P Palthera
Signalling Peptides

Thymosin Alpha-1

Tα1 / Thymalfasin / Zadaxin

Thymosin Alpha-1 (Tα1, thymalfasin, marketed as Zadaxin) is a synthetic 28- immunomodulatory peptide based on a thymic peptide . It is approved in many jurisdictions (including Italy and China) for chronic hepatitis B and as an immunomodulator, and remains unapproved by the FDA in the United States. The most recent Phase III data (Wu 2025, BMJ) examined sepsis.

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Signalling Peptides
Classification
Synthetic 28-residue immunomodulatory peptide · Approved in multiple jurisdictions (not FDA-approved in the US)
Research stage
Phase III clinical evidence including sepsis (BMJ 2025); approved in Italy, China, and other jurisdictions for hepatitis B/C and as an immunomodulator
Sequence
Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn
Molecular weight
3108.3 Da

Snapshot

Key takeaways

A three-bullet snapshot before reading the full dossier.

  1. 01

    Synthetic 28- peptide based on the thymic protein prothymosin α.

  2. 02

    Approved as Zadaxin in many countries; not FDA-approved in the US at the time of writing.

  3. 03

    Recent Phase III evidence (Wu 2025, BMJ) reported overall non-significant mortality benefit in sepsis with subgroup signals.

Dossier overview

5

research areas

3

references

3

handling notes

01

Mechanism of action

Thymosin Alpha-1 has been characterised as an immunomodulatory peptide affecting T-cell maturation and TLR signalling. Mechanism literature describes effects on macrophage polarisation, T-cell function, and Toll-like 7 / SHIP1 pathways in research models.

02

Research applications

  • Immunomodulation clinical research
  • Chronic hepatitis B and C clinical research
  • Sepsis and critical-care clinical research
  • Cancer immunology research (macrophage polarisation, TAM phenotype)
  • Influenza vaccine adjuvant research

Evidence at a glance

What's behind this profile

3 citations · 2015–2025

Human
2

Studies in human volunteers or patients (incl. early-phase trials).

Review
1

Narrative or systematic reviews; no primary data.

Publication years

  1. 15
  2. 16
  3. 17
  4. 18
  5. 19
  6. 20
  7. 21
  8. 22
  9. 23
  10. 24
  11. 25
20152025

Counts are derived from the cited studies below. A study covering both in vivo and in vitro work is counted by its primary model. Sample size is reported in 2 of 3 citations. Findings remain model-specific and are not extrapolated to therapeutic use.

03

Study references

Each profile cites a minimum of two peer-reviewed sources, with model type and reported sample size where the source provides it. Findings are model-specific and must not be extrapolated to therapeutic use.

The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial

2025

Wu J et al. · BMJ

Model
Phase 3 multicentre double-blind randomised placebo-controlled trial in adults with sepsis
Sample
n=1106

Thymosin α1 was not associated with a significant reduction in 28-day all-cause mortality overall, though subgroup analyses suggested potential differential effects by age and diabetes status.

PMID 39814420 DOI 10.1136/bmj-2024-082583

A Pilot Trial of Thymalfasin (Thymosin-α-1) to Treat Hospitalized Patients With Hypoxemia and Lymphocytopenia Due to Coronavirus Disease 2019 Infection

2023

Shehadeh F et al. · Journal of Infectious Diseases

Model
Prospective open-label randomised pilot trial in hospitalised COVID-19 patients with hypoxaemia and lymphocytopenia
Sample
n=49

Thymosin α1 was associated with accelerated CD4+ T-cell recovery versus standard care in the pilot cohort of hospitalised COVID-19 patients with baseline low-flow oxygen support.

PMID 36056913 DOI 10.1093/infdis/jiac362

Thymosin alpha-1 treatment in chronic hepatitis B

2015

Wu X et al. · Expert Opinion on Biological Therapy

Model
Narrative review of thymosin α1 monotherapy and combination therapy in chronic hepatitis B
Sample
N/A (review)

Reviewed the chronic-hepatitis-B clinical literature in which thymosin α1 alone or with antivirals was associated with HBV DNA suppression and HBeAg seroconversion in subsets of treated patients.

PMID 25640173 DOI 10.1517/14712598.2015.1007948

Evidence caveats

  • Approval status varies widely by jurisdiction. The compound is not FDA-approved in the United States.
  • The most recent Phase III sepsis trial (Wu 2025) did not show a significant primary outcome benefit overall; subgroup effects require confirmation in further trials.

04

Storage and handling

Approved product follows manufacturer instructions where marketed. Research-grade material must be stored under controlled laboratory conditions per protocol.

  • Approved product (where marketed) follows the manufacturer label and pharmacy cold-chain.
  • Research-grade material requires controlled laboratory storage and full batch documentation.
  • Regulatory status varies by jurisdiction — verify before any clinical reference.