Table 2.

Biodistribution after IV 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
Krueger et al. [126] (2018)	Adult baboons [26]	Lethal total body irradiation (3 animals)	Intravenous (autogenic and allogenic MSCs)	Genetic transduction with green fluorescent protein retroviral construct, which was later evaluated by PCR.	Necropsies were performed between 9 and 21 months following MSC infusion. Several tissues were found to have MSCs: Gastrointestinal, kidney, skin, lung, thymus, and liver.	Gastrointestinal tissues had the highest MSCs concentration. MSCs distribute to a wide variety of tissues following systemic administration.
	Mongrel dogs [24]	Miocardial infarction (7 animals)	Intravenous (allogenic MSCs)	111In oxine–labeled MSCs colabeled with ferumoxides–poly-l-lysine. Single-photon emission CT (SPECT) and x-ray CT (SPECT/CT) and MRI studies were used to evaluate the distribution.	Imaging was performed immediately after injection and at multiple time points between 1 and 7 days after infusion. Early imaging showed a high distribution to lungs, which later decreased drastically. After day 1, MSCs distributed from lungs to different organs (kidney, bone marrow, liver, spleen) and also to the infarcted area.	A high and early distribution to lungs is showed, with a progressive decrease of MSCs and a later redistribution to a wide variety of tissues.
	Mice [25]	Miocardial infarction (number unknown)	Intravenous (xenogenic MSCs—human MSCs)	Human MSCs were infused, Quantitative assays for human DNA and mRNA were used to evaluate the distribution,	Tests were done at 15 min, and up to 100 h post infusion. Early distribution to the lungs was detected (15 min). Later distribution to other organs was insignificant: less than 1% of cells was detected in any other organ after 48 h.	Authors conclude that effects of intravenous MSCs might be due to soluble mediators rather than engraftment of MSCs in target tissues.
Mello et al. [39] (2020)	Rats	Intracerebral hemorrhage	Intravenous (xenogenic MSCs—human MSCs)	99mTc was used to label MSCs. Scintigraphy and radioactivity measurements (cerebral hemispheres, heart, lungs, liver, kidneys, intestines, and spleen) were performed to assess biodistribution.	Scintigraphy was performed 2 h after cell injection and ex vivo radioactivity was evaluated 24 h after cell transplantation. MSCs were mainly distributed to the lungs, kidneys, spleen and liver. Brain captation was low but it was relatively higher in the damaged hemisphere.
Patrick et al. [127] (2020)	Mice	Lung cancer	Intravenous (xenogenic MSCs—human MSCs)	89Zr-oxine and luciferase were used to label MSCs. PET-CT, bioluminescence and ex vivo radioactivity measures were used to assess biodistribution.	PET-CT at 1 h and 1, 2, and 7 days post-injection. At 7 days, radioactivity was measured from ex vivo organs. The majority of signal (60%) was found in the lung at 1 h before decreasing, while liver signal increased. From 1 to 7 days post-injection, the proportion of the 89Zr signal in the lung fell further from 24.6%.
Wuttisarnwattana et al. [128] (2020)	Mice	Bone marrow transplanted animals	Intravenous (xenogenic MSCs—human MSCs)	Red quantum dots were used to label MSCs. Ex vivo cryo-imaging was performed to assess biodistribution in different tissues (lung, liver, spleen, kidneys, bone marrow).	Animal sacrifice was performed at different time points following stem cell infusion (24, 48, 72 h). Initially, MSCs were found as clusters in the lung and eventually dissociated to single cells and redistributed to other organs within 72 h, mainly to the spleen and liver.
De White et al. [32] (2018)	Mice	Healthy animals (number unknown)	Intravenous (xenogenic MSCs—human MSCs)	Qtracker 605 beads and Hoechst33342, which labelled alive and dead cells, respectively. Anatomical and molecular fluorescence videos were generated with CryoViz Technology. Blood tests were performed to analyze phagocytosis.	Necropsies were performed at 5 min, 24 h and 72 h post-infusion. Early accumulation of MSCs in the lungs (5 min) was demonstrated. MSCs were phagocytized in the lungs and redistributed to liver within the monocytes at 24 and 72 h. Monocytes change their immunophenotype after phagocyting MSCs, and induce Treg cells.	Authors conclude that the action of MSCs in many organs may be due to the phagocytosis of MSCs by monocytes and the later change in their phenotype, which leads to the induction of Treg cells.
