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For research use only. Not for human or veterinary use. Not a drug, food, or dietary supplement.
AMIRAVOResearch Library

KPV vs Thymosin alpha-1

KPV and thymosin alpha-1 are both discussed as immune-modulating peptides, but they differ in size, origin and how far they have been tested in people 1,7. KPV is the three-residue C-terminal fragment of alpha-melanocyte-stimulating hormone and has been studied only in cells and animals 1,6. Thymosin alpha-1 is a 28-amino-acid peptide originally isolated from a bovine thymus extract; as thymalfasin (Zadaxin) it is approved in more than 35 countries for hepatitis B and C, and it has been tested in a phase 3 sepsis trial 7,8,10. Neither is FDA-approved, and the FDA lists both among bulk substances for compounding that may present significant safety risks, as of 22 April 2026 13,14.

Unbranded reference vial illustrating KPV; not an actual product
KPV
Not approved — research use only
Unbranded reference vial illustrating Thymosin Alpha-1; not an actual product
Thymosin Alpha-1
Approved outside the US

Side by side

FieldKPVThymosin Alpha-1
ClassMelanocortin-derived tripeptide, alpha-MSH(11-13) 1Thymic immunomodulatory polypeptide (synthetic thymalfasin) 7
Origin and structureLys-Pro-Val, the carboxy-terminal three residues of alpha-MSH 428 amino acids; originally isolated from thymosin fraction 5, a bovine thymus extract, and now produced synthetically 7,8
Proposed mechanismIn cells, PepT1-mediated uptake with inhibition of NF-kappaB and MAP kinase signalling 2; mouse data suggest action largely independent of melanocortin receptors 3Described as a toll-like receptor 9 and 2 agonist in myeloid and dendritic cells that activates natural killer cells and CD8+ T cells 8
Half-lifeNot located in the sources reviewedSerum half-life of about 2 hours in humans, per a drug review 9
Highest human trial phaseNo registered trials located on ClinicalTrials.gov (searched 24 October 2026) 6Phase 3 (TESTS sepsis trial, 1,106 adults) 10
FDA statusNot FDA-approved; listed among bulk substances that may present significant safety risks (nomination withdrawn), as of 22 April 2026 14No Drugs@FDA application record located for thymalfasin (searched 24 October 2026) 13; listed among bulk substances that may present significant safety risks (nomination withdrawn), as of 22 April 2026 14. Approved in more than 35 countries for hepatitis B and C per a 2020 review 8
Published human outcomesNone located 6In the phase 3 TESTS trial, 28-day mortality did not differ from placebo 10; an earlier single-blind randomized sepsis trial reported a marginal mortality difference 11
Safety signalsFDA has not identified any human exposure data for KPV by any route 14No secondary or safety outcome differed from placebo in TESTS 10; injection-site irritation is the most commonly reported adverse effect 8; FDA cites immunogenicity and impurity concerns for compounding 14
WADA statusNot named on the 2026 List; S0 covers unapproved pharmacological substances not addressed elsewhere 15Not named on the 2026 List (thymosin-beta-4, a different peptide, is named under S2.3) 15
Who funded the evidenceAcademic groups; mechanistic colitis work was supported by US NIH (NIDDK) grants 2,5TESTS was supported by Sun Yat-sen University, a Guangdong clinical research centre and SciClone Pharmaceuticals, the marketer of Zadaxin 7,10

KPV: what the data says

KPV research is preclinical. In two mouse colitis models (animal data), KPV reduced inflammatory infiltrates and colonic myeloperoxidase activity, including in mice lacking a functional melanocortin-1 receptor 1. In human intestinal epithelial and T-cell lines (cell data), KPV entered cells through the PepT1 transporter and reduced NF-kappaB and MAP kinase signalling 2.

  • In a mouse peritonitis model (animal data), KPV reduced leukocyte accumulation without raising cAMP, suggesting a mechanism distinct from melanocortin receptor signalling 3.
  • In vitro, KPV and alpha-MSH inhibited Staphylococcus aureus and Candida albicans 4.
  • Nanoparticle formulations have been tested in a mouse colitis model (animal data) 5. No human trials were located 6.

Thymosin Alpha-1: what the data says

Thymosin alpha-1 has been studied in humans for decades, mainly in hepatitis B and C, sepsis and cancer 8,9. A 2001 drug review summarised mixed results across hepatitis trials, including HBV DNA clearance in some randomized studies (humans) 9.

