Thymosin Alpha-1

Thymosin alpha-1 (Tα1) is a highly acidic, heat-stable peptide of 28 amino acids with an N-terminal acetyl group. It was isolated from calf thymus and sequenced by Goldstein and colleagues in 1977 as one of the active components of “thymosin fraction 5”, and it is now known to be cleaved from the N-terminus of the precursor prothymosin alpha [1]. The synthetic peptide, known generically as thymalfasin, has been approved in more than 30 countries (mainly in Asia, Latin America and parts of Europe) for chronic hepatitis B and as a vaccine adjuvant; it is not approved by the FDA or EMA. Unlike Thymalin, which is a crude extract, Tα1 is a single defined molecule with a verified structure, which is why it is the preferred thymic peptide for mechanistic work.

Mechanism

Tα1 does not act through a single dedicated receptor. Work from Romani and colleagues showed that it primes dendritic cells through Toll-like receptor (TLR) signalling: it drove Th1-type antifungal resistance through TLR/MyD88-dependent signalling, protecting mice against aspergillosis, and it activated plasmacytoid dendritic cells through TLR9/MyD88 to induce interferon regulatory factor 7 and an IFN-α/IFN-γ effector programme [2]. The same body of work described induction of indoleamine 2,3-dioxygenase and regulatory T cells, which is why the authors characterised the peptide as a regulator of both immunity and tolerance rather than a simple immunostimulant. Downstream effects reported in vitro and in animals include increased MHC class I expression, enhanced natural-killer and cytotoxic T-cell activity, and reduced apoptosis of thymocytes.

Randomised trials in chronic hepatitis B

Two randomised trials in the late 1990s form the core clinical evidence. Chien and colleagues randomised 98 patients with biopsy-proven chronic hepatitis B to 26 weeks of Tα1, 52 weeks of Tα1, or untreated follow-up. Assessed 18 months after entry, complete virological response (loss of serum HBV DNA and HBeAg) was 40.6% with the 26-week course versus 9.4% in controls (P = 0.004), with a trend for responses to accumulate after treatment ended; no responder lost HBsAg, and no significant side effects were reported [3]. Mutchnick and colleagues ran a phase III, multicentre, double-blind, placebo-controlled study in 97 HBeAg-positive patients (49 Tα1, 48 placebo, six months of treatment plus six months of follow-up). Complete response occurred in 14% of the treated group versus 4% of placebo, a difference that did not reach statistical significance (P = 0.084) [4]. The divergence between the two trials, one open-label with a positive result and one blinded with a non-significant result, is the reason Tα1 monotherapy did not progress to Western approval for hepatitis B.

The COVID-19 studies

Tα1 was used widely in China during the early pandemic and generated several observational analyses. Liu and colleagues retrospectively reviewed 76 severe cases in two Wuhan hospitals and reported lower mortality with Tα1 (11.1% versus 30.0%, P = 0.044), together with restoration of CD4+ and CD8+ T-cell counts and reduced PD-1 and Tim-3 exhaustion markers on CD8+ cells [5]. A larger multicentre retrospective study by Sun and colleagues analysed 771 critically ill patients from 19 hospitals; crude 28-day mortality was lower in the Tα1 group, but after propensity-score matching (n = 522) mortality was 51.0% versus 52.9%, with no significant difference and no benefit in subgroup or phenotype analyses [6]. A small pilot trial in haemodialysis patients examined thymalfasin as prophylaxis and reported preliminary findings only [7]. No large randomised trial has established a benefit in COVID-19.

What the compound is examined for

• TLR-dependent dendritic-cell maturation and cytokine output in vitro [2].
• T-cell exhaustion markers and thymic output (TREC) in lymphocyte preparations [5].
• Vaccine-adjuvant activity in animal models.
• Analytical reference for acetylated acidic peptides.

What the research does not establish

The hepatitis B evidence is mixed: the only blinded placebo-controlled trial was not statistically positive, and neither trial reported HBsAg loss. The COVID-19 signal from the small Wuhan series disappeared in the larger propensity-matched analysis, and no randomised trial has confirmed a mortality benefit. Approvals in some jurisdictions rest on older and smaller datasets than would be required today in the United States or Europe. The mechanistic work is largely in mice and cell culture. This material is supplied for in-vitro laboratory research only.

Format. Lyophilised white powder (acetate salt) in a sealed glass vial with rubber stopper and aluminium crimp cap.

Reconstitution. Add bacteriostatic water or sterile buffer slowly down the side of the vial and swirl gently until dissolved; do not shake. The peptide is highly acidic and dissolves readily at neutral pH. Use the reconstitution calculator to convert vial content to a working concentration.

Storage. Lyophilised vials: 2–8 °C, protected from light; suitable for longer-term storage at −20 °C. Reconstituted solution: 2–8 °C and use within 14 days; avoid repeated freeze–thaw cycles.

Handling. Thymosin alpha-1 is heat-stable and contains no cysteine, methionine or tryptophan, making it more robust than many peptides, but asparagine and aspartate residues remain susceptible to deamidation and isomerisation at high pH. Wear gloves and eye protection. For in-vitro laboratory research only — not for human or veterinary use.