Frontline Science: Characterization of a novel mouse strain expressing human Siglec-8 only on eosinophils

Abstract

Sialic acid-binding immunoglobulin-like lectin (Siglec)-8 is a human cell surface protein expressed exclusively on eosinophils, mast cells, and basophils that, when engaged, induces eosinophil apoptosis and inhibits mast cell mediator release. This makes Siglec-8 a promising therapeutic target to treat diseases involving these cell types. However, preclinical studies of Siglec-8 targeting in vivo are lacking because this protein is only found in humans, apes, and some monkeys. Therefore, we have developed a mouse strain in which SIGLEC8 transcription is activated by Cre recombinase and have crossed this mouse with the eoCre mouse to achieve eosinophil-specific expression. We confirmed that Siglec-8 is expressed exclusively on the surface of mature eosinophils in multiple tissues at levels comparable to those on human blood eosinophils. Following ovalbumin sensitization and airway challenge, Siglec-8 knock-in mice generated a pattern of allergic lung inflammation indistinguishable from that of littermate controls, suggesting that Siglec-8 expression within the eosinophil compartment does not alter allergic eosinophilic inflammation. Using bone marrow from these mice, we demonstrated that, during maturation, Siglec-8 expression occurs well before the late eosinophil developmental marker C-C motif chemokine receptor 3, consistent with eoCre expression. Antibody ligation of the receptor induces Siglec-8 endocytosis and alters the phosphotyrosine profile of these cells, indicative of productive signaling. Finally, we demonstrated that mouse eosinophils expressing Siglec-8 undergo cell death when the receptor is engaged, further evidence that Siglec-8 is functional on these cells. These mice should prove useful to investigate Siglec-8 biology and targeting in vivo in a variety of eosinophilic disease models.

Hypersialylation in Cancer: Modulation of Inflammation and Therapeutic Opportunities

“…Studies examining sialylated glycans as immune checkpoints are in their infancy but advancing at a rapid pace. Due to the differences between Siglecs in mouse and humans, development in mouse models expressing human Siglecs on relevant immune cells [ 113 , 147 , 148 , 149 ], or mouse models engrafted with human immune cells that have been genome-edited to modulate Siglec expression [ 150 ], should greatly accelerate our understanding of the role Siglecs play in the tumor microenvironment and enable the testing of therapies aimed at abrogating sialic acid-Siglec interactions.…”

Siglec-8 antibody reduces eosinophils and mast cells in a transgenic mouse model of eosinophilic gastroenteritis

“…Like other members of the CD33-related Siglecs, Siglec-8 appears to have evolved recently, with close homologs found only in some primate species (11,22). Therefore, to examine the in vivo activity of anti-Siglec-8 mAb, we generated a human Siglec-8-expressing transgenic mouse, distinct from previously generated mice (e.g., ROSA26-Siglec-8-knockin mice) (23,24). Instead, Siglec-8-transgenic founder mice were generated via the pronuclear microinjection of DNA (Supplemental Figure 3A) as described in Methods.…”

Frontline Science: Superior mouse eosinophil depletion in vivo targeting transgenic Siglec-8 instead of endogenous Siglec-F: Mechanisms and pitfalls

“…Other strategies, such as those involving mouse, rat, or sheep antibody‐based depletion by targeting sialic acid‐binding immunoglobulin‐like lectin (Siglec)‐F, have also been used, with variable but consistently incomplete blood and tissue depletion 7–11 . In particular, administration of several commercial rat anti‐mouse Siglec‐F antibodies, or liposomes that selectively engage Siglec‐F, also do a suboptimal job of depleting eosinophils 12–16 . Furthermore, Siglec‐F is expressed on other cells including alveolar macrophages and intestinal cells 17,18 and, therefore, effects seen with these targeting strategies may not be eosinophil specific.…”