Stromal colonies from mouse marrow: characterization of cell types, optimization of plating efficiency and its effect on radiosensitivity.

Modifications to the colony assay in vitro for stromal progenitor cells in mouse femoral marrow have been studied so as to optimize the efficiency of colony formation (CFE). The highest reproducible concentration achieved was about 30 colonies (containing fibroblasts, macrophages and endothelioid cells) per 10(6) nucleated marrow cells (range 20-50) in mice 3-4 months old, and higher by 50% in mice 14-15 months old. Each of many slight technical modifications could reduce these values by more than 30%. The importance of optimization was demonstrated by a reduced radiosensitivity when the CFE was reduced by a factor of 3 using alpha-medium stored at 4 degrees C for 15 days. The D0 value was 3.9 +/- 0.8 Gy compared to 1.6 +/- 0.1 Gy using freshly prepared medium, and this could be due to the selection of a radioresistant subpopulation. The modifications studied may partly explain the marked variations in CFE and in radiosensitivity reported in the literature.