Kinetic Assembly of Polymer-mRNA Nanoparticles Targets Circulating Monocytes to Enhance Cancer Immunotherapy

PROJECT SUMMARY Cancer vaccines have significantly advanced cancer immunotherapy; and recent successes of mRNA vaccines have raised prospect of generating potent anti-tumor response by specifically delivering mRNAs encoding tumor-associated antigens to antigen presenting cells (APCs). However, APC activation elicited by nanoparticles containing antigen mRNAs is rather limited. Circulating monocytes offer a promising cell target as an abundant APC precursor that can be deposited to spleen, lymph nodes, and tumor tissue following polarization and activation. The overall objective of this study is to engineer kinetically assembled poly(beta- amino ester) (PBAE) /mRNA nanoparticles (KaNPs) that can specifically deliver mRNAs encoding tumor antigens and immunoadjuvants into circulating monocytes in vivo and demonstrate the safety and efficacy of this new mRNA cancer vaccine platform. This study is built on the preliminary results showing biodegradable PBAE/mRNA KaNPs with an optimized size of 400 nm mediated preferential transfection of circulating monocytes following intravenous (i.v.) injection, leading to more effective transfection and deposition of circulating monocytes and a higher level of tumor-killing activity compared to the standard small size PBAE/mRNA nanoparticles. In this proposed study, we plan to pursue four specific aims: (1) optimize the composition, size, and surface functionality of PBAE/mRNA KaNPs to improve targeted mRNA delivery efficiency into circulating monocytes in vivo, (2) characterize pharmacokinetic profile of PBAE/mRNA KaNPs and define functions of transfected circulating monocytes in vivo, (3) assess the immunotherapeutic efficacy of PBAE/mRNA KaNPs in suppressing tumor growth in combination with TLR9 and STING agonists in mouse tumor models, and (4) develop an GMP-compliant, shelf-stable, lyophilized PBAE/mRNA KaNP formulation and validate the efficacy in a mouse model. If successful, this study will uncover structure-function relationships in a previously inaccessible size range (200–1000 nm) for gene therapy carriers, demonstrate circulating monocytes as a potent mRNA therapeutic target and the role of KaNP-transfected circulating monocytes in potentiating antitumor immune responses, and inspire rational design of new mRNA-based immunotherapies for treatment of solid tumors and metastatic cancers.