The risks of severe ionizing radiation exposure are increasing due to the involvement of nuclear powers in combat operations, the increasing use of nuclear power, and the existence of terrorist threats. Exposure to a whole-body radiation dose above about 0.7 Gy results in H-ARS (hematopoietic acute radiation syndrome), which is characterized by damage to the hematopoietic system; higher doses result in further damage to the gastrointestinal and nervous systems. Only a few medical countermeasures for ARS are currently available and approved for use, although others are in development. Cell therapies (cells or products produced by cells) are complex therapeutics that show promise for the treatment of radiation injury and have been shown to reduce mortality and morbidity in animal models. Since clinical trials for ARS cannot be ethically conducted, animal testing is extremely important. Here, we describe cell therapies that have been tested in animal models. Both cells and cell products appear to promote survival and lessen tissue damage after whole-body irradiation, although the mechanisms are not clear. Because radiation exposure often occurs in conjunction with other traumatic injuries, animal models of combined injury involving radiation and future countermeasure testing for these complex medical problems are also discussed.

BACKGROUND There is broad interest in the use of cell therapies and cell products for treatment of a variety of diseases and problems. Of interest to the military, cellular therapies have the potential to confer tremendous benefit for treatment of both acute and chronic injuries. Although many different cell therapy products are currently under investigation, mesenchymal stromal cells (MSCs) are good candidates, based on their ability to respond to inflammation, limit vascular permeability, and modulate immune responses to injury. Although a large number of clinical trials utilize MSCs or their products, there is no firm consensus defining the characteristics and activities of a good MSC product. Here, we test multiple human MSCs in several assays designed to test potency, to determine if functionally relevant differences between MSCs can be defined using in vitro assays, allowing identification of superior MSC products for preclinical or clinical testing. METHODS Human MSCs derived from several tissue sources (adipose, bone marrow, umbilical cord) were evaluated for their ability to respond to inflammatory signaling by upregulating indoleamine-2,3-dioxygenase and TSG6, suppress lymphocyte proliferation, alter the polarization of macrophages, and affect tube formation by endothelial cells. RESULTS All MSCs tested displayed activity in the functional assays utilized, but differences in potency were observed in each assay. CONCLUSION The indoleamine-2,3-dioxygenase enzyme activity assay represents a simple way to screen multiple samples. The mixed lymphocyte reaction and monocyte assays used to test interactions between MSCs and immune cells are more involved but give direct information on immunomodulation potential. The endothelial cell tube formation assay is relatively simple to perform but a large number of images must be generated and analyzed. However, it tests a functional activity other than immunomodulation and, therefore, adds another facet to MSC evaluation.

BACKGROUND: Cellular therapeutic agents may benefit trauma patients by modulating the immune response to injury, and by reducing inflammation and vascular leakage. Administration of allogeneic mesenchymal stromal cells (MSCs) shows some benefit in preclinical and clinical trials, but less testing has been performed with other cell types. Human primary fibroblasts (FBs) were compared to MSCs in assays designed to evaluate MSCs to determine if these assays actually evaluate properties unique to MSCs or whether related cell types perform similarly.STUDY DESIGN AND METHODS: MSC‐related surface marker expression, tissue factor, and human leukocyte antigen–D related were evaluated by flow cytometry, and in vitro adipogenic and osteogenic differentiation potential were determined. Procoagulant activity was determined by thromboelastography. Two potency assays correlated with immunomodulation potential were utilized: the mixed lymphocyte reaction and indoleamine 2,3‐dioxygenase enzyme activity assays.RESULTS: Human primary FBs performed similarly to MSCs in assays designed to evaluate MSC characteristics and potency. Although similar for MSC‐positive cell surface marker expression, FBs did not show robust adipose differentiation and expressed some level of markers not expected on MSCs.CONCLUSIONS: Human primary FBs are very similar to human MSCs, at least in assays currently used to evaluate MSC potency. Preclinical and clinical testing are required to determine if FBs show similar activity to MSCs in vivo. If FBs show inferior activity in vivo, development of new MSC‐specific potency assays will be necessary to evaluate properties relevant to their unique clinical benefits.

BACKGROUND: Mesenchymal stromal cells (MSCs) express surface tissue factor (TF), which may affect hemostasis and detract from therapeutic outcomes of MSCs if administered intravenously. In this study, we determine a safe dose of MSCs for intravenous (IV) administration and further demonstrate the impact of IV-MSC on acute traumatic coagulopathy (ATC) in rats. METHODS: Tissue factor expression of rat bone marrow–derived mesenchymal stromal cell (BMSC) or adipose-derived mesenchymal stromal cell (AMSC) was detected by immunohistochemistry and enzyme-linked immunosorbent assay. The coagulation properties were measured in MSC-treated rat whole blood, and blood samples were collected from rats after IV administration of MSCs. Acute traumatic coagulopathy rats underwent polytrauma and 40% hemorrhage, followed by IV administration of 5 or 10 million/kg BMSCs (BMSC-5, BMSC-10), or vehicle at 1 hour after trauma. RESULTS: Rat MSCs expressed TF, and incubation of rat BMSCs or AMSCs with whole blood in vitro led to a significantly shortened clotting time. However, a dose-dependent prolongation of prothrombin time with reduction in platelet counts and fibrinogen was found in healthy rat treated with IV-MSCs. Bone marrow–derived mesenchymal stromal cells at 5 million/kg or less led to minimal effect on hemostasis. Mesenchymal stromal cells were not found in circulation but in the lungs after IV administration regardless of the dosage. Acute traumatic coagulopathy with prolonged prothrombin time was not significantly affected by 5 or 10 million/kg BMSCs. Intravenous administration of 10 million/kg BMSCs led to significantly lower fibrinogen and platelet counts, while significantly higher levels of lactate, wet/dry weight ratio, and leukocyte infiltration in the lung were present compared with BMSC-5 or vehicle. No differences were seen in immune or inflammatory profiles with BMSC treatment in ATC rats, at least in the acute timeframe. CONCLUSION: Intravenous administration of MSCs leads to a risk of coagulopathy associated with a dose-dependent reduction in platelet counts and fibrinogen and is incapable of restoring hemostasis of rats with ATC after polytrauma and hemorrhagic shock.