  • In the TESTS phase 3 trial of 1,106 adults with sepsis at 22 Chinese centres (humans), 28-day all-cause mortality was 23.4% with thymosin alpha-1 and 24.1% with placebo, a non-significant difference 10.
  • The earlier ETASS trial of 361 patients with severe sepsis (humans) reported 26.0% versus 35.0% mortality, with a marginal P value 11.
  • In a 488-patient randomized study in metastatic melanoma (humans), adding thymosin alpha-1 to dacarbazine-based therapy was associated with more tumour responses than control, and overall survival differences did not reach conventional significance 12.

Key research differences

  • Size and source: KPV is a three-residue fragment of alpha-MSH 4, whereas thymosin alpha-1 is a 28-residue peptide first isolated from bovine thymus extract 7.
  • Human evidence: no human trials of KPV were located 6, while thymosin alpha-1 has randomized trials including a 1,106-person phase 3 sepsis trial 10.
  • Approval outside the US: thymosin alpha-1 is approved in more than 35 countries for hepatitis B and C 8; no approval for KPV was located in any source reviewed 6,14.
  • Proposed mechanism: KPV is linked to PepT1 uptake and NF-kappaB inhibition in epithelial cells 2, whereas thymosin alpha-1 is described as a toll-like receptor agonist acting on dendritic and T cells 8.

Where the evidence is limited

No study has compared KPV and thymosin alpha-1 directly. KPV evidence comes from mouse models and cell lines 1,2,3, whereas thymosin alpha-1 evidence comes largely from human trials in hepatitis, sepsis and cancer 9,10,12, so the two cannot be compared on outcomes. The largest thymosin alpha-1 trial found no mortality difference, and it received support from the drug's marketer 10. Half-life data exist only for thymosin alpha-1 9.

Frequently asked questions

Is thymosin alpha-1 approved anywhere?
A 2020 review states thymosin alpha-1 is approved in more than 35 countries for hepatitis B and C 8. No FDA application record was located for thymalfasin 13.
Has KPV been tested in humans?
No registered human trials of KPV were located, and the FDA states it has not identified any human exposure data 6,14.
Can KPV and thymosin alpha-1 be compared directly?
No. No head-to-head study was located, and KPV has only animal and cell data while thymosin alpha-1 has been studied in human trials 6,10.
Did thymosin alpha-1 change sepsis mortality in trials?
In the 1,106-person phase 3 TESTS trial, 28-day mortality did not differ significantly from placebo 10.

References

  1. Melanocortin-derived tripeptide KPV has anti-inflammatory potential in murine models of inflammatory bowel disease Inflammatory Bowel Diseases. 2008
  2. PepT1-mediated tripeptide KPV uptake reduces intestinal inflammation Gastroenterology. 2008
  3. Dissection of the anti-inflammatory effect of the core and C-terminal (KPV) alpha-melanocyte-stimulating hormone peptides Journal of Pharmacology and Experimental Therapeutics. 2003
  4. Antimicrobial effects of alpha-MSH peptides Journal of Leukocyte Biology. 2000
  5. Orally Targeted Delivery of Tripeptide KPV via Hyaluronic Acid-Functionalized Nanoparticles Efficiently Alleviates Ulcerative Colitis Molecular Therapy. 2017
  6. ClinicalTrials.gov API search for KPV (0 studies returned, 24 October 2026) ClinicalTrials.gov. 2026
  7. Thymalfasin for the treatment of chronic hepatitis B Expert Review of Anti-infective Therapy. 2004
  8. Thymosin alpha 1: A comprehensive review of the literature World Journal of Virology. 2020
  9. Thymosin alpha-1 American Journal of Health-System Pharmacy. 2001
  10. The efficacy and safety of thymosin alpha1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial BMJ. 2025
  11. The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial Critical Care. 2013
  12. Large randomized study of thymosin alpha 1, interferon alfa, or both in combination with dacarbazine in patients with metastatic melanoma Journal of Clinical Oncology. 2010
  13. Drugs@FDA (openFDA) query for active ingredient thymalfasin: no matches FDA openFDA. 2026
  14. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (content current as of 04/22/2026) FDA (Human Drug Compounding). 2026
  15. Prohibited List 2026 (in force 1 January 2026) World Anti-Doping Agency. 2026

For research use only. Not for human or veterinary use. Not a drug, food, or dietary supplement. This page compares published research and is not medical advice or a recommendation.