Improving CAR T cell therapy for brain tumors using immune competent models

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PROJECT SUMMARY/ABSTRACT The overall objective of this study is to engineer a potent CAR T cell therapy for high grade glioma (HGG), a subgroup of brain tumors for which outcomes remain poor. CAR T cell therapy is an innovative technology based on adoptive transfer of antigen-specific T cells engineered to elicit a clinically effective and specific immune response against tumor cells. Early clinical studies in HGG patients demonstrated safety of CAR T cell therapy for brain tumors; yet, only limited benefits were observed. Lack of efficacy is most likely multifactorial and include heterogenous antigen expression, limited homing to and penetration of tumors, T cell exhaustion and limited persistence, as well as the immunosuppressive tumor microenvironment (TME). Therefore, the central hypothesis of this proposal is that optimized design and additional genetic modifications of CAR T cells will improve their antitumor effects, and that these interventions will be evaluated in immune competent mouse models that closely mimic human disease. Three interrelated research aims are proposed to test this hypothesis and the rationale of each is outlined below. First, CAR design has to be optimized and evaluated in immune competent glioma models. In Aim 1, I will generate CAR T cells containing different co- stimulatory domains (CD28.ζ, 41BB.ζ, CD28.mutζ, and 41BB.mutζ), and compare their activity in vitro and in vivo. Second, a genome wide screen in primary T cells has identified key regulators of T cell activation post T- cell receptor (TCR) stimulation. Identified genes belong to molecules that regulate cell cycle, proliferation, and downstream TCR signaling including SOCS1, RASA2, or CBLB. In Aim 2, I will therefore explore if CRISPR- Cas9 mediated silencing of Socs1, Rasa2, and/or Cblb enhances the effector functions of CAR T cells. The independent Aim 3 will then explore a dual CAR targeting approach in which I will not only target glioma cells but also immunosuppressive cells within the glioma microenvironment. These studies are focused on tumor associated macrophages (TAMs), since they are abundantly present in gliomas and play a critical role in shaping the TME. To support the feasibility of this project, I have adapted the well-established immune competent GL261 glioma model to study CAR T cell therapies targeting the relevant tumor antigen B7-H3, which is not only expressed by GL261 cells but also in a broad range of pediatric and adult brain tumors. In addition, my preliminary studies indicate that `prototype' B7- H3 CAR T-cells readily recognize and kill GL261 cells in vitro and have antitumor activity in vivo, highlighting that the developed model is well suited for the proposed aims of this project. State of the art technique will be used in all three Aims to not only study the function and in vivo fate of CAR T-cells, but also their antitumor activity, and how CAR T-cells interact with glioma- infiltrating immune cells. Completion of this study will define the most optimal CAR design that best controls HGG tumors and persists longer in the context of inflammatory brain tumors. Additionally, results will illustrate if targeting TAMs will overcome the suppressive effects of TME on B7-H3 CAR T cells.