MCL1 and acute lymphoblastic leukemia: As silencing of MCL1 induced cell death in PDX AML-388, but not in ALL-199 nor ALL-265, we next asked whether this correlates with response towards pharmacological inhibition of MCL1. We studied the small molecule antagonist S63845 (Fig. 2d), which has previously been shown to be effective in AML cell lines and PDX samples31,35,36 and is currently under clinical investigation as single agent (NCT02979366) or in combination regimens (NCT03672695).