Drug response profiles of xenografts remain stable. Xenograft cells from up to 4 passages from 3 VHR-ALL (A) and 4 SR-ALL (B) were cocultured on hTERT-immortalized mesenchymal stroma cells and treated for 3 days with increasing concentrations of chemotherapeutic agents. Drug concentrations (in nanomolar) are given on the x-axis in a log scale. Measurement of ALL cell survival using 7-AAD and flow cytometry and compared with vehicle-treated controls revealed conserved resistance profiles. DEX indicates dexamethasone; VCR, vincristine; DNR, daunorubicin; and AraC, cytarabine. Experiments were performed twice, and one representative example is shown.