Thymosin alpha-1 and the sepsis trials

ETASS, 2013

The ETASS trial enrolled 361 patients with severe sepsis. It reported 28-day all-cause mortality of 26.0 percent with thymosin alpha-1 and 35.0 percent in controls, alongside improved expression of the immune marker HLA-DR on monocytes. It was randomised, multicentre and single-blind: patients were blinded, investigators were not.

Those figures tempt even my sceptical side. The statistical result is more awkward. The nonstratified p-value was 0.062, while the log-rank p-value was 0.049. Different analyses of the same comparison landed on opposite sides of the conventional 0.05 threshold. The paper leaves a signal to investigate and a strong temptation to quote only the friendlier analysis.

TESTS, 2025

The double-blind, placebo-controlled phase 3 TESTS trial enrolled 1,106 adults with sepsis across 22 centres. At 28 days, all-cause mortality was 23.4 percent with thymosin alpha-1 and 24.1 percent with placebo: hazard ratio 0.99, 95 percent confidence interval 0.77 to 1.27, p-value 0.93. It found no statistically significant mortality benefit.

I give TESTS priority when weighing claims about sepsis survival. It leaves uncertainty, as the interval shows, while giving little support to the expected survival advantage. The trials involved different participants and designs. Their comparison cannot identify blinding, sample size or any other single difference as the cause of the changed result.

For sepsis, the newer trial has earned first billing. It also has a boundary: a sepsis result answers a sepsis question, rather than every possible use of an immune-modulating molecule.

Immune biology and other illnesses

Thymosin alpha-1 is a 28-amino-acid peptide; the synthetic version, thymalfasin, has the same sequence. The comprehensive literature review describes a long international clinical history. Its biology includes dendritic-cell and T-cell activity, with a regulatory arm that can also damp excessive inflammation. The phrase immune boost makes that dual action sound much simpler than it is.

There are other clinical questions. A retrospective cohort of 76 patients with severe COVID-19 reported mortality of 11.11 percent with treatment and 30.00 percent in the comparison group, alongside increased T-cell numbers in patients with severe lymphocytopenia and changes in markers of T-cell exhaustion. Treatment allocation was not randomised, leaving differences between the groups as a possible explanation for the association.

A reappraisal in cancer therapy discusses thymosin alpha-1 as an adjunct to chemotherapy and immunotherapy. I want the oncology combination question answered on its own terms. It requires its own clinical evidence; the sepsis verdict cannot stand in for an oncology verdict, favourable or otherwise.

Safety and international approval

The review of clinical experience reports approval in more than 35 countries, with generally good tolerability and mild local injection-site irritation, redness or discomfort as the most common adverse effects. Thymosin alpha-1 has no United States marketing authorisation. Historical orphan-drug designations concern development for particular rare conditions and do not amount to marketing approval.

Thymosin alpha-1 also appears in the FDA’s table of withdrawn nominations, following its earlier Category 2 listing. The nomination’s withdrawal leaves FDA safety concerns unresolved and grants no permission to compound it. Material described as research-grade sits outside the regulated drug-quality chain, with uncertainty about identity, content, purity and sterility.

Immune stimulation raises theoretical cautions in established autoimmune disease and in solid-organ transplant recipients, whose immune suppression is deliberate. These are mechanism-based concerns, not established clinical harms. Dedicated pregnancy and lactation safety data are absent. The mild reactions reported in clinical experience cannot settle those separate questions.

Accounts of resilience

Some community accounts describe fewer respiratory infections, faster recovery from feeling run-down or steadier energy. Others describe no perceived effect, while redness, itching, aching, headache or tiredness also appear. These are anecdotal accounts, not clinical evidence. A feeling of resilience is especially open to expectation and to the ordinary variation in how often someone gets ill.

Resilience has emotional appeal. I trust the mortality endpoint in TESTS more than an impression of resilience. For the related problem of a persuasive repair mechanism with very little human testing, there is BPC-157.