CXB-12 HSC engraftment advantage persists despite hybrid resistance.

Bone marrow cells pooled from young CXB-12 donors (Gpi1^a) were mixed with 2 × 10⁶BMCs from CByB6F1 competitors (Gpi1^b) using 0.25, 1, 2, or 4 × 10⁶ donor cells, respectively, and were injected into lethally irradiated CByB6F1 recipients that were not pretreated to remove NK cells, using 4 recipients per dose. At 1 (■), 3 (▩), and 6 (▪) months after reconstitution, percentage donor erythrocytes and percentage donor lymphocytes were averaged for each recipient and presented as means with standard error bars. If there were no repopulating advantage in CXB-12 HSCs, the expected percentages from CXB-12 donors were 11%, 33%, 50%, and 68% for the 4 donor:competitor ratios, respectively. The differences between observed and expected CXB-12 contributions translate to 2.3-, 1.6-, 1.8-, and 2.4- (average, 2.0)-fold CXB-12 HSC repopulating advantages after 1 month; 4.2-, 2.9-, 4.0-, and 4.4- (average, 3.9)-fold advantages after 3 months; and 6.6-, 3.2-, 5.3-, and 6.7- (average, 5.4)-fold advantages after 6 months.