Thymosin Alpha-1 Research Guide: The 28-Residue Thymic Peptide
By UK Peptide Lab Research Team•15 September 2026•7 min read
What is Thymosin Alpha-1?
Thymosin alpha-1 (TA1, INN thymalfasin) is a 28-residue peptide with an acetylated N-terminus and the sequence Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN. Its molecular weight is 3108.28 g/mol, its molecular formula C₁₂₉H₂₁₅N₃₃O₅₅, and its CAS number 62304-98-7. Three chemical features define the molecule. The N-terminal acetylation blocks aminopeptidase attack and is generally considered necessary for full activity. The sequence contains no cysteine, so there are no disulfides, and no methionine, so the oxidation liabilities that dominate handling guidance for many research peptides do not apply. And the C-terminus is an asparagine, which makes deamidation the degradation route to design around. TA1 is the N-terminal fragment of prothymosin alpha, the acidic nuclear protein from which it is released by proteolysis, and was first isolated from bovine thymus and sequenced by Goldstein and colleagues (Proc Natl Acad Sci USA, 1977). UK Peptide Lab supplies Thymosin Alpha-1 10mg as lyophilised powder for in-vitro laboratory research.
From Bovine Thymus to a Licensed Medicine
TA1's trajectory is unusual. Goldstein's group isolated it from calf thymosin fraction 5 in the mid-1970s as one of the immunologically active components of the crude thymic extract, and the peptide moved from immunology laboratories into pharmaceutical development faster than almost any research peptide before or since. Under the brand name Zadaxin, developed by SciClone Pharmaceuticals, thymosin alpha-1 is licensed as a prescription medicine in more than 35 countries, principally in Asia and the Middle East, for immunomodulatory indications most notably including chronic hepatitis B. The dossier includes randomised controlled trials such as Chien and colleagues' 98-patient trial (Hepatology, 1998), and the history is reviewed by Camerini and Garaci (Expert Opin Biol Ther, 2015). Zadaxin has never been licensed in the UK, the EU or the United States, and the material supplied here is for laboratory research only, not for any medical use.
Proposed Mechanism: Toll-Like Receptor Signalling
For a long time TA1 was described as a T-cell maturation factor, and the older literature does report effects on thymocyte differentiation and T-cell function. The modern mechanistic picture is different and more precise. Romani and colleagues reported in Blood (2004) that thymosin alpha 1 activates myeloid dendritic cells through a TLR9-dependent, MyD88-mediated pathway, driving Th1-type cytokine induction, and that this signalling underlies its activity in antifungal resistance models. That reframed TA1 as an endogenous regulator of innate immune sensing rather than a simple T-cell factor. Around this anchor sit reports of natural killer cell activity, dendritic cell maturation and broad cytokine regulation, reviewed by Garaci (Ann N Y Acad Sci, 2007) — although much of that older work consists of small, heterogeneous studies that have not all been reproduced, a point expanded below.
Thymosin Alpha-1 vs TB-500
Researchers often ask how TA1 relates to TB-500. The honest answer is that they share a name, a tissue of origin, and nothing else. TA1 is a 28-residue acetylated peptide of 3108.28 g/mol derived from prothymosin alpha, and its literature concerns the immune system — toll-like receptor signalling, T-cell function, cytokine networks. TB-500 is the research-market designation for a synthetic fragment of thymosin beta-4, a 43-residue acetylated polypeptide of 4963.4 g/mol (CAS 77591-33-4) studied for G-actin sequestration, cell migration and angiogenesis via the LKKTETQ actin-binding motif (Philp et al., FASEB J, 2003), with no dedicated cell-surface receptor. The TB-500 vs BPC-157 comparison covers the other side of that family. Choosing between them is choosing between an immunology tool and a cytoskeletal-motility tool.
Current Research Directions: Checkpoint Inhibitor Combinations
The most active current direction is oncology. Because TA1's proposed mechanism — dendritic cell activation and Th1 cytokine induction — complements the pharmacology of immune checkpoint inhibitors, recent literature has examined combinations. Wang and colleagues published a retrospective analysis (Cancer Manag Res, 2025) of thymosin alpha 1 added to PD-1/PD-L1 inhibitor plus chemotherapy in platinum-resistant recurrent ovarian cancer, reporting improved response rates and progression-free survival in the TA1 group. That finding is real but its evidential weight is limited: it is a retrospective, single-centre analysis, and combination data of this kind are prone to confounding. It is best read as a signal worth prospective testing rather than settled pharmacology, and it is clinical literature rather than a bench protocol.
The Honest Limits of the Evidence
Three caveats should be stated plainly. First, the licensed indications for Zadaxin are prescription medicine uses in specific jurisdictions; nothing about this page's research framing transfers to human use, and TA1 is not an approved medicine in the UK, the EU or the United States. Second, much of the older immunology literature is small and heterogeneous — studies with modest cohorts, variable endpoints, and findings that have not consistently replicated. Third, the recent oncology combination data are largely retrospective. What remains solid is the chemistry — a well-characterised, acetylated 28-residue peptide — and a credible modern mechanism in TLR signalling (Romani et al., Blood, 2004). Researchers should design around those, and treat the older claims as hypotheses.
Laboratory Handling and Storage
Store lyophilised vials at -20°C, protected from light and moisture, for up to 24 months. Reconstitute with bacteriostatic water injected slowly down the inner glass wall, then swirl gently; never shake or vortex. The sequence contains no cysteine or methionine, so disulfide and oxidation handling are not required, but the C-terminal asparagine deamidates in solution, so keep the reconstituted vial at 2-8°C and use within approximately 4 weeks. Prepare single-use aliquots for longer storage and avoid repeated freeze-thaw cycles. See the peptide storage guide for the general principles.
Sourcing Thymosin Alpha-1 in the UK
UK Peptide Lab supplies Thymosin Alpha-1 10mg as lyophilised powder, batch UKPL-9504 at 99.76% purity by HPLC, with the supplier certificate of analysis available on request. Independent third-party verification in progress, certificate published on the product page once complete. Same-day UK dispatch on orders placed before 2pm GMT, free Royal Mail Tracked shipping over £45. For in-vitro laboratory research use only, not for human or veterinary use.
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Disclaimer: This article is for research and educational purposes only. All information provided is not intended as medical advice. UK Peptide Lab products are not for human consumption and are sold strictly for laboratory research use only.