Thymosin α1

Thymosin α1 is a 28-amino-acid N-acetylated peptide derived from prothymosin α. Its synthetic form, thymalfasin (Zadaxin), is approved in several countries outside the US and has been studied as an immune modulator in clinical trials.

Last reviewed 2026-10-25 by the PeptideWiki editorial team. Editorial policy.

Overview

Thymosin α1 was first isolated from thymosin fraction 5, a partially purified calf thymus extract studied for effects on immune function. It was later shown to correspond to the N-terminal region of prothymosin α, a larger protein expressed in many tissues. A synthetic version, thymalfasin, has been developed as a pharmaceutical product and is marketed under the name Zadaxin in several countries outside the United States.

Clinical research on thymosin α1 has examined chronic viral hepatitis, use alongside vaccines in people with weakened immune responses, cancer as an adjunct to other therapies, and severe infections including sepsis. Results vary across indications and study designs. It is not approved in the US, and its regulatory status differs from country to country, so current national labeling should be checked.

Compare: Thymosin α1 vs thymosin β4.

Structure

Thymosin α1 is a linear 28-residue peptide with an acetylated N-terminal serine and a free C-terminal acid. Its sequence begins Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser and ends with Glu-Ala-Glu-Asn. It is highly acidic, with many glutamate and aspartate residues, and contains no cysteine, methionine or tryptophan. It is largely unstructured in water and can adopt partially helical structure in membrane-mimetic environments. Pharmaceutical thymalfasin is made by chemical synthesis. Research material may be supplied as different salt forms, which should be specified.

Mechanism

Thymosin α1 is described as an immune modulator rather than a direct antiviral or antimicrobial agent. Cell and animal studies have reported effects on T-cell maturation and function, on dendritic cell activity, and on cytokine production. Signaling through Toll-like receptors, including TLR2 and TLR9, in dendritic cells and other immune cells has been proposed as one mechanism. The relative importance of these pathways in people, and why responses differ across conditions, are not fully established.

Research

Chronic viral hepatitis

Thymalfasin has been evaluated in clinical trials in chronic hepatitis B and hepatitis C, alone and in combination with interferon or antiviral drugs. Results have varied between studies, and newer direct-acting antivirals have changed the treatment landscape. Hepatitis B is among the indications for which thymalfasin has been approved in some countries outside the US. Its role in current US practice is not established.

Vaccine responses

Thymosin α1 has been studied as an addition to vaccination in groups with weaker immune responses, such as older adults and people receiving dialysis, with some studies reporting improved antibody responses to vaccines such as influenza and hepatitis B. These trials are generally modest in size, and use as a vaccine adjunct is not established practice in the US. Results are mixed.

Sepsis and severe infection

Thymalfasin has been investigated in patients with sepsis, particularly in China, on the hypothesis that it may counter sepsis-associated immune suppression. Earlier smaller studies suggested possible benefit, while larger trials have not clearly shown a mortality benefit. It was also studied observationally in COVID-19. The evidence in severe infection remains mixed. Patient selection, timing and outcome measures differ between trials, which may help explain inconsistent findings.

Oncology

Thymosin α1 has been studied as an adjunct to chemotherapy, immunotherapy or other treatments in cancers including melanoma, lung cancer and hepatocellular carcinoma. Many studies are small or not randomized, and findings have not led to US approval in any oncology indication. Research in this area continues with combination approaches. Heterogeneous designs and small sample sizes limit firm conclusions about benefit in any cancer type.

Regulatory status

Thymosin α1 (thymalfasin, marketed as Zadaxin) is approved in several countries outside the US, but it is not approved by the FDA. Approved indications and status vary by country, so current national labeling should be checked. Its US compounding status should be checked against current FDA lists. For sport, check the current WADA Prohibited List.

Status changes often. See the regulatory tracker for dated updates.

Quality and identity testing

A good certificate of analysis should confirm identity by mass spectrometry, with the observed mass matching the expected mass shown on this page for the N-acetylated sequence, and report HPLC purity with the chromatogram. Check for the presence of the N-terminal acetyl group, since a non-acetylated peptide differs by 42 Da. As a 28-residue synthetic peptide, deletion and truncation impurities should be reported as related substances. The many aspartate and glutamate residues and the C-terminal asparagine can be sites of isomerization or deamidation, which may produce peaks close to the main peak. The salt form and net peptide content should be stated, and endotoxin results are relevant for cell work.

Open Thymosin α1 in the sequence analyzer to see the expected [M+H]⁺ and multiply charged ions for an MS identity check (set the N-acetyl, amide and disulfide options to match).

For a walkthrough of each section of a certificate, see how to read a COA.

Storage and stability

Store lyophilized thymosin α1 sealed at -20 °C or colder, or at 2–8 °C if a product's labeling specifies, protected from light and moisture, and equilibrate before opening. It lacks oxidation-prone residues, but in solution its aspartate and asparagine residues can slowly degrade, especially at elevated temperature or extreme pH. Prepare solutions in sterile water or buffer for lab use, refrigerate for short-term work, aliquot for frozen storage, and avoid repeated freeze-thaw cycles.

Download the Thymosin α1 data sheet (PDF): sequence, masses, expected MS ions and handling on one printable page.

Latest research

Frequently asked questions

Related compounds

• Thymosin β4

  Thymosin β4 is a naturally occurring 43-amino-acid peptide that binds monomeric actin and is abundant in many cell types. It has been studied in animal models of tissue repair and in human trials of ophthalmic and topical formulations, and is not approved.

• LL-37

  LL-37 is the 37-amino-acid antimicrobial peptide released from human cathelicidin hCAP18. It is studied for direct antimicrobial activity and immune-modulating effects in cell, animal and early human studies, and is not approved for any use.

• KPV

  KPV is the tripeptide lysine-proline-valine, the C-terminal sequence of alpha-melanocyte-stimulating hormone. It is studied for anti-inflammatory effects in cell and rodent models, particularly of intestinal inflammation, and is not approved for any use.

• TB-500

  TB-500 is a research name most often applied to a short synthetic N-acetylated fragment of thymosin β4, Ac-LKKTETQ, but it is also used loosely for full-length thymosin β4. There are no direct human studies of the fragment.

References

1. PubMed: all indexed literature on Thymosin α1
2. ClinicalTrials.gov: registered studies mentioning Thymosin α1