Eosinophils and mast cells are two types of immune cells with critical roles in responding to foreign assaults. When these cells do not function properly, several disease outcomes can develop (e.g. allergic and autoimmune disorders, cancer, heart disease, etc.). Severe disease caused by dysfunctional eosinophils and mast cells can be treated with monoclonal antibodies that mask receptors on these cells or neutralize secreted factors that activate these cells to restrict their ability to cause disease. However, in practice the current monoclonal antibodies have limited potency and are relatively ineffective for disease treatment. The lab of Dr. Roland Walter, a José Carreras / E. Donnall Thomas Endowed Chair for Cancer Research and Professor of Translational Science and Therapeutics Division at Fred Hutchinson Cancer Center, sought to develop novel monoclonal antibody tools to recognize these immune cells—eosinophils and mast cells—and use the antibodies to inform immunotherapy-based strategies for boosted therapeutic potency. Their research findings published in Cancers (Basel) describe novel monoclonal antibodies that recognize new sites on a specific receptor, Siglec-8, that is expressed on eosinophils and mast cells. The researchers also demonstrate that engineered variants of these antibodies can successfully recruit other immune cells to Siglec-8 expressing cells and activate cell-mediated killing of eosinophils and mast cells to abrogate disease. These new immunotherapy strategies enable potent neutralization of dysfunctional eosinophil and mast cells, prompting the continued study of these therapeutic approaches and clinical application.
Since therapies for eosinophil and mast cell diseases were limited, the discovery of a unique receptor that was expressed on the surface of these cells and absent from most other cell types, generated interest in using this receptor in targeted therapy strategies. This surface localized receptor was called sialic acid-binding immunoglobulin-like lectin-8 or Siglec-8 for short. Siglec-8 has three major domains that are accessible to monoclonal antibody binding and most available antibodies bind to the receptor at the domain furthest from the cell membrane. To generate new antibody tools, the researchers raised antibodies in mice to the human Siglec-8 peptides from the three extracellular domains. Nine of the eleven antibodies produced could bind cells expressing Siglec-8 and internalize into these cells, suggesting that a cell-killing payload may be delivered to these cells if attached to one of these internalized antibodies. Also of interest, a few of these antibodies bound Siglec-8 at sites located proximal to the cell surface.
Current antibodies that block Siglec-8 receptors modestly disrupt eosinophil and mast cell function. To boost the potency of targeting antibodies, the researchers investigated the ability of engineered, bispecific antibodies to recruit T cells and separately engineered CAR-NK cells both of which can mediate cell-based killing of the Siglec-8 positive cells. For the bispecific antibodies and CAR-NK cells, the researchers selected antibodies/CAR epitopes that bound to the Siglec-8 domain closest to the cell membrane since these were likely to have improved effector functions. Dr. Sheryl Lim, a postdoctoral fellow in Dr. Walter’s lab shared their exciting findings. “We found that targeting Siglec-8 membrane proximally enhances the efficacy of NK and T-cell based immunotherapies” and that these methods potently induce killing of Siglec-8 expressing cells.
Next steps for the lab include use of clinical samples. “It will be interesting to test the activity of the Siglec-8-directed therapies we developed against primary human mast cells,” stated Dr. Walter. These studies would confirm the compatibility of these Siglec-8 specific immunotherapies with patient cases. “In the longer term, we are working towards clinical translation of these Siglec-8-directed therapies, hopefully providing better treatment options for patients with eosinophilic and mast cell diseases,” concluded Dr. Walter.
The spotlighted research was funded by the National Institutes of Health and the José Carreras / E. Donnall Thomas Endowed Chair for Cancer Research.
Fred Hutch/University of Washington/Seattle Children's Cancer Consortium members Drs. Roland Strong and Roland Walter contributed to this work.
Lim SYT, Huo J, Laszlo GS, Cole FM, Kehret AR, Li J, Lunn-Halbert MC, Persicke JL, Rupert PB, Strong RK, Walter RB. 2024. Optimizing Siglec-8-Directed Immunotherapy for Eosinophilic and Mast Cell Disorders. Cancers (Basel). 16(20):3476.
Science spotlight writer Annabel Olson is a postdoctoral research fellow in the Nabet lab at Fred Hutchinson Cancer Center. Her research focuses on studying the mechanisms that drive cancer development for both genetic and virus-associated cancers. A key tool in her research is the use of targeted protein degradation to dissect dysregulated signaling pathways in cancer and to double as a relevant pre-clinical therapeutic platform.
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