Introduction: Intra-arterial cell infusion is an efficient delivery route with which to target organs such as the ischemic brain. However, adverse events including microembolisms and decreased cerebral blood flow were recently reported after intra-arterial cell delivery in rodent models, raising safety concerns. We tested the hypothesis that cell dose, infusion volume, and velocity would be related to the severity of complications after intra-arterial cell delivery. Methods: In this study, 38 rats were subjected to a sham middle cerebral artery occlusion (sham-MCAO) procedure before being infused with allogeneic bone-marrow mesenchymal stem cells at different cell doses (0 to 1.0 × 10⁶), infusion volumes (0.5 to 1.0 ml), and infusion times (3 to 6 minutes). An additional group (n = 4) was infused with 1.0 × 10⁶ cells labeled with iron oxide for in vivo tracking of cells. Cells were infused through the external carotid artery under laser Doppler flowmetry monitoring 48 hours after sham-MCAO. Magnetic resonance imaging (MRI) was performed 24 hours after cell infusion to reveal cerebral embolisms or hemorrhage. Limb placing, cylinder, and open field tests were conducted to assess sensorimotor functions before the rats were perfused for histology. Results: A cell dose-related reduction in cerebral blood flow was noted, as well as an increase in embolic events and concomitant lesion size, and sensorimotor impairment. In addition, a low infusion velocity (0.5 ml/6 minutes) was associated with high rate of complications. Lesions on MRI were confirmed with histology and corresponded to necrotic cell loss and blood-brain barrier leakage. Conclusions: Particularly cell dose but also infusion velocity contribute to complications encountered after intra-arterial cell transplantation. This should be considered before planning efficacy studies in rats and, potentially, in patients with stroke.

Functional recovery after an experimental stroke can be assessed by multiple behavioral tests, however, there is no consensus about which test to use in long-term stroke recovery studies or whether the tests are affected by stroke surgery, post-operative care or behavioral compensation due to repeated testing. This review describes the tests most commonly used to assess motor and sensorimotor function, cognition and mood in stroke animals. Although it is difficult to predict the direction of future research, it may be possible to prevent false-positive results by selecting an appropriate task or a battery of tasks. It is also expected that the upcoming stroke recovery recommendations and the improved dialogue between academy, industry and healthcare professionals will further promote translational success.

Intra-arterial (IA) delivery of bone marrow-derived mesenchymal stem cells (BM-MSCs) has shown potential as a minimally invasive therapeutic approach for stroke. The aim of the present study was to determine the whole-body biodistribution and clearance of technetium-99m (^99mTc)-labeled rat and human BM-MSCs after IA delivery in a rat model of transient middle cerebral artery occlusion (MCAO) using single-photon emission computed tomography (SPECT). Our hypothesis was that xenotransplantation has a major impact on the behavior of cells. Male RccHan: Wistar rats were subjected to sham operation or MCAO. Twenty-four hours after surgery, BM-MSCs (2×10⁶ cells/animal) labeled with ^99mTc were infused into the external carotid artery. Whole-body SPECT images were acquired 20 min, 3 h, and 6 h postinjection, after which rats were sacrificed, and organs were collected and weighed for measurement of radioactivity. The results showed that the majority of the cells were located in the brain and especially in the ipsilateral hemisphere immediately after cell infusion both in sham-operated and MCAO rats. This was followed by fast disappearance, particularly in the case of human cells. At the same time, the radioactivity signal increased in the spleen, kidney, and liver, the organs responsible for destroying cells. Further studies are needed to demonstrate whether differential cell behavior has any functional impact.

Background and Purpose—: Very late antigen-4 (integrin α4β1)/vascular cell adhesion molecule-1 mediates leukocyte trafficking and transendothelial migration after stroke. Mesenchymal stem cells (MSCs) typically express integrin β1 but insufficient ITGA4 (integrin α4), which limits their homing after intravascular transplantation. We tested whether ITGA4 overexpression on MSCs increases cerebral homing after intracarotid transplantation and reduces MSC-borne cerebral embolism. Methods—: Rat MSCs were lentivirally transduced to overexpress ITGA4. In vitro transendothelial migration was assessed using a Boyden chamber assay. Male Wistar rats intracarotidly received 0.5×10 ⁶ control or modified MSCs 24 hours after sham or stroke surgery. In vivo behavior of MSCs in the cerebral vasculature was observed by intravital microscopy and single-photon emission computed tomography for up to 72 hours. Results—: Transendothelial migration of ITGA4-overexpressing MSCs was increased in vitro. MSCs were passively entrapped in microvessels in vivo and occasionally formed large cell aggregates causing local blood flow interruptions. MSCs were rarely found in perivascular niches or parenchyma at 72 hours post-transplantation, but ITGA4 overexpression significantly decreased cell aggregation and ameliorated the evoked cerebral embolism in stroke rats. Conclusions—: ITGA4 overexpression on MSCs enhances transendothelial migration in vitro, but not in vivo, although it improves safety after intracarotid transplantation into stroke rats.