Thymosin alpha-1

What thymosin alpha-1 is

Thymosin alpha-1 (Tα1) is a peptide of 28 amino acids with an acetyl group on its N-terminus. It was isolated from calf thymus by Goldstein and colleagues in 1977, from a preparation called thymosin fraction 5 that had been shown to restore immune function in thymectomised animals, and its sequence was determined in the same paper [1]. It is now known to be the N-terminal fragment of a larger precursor, prothymosin α, which is present in the nucleus of most cells and is cleaved to release Tα1.

The sequence is highly acidic: of 28 residues, nine are glutamate or aspartate, and there are no aromatic residues, no cysteine and no methionine. The acetylation of the N-terminal serine is native and is carried over in the synthetic peptide. The research material is a white lyophilised powder, and the synthetic peptide is identical in sequence to the pharmaceutical substance thymalfasin.

How the literature describes its mechanism

Tα1 was characterised for decades by its effects before its targets were identified. The effects are on the innate and adaptive immune system: it promotes the maturation and function of T cells, increases the activity of natural killer cells, and enhances the production of interleukin-2 and interferons by stimulated lymphocytes.

The mechanistic picture clarified in the 2000s. Romani and colleagues showed that Tα1 acts on dendritic cells through Toll-like receptors, particularly TLR9 and, in some settings, TLR2, activating the MyD88 signalling pathway and driving the cells towards a profile that promotes T-helper 1 responses and, in other contexts, regulatory T cells [2]. The same group described Tα1 as an endogenous regulator that can both promote protective immunity and restrain inflammation depending on the setting, which is why it has been studied in infections, in cancer and in conditions of immune dysregulation [2, 3]. The peptide's intrinsically disordered structure, which adopts a helical conformation in membrane-mimicking environments, is thought to be relevant to how it engages its targets.

For an in-vitro programme the relevant readouts are dendritic-cell maturation markers and cytokine output after Tα1 exposure, with and without TLR ligands; NK-cell cytotoxicity assays; T-cell proliferation and cytokine assays; and TLR reporter assays. Doses in the literature are in the microgram-per-millilitre range in cell culture.

The clinical research record

Tα1 has a clinical record unusual for a peptide in this catalogue. It was developed as thymalfasin and has been studied in randomised trials in chronic hepatitis B and C, as an adjunct to vaccination in immunocompromised people, in sepsis, and alongside chemotherapy in several cancers. King and Tuthill reviewed the immunological basis and the trial record in 2016 [3]; Dominari and colleagues provided a more recent survey of the literature, including the studies during the COVID-19 pandemic in which it was tested as an immune adjunct [4].

The results are mixed in the way a long clinical record usually is: consistent evidence of immunological activity and a good safety profile, with efficacy in specific indications that was sufficient for regulators in some countries but not in the major Western jurisdictions. Thymalfasin is licensed in more than thirty countries, including China and Italy, mainly for hepatitis B and as a vaccine adjuvant. It is not licensed in the UK, the EU as a whole, or the United States, where it holds orphan designations but no approval.

Regulatory status in the United Kingdom

Thymosin alpha-1 has no marketing authorisation in the UK, and the research material is not a medicine, is not manufactured or presented as one, and carries no therapeutic claim. Its licensed status in other countries has no legal effect here. It is not controlled under the Misuse of Drugs Act. It is supplied as a chemical for in-vitro laboratory use under the Terms of Sale, not for human or veterinary administration. Purchasers must be 18 or over and are responsible for compliance with the laws and institutional rules that apply to them. Our guide to the UK rules on research compounds sets this out in more detail.

Thymosin alpha-1 is not on the WADA Prohibited List by name. The List's S2.3 entry names thymosin β4 and its derivatives, which are a different family of peptides with no sequence relationship to Tα1.

Handling, storage and stability

Thymosin alpha-1 is supplied lyophilised, sealed under nitrogen in a glass vial with a rubber stopper and an aluminium crimp.

Sealed vial. Store at 2–8 °C for routine use and at −20 °C for longer storage. Protect from light and moisture. Allow the vial to reach room temperature before opening.

Reconstitution. The peptide is very soluble in water and in buffers at neutral pH, as expected for a sequence with nine acidic residues. Add the solvent down the side of the vial and swirl. Avoid strongly acidic solvents, in which the peptide is less soluble. The reconstitution calculator gives the volume for a target concentration.

