Abstract 1368: Novel mRNA encoding anti-PD-L1 monoclonal antibodies for cancer immunotherapy
Authors: Chung Ezra , Bong Yong Sik , Chen Renxiang , Zhang Michael , Long Steven , Shen Dong 
Published: March 2024

Abstract
The difficulties with antibody-based therapies stem from their steep costs, complex procedures, and contamination risks. We investigate the use of in vitro transcription (IVT) for mRNA production, presenting a novel approach to traditional antibody treatments by promoting internal protein or antibody synthesis. We aim to create innovative mRNA-based anti-PD-L1 antibodies with strong immunotherapeutic effectiveness. The study begins with mouse immunization and hybridoma generation. Immunizing mice with the glycosylated extracellular domain of PD-L1 produces mouse antibodies against human PD-L1. Hybridomas, derived from post-immunization splenocytes, yield monoclonal antibodies screened for PD-L1 binding affinity via flow cytometry. A neutralizing assay identifies 22 antibodies with similar IC50 values and shared binding epitopes. M1, chosen for glycospecificity, affinity, and neutralizing activity, undergoes additional evaluation for the expression and anti-tumor efficacy of mRNA-encoded antibodies. The expression of M1 and atezolizumab antibodies is facilitated through an mRNA-lipid nanoparticles (LNPs) delivery system. Following intravenous administration in mice, sustained serum levels of M1 (ranging from 100 to 700 μg/mL at 24 hours post-injection) are observed. Serum concentrations of M1 and atezolizumab antibody peak at the first timepoint (24 or 48 h) after mRNA-LNP injection, respectively, and then significantly decrease within the next 4 days, with a gradual decline over the next 2 weeks. Conversely, the serum concentrations of M1 or atezolizumab protein decline significantly 24 hours post-injection and consistently stay at a baseline level (t1/2 of 94 and 4 h for M1 mRNA-LNP and protein, respectively). This indicates that the injection of encoded mRNA in mice can stably and continuously express antibodies.Administering Atezolizumab mRNA-LNP through two intravenous injections leads to a significant decrease in MC38 tumor growth, exhibiting a dose-dependent effect (TGI% = 8.1, 43.1, and 62.8 for doses of 0.2, 0.6, and 1 mg/kg, respectively). A complete tumor regression was observed up to day 19 following injection with a 2 mg/kg dose of mRNA-LNP (TGI% = 90.8%). Remarkably, a 3 mg/kg dose of atezolizumab antibody demonstrates a similar reduction in tumor growth as 0.6 mg/kg of the mRNA-LNP formulation in this model. In conclusion, this research underscores the potential of LNP-formulated mRNA as a transformative approach, converting the human body into a site for the continuous, stable expression of antibodies, offering a promising alternative to traditional protein-based therapies for combating cancer. This innovative approach shows promise in overcoming the limitations associated with traditional antibody production and clinical utilization.
Citation Format: Ezra Chung, Yong Sik Bong, Renxiang Chen, Michael Zhang, Steven Long, Dong Shen. Novel mRNA encoding anti-PD-L1 monoclonal antibodies for cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1368.