First-in-Class Immunotoxin Shows Durable Response in Hairy Cell Leukemia

Moxetumomab pasudotox, a first-in-class recombinant immunotoxin targeting CD22, produced deep and durable responses in a substantial proportion of pretreated patients with relapsed/refractory hairy cell leukemia (HCL). In a pivotal multicenter, single-arm study, best overall response was a complete remission (CR) in 41% of patients and a CR with no minimal residual disease (MRD) in 34% by blinded independent central review.¹ A durable CR was achieved in 30% of patients, said Robert J. Kreitman, MD, at the 2018 ASCO Annual Meeting.

“We believe that moxetumomab is a nonchemotherapeutic agent that has the potential to become a standard of care option for patients with relapsed/refractory HCL,” said Kreitman, chief, Clinical Immunotherapy Section, Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland.

HCL is a rare B-cell malignancy characterized by high CD22 expression. “Although first-line treatment offers durable response, relapsed/refractory HCL is not known to be curable and there remains an unmet need for new treatments,” he said. When moxetumomab binds to CD22 on the hairy cell and internalizes, it inhibits protein synthesis leading to an apoptotic cell death.

The primary objective of the study was to establish the rate of durable CR followed by hematologic remission (HR) for at least 6 months. HR was defined by resolution of cytopenias without the use of transfusions or growth factors for at least 4 weeks. CR was defined as HR for at least 4 weeks, clearing of hairy cells in the bone marrow by hematoxylin and eosin (H&E) stain, and resolution of hepatomegaly and lymphadenopathy by imaging.

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