Table 6.

Biodistribution after intra-central nervous system administration of MSCs in animal models.

Article	Model	Disease (Number of Animals)	Route of Administration (Source of Cells)	Cell-Marking Technique	Detection Time and Outcome	Comments
Li et al. [98] (2015)	Different animals and models (the article is a review)		Intranasal (different sources)	Different techniques.	Some results are: MSCs reached an intracerebral glioma site within 6 h after i.n. delivery, with a further significant increase in cell numbers within 24 h; Intranasal application of MSCs resulted in the appearance of cells in the olfactory bulb, brain and spinal cord, and about one-fourth of MSCs survived for at least 4.5 months in the brain.
Zhang et al. [138] (2017)	Rats	Spinal cord injury	Intra-spinal cord (allogenic MSCs)	MSCs were labeled with Gd-DTPA-FA and neurofilament-200. MRI and histological examinations were performed to assess biodistribution.	Examinations were performed at day 1, 7, 14 and 28 post delivery. In the first 7 days, transplanted cells were observed near the injection point. The number of cells reached a maximum at day 14 and then gradually distributed along the segmental injury. No systemic distribution was observed.
Barberini et al. [83] (2018)	Horses	Healthy and myelopathy-model animals. (9 animals)	Intrathecal, both atlanto-occipital (AO) and lumbo-sacral (LS) injection. (allogenic MSCs)	99mTc-HMPAO was used to label MSCs. Later evaluation was performed with a gamma camera and histologic samples.	Imaging was performed each hour until 5 h post-infusion. MSCs administered by AO injection were found to distribute caudally through-out the vertebral canal. MSCs administered by LS injection did not distribute cranially. Histologic tests did not show the presence of MSCs in diseased areas.	LS injection of MSCs does not seem to be proper to treat central nervous system distant lesions.
Quesada et al. [85] (2019)	Mice	Non-obese diabetic severe combined immunodeficiency mice	Intrathecal (xenogenic MSCs—Human MSCs)	Human MSCs were used. Histologic evaluation and qPCR were performed in different tissues (Heart, brain, cerebellum, spinal cord, liver, spleen, lungs, kidneys and gonads).	Evaluation was performed 24 h and 4 months after injection. 24 h post-injection, MSCs were detected in the spinal cord and in 1 heart. 4 months after injection, MSCs were detected in 3 hearts and in 1 brain.
Kim et al. [84] (2020)	Rats	Healthy rats	Intrathecal (injected via L2-L3 space) (xenogenic MSCs—Human MSCs)	Fluorescent dye DiD was used to label MSCs. Ex vivo bioluminescence and qPCR of brain, spine and heart, lung, liver, spleen, and kidney was used to assess biodistribution.	Imaging was performed at 0, 6, and 12 h post injection. MSCs were detected in the spinal cord at all times. MSCs were found in the brain only at 12 h. No other organs showed MSCs. Increasing the Cell Injection dose of MSCs improved the migration of MSCs to the brain.	MSCs are able to migrate from spinal cord to the brain. This migration can be improved by the increase of the dose.
Violatto et al. [97] (2015)	Mice	Amyotrophic lateral sclerosis model	Intracerebral (lateral ventricles) and intravenous (xenogenic MSCs—Human MSCs)	MSCs were double labeled with fluorescent nanoparticles and Hoechst-33258. Bioluminescence and histologic examinations were used to assess biodistribution.	In vivo and ex vivo analyses were performed at 1, 7, 21 days. By intravenous administration cells were sequestered by the lungs and rapidly cleared by the liver. MSCs transplanted in lateral ventricles remained on the choroid plexus for the whole duration of the study even if decreasing in number. Few cells were found in the spinal cord, and no migration to brain parenchyma was observed
Geng et al. [91] (2015)	Rats	Cerebral ischemia	Intracerebral (allogenic MSCs)	A gadolinium-based cell labeling technique was used. MRI images were used to assess biodistribution.	MRI was used to image the cells 1,3, 5 and 7 days after the Gd-MSC injection. MSCs did not distribute systemically.
Mastro-Martinez et al. [90] (2015)	Rats	Traumatic brain injury	Intracerebral (allogenic MSCs)	Green fluorescent protein was used to label cells. Histological examinations and immunochemistry were used to assess biodistribution.	Histologic examination was performed at 24 h and 21 days after transplantation. MSC were found in the perilesional area at 24 h, and their number decreased with time after transplantation. MSC treatment increased the cell density in the hippocampus and enhanced neurogenesis in this area.
Park et al. [96] (2016)	Beagle dogs	Healthy animals	Intracerebral (intra-ventricular) (xenogenic MSCs—Human MSCs)	Human MSCs were used. Immunohistochemical and qPCR were performed to assess biodistribution.	Brains were collected 7 days after infusion. MSCs migrated from ventricles towards the cortex, being found in the brain parenchyma, especially along the lateral ventricular walls. MSCs were also detected in the hippocampus and the spinal cord. No systemic distribution of MSCs was detected.
