Serial single-HSC transplantation. (A-D) 1° Transplant: single LT-HSC from juvenile WT mice and PtenΔ/ΔNf1^LOH mice with JMML was transplanted with 2 × 10⁵ rescue cells into WT recipient mice with CD45.1⁺, respectively. Sixteen weeks posttransplant, WT donor HSCs reconstituted balanced progenies, whereas HSCs with JMML (PtenΔ/ΔNf1^LOH) reconstituted various degrees of myeloid-biased progenies with elevated ratios of MZ/Fo B cells. Recipient 1°-G, which had the worst myeloid-biased blood, died before spleen tissue collection for MZ cell analysis. (E-F) 2° Transplant: single donor-derived HSC (CD45.2⁺) from primary recipient 1°-B was retransplanted into 2° BMT recipients. 2° Recipient mice continuously reconstituted various degrees of myeloid-biased progenies with elevated MZ/Fo B-cell ratios. Recipient 2°-BC reconstituted balanced progenies with the least splenic MZ cells. (G-H) 3° Transplant: single donor-derived HSC (CD45.2⁺) from recipient 2°-BA was retransplanted to 3°-BMT recipients. Recipient 3°-BAK had the worst myeloid-biased engraftment with the highest MZ/Fo B-cell ratio. Data represent ≥2 sets of paired experiments. See additional supportive data in supplemental Figures 11 and 12.