# thymosin alpha 1 Review — The Immunomodulation Research Record > thymosin alpha 1: what thirty years of hepatitis, sepsis, HIV, and aging trials actually measured. An independent editorial digest of the published research literature. A peer-reviewed digest of the mechanism, the dose-response data, the evidence gaps, and the open regulatory questions — with every quantitative claim sourced and cited. ## What the thymosin alpha 1 literature has demonstrated thymosin alpha 1 (thymalfasin, Tα1) is a 28-amino-acid peptide originally isolated from bovine thymus by Goldstein et al. in 1977 [16]. The molecular weight is 3,108 Da; the sequence is N-terminally acetylated, highly acidic (isoelectric point 4.2), and devoid of aromatic amino acids and disulfide bonds — structural properties that confer stability against proteolysis [16]. Over nearly five decades the published record has grown to include randomized controlled trials in chronic viral hepatitis, sepsis, HIV immune reconstitution, oncology, COVID-19, and aging-related immune decline. The most clinically mature evidence base concerns [hepatitis B clinical trial evidence](/research#hepatitis). Multiple RCTs established thymosin alpha 1 monotherapy at 1.6 mg subcutaneous twice weekly for 6 months as producing HBeAg seroconversion in 55.6% of treated patients at 12-month follow-up, compared with 27.3% for interferon-alpha and 3.3% for untreated controls [1]. A meta-analysis of 8 trials (583 patients) confirmed combination therapy with lamivudine achieved seroconversion in 45.1% versus 15.2% for lamivudine alone (P<0.00001) [15]. This evidence base drove regulatory approval of thymalfasin (Zadaxin) in 35 or more countries. In sepsis, thymosin alpha 1 addressed a specific pathophysiology — immunoparalysis, the failure of immune cells to respond to pathogens after the initial inflammatory cascade. The ETASS multicenter RCT (2013) documented a 9-point reduction in 28-day mortality (26.0% vs 35.0%) and significant improvement in monocyte HLA-DR expression, a biomarker of immune activation status [2]. A 2016 systematic review of 19 RCTs (1,354 patients) calculated a mortality relative risk of 0.59 (P=0.0001) [3]. The 2025 Phase 3 TESTS trial (1,106 patients, 22 centers) did not replicate this survival benefit in an unselected sepsis population (23.4% vs 24.1%, HR 0.99) [4], suggesting that patient selection — by immune phenotype, severity, or comorbidity — may determine which populations respond. Thymosin alpha 1 is not FDA-approved for any indication in the United States as of 2025. It is the subject of a large, active, and multi-indication clinical trial literature, which is what this site documents. ## Thymosin Alpha-1 Peptide: Structure and Origin thymosin alpha 1 peptide chemistry defines its behavior. The N-terminal acetylserine modification is not incidental: it protects the sequence from rapid aminopeptidase degradation, extending the effective half-life after subcutaneous injection to approximately 2 hours in human plasma [17]. The lack of disulfide bonds means the molecule is not vulnerable to the oxidative degradation that affects many other peptide therapeutics. The structure was elucidated by Goldstein and colleagues at George Washington University from bovine calf thymus [16]. The 28-amino-acid sequence is identical between species at the N-terminal end and has been preserved through synthetic manufacture for clinical use. Commercial thymalfasin (Zadaxin) is synthetically produced and chemically identical to the endogenous sequence — no bovine source material is used in modern formulations. Thymosin alpha 1 was the first member of the thymosin fraction 5 family to have its complete primary structure characterized. Thymosin beta-4 (TB-500), a structurally and functionally distinct peptide primarily studied for tissue repair via actin sequestration, belongs to a different thymosin subfamily and shares only the thymic isolation origin with thymosin alpha 1. The two molecules target different biological pathways and have independent pharmacological profiles. The thymus naturally produces thymosin alpha 1 throughout life, but production declines markedly after puberty as the thymus involutes — the same process that reduces T-cell output with age and contributes to immunosenescence [14]. ## What Is Thymosin Alpha-1 Used For? The approved and investigational uses of thymosin alpha 1 span five clinical domains. **Chronic viral hepatitis.** The most established indication: approved as Zadaxin in 35+ countries for chronic hepatitis B and C. Monotherapy seroconversion rates exceed interferon-alpha; combination protocols with nucleoside analogs amplify response [1, 15]. **Sepsis and critical illness immunoparalysis.** Multiple trials investigated thymosin alpha 1 for the immunosuppressed phase of sepsis, when HLA-DR expression on monocytes falls below threshold and infection risk rises. Results are mixed — ETASS (2013) showed benefit [2], TESTS (2025) did not in an unselected population [4]. Ongoing research focuses on patient phenotyping to identify responders. **HIV immune reconstitution.** In immunological nonresponders — patients who fail to restore CD4+ T cells despite viral suppression with antiretroviral therapy — thymosin alpha 1 at 1.6 mg twice weekly for 24 weeks increased CD4+ T cell proportion from 17.2% to 29.1% (P<0.001) and reduced markers of T cell exhaustion [10]. **Oncology adjuvant.** Chinese clinical protocols use thymosin alpha 1 alongside chemotherapy and transarterial chemoembolization for hepatocellular carcinoma. A randomized trial reported median overall survival of 110.3 weeks for the combination arm versus 57.0 weeks for chemoembolization alone [6]. Melanoma data reported 38.4-month median overall survival with thymosin alpha 1 before checkpoint inhibitor therapy versus 8 months with the checkpoint inhibitor alone [7]. **Aging and immune senescence.** The 2025 review in IJMS confirmed thymosin alpha 1 improves vaccine responses in the elderly, restores thymopoiesis markers (TRECs), and partially reverses immunosenescence at the preclinical level [14]. See [thymosin alpha-1 benefits in immune research](/immune-function) for the full evidence review. ## Thymosin Alpha-1 and Zadaxin: Same Molecule Zadaxin is the trade name for the synthetic thymalfasin formulation approved in 35 or more countries. The active molecule is identical: the 28-amino-acid sequence originally isolated from bovine thymus by Goldstein et al. in 1977 [16]. SciClone Pharmaceuticals holds commercial rights in many markets; regulatory approvals are in place across China, Italy, and 33 additional countries. No NDA has been filed with the FDA as of 2025. FDA restrictions on compounding pharmacy production introduced in 2023 created regulatory uncertainty for US access via the 503A compounding pathway. The [frequently asked questions](/faq) page addresses the US regulatory situation in detail. ## The Bidirectional Modulation Problem — and Why It Matters Most immunomodulatory compounds work in one direction: they stimulate or they suppress. thymosin alpha 1 is documented in both directions depending on immune context. Serum Tα1 levels are significantly lower in patients with chronic inflammatory autoimmune diseases — psoriatic arthritis, rheumatoid arthritis, systemic lupus erythematosus — compared to healthy controls (P<0.0001 across all groups, N=320) [9], suggesting the molecule is depleted when immune overactivation is occurring. At the same time, the same molecule activates T-cell maturation, dendritic cell maturation, and NK cell cytotoxicity in immunocompromised states [8]. This bidirectional profile is the central reason thymosin alpha 1 has been studied in both infection (where immune activation is needed) and autoimmune contexts (where normalization may be the mechanism). It also complicates clinical trial design: an endpoint of benefit in an immunocompromised population does not directly predict benefit in an overactivated one. The [mechanism of action](/research#mechanism) page details the TLR signaling pathways that underlie this bidirectional behavior. --- The thymosin alpha-1 research record — hepatitis trials, sepsis RCTs, immune reconstitution data — read at the source and indexed here, held by no clinic and sold by no one.