Abstract
Culture-adapted bone marrow mesenchymal stromal cells (MSCs) deploy paracrine anti-inflammatory and tissue regenerative functionalities that can be harnessed as a living cell pharmaceutical product. Independent of clinical indication, a near majority of human clinical trials administer MSC IV, often with an allogeneic MSC cell product immediately after thawing from cryostorage. Despite hundreds of studies in a wide assortment of inflammatory, degenerative, and acute tissue injury syndromes, human clinical outcomes often fail to mirror promising rigorously conducted preclinical animal studies. Using a mouse model of toxic colitis, we demonstrate that replication fit MSCs harvested in log phase of growth have substantial impact on colitis clinical and pathologic endpoints when delivered subcutaneously or intraperitoneally, whereas the maximum tolerated IV bolus dosing failed to do so. We also demonstrate that heat-inactivated MSCs lose all therapeutic utility and the observation is mirrored by use of viable MSC administered immediately postthaw from cryostorage. Using luciferase transgenic MSC as donor cells, we demonstrate that transient in vivo engraftment is severely compromised when MSCs are dead or thawed and further demonstrate that MSC redosing is feasible in relapsing colitis, but only syngeneic MSCs lead to sustained improvement of clinical endpoints. These data support the notion that pharmaceutical potency of MSC requires viability and functional fitness. Reciprocally, IV administration of thawed MSC products may be biased against positive clinical outcomes for treatment of colitis and that extravascular administration of syngeneic, fit MSCs allows for effect in a recurrent therapy model.