This study enrolls patients that have been diagnosed with acute leukemia associated with a KMT2A (MLL) gene rearrangement (referred to as KMT2Arearranged, or KMT2A-R). The KMT2A-R leukemia has come back after treatment (relapsed) or is not responding to treatment (it is refractory). This study involves taking a study drug called SNDX-5613. The study is divided into two phases: one in which the study drug is given in combination with chemotherapy and a phase where the study drug is given alone. The purpose of the study is to test the safety of the study drug with chemotherapy, and how well the treatment regimen works for infants and young children with relapsed or refractory KMT2A-R leukemia.

This study involves taking a study drug called SAR443579. The overall goal of this study is to find out if the study drug is safe and effective at treating adults and children with relapsed or refractory acute myeloid leukemia (R/R AML), high risk myelodysplastic syndrome (HR-MDS), or B-cell acute lymphoblastic leukemia (B-ALL). This is a first-in-human research study.