Chromosome segregation defects as early underlying pathogenic mechanism in hyperdiploid childhood B-cell acute lymphoblastic leukaemia

High-hyperdiploid (HHD) B-cell precursor (BCP) acute lymphoblastic leukaemia (ALL) (HHD-BCP-ALL) is defined by the presence of 51 to 67 chromosomes in leukemic cells. Despite being a major BCP-ALL subgroup in childhood, the molecular mechanisms leading to HHD remains unknown.

We set out to study the contribution of mitotic defects in both the HHD-BCP-ALL cell line MHH-CALL2 and in HHD-BCP-ALL primary patient samples. Non-HHD BCP-ALL cell lines (SEM and REH) and primary BCP-ALL patient samples were used as controls.

Our results showed that HHD-BCP-ALL cells grow significantly slower than non-HHD BCP-ALL cells, which was associated to cell cycle defects as revealed by the accumulation of HHD-BCP-ALL cells in the G2/M phases. Immunofluorescence analysis confirmed an accumulation of HHD-BCP-ALL cells in prometaphase coupled with defects on chromosome biorientation at the metaphase plate. Supporting these mitotic progression defects, HHD-BCP-ALL cells commonly displayed defects in chromosome segregation. Importantly, gene ontology analysis using the genes observed by RNA-sequencing to be differentially expressed in HHD- versus NK-BCP-ALL primary cells supported a “mitotic” and “chromosome segregation” gene signatures. Preliminary data on the molecular mechanisms underlying these mitotic defects suggest that HHD may arise from defects in centromere function in human BCP.