Thy Alpha 1

Thymosin Alpha 1 (Tα1), also known as thymalfasin (trade name Zadaxin), is a highly conserved, acidic polypeptide consisting of 28 amino acid residues with a molecular weight of 3,108.3 Da and an isoelectric point (pI) of 4.2. [1] [2]

Origin: Tα1 was originally isolated from thymosin fraction 5 (TF5) — a crude extract from calf thymus — in 1977 by Dr. Allan L. Goldstein at the Albert Einstein College of research compound. [2] It is derived from a larger precursor protein called prothymosin alpha (ProTα) (109–111 amino acids) via cleavage by the lysosomal asparaginyl endopeptidase legumain (δ-secretase). [3]

Structural Features: Linear polypeptide, N-terminally acetylated, no disulfide bonds, no glycosylation. In aqueous solution, Tα1 is intrinsically disordered; upon binding to membranes or receptors, it adopts an α-helix conformation (residues 14–26). [8]

Regulatory Status:

• International: Approved in 30+ countries (China, Italy, Asia, Latin America, Eastern Europe) for chronic hepatitis B, hepatitis C, and as a vaccine adjuvant/chemotherapy adjunct. [5]
• FDA: Orphan compound designation for HCC, malignant melanoma, and DiGeorge anomaly. NOT generally registered for marketing. [6]
• FDA Category 2: As of 2023/2024, placed on the Category 2 Bulk Drug Substances list, restricting compounding pharmacy use. [7]
• WADA: May fall under broader banned peptide categories (note: Thymosin Beta-4 is explicitly prohibited; Tα1 status is context-dependent).

Developer: Originally developed by Alpha 1 Biomedicals Inc.; commercial rights acquired by SciClone Pharmaceuticals, which launched Zadaxin globally. [9]

Pharmacokinetic Highlights:

• Half-Life: ~2 hours (serum)
• Peak Levels: 1–2 hours post-subcutaneous injection
• Urinary Excretion: 31–60% of administered dose
• Route: Subcutaneous (standard clinical route)
• Standard Clinical Dose: 1.6 mg SC (Zadaxin formulation)

1. Parent Molecule — Prothymosin Alpha

Tα1 is the N-terminal fragment (residues 1–28) of the larger precursor protein prothymosin alpha (ProTα), an acidic nuclear protein of 109–111 amino acids involved in chromatin remodeling and cell proliferation. ProTα is cleaved by the lysosomal enzyme legumain (δ-secretase) to release the bioactive Tα1 peptide. [3]

Structural Conformation: In aqueous solution, Tα1 is intrinsically unstructured (disordered). Upon interaction with negatively charged membranes (especially those exposing phosphatidylserine) or organic solvents, it adopts a structured conformation with an α-helix from residues 14–26 and two double β-turns in the N-terminal residues. [8]

2. Primary Receptor Targets

Tα1 functions as a pleiotropic modulator by interacting with pattern recognition receptors (PRRs) and specific membrane components:

• TLR9 and TLR2 Agonist: Signals through TLR9 in plasmacytoid dendritic cells (pDCs) and TLR2 in myeloid dendritic cells (mDCs). [4]
• Membrane Interaction: N-terminal inserts into hydrophobic regions of cell membranes, particularly those exposing phosphatidylserine (PS) (found on apoptotic cells), triggering signal transduction.
• Hyaluronic Acid (HA) Interaction: C-terminal “LKEKK” motif interacts electrostatically with HA, potentially interfering with CD44/RHAMM binding and suppressing tumor progression.

3. Downstream Signaling Cascades

A. MyD88 → TRAF6 → IKK → NF-κB (Immune Activation):

TLR9/TLR2 stimulation recruits the adaptor protein MyD88, activating TRAF6 → IKK complex → NF-κB transcription factor, promoting cytokine gene expression (IL-2, IFN-γ, IL-12). Often involves atypical PKC. [4] [10]

B. p38 MAPK / JNK (DC Maturation):

Tα1 induces phosphorylation of p38 MAPK and JNK (c-Jun N-terminal kinase). The p38 MAPK pathway is critical for dendritic cell maturation and production of Th1-priming cytokines. [11]

C. cAMP / PKC (Anti-Apoptosis in Thymocytes):

In thymocytes, Tα1 antagonizes steroid-induced apoptosis by stimulating cAMP production and activating PKC-dependent pathways.

D. IDO1 Pathway → Immune Tolerance:

Through TLR9 and Type I interferon receptor signaling, Tα1 induces IDO1 in dendritic cells, activating tryptophan catabolism (kynurenines), which promotes generation of regulatory T cells (Tregs) — inducing immune tolerance and dampening excessive inflammation/cytokine storms. [12]

The product supplied here is for research use only regardless of regulatory status of related formulations.

