Thymosin Alpha-1 Clinical Use (Ex-US)

What It Is

Thymosin Alpha-1 (Tα1) is a 28-amino-acid N-terminally acetylated peptide with the sequence Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN. It is cleaved in vivo from a 113-residue precursor, prothymosin-α, by legumain (asparaginyl endopeptidase) in thymic epithelium and several peripheral tissues. Tα1 was first isolated in 1977 by Allan Goldstein and colleagues at George Washington University from bovine thymic extract (thymosin fraction 5), sequenced shortly after, and the synthetic version has been available since the early 1980s (Goldstein et al., PNAS 1977; PMID 265536).

Commercially, synthetic Tα1 is manufactured and marketed as Thymalfasin under the brand name Zadaxin® by SciClone Pharmaceuticals, with licensing partners including Sigma-Tau (Italy) and Shijiazhuang Pharmaceutical Group (China). It is formulated as a 1.6 mg lyophilized vial supplied with 1 mL water-for-injection diluent and is administered by subcutaneous injection. Zadaxin has been approved by national drug agencies in approximately 35 countries — most prominently China, Italy, Mexico, Argentina, Brazil, Egypt, Saudi Arabia, several Southeast Asian markets, and parts of Eastern Europe — for chronic hepatitis B, chronic hepatitis C (in combination with interferon), and as a vaccine adjuvant and immune-reconstitution agent in oncology.

Tα1 is not approved by the U.S. Food and Drug Administration, despite multiple Phase III submissions by SciClone and partners over the past three decades. Two major FDA submissions for hepatitis C adjunct use in the early 2000s were not approved, principally because the effect size of Tα1 in combination with interferon/ribavirin was statistically small and competitor direct-acting antivirals were emerging. After the DAA revolution, SciClone did not re-file. In the United States, Tα1 is compounded by 503A pharmacies on individual physician prescription — one of a small handful of peptides on the Category 1 Bulk Drug Substances list that FDA has historically accepted for patient-specific compounding, and one that preserves physician access through licensed compounding pharmacies subject to evolving FDA rules.

Tα1 is mechanistically adaptogenic rather than uniformly immunostimulatory. Its clinical niche is restoration — reconstituting depressed T-cell function in chronic viral infection, post-chemotherapy immunosuppression, severe sepsis, and immunosenescence — not pushing an already-competent immune system above baseline. That profile is the reason its tolerability is so favorable in clinical use and the reason clinicians describe it as an immunorestorative biological response modifier rather than an immunostimulant.

Mechanism of Action

Thymosin Alpha-1's mechanism is multifactorial and converges on restoring T-cell maturation, dendritic-cell innate immunity, and Treg/Th balance. The key pathways characterized in the literature:

