Heterogeneous niche activity of ex-vivo cultured MSCs as a parameter for outcomes in MSC-based cell therapy for hematopoietic recovery

Ex-vivo expanded mesenchymal stromal cells (MSCs) are increasingly used for paracrine support of hematopoietic stem cell (HSC) regeneration, but inconsistent outcomes have been the huddle for on-going clinical trials. Here, we hypothesized that the heterogeneity in the niche activity of manufactured MSCs can be a parameter for variable outcomes in MSC-based cell therapy. We first screened MSC culture medium and found that serum batches caused larger variations in colony forming unit-fibroblast (CFU-F) content of MSCs than individual donor variations. The culture conditions supporting high (stimulatory) and low (non-stimulatory) CFU-F caused distinct niche activity of MSCs; MSCs under stimulatory condition exhibited higher level expression of cross-talk molecules (Jagged-1 and CXCL-12) and higher support for HSCS during long-term culture than MSCs under non-stimulatory culture. Moreover, the effects of MSCs enhancing hematopoietic engraftment were only visible when HSCs were co-transplanted with MSCs expanded under stimulatory, but not non-stimulatory conditions. However, these differences of MSCs were readily reversed by switching the culture mediums, indicating their distinct functional state, rather than clonal heterogeneity. Accordingly, transcriptomic analysis showed distinct gene set enrichment between the different MSCs and revealed distinct upstream signaling pathways such as inhibition of P53 and activation of ATF4 for MSCs under stimulatory conditions. Taken together, our study shows that the heterogeneity in the niche activity of MSCs can be created during ex-vivo expansion to cause a difference in the hematopoietic engraftment and raise the possibility that MSCs can be pre-screened for more predictable outcomes in clinical trials of MSCs.

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