Thymosin-ɑ1 for people with chronic hepatitis B.
RATIONALE: Chronic hepatitis B is a global public health concern. It is caused by infection with the hepatitis B virus (HBV). The goal of treating chronic HBV infection is to prevent progression to chronic hepatitis, cirrhosis, hepatic decompensation, liver failure, hepatocellular carcinoma, and death. Individual studies have evaluated various immunomodulatory therapies with inconsistent results. Thymosin-ɑ1 is known to have antiviral effects; however, results of randomised clinical trials on the effects of thymosin-α1 as a potential treatment for people with chronic HBV have been inconsistent. OBJECTIVES: To assess the benefits and harms of thymosin-ɑ1 therapy in people with chronic hepatitis B. SEARCH METHODS: We searched the Cochrane Hepato-Biliary Group Controlled Trials Register, CENTRAL, MEDLINE, four other databases and six trials registers, in addition to reference checking, citation searching, and contacting study authors to identify trials for inclusion. The latest search date was 10 June 2026. ELIGIBILITY CRITERIA: We included randomised controlled trials (RCTs) that evaluated thymosin-α1 at any dose, route of administration, or formulation type, in people with chronic hepatitis B regardless of age, sex, or ethnicity. Thymosin-α1 could have been administered as monotherapy, in combination with an additional drug, or in addition to standard medical treatment and compared with placebo, no intervention, the same additional drug, or the same standard medical treatment. OUTCOMES: Our critical outcomes were all-cause mortality, serious adverse events, and health-related quality of life. Among our important outcomes were HBV-related morbidity, HBV-related mortality, non-serious adverse events, and the proportion of people without histological improvements. RISK OF BIAS: We used the Cochrane Risk of bias 2 tool (RoB 2) to assess risk of bias. SYNTHESIS METHODS: We followed Cochrane methods. We conducted meta-analyses for predefined outcomes using data from the longest follow-up period, irrespective of the risk of bias judgements. We presented dichotomous outcome results as risk ratios (RRs) and continuous outcome results as mean differences, with 95% confidence intervals (CIs) at their longest follow-ups. We used the random-effects model for our primary analyses. We used GRADE to assess the certainty of the evidence for each outcome. INCLUDED STUDIES: We included 10 RCTs conducted in Bangladesh, China, Italy, Korea, Singapore, and Taiwan, with 1349 randomised participants (range: 12 to 690; 1045 (77.5%) were male). Among the trials reporting age, none included participants younger than 17 years (age range: 17 to 75 years). The trials were published between 1991 and 2018, and assessed thymosin-ɑ1 in adults with chronic hepatitis B infection, with or without comorbidities. Only two trials mentioned comorbidities (cirrhosis and acute-on-chronic liver failure). The trials compared thymosin-ɑ1, with or without a cointervention, with placebo or no intervention, or with the same cointervention. The control interventions were placebos in two trials and no intervention in two. The remaining six trials administered co-interventions, such as interferon, pegylated interferon, lamivudine, and standard medical therapy (entecavir or tenofovir), and entecavir. Follow-ups ranged from six months to five years after the end of treatment (median: 12 months). Four trials were funded by industry, five by research grants, and one provided no information. All 10 trials (11 records) provided data on at least one outcome in our review. We identified no ongoing trials. Sixteen studies are awaiting assessment due to incomplete reporting. We received no responses to our enquiries. SYNTHESIS OF RESULTS: Thymosin-ɑ1, compared with the control interventions, may reduce all-cause mortality (RR 0.53, 95% CI 0.29 to 0.96; I² = 0%; 3 studies, 907 participants; very low-certainty evidence), serious adverse events (RR 0.72, 95% CI 0.53 to 0.99; I² = 0%; 5 studies, 1056 participants; low-certainty evidence), HBV-related mortality (RR 0.53, 95% CI 0.29 to 0.96; I² = 0%; 3 studies, 907 participants; very low-certainty evidence), non-serious adverse events (RR 0.47, 95% CI 0.27 to 0.83; I² = 0%; 5 studies, 300 participants; very low-certainty evidence), and may have little to no effect on health-related quality of life (MD 0.70, 95% CI -2.55 to 3.95; I² not applicable; 1 study, 161 participants; very low-certainty evidence; score range: 0 to 100; the higher the score, the better) and on histological improvement (RR 0.51, 95% CI 0.13 to 2.06; I² = 74%; 2 studies, 702 participants; very low-certainty evidence). The evidence is very uncertain about the effect of thymosin-ɑ1 on hepatitis B-related morbidity (RR 0.86, 95% CI 0.54 to 1.40; I² = 3%; 3 studies, 854 participants; very low-certainty evidence). We judged the certainty of evidence to be low for serious adverse events and very low for the remaining outcomes. Reasons for downgrading were mainly due to study limitations, including overall high or some concerns for risk of bias; imprecision of the pooled effect estimates (including wide or very wide confidence intervals crossing the line of no effect, and small participant numbers); and inconsistency due to substantial heterogeneity (I² = 74%). The test for subgroup differences provided no evidence of differences in effect according to thymosin‑α1 administration for any outcome (P ≥ 0.05). AUTHORS' CONCLUSIONS: We assessed the certainty of evidence as very low for all outcomes except for serious adverse events (low). Therefore, we are not sure whether thymosin-α1 monotherapy versus placebo or no intervention, or with the same co-interventions, reduces all-cause mortality, serious adverse events, HBV-related mortality, and non-serious adverse events, nor whether it has any effect on quality of life (based on one trial) and histological improvement. The effect of thymosin-ɑ1 on HBV-related morbidity is very uncertain. We observed no statistically significant differences between trials with and without cointerventions. We found no ongoing trials. FUNDING: This Cochrane review had no dedicated funding. REGISTRATION: Protocol available via DOI: 10.1002/14651858.CD014610.