517. Improving CAR T Cell Efficacy for Solid Tumors By Nanogel-Based Delivery of Immunomodulatory Proteins

Abstract

Adoptive T cell therapies utilizing T lymphocytes transduced to stably express an anti-CD19 chimeric antigen receptor (CAR) have shown remarkable success against refractory B cell malignancies in multiple clinical trials. Studies are underway to adapt this technology towards the treatment of solid tumors, however, the immunosuppressive tumor microenvironment of many solid tumors may represent a significant barrier to CAR T cell efficacy. In this study, we investigate a means to enhance CAR T cell function by loading them with nanogel “backpacks” containing the T and NK cell stimulatory molecule IL-15N72D:IL-15RaSu/Fc superagonist complex (IL-15sa, also referred to as ALT-803 and currently in clinical trials). The IL15sa nanogel is a crosslinked, protein-polyethylene glycol (PEG) complex that breaks down slowly under physiological conditions allowing for pseudoautocrine stimulation of the CAR T cells with the IL15sa cargo. The effects of IL15sa nanogel loading on CAR T cell function were tested in a glioblastoma multiforme tumor model. Human T lymphocytes were lentivirally-transduced with a CAR targeting the epidermal growth factor variant III (EGFRvIII) antigen, as is currently being tested in early human clinical trials. EGFRvIII is expressed in up to 30% of glioblastoma multiforme cells but not on normal cells. EGFRvIII CAR T cells were loaded with a fluorophore-labeled IL15sa nanogel and examined in vitro for nanogel breakdown and effects on CAR T cell functions. The nanogel was detected on labeled cells for up to five days. Nanogels loaded with either control or IL-15sa did not alter antigen-specific cytolytic activity of EGFRvIII CAR T cells towards glioblastoma target cells. EGFRvIII CAR T cells loaded with control nanogel proliferated with the same kinetics as non-loaded CAR T cells upon co-culture with EGFRvIII+ glioblastoma targets. In contrast, IL15sa nanogel loaded CAR T cells had increased proliferation upon co-culture with antigenbearing targets. Additionally, IL15sa nanogel loaded EGFRvIII CAR T cells proliferated more with repeated stimulation of EGFRvIII-expressing glioblastoma cells. Studies are currently underway to test the efficacy of IL15sa nanogel-loaded EGFRvIII CAR T cells in vivo using a xenogeneic murine model of glioblastoma. These results indicate that nanogel loading of T cells can be a viable way of delivering immunostimulatory agents with CAR T cells. Nanogel loading of immune-modulating or tumoricidal drugs coupled to CAR T cells represents a novel platform for enhancing T cell function, and potentially for delivering systemically toxic drugs, into a specific and hostile tumor microenvironment.