Vectorized Human Antibody-Mediated Anti-Eosinophil Gene Therapy

Chronic hypereosinophilia, defined as persistent elevated blood levels of eosinophils ≥1,500/μL, is associated with tissue infiltration of eosinophils and consequent organ damage by eosinophil release of toxic mediators. The current therapies for chronic hypereosinophilia have limited success, require repetitive administration, and are associated with a variety of adverse effects. As a novel approach to treat chronic hypereosinophilia, we hypothesized that adeno-associated virus (AAV)-mediated delivery of an anti-human eosinophil antibody would provide one-time therapy that would mediate persistent suppression of blood eosinophil levels. To assess this hypothesis, we first generated a human monoclonal antibody (mAb) directed against Siglec8, a sialic-acid binding immunoglobulin-like lectin, expressed at high levels on the cell surface of human eosinophils. Transgenic mice with a human immunoglobulin repertoire were immunized with human Siglec8 protein or DNA encoding human Siglec8. Based on target binding assessments, the 08C07 mAb was chosen for further study. The human variable regions of 08C07 were joined to the human Ig constant region, creating H08C07 (hAntiEos), a fully human anti-human eosinophil mAb. Using the gene sequence of hAntiEos, we created AAVrh.10hAntiEos, an AAVrh.10-based vector expressing the heavy and light chains of H08C07. Intravenous administration of AAVrh.10hAntiEos (10¹¹ genome copies or gc) to C57Bl/6 mice resulted in persistent elevated serum levels of hAntiEos. <i>In vivo</i> gene therapy generated hAntiEos bound to recombinant human Siglec8 protein in a dose-dependent manner and to human eosinophils, mediated apoptosis of human eosinophils, and antibody-dependent cellular cytotoxicity activity against human eosinophils. Consistent with these data, administration of AAVrh.10hAntiEos to human CD34⁺ transplanted NSG-SGM3 immunodeficient mice suppressed levels of human eosinophils <i>in vivo</i>. AAVrh.10hAntiEos holds the potential to offer therapeutic benefit to patients with chronic hypereosinophilia.