A Study to Learn More About the Study Medicine Called Inotuzumab Ozogamicin (InO) in Children (1 to <18 Years) With First Relapse ALL

This prospective, randomized, multicenter, open-label, Phase 2 study is designed to evaluate the superiority of InO monotherapy vs ALLR3, after 1 cycle of induction treatment in paediatric participants (between 1 and \<18 years) with HR or VHR first bone marrow relapse CD22-positive BCP ALL, and to evaluate the safety and tolerability, PK and long-term efficacy. Treatment with study intervention will end after induction therapy; follow-up for efficacy and safety will continue for up to 5 years from randomization.

End of Treatment is defined as occurring upon recovery from 1 cycle of study therapy (Day 28 ± 2 days), or one day before initiation of new anticancer therapy, whichever occurs first.

Approximately 100 participants will be randomized (2:1) to receive 1 cycle of either InO monotherapy or ALLR3 (block 1) therapy during induction. Two interim analyses (approximately 50% and 75% enrollment) fort the primary outcome measure followed by a final analysis are planned to assess efficacy and futility (non-binding).

After completion of induction therapy (ie, study therapy), it is anticipated that the majority of responding participants will proceed immediately to consolidation therapy. Non-responders are expected to proceed with salvage therapy at the investigator's discretion. Participants responding to induction therapy are expected to proceed to SOC consolidation therapy upon recovery of blood counts, but no sooner than 7 days after last dose of study intervention.

All participants (responders and non-responders) will proceed to long-term follow-up for this study. All subsequent anticancer therapy will be determined by the treating physician.