Analysis of Abelson-transformed Jak1(+/–) and Jak1(–/–) tumors. (A) Tumor formation in SCID mice after injection with 3 × 10⁶ transformed cells. Jak1(–/–) cells form tumors more rapidly than the Jak1(+/–) control cells. One representative tumor of each genotype is shown. (B) FACS analysis of the excised tumors. All tumors investigated express the surface markers CD19, CD43, and B220 and were therefore classified as B-cell lineage tumors. One example for each genotype is shown. (C) Analysis of v-abl expression in tumor tissue by Western blot analysis. The first 4 lanes show tumor tissue derived from Jak1(+/–)–transformed cells; the last 5 lanes show tumors derived from Jak1(–/–)–transformed cells.