Thymosin Alpha-1: The Thymic Immunomodulating Peptide

What is Thymosin Alpha-1

Thymosin Alpha-1 (Tα1) is a 28-amino-acid peptide released by cleavage of prothymosin α. It was isolated from bovine thymus by Allan Goldstein in the 1970s, as part of thymosin fraction 5. The thymus is where T lymphocytes mature, and Tα1 is one of its peptide mediators.

Its synthetic version is marketed as a drug under the generic name thymalfasin (brand Zadaxin) and is approved in roughly 35 countries for chronic viral hepatitis, as an immune adjuvant, and in certain oncology settings. It is not FDA-approved in the U.S., where it remains investigational.

Unlike a simple immune stimulant, Tα1 acts as a pleiotropic immunomodulator: it boosts the response when the immune system is depressed and helps temper inflammation when it is over-activated.

Immunomodulatory mechanism

Tα1 does not act on a single receptor; it reprograms several arms of immunity:

• Toll-like receptors (TLR2 and TLR9) — on dendritic cells and monocytes; one of its best-characterized entry points for activating innate immunity.
• Dendritic-cell maturation — improves antigen presentation and MHC expression, bridging innate and adaptive immunity.
• T-cell differentiation and Th1 bias — promotes T-lymphocyte maturation and a Th1 cytokine profile (IFN-γ, IL-2), key to antiviral and antitumor defense.
• NK cells and cytotoxic (CD8) T cells — increases their number and cytolytic activity.
• Reversal of exhaustion/lymphopenia — in states of immune exhaustion (severe infection), recovery of T-cell counts has been observed.
• Antioxidant and immunomodulatory effect — reduces oxidative-stress markers and helps balance pro- and anti-inflammatory cytokines.

The core idea: Tα1 doesn't simply "switch on" the immune system — it rebalances it. That's why it has been studied both in immunosuppression (chronic infections, aging, chemotherapy) and in uncontrolled-inflammation settings (sepsis).

Clinical evidence

Chronic viral hepatitis (B and C)

This is thymalfasin's most established indication. In chronic hepatitis B and C it has been used alone or combined with interferon/antivirals to improve virologic response, leveraging its ability to restore a Th1 antiviral immune response.

Sepsis

The ETASS trial (China, 2013), an RCT in severe sepsis, reported reduced 28-day mortality with Tα1 versus control. It is one of the most cited data points; larger follow-up trials aim to confirm it. The signal is promising but not yet definitive.

Oncology (adjuvant)

As a chemotherapy adjuvant it has been investigated in melanoma, hepatocellular carcinoma and non-small-cell lung cancer, aiming to sustain patient immunity and improve tolerance/response.

Vaccine adjuvant

In populations with weak immune responses (older adults, dialysis patients, the immunocompromised) it has been studied to improve seroconversion to influenza and hepatitis B vaccines.

COVID-19

During the pandemic, observational and retrospective studies in China associated Tα1 with lower mortality in severe COVID-19, attributed to reversing lymphopenia and T-cell exhaustion. The evidence is preliminary (mostly non-randomized) and should be interpreted with caution.

Thymosin Alpha-1 vs Thymalin

Both are thymic-derived peptides, but they are not the same:

	Thymosin Alpha-1	Thymalin
What it is	A single defined 28-aa peptide (thymalfasin)	A thymic peptide complex (bioregulator, Khavinson school)
Focus	Immunomodulation with the best-characterized molecular target	General thymic restoration / bioregulation
Evidence	Approved drug in ~35 countries; multiple RCTs	Mostly Russian preclinical and early clinical research

In research, Thymosin Alpha-1 is usually chosen when a single, well-characterized compound with standardized dosing is needed; and Thymalin when the interest is the broader thymic bioregulation of the Khavinson family.

Routes & research dosing

The standard route in the literature is subcutaneous (SC). The reference thymalfasin dose is 1.6 mg:

• Maintenance / chronic immunomodulation — 1.6 mg twice weekly (the classic hepatitis schedule).
• Acute settings — sepsis research has used more frequent schedules (e.g. 1.6 mg/day in divided doses), always under protocol.

Exact ranges depend on the model and research protocol. These figures describe the published literature; they are not a human dosing recommendation.

Reconstitution

10 mg vial + 2 mL bacteriostatic water = 5 mg/mL.

For a 1.6 mg dose: 1.6 ÷ 5 = 0.32 mL = 32 units on a U100 insulin syringe.

Store the lyophilized powder at −20 °C; once reconstituted, refrigerate at 2–8 °C and use within the indicated weeks. See our reconstitution guide for detailed formulas and examples.

Availability

We offer Thymosin Alpha-1 10 mg, verified by HPLC + mass spectrometry (Janoshik) at ≥99% purity per lot. View Thymosin Alpha-1 in the catalog →