Funded Grants

Improving EphA2-targeted T-cell Therapy for Glioma

SCIENTIFIC SUBSTANCE AND SIGNIFICANCE

Introduction

We propose to develop antigen-specific T cells as an effective immunotherapy for GBM, the most aggressive primary human brain tumor. 1 Since T-cell immunotherapies are highly tumor-specific and cause minimal bystander cell damage, they are an attractive therapeutic strategy to improve the current dismal outcome for GBM patients. 2;3

Genetic modification of T cells to generate GBM-specific T cells

Gene transfer allows the rapid generation of antigen-specific T cells for adoptive immunotherapy, and this approach can circumvent tolerance to self-antigens overexpressed by tumor cells. 4-6 Successful gene transfer strategies include the forced expression of antigen-specific chimeric antigen receptors (CARs) or α/β T-cell receptors (TCR). We propose to take advantage of CARs to target GBM antigens. CARs consist of a single chain variable fragment (scFv), a transmembrane domain, and signaling domains derived from the T-cell receptor (TCR) complex and costimulatory molecules. CARs combine the antigen-binding property of monoclonal antibodies (MAbs) with the lytic capacity and self-renewal of T cells and have several advantages over α/β TCR. 7 CAR-expressing T cells recognize and kill tumor cells in an MHC unrestricted fashion, so that target cell recognition by CAR-T cells is unaffected by some of the major mechanisms by which tumors avoid MHC-restricted T-cell α/β TCR) recognition, such as downregulation of HLA class I molecules and defective antigen processing. Other advantages of CARs include the ability to change T-cell specificity by expressing a single molecule, which obviates the need to express two different receptor molecules at high levels from a single vector; and to ensure correct pairing of the introduced molecules, requirements that have proved problematic for transgenic α/β TCRs. Lastly, most tumors do not express costimulatory molecules so that α/β TCR engagement is followed by incomplete T-cell activation. This limitation can be overcome for CARs by incorporating costimulatory endodomains within the chimeric receptor sequence. The clinical experience with CAR-T cells for GBMs is limited, but given the recent encouraging clinical results using CAR-T cells to treat GD2-positive neuroblastoma and CD19-positive leukemia, further exploration is warranted. 8;9

Targeting EphA2 in GBM

CAR-T cells can recognize antigens expressed on the cell surface of GBMs. Potential membrane-bound tumor antigens include EGFRvIII, IL13Rα2, GPNMB, and EphA2. 10-17 Immune escape mutants have been described for EGFRvIII- and IL13Rα2-targeted therapies. 15;18 Targeting antigens that are important for sustaining the malignant GBM phenotype should reduce the inherent risk of immune escape and we therefore propose to target EphA2, an antigen that is important for the malignant phenotype of GBMs. EphA2 is overexpressed in GBM 10;11 and is associated with poor outcomes. 12;19 EphA2 overexpression induces pro-oncogenic effects including enhanced tumorigenesis, 20 tumor cell migration and invasion, 21 angiogenesis, and metastasiss. 22-25 We have shown in preclinical models that T cells, genetically engineered to be specific for EphA2, recognize not only the bulk of GBM cells but also glioma stem cells. 26 In addition, these cells induced the regression of human GBMs grown in the brain of SCID mice. Approximately half of the animals become long-term survivors in the absence of evident toxicities. The goal of this grant is now to build on these accomplishments and further enhance the efficacy of our EphA2-targeted T-cell therapy approach with the ultimate goal of developing a Phase I/II clinical study.

Theme of grant submission

In an effort to further increase the success rate of EphA2-targeted GBM therapies and move closer to a Phase I clinical study in humans we will pursue 2 strategies and expand the preclinical animal models we currently use to evaluate our GBM targeted T-cell therapies. First, we will explore mechanisms by which we can increase the in vivo expansion of CAR-T cells and sustain their survival. Second, we will determine if targeting one additional GBM antigen will result in enhanced anti-GBM effects. Lastly, we will adapt an immune competent animal model to evaluate EphA2-targeted T-cell Therapies. Thus, the central theme of this grant application is to optimize cell-based immunotherapy for GBMs through genetic manipulation of T cells, enabling them to optimally persist and expand in vivo and recognize multiple GBM antigens, resulting in sustained tumor regressions.

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