Abstract 282: Novel delivery system to bring immune checkpoint antibodies to tumor microenvironment
Authors: Shioya Koichiro , Koseki Koichi , Matsumura Tomio , Shimizu Hitomi , Shimatani Yuko , Taniguchi Shun'ichiro 
Published: August 2015

Abstract
Introduction: Cancer immunotherapy by blocking immune checkpoint (ICP) pathways with antibodies, such as anti PD-1 antibodies (Nivolumab, Pembrolizumab) and anti CTLA-4 antibody (Ipilimumab), has been reported to be clinically effective for several solid tumors. However, when the antibodies are systemically administered, they exhibit immune-related adverse events (ir-AE), that is, serious autoimmune toxicities, probably because their immunosuppressive function through binding to ICP molecules cannot discriminate normal tissues from solid cancers. If it is possible to selectively block immune-suppressive pathways only at the tumor site, both more anti-tumor effects and less ir-AE will be expected. In this context, we have been trying to establish engineered Bifidobacterium, which is nonpathogenic anaerobic bacteria and selectively colonizes in the hypoxic tumors, to express and secrete scFvs for antibodies against ICP molecules.
Materials and Methods: We transformed Bifidobacterium with expression vector encoding a single chain fragment of the variable region (scFv) for anti-murine PD-1 (mPD-1) antibody. The biological activity of the product was examined by binding ELISA, competitive ELISA and cell binding by FACS. The anti-tumor activity was assessed by i.v. administration with the engineered Bifidobactrerium to mice bearing murine colorectal tumor (CT-26).
Results: First, we succeeded in establishing a Bifidobactrerium strain producing and secreting anti-mPD-1 scFv. Binding of the recombinant scFv to mPD-1 was observed by ELISA and FACS, and its inhibition ability against mPD-1/mPD-L1 interaction was also confirmed in the system of ELISA. Furthermore, tumor growth of CT-26 formed in the syngenic mice was markedly suppressed by i.v. treatment with the engineered Bifidobactrerium producing anti-mPD-1 scFv. The antitumor effect was comparable with that obtained by a commercially available anti-mPD-1 antibody that was i.t. injected. As expected, both the scFv and the recombinant bacteria were specifically detected at the tumor sites by immunohistochemistry and colony plating assay, respectively, 7 days after i.v. injection of the recombinant Bifidobacterium to tumor bearing mice.
Conclusion: Thus, the engineered Bifidobacterium modified to produce and secrete scFv against ICP molecules will provide a new promising immune-therapeutic modality to target hypoxic solid tumors. The clinical application of the present study will be prospectively expected by referring the ongoing clinical trial of APS001F, a recombinant Bifidobacterium modified to express cytosine deaminase that converts 5-FC, a pro-drug to 5-FU specifically in tumor lesions.
Citation Format: Koichiro Shioya, Koichi Koseki, Tomio Matsumura, Hitomi Shimizu, Yuko Shimatani, Shun'ichiro Taniguchi. Novel delivery system to bring immune checkpoint antibodies to tumor microenvironment. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 282. doi:10.1158/1538-7445.AM2015-282