We have recently contributed to establish a robust xenotransplantation model (NSG, NRG) to study the leukemic engraftment as well as the stem cell biology in acute leukemias. rnrnOthers and we also suggest that these highly immunocompromised mice represent a powerful in vivo model to screen new therapeutic strategies (kinase inhibitors, epigentic agents, metabolic agents) and to mimic the chemoresistance and minimal residual disease observed in leukemic patients after chemotherapy.rnrnThe study of the in vivo chemoresistance is crucial to improve therapeutic outcome of leukemia patients.