Ex vivo culture of Fancc^-/- hematopoietic stem cells alters graft stability in competitive repopulation assays. Following culture for 0, 2, or 4 days in SCF and IL-6, Fancc^-/- and WT “test cells” that express the CD45.2 isoantigen were cotransplanted into irradiated syngeneic recipients with isogenic bone marrow cells that express the CD45.1 antigen. WT cells were transplanted at a 3:1 test-competitor cell ratio and Fancc^-/- cells were transplanted at a 6:1 test-competitor cell ratio. (A) Evaluation of test cell chimerism as a function of time. Peripheral blood test cell chimerism was determined using fluorescence cytometry at the indicated time points. The length of cell culture and the genotype of test cells are indicated. Each symbol represents the test cell chimerism of an individual recipient. Symbols with numbers or letters indicate specimens where SKY analysis was determined at postmortem. Red symbols indicate recipients with abnormal karyotypes. Horizontal lines indicate the mean chimerism of the experimental group. (B) The relationship between cytogenetic abnormalities and the flux in test cell chimerism following transplantation of Fancc^-/- cells is shown. Symbols indicate individual mice.