Also known as: Thymalfasin, Zadaxin, Thymosin ฮฑ1
Immune modulation for chronic hepatitis B, cancer adjuvant immunotherapy, and immune reconstitution
Amount
1.6 mg
Frequency
Twice weekly (standard); daily during chemotherapy cycles (cancer adjuvant)
Duration
6-12 months (hepatitis B); 3-6 months (immune support); per chemo cycle (cancer)
Route
SCSchedule
Twice weekly (standard); daily during chemotherapy cycles (cancer adjuvant)
Timing
No specific time of day; maintain consistent schedule with 3-4 days between doses
โ Rotate injection sites
Duration
6-12 months (hepatitis B); 3-6 months (immune support); per chemo cycle (cancer)
Repeatable
Yes
Diluent: Sterile water
Use within: Use immediately after reconstitution
Storage: Store lyophilized vials at 2-8 degrees Celsius (36-46 degrees Fahrenheit), protected from light. Do not freeze. Unopened vials are stable for 24 months under recommended storage conditions. Reconstituted solution should be used immediately and any unused portion discarded. Do not use if the reconstituted solution appears discolored or contains particulate matter.
CBC with differential
When: Baseline
Why: Baseline immune cell counts
Lymphocyte subset panel (CD4, CD8, NK cells)
When: Baseline
Why: Ta1 targets T-cell and NK cell function
Hepatitis B panel (HBV DNA, HBeAg, HBsAg)
When: Baseline
Why: Required for hepatitis B indication; baseline viral status
CMP with liver enzymes
When: Baseline
Why: Liver function baseline
Immunoglobulin levels
When: Baseline
Why: Baseline humoral immunity
HBV DNA and HBeAg
When: 3 months (hepatitis B indication)
Why: Assess virological response; seroconversion may be delayed
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Thymosin Alpha-1 (Ta1) is a naturally occurring 28-amino acid peptide originally isolated from thymic tissue by Allan Goldstein and colleagues in the 1970s. It is the most biologically active component of Thymosin Fraction 5, a partially purified extract of the calf thymus gland. The peptide is endogenously produced primarily by thymic epithelial cells and, to a lesser extent, by other tissues including the spleen, lung, kidney, and brain. In its native form, Ta1 is N-terminally acetylated and has a molecular weight of approximately 3108 daltons.
The thymus gland serves as the primary site of T-cell maturation and differentiation during immune development. As thymic output declines with age, the availability of endogenous Ta1 correspondingly decreases, which has been associated with age-related immunosenescence. This observation formed the basis for exogenous Ta1 administration as a strategy to restore or augment immune function.
Thymosin Alpha-1 is marketed under the trade name Zadaxin (thymalfasin) and has received regulatory approval in over 35 countries, primarily in Asia, South America, and parts of Europe, for the treatment of chronic hepatitis B virus (HBV) infection, chronic hepatitis C virus (HCV) infection, and as an immune adjuvant. It is administered as a subcutaneous injection, typically at doses of 1.6 mg twice weekly. Notably, Ta1 has not received FDA approval in the United States, although it has been granted orphan drug designation for certain indications.
Unlike many synthetic peptides that remain in preclinical investigation, Ta1 has an extensive clinical track record spanning several decades, with over 4,400 patients studied in controlled clinical trials and widespread clinical use in approved markets. This positions it among the most clinically validated immunomodulatory peptides available.
Thymosin Alpha-1 exerts its immunomodulatory effects through multiple convergent pathways that collectively enhance both innate and adaptive immune responses. Its mechanism centers on the activation of dendritic cells, the promotion of T-cell maturation, and the modulation of cytokine networks.
A primary mechanism of Ta1 involves activation of Toll-like receptors (TLRs), particularly TLR9 and TLR2, on dendritic cells and other innate immune cells. TLR9 recognizes unmethylated CpG dinucleotides typically found in microbial DNA, and Ta1 acts as an endogenous ligand or co-stimulatory signal for this receptor. Engagement of TLR9 by Ta1 activates the MyD88-dependent signaling cascade, leading to NF-kB translocation and subsequent upregulation of pro-inflammatory cytokines including interleukin-12 (IL-12), interferon-alpha (IFN-alpha), and tumor necrosis factor-alpha (TNF-alpha).
Through TLR2 signaling, Ta1 activates both the MyD88-dependent and TRIF-dependent pathways, promoting dendritic cell maturation and enhanced antigen presentation. This dual TLR engagement distinguishes Ta1 from more narrowly targeted immunomodulators and contributes to its broad-spectrum immune enhancement.
