Efficacy of ‘Off-the-Shelf’, Commercially-Available, Third-Party Mesenchymal Stem Cells (MSC) in Ex Vivo Cord Blood (CB) Co-Culture Expansion.

INTRODUCTION: Our previous studies have shown that clinically-relevant levels of hematopoietic stem and progenitor cell (HSPC) expansion are possible by ex vivo co-culture of cord blood (CB) mononuclear cells (MNC) with third-party bone marrow (BM)-derived mesenchymal stem cells (MSC) and growth factors.¹ A recently activated M. D. Anderson protocol requires that BM from a haplo-identical family member be used for the de novo generation of sufficient MSC for subsequent co-culture, a process requiring ∼3 weeks. Time constraints, uncertainties associated with the identification of a suitable BM donor and potential variation in MSC performance make logistical execution of this strategy difficult. We therefore investigated the potential efficacy of ‘off-the-shelf’ commercially-available sources of MSC. Since MSC do not express HLA-II (DR) they are non-immunogenic, suggesting that this might be a valuable alternative strategy. We compared ex vivo CB HSPC expansion obtained following CB MNC co-culture with 2 commercially-available research-grade MSC isolated by density separation and plastic adherence (MSC#1, Cambrex, Walkersville, MD and MSC#2, Allcells, Emeryville, CA). A third MSC, isolated by Stro-1² selection (MSC#3, supplied by PJS) was also evaluated.

METHODS: Two MDACC frozen CB units (CB#1&2) were thawed, washed and co-cultured with adherent monolayers from each MSC. Total nucleated cell (TNC) and HSPC (CD34⁺ cells and colony-forming units, CFU) numbers were measured at input (Day 0) and output (Day 14).

RESULTS: TNC and HSPC numbers revealed that the 2 commercially-available research-grade MSC (MSC#1&2) supported ex vivo CB HSPC expansion.

MSC#2 performed less well than MSC#1 for both CB units suggesting that variation may exist between individual MSC. These data suggest that the screening of clinical-grade MSC that perform optimally during ex vivo expansion co-culture might be warranted to best utilize this ‘off-the-shelf’ strategy. Data were similar to previous reports where TNC, CD34⁺ and CFU numbers were shown to increase approximately 13, 14 and 25-fold, respectively.¹ Data were also similar for MSC#3, suggesting that the method used to isolate MSC does not appear to be an important variable for effective CB MNC/MSC co-culture.

CONCLUSION: Although research-grade MSC were compared from different commercial sources, these data suggest that, in principle, commercially-available clinical-grade MSC might prove a valuable ‘off-the-shelf’ option, potentially reducing the time to therapy and addressing concerns associated with identifying a BM donor and variation in MSC performance. Future studies will evaluate FDA-compliant MSC that could be used clinically.