IDENTIFICATION AND CHARACTERIZATION OF A LARGE SOURCE OF PRIMARY MESENCHYMAL STEM CELLS TIGHTLY ADHERED TO BONE SURFACES OF HUMAN VERTEBRAL BODY MARROW CAVITIES

ABSTRACT Therapeutic allogeneic mesenchymal stem/stromal cells (MSC) are currently in clinical trials for evaluating their effectiveness in treating many different disease indications. Eventual commercialization for broad distribution will require further improvements in manufacturing processes to economically manufacture MSC at sufficient scales required to satisfy projected demands. A key contributor to the present high cost of goods (COG) for MSC manufacturing is the need to create master cell banks (MCBs) from multiple donors, which leads to variability in large-scale manufacturing runs. Therefore, the availability of large single donor depots of primary MSC would greatly benefit the cell therapy market by reducing costs associated with manufacturing. We have discovered that an abundant population of cells possessing all the hallmarks of MSC is tightly associated with the vertebral body (VB) bone matrix and are only liberated by proteolytic digestion. Here we demonstrate that these vertebral bone-adherent (vBA) MSC possess all the International Society of Cell and Gene Therapy (ISCT)-defined characteristics (e.g., plastic adherence, surface marker expression, and trilineage differentiation) of MSC and, therefore, have termed them vBA-MSC, to distinguish this population from loosely associated MSC recovered through aspiration or rinsing of the bone marrow (BM) compartment. Pilot banking and expansion was performed with vBA-MSC obtained from 3 deceased donors and it was demonstrated that bank sizes averaging 2.9×10 8 ± 1.35×10 8 vBA-MSC at passage one were obtainable from only 5 g of digested VB bone fragments. Each bank of cells demonstrated robust proliferation through a total of 9 passages without significant reduction in population doubling times. The theoretical total cell yield from the entire amount of bone fragments (approximately 300g) from each donor with limited expansion through 4 passages is 100 trillion (1×10 14 ) vBA-MSC, equating to over 10 5 doses at 10×10 6 cells/kg for an average 70 kg recipient. Thus, we have established a novel and plentiful source of MSC which will benefit the cell therapy market by overcoming manufacturing and regulatory inefficiencies due to donor-to-donor variability.