Ehrhart et al. [35] (2016)	Mice and rats	Alzheimer’s disease model	Intravenous (xenogenic MSCs—human MSCs)	Human MSCs were used. Tisular PCR analyses (blood, bone marrow, brain, spinal cord, spleen, kidney, liver, heart, lung, gonad) were used to assess biodistribution.	Harvesting of tissues was performed at 24 h, 7 days, and 30 days after injection. MSCs were broadly detected both in the brain and several peripheral organs, including the liver, kidney, and bone marrow, of both species, starting within 7 days and continuing up to 30 days post-transplantation.
Tang et al. [129] (2016)	Rats	Cirrhosis rats (splenectomized)	Intravenous (allogenic MSCs)	Qtracker705 nanoparticle-labelled MSCs were infused. Fluorescence imaging was performed to assess biodistribution.	Images were taken at 2 h and 5 days after cell infusion. Splenectomy improved the homing of MSCs in the liver when compared to non-splenectomy group.
Cao et al. [130] (2016)	Rats	Healthy animals	Intravenous (allogenic MSCs)	Luciferase and green fluorescent protein were used to label MSCs. Bioluminescence imaging, ex vivo organ imaging, immunohisto-chemistry (IHC), and RT-PCR were used to assess biodistribution.	Images were taken up to 1 month. After that, histological analysis was performed. MSCs were detected initially in the lungs with subsequent distribution to liver, kidneys and other abdominal organs. The dorsal skin was also detected to have MSCs. The signals disappeared at day 14.
Zhou et al. [131] (2015)	Rats	Hepatic fibrosis	Selective intravenous (superior mesenteric vein) (allogenic MSCs)	MSCs were double-labeled with superparamagnetic iron oxide and green fluorescent protein. MRI, histology and qPCR tests were used to assess biodistribution.	MR imaging of the liver was carried out before and 1, 3, 7 and 12 days after injection. Liver, lung, kidney, muscle and heart tissues were harvested at 1, 7, 15 and 42 days after cell injection. Dual-labeled MSCs were retained in the fibrotic liver of rats. SPIO particles and EGFP-labeled BMSCs showed a different tissue distribution pattern in rats with liver fibrosis at 42 days after transplantation.	SPIO-based MR imaging may not be suitable for long-term tracking of transplanted BMSCs in vivo.
Kim et al. [36] (2015)	Mice (athymic)	Brain tumor	Intravenous and intracerebral (xenogenic MSCs—human MSCs)	MSCs were labeled with near-infrared fluorescent dye. Bioluminescence and fluorescence imaging, qPCR and histologic examinations were performed.	Imaging techniques were performed at 1 and 4 h, 1, 7, 14 and 21 days. MSCs resided predominantly in the lung up to day 1 and the signal intensity decreased over time. Many cells moved from the lung toward other organs (liver and spleen) after day 1, and the signal remained stable in these regions for 14 days. From day 1 to day 14, MSCs were clearly detectable in the tumor area.
Kim et al. [38] (2015)	Beagle dogs	Spinal cord injury	Intravenous (allogenic MSCs)	MSCs were labeled with green fluorescent protein. Ex vivo bioluminescence was used to assess biodistribution.	Ex vivo examination was performed 7 days after injection. The green fluorescent protein-expressing AD-MSCs were clearly detected in the lung, spleen, and injured spinal cord; however, these cells were not detected in the liver and un-injured spinal cord.
Li et al. [45] (2015)	Mice	Acute liver injury	Selective intravenous: Inferior vena cava (IVC), superior mesenteric vein (SMV) and intrahepatic (IH) injection. (allogenic MSCs)	MSCs were labeled with luciferase. Bioluminiscece images were used to assess biodistribution.	Images were taken at 3 h, and at 1, 3, 7, 10, 14 and 21 days. After IVC infusion, MSCs were quickly trapped inside the lungs, and no detectable homing to the liver was observed. By IH injection, lung entrapment was bypassed, but MSCs-R distribution was only localized in the injection region of the liver. After SMV infusion, MSCs-R were dispersedly distributed and stayed as long as 7-day post-transplantation in the liver.	SMV is the optimal MSCs delivery route for liver disease.
Zhang et al. [33] (2015)	Rabbit	Acute ischemic kidney injury	Intravenous (allogenic MSCs)	MSCs were labeled with SPION particles. MRI images and histological analysis were used to assess biodistribution	Images and histological analysis were taken at 1, 3, 5 and 8 days. MSCs were detected up to 8 days, with a maximum amount of cells at day 3. No systemic distribution was assessed.