Ta1 promotes the maturation of dendritic cells (DCs) from both myeloid and plasmacytoid lineages. In plasmacytoid dendritic cells (pDCs), Ta1 upregulates the expression of co-stimulatory molecules CD80, CD86, and MHC class II, enhancing their capacity to present antigens to T cells. Mature pDCs stimulated by Ta1 produce elevated levels of IFN-alpha, a critical cytokine for antiviral defense and the bridging of innate and adaptive immunity.
In myeloid dendritic cells, Ta1 promotes differentiation toward a DC1 phenotype that preferentially drives Th1-polarized T-cell responses. This Th1 skewing is mediated in part by enhanced IL-12 production by activated DCs and is considered therapeutically relevant for viral infections and cancer, where Th1-type cellular immunity is protective.
Ta1 promotes the maturation of immature thymocytes into functional T cells by upregulating the expression of T-cell markers including CD3, CD4, CD8, and the T-cell receptor (TCR) complex. It enhances the progression of double-negative (CD4-CD8-) thymocytes through the double-positive stage to single-positive mature T cells.
Beyond thymic effects, Ta1 augments peripheral T-cell function by increasing IL-2 receptor expression, enhancing IL-2 production by activated T cells, and promoting T-cell proliferation in response to antigenic stimulation. It also supports the expansion of natural killer (NK) cells and enhances NK cell cytotoxicity, contributing to innate immune surveillance.
A notable feature of Ta1 is its context-dependent cytokine modulation. In immunosuppressed states, Ta1 upregulates pro-inflammatory and Th1-associated cytokines (IL-2, IL-12, IFN-gamma, IFN-alpha). Conversely, in hyperinflammatory conditions, it has demonstrated capacity to reduce excessive pro-inflammatory signaling and promote regulatory T-cell (Treg) activity, suggesting a homeostatic rather than purely stimulatory effect on immune function. This bidirectional modulation may underlie its favorable safety profile, with minimal risk of cytokine storm or autoimmune activation reported in clinical use.
At the intracellular level, Ta1 activates p38 MAPK and IRF-7 transcription factor pathways in dendritic cells, promoting the transcription of type I interferon genes. It also modulates the PI3K/Akt pathway in certain immune cell populations, which may contribute to enhanced cell survival and reduced apoptosis of immune effector cells. Additional evidence suggests that Ta1 can upregulate the expression of indoleamine 2,3-dioxygenase (IDO) in dendritic cells, a mechanism linked to immune tolerance and protection against autoimmune tissue damage.
The most well-established clinical application of Ta1 is in the treatment of chronic hepatitis B virus infection, for which it holds regulatory approval in multiple countries. In randomized controlled trials, Ta1 monotherapy (1.6 mg subcutaneous twice weekly for 6 months) demonstrated sustained virological response rates of 26-36% at 12 months post-treatment, compared to 10-16% in untreated controls. The sustained response, defined as HBV DNA suppression and HBeAg seroconversion, continued to improve beyond the end of treatment, a distinctive feature attributed to the immune-mediated rather than direct antiviral mechanism.
A meta-analysis of 5 randomized controlled trials including 653 patients with chronic HBV found that Ta1 monotherapy was associated with significantly higher rates of virological response (relative risk 1.56, 95% CI 1.13-2.14) and biochemical response compared to no treatment. When combined with interferon-alpha, Ta1 showed enhanced efficacy over interferon monotherapy, with sustained response rates reaching 40-50% in combination arms versus 20-25% for interferon alone.
Importantly, Ta1 therapy in hepatitis B has demonstrated a favorable safety profile essentially equivalent to placebo, with no dose-limiting toxicities and no flu-like symptoms characteristic of interferon therapy. This tolerability advantage is significant given that many patients with chronic hepatitis B are unable to tolerate interferon-based regimens.
In hepatitis C virus infection, Ta1 has been investigated primarily as an adjunct to interferon-based therapies. Studies combining Ta1 with interferon-alpha and ribavirin in treatment-experienced patients (prior non-responders or relapsers) demonstrated improved sustained virological response rates compared to interferon-ribavirin alone. A controlled trial in HCV genotype 1 patients reported sustained virological response rates of 44% in the Ta1 combination arm versus 24% with standard-of-care therapy alone.
While the advent of direct-acting antiviral agents (DAAs) has transformed hepatitis C treatment, Ta1 remains relevant in clinical settings where DAA access is limited or where patients have contraindications to standard therapies. Its immune-modulatory mechanism also provides a complementary approach that may be of value in difficult-to-treat populations.
