Thymulin: The Complete Guide

Thymulin is a synthetic nonapeptide with sequence pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn — nine amino acids, with N-terminal pyroglutamate (a cyclized glutamine) and C-terminal asparagine.

• One-letter: <Q-A-K-S-Q-G-G-S-N (where <Q denotes pGlu)
• Free peptide MW (apo form): ~857.9 Da
• Molecular formula (apo): C₃₃H₅₅N₁₃O₁₅

Original name and discovery:

Isolated from porcine serum at Hôpital Necker (Paris) by the Bach group in 1977 under the original name Facteur Thymique Sérique (FTS) — French for "serum thymic factor." Renamed thymulin around 1981–1985 as the broader thymic-hormone field consolidated nomenclature.

Foundational papers:

• PMID 303241 — Dardenne M, Pleau JM, Man NK, Bach JF. J Biol Chem 1977. Isolation and purification.
• PMID 914862 — Pleau JM, Dardenne M, Blouquit Y, Bach JF. J Biol Chem 1977. Amino-acid sequence.
• PMID 6276717 — Pleau JM, Dardenne M, Bach JF. Mol Cell Biochem 1981. Chemistry consolidation.
• PMID 3878920 — Pleau JM, Gastinel LN, Bach JF. Methods in Enzymology 1985. The chapter that effectively renamed FTS to "thymulin" and consolidated synthetic-peptide methodology.
• PMID 3497643 — Auger G, Blanot D, et al. Biol Chem Hoppe-Seyler 1987. Eight thymulin analogs — structure-activity work.

Active form: zinc-thymulin (Zn-FTS)

The 1:1 zinc-thymulin complex is the bioactive form. Apo-thymulin (the zinc-free peptide) is biologically inactive in standard rosette-formation assays. Zinc-binding stoichiometry was characterized in:

• PMID 2657247 — Bach & Dardenne, "Thymulin, a zinc-dependent hormone." Med Oncol Tumor Pharmacother 1989.
• PMID 7681212 — Dardenne et al., "Biochemical and biological aspects of the interaction between thymulin and zinc." 1993.

Origin and physiology:

Endogenous to humans and other mammals; secreted by thymic epithelial cells (subcapsular and medullary TEC subsets) into systemic circulation. Production declines with age — an aspect of immunosenescence. Thymulin levels are sensitively reduced in zinc deficiency and partially restored with zinc repletion (Prasad et al. 1988, PMID 3262625, J Clin Invest).

Regulatory status:

• FDA (US): never approved. No NDA, no IND on file. Not on the 503A bulks list. Sold as research chemical.
• EMA (EU): not approved.
• France (origin country) — never registered as a pharmaceutical despite the foundational research at Hôpital Necker. Bach-group work was academic / mechanistic.
• Russia: synthetic thymulin (FTS, the 9-mer) is not in the Russian State Register of Medicines. Confusable Russian-market products (Thymalin / Thymogen / Vilon) are different molecules — see the disambiguation section.
• WADA 2026: not on the prohibited list by name. As an unapproved investigational substance, S0 (non-approved substances) catch-all may apply.

Audit-correction: the existing StackTrax encyclopedia entry says "WADA Banned: Yes" for Thymulin. That is overstated — thymulin is not specifically named on the 2026 Prohibited List. Correct framing: not specifically named, but S0 catch-all may apply for athletes; not affirmatively permitted either. Consult your governing body.

Thymulin’s mechanism has been worked on for nearly five decades and is partially characterized but not fully resolved at the receptor level.

1. Zinc-dependent biological activity

The 1:1 Zn²⁺-thymulin complex is the bioactive form. Apo-thymulin shows little to no activity in T-cell rosette assays. Zinc binding involves coordination through residues clustered near the C-terminal half of the peptide (Auger 1987 PMID 3497643; Bach & Dardenne 1989 PMID 2657247; Dardenne 1993 PMID 7681212).

2. T-cell maturation / differentiation

Thymulin promotes the differentiation of bone-marrow-derived precursors into T lymphocytes, including the appearance of T-cell-specific surface markers. Demonstrated in the original Bach-group rosette assays (1977–1980) and confirmed in subsequent groups. Thymulin influences the CD4/CD8 balance and the maturation of regulatory T-cell subsets, though specific receptor identification has been elusive.

3. Cytokine modulation (anti-inflammatory at physiological doses)

Thymulin modulates release of multiple cytokines from peripheral blood mononuclear cells (IL-1, IL-2, IL-6, IFN-γ, TNF-α). The pattern is generally anti-inflammatory at physiological doses — suppressing overproduction of pro-inflammatory cytokines in inflammation-bearing animals.

• Safieh-Garabedian 1993 (PMID 8508050) — early healthy-vs-autoimmune comparison.
• Lunin 2008 (PMID 18991101) — thymulin prevents pro-inflammatory cytokine and Hsp70 overproduction in inflammation-bearing mice.

