Clonal analysis confirms the heterogeneity of the HSC compartment.

Cells (Ly5.1) from individual positive wells (closed symbols) from the limiting-dilution cultures were injected into W⁴¹W⁴¹ hosts (Ly5.2). Donor-type cells in blood were assessed at the indicated time points after injection. Two representative W⁴¹W⁴¹ hosts that received 10⁵ freshly explanted BMCs (open circles, dotted lines; designated BM1 and BM2) are also shown. Cells cultured on the stromal cell line S17 in bulk culture and then injected into lethally irradiated B6 mice are indicated by open squares. Names for HSC clones are indicated at the right. Data for clones C2, B2, B4, A3, and r16.4 have been published,24 and these clones are included here to provide a baseline for the data in Figures 3 to8.