Mesenchymal stem/stromal cells (MSCs) are widely studied by both academia and industry for a broad array of clinical indications. The collective body of data provides compelling evidence of the clinical safety of MSC therapy. However, generally accepted proof of therapeutic efficacy has not yet been reported. In an effort to generate a more effective therapeutic cell product, investigators are focused on modifying MSC processing protocols to enhance the intrinsic biologic activity. Here, we report a Good Manufacturing Practice-compliant two-step MSC manufacturing protocol to generate MSCs or interferon c (IFNc) primed MSCs which allows freshly expanded cells to be infused in patients on a predetermined schedule. This protocol eliminates the need to infuse cryopreserved, just thawed cells which may reduce the immune modulatory activity. Moreover, using (IFNc) as a prototypic cytokine, we demonstrate the feasibility of priming the cells with any biologic agent. We then characterized MSCs and IFNc primed MSCs prepared with our protocol, by karyotype, in vitro potential for malignant transformation, biodistribution, effect on engraftment of transplanted hematopoietic cells, and in vivo toxicity in immune deficient mice including a complete post-mortem examination. We found no evidence of toxicity attributable to the MSC or IFNc primed MSCs. Our data suggest that the clinical risk of infusing MSCs or IFNc primed MSCs produced by our two-step protocol is not greater than MSCs currently in practice. While actual proof of safety requires phase I clinical trials, our data support the use of either cell product in new clinical studies. STEM CELLS TRANSLATIONAL MEDICINE 2017;6:1868-1879 SIGNIFICANCE STATEMENTMesenchymal stem/stromal cells (MSCs) are one of the most widely studied cells for the development of cellular therapies. While these cells are unequivocally safe to use in humans, the efficacy of MSCs to treat diseases has not been established. Hence, current efforts are focused on developing the technology to enhance the efficacy of MSCs. Here, we report a novel strategy to prepare MSCs that would mitigate the potential reduction of cell potency observed when infusing freshly thawed, cryopreserved cells. Additionally, we show extensive preclinical data to support the safety of interferon g-primed MSCs, which are designed to enhance the immune modulatory potency of MSCs.

Statins possess potent immunomodulatory effects that may play a role in preventing acute GVHD (aGVHD) following allogeneic hematopoietic cell transplantation (allo-HCT). We performed a Phase II study of atorvastatin for aGVHD prophylaxis when given to allo-HCT recipients and their HLA-matched sibling donors. Atorvastatin (40mg/day) was administered to sibling donors, beginning 14 days before the anticipated start of stem cell collection. Allo-HCT recipients (n=40) received atorvastatin (40mg/day) in addition to standard aGVHD prophylaxis. The primary endpoint was cumulative incidence of grades 2-4 aGVHD at day 100. Atorvastatin was well tolerated and there were no attributable grade 3-4 toxicities in donors or their recipients. Day 100 and 180 cumulative incidences of grade 2-4 aGVHD were 30% (95% CI 17- 45%) and 40% (95% CI 25-55%), respectively. One-year cumulative incidence of chronic GVHD was 43% (95% CI 32- 69%). One year non-relapse mortality and relapse incidences were 5.5% (95% CI 0.9-16.5%) and 38% (95% CI 18- 47%), respectively. One-year progression-free survival and overall survival were 54% (95% CI 38-71%) and 82% (95% CI 69-94%). One-year GVHD-free, relapse-free survival (GRFS) was 27% (95% CI 16-47%). These results did not differ from our historical controls (N=96). While safe and tolerable, the addition of atorvastatin did not appear to provide any benefit to standard GVHD prophylaxis alone.

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