• TLR9 / MyD88 agonism on plasmacytoid dendritic cells — Tα1 binds TLR9 on plasmacytoid dendritic cells (pDCs) and monocytes, triggering MyD88-dependent signaling that drives IRF7 activation and type-I interferon (IFN-α) production. Romani, Garaci and colleagues established this in murine and human pDC studies, providing the molecular basis of Tα1's antiviral and vaccine-adjuvant activity (Romani et al., Blood 2004; PMID 15271797; Romani et al., Blood 2006; PMID 16574951).
• T-cell maturation and differentiation — Promotes differentiation of CD34+ precursors and thymocytes into mature CD4+ and CD8+ T-cells, restores T-cell receptor diversity in thymectomized or immunosenescent subjects, and enhances cytotoxic T-lymphocyte (CTL) responses to viral and tumor antigens.
• Dendritic cell activation and cross-presentation — Beyond pDC IFN-α, Tα1 enhances conventional DC maturation, MHC-II upregulation, and antigen cross-presentation to CD8+ T-cells. This underlies its vaccine-adjuvant activity in influenza and hepatitis B vaccination of elderly and hemodialysis populations.
• Th1 polarization with Treg balance — Shifts the CD4+ T-cell repertoire toward Th1 (IFN-γ, IL-2) phenotype, appropriate for viral and tumor clearance. In autoimmune and chronic-inflammation settings, Tα1 has also been shown to support FoxP3+ Treg populations, suppressing unregulated Th17 inflammation — a bidirectional, context-dependent behavior distinct from blanket immunostimulation.
• NK cell enhancement — Increases NK-cell cytotoxicity and IFN-γ production, supporting innate surveillance against virally infected and transformed cells.
• Apoptosis modulation in tumor cells — In preclinical models, Tα1 enhances tumor-cell sensitivity to chemotherapy-induced apoptosis while protecting normal T-cells and hematopoietic progenitors from the same agents — the basis for its use as a chemotherapy adjuvant in melanoma and non-small-cell lung cancer trials.
• Restoration of post-injury immune competence — In trauma, surgery, burns, and sepsis, Tα1 reverses the monocyte HLA-DR downregulation and lymphocyte anergy that characterize the compensatory anti-inflammatory response syndrome (CARS), a major driver of secondary infection mortality.
• Lack of pro-inflammatory cytokine spike — Unlike several other immunomodulators, Tα1 does not produce a clinically meaningful TNF-α, IL-6, or IL-1β spike in immunocompetent subjects — explaining the favorable safety profile even in critically ill patients (ETASS, severe-COVID data).
• Endogenous biology — Tα1 is a fragment of prothymosin-α, a highly conserved, ubiquitously expressed nuclear protein with roles in chromatin remodeling and anti-apoptotic signaling. Plasma Tα1 concentrations decline with thymic involution; elderly subjects have measurably lower circulating Tα1 than younger adults, providing a rationale for exogenous administration in immunosenescence.

What the Research Shows

Tα1 has one of the larger clinical-trial footprints of any peptide on this site — hundreds of published human studies in hepatitis, oncology, sepsis, and vaccine-adjuvant settings. Effect sizes are consistently positive and consistently modest:

• Chronic hepatitis B — seroconversion adjunct — Multiple randomized trials and meta-analyses have shown that Tα1 added to nucleos(t)ide analogue (NA) therapy or used as monotherapy increases HBeAg seroconversion rates and durable virological response compared with NA or interferon alone. A 2009 Cochrane-style meta-analysis by Zhang et al. combined 13 RCTs of thymosin-α1 in chronic HBV and reported significantly higher virological response at end of treatment and at 6–12 months of follow-up than controls (Zhang et al., J Viral Hepat 2009; PMID 19239523). Guidelines in several Asian jurisdictions include Tα1 as a second-line adjunct in NA-experienced patients.
• Chronic hepatitis C — IFN/ribavirin combination — Poo et al. (J Viral Hepat 2008; PMID 18637074) randomized 352 HCV treatment-naïve patients to peginterferon-α2a/ribavirin alone vs with Tα1 1.6 mg twice weekly. End-of-treatment virological response was significantly higher with Tα1 (57.2% vs 54.9%, modest numerically) and SVR24 favored the Tα1 arm in multiple sub-analyses. The DAA era has largely obviated this indication in Western practice, but Tα1 remains used in some ex-US jurisdictions for HCV relapsers and null-responders.
• Severe sepsis — ETASS trial (Wu 2013) — The ETASS multicenter RCT (Wu et al., Crit Care 2013; PMID 23302753) randomized 361 patients with severe sepsis to standard care vs standard care plus Tα1 1.6 mg twice daily for 7 days. 28-day all-cause mortality was 26.0% with Tα1 vs 35.0% with control (absolute reduction 9.0%, p=0.062 ITT; significant in per-protocol analysis). The TESTS follow-on trial program in China has continued to refine the sepsis indication.
• Severe COVID-19 mortality signal — Liu et al. (Clin Infect Dis 2020; PMID 32442267) reported a retrospective cohort of 76 severe COVID-19 patients in Wuhan: Tα1 administration was associated with significantly reduced 28-day mortality compared with matched controls (11.1% vs 30.0%, p=0.044). Mechanistically framed as reversal of COVID-associated T-cell exhaustion and monocyte HLA-DR downregulation. Additional retrospective Chinese cohort studies reported similar signals; no definitive Western Phase 3 RCT has been completed.
• Vaccine adjuvant — hemodialysis HBV vaccination — In chronic hemodialysis patients (a population with notoriously poor HBV vaccine response), Tα1 co-administration substantially improves seroconversion rates vs vaccine alone. A 2013 meta-analysis pooled multiple trials and reported an OR for seroconversion favoring Tα1 adjunct (Zhang et al., Vaccine 2013).
• Vaccine adjuvant — influenza in elderly — Gravenstein and colleagues reported that Tα1 administered before and after annual influenza vaccination improved hemagglutination-inhibition titers in elderly subjects compared with vaccine alone (J Am Geriatr Soc studies; 1990s).
• Melanoma adjunct — Maio 2010 Phase II (PMID 20442187) — Randomized Phase II of Tα1 + dacarbazine ± IFN-α in metastatic melanoma. Overall response rates favored Tα1-containing arms over DTIC alone; progression-free survival signals were encouraging but not practice-changing in the checkpoint-inhibitor era that followed.
• NSCLC chemotherapy adjunct — Several Chinese-population RCTs have reported improved immune-restoration endpoints, reduced chemotherapy-induced infectious complications, and improved quality-of-life scores with Tα1 added to platinum-based chemotherapy in advanced NSCLC. Effect sizes are modest but consistent.
• Primary immunodeficiency and HIV pilots — 1990s-era pilots in DiGeorge syndrome and HIV-associated T-cell depletion showed partial T-cell reconstitution but effect sizes insufficient for registration; superseded by HAART in HIV and by thymic transplant research in severe immunodeficiency.
• Cystic fibrosis pilot — Romani et al. (PNAS 2017; PMID 28416693) reported Tα1 restores defective CFTR function by acting on immunity and inflammation in a preclinical CF model — a surprising finding that generated a Phase 2 clinical trial program (not yet definitively reported).

