PCLP1⁺ cells in adult BM are a subpopulation of HSCs. (A) RT-PCR analyses of Lin⁺ (stem cell depleted) and Lin^- (stem cell enriched) BM from 1-week-old mice and the PCLP1⁺ cell line, FDCP-1. (B) FACS profiles showing expression of PCLP1 by a subset of the LSK HSC population in adult BM. Percentages indicate total frequency in BM. (C) Donor-derived lymphoid (B220) and myeloid (Mac-1) composition of BM 16 weeks after reconstitution of lethally irradiated mice with 500 cells of either PCLP1⁺ or PCLP1^- LSK BM cells. Ly5.1⁺ cells are donor derived. (D) Percentage (determined by frequency of Ly5.1⁺ staining) of donor-derived cells in the blood of mice reconstituted with PCLP1⁺ and PCLP1^- LSK cells after primary, secondary, and tertiary transplantation. In primary recipients, each colored line represents an individual mouse reconstituted with either 500, 50, or 10 enriched stem cells. In each case, 10⁶ BM cells from the most highly reconstituted primary recipients (red) were used for subsequent transplantations in secondary and tertiary recipients.