Abstract 2655: Drug resistant B-cell tumors eliminated by novel therapeutic antibodies in vivo
Authors: Qin Hong , Wei Guowei , Sakamaki Ippei , Dong Zhenyuan , Cheng Wesley A. , Smith Diane L. , Wen Feng , Sun Han , Cha Soung-chul , Neelapu Sattva S. , Kwak Larry W. 
Published: July 2017

Abstract
B-cell malignancies have been successfully targeted in the clinic by therapies such as anti-CD20 antibody rituximab or Bruton’s tyrosine kinase inhibitor ibrutinib. However, leukemias and lymphomas remain incurable due to primary or acquired resistance, ultimately leaving patients without an effective treatment option. We sought to circumvent this drug resistance by pursuing an alternative target known as B cell activating factor receptor (BAFF-R). Despite past limited success, BAFF-R remains a prime target for B-cell lymphoma and leukemia therapeutic antibody development due to its key role in B-cell proliferation and development.
We report the development of two novel monoclonal antibodies (mAbs) against human (h) BAFF-R. The mAbs were generated by immunizing mice with (h)BAFF-R-expressing mouse fibroblast cells presenting a natively folded, cell-surface immunogen. The two mAbs presented unique complementarity determining regions that specifically bound (h)BAFF-R-expressing mouse fibroblast cells but not the parental counterpart. Furthermore, the antibodies were specific to B-cell containing organs such as tonsil and spleen, by immunohistochemical staining and without detectable reactivity in heart, lung, brain, liver, and kidney tissues. To tailor the antibodies for clinical application, a human IgG1 Fc capable of eliciting an immune response was substituted, creating chimeric versions. We showed that both chimeric mAbs bound with high affinity to human B-cell lymphoma cell lines including JeKo-1 (mantle cell lymphoma; MCL), SU-DHL-6 (diffuse large B cell lymphoma; DLBCL), Raji (Burkitt lymphoma), and RL (follicular lymphoma). The chimeric antibodies also elicited antibody-dependent cell-mediated cytotoxicity (ADCC) with primary human natural killer (NK) cells in vitro against these tumor lines as well as primary lymphoma samples (n=5) from patients who progressed after rituximab exposure. Most notably, the antibodies demonstrated efficacy in two in vivo drug resistant lymphoma models we developed, a rituximab-resistant CD20 genomic knockout variant of JeKo-1 and the naturally ibrutinib-resistant Z-138. Using these lymphomas lines for xenogeneic tumor models in NOD scid gamma (NSG) mice, we found our antibodies significantly inhibited tumor growth, conferring long-term and tumor free survival on the mice.
Our in vitro and in vivo results robustly demonstrate the high specificity and significant anti-tumor effects of our anti-BAFF-R antibodies against a broad variety of B-cell malignancies, especially against cases of rituximab and ibrutinib resistance. This successful development of novel anti-BAFF-R therapeutic antibodies warrants support for further translational development for clinical use in light of current resistance cases.
Citation Format: Hong Qin, Guowei Wei, Ippei Sakamaki, Zhenyuan Dong, Wesley A. Cheng, Diane L. Smith, Feng Wen, Han Sun, Soung-chul Cha, Sattva S. Neelapu, Larry W. Kwak. Drug resistant B-cell tumors eliminated by novel therapeutic antibodies in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2655. doi:10.1158/1538-7445.AM2017-2655