Thymosin Beta-4 (Tβ4)

The upside is broader than for most peptides in this class, but the dose-for-dose intensity per indication is moderate rather than spectacular. Tβ4 has the cleanest Phase 1 intravenous safety record in its peptide class, a Phase 3 primary-endpoint win in neurotrophic keratopathy, per Sosne 2023, and consistent preclinical evidence across wound, cardiac, nerve, and hair models. The single strongest human result is SEER-1 hitting both healing and comfort endpoints in NK at 5 drops per eye per day. The Evidence dimension is the most distinctive feature here: more registered Phase 2 and 3 human trials than the rest of this peptide class combined. The key boundary is that breadth of mechanism has not translated into breadth of registered human wins. Multiple Phase 3 dry-eye trials missed, the cardiac program never finished, and the off-label subcutaneous market has zero published human efficacy data.

Efficacy (3.3/5.0): The cleanest efficacy signal is corneal healing in neurotrophic keratopathy. The SEER-1 Phase 3 randomized, double-masked, placebo-controlled trial of 0.1 percent RGN-259 at 5 drops per eye per day promoted complete epithelial defect healing and improved patient comfort versus placebo, per Sosne 2023. The earlier Phase 2 dry-eye study (n=72) using the controlled adverse environment model showed a 35.1 percent reduction in ocular discomfort (p=0.0141) and 59.1 percent reduction in total corneal fluorescein staining (p=0.0108) versus vehicle, per Sosne 2015. Wound trials were safe with a mid-dose initiation signal, per Guarnera 2007. Efficacy does not score higher because the dry-eye Phase 3 program (ARISE-2 and ARISE-3) and a separate European NK Phase 3 missed primary endpoints, the cardiac Phase 2 never delivered an efficacy readout, and there is no human trial for the off-label subcutaneous recovery use case.

Breadth of Benefits (3.8/5.0): Breadth is genuine because Tβ4 mechanistically touches multiple repair systems and at least four have registered human or rodent data. Eye: SEER-1 Phase 3 healing win plus the multi-trial ARISE and SEER ophthalmic program, per Sosne 2023. Wound: Phase 2 pressure ulcer, venous stasis ulcer, and epidermolysis bullosa data showing safety and mid-dose healing signals, per Guarnera 2007. Cardiac: foundational mouse post-MI data showing integrin-linked kinase activation and epicardial progenitor mobilization, per Bock-Marquette 2004.

Neurorestoration: rodent stroke and TBI improvements out to 6-hour delayed treatment, per Xiong 2012. Hair: preclinical mouse follicle activation, per Gao 2015. The boundary is that breadth in mechanism has not translated to breadth in proven human efficacy, which keeps the score below 4.0; only the eye program has a Phase 3 primary-endpoint win.

Evidence Quality (3.8/5.0): Evidence is the standout dimension and the main reason Tβ4 outpaces the rest of this peptide class. The human trial roster includes a Phase 3 win (SEER-1), multiple Phase 3 dry-eye misses, multiple Phase 2 ophthalmic and wound trials, and two independent Phase 1 IV programs in Western and Chinese healthy volunteers, per Ruff 2010 and Wang 2021.

Mechanism is unusually well-mapped, with the Ac-SDKP cleavage axis independently validated, per Cavasin 2016, and Tβ4 knockout mice showing exacerbated organ injury under angiotensin II challenge, per Pipes 2019. Evidence does not score higher because there is no completed Phase 3 outside the narrow NK indication, no human efficacy data for off-label subcutaneous use, and the Phase 3 dry-eye misses dent confidence in the consumer-facing efficacy story.

Speed of Onset (2.5/5.0): Onset is slow because the benefit is tissue repair rather than acute pharmacology. Trials measured corneal healing over 28 days (SEER-1 and dry-eye programs), wound endpoints over 12 weeks (RGN-137), and nerve repair over similar windows in preclinical models. The plasma half-life is roughly 1 to 2 hours IV, dose-dependent, per Ruff 2010, so the speed you care about is biological regrowth, not drug exposure. A few weeks is the realistic read-out window for any tissue endpoint.

Durability (2.5/5.0): Durability is the weak point because human dosing windows were short. Trials ran 28 days for ophthalmic, up to 12 weeks for wound and IV, and almost nothing extends beyond that in published peer-reviewed human data. The Phase 1 IV program ended at 14 days, with no long-term human follow-up. Because Tβ4 promotes actual tissue repair rather than masking symptoms, some durability from a completed repair cycle is plausible, but the short half-life means continued or repeat dosing is almost certainly needed for sustained anti-inflammatory and anti-fibrotic effects. Treat durable remission from a finite course as unproven.

Bioindividuality Upside (3.5/5.0): Response is concentrated in people with deficient or inflamed tissue, which gives Tβ4 a clean responder profile for targeted use. In the dry-eye Phase 2, the strongest effects were in subjects with the worst baseline tear-film instability and corneal staining, per Sosne 2015. For wound healing, the strongest signals came from the most affected ulcers. For nerve repair in rodents, the largest effects came in the most injured cohorts. The corollary is that people with mild inflammation, intact tissue, or general optimization goals have proportionally less to gain. That clear responder gradient (more benefit where there is more damage) lifts this dimension above neutral.