Comparison of Gene Editing versus a Neutrophil Elastase Inhibitor as Potential Therapies for Neutropenia.

Heterozygous mutations in , the gene for neutrophil elastase, cause cyclic and congenital neutropenia through the programed cell death of neutrophil progenitors in the bone marrow. Granulocyte colony-stimulating factor is an effective therapy for these diseases, but alternative therapies are needed, especially for patients who do not respond well or are at high risk of developing myeloid malignancies. We developed an HL60 cell model for neutropenia and previously demonstrated that transient and regulated expression of mutant causes cell death by accelerated apoptosis. Knocking down the mutant gene or exposure to a potent inhibitor of neutrophil elastase rescued neutrophil development. Because of the great diversity in causative mutations, we generated stable HL60 clones expressing mutant P139L, C151Y and G214R and compared the effects of elastase inhibitor exposure to an knock-out line on cell development and function. ATRA induced differentiation demonstrated comparably impaired myeloid cell development for all three lines with upregulated expression of GRP78/BIP, an abnormality corrected by exposure of these cells to the elastase inhibitor MK-0339. The inhibitor and KO of mutant led to formation of neutrophils with comparable chemotactic and bactericidal capacities. We concluded that both strategies have great potential for the treatment of cyclic and congenital neutropenia. However, an orally absorbed, cell permeable inhibitor of neutrophil elastase, if proven safe and effective in a clinical trial, might be the better alternative to G-CSF or gene editing to treat neutropenia.