Schmuck et al. [43] (2016)	Sprague-Dawley rats	Acute lung injury (12 animals)	Intravenous (xenogenic MSCs—human MSCs)	MSCs were labeled with QTracker65. 3D cryo-imaging of lungs, liver, spleen, heart, kidney, testis, and intestine was performed to assess biodistribution.	Tissue samples were collected and analyzed at 60, 120 and 240 min and 2, 4 and 8 days after infusion. Distribution up to 240 min was detected mostly in liver, and also in lungs and spleen. The number of cells detected at 2, 4, and 8 days was less than 0.06% of the total cells infused on day 0 and were mainly distributed also in lungs, liver and spleen but relatively higher captation was seen in the rest of the tissues studied.	Authors conclude that studies using bioluminescence to track cells underestimate cell retention in the liver because of its high tissue absorption coefficient
Li et al. [27] (2018)	Rats	Silicosis (54 animals)	Intravenous (allogenic MSCs)	MSCs were labelled with 1,1′-dioctadecyltetramethyl indotricarbocyanine iodide. Fluorescence imaging was performed to assess biodistribution.	Images were taken 1 h, 6 h, 24 h, 3 days, 15 days, and 30 days after injection both in vivo and ex vivo. MSCs distributed mostly in liver and lungs, with a peak at 6 h, and a dramatic decrease by day 3. At day 30, no MSCs were detected.	Distribution in lungs was significantly higher in rats with damaged lungs compared to healthy rats.
Park et al. [34] (2018)	Mice	Alzeimer’s disease (53 animals)	Intravenous (allogenic MSCs)	MSCs were 111In-tropolone labeled. Imaging with SPECT (in vivo) and gamma-counter (ex vivo) was performed to assess biodistribution.	Imaging and gamma-counter studies were performed at 24 h and 48 h post infusion. In Alzheimer’s model, brain uptake of MSCs was significantly higher than in healthy animals. In both groups, MSCs distributed mainly to lungs, liver and spleen.	Distribution to brain seem to be higher in Alzheimer’s models.
Leibacher et al. [28] (2017)	Mice	Healthy animals (number unknown)	Intravenous (xenogenic MSCs—Human MSCs)	Human MSCs were injected and PCR techniques were used to assess biodistribution by searching for SRY sequences.	Ex vivo assessment was performed at 5 min, 30 min, 2 h, 6 h, and 24 h. The majority of injected MSCs were detected by qPCR in the lungs 5 min after transplantation, whereas <0.1% were detected in other tissues over 24 h	After intravenous injection, most cells distribute to lungs.
Yun et al. [31] (2016)	Rats	Acute liver injury	Intravenous (xenogenic MSCs—Human MSCs)	Human MSCs were injected and PCR techniques were used to assess biodistribution.	Mice were euthanized at 1, 3, 12, or 24 h and at 1, 4, or 13 weeks post injection. MSCs were detected soon in the lungs and disappeared before 1 week post injection. Then, MSCs were found mainly in the liver. No MSCs were found in other tissues (testis, ovary, spleen, pancreas, kidney, adrenal gland, thymus, and brain).
Abramowski et al. [42] (2016)	Mice	Experimental autoimmune encephalomyelitis model (number unknown)	Intravenous (allogenic MSCs)	MSCs were injected and a variety of techniques, including magnetic resonance imaging, immunohistochemistry, fluorescence in-situ hybridization, and quantitative polymerase chain were performed to assess biodistribution.	Assessment was focalized in the brain area. No evidence for immediate migration of infused MSC into the central nervous system of treated mice was found.
Kim et al. [30] (2016)	Rats	Healthy rats	Intravenous (allogenic MSCs)	MSCs were surface-modified with HA—wheat germ agglutinin (WGA) conjugate for targeted systemic delivery of MSCs to the liver and labeled with fluorescent dyes. Histologic examinations were performed.	Assessment was performed at 4 h post injection. Lungs and livers were collected. HA-WGA-MSCs had a greater distribution to the liver when compared to control MSCs, which were mainly trapped in the lungs.	HA-WGA conjugate has great potential to deliver MSCs to the liver efficiently within a short time and to reduce the entrapment of MSCs in the lung.
Lu et al. [40] (2016)	Mice	Acute distress respiratory syndrome model	Intravenous (allogenic MSCs)	Fluorescein isothiocyanate– dextran was used to label MSCs. Histological analyses and qPCR were used to assess biodistribution.	Assessment was performed immediately after cell injection, 2, 24, and 48 h later. Lung, heart, spleen, kidney, brain, and liver were collected. MSCs accumulated mainly in the lungs of control and diseased mice, with minor amounts distributed to other organs up to 2 h. Diseased animals showed less early distribution to lungs and higher distribution to the rest of the organs when compared to healthy animals.	Acute distress respiratory syndrome might lessen the pulmonary capillary occlusion by MSCs immediately following cell delivery while facilitating pulmonary retention of the cells.
