US regulators have assigned priority review status to AstraZeneca and MedImmune’s moxetumomab pasudotox, which is being developed as a treatment for hairy cell leukaemia (HCL).

The submission seeks approval for the investigational anti-CD22 recombinant immunotoxin as a treatment for adult patients who have received at least two prior lines of therapy.

Moxetumomab pasudotox is composed of a binding portion of an anti-CD22 antibody fused to a toxin. After binding to CD22, the molecule is internalised, processed and releases its modified protein toxin that inhibits protein translation, leading to apoptotic cell death.

The filing contains data from the Phase III moxetumomab pasudotox clinical trial, which met its primary endpoint of durable complete response in adults with relapsed or refractory HCL.

HCL is a rare, incurable slow-growing leukaemia in which the bone marrow overproduces abnormal B cells or lymphocytes, possibly leading to serious and life-threatening conditions such as infection, bleeding and anaemia.

The firms note that around 1,000 people are diagnosed with HCL in the US each year, and while many initially respond to treatment, up to 40 percent will experience a relapse of the disease.

Currently, there is no established standard of care and few treatments available for HCL; moxetumomab pasudotox has the potential to become a first-in-class therapy for the condition.