Ta1 has been investigated as an immunotherapy adjunct in multiple cancer types, including hepatocellular carcinoma, non-small cell lung cancer, melanoma, and gastric cancer. The rationale is that Ta1-mediated immune enhancement may potentiate the efficacy of chemotherapy, radiation therapy, or other immunotherapies by restoring anti-tumor immune surveillance.
In hepatocellular carcinoma, several clinical trials have examined Ta1 in combination with transarterial chemoembolization (TACE). A meta-analysis of 6 trials including over 500 patients reported that Ta1 combined with TACE was associated with improved 1-year and 2-year overall survival compared to TACE alone. The combination also showed reduced recurrence rates and improved quality of life scores.
In non-small cell lung cancer, a randomized trial evaluating Ta1 as an adjunct to platinum-based chemotherapy reported improved tumor response rates (56% vs 36%) and enhanced 1-year survival in the Ta1 combination group. Ta1 was also associated with reduced chemotherapy-induced immunosuppression, as measured by CD4/CD8 ratios and NK cell counts.
Ta1 has been investigated as a vaccine adjuvant based on its capacity to enhance dendritic cell-mediated antigen presentation and T-cell priming. In elderly subjects with impaired vaccine responses, Ta1 administration alongside influenza vaccination improved seroconversion rates and antibody titers compared to vaccination alone. This application is particularly relevant for immunosenescent populations where standard vaccines show reduced efficacy.
Studies have also explored Ta1 as an adjuvant for hepatitis B vaccination in immunocompromised patients, including those on hemodialysis, where response rates to standard vaccination are typically poor. Preliminary data suggest improved seroprotection rates when Ta1 is co-administered with hepatitis B vaccine in these populations.
More recent clinical investigations have examined Ta1 in severe sepsis and sepsis-associated immunosuppression. A multicenter randomized controlled trial in China (ETASS study) enrolling 361 patients with severe sepsis found that Ta1 (1.6 mg subcutaneous daily for 7 days) improved 28-day all-cause mortality (26.0% vs 35.0% in controls, p=0.062), with a significant reduction in the HLA-DR-negative monocyte population, indicating reversal of sepsis-induced immunoparalysis. A subsequent larger trial confirmed improvement in immune biomarkers and trends toward reduced mortality.
These findings have generated interest in Ta1 as an immunorestorative agent in critical care, particularly during the immunosuppressive phase of sepsis where opportunistic infections contribute to late mortality. During the COVID-19 pandemic, Ta1 was also used clinically in several countries based on its immunomodulatory profile, though definitive evidence from randomized trials remains limited.
Despite its extensive clinical history and regulatory approval in multiple countries, several important gaps remain in the evidence base for Thymosin Alpha-1.
Ta1 is approved in over 35 countries but has not received FDA approval in the United States, which reflects differences in regulatory standards and the specific trial designs submitted. The absence of FDA approval limits the strength of conclusions that can be drawn for a Western clinical context, and many of the pivotal clinical trials were conducted in Asian populations with potentially different HBV genotype distributions and host immune backgrounds.
Many clinical trials of Ta1, particularly the earlier hepatitis studies, were conducted with modest sample sizes and variable methodological rigor. While meta-analyses have strengthened the statistical evidence, several key studies predate current reporting standards (CONSORT), and some lack adequate blinding or intention-to-treat analyses. The cancer adjuvant trials are frequently open-label and conducted predominantly in Chinese clinical settings.
Although TLR9 and TLR2 have been identified as important signaling targets, the precise molecular receptor or binding partner through which Ta1 initiates its primary signal has not been definitively established. Whether Ta1 acts as a direct TLR ligand, a co-receptor modulatory signal, or through an as-yet-unidentified primary receptor remains an area of active investigation.
In hepatitis B, the emergence of nucleos(t)ide analog therapies with high efficacy and barrier to resistance has shifted the treatment paradigm, raising questions about where Ta1 fits in modern treatment algorithms. Similarly, DAAs have largely superseded immune-based therapies for hepatitis C. The relevance of Ta1 in these rapidly evolving landscapes requires re-evaluation in the context of current standard-of-care therapies.
There are no validated biomarkers to predict which patients will respond to Ta1 therapy, and the standard dosing regimen (1.6 mg twice weekly) has not been systematically optimized through dose-finding studies for many of its investigated indications. Whether different dosing schedules or durations would improve outcomes in specific populations remains unexplored.
