Thymosin beta-4 (Tβ4) is a naturally occurring 43-amino acid protein found in virtually all human and animal cells. It is the most abundant member of the beta-thymosin family and plays fundamental roles in cell migration, wound healing, and tissue repair. Tβ4 is distinct from TB-500, which is a synthetic peptide containing only the active heptapeptide region (Ac-LKKTETQ) of Tβ4. The full-length protein is being developed as RGN-259 (RegeneRx Biopharmaceuticals) eye drops for dry eye, neurotrophic keratopathy, and other ophthalmic conditions, with multiple Phase II/III clinical trials completed or ongoing.
Category: Healing & Recovery. Evidence rating: B (meaningful human data).
Clinical status: Multiple Phase II and Phase III clinical trials for ophthalmic indications. No full FDA approval yet.
Thymosin beta-4 is the primary intracellular G-actin sequestering protein, maintaining actin monomer pools and regulating cytoskeletal dynamics essential for cell migration. Beyond actin binding, it promotes angiogenesis, reduces inflammation (downregulates NF-kB, reduces pro-inflammatory…
Safety considerations: RGN-259 ophthalmic solution was well-tolerated in clinical trials with no significant drug-related adverse events; A safety-focused study in 40 healthy adults receiving injectable Tβ4 found minimal adverse effects; Topical (eye drop) administration has minimal systemic exposure.
Reviewed by the PeptideAtlas Editorial Team.
| Amino-acid sequence | SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES (43 amino acids) |
|---|---|
| Molecular weight | ~4963.5 g/mol |
| CAS number | 77591-33-4 |
| Production method | synthetic |
| Anti-doping status | Prohibited in sport (WADA) |
| US regulatory status | Not FDA-approved. RGN-259 has FDA Fast Track designation for neurotrophic keratopathy. Multiple IND applications active. Injectable Tβ4 was previously on FDA Category 2 list; removed April 15, 2026. |
Related peptides: BPC-157, TB-500, Larazotide.
Thymosin Beta-4 is the full-length 43-amino acid protein found naturally in human cells. TB-500 is a short synthetic fragment containing only 7 amino acids (Ac-LKKTETQ) from the active region of Tβ4. While they share core biological activity related to actin binding and cell migration, the full-length protein has additional functions. RGN-259 clinical trials use the full-length Tβ4, not TB-500.
RGN-259 is a sterile ophthalmic solution containing 0.1% thymosin beta-4, developed by RegeneRx Biopharmaceuticals (now Immune Therapeutics). It has been studied in Phase II and Phase III clinical trials for dry eye syndrome and neurotrophic keratopathy, with FDA Fast Track designation for the latter.
No. Thymosin alpha-1 (Zadaxin) is a completely different 28-amino acid peptide with immunomodulatory activity, approved in some countries for hepatitis B and as an immune adjuvant. Thymosin beta-4 is a 43-amino acid actin-sequestering protein involved in tissue repair. They come from different thymosin families.
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