Background and importance Inotuzumab–ozogamicin is an antibody–drug conjugate composed of a recombinant humanised IgG4 kappa CD22 directed monoclonal antibody that is covalently linked to N-acetyl-gamma-calicheamicin dimethylhydrazide. It is indicated as monotherapy for the treatment of adults with relapsed or refractory CD22 positive B cell precursor acute lymphoblastic leukaemia (ALL).

Aim and objectives To describe a post-transplant relapsed adult case with B precursor ALL in which inotuzumab was successfully used as a bridging therapy to perform a second haematopoietic stem cell transplantation (HSCT).

Material and methods This was an observational retrospective study on the use of inotuzumab in a 32-year-old woman diagnosed with post-transplant relapsed B precursor ALL. The study variable was minimal residual disease (MRD) response, defined as MRD level <10^-4 at the end of treatment and complete remission. The data were obtained from the digital clinical history.

Results Initially the patient was treated according to HR-ALL PETHEMA-2011 <55 years protocol. The patient received phase 1 induction, phase 2 induction and phase 1 consolidation, achieving a negative MRD and complete remission. After this treatment, the patient underwent HSCT without early or late complications during follow-up. One year later, a bone marrow aspirate was performed that showed relapse of her leukaemia. The patient was started on treatment with donor lymphocyte infusion achieving a partial response, which was not maintained over time and the disease eventually progressed. Because this patient had a high level of expression of CD-22 B lymphocytes and based on the results of the INO-VATE phase III clinical trial, she was treated with two cycles (28 day cycles) of inotuzumab. The drug was administered by intravenous infusion for 1 hour. The doses were administered on days 1, 8 and 15; the first dose was 0.8 mg/m² and the remaining doses were 0.5 mg/m². The patient achieved negative MRD and complete remission after the first cycle, but according to the summary of product characteristic, the patient received two cycles without suffering from hepatotoxicity.

Conclusion and relevance In this case of an adult patient with high risk ALL who relapsed after allogeneic transplantation of haematopoietic progenitors, the use of inotuzumab was found to be safe and effective, achieving MRD and complete remission and therefore the initial goal of the study. Nevertheless, more studies are needed to demonstrate its efficacy and safety profile.

References and/or acknowledgements No conflict of interest.