DNA polymerase III x RNA polymerase II x RNR

The purpose of this study is to determine the recommended Phase 2 dose(s) (RP2Ds) of JNJ-75276617 in combination with a conventional chemotherapy backbone in pediatric and young adult participants with relapsed/refractory acute leukemia harboring histone-lysine N-methyltransferase 2A1 ([KMT2A1], nucleophosmin 1 gene (NPM1), or nucleoporin alterations in Part 1 (Dose Escalation) and to further evaluate safety at the RP2D(s) of JNJ-75276617 in combination with chemotherapy in pediatric and young adult participants with relapsed/refractory acute leukemia harboring KMT2A1, NPM1, or nucleoporin alterations and safety at the RP2D(s) of JNJ-75276617 as monotherapy in a select low burden of disease cohort in Part 2 (Dose Expansion).