Thymosin beta-4 is a forty three amino acid protein found throughout the body, involved in cell movement, blood vessel formation and tissue repair. It binds actin, part of the internal scaffolding cells use to move and change shape. This is the real molecule that TB-500 is a fragment of, and the distinction matters because this one has an actual development history. RegeneRx Biopharmaceuticals took it through mid-stage trials in dry eye disease, pressure ulcers and cardiac repair, with the eye programme progressing furthest. It has not reached approval anywhere. When marketing for TB-500 cites research, it is almost always citing work performed on this molecule rather than on the fragment being sold.