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Research profile · Peptide

Thymosin alpha-1

Also known as Thymalfasin

Clinical — evidence level 4 of 4: Established clinical evidenceExperimental — UK regulatory status: Experimental — not authorised for human use in the UK

Overview

A 28-amino-acid peptide corresponding to a naturally occurring thymic peptide, studied as an immune modulator in infection and sepsis.

Category
Peptide
Highest evidence level identified
Established clinical evidence
Last scientifically reviewed
20 August 2026
Last regulatory review
20 August 2026

Mechanism under investigation

Thymosin alpha-1 is a 28-amino-acid peptide corresponding to a naturally occurring thymic peptide; the synthetic form is termed thymalfasin. It is proposed to act as an immune modulator, with laboratory work indicating that it primes dendritic cells through Toll-like receptor 9 signalling and influences T-helper cell polarisation. These mechanisms derive largely from cell and animal models, and the extent to which they explain any clinical effect in humans remains proposed rather than established.

Research areas

  • Immune modulation
  • Infection research

These are fields in which the compound has been investigated. Listing a field is not a statement that anything was demonstrated within it.

Current evidence

In-vitro evidence

Cells, tissues or biochemical systems outside a living organism.

Present and reasonably developed. Work in human and murine dendritic cells demonstrates receptor-dependent signalling, enzyme induction and interleukin-10 production.

Animal evidence

Studies in living non-human animals.

Present. The same body of work includes murine transfer experiments in fungal and viral challenge models.

Human observational evidence

Studies observing people without assigning an intervention.

Present, including retrospective cohort work in COVID-19 and various infection settings, though generally small and subject to confounding.

Clinical-trial evidence

Studies assigning an intervention to human participants.

Substantial and unusually strong for this class — but the headline result is negative. Multiple randomised controlled trials exist in chronic hepatitis B, plus two randomised sepsis trials. The larger and better-conducted of the two, a double-blind trial in 1,106 patients, found no mortality benefit: 23.4 per cent versus 24.1 per cent, hazard ratio 0.99, P=0.93.

Study limitations

  • The evidence level reflects the scale and quality of evidence available, not proven benefit. The largest and best-conducted trial was negative on its primary endpoint.
  • The great majority of randomised evidence, including both sepsis trials, was conducted in China, raising questions about generalisability to UK populations and standards of care.
  • The hepatitis B meta-analysis pooled only four trials totalling 199 patients, with benefit not apparent at end of therapy and emerging only during follow-up.
  • Trials have used heterogeneous endpoints, comparators and disease definitions, which limits pooling.
  • Mechanistic claims rest heavily on dendritic-cell and murine models that have not been confirmed to operate at clinically relevant exposures in humans.

UK regulatory context

Experimental — not authorised for human use in the UK

A compound appearing in research literature that holds no UK authorisation for human use in any indication.

Source: Thymalfasin — orphan designation EU/3/02/110 (opens ema.europa.eu in a new tab) (European Medicines Agency)

Regulatory classification is jurisdiction-specific. A compound authorised elsewhere is not thereby authorised in the UK, and a supplier’s description of a substance does not determine how it is classified in law. See safety and regulation for the framework and the authoritative sources.

Safety and interpretation

In the large double-blind sepsis trial, adverse event rates did not differ meaningfully from placebo, and the peptide has been administered to substantial numbers of trial participants without a distinctive safety signal emerging. This provides more reassurance about short-term tolerability than exists for most compounds in this category. Long-term safety data, and safety outside the studied indications, remain limited.

References