XRCC4 and chronic myelogenous leukemia, BCR-ABL1 positive: Second, the expression of LIG4, XRCC4 and XRCC6 genes was not changed in the KCL-22 (and CML-T1) model, and DNA methylation associated with repressive chromatin marks was found in the regulatory regions of LIG4. However, it should be noted, that upregulation of LIG4 expression, along with upregulation of alt-NHEJ genes, was observed during mutation acquisition in PB leukocytes of CML patients.