To confirm that the observed increase in MAF is because of positive selection of NFKBIE-mutated cells and not because of continuous Cas9 editing in CD40L- or CpG-stimulated CLL cells, we used the same approach to investigate the outcome of loss-of-function mutations in the CXCR4 or CD19 gene. Here, CD19 is linked to B-cell chronic lymphocytic leukemia.