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Inotuzumab ozogamicin in relapsed or refractory ALL (Brivio et al., 2020)

Acute lymphoblastic leukemia (ALL) is the most predominant type of cancer in children. With the current standard treatment, consisting of intensive chemotherapy, the cure rate is more than 85-90%. However, approximately 10-15% of children with ALL relapse or do not respond to standard treatment. These children unfortunately have a poor prognosis. At the Princess Máxima Center we are therefore looking for new treatments.
The protein CD22 is present on the surface of leukemic cells (and healthy immune cells, so-called lymphocytes) in a vast majority of children with ALL. Inotuzumab ozogamicin (InO) is a novel drug that specifically binds to CD22 and then releases a cytotoxic agent (calicheamicin) that kills the leukemic cell. Although InO has been approved for the treatment of adults with ALL who do not or no longer respond to standard treatment, there is little experience in children.

Safe dose
In order to determine the safety and efficacy of InO in children, Dutch researchers, among whom dr. Erica Brivio and prof. dr. Michel Zwaan from the Princess Máxima Center, initiated and coordinated an international study. In phase 1 of this study the researchers determined which dose is tolerable and can be safely given to children. InO was well tolerated in children at the same dose as in adults (converted to body weight and height). At this dose InO also demonstrated anti-leukemic activity: after one course of treatment 85% of the patients responded, and no residual leukemic cells could be detected anymore (no minimal residual disease). Nine of these children went on to receive a bone marrow transplant or CAR T-cell therapy, improving their chance of a cure. These latter treatments could otherwise not have been given.
These are promising but preliminary results in a small number of patients (25 in total) with a relatively short follow-up time (eight months on average). The safe dose determined in phase 1 will be used in phase 2 of the study to further evaluate the anti-leukemic activity of InO in a larger number of children.