Patient-derived Siglec-6-targeting antibodies engineered for T-cell recruitment have potential therapeutic utility in chronic lymphocytic leukemia. Issue 11 (28th November 2022)

• Record Type: Journal Article
• Authors: Cyr, Matthew G; Mhibik, Maissa; Qi, Junpeng; Peng, Haiyong; Chang, Jing; Gaglione, Erika M; Eik, David; Herrick, John; Venables, Thomas; Novick, Scott J; Courouble, Valentine V; Griffin, Patrick R; Wiestner, Adrian; Rader, Christoph
• Is Part Of: Journal for immunotherapy of cancer. Volume 10:Issue 11(2022)
• Publication Date: 2022-11-28
• Subjects: Antibodies, Neoplasm -- Antigens, Neoplasm -- B-Lymphocytes -- Epitope Mapping -- Hematologic Neoplasms; Cancer -- Immunotherapy -- Periodicals; Cancer -- Immunological aspects -- Periodicals; Tumors -- Immunological aspects -- Periodicals; Immunotherapy -- Periodicals; 616.99406105
• DOI: 10.1136/jitc-2022-004850
• Languages: English
• ISSNs: 2051-1426

Abstract

Abstract : Background: Despite numerous therapeutic options, safe and curative therapy is unavailable for most patients with chronic lymphocytic leukemia (CLL). A drawback of current therapies such as the anti-CD20 monoclonal antibody (mAb) rituximab is the elimination of all healthy B cells, resulting in impaired humoral immunity. We previously reported the identification of a patient-derived, CLL-binding mAb, JML-1, and identified sialic acid-binding immunoglobulin-like lectin-6 (Siglec-6) as the target of JML-1. Although little is known about Siglec-6, it appears to be an attractive target for cancer immunotherapy due to its absence on most healthy cells and tissues. Methods: We used a target-specific approach to mine for additional patient-derived anti-Siglec-6 mAbs. To assess the therapeutic utility of targeting Siglec-6 in the context of CLL, T cell-recruiting bispecific antibodies (T-biAbs) that bind to Siglec-6 and CD3 were engineered into single-chain variable fragment–Fc and dual-affinity retargeting (DART)–Fc constructs. T-biAbs were evaluated for their activity in vitro, ex vivo, and in vivo. Results: We discovered the anti-Siglec-6 mAbs RC-1 and RC-2, which bind with higher affinity than JML-1 yet maintain similar specificity. Both JML-1 and RC-1 T-biAbs were effective at activating T cells and killing Siglec-6 + target cells. The RC-1 clone in the DART–Fc format was the most potent T-biAb tested and was the only anti-Siglec-6 T-biAb that eliminated Siglec-6 + primary CLL cells via autologous T cells at pathological T-to-CLL cell ratios. Tested at healthy T-to-B cell ratios, it also eliminated a Siglec-6 + fraction of primary B cells from healthy donors. The subpicomolar potency of the DART–Fc format was attributed to the reduction in the length and flexibility of the cytolytic synapse. Furthermore, the RC-1 T-biAb was effective at clearing MEC1 CLL cells in vivo and demonstrated a circulatory half-life of over 7 days. Conclusion: Siglec-6-targeting T-biAbs are highly potent and specific for eliminating Siglec-6 + leukemic and healthy B cells while sparing Siglec-6 − healthy B cells, suggesting a unique treatment strategy for CLL with diminished suppression of humoral immunity. Our data corroborate reports that T-biAb efficacy is dependent on synapse geometry and reveal that synapse architecture can be tuned via antibody engineering. Our fully human anti-Siglec-6 antibodies and T-biAbs have potential for cancer immunotherapy. Trial registration number: NCT00923507 .