STAT3 and leukemia: To address whether this improvement in the relative activities of MutSC1 and MutSC2 was specific to the species cell type used in the assay, we assessed STAT3 phosphorylation (p‐STAT3) upon ligand stimulation by FACS in two different cell lines: murine HAFTL (a mouse pre‐B cell line) and human BLaER1 (a B‐cell precursor leukaemia cell line).