Pre-B ALL with thymic involvement in CD19^+/CreSfpi1^lox/loxSpib^−/− mice. (A) Kaplan-Meier survival plot for aging mice of the indicated genotype and sex. (B) Enlarged thymus (arrow), enlarged spleen, and enlarged liver are shown in a moribund CD19^+/CreSfpi1^lox/loxSpib^−/− mouse. (C) Histology of the thymus in a moribund CD19^+/CreSfpi1^lox/loxSpib^−/− mouse (original magnification ×4). (D) Enlargement of thymic section shown in panel C, original magnification ×60. (E) Histology of the liver in moribund CD19^+/CreSfpi1^lox/loxSpib^−/− mice. (F) Enlargement of liver section shown in panel E to demonstrate the presence of lymphocytes in sinusoids, original magnification ×60. (G) High frequency of immature B cells in the thymus of a moribund CD19^+/CreSfpi1^lox/loxSpib^−/− mouse. Flow cytometric analysis was performed to determine the frequency of cells expressing the indicated cell surface markers in the thymus of a moribund CD19^+/CreSfpi1^lox/loxSpib^−/− mouse. (H) Measurement of Sfpi1^lox allele frequencies in thymic pre-B cells. qPCR was performed to determine the relative frequency of intact Sfpi1^lox alleles in pre-B cells from the thymus of a moribund CD19^+/CreSfpi1^lox/loxSpib^−/− mouse (right bar). As a control, the Sfpi1^lox allele frequency in splenic B cells enriched from an 8-week-old CD19^+/+Sfpi1^lox/loxSpib^−/− mice was determined and set to 1.00 (left bar). qPCR also was performed on C57Bl/6 B cell genomic DNA (center bar) as an additional negative control to demonstrate specificity of the qPCR reaction.