al.European journal of pharmacology2026PMID 42641753

    journal articlereview

  2. Aging and Thymosin Alpha-1.

    Simonova MA, et al.International journal of molecular sciences2025PMID 41373628

    journal articlereview

  3. The Immunomodulatory Activity of Thymosin Alpha 1 on Tumor Cell Lines and Distinct Immune Cell Subsets.

    Solmonese L, et al.OncoTargets and therapy2025PMID 40955371

    journal article

  4. Thymosin α1 reverses oncolytic adenovirus-induced M2 polarization of macrophages to improve antitumor immunity and therapeutic efficacy.

    Liu K, et al.Cell reports. Medicine2024PMID 39357524

    journal articleresearch support, non-u.s. gov't

  5. Comprehensive Review of the Safety and Efficacy of Thymosin Alpha 1 in Human Clinical Trials.

    Dinetz E, et al.Alternative therapies in health and medicine2024PMID 38308608

    systematic reviewjournal article

  6. Thymosin alpha 1 restores the immune homeostasis in lymphocytes during Post-Acute sequelae of SARS-CoV-2 infection.

    Minutolo A, et al.International immunopharmacology2023PMID 36989892

    journal article

  7. Therapeutic applications of thymosin peptides: a patent landscape 2018-present.

    Quagliata M, et al.Expert opinion on therapeutic patents2023PMID 38131310

    journal articlereview

  8. Cellular proteostasis: a new twist in the action of thymosin α1.

    Stincardini C, et al.Expert opinion on biological therapy2018PMID 30063867

    journal articleresearch support, non-u.s. gov'treview

  9. Immune Modulation with Thymosin Alpha 1 Treatment.

    King R, et al.Vitamins and hormones2016PMID 27450734

    journal articlereview

  10. Historical review of thymosin α 1 in infectious diseases.

    Camerini R, et al.Expert opinion on biological therapy2015PMID 26098768

    historical articlejournal articlereview

  11. Utility of thymosin alpha-1 (Zadaxin) as a co-adjuvant in influenza vaccines: a review.

    Panatto D, et al.Journal of preventive medicine and hygiene2011PMID 22010537

    journal articlereview

  12. Thymalfasin (thymosin-alpha 1) therapy in patients with chronic hepatitis B.

    Liaw YFJournal of gastroenterology and hepatology2004PMID 15641208

    journal articlereview

  13. Thymalfasin (thymosin-alpha 1) therapy in patients with chronic hepatitis B.

    Liaw YFJournal of gastroenterology and hepatology2004PMID 15546254

    journal articlereview

  14. Thymosin alpha-1.

    Ancell CD, et al.American journal of health-system pharmacy : AJHP : official journal of the American Society of Health-System Pharmacists2001PMID 11381492

    journal articlereview

  15. Clinical applications of thymosin alpha-1.

    Goldstein ALCancer investigation1994PMID 7922712

    editorialreviewcomment

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For Research & Educational Discussion Only. Not Medical Advice

This guide is educational reference material compiled from published literature. It is not medical advice, not a recommendation, and not a substitute for a clinician who knows your history. Nothing here should be used to make a decision about your own health without one.

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