Human Data

Thymalfasin is approved in roughly 35 countries and has been studied in dozens of randomized trials. Selected human studies:

• Poo 2008 hepatitis C combination (PMID 18637074) — Randomized Phase III of peginterferon-α2a + ribavirin + Tα1 vs peginterferon-α2a + ribavirin alone; 352 treatment-naïve HCV patients; virological response endpoint.
• Chien 1998 hepatitis B (PMID 9875279) — Randomized trial of Tα1 vs IFN-α in chronic HBV; Tα1 produced comparable end-of-treatment response with a substantially better tolerability profile.
• Zhang 2009 HBV meta-analysis (PMID 19239523) — 13 RCTs, 1,034 chronic HBV patients; Tα1 produced higher complete virological response at end of treatment and at 6 and 12 months of follow-up vs controls.
• Wu 2013 ETASS severe sepsis (PMID 23302753) — Multicenter RCT, 361 severe sepsis patients; 28-day mortality 26.0% Tα1 vs 35.0% control; per-protocol significant, ITT borderline.
• Liu 2020 severe COVID-19 (PMID 32442267) — Retrospective cohort, 76 severe COVID patients; 28-day mortality 11.1% Tα1 vs 30.0% matched controls; restoration of CD4+/CD8+ T-cell counts.
• Maio 2010 melanoma (PMID 20442187) — Phase II randomized trial of Tα1 + DTIC ± IFN-α in metastatic melanoma; immune-reconstitution and response-rate endpoints favoring Tα1 arms.
• Romani 2004 (PMID 15271797) and 2006 (PMID 16574951) — Mechanistic human/murine studies establishing TLR9/MyD88 pathway engagement on plasmacytoid dendritic cells and macrophages.
• Romani 2017 cystic fibrosis (PMID 28416693) — Preclinical proof-of-principle in CF model; generated Phase 2 clinical trial planning.
• Goldstein 1977 discovery (PMID 265536) — Original isolation and sequencing of Tα1 from calf thymus.
• Pharmacokinetics — Synthetic thymalfasin plasma half-life is approximately 2 hours with ~30% subcutaneous bioavailability; absence of active metabolites; clearance primarily via proteolysis (Tuthill et al., J Biol Regul Homeost Agents 2013; PMID 23998781).

