What is thymosin alpha 1? Thymalfasin in published research

Where does thymosin alpha 1 come from?

The story starts with thymosin fraction 5, a partly purified extract of calf thymus. In animal models and in early human studies, fraction 5 was reported to restore immune function that had been lost through absence or failure of the thymus. Fraction 5 turned out to be a family of polypeptides with molecular weights from about 1,000 to 15,000, and researchers set out to identify which components were active.

In 1977, Goldstein and colleagues isolated one of these components and determined its amino acid sequence. They named it thymosin alpha 1, proposed a naming system for the other fraction 5 polypeptides, and described it as a heat stable, highly acidic molecule of 28 amino acid residues. A follow up paper in 1979 reported that thymosin alpha 1 was 10 to 1,000 times as active as fraction 5 in assays designed to measure the differentiation and function of T cells, while another fraction 5 component, polypeptide beta 1, was inactive in the same assays.

Later work established that thymosin alpha 1 is not made only in the thymus. It is produced by cleavage of a larger precursor protein, prothymosin alpha, which is found in many mammalian tissues. The synthetic peptide is known as thymalfasin. A 2009 review reported that thymalfasin had been approved in over 35 countries for hepatitis B and C and as an immune adjuvant, and a 2010 review described a clinical development history running from small early studies with impure peptide mixtures to large phase 3 trials with the synthetic peptide.

How is it described at the molecular level?

Most mechanism studies place dendritic cells at the centre. In a 2004 study, thymosin alpha 1 induced maturation and IL-12 production by mouse dendritic cells exposed to the fungus Aspergillus fumigatus. The effect ran through the p38 MAP kinase and NF-kappaB pathways and depended on MyD88, an adaptor protein used by several Toll-like receptors. A later review from the same group described activation of plasmacytoid dendritic cells through TLR9, leading to activation of the transcription factor IRF7 and production of interferon alpha.

The same research line reported a second, more regulatory effect. In a 2006 study, thymosin alpha 1 induced the enzyme indoleamine 2,3-dioxygenase (IDO) in mouse dendritic cells. This required TLR9 and type I interferon receptor signalling, and it led to IL-10 production and the generation of regulatory T cells. The authors described the peptide as able to support T helper 1 immunity and tolerance at the same time, depending on context.

Beyond dendritic cells, a transcription study exposed human peripheral blood mononuclear cells to thymosin alpha 1 in vitro and profiled 8,300 genes. It found changes in many genes already linked to the peptide and in a number of genes not previously described, which the authors read as evidence of a broad regulatory role in lymphocytes. Reviews summarise the overall picture as pleiotropic: the peptide acts on several immune cell types rather than on one defined receptor.

What has been observed in published research?

Unlike most research peptides, thymosin alpha 1 has both a preclinical and a substantial clinical literature. The findings below name the model and the measured outcome in each case.