4. Cellular and Tissue-Level Effects

Dendritic Cells:

• Promotes functional maturation, increasing expression of HLA-DR, CD86, and CD40
• Stimulates IL-12 production → drives Th1 phenotype (antiviral/antitumor) [4]
• Can also promote tolerance via IDO1 pathway [12]

T-Cells:

• Promotes differentiation of stem cells into thymocytes
• Increases activated CD4+ and CD8+ T cell numbers
• Antagonizes glucocorticoid-induced apoptosis in immature thymocytes

Macrophages:

• Activates complement receptor (CR)-mediated phagocytosis (via actin/vinculin recruitment), distinct from Fc receptor mechanisms [13]
• Dose-dependent response at 50–100 ng/mL

Tumor Cells:

• Upregulates MHC Class I expression, making tumors more visible to cytotoxic T cells
• Can directly inhibit cell proliferation in certain cancer lines

NK Cells:

• Enhances NK cell activity and function [5]

5. Selectivity and Cross-Reactivity

Tα1 acts as a “regulator of regulators” — modulating the sensitivity of TLRs to other stimuli (e.g., viral antigens) rather than solely acting as a direct agonist. It is highly conserved across mammalian species (human, bovine, porcine, ovine). [5]

Distinct from Thymosin Beta-4 (TB-500): While Tα1 focuses on adaptive/innate immune modulation (TLR/T-cell maturation), TB-500 is primarily an actin-sequestering protein involved in cell motility, wound healing, and tissue repair.

6. Pharmacokinetics

Parameter	Value
Route	Subcutaneous (standard)
Peak Serum Levels	1–2 hours post-SC injection
Half-Life (T½)	~2 hours
Urinary Excretion	31–60% of administered dose
Dose-Response	Proportional Cmax/AUC for 0.8–6.4 mg single / 1.6–16 mg multiple
Accumulation	No evidence of accumulation with repeated dosing
Albumin Binding	C-terminal residues 11–20 bind HSA (carrier)

🦠 Viral Infections (Hepatitis B & C)

Tα1 is most established for chronic Hepatitis B (CHB) and Hepatitis C (CHC). Clinical data demonstrates induction of HBeAg seroconversion, ALT normalization, and viral suppression, with synergistic effects when combined with interferon-alpha or nucleoside analogs. [5]

🎯 Oncology (Solid Tumors)

Research demonstrates efficacy in malignant melanoma, hepatocellular carcinoma (HCC), and NSCLC. Tα1 is used as an adjuvant to chemotherapy (e.g., dacarbazine) or immunotherapy (e.g., ipilimumab), reducing tumor growth, increasing survival, and mitigating chemo-induced toxicity. [14] [15]

🏥 Sepsis

In severe sepsis, Tα1 reverses immunosuppression by upregulating HLA-DR expression on monocytes and preventing lymphocyte apoptosis. The ETASS trial (n=361) showed 26% vs 35% mortality (P=0.049). [16]

🦠 COVID-19 / SARS

During the COVID-19 pandemic, Tα1 was used in severe cases to restore lymphocytopenia and reverse T-cell exhaustion. A Wuhan retrospective study (n=76) showed 11.1% vs 58.8% mortality in severe cases. [17]

💉 HIV/AIDS

Studied as adjunct to HAART, facilitating immune reconstitution by increasing CD4+ T-cell counts and sjTRECs (markers of thymic output). [18]

💉 Vaccine Adjuvant

Enhances immunogenicity of influenza, H1N1, and HBV vaccines, particularly in immunocompromised populations (elderly, hemodialysis study subjects). In hemodialysis study subjects, 89% vs 53% seroconversion with H1N1 vaccine (P<0.01). [19]

🫁 Cystic Fibrosis (CF)

Tα1 has shown potential to correct maturation/activity of mutated F508del-CFTR protein while simultaneously reducing lung inflammation, though reproducibility has been debated. [20]

🍄 Fungal & Bacterial Infections

Activates dendritic cells for Th1 resistance against invasive aspergillosis and enhances resistance to Pseudomonas in bone marrow transplant settings. [4]

🔬 Autoimmune Diseases

study subjects with psoriatic arthritis, rheumatoid arthritis, and SLE exhibit lower serum Tα1 levels. Administration may restore immune homeostasis and regulate inflammation. [21]

Clinical Trials

Preclinical Animal Data (Selected)

• Lung Cancer (LLC/H460): 0.25 mg/kg SC × 11 days — 40.5% tumor volume inhibition (LLC), 21.9% inhibition (H460). Promoted CD4+/CD8+ T cell infiltration. [22]
• Melanoma (B16F10): Monotherapy reduced lung metastases by 32% (P<0.05); tumor growth decreased 34–46% (P=0.001–0.015). [5]
• Lung Adenoma Prevention: 0.4 mg/kg SC daily — reduced adenoma multiplicity by ~45% at 2.5 months.
• Leukemia/Carcinoma Combo: Tα1 (200 µg/kg) + IL-2/IFN + cyclophosphamide achieved complete tumor regression in FLC and 3LL models. [23]
• Sepsis (CLP): Tα1 + dexamethasone achieved highest survival rate; reversed DC depletion.
• Immunosuppression: 100–1,000× more active than thymosin fraction 5 in restoring immunity in 5-FU models.
• Aging: Restored antibody and T-cell responses in aged mice (23–24 months) to levels comparable to young animals. [24]
• Arthritis (CIA): 0.25–1 mg/kg reduced paw volume, weight, and arthritic scores.

Reported Tolerability Profile

Tα1 is consistently reported as well-tolerated across 2,000+ clinical subjects. [1]

• Common: Local injection site discomfort/redness (most frequent)
• Rare: Fever, fatigue, muscle aches, nausea (usually when combined with IFN)
• Hepatic: Transient ALT flares in HBV research application (often a sign of experimental effect)
• Serious (rare): Fatal immune hemolytic anemia and engraftment failure in HSCT recipients
• Preclinical: Single doses up to 20 mg/kg and 13-week repeated doses up to 6 mg/kg/day showed no adverse reactions

Contraindications: Hypersensitivity to Tα1; organ transplant recipients (risk of rejection/GVHD via immune stimulation). [1]