PROJECT SUMMARY Adoptive cellular therapy (ACT) treatments, in which cancer patients are infused with autologous tumor- specific cytotoxic (CD8+) T cells expanded and activated ex vivo, have become gradually more appealing for cancer patients. Although ACT has shown great clinical success with melanoma, universal adoption has been limited, as ACT relies on extremely complex cell-based methods with a significant price tag. Recently, increased emphasis has been placed on enhancing acellular platforms, such as artificial antigen presenting cells (aAPCs), that show promise in activating tumor-specific CD8+ T cells in a quicker, more tunable manner. While a majority of aAPC systems have been applied in ex vivo settings, the development of biocompatible materials for aAPC platforms have expanded the potential of these systems to be used in vivo, lessening the lengthy culture times and costs associated with therapy. The goal of the proposed project is to develop a novel biomaterial aAPC for direct, antigen-specific activation of CD8+ T cells in vivo for cancer immunotherapy. The particulate platform is made from a novel blend of biodegradable and biocompatible polymers, Poly(lactic-co-glycolic) acid (PLGA) and Poly(beta amino ester) (PBAE), that promotes inclusion of the three signals required for optimal T cell activation and expansion. We will investigate the effects of biomaterial properties and signal incorporation on in vitro T cell activation, as well as gain insight into in vivo antigen-specific T cell activation in a tumor-burdened host. We will develop immunologically compatible, particulate PLGA/PBAE aAPCs for in vivo injection and T cell activation. First, we will investigate physicochemical properties of these aAPCs, including biomaterial composition, size, and surface protein density. We will optimize these properties in the context of enhanced CD8+ T cell activation and biological function. Second, we will focus on incorporating cytokines, additional signals that are important in T cell activation, in a local and sustained manner. We will investigate various cytokines, such as IL-2, IL-15, and IL-21, that may play a role in generating effector and memory T cells. Taken together, we will identify leading tri-signal aAPCs that are optimized for both murine and human T cell activation in vitro. Finally, we will apply our leading aAPCs in vivo, to analyze their CD8+ T cell activation, expansion, and anti- tumor capacities. If successful, this proposal will generate a novel biomimetic approach for harnessing optimal antigen-specific CD8+ T cell responses, with the potential of expanding patient access to cancer immunotherapies and reducing health disparities.