4. HPA-axis / neuroendocrine interactions

Thymulin both influences and is influenced by the hypothalamic-pituitary-adrenal axis:

• Glucocorticoids upregulate thymulin secretion at physiological levels but suppress it at supraphysiological levels (U-shaped dose-response).
• Thyroid hormone and growth hormone both stimulate thymulin secretion (Mocchegiani & Fabris 1992, PMID 1605502).
• Conversely, intra-pituitary thymulin gene therapy in aged rodents partially restores pituitary corticotrope and gonadotrope function (Goya/Reggiani group, PMIDs 21360440, 22700775, 21952687).
• Goya 2004 (PMID 15003367) is the canonical review of thymulin neuroendocrine biology.

5. Anti-inflammatory / analgesic activity (independent of immunomodulation)

The Safieh-Garabedian / Saádé group at AUB Beirut has produced a substantial series demonstrating thymulin and a thymulin-related peptide analog (PAT) attenuate inflammatory hyperalgesia in rodent models, apparently through cytokine modulation locally and centrally. Key PMIDs: 9876233, 14580936, 17192563, 21059360, 22861065, 30503917, 30851702.

Receptor identity — incompletely resolved

The "thymulin receptor" on T-cells has been studied since the 1980s but a single, definitive G-protein-coupled or single-pass-transmembrane receptor has not been cleanly cloned and characterized in the way the GLP-1 receptor or melanocortin receptors have. Modern proposals include direct interaction with a TCR-adjacent surface complex on T-cells, but no published high-resolution structure of a thymulin-receptor complex exists.

No modern Phase 2/3 RCT exists for thymulin in any indication. The clinical record is dated 1980s/1990s biomarker observations and small open-label treatment studies.

Biomarker / observational anchors:

• Zinc deficiency / immune function (Prasad 1988, PMID 3262625, J Clin Invest): in zinc-deficient subjects, serum thymulin activity is reduced and is restored with zinc supplementation. Established thymulin as a sensitive biomarker of zinc status in immune function.
• Anorexia nervosa (Wade 1985, PMID 3927699, Am J Clin Nutr): patients show reduced Zn-FTS activity, partially restored with refeeding and zinc repletion.
• Thyroid / GH axis interactions in elderly (Mocchegiani & Fabris 1992, PMID 1605502): bidirectional dependence of thymulin and the GH/thyroid axes in aging-related immunosenescence.

Small open-label treatment trials (1980s/1990s):

• Several small open-label studies in rheumatoid arthritis and SLE patient populations (PMIDs 1418292, 8508050).
• Small-cohort Italian / EU work on synthetic thymulin in children with primary immune deficiencies (PMIDs 1427431, 27634199).
• Outcomes mixed; no controlled Phase 2/3 conducted.
• Did not lead to regulatory approval.

Modern preclinical (substantial, multi-group):

• Allergic asthma — DNA-nanoparticle-delivered thymulin gene therapy reverses key pathology in murine models. da Silva 2014 (PMID 24556417, J Control Release); da Silva 2020 (PMID 32577505, Sci Adv). Morales/Rocco group, UFRJ.
• Septic inflammation — Novoselova 2018 (PMID 29795607, PLoS One).
• Pulmonary hypertension — Henriques-Coelho 2008 (PMID 18511508, Endocrinology).
• Pituitary aging / gene therapy — Goya/Reggiani group, La Plata. Intra-pituitary adenoviral or naked-DNA thymulin gene therapy partially restores hormone secretion in aged or genetically immunodeficient rodents (PMIDs 21952687, 22700775, 21360440, 24588820 review, 28501652).
• Inflammatory / neuropathic pain — Safieh-Garabedian/Saádé group multi-paper series above.
• Lung diseases review — Santos 2010 (PMID 20055713, Expert Opin Ther Targets).

Honest framing: demonstrated mechanistic / preclinical activity, with limited dated human data and no modern controlled trial. Any claim of "demonstrated efficacy in humans" is overreach.

Half-life: minutes

Thymulin’s plasma half-life is on the order of 5–15 minutes for IV administration in animal models. The molecule is small (~858 Da apo), unprotected by terminal modifications other than the natural N-terminal pGlu cyclization, and is rapidly cleared by glomerular filtration and proteolytic degradation.

Why this matters:

The very short half-life is the design driver for the modern preclinical work. The Goya/Reggiani gene-therapy program and the Morales/Rocco DNA-nanoparticle program both exist explicitly to circumvent the very short biological half-life of free thymulin. Direct subcutaneous or intravenous dosing of free thymulin requires either continuous infusion or frequent boluses to maintain biologically meaningful plasma concentrations.

Vendor claims of "long-acting thymulin" or "extended-release thymulin" without specific delivery-system citation should be treated as unsupported.

Bioavailability / route:

• Not characterized in published controlled studies for SC or oral routes in humans.
• Oral bioavailability presumed near-zero (proteolytic degradation).
• Intranasal not quantified in published studies.
• Thymulin-related-peptide analogs cross the BBB (basis for the analgesia work in CNS endotoxin models).

