Session: 704. Immunotherapies: Poster II
Hematology Disease Topics & Pathways:
Biological, Leukemia, ALL, Diseases, Therapies, Pediatric, Biological Processes, immunotherapy, Lymphoid Malignancies, Study Population, immune mechanism
Siglec-15 (Sig15) was recently reported to have immune modulatory functions in the context of solid tumors. We have found that SIGLEC15 is overexpressed at the RNA level in primary B cell acute lymphoblastic leukemia (B-ALL), acute myelogenous leukemia (AML), and diffuse large B cell lymphoma as compared to healthy donor controls. As compared to healthy donor PBMCs, we have confirmed higher expression of Sig15 at the RNA and protein levels through RT-qPCR, immunoblotting, and flow cytometry across a panel of human B-ALL, AML, DLBCL, and T cell acute lymphoblastic leukemia (T-ALL) cell lines. Knockout of Sig15 expression in a BCR-ABL1+ murine model of B-ALL engrafted in immunocompetent and Rag1-/- immunodeficient recipients resulted in leukemia clearance in immunocompetent, but not immunodeficient, recipients and 100% survival (Figure 1). These data suggest a prominent role for Sig15 in the suppression of adaptive immune response to B-ALL as well as other hematological malignancies.
Additional studies suggest that SIGLEC15 expression is positively regulated by NFκB signaling, which is known to be constitutively activated in certain B-ALL subsets. Importantly, we have observed release of a soluble form of Sig15 (sSig15) from B-ALL cells, which is regulated by PKC and calcineurin-mediated signaling. To discover translational application, we measured sSig15 in the plasma of both healthy and pediatric leukemia patients and found significantly higher levels of sSig15 as compared to healthy individuals (Figure 2; LLD = 5 pg/ml; **P<0.01).
Together, these results suggest Siglec-15 is a novel and potent immunosuppressive molecule active in leukemia that may be targeted therapeutically to activate lymphocytes against leukemia cells.
Disclosures: Abukharma: NextCure, Inc.: Current Employment. Liu: NextCure, Inc.: Current Employment.
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