Thymosin Alpha-1

Thymosin alpha-1 is also written thymosin alpha 1, Tα-1 or TA1 peptide. As a pharmaceutical substance, it is named thymalfasin. It is a 28-residue, N-terminally acetylated peptide. It was first isolated from calf thymus tissue and sequenced in 1977 (Goldstein et al., 1977). It is one part of a mixture once called thymosin fraction 5. The chemistry and biology of that fraction were studied. This work placed the peptide among the fraction's more active parts in the assays of the time (Low et al., 1979).

So do the peptide class and sizes. Aliases and the PubChem weight come from PubChem CID 16130571. PubChem agrees on the formula.

A PubMed search across the name variants returns about 960 records. About 100 of them are typed as clinical trials. So there is far more published work here than for most research peptides. This work falls into five areas. Each summary below states the model used.

Identity, origin and the precursor protein

The first isolation work purified the peptide from thymosin fraction 5. This was a partly purified calf thymus extract. That work reported a heat-stable, highly acidic 28-residue peptide (Goldstein et al., 1977; Low et al., 1979). Later work in rat thymus made that picture more complex. It used an antibody raised against the synthetic peptide. With it, a polypeptide of about 112 residues was isolated. It was named prothymosin alpha.

It carries the same sequence at its N-terminus. It was the major cross-reacting species in rat thymus extracts. It was proposed that the 28-residue peptide is made from it during isolation of fraction 5 (Haritos et al., 1984). A later study combined chromatography with immunoassay. It reported the 28-residue peptide, not the precursor, as the main immunoreactive species in serum and thymus (Naylor et al., 1992). Check which species an assay actually measured before comparing papers.

Conformation and membrane interaction

Structural studies agree that the peptide is unstructured in water. With sodium dodecyl sulfate micelles, it adopts a helical fold. The fold has a structural break around residues 9 and 14. Paramagnetic relaxation data placed residues 1 to 5 inside the hydrophobic region of the micelle (Nepravishta et al., 2015). A review of the same programme reported that interaction was preferred on surfaces with negative charge. These included vesicles with phosphatidylserine and cultured K562 cells exposing it after induced apoptosis (Nepravishta et al., 2016).

Separate work pointed to a preliminary interaction with hyaluronan around the C-terminal LKEKK lysines (Mandaliti et al., 2017). A survey of thymosin structures places all of these peptides in the intrinsically unstructured class. Charge neutralisation or metal ions can induce structure in them. So can organic cosolvents or binding partners (Hoch and Volk, 2016). No specific receptor has been confirmed. One study did report antibody-detected receptors on lung cancer cells. Dendritic cell work also points to Toll-like receptor signaling.

Dendritic cell and innate signaling studies

A group in Perugia wrote a series of papers on the peptide. They used mouse and human dendritic cell culture and mouse infection models. In fungus-pulsed dendritic cells, the peptide was reported to induce maturation markers and interleukin-12 production. The reported pathway was p38 MAPK and NF-kB dependent and required MyD88. Matching T helper cell responses were reported in mice challenged with Aspergillus fumigatus (Romani et al., 2004). A follow-up reported that the same signaling also activated indoleamine 2,3-dioxygenase in murine dendritic cells.

It also reported interleukin-10 production and regulatory T cell generation. The authors read this as a push toward response and tolerance at the same time (Romani et al., 2006). Another paper used mice infected with murine cytomegalovirus. There, the antiviral effect was reported to run through TLR9 and MyD88 dependent sensing in plasmacytoid dendritic cells. Activation of interferon regulatory factor 7 was also reported. The work included TLR-deficient mice (Bozza et al., 2007; reviewed in Romani et al., 2007).

Tumor cell culture and xenograft models

The peptide was studied in human non-small cell lung cancer lines. It raised the rate of arachidonic acid release and cut colony number in clonogenic assays at 10⁻⁶ M. Its N-terminal and C-terminal fragments and thymosin beta-4 were less active. Nude mice carrying xenografts of the same lines were also studied. There, the full-length peptide cut xenograft formation. The fragments did not (Moody et al., 1993). This is cell-culture and mouse work, not a human cancer finding.

Human clinical literature, including a negative phase 3 result

Two randomized studies in adults with sepsis bracket this literature. A six-centre single-blind study in China enrolled 361 patients. It reported 28-day mortality of 26.0 percent against 35.0 percent in controls. The difference was marginal on the non-stratified analysis (p = 0.062). It was conventionally significant only on the log-rank test (p = 0.049). The study also reported a greater rise in monocyte HLA-DR expression on days 3 and 7 (Wu et al., 2013). The follow-up was a 22-centre phase 3 trial in 1106 adults. It was double-blinded and placebo-controlled.

Its 28-day all-cause mortality was 23.4 percent against 24.1 percent. The hazard ratio was 0.97 (95 percent confidence interval 0.76 to 1.24). That value comes from a May 2025 correction. It replaced the first published value, 0.99 (BMJ correction, 2025). No secondary or safety outcome separated the groups. There were only exploratory subgroup signals by age and diabetes status (Wu et al., 2025). Reviews written before that trial listed many proposed clinical applications (Goldstein and Goldstein, 2009). The 2025 result is the strongest evidence in the field. It was null for its primary endpoint.