Examining treatment responses of diagnostic marrow in murine xenografts to predict relapse in children with acute lymphoblastic leukaemia.

While current chemotherapy has increased cure rates for children with acute lymphoblastic leukaemia (ALL), the largest number of relapsing patients are still stratified as medium risk (MR) at diagnosis (50–60%). This highlights an opportunity to develop improved relapse-prediction models for MR patients. We hypothesised that bone marrow from MR patients who eventually relapsed would regrow faster in a patient-derived xenograft (PDX) model after induction chemotherapy than samples from patients in long-term remission. Diagnostic bone marrow aspirates from 30 paediatric MR-ALL patients (19 who relapsed, 11 who experienced remission) were inoculated into immune-deficient (NSG) mice and subsequently treated with either control or an induction-type regimen of vincristine, dexamethasone, and L-asparaginase (VXL). Engraftment was monitored by enumeration of the proportion of human CD45+ cells (%huCD45+) in the murine peripheral blood, and events were defined a priori as the time to reach 1% huCD45+, 25% huCD45+ (TT25%) or clinical manifestations of leukaemia (TTL). The TT25% value significantly predicted MR patient relapse. Mutational profiles of PDXs matched their tumours of origin, with a clonal shift towards relapse observed in one set of VXL-treated PDXs. In conclusion, establishing PDXs at diagnosis and subsequently applying chemotherapy has the potential to improve relapse prediction in paediatric MR-ALL.