The U.S. Food and Drug Administration (FDA) granted priority review to the anti-CD22 recombinant immunotoxin moxetumomab pasudotox for the treatment of adult patients with hairy cell leukemia (HCL) who have received at least two prior lines of therapy.
The decision was based on the updated results of a phase I study of patients with relapsed/refractory HCL published in Blood. The expanded study included 12 patients from the original study who received the upper dose level of moxetumomab (50 Î¼g/kg every other day for three doses in 4-week cycles), plus 21 additional patients enrolled in an expanded 50 Î¼g/kg cohort.
In the combined 33-patient cohort, 29 (88%) responded to moxetumomab treatment and 21 (64%) achieved complete remission (CR). The median duration of CR was 42.4 months (range not provided). No patients relapsed after receiving consolidation therapy, while nine of 14 participants who did not receive consolidation relapsed a median of 13.5 months (range = 4.9-42.4 months; p=0.004) after finishing moxetumomab treatment.
The authors assessed lymphocyte subsets in nine patients before and after treatment: Circulating HCL cells cleared in all patients, while normal B cells decreased by <50 percent in three patients and increased in all others. T cells and their subsets increased in all but one patient, "thus, [the anti-CD22 drug] spared T cells and, with its short half-life, avoided prolonged B-cell depletion," they noted.
Four patients died from disease progression after relapsing and going off study. They died a median of 17 months (range = 2-29 months) after the last study dose.
Sources: AstraZeneca press release, April 3, 2018; Kreitman RJ, Tallman MS, Robak T, et al. Minimal residual hairy cell leukemia eradication with moxetumomab pasudotox: phase I results and long-term follow-up. Blood. 2018 February 27. [Epub ahead of print]