Thymosin Alpha-1 Cuts Sepsis Death Risk But Only in Specific Patient Subgroups

Sepsis remains one of the leading causes of death worldwide, responsible for nearly 20% of all global mortality. Its hallmark is a dysregulated immune response that drives organ failure, and despite hundreds of clinical trials testing immunomodulatory agents, no therapy has convincingly reduced mortality. Thymosin alpha-1 (Tα1) — a synthetic peptide that promotes T-cell maturation, reverses T-cell exhaustion, and modulates cytokine responses — has been studied as a candidate immunotherapy for sepsis for decades, but its true clinical value has remained contested.

This 2025 systematic review and meta-analysis, registered on PROSPERO (CRD42024628937), searched seven English and Chinese databases through January 2025 and identified 11 RCTs meeting strict inclusion criteria: adult sepsis patients, 28-day mortality as the primary endpoint, Tα1 as the sole intervention difference, and standard Surviving Sepsis Campaign care as the control. The final pooled analysis included 967 patients in the Tα1 group and 960 in the control group. The overall meta-analysis using a random-effects model showed a statistically significant reduction in 28-day mortality with Tα1 (OR 0.73, 95% CI: 0.59–0.90, p = 0.003), suggesting a meaningful survival benefit at the population level.

However, the picture changed substantially when the authors stratified by study quality. When restricted to high-quality trials (scored 11–14 on the Cochrane risk-of-bias tool), the mortality benefit was no longer significant (OR 0.82, 95% CI: 0.65–1.03, p = 0.09). Similarly, analysis limited to multicenter RCTs — which are generally considered more generalizable — also failed to show a significant benefit (OR 0.86, 95% CI: 0.68–1.08, p = 0.20). This divergence between the overall pooled result and the higher-quality subsets is a critical finding, suggesting that the apparent overall benefit may be partly driven by lower-quality, single-center studies with higher risk of bias.

A key methodological strength of this review was the heterogeneity of treatment effects (HTE) analysis, conducted using individual patient data from two large multicenter RCTs that together accounted for 75% of the total patient population. This analysis revealed meaningful variation in Tα1's effects across patient subgroups. Patients with cancer showed a potential benefit with moderate credibility per the ICEMAN tool. Patients with diabetes or coronary heart disease also showed signals of benefit, though these were rated as low credibility. These findings align with the TESTS trial — the largest double-blind RCT of Tα1 in sepsis (n=1,106) — which found no overall mortality reduction but did identify potential effects in elderly and diabetic subgroups.

Trial sequential analysis (TSA) was used to assess whether the cumulative evidence is sufficient to draw firm conclusions. The TSA confirmed that the current total sample size remains inadequate to reliably detect or exclude a clinically meaningful mortality benefit, meaning the field has not yet crossed the information threshold needed for definitive guidance. This underscores the need for larger, well-designed trials — ideally enriched for subgroups most likely to respond. The authors conclude that Tα1 should not be dismissed outright, but that a personalized immunotherapy approach, targeting patients with specific immune profiles or comorbidities, is the most scientifically justified path forward for future clinical investigation.