HAP1 and chronic myelogenous leukemia, BCR-ABL1 positive: Reverse transcription–polymerase chain reaction (RT–PCR) was performed on RNA extracted from mouse brain cortex and human HAP1 (a near-haploid derived from the KBM-7 chronic myeloid leukemia cell line) and RPE1 (retinal pigment epithelial-1) cells, using a pair of primers designed to amplify the corresponding human and mouse loci (Fig 3C).