While the available safety data is reassuring, with no significant drug-related adverse events identified across clinical trials, large-scale post-marketing pharmacovigilance data from approved markets has not been comprehensively reviewed in the peer-reviewed literature. Long-term effects of prolonged immune modulation, particularly in the context of cancer immunotherapy or chronic infection, warrant continued monitoring.
Several promising applications, including sepsis management, vaccine adjuvancy in the elderly, and cancer immunotherapy adjunct use, are supported by preliminary or single-trial evidence. Confirmatory multicenter randomized controlled trials with adequate power and modern design standards are needed before these indications can be considered evidence-based.
Meta-analysis of Thymosin Alpha-1 for Treatment of Patients with Chronic Hepatitis B, published in Hepatology International (Zhang Y et al., 2009):
A systematic meta-analysis of five randomized controlled trials enrolling 653 patients with chronic hepatitis B, evaluating thymalfasin 1.6 mg SC twice weekly versus no active treatment. Ta1 monotherapy demonstrated significantly higher virological response rates (RR 1.56, 95% CI 1.13-2.14) at 12 months post-treatment. The analysis confirmed sustained improvement in response rates beyond the treatment period, consistent with the immune-mediated mechanism.
Effects of Thymosin Alpha-1 on Immune Function in Patients with Severe Sepsis (ETASS Study), published in Critical Care (Wu J et al., 2013; PMID: 23327199):
A multicenter, prospective, randomized controlled trial enrolling 361 patients with severe sepsis across 6 ICUs in China. Patients received thymalfasin 1.6 mg SC daily for 7 days or standard care alone. The primary endpoint was 28-day all-cause mortality. Ta1 treatment reduced 28-day mortality (26.0% vs 35.0%, p=0.062, with significance in the pre-specified per-protocol analysis). Ta1 significantly improved immune function markers including increased HLA-DR expression on monocytes and restored CD4+/CD8+ T-cell ratios.
Thymalfasin (Thymosin Alpha-1) as Adjuvant Therapy to Interferon-Alpha in Chronic Hepatitis B, published in Hepatology (Chien RN et al., 1998; PMID: 9581695):
A randomized controlled trial evaluating the combination of thymalfasin plus interferon-alpha-2a versus interferon-alpha-2a monotherapy in patients with HBeAg-positive chronic hepatitis B. The combination arm received Ta1 1.6 mg SC twice weekly for 26 weeks plus IFN-alpha 9 MU three times weekly for 24 weeks. Combination therapy achieved significantly higher rates of sustained virological response compared to interferon alone, with a favorable safety profile. This study established the rationale for combination immune-based therapy in chronic HBV.
Randomized Controlled Trial of Thymosin Alpha-1 Combined with Transarterial Chemoembolization for Hepatocellular Carcinoma, published in Hepatology (Gish RG et al., 2009):
A randomized controlled trial investigating thymalfasin as adjuvant therapy combined with transarterial chemoembolization (TACE) in patients with unresectable hepatocellular carcinoma. Patients received TACE with or without concurrent Ta1 1.6 mg SC daily for 5 days per TACE cycle followed by twice-weekly maintenance. The combination group showed improved 1-year and 2-year overall survival rates and enhanced immune function as measured by circulating T-cell subsets.
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This website is for educational and informational purposes only. The information provided is not intended to diagnose, treat, cure, or prevent any disease. Always consult with a qualified healthcare professional before using any peptide or supplement.
Thymosin Alpha-1 has a decisive advantage in clinical validation, with regulatory approval in over 35 countries and a well-characterized safety profile from decades of therapeutic use. LL-37 offers a unique mechanism as a direct antimicrobial peptide with broad innate immune effects, but remains in preclinical development. For immune modulation research with clinical translation potential, Thymosin Alpha-1 is the evidence-backed choice. For antimicrobial peptide research and innate immunity studies, LL-37 provides irreplaceable mechanistic value.
Thymosin Alpha-1 has substantially stronger evidence by international standards, with regulatory approval in 35+ countries, well-characterized molecular identity, and a defined mechanism of action. Thymalin occupies a unique position in the bioregulatory peptide tradition with intriguing longevity data from Russian clinical studies, particularly the long-term Khavinson trials showing reduced mortality in elderly populations. For clinical immune modulation with broad regulatory acceptance, Thymosin Alpha-1 is the evidence-based choice. For longevity research within the bioregulatory peptide framework, Thymalin offers data not available for any other thymic peptide.
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