Description
Summary Abstract
Thymosin Alpha-1 (Thymalfasin; Tα1; Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN-OH; C129H215N33O55; MW 3,108.3 g/mol; CAS 62304-98-7; PubChem CID 16130571) is a 28-amino acid thymic peptide, N-terminally acetylated, originally isolated from thymosin fraction 5 and now produced synthetically under the international nonproprietary name thymalfasin. First characterized by Allan Goldstein and colleagues in the 1970s, Tα1 is endogenously generated by caspase-3 cleavage of the nuclear protein prothymosin alpha (ProTα) during cellular stress and acts extracellularly as a pleiotropic immunomodulatory signal. Its primary mechanism centers on agonism of Toll-Like Receptors 9 and 2 (TLR-9, TLR-2) on myeloid and plasmacytoid dendritic cells (DCs), triggering MyD88/NF-κB and IRF-7/STAT1 cascades that drive Th1 polarization, IL-12 and IFN-α secretion, and T-cell maturation from double-negative to CD4+ and CD8+ single-positive phenotypes. Thymalfasin is approved in more than 35 countries for the treatment of chronic hepatitis B and has been evaluated in clinical trials for sepsis, hepatocellular carcinoma, lung cancer, and severe infectious disease including COVID-19, where it reduced mortality in critically ill patients by reversing T-cell exhaustion and restoring thymic output.
Clinical Indications
Thymosin Alpha-1 has been evaluated across a broad spectrum of conditions requiring immune restoration or amplification:
- Chronic Hepatitis B and C: Approved in over 35 countries; clinical trials demonstrated enhanced clearance of viral antigens through restored cell-mediated immunity and normalized T-lymphocyte subsets.
- Severe Sepsis: Large-scale trials showed significant improvements in 28-day mortality, linked to restoration of DC function and resolution of the immunoparalysis characteristic of sepsis.
- Oncology (Adjunctive): Reduces chemotherapy-associated immunosuppression, improves NK and CD8+ T-cell counts, and has demonstrated anti-tumor activity in melanoma, hepatocellular carcinoma, and non-small cell lung cancer clinical studies.
- Vaccine Adjuvancy in the Elderly and Immunocompromised: Enhances seroconversion rates for influenza and hepatitis B vaccines in elderly and renally impaired populations where standard vaccine efficacy is diminished.
- COVID-19 / Severe Viral Pneumonia: Clinical data show reduced mortality in critically ill patients; reverses CD4+ lymphopenia, inhibits cytokine storm in CD8+ T-cell subsets, and increases thymic output.
Contraindications
- Active Autoimmune Disease (caution): Tα1 shifts immune balance toward Th1; use in conditions driven by dysregulated Th1 responses (e.g., active rheumatoid arthritis, autoimmune hepatitis) warrants careful clinical assessment.
- Organ Transplant Recipients on Immunosuppression: Potential for immune augmentation to challenge immunosuppressive regimens; concurrent use should be managed under specialist supervision.
- Pregnancy: Insufficient safety data; use during pregnancy should be avoided unless clinically compelling.
Mechanism of Action (MOA)
Thymosin Alpha-1 engages both innate and adaptive immune compartments through convergent TLR-mediated and direct cellular pathways:
TLR-9 / TLR-2 Agonism on Dendritic Cells
Tα1 acts as an endogenous ligand for Toll-Like Receptors 9 and 2 on myeloid and plasmacytoid dendritic cells. TLR-9 engagement activates the MyD88 → IRAK-4/TRAF6 → IKKβ → NF-κB cascade, inducing transcription of IL-12, IFN-α, and TNF-α; concomitant IRF-7 activation drives type I interferon gene expression, supporting antiviral innate immunity. Dendritic cells mature into efficient antigen-presenting cells that polarize naïve CD4+ T cells toward a Th1 effector phenotype.
T-Cell Maturation and IL-2 Axis Enhancement
Tα1 promotes progression of double-negative thymocytes through double-positive to CD4+/CD8+ single-positive T cells in the thymus. In the periphery, it upregulates IL-2 receptor (CD25) expression and stimulates IL-2 production, amplifying clonal T-cell expansion. CD8+ cytotoxic T-lymphocyte (CTL) activity against virally infected cells and tumor targets is correspondingly enhanced.
NK Cell Activation and Innate Cytotoxicity
Tα1 upregulates activating receptors NKG2D and NKp46 on natural killer (NK) cells and promotes perforin/granzyme B expression, augmenting cytolytic surveillance of tumor cells and virally infected cells. This NK axis provides rapid innate cytotoxicity independent of MHC restriction.
Homeostatic Anti-Inflammatory Modulation
In hyperinflammatory states (e.g., sepsis, cytokine storm), Tα1 exhibits a paradoxical homeostatic function — reducing IL-1β and TNF-α overproduction and promoting expansion of regulatory T-cells (Tregs). Upregulation of Indoleamine 2,3-dioxygenase (IDO) in DCs further temperes excessive inflammation without abolishing protective immunity, explaining its beneficial role in both immunodeficiency and hypercytokinemia.
Key Features & Specifications
Pharmacological and structural attributes of Thymosin Alpha-1:
Chemical Analysis
| Property | Specification Reference Data |
|---|---|
| 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-OH (Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN-OH) |
| CAS Number | 62304-98-7 |
| Molecular Formula | C129H215N33O55 |
| Molecular Weight | 3,108.3 g/mol |
| PubChem CID | 16130571 |
| Synonyms | Thymalfasin, Zadaxin, Tα1, TA-1, Thymosin α1 |
| Form / Variation | 5 MG Lyophilized (P-043) / 10 MG Lyophilized (P-081) |
Storage, Safety, and Handling
Storage Protocol
Store lyophilized Thymosin Alpha-1 at −20 °C in a dry environment, protected from light. Once reconstituted with sterile or bacteriostatic water, the solution is stable at 2–8 °C for up to 14–21 days and should not be subjected to repeated freeze-thaw cycles. The short plasma half-life (approximately 2 hours) after subcutaneous administration reflects rapid tissue distribution rather than degradation of the lyophilized form.
Handling & Compliance
Handle with standard PPE under aseptic conditions. Thymalfasin has an extensively characterized safety profile with decades of clinical use; no serious adverse events have been attributed to the compound across major trials, and injection-site reactions remain the primary mild adverse effect. The compound is not classified as a prohibited substance by WADA. Regulatory status varies by jurisdiction; thymalfasin holds full drug approval in numerous Asian and European markets.