Actin-sequestering regenerative peptide

Thymosin β4

Clinical

Also known as Tβ4, RGN-259 (eye drops), Timbetasin

The full-length protein the recovery fragment borrows its name from.

Cited sources: 4
Human-tested claims: 1 of 3
Best evidence: Tier 2 · Clinical
Status: Research-only

A 43-residue peptide found in nearly every human cell, where it holds actin monomers in reserve and, when released at injury, drives cell migration and repair. It has been through controlled eye trials and is in Phase 3 for dry eye and neurotrophic keratopathy. The grey-market 'TB-500' is a seven-residue fragment of it, not this molecule.

repairangiogenesisinvestigational

How it works

Thymosin β4 binds G-actin, controlling the pool available to build the cytoskeleton. After injury it is released by platelets and immune cells, promotes migration of keratinocytes, endothelial and progenitor cells, reduces inflammation and myofibroblast scarring, and supports new vessel growth. The eye is the organ where that biology has come closest to a drug.

Sequence: Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES43 residues, N-acetylated. The LKKTET motif (residues 17–22) is the actin-binding site that TB-500 copies.

What it's studied for

One claim per card, each with its own tier and source. Tiers 1 and 2 are human data. Tiers 3 and 4 are not yet.

Missed both primary endpoints (discomfort, inferior corneal staining) but improved several secondary measures in a 72-patient placebo-controlled Phase 2 dry-eye trial.
Clinical
[1]Sosne & Ousler, 2015 (Clin Ophthalmol, Phase 2)(opens in a new tab)
Promotes cell migration, angiogenesis and wound repair and reduces scarring in animal models of skin, eye, heart and brain injury.
Preclinical
[2]Goldstein et al., 2012 (Expert Opin Biol Ther)(opens in a new tab)
Phase 3 trials in dry eye and neurotrophic keratopathy are ongoing; no result has been published at review.
Emerging
[3]Sosne, 2018 (Expert Opin Biol Ther)(opens in a new tab)

Safety & limitations

In the controlled dry-eye trial, safety measures including visual acuity, intraocular pressure and corneal sensitivity showed no concern. Those are local, short-course data; systemic use in people has no safety record.

[1]Sosne & Ousler, 2015 (Clin Ophthalmol, Phase 2)

Its angiogenic and migratory activity is the basis of a theoretical tumor-promotion concern that has not been resolved either way in humans.

[2]Goldstein et al., 2012 (Expert Opin Biol Ther)

Regulatory & legal status

Research-only

Not approved in any jurisdiction. The ophthalmic formulation (RGN-259) has completed Phase 2 and entered Phase 3 for dry eye and neurotrophic keratopathy.

[3]Sosne, 2018 (Expert Opin Biol Ther)

Frequently asked

Is thymosin β4 the same as TB-500?

No. Thymosin β4 is the whole 43-residue protein studied in the eye trials. TB-500 is a synthetic seven-residue fragment with no human trials of its own. Results for one do not transfer to the other.

Did the dry-eye trial succeed?

Partly. The Phase 2 trial missed both primary endpoints but improved several secondary measures, which was enough to justify Phase 3. Until those read out, the honest status is promising and unproven.

References

Written by Twenty Residues editorial. Medical review: pending; a named reviewer is being assigned.

Last updated October 1, 2026.

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Update history

2026-10-01 — Entry added.