Population size and radiosensitivity of murine hematopoietic endogenous long-term repopulating cells

A new assay is described that measures the numbers (n) of endogenous long-term repopulating cells (eLTRC) surviving sublethal irradiation. The assay is based on analysis of variances of Pgk-1(a) phenotypes within groups of sublethally irradiated Pgk-1(a/b) mice. When In n is plotted as a function of dose, the radiosensitivity (D-0) is the negative reciprocal of the slope and the y-intercept is N or total numbers of eLTRC per mouse. The assay is unique in that N is an absolute Value not requiring correction for seeding efficiency, or f. From two independent estimates, total numbers of eLTRC were determined to be 8,700 or 11,900 cells per mouse and D-0 was found to be 0.82 or 0.83 Gy, If eLTRC are, in fact, the long-term repopulating cells (LTRC) defined by classical transfer assay, then LTRC can home to the marrow with nearly unit efficiency, only one to two LTRC are required for a mouse to survive a radiation LD(50/30), and LTRC possess nearly unlimited self-renewal potential, (C) 1997 by The American Society of Hematology.