Survival curves for lethally irradiated mice as a measure of the radioprotective capacity of subsets of PHSC.

(A) Lethally irradiated Ly5.2 mice were given transplants of either 300 38⁺34⁻ cells (carrying the Ly5.1 surface marker), 300 38⁻34⁺ cells (carrying both the Ly5.1 and the Ly5.2 surface markers and obtained by using cells from a first-filial-generation hybrid of Ly5.1 and Ly5.2), or 300 cells as a 1:1 mixture of the 2 subsets (150 cells of each). Only the 1:1 mixture provided both short- and long-term reconstitution. (B) In peripheral blood collected 8 months after BMT of the 1:1 mixture, more than 80% of the blood cells were derived from the donor (ie, Ly5.1-positive cells), and (C) 98% were derived from 38⁺34⁻cells (ie, only Ly5.1-positive cells). The data suggest that reconstitution came primarily from the 38⁺34⁻subset of PHSC, not the 38⁻34⁺ subset, although the 38⁻34⁺ subset is required for efficient radioprotection.