Cells isolated from the umbilical cord they must be expanded. As MSCs expand in culture, they start to loose their secretome (ability to communicate), or the secretions that come off of the cells and communicate to other cells to repair (exosomes). Passage 1 or P1 cells are only grown to one confluence, meaning after the dish is 80% full, it is split and put into another dish. Once those two dishes are at 80% confluence, the cells are flash frozen and still in a prime mortal state and are the most clinically effective according to published peer reviewed research.  If the cells are cultured further to passage 3, 4 or even 9 they become unstable, very large and lose the ability to communicate. The resulting clinical outcomes are very poor as well as patient satisfaction. Passage 1 cells provide doctors very consistent outcomes and the ability to predict how well treatments and conditions will improve using regenerative medicine.