Xie et al. [87] (2016)	Rats	Intracerebral hemorrhage	Intracerebral and intravenous (xenogenic MSCs—Human MSCs)	A fluorescent dye was used to label MSCs (CM-DiI). Histologic evaluation was used to assess distribution of MSCs.	Histologic examination was performed at 28 days. After intracerebral injection, MSCs stayed in the injection place, distributed around the hemorrhage. A small amount of cells migrated to the contralateral hemisphere. After intravenous injection, MSCs were also found in the cerebral area.	Both intracerebral and intravenous routes are appropriate for treating intracerebral hemorrhage.
Duan et al. [88] (2017)	Rats	Cerebral ischemia (54 animals)	Intracerebral injection (right striatum)	Green fluorescent protein MSCs (GFP-MSCs) and SPION labeled. MRI and histology were used to assess biodistribution.	Imaging and/or histology were performed weekly from week 1 to 8 weeks after cells transplantation. MSCs were found to remain in the area in a high quantity in week 1. Later, MSCs number decreased drastically, being detectable up to week 8. A small amount of cells migrated to corpus callosum.
Dong et al. [95] (2017)	Rats	Brain traumatic injury (30 animals)	Intracerebral injection (intraventricular) (allogenic MSCs)	Green fluorescent protein MSCs (GFP-MSCs). Imaging techniques and histology were used to assess biodistribution in blood vessels.	Techniques were performed at 10, 14, and 17 days. MSCs were found to home in large arteries (thoracic aorta, abdominal aorta, common iliac artery) 10, 14, and 17 days after transplantation.	MSCs seem to distribute after brain injury when injected intraventricularly.
Lee et al. [89] (2017)	Mice	Familial Alzheimer’s disease	Intracerebral injection (Injection into the hippocampi) (xenogenic MSCs—Human MSCs)	Ferumoxytol was used to label MSCs. MRI and histology were used to assess biodistribution.	Techniques were performed at 1, 7 and 14 days. MSCs were found to remain in the injection site up to 14 days after injection.
Wang et al. [86] (2018)	Sprague Dawley rats	Glioma (unknown number)	Intracerebral (MSCs were injected contralaterally to glioma) (allogenic MSCs)	CM-Dil staining was used to label MSCs, which also contained Paclitaxel. Confocal laser-scanning microscopy was used to assess the distribution of MSCs. Later histological examinations assessed the distribution of MSCs within the brain.	Necropsies were performed 2 days after MSCs injection. MSCs were distributed in clusters in the injection area, and were also found within the glioma.	MSCs seem to spread within a short period of time from one hemisphere to another, after intracerebral injection.
Mezzanote et al. [94] (2017)	Mice	Healthy mice (unknown number)	Intracerebral injection (brain cortex)	MSCs were transfected with a novel bioluminescent/near infrared fluorescent (NIRF) fusion gene. Fluorescence images and bioluminescence were used to assess the distribution of the cells.	Images were taken up to week 7 after transplantation. Movement of the MSCs was not assessed. MSCs were detected for 7 weeks without a significant drop in bioluminescent signals, suggesting the sustained viability of hMSCs transplanted into the cortex.	No specific biodistribution assessment.
Da Silva et al. [92] (2019)	Rats	Ischemic stroke model	Intracerebral injection (xenogenic MSCs—Human MSCs).	MSCs were labeled with luciferase and multimodal nanoparticles with iron. In vivo bioluminescence, near-infrared imaging and ex vivo MRI were used to assess biodistribution.	Biodistribution was assessed at 4 h and 6 days after cell injection. MSCs did not distribute. The amount of MSCs decreased drastically from 4 h to 6 days.
Ohki et al. [93] (2020)	Rats	Healthy model	Intracerebral injection (xenogenic MSCs—Human MSCs).	MSCs were labeled with SPIO or USPIO. MRI and histological examinations were performed to assess biodistribution.	MRI images were obtained immediately and at 7- and 14-days post injection. No MSCs demonstrated migration.
Sukhinich et al. [53] (2020)	Rats	Healthy model	Intracerebral and selective intra-arterial (internal carotid artery) (xenogenic MSCs—Human MSCs).	MSCs were labeled with SPION and PKH26. MRI imaging and histology were performed to assess biodistribution.	The distribution and migration of MSC were analyzed by MRI from day 1 to day 15, and histological methods on days 1, 2, 3, 7, and 15. After intracerebral injection, MSCs moved to corpus callosum and blood vessels. After intraarterial injection, most MSCs were detected in the ipsilateral hemisphere and most of them within the blood vessels.
Teo et al. [139] (2015)	Mice	Dermal inflammation (unknown number)	Retro-orbital injection. (xenogenic MSCs—Human MSCs).	MSCs were labelled with specific techniques for intravital confocal microscopy (DiI, DiO, DiD or DiR solution). Later confocal microscopy was used to assess the histologic distribution of MSCs	Imaging was performed 2 h, 4 h and 6 h after the MSC had been infused. When MSCs were detected, images were taken every 5 min. By 2 h post-infusion, arrested and transmigrating MSC were equally distributed within both small capillaries and larger venules. These MSCs were in contact with neutrophil-platelet clusters. Platelet depletion led to significantly reduced the preferential homing of MSC to the inflamed	Authors concluded that MSCs transmigrate to tissues due to the existence of an active adhesion mechanism. Platelets seem to play a crucial role in MSCs trafficking.