Limited human safety data exists. No Western pharmacovigilance database (FAERS, EudraVigilance) data — thymulin has never been an approved drug.

What has been reported:

1980s/1990s open-label trials in immunodeficiency and autoimmune populations did not surface a distinctive thymulin-attributable adverse event signal beyond local injection-site reactions. Sample sizes were small (tens of patients).

Theoretical immune-modulation concerns:

• Provoking or worsening autoimmune flares in susceptible individuals.
• Interfering with vaccine response.
• Interfering with concurrent immunosuppressive therapy.
• Possible effect on tumor immunosurveillance in patients with active or recent malignancy.
• Concurrent zinc supplementation interaction — not formally studied for safety.

No published carcinogenicity, reproductive toxicity, or chronic-toxicity studies meeting modern regulatory standards. The 1970s–1990s preclinical work predates standardized ICH safety-pharmacology requirements.

Vendor / community reports (anecdotal, unverifiable): mild injection-site soreness, occasional fatigue or headache, no consistent serious adverse event reports.

• Pregnancy / breastfeeding — not studied; default contraindication.
• Active or prior cancer — theoretical immune-modulation concern around tumor immunosurveillance.
• Active autoimmune flare — immune-modulating peptides can theoretically worsen autoimmune disease.
• Concurrent immunosuppressive therapy (transplant patients, biologics for autoimmune disease) — uncharacterized interactions.
• Recent vaccination — theoretical concern about altered vaccine response.
• Pediatric routine use — only limited dated open-label data; not a substitute for evaluated immune-deficiency therapy.
• Athletes subject to anti-doping testing — consult your governing body. WADA S0 catch-all may apply.

Multiple peptides in the immune / thymic-hormone space have similar names, similar marketing positioning, or both. Vendor product naming is inconsistent. Be precise about which molecule is being described.

Compound	What it actually is	Difference from Thymulin
Thymalin (Тималин)	Polypeptide complex (multi-component extract from calf/bovine thymus). Khavinson group, St. Petersburg.	Different molecule. Not a synthetic 9-mer; a multi-component extract. Russian-registered as a pharmaceutical (in Russia), unlike thymulin. Mechanism framed as Khavinson "bioregulator" rather than classical hormone. Highest confusion-risk pair.
Thymosin Alpha-1 (Tα1, thymalfasin, Zadaxin)	28-amino-acid acetylated peptide; FDA-approved-internationally Hep B/C / immune indications (NOT US).	Different molecule. 28-mer, not 9-mer. Approved in 35+ countries (NOT US — FDA never approved despite multiple submissions). Has a real regulatory dossier; thymulin does not.
Thymopoietin	49-amino-acid protein; full-length thymic hormone (Goldstein 1970s)	Different molecule. Originally identified as a 49-mer; gene encodes nuclear-envelope protein with a separate biological role.
Thymopentin (TP-5)	Pentapeptide RKDVY (residues 32–36 of thymopoietin); the minimal-active fragment	Different molecule. 5-mer not 9-mer. Studied for atopic dermatitis, hep B, RA in 1980s/1990s; some Italian / European registration but not FDA.
Thymogen (Тимоген)	Dipeptide Glu-Trp (EW). Khavinson group, 1980s	Different molecule. Dipeptide, not nonapeptide. Russian registration as a pharmaceutical.
TB-500 / Thymosin Beta-4 (Tβ4)	43-amino-acid actin-binding protein; cell migration / wound healing / angiogenesis	Completely different molecule, different mechanism. Despite the "thymosin" naming, Tβ4 is in the actin-sequestering / wound-healing space, not the immune-cell-maturation space.
Vilon (KE)	Khavinson dipeptide (Lys-Glu)	Different molecule. Dipeptide. Khavinson framework, not Bach framework.
Thymostimulin (TP-1)	Calf-thymus polypeptide extract	Different molecule. Extract, not synthetic peptide. Italian registration; never FDA.

The two disambiguations to memorize:

1. Thymulin ≠ Thymalin. Thymulin is the Bach 9-mer (synthetic, never registered). Thymalin is the Khavinson polypeptide complex extract (Russian-registered, multi-component, undefined exact composition). Different research lineages (French vs Russian), different molecular categories (synthetic short peptide vs tissue extract), different regulatory categories (research-only vs Russian-registered drug).
2. Thymulin ≠ Thymosin Alpha-1. Thymulin is a 9-mer never approved. Thymosin Alpha-1 is a 28-mer approved in 35+ countries. The "thymosin" naming is historical and refers to a heterogeneous family; thymulin is not part of the thymosin family in the modern molecular-biology sense.

Vendor product identity:

Research-chem vendors selling "Thymulin" 5 mg or 10 mg vials may be supplying the synthetic 9-mer (most common), or may be mislabeling another thymic peptide. There is no industry-standard verification — no analytical certificate verified to a USP / EP monograph (because thymulin has no monograph). Buyer-beware framing applies.