Siglec-8 in eosinophilic disorders: receptor expression and targeting using chimeric antibodies

Publication date: Available online 10 December 2018

Source: Journal of Allergy and Clinical Immunology

Author(s): Fanny Legrand, Yun Cao, Joshua Wechsler, Xiang Zhu, Nives Zimmermann, Shakuntala Rampertaap, Joseph Monsale, Kimberly Romito, Bradford A. Youngblood, Emily C. Brock, Michelle Makiya, Nenad Tomasevic, Christopher Bebbington, Irina Maric, Dean D. Metcalfe, Bruce S. Bochner, Amy D. Klion

Abstract

Background

Sialic acid–binding immunoglobulin-like lectin (Siglec)-8 is selectively expressed on eosinophils, mast cells and basophils, and, when engaged on eosinophils, can cause cell death.

Objective

To characterize surface and soluble Siglec-8 levels in normal (ND) and eosinophilic (EO) subjects and assess the efficacy of anti-Siglec-8 antibodies in inducing eosinophil cell death in vitro.

Methods

Eosinophil expression of Siglec-8 was assessed using flow cytometry and quantitative PCR. Serum soluble Siglec-8 levels were measured by ELISA. Induction of eosinophil death by IgG4 (c2E2 IgG4) and afucosylated IgG1 (c2E2 IgG1) anti-Siglec-8 antibodies was evaluated in vitro by flow cytometry and in vivo in humanized mice.

Results

Siglec-8 was consistently expressed on eosinophils from ND and EO and did not correlate with absolute eosinophil count (AEC) or disease activity. Soluble Siglec-8 levels were measurable in serum from most donors, unrelated to AEC or Siglec-8 surface expression. c2E2 IgG1 and c2E2 IgG4 were equally effective at inducing cell death (Annexin-V positivity) of purified eosinophils from ND and EO after overnight IL-5 priming. In contrast, killing of purified eosinophils without IL-5 was only seen in EO subjects, and NK-mediated eosinophil killing was seen only with c2E2 IgG1. Finally, treatment of humanized mice with anti-Siglec antibody led to robust depletion of IL-5-induced eosinophilia in vivo.

Conclusions

Siglec-8 is highly expressed on blood eosinophils from EO and ND and represents a potential therapeutic target for eosinophilic disorders. Enhanced killing of eosinophils in the presence of IL-5 may lead to increased efficacy in patients with IL-5-driven eosinophilia.

Graphical abstract

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