Fabian et al. [46] (2017)	Young and old mice	Alzheimer disease (unknown number)	Intravenous (syngenic MSCs)	Histologic and genetic tests (PCR) were performed to evaluate MSCs distribution.	Genetic tests and histology were assessed after 28 days. Transplantation of MSCs obtained from old mice showed biodistribution only in the blood and spleen in both young and old mice. MSCs obtained from young mice showed a wide distribution in young receptors (lung, axillary lymph nodes, blood, kidney, bone marrow, spleen, liver, heart, and brain cortex). In contrast, these cells showed distribution only in the brain cortex in old mice.	Authors conclude that aging of both the recipient and the donor MSCs used attenuates transplantation efficiency.
Ohta et al. [37] (2017)	Rats	Spinal cord injury	Intravenous (allogenic MSCs)	MSCs were labeled with 3H-thymidine. Histologic and radioactivity examination of the spinal cord segment containing the damaged region, blood and target organs were harvested.	After 3, 24 and 48 h, organs were collected and radioactivity measured. The highest radioactivity was detected in the lungs 3 h after infusion, while radioactivity in the injured spinal cord was much lower. However, brain radioactivity was lower than damaged spinal cord.	MSCs distribute to the injured spinal crod.
Liu et al. [29] (2018)	Mice	Acute lung injury	Intravenous (xenogenic MSCs—Human MSCs)	MSCs were labeled with fluorophore Cy7. Histology was performed to assess biodistribution.	Ex vivo assessment of lungs, heart, spleen, kidneys and liver was performed at 30 min, 1 day, 3 days and 7 days following injection. MSCs distributed to the lungs up to day 1; and to the liver up to day 3, with progressive subsequent decrease. No significant distribution was observed to heart, spleen and kidneys
Qin et al. [41] (2018)	Rabbits	Liver tumors	Intravenous (allogenic MSCs)	MSCs were colabeled with superparamagnetic iron oxide (SPIO) particles and 4′,6-diamidino-2-phenylindole (DAPI). MRI and histologic examination were performed.	MRI was performed at days 0, 3, 7 and 14 after cells transplantation. Histological analyses were performed immediately after the MRI examination. MSCs were detected in the liver tumors, rather than the non-tumor liver tissue and other organs. At day 3, MSCs were mainly in the central part of the tumor, showing a posterior distribution in the periphery.	MSCs distribute mainly to the damaged liver when injected intravenously.
Leibacher and Henschler [132] (2016)	Wistar rats [133]	Transient cerebral ischemia (25 animals)	Intravenous and intraarterial (allogenic MSCs)	Feridex (Berlex Imaging) mixed with the transfection agent poly-l-lysine. Later evaluation with MRI and necropsies.	Imaging was performed before and after the infusion (2 to 24 h after). After intraarterial infusion, MSCs were detected in the brain of the rats. After intravenous infusion, no MSCs were detected in the brain.	Authors conclude that MSCs may engraft in peripheral tissues after intraarterial infusion. Intravenous infusion might not be quite effective to deliver MSCs to peripheral tissues.
	Mice [47]	Healthy animals and acute kidney injury (AKI) model (Unknown number)	Intravenous and intraarterial. (allogenic MSCs)	Transfection with luciferase-neomycin phosphotransferase construct. Later evaluation with Xenogen IVIS 100 imaging system.	Imaging was performed immediately after infusion, at 24 h, 72 h and 7 days. Intravenous infusion led to a majority of cells distributing to lungs. Intraarterial infusion lacked pulmonary retention and caused distribution to kidneys, especially in AKI mice. MSCs gradually disappeared after 24 h.	Intraarterial infusion might be adequate when treating kidney conditions.
Schubert et al. [44] (2018)	Mice	Acute kidney injury model (Unknown number)	Intravenous. (autogenic MSCs)	MSCs from luciferase transgenic mice. Evaluation was performed with bioluminescence imaging and RT-PCR.	Imaging was performed on days 1, 3 and 6. RT-PCR was performed in kidney, lung, liver tissue and blood on day 6. Bioluminescence showed a high distribution of MSCs to lungs on day 1, which disappeared on days 3 and 6. RT-PCR on day 6 showed variables amounts of MSCs-mRNA in blood, liver and kidneys	RT-PCR seems to be a more sensitive technique to demonstrate the late presence of MSCs in different tissues when compared to bioluminescence.
