RS-PDX cells with CRISPR/Cas9-disrupted IGHM gene are negatively selected in vivo. (A) Indel analysis of the targeted region of the IGHM gene in injected and recovered leukemia cells isolated from subcutaneous tumor, PC, and spleen of xenografted NSG mice. The wild type allele is indicated by a red arrow, and mutant alleles are indicated by black arrows. (B) Flow cytometry analysis of surface IgM expression in IGHM-edited tumor cells before injection and after recovery from subcutaneous tumor, PC, and spleen of xenografted NSG mice. Control refers to mock-transfected cells. (C) IGHM MAF in injected leukemia cells and cells isolated from subcutaneous tumors, PCs, and spleens of NSG mice. The tumor cells were recovered 30 to 31 days after transplantation. Twelve independent experiments were performed, 3 each with RS1316, RS9737, IP867/17, and RS1050 cells. Statistical analysis was done with 1-way repeated measures ANOVA with Tukey test for multiple comparisons.