Long-term regeneration of marrow cellularity and CFCs in primary and secondary recipients of cells selected on the basis of marrow or splenic homing. Shown are the mean ± SEM number of cells (A) and CFCs (B) per femur in lethally irradiated primary mice (▨) injected 120 days previously with BM-homed, SPL-homed, or nonhomed cells. Lethally irradiated secondary mice were transplanted with 0.5 femur/mouse and analyzed 10 weeks later (). Hematologic parameters for age-matched normal B6.SJL mice are shown for comparison (□). Pooled data from 5 to 14 mice/population. Differences in femoral cellularity between secondary recipients of BM-homed and SPL-homed cells are significant to P = .1; differences in femoral CFC content between primary recipients of BM-homed and SPL-homed cells are significant to P < .05, and between secondary recipients of SPL-homed cells and either BM-homed or nonhomed cells are significant to P < .05.