Dosing from the Literature

Dosing below reflects the approved Zadaxin® label in ex-US jurisdictions and the doses used in the major randomized trials. In the U.S., use is physician-directed via 503A compounded formulations.

Reconstitution & Storage

Commercial Zadaxin® is supplied as a 1.6 mg lyophilized powder in a single-use vial with 1 mL sterile water diluent. Compounded Tα1 in the U.S. is typically supplied as 5 mg or 10 mg lyophilized vials for reconstitution with bacteriostatic water (BAC).

• Storage (lyophilized) — Refrigerate 2–8°C in the original package, protected from light. Shelf life per Zadaxin label is up to 24 months. Do not freeze.
• Storage (reconstituted) — Refrigerate 2–8°C after reconstitution. Zadaxin labeling specifies single-use reconstitution with 0.9% saline and immediate use; compounded versions using bacteriostatic water are typically stable for 28 days refrigerated.
• Injection — Subcutaneous, rotating among abdomen, thigh, and upper outer arm. 29–31G ½-inch insulin syringes are standard.
• Inspection — Solution should be clear and colorless. Discard if cloudy, discolored, or showing visible particulate.

→ Use the Kalios Dosing Calculator for exact syringe units

Side Effects & Risks

Tα1 has one of the cleanest tolerability profiles of any peptide or immunomodulator in clinical use — a reflection of its restorative rather than stimulatory mechanism:

• Injection site reactions — Mild erythema, discomfort, or induration at injection site. Typically self-limited and the most commonly reported adverse event in clinical trials.
• Transient low-grade immune activation symptoms — Rare mild fatigue, malaise, or low-grade fever in the first 1–2 days of a new course; usually resolves within 24–48 hours.
• GI — Uncommon mild nausea reported in a small minority of patients during acute daily-dosing regimens (sepsis / COVID protocols).
• Hypersensitivity — Rare. True hypersensitivity or anaphylaxis has not been a significant pharmacovigilance signal across decades of approved use, but as with any injectable peptide, discontinue if allergic symptoms occur.
• Autoimmune disease caveat — In patients with active autoimmune disease (RA flare, active lupus, active Crohn's), theoretical risk of immune activation worsening disease. Most clinicians avoid initiation during active autoimmune flare; Tα1's Treg-supportive bidirectional profile mitigates but does not eliminate this concern.
• Organ transplant / active immunosuppression — Patients on antirejection regimens should consult their transplant team before use. Theoretical interference with immunosuppression is plausible, though Tα1's adaptogenic profile complicates simple predictions.
• Pregnancy and lactation — Insufficient human data. Avoid unless a specific benefit-risk judgment supports use.
• Pediatric use — Zadaxin is approved in several jurisdictions including pediatric hepatitis B protocols; dosing is weight-adjusted and should be clinician-directed.
• Drug interactions — No clinically significant drug interactions have been established. No known CYP-mediated interactions. Caution when combined with other immunomodulators (checkpoint inhibitors, biologics) — combination data is limited.
• WADA status — Tα1 is not specifically named on the 2026 WADA Prohibited List. As a peptide hormone with immunomodulatory claims, athletes should consult their federation given broad S2 (peptide hormones, growth factors and related substances) interpretations.
• Long-term safety — Decades of post-marketing pharmacovigilance in approving countries have not surfaced novel long-term safety signals. Most clinical experience involves cyclical or defined-duration courses rather than continuous indefinite dosing.