Reconstituted solution. With no methionine, cysteine or aromatic residues, Tα1 has none of the common chemical degradation routes and is stable in solution at 2–8 °C for several weeks. The slow routes are deamidation of the C-terminal asparagine, and microbial growth; use bacteriostatic water for solutions that will be kept, and aliquot and freeze at −20 °C for longer storage.

Surfaces. An acidic peptide is less prone to adsorption on plastics than a basic one; standard tubes are adequate at ordinary concentrations. The storage and stability guide covers acidic peptides.

What a sound certificate for thymosin alpha-1 looks like

Every batch we release carries an independent certificate of analysis, transcribed on the product page and in the certificate register.

Purity by RP-HPLC. Reversed-phase HPLC on a C18 column with UV detection at 214 or 220 nm, reporting the main peak as a percentage of all integrated peaks. The peptide has no aromatic residues, so 280 nm detection is uninformative, and a certificate quoting purity at that wavelength should prompt questions. A good batch shows a single dominant peak at 98% or above. The impurities to look for are the des-acetyl peptide, which elutes close to the parent and is 42 Da lighter, and deamidated species, which elute slightly later and are 1 Da heavier.

Identity by LC-MS. The average molecular weight is 3,108.3 Da and the monoisotopic mass is 3,106.5 Da. An acidic peptide of this size ionises well in negative mode and in positive mode appears as [M+2H]²⁺ at about m/z 1,555 or [M+3H]³⁺ at about m/z 1,037; the certificate should say which it reports. A deconvoluted mass within a few tenths of a dalton of the theoretical value confirms identity, and the presence of the acetyl group is confirmed by the mass being 42 Da above that of the free peptide.

Net peptide content. An acidic peptide carries fewer trifluoroacetate counter-ions than a basic one, but bound water is still substantial, and net peptide content should be reported where available. Amino-acid analysis, where provided, is the definitive method.

Endotoxin. Essential for an immunomodulatory peptide that will be used in immune-cell assays, since endotoxin activates the same TLR pathways that Tα1 is studied for. A LAL result in endotoxin units per milligram should be reported, and a laboratory running dendritic-cell or macrophage assays should regard it as the most important line on the certificate.

Our guide to reading a certificate of analysis goes through a complete report line by line.

Related compounds

TB-500 is the fragment of thymosin β4, which despite the shared name belongs to a different protein family with no sequence relationship to Tα1; the two are often confused and should not be. Selank, derived from the immunoglobulin fragment tuftsin, is the other peptide in the catalogue with an immunological origin. KPV is a short anti-inflammatory tripeptide studied in overlapping immune models.

Frequently asked questions

Is thymosin alpha-1 the same as thymalfasin? Thymalfasin is the international non-proprietary name for the synthetic peptide with the Tα1 sequence. The research material has the same sequence but is not manufactured as a medicine and is not one.

Is it related to TB-500 or thymosin β4? No. Both were originally isolated from thymus preparations, which is where the shared name comes from, but they are unrelated peptides with different sequences, sizes and biology.

Is it licensed in the UK? No. It is licensed in some other countries, which has no effect on its status here.

Why does the certificate's endotoxin result matter so much? Because Tα1 is studied for effects on Toll-like receptor signalling, and endotoxin is a potent Toll-like receptor ligand. Contamination would produce the effect being looked for.

References

1. Goldstein AL, Low TLK, McAdoo M, et al. Thymosin α1: isolation and sequence analysis of an immunologically active thymic polypeptide. Proceedings of the National Academy of Sciences. 1977;74(2):725–729. doi:10.1073/pnas.74.2.725.
2. Romani L, Bistoni F, Montagnoli C, et al. Thymosin α1: an endogenous regulator of inflammation, immunity, and tolerance. Annals of the New York Academy of Sciences. 2007;1112:326–338. doi:10.1196/annals.1415.002.
3. King R, Tuthill C. Immune modulation with thymosin alpha 1 treatment. Vitamins and Hormones. 2016;102:151–178. doi:10.1016/bs.vh.2016.04.003.
4. Dominari A, Hathaway D III, Pandav K, et al. Thymosin alpha 1: a comprehensive review of the literature. World Journal of Virology. 2020;9(5):67–78. doi:10.5501/wjv.v9.i5.67.
5. Garaci E, Pica F, Serafino A, et al. Thymosin α1 and cancer: action on immune effector and tumor target cells. Annals of the New York Academy of Sciences. 2012;1269:26–33. doi:10.1111/j.1749-6632.2012.06697.x.

This monograph summarises the published literature for laboratory researchers. It is not medical advice, and nothing on this site is for human or veterinary use.