(556d) MRI/S Based Assessment of Donor Efficacy in Stroke Treatment with Human Mesenchymal Stem Cells (Industry Candidate)

Human mesenchymal stem cells (hMSC) have become a potential candidate for cell therapy in stroke treatment due to their strong secretion of trophic factors, immunomodulation and linage-specific differentiation. However, in vitro culture expansion leads to cellular senescence and reduced therapeutic functions after transplantation of 2D cultured hMSC, which remains one of the major barriers for biomanufacturing of clinical grade hMSC for stroke patients. To preserve and enhance stem cell properties during hMSC culture, preconditioning strategies such as 3D aggregation and hypoxia culture have been studied widely and show promising results both for in vitro and vivo hMSC efficacy. However, preclinical studies with preconditioned hMSC for stroke treatment still can provide inconsistent outcomes due to donor age and morbidity. For instance, it is challenging to determine the quality of donors with diseases or from an aged population by efficient in vitro cellular assays without long-term expansion, as most clinical procedures mandate short duration culture and limited modifications of cells prior to implant. Magnetic resonance imaging (MRI) provides excellent soft tissue contrast and is commonly applied to stroke diagnosis in both clinical and preclinical studies. However, MR techniques also can provide feedback on the efficacy of stroke therapies applied after the initial diagnosis.

In this study, treatment efficacy between two hMSC donors is investigated in a rat model of transient ischemia created by middle cerebral artery occlusion (MCAO). First, several key in vitro characteristics of hMSC with 3D aggregation preconditioning were analyzed. Second, to monitor the in vivo therapeutic effect from transplanted hMSC (health donor, compromised donor versus saline-injected immediately after MCAO), biochemical markers were measured longitudinally over 21 d using sodium chemical shift imaging (²³Na CSI), proton relaxation-enhanced MR spectroscopy (RE-MRS) and T₂-weighted proton imaging. Applying these techniques at the ultra-high field of 21.1 T provided increased sensitivity, enabling insight into ionic and metabolic homeostasis and displaying the dependence of tissue recovery on donor metrics.

In vitro results showed that hMSC from different donors have similar senescence, proliferation, migration and immunomodulation at passage 5, which is expansion point used for transplantation in MCAO rats. The functional decline in these assays for the compromised donor only can be observed beyond passage 7. In vivo results indicate ischemic lesion volume, as determined by ²³Na CSI, is significantly reduced by day 3 for the healthy donor hMSC cohort compared to the compromised donor and saline-injected MCAO controls, which both display expansion of the lesion. Percent change in both ²³Na and ¹H absolute signal within the ischemic lesion also is significantly reduced by day 3 for the healthy donor compared to the compromised donor and saline MCAO controls. Furthermore, widespread systemic effects are measurable as early as 24 h post-transplantation for ²³Na signal levels in the contralateral hemisphere, with significant elevation seen for the compromised and saline cohorts compared to the healthy donor, which displays a longitudinally stable and lower sodium signal. RE-MRS results support the ²³NaCSI analysis with reduced lactate-to-choline levels by day 3 and increased N-acetyl-aspartate and creatine ratios at day 1 for the healthy donor cohort only. In summary, in vivo MRI analysis demonstrates the possibility to evaluate donor efficacy of hMSC in preclinical studies and remedy inaccurate, low passage in vitro assessments based on traditional stem cell properties.

This work is supported by NIH (R01 NS102395).