Inotuzumab Ozogamicin (InO) is an antibody-calicheamicin conjugate with striking efficacy in B-cell acute lymphoblastic leukemia (B-ALL). However, there is wide inter-patient variability in treatment response, and the genetic basis of this variation remains largely unknown. Using a genome-wide CRISPR screen, we discovered the loss of DNTT as a primary driver of InO resistance. Mechanistically, DNTT downregulation attenuated InO-induced DNA damage response, cell cycle arrest, and …