All ex vivo–expanded BM HSCs are PrP^-. (A) Either 10⁵ PrP^- or 2 × 10⁴ PrP⁺ freshly isolated CD45.2 donor BM cells were mixed with 10⁵ competitor CD45.1 cells and transplanted into lethally irradiated CD45.1 mice (n = 4). Donor CD45.2 contribution at 3 weeks (left) and 7 months (right) after transplantation are shown. (B) PrP⁺ and PrP^- cells (5000) sorted from 10-day cultured total BM or 3000 Lin^-Sca-1⁺PrP⁺ and Lin^-Sca-1⁺PrP^- cells sorted from 4-day cultured total BM cells were transplanted together with 2 × 10⁵ CD45.1 competitor cells into lethally irradiated CD45.1 mice (n = 4). Peripheral blood engraftments at 3 weeks (left) and 7 months (right) after transplantation are shown. Error bars indicate SEM.