• Fungal infection in mice: in mice that had received haematopoietic transplants and were highly susceptible to aspergillosis, the synthetic peptide activated T helper 1 antifungal immunity, accelerated recovery of myeloid cells and protected the animals from infection.
• Tolerance in mice: in transfer experiments, dendritic cells primed with thymosin alpha 1 induced T helper 1 immunity within a regulatory environment. A review from the same group reported protection against primary murine cytomegalovirus infection, transplantation tolerance and protection from inflammatory allergy in mouse models.
• Sepsis, ETASS trial: a multicentre, single blind randomised trial in six Chinese teaching hospitals enrolled 361 patients with severe sepsis. Mortality at 28 days was 26.0 percent in the thymosin alpha 1 group and 35.0 percent in controls (relative risk 0.74, 95 percent confidence interval 0.54 to 1.02), a borderline result. Monocyte HLA-DR, a marker of immune function, improved more in the thymosin alpha 1 group on days 3 and 7.
• Sepsis, TESTS trial: a double blind, placebo controlled phase 3 trial at 22 centres in China randomised 1,106 adults with sepsis. Mortality at 28 days was 23.4 percent with thymosin alpha 1 and 24.1 percent with placebo (hazard ratio 0.99), and no secondary or safety outcome differed significantly. Prespecified subgroups suggested possible differences by age and diabetes status.
• Sepsis, combined trials: a 2025 systematic review of 11 randomised trials (967 patients receiving thymosin alpha 1, 960 controls) reported lower pooled 28 day mortality overall, but no significant difference in the high quality or multicentre subgroups, and trial sequential analysis judged the total sample size inadequate.
• Chronic hepatitis B: a systematic review of four randomised trials with 199 patients compared thymosin alpha 1 with interferon alpha. At the end of six months of therapy there was no clear advantage, while at follow up six months later virological, biochemical and complete response rates were higher in the thymosin alpha 1 groups.
• Hepatitis C: a 2010 review concluded that clinical trials had not conclusively supported adding thymosin alpha 1 to interferon based therapy, and that large randomised trials would be needed.
• Vaccine response: a review of influenza vaccine studies reported that giving thymosin alpha 1 alongside vaccination improved vaccine performance in elderly and other at risk subjects, while noting that further studies of such adjuvant combinations were needed.
• Serum levels: a review of measurement studies reported lower serum thymosin alpha 1 than in healthy individuals in hepatitis B, psoriatic arthritis, multiple sclerosis and sepsis, and lower levels in the sputum of people with cystic fibrosis. These are associations and do not show cause.
• COVID-19: a 2023 systematic review of eight studies in moderate to critical patients reported lower mortality with thymosin alpha 1, but with high heterogeneity and no difference in mechanical ventilation or length of hospital stay.

What the evidence does not establish

Thymosin alpha 1 has more human data than most peptides in this catalogue, but more data has not produced a clear answer. The largest and most rigorous sepsis trial, TESTS, found no difference in 28 day mortality, and the positive signal in pooled analyses weakened when only high quality or multicentre trials were counted. Both large sepsis trials were run in China, the trials pooled in pooled analyses used different patient groups and outcome measures, and some, such as ETASS, were single blind rather than double blind. That limits how far results can be compared or generalised. The COVID-19 analysis showed the same pattern: a pooled mortality signal, high heterogeneity between studies, and no difference in other outcomes.

Several basic questions are also unresolved. A review of serum studies noted that physiological baseline levels of the peptide and the most effective regimen are still debated. A historical review of infectious disease trials, which noted that the peptide had been used in thousands of patients, also listed schedule, combinations and trial end points as issues not yet properly addressed. The dendritic cell studies cited here come mainly from mouse models and from one research group in Perugia, and no single receptor has been confirmed. Finally, the clinical data describe a pharmaceutical product given under medical supervision. They do not describe research grade peptide, and they say nothing about effects outside the conditions and populations that were studied.

Which formats does Vitality Peps supply?

Vitality Peps supplies thymosin alpha 1 as Thymosin Alpha 1 10 mg, a lyophilised powder in a sealed vial. For reconstitution, Vitality Peps also supplies bacteriostatic water in 10 ml vials. Both are sold for in vitro laboratory research only. The vial contains research grade peptide. It is not the pharmaceutical thymalfasin product used in the clinical trials described above, and those trial results should not be read as properties of this material.

How is it handled in the laboratory?

Lyophilised thymosin alpha 1 is stored cold and dark until it is needed. Before reconstitution the vial is allowed to reach room temperature, and the powder is dissolved in bacteriostatic water at room temperature by gentle swirling rather than shaking. The working concentration is calculated from the actual peptide mass in the vial, as stated on the certificate of analysis, rather than from the nominal label alone.

Once reconstituted, the solution is kept refrigerated, labelled with its concentration and dated on the day it was prepared. Repeated warming and cooling is avoided. Our guides to storing research peptides, reading a peptide certificate of analysis and what a vial should look like give more detail.

Research use only

Thymosin alpha 1 supplied by Vitality Peps is for in vitro laboratory research only. Not a medicine, not a supplement, not for human or veterinary consumption. Nothing above is instructions for use.