Thymosin β4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial
Sosne G, Dunn SP, Kim C
Cornea (2015) · n=9
In a 9-patient Phase 2 dry eye trial, 0.1% thymosin β4 ophthalmic solution reduced ocular discomfort by 35.1% and corneal fluorescein staining by 59.1% versus vehicle control — small but the cleanest published signal that the cardiac-mechanism literature on thymosin β4 might translate clinically.
This 2015 *Cornea* paper is one of the small clinical signals connecting thymosin β4's deep preclinical literature to a real human therapeutic effect. The Phase 2 trial enrolled nine patients with severe dry eye disease and randomized them in a multicenter double-masked design to either RGN-259 (0.1% thymosin β4 ophthalmic solution) or vehicle control, dosed six times daily for 28 days with follow-up extending to day 56. The treatment group (12 eyes) showed a 35.1% reduction in ocular discomfort and a 59.1% reduction in total corneal fluorescein staining at day 56 versus the vehicle control group (6 eyes), with both differences statistically significant despite the small sample size. Tear film breakup time and tear volume production also improved on RGN-259. Safety was unremarkable — local irritation only. The result formed part of the evidence base that supported RegeneRx's continued development of RGN-259 in subsequent dry eye and neurotrophic keratopathy programs, including the Phase 3 neurotrophic keratopathy trial that ultimately reported positive efficacy.
The sample size is genuinely tiny — nine patients, with an unequal eye-level allocation (12 vs 6 eyes). Statistical significance with effect sizes this large is plausible but the wide confidence intervals around the point estimates mean the true effect could be substantially smaller or larger than the reported numbers. The trial population is severe dry eye specifically — generalizability to mild-to-moderate dry eye, to other ophthalmic indications, or to non-ophthalmic uses of thymosin β4 (which is the dominant biohacker context for "TB-500") is not directly established. The "TB-500" market name in research-peptide channels is sometimes claimed to be a synthetic fragment of thymosin β4 rather than the full 43-amino-acid molecule used in this trial; this paper studies the full peptide formulated as an ophthalmic solution. Industry sponsorship by RegeneRx Biopharmaceuticals is disclosed; the trial is small but methodologically sound for a Phase 2 dry-eye design.