The possibility of assaying Wistar rat bone marrow CFUs in a xenogeneic (rat-to-mouse) system

The possibility of replacing the space-consuming rat-to-rat colony-forming unit (CFUs) assay by rat-to-mouse assay systems was examined using Wistar rat bone marrow. After considering the published results on the responsiveness of mouse strains to hemopoietic xenografts and on the ways to abrogate "xenogeneic resistance', we tested C57B1/6J and C3H/He mice conditioned by cyclophosphamide (CY) and/or whole-body irradiation in the following combinations: 850 rad C57Bl; 850 rad + CY C57Bl; 800 rad + CY C3H. A linear relationship between the number of cells injected and the macroscopical spleen colony count could be demonstrated with all three combinations. However, we observed a high number of endogenous colonies in the 850 rad C57B1 system. The results were confirmed by karyotype analysis. Colony yield and seeding efficiency with 800 rad + CY C3H were comparable to the rat-to-rat assay, but were considerably lower in the case of 850 rad + CY C57B1. In the latter system, the colonies were primarily erythroid.