Minimally manipulated whole human umbilical cord is a rich source of clinical-grade human mesenchymal stromal cells expanded in human platelet lysate

Background aims. Mesenchymal stromal cells (MSC) have recently been identified as a therapeutic option in several clinical conditions. Whereas bone marrow (BM) is considered the main source of MSC (BM-MSC), the invasive technique required for collection and the decline in allogeneic donations call for alternative sources. Human umbilical cord (UC) represents an easily available source of MSC (UC-MSC). Methods. Sections of full-term UC were transferred to cell culture flasks and cultured in 5% human platelet lysate (PL)-enriched medium. Neither enzymatic digestion nor blood vessel removal was performed. After 2 weeks, the adherent cells were harvested (P1), replated at low density and expanded for two consecutive rounds (P2 and P3). Results. We isolated and expanded MSC from 9/9 UC. UC-MSC expanded with a mean fold increase (FI) of 42 735 +/- 16 195 from PI to P3 in a mean of 29 +/- 2 days. By processing the entire cord unit, we theoretically could have reached a median of 9.5 x 10(10) cells (ranging from 1.0 x 10(10) to 29.0 x 10(10)). UC-MSC expressed standard surface markers; they contained more colony-forming unit (CFU)-fibroblast (F) and seemed less committed towards osteogenic, chondrogenic and adipogenic lineages than BM-MSC. They showed immunosuppressive properties both in vitro and in an in vivo chronic Graft versus Host disease (cGvHD) mouse model. Both array-Comparative Genomic Hybridization (CGH) analysis and karyotyping revealed no chromosome alterations at the end of the expansion. Animal studies revealed no tumorigenicity in vivo. Conclusions. UC constitute a convenient and very rich source of MSC for the production of third-party 'clinical doses' of cells under good manufacturing practice (GMP) conditions.