Thymosin alpha-1
Thymosin alpha-1 (thymalfasin) is a 28-amino-acid acetylated thymic peptide that acts as an immunomodulator and is marketed as the prescription drug Zadaxin in many countries, though it is not FDA-approved.
SDAAVDTSSEITTKDLKEKKEVVEEAEN
- Nonpolar8
- Polar7
- Acidic (−)9
- Basic (+)4
- 28 residues
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-OH (N-terminally acetylated, 28 residues)
Thymosin alpha-1 (Tα1) is a 28-residue, N-terminally acetylated peptide originally isolated from the thymus gland. Its chemically synthesised, sequence-identical form is the drug thymalfasin (brand name Zadaxin), which is approved as a prescription medicine in more than 35 countries for chronic hepatitis B, chronic hepatitis C, and as an immune adjuvant. It is not approved by the U.S. FDA (holding only orphan-drug designations) or by the European Medicines Agency, and in the UK it is sold only as a research chemical for laboratory use.
Mechanistically, Tα1 acts as an immunomodulator that signals through Toll-like receptors — most prominently TLR2 and TLR9, with reported engagement of TLR3/4/7 — on dendritic cells, driving downstream IRF and NF-κB pathways. In preclinical and clinical research it has been associated with enhanced T-cell maturation and differentiation, modulation of T-regulatory/effector balance and natural-killer-cell activity, and changes in cytokine production. The peptide contains no cysteine residues (and therefore no disulfide bonds) and no glycosylation, and is an acidic peptide with an isoelectric point of about 4.2.
The canonical sequence is Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN (molecular formula C129H215N33O55, MW ≈ 3108 Da, CAS 62304-98-7, PubChem CID 16130571). Research interest centres on its use as an immunomodulator in immune-depressed states, as an adjuvant in viral hepatitis and in oncology (alongside chemotherapy and vaccines), and as a tool compound for probing TLR signalling. Research-grade material is not a medicine, carries no quality or purity guarantees, and is intended for laboratory use only.
Thymosin alpha-1 is a 28-residue N-terminally acetylated thymic peptide that acts as an immunomodulator, signalling through Toll-like receptors (notably TLR2 and TLR9, with reported engagement of TLR3/4/7) to activate dendritic cells and downstream IRF and NF-κB pathways. In preclinical and clinical research it has been associated with enhanced maturation and differentiation of T cells and modulation of T-regulatory/effector balance, natural killer cells, and cytokine production. It contains no cysteine residues (and therefore no disulfide bonds) and no glycosylation, and is reported to be an acidic peptide with a low isoelectric point (~4.2).
- Human evidence
- Approved medicine in 35+ countries (hepatitis B/C, immune adjuvant); multiple clinical trials, but not FDA- or EMA-approved
- Regulatory status
- Marketed as the synthetic drug thymalfasin (brand Zadaxin) and approved as a prescription medicine in more than 35 countries for hepatitis B, hepatitis C, and as an immune adjuvant. It is NOT approved by the U.S. FDA (it holds only orphan-drug designations, which are not approvals) and is not approved by the European Medicines Agency. In the U.S. pharmacy-compounding context it was placed on the FDA's interim 503A Category 2 bulks list in 2023, then withdrawn from that list in 2024 and referred to the Pharmacy Compounding Advisory Committee, which in December 2024 recommended against adding it to the 503A bulks list. In the UK it is not a licensed/authorised medicine and is sold only as a research chemical.
- Investigated as an immunomodulator for restoring T-cell and dendritic-cell function in immune-depressed states (research context).
- Studied as an adjuvant in chronic viral hepatitis B and C models and trials (research context).
- Examined as an adjuvant alongside chemotherapy and vaccines for chemotherapy-induced immune suppression in oncology research.
- Used as a tool compound to probe Toll-like receptor (TLR2/TLR9) signalling in innate and adaptive immunity.
- The most commonly reported adverse reactions in clinical use are local injection-site effects such as redness, irritation, or discomfort (PMC10144173).
- By its immunomodulatory mechanism it is generally contraindicated in immunocompromised patients undergoing organ transplantation, where immune activation is undesirable (PMC10144173).
- It is NOT approved by the FDA or EMA; research-grade material is not a medicine, has no quality/purity guarantees, and is for laboratory use only.
- Prescribing information for the approved drug Zadaxin (thymalfasin) documents warnings, interactions, and dosing that apply only under medical supervision (RxList).