Siglec-6 on Chronic Lymphocytic Leukemia Cells Is a Target for Post-Allogeneic Hematopoietic Stem Cell Transplantation Antibodies

• DOI: 10.1158/2326-6066.cir-18-0102
• Publication Date: 2018-07-06T13:59:34Z
• Authors: Jing Chang; Haiyong Peng; Brian C. Shaffer; Sivasubramanian B...; Ina C. Wecken; Matthew G. Cyr; Gustavo J. Martinez; Jo Soden; Jim Freeth; Adrian Wiestner; Christoph Rader
• Keywords: 0303 health sciences; Hematopoietic Stem Cell Transplantation; Antibodies, Monoclonal; Antigens, Differentiation, Myelomonocytic; High-Throughput Nucleotide Sequencing; Enzyme-Linked Immunosorbent Assay; Flow Cytometry; Leukemia, Lymphocytic, Chronic, B-Cell; Cell Line; 3. Good health; 03 medical and health sciences; Antigens, CD; Tissue Array Analysis; Gene Knockdown Techniques; Lectins; Leukocytes, Mononuclear; Humans; RNA, Small Interfering; Cell Surface Display Techniques; Immunoglobulin Heavy Chains

Abstract Although the 5-year survival rate of chronic lymphocytic leukemia (CLL) patients has risen to >80%, the only potentially curative treatment is allogeneic hematopoietic stem cell transplantation (alloHSCT). To identify possible new monoclonal antibody (mAb) drugs and targets for CLL, we previously developed a phage display–based human mAb platform to mine the antibody repertoire of patients who responded to alloHSCT. We had selected a group of highly homologous post-alloHSCT mAbs that bound to an unknown CLL cell surface antigen. Here, we show through next-generation sequencing of cDNAs encoding variable heavy-chain domains that these mAbs had a relative abundance of ∼0.1% in the post-alloHSCT antibody repertoire and were enriched ∼1,000-fold after three rounds of selection on primary CLL cells. Based on differential RNA-seq and a cell microarray screening technology for discovering human cell surface antigens, we now identify their antigen as Siglec-6. We verified this finding by flow cytometry, ELISA, siRNA knockdown, and surface plasmon resonance. Siglec-6 was broadly expressed in CLL and could be a potential target for antibody-based therapeutic interventions. Our study reaffirms the utility of post-alloHSCT antibody drug and target discovery. Cancer Immunol Res; 6(9); 1008–13. ©2018 AACR.