Nakada and Kuroki [62]	Mice	Healthy animals (Unknown number)	Intravenous and intramuscular (allogenic MSCs)	MSCs were labelled with chromium. Laser ablation inductively coupled plasma imaging mass spectrometry (LAICP-IMS) was used to assess biodistribution,	Detection time is not recorded. After intramuscular injection, MSCs remain in the muscular tissue. After intravenous injection, MSCs are detected in the lungs.	Authors conclude that chromium labelling could be a promising technique.
Mäkelä et al. [22] (2015)	Pigs	Healthy animals (12 animals)	Intravenous and intraarterial (autogenic and allogenic MSCs)	99mTc- hydroxymethyl-propylene-amine-oxime. Evaluation was performed with SPECT/TC. Biopsies were also performed.	Imaging was performed 8 h later. Intravenous infusion led to a high distribution of MSCs into the lungs. Intraarterial infusion decreased the deposition in the lungs and increased the uptake in other organs, specially the liver and kidneys.	Intraarterial infusion might improve the distribution to peripheral tissues and may avoid pulmonary retention.
Wang et al. [134] (2015)	Mice	Bone marrow transplanted animals	Intravenous and intraarterial (xenogenic MSCs—Human MSCs)	99mTc- hydroxymethyl-propylene-amine-oxime and luciferase. Bioluminescence, scintigraphy and histologic examination were used to assess biodistribution.	Bioluminescence was performed at 30 min, 24 h, 48 h, 96 h and once a week for up to two month. Scintigraphic imaging and X-ray imaging were performed at 5 h, 10 h and 1 d after injection. After 2 months, animals were sacrificed and ex vivo histology was performed. After intraarterial injection persistent whole–body MSC distribution in allo-trasplant recipients was shown, while MSCs were rapidly cleared in the syngeneic animals within one week. In contrast, intravenous injected MSCs were mainly seen in the lungs with fewer cells traveling to other organs.
Silachev et al. [49] (2016)	Rats	Traumatic brain injury model	Intravenous and intraarterial (allogenic MSCs)	9mTc and iron microparticles labelled MSCs. Evaluation was performed with SPECT/TC, MRI and histology.	Evaluation was performed at 1 h and 16 h after trasplantateion. After intravenous injection, MSCs distributed to lung, kidney, and partially in the liver and bladder, with progressive decrease to 16 h. After intraarterial injection, MSCs distributed significantly to damaged hemisphere.	Intraarterial injection improves the distribution to the damaged cerebral area.
Cao et al. [50] (2018)	Rats	Orthotopic glioma model	Intravenous, intraarterial and intratumoral (allogenic MSCs)	MSCs were transduced to express ferritin heavy chain and green fluorescent protein. MRI and histology evaluations were performed.	MRI was performed at days 0, 1, 3, 5, 7 and 9 after cell injection. Histological analysis was performed at days 8, 12 and 18. Intravenous injection did not lead to accumulation of MSCs in the tumor. However, intralesional and intraarterial injections showed a rapid accumulation of MSCs in the core of the tumor with a gradual decrease of the cells in the zone.	Intravenous injections does not lead to MSCs migration to central nervous system tumors, whereas intraarterial and intralesional injections do.
Taylor et al. [55] (2020)	Mice	Renal injury model	Intravenous and intracardiac (allogenic MSCs)	MSCs were labelled with luciferase and SPIO. MRI and bioluminescence were used to assess biodistribution.	Images were taken up to 2 days after injection. Following intravenous administration, no MSCs were detected in the kidneys, irrespective of whether the mice had been subjected to renal injury. After intracardiac injection, MSCs transiently populated the kidneys, but no preferential homing or persistence was observed in injured renal tissue.
Scarfe et al. [48] (2018)	Mice	Healthy animals (unknown number)	Intravenous and intracardiac (left ventricle) (allogenic MSCs and xenogenic MSCs—human MSCs)	MSCs were labelled with luciferase (Luc) or a bicistronic construct of Luc and ZsGreen for bioluminescence imaging. For MR tracking, cells were labelled with diethylaminoethyl-dextran-coated SPIONs.	In vivo biodistribution of cells was monitored by BLI immediately after cell administration and at multiple time points up to 30 day. Ex vivo MRI at baseline and up to 2 days post administration. Intravenous MSCs distributed mainly to the lungs. Intracardiac MSCs distributed to the brain, heart, lungs, kidney, spleen and liver, with also a majority of cells distributing to the lungs.	Intracardiac injection led to a wide distribution of MSCs to peripheral organs.