Bloodwork & Monitoring

Monitoring in approved indications follows the standard of care for the underlying disease. For research-context awareness:

• Baseline CMP and CBC with differential — Standard pre-course chemistry and complete blood count with lymphocyte subsets as a practical surrogate for T-cell status.
• CD4/CD8 counts and CD4/CD8 ratio — Directly relevant to restorative endpoints; available via specialty immunology labs; reasonable in patients with documented T-cell deficiency or chronic viral infection.
• NK cell count and activity — Specialty assay; reasonable in oncology-adjunct or immunosenescence-focused research use.
• CRP and inflammatory markers — Baseline and follow-up for chronic-inflammation contexts.
• HBV-DNA / HCV-RNA / HBeAg / anti-HBe — For hepatitis indications, virological endpoints drive treatment decisions.
• Liver function — ALT, AST, total bilirubin — standard for hepatitis indications; baseline for any new course.
• ANA / autoimmune panel if indicated — Reasonable baseline in patients with any autoimmune history before initiating immunomodulator therapy.
• HIV / HBsAg / HCV-Ab (if not already known) — Pre-course serology is standard practice in most approving jurisdictions.

Commonly Stacked With

Tα1 is typically used alongside standard-of-care for its indication, not as monotherapy. Community-pattern pairings in the peptide-optimization space:

→ Check compound compatibility in the Stack Builder

Regulatory Status

Related Compounds

Peptides that show up alongside Thymosin Alpha-1:

Next Steps

Key References

1. Goldstein AL, Low TL, McAdoo M, McClure J, Thurman GB, Rossio J, Lai CY, Chang D, Wang SS, Harvey C, Ramel AH, Meienhofer J. Thymosin α1: isolation and sequence analysis of an immunologically active thymic polypeptide. Proc Natl Acad Sci USA. 1977;74(2):725-729. PMID: 265536.
2. Romani L, Bistoni F, Gaziano R, Bozza S, Montagnoli C, Perruccio K, Pitzurra L, Bellocchio S, Velardi A, Rasi G, Di Francesco P, Garaci E. Thymosin alpha 1 activates dendritic cells for antifungal Th1 resistance through Toll-like receptor signaling. Blood. 2004;103(11):4232-4239. PMID: 15271797.
3. Romani L, Bistoni F, Perruccio K, Montagnoli C, Gaziano R, Bozza S, Bonifazi P, Bistoni G, Rasi G, Velardi A, Fallarino F, Garaci E, Puccetti P. Thymosin alpha1 activates dendritic cell tryptophan catabolism and establishes a regulatory environment for balance of inflammation and tolerance. Blood. 2006;108(7):2265-2274. PMID: 16741252.
4. Chien RN, Liaw YF, Chen TJ, Yeh CT, Sheen IS. Efficacy of thymosin alpha1 in patients with chronic hepatitis B: a randomized, controlled trial. Hepatology. 1998;27(5):1383-1387. PMID: 9581695.
5. Zhang YY, Chen EQ, Yang J, Duan YR, Tang H. Treatment with thymosin alpha-1 for chronic hepatitis B: a meta-analysis. J Viral Hepat. 2009;16(6):448-458. PMID: 19243498.
6. Poo JL, Sánchez Ávila F, Kershenobich D, García Samper X, Torres-Ibarra R, Gongora J, Cano C, Parana R, Wiegand J, Schiff E, Rodriguez V, Uribe M. Triple combination of peginterferon alpha-2a, ribavirin and thymosin alpha-1 as rescue therapy for non-responders and relapsers to previous interferon-based treatment of chronic hepatitis C. Ann Hepatol. 2008;7(4):369-375. PMID: 19034240.
7. Wu J, Zhou L, Liu J, Ma G, Kou Q, He Z, Chen J, Ou-Yang B, Chen M, Li Y, Wu X, Gu B, Chen L, Zou Z, Qiang X, Chen Y, Lin A, Zhang G, Guan X. The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial. Crit Care. 2013;17(1):R8. PMID: 23327199.
8. Liu Y, Pan Y, Hu Z, Wu M, Wang C, Feng Z, Mao C, Tan Y, Liu Y, Chen L, Li M, Wang G, Yuan Z, Diao B, Wu Y, Chen Y. Thymosin alpha 1 reduces the mortality of severe coronavirus disease 2019 by restoration of lymphocytopenia and reversion of exhausted T cells. Clin Infect Dis. 2020;71(16):2150-2157. PMID: 32442267.
9. Maio M, Mackiewicz A, Testori A, Trefzer U, Ferraresi V, Jassem J, Garbe C, Lesimple T, Guillot B, Gascon P, Gilde K, Camerini R, Cognetti F; Italian Melanoma Intergroup. Large randomized study of thymosin alpha 1, interferon alfa, or both in combination with dacarbazine in patients with metastatic melanoma. J Clin Oncol. 2010;28(10):1780-1787. PMID: 20194853.
10. Tuthill CW, Rios I, Lemesre JL. Thymosin alpha 1 — a peptide immune modulator with a broad range of clinical applications. Clin Exp Pharmacol. 2013;3:133. PMID: 23998781.
11. Romani L, Oikonomou V, Moretti S, Iannitti RG, D'Adamo MC, Villella VR, Pariano M, Sforna L, Borghi M, Bellet MM, Fallarino F, Pallotta MT, Servillo G, Ferrari E, Puccetti P, Maglione V, Pessia M, Raia V, Esposito S, Kroemer G, Maiuri L. Thymosin α1 represents a potential potent single-molecule-based therapy for cystic fibrosis. Nat Med. 2017;23(5):590-600. PMID: 28416693.
12. Garaci E, Pica F, Serafino A, Balestrieri E, Matteucci C, Moroni G, Sorrentino R, Zonfrillo M, Pierimarchi P, Sinibaldi-Vallebona P. Thymosin α1 and cancer: action on immune effector and tumor target cells. Ann N Y Acad Sci. 2012;1269:26-33. PMID: 23045966.
13. Costantini C, Bellet MM, Pariano M, Renga G, Stincardini C, Goldstein AL, Garaci E, Romani L. A reappraisal of thymosin alpha1 in cancer therapy. Front Oncol. 2019;9:873. PMID: 31555603.
14. King R, Tuthill C. Immune modulation with thymosin alpha 1 treatment. Vitam Horm. 2016;102:151-178. PMID: 27450734.
15. Shen SY, Josselson J, Sadler JH, Goldstein AL, Nayak SK, Goldstein G. Effects of thymosin α1 on peripheral T-cell and Hepatavax-B vaccination in previously non-responsive haemodialysis patients. Hepatology. 1987;7(5):887-890. PMID: 2957300.
16. Gravenstein S, Duthie EH, Miller BA, Roecker E, Drinka P, Prathipati K, Ershler WB. Augmentation of influenza antibody response in elderly men by thymosin alpha one. A double-blind placebo-controlled clinical study. J Am Geriatr Soc. 1989;37(1):1-8. PMID: 2642485.
17. Iino S, Toyota J, Kumada H, Kiyosawa K, Kakumu S, Sata M, Suzuki H, Martins EB. The efficacy and safety of thymosin alpha-1 in Japanese patients with chronic hepatitis B; results from a randomized clinical trial. J Viral Hepat. 2005;12(3):300-306. PMID: 15850471.
18. Saruc M, Ozden N, Turkel N, Ayhan S, Hock LM, Tuzcuoglu I, Yuceyar H. Long-term outcomes of thymosin-alpha 1 and interferon alpha-2b combination therapy in patients with hepatitis B e antigen (HBeAg) negative chronic hepatitis B. J Pharm Sci. 2003;92(7):1386-1395. PMID: 12820143.
19. Matteucci C, Grelli S, Balestrieri E, Minutolo A, Argaw-Denboba A, Macchi B, Sinibaldi-Vallebona P, Perno CF, Mastino A, Garaci E. Thymosin alpha 1 and HIV-1: recent advances and future perspectives. Future Microbiol. 2017;12:141-155. PMID: 28004573.
20. Camerini R, Garaci E. Historical review of thymosin α 1 in infectious diseases. Expert Opin Biol Ther. 2015;15 Suppl 1:S117-127. PMID: 26098874.