Developing Multivalent T Cell Engagers Towards Local Cancer Immunotherapies

Abstract

Immunotherapeutics that redirect the immune system toward cancerous cells have been extensively researched over the past decades. T cell engagers, such as BiTEs, are moving through clinical trials for many types of cancers. However, their small hydrodynamic radius and lack of Fc mediated recycling results in short plasma half-lives upon intravenous administration, which prevents the achievement of minimum effective concentrations in solid tumors. The local administration of T cell engagers provides a method to achieve therapeutic concentrations in tumor tissue. Herein, we developed a new T cell engager scaffold optimized for local delivery by increasing the size of the conjugate to extend tissue residence time and established a synthetic protocol to rapidly exchange the cancer targeting ligand towards addressing tumor heterogeneity. Redesigning T cell engagers for local administration utilized a full anti-CD3 antibody modified with short ethylene oxide ((EO)x) linkers for the grafting of cancer targeting peptides. Additionally, creating a scaffold using SPAAC-based conjugation allows for rapid fabrication of multivalent T cell engagers (MuTEs) for many cancers, utilizing an already existing library of cancer targeting peptides. Ideal grafting densities for short ethylene oxide ((EO)x) linkers were determined and tested in vitro in PSMA positive and HER2 positive cancer cell lines. In a local delivery in vitro model using embedded PSMA expressing spheroids, MuTEs resulted in greater cancer spheroid killing compared to traditional bispecific T cell engagers (BiTEs) over a 2-week period, with 2.5-fold greater cytotoxicity with MuTEs than BiTEs after 12 days. MuTEs have the potential to improve efficacy of T cell engagers for local delivery applications and offer a simplified synthetic pathway to develop a library to T cell engagers that target various cancer cell antigens.