Search

Marrow stromal cells from wild-type mice were infused into transgenic mice that had a phenotype of fragile bones resembling osteogenesis imperfecta because they expressed a human minigene for type I collagen. In mice that were irradiated with potentially lethal levels (700 cGy) or sublethal levels (350 cGy), DNA from the donor marrow stromal cells was detected consistently in marrow, bone, cartilage, and lung either 1 or 2.5 mo after the infusions. The DNA also was detected but less frequently in the spleen, brain, and skin. There was a small but statistically significant increase in both collagen content and mineral content of bone 1 mo after the infusion. Similar results were obtained with infusion of relatively large amounts of wild-type whole marrow cells into the transgenic mice. In experiments in which male marrow stromal cells were infused into a female osteogenesis imperfecta-transgenic mouse, fluorescense in situ hybridization assays for the Y chromosome indicated that, after 2.5 mo, donor male cells accounted for 4–19% of the fibroblasts or fibroblast-like cells obtained in primary cultures of the lung, calvaria, cartilage, long bone, tail, and skin. In a parallel experiment in which whole marrow cells from a male mouse were infused into a female immunodeficient rag - 2 mouse, donor male cells accounted for 4–6% of the fibroblasts or fibroblast-like cells in primary cultures. The results support previous suggestions that marrow stromal cells or related cells in marrow serve as a source for continual renewal of cells in a number of nonhematopoietic tissues.

Cells from transgenic mice expressing a human mini-gene for collagen I were used as markers to follow the fate of mesenchymal precursor cells from marrow that were partially enriched by adherence to plastic, expanded in culture, and then injected into irradiated mice. Sensitive PCR assays for the marker collagen I gene indicated that few of the donor cells were present in the recipient mice after 1 week, but 1-5 months later, the donor cells accounted for 1.5-12% of the cells in bone, cartilage, and lung in addition to marrow and spleen. A PCR in situ assay on lung indicated that the donor cells diffusely populated the parenchyma, and reverse transcription-PCR assays indicated that the marker collagen I gene was expressed in a tissue-specific manner. The results, therefore, demonstrated that mesenchymal precursor cells from marrow that are expanded in culture can serve as long-lasting precursors for mesenchymal cells in bone, cartilage, and lung. They suggest that cells may be particularly attractive targets for gene therapy ex vivo.

Scid mice are severely immunodeficient as a result of a defective recombinase system. Mice with the scid mutation have been shown to have an increased sensitivity to ionizing radiation, presumably as a result of an inability to repair DNA damage. Little is known of the impact of this mutation on the thermal response and on hyperthermic radiosensitization. This investigation established the thermal response (42-44 degrees C), patterns of thermotolerance development, and the impact of hyperthermia (60 min at 40 degrees C or 42 degrees C) on the radiation response of bone marrow colony forming unit-culture cells (CFU-C) in scid mice.Anesthetized scid mice (pentobarbital, 90 mg/kg) were killed by cervical dislocation and the nucleated marrow obtained from both tibia and femora by passing 2 ml of cold McCoy's 5A medium supplemented with 15% fetal bovine serum through each bone. Single cell suspensions of nucleated marrow were heated in 12 x 75 mm sterile tissue culture tubes at a concentration of approximately 5 x 10(6) cells/ml. Radiation, when used, was delivered immediately prior to hyperthermia by a 137Cs irradiator (dose rate of 1.20 Gy/min). Colony forming unit-culture were cultured in semisolid agar in the presence of colony stimulating factor (conditioned medium from L929 cells) for 7 days.The slope of the radiation dose-response curve for CFU-C in scid mice was biphasic, the Dos (+/- SE) were 0.29 +/- 0.03 Gy and 1.09 +/- 0.20 Gy, respectively. The Dos of the radiation dose-response curve for wild type marrow from CB-17 and Balb/c mice were 1.28 +/- 0.05 Gy and 1.47 +/- 0.15 Gy, respectively. The Dos of the hyperthermia dose-response curves for scid mice were 75 +/- 5, 10 +/- 1.4, and 4 +/- 0.2 min, respectively, for temperatures of 42 degrees, 43 degrees, and 44 degrees C. Thermotolerance development at 37 degrees C increased to a maximum at approximately 240 min after acute hyperthermia (15 min at 44 degrees C) and thereafter, decreased to control levels within 15 h. Thermotolerance did not develop in scid CFU-C during chronic hyperthermia at temperatures42.5 degrees C. Hyperthermia (60 min at 40 degrees or 42 degrees C) immediately after ionizing radiation did not significantly alter the terminal slope of the radiation dose-response curve of scid CFU-C (Do = 1.28 +/- 0.08 Gy). By contrast, hyperthermia following radiation of wild type CFU-C resulted in a decrease in the Do from 1.47 +/- 0.05 Gy (Balb/c, rad only) to 1.31 +/- 0.08 or 1.06 +/- 0.18 Gy for 60 min at 40 degrees or 42 degrees C, respectively.These results show that the thermal response and the pattern of thermotolerance development of scid CFU-C were similar to that of wild type Balb/c CFU-C, but that hyperthermia given immediately after ionizing radiation did not alter the radiation response of scid CFU-C. The scid mutation does not increase hyperthermic sensitivity or change the pattern of thermotolerance development of scid mouse CFU-C, implying that the scid mutation is not involved with thermal response, but does render the already radiation-sensitive scid cells incapable of thermal radiosensitization.