IMMU-33. PRECISION ANTIGEN-DIRECTED IMMUNOTHERAPY TREATMENT OF BRAIN TUMORS INCREASES TUMOR-INFILTRATING EFFECTOR LYMPHOCYTE RESPONSES

Abstract

Abstract BACKGROUND Despite considerable advancements in the successful use of immunotherapy in treating a variety of solid tumors, applications in treating brain tumors have lagged considerably. This is due, at least in part, to the lack of well-characterized tumor antigens expressed within brain tumors that can mediate tumor rejection; the limited mutational burden within these cancers that limits the abundance of targetable neoantigens; and the immunologically “cold” tumor microenvironment that hampers the generation of sustained and productive immunologic responses. Our OBJECTIVE is to develop a precision immunotherapy approach for brain tumor patients utilizing prospectively identified tumor-specific antigens using cancer immunogenomics and selective amplification of patients’ tumor-specific antigens for generating tumor antigen-specific lymphocyte therapy. METHODS We identified neoantigens and tumor-associated antigens that were uniquely expressed in preclinical glioblastoma and medulloblastoma tumors using our cancer immunogenomics pipeline called Open Reading Frame Antigen Network (ORAN). A tumor antigen-specific RNA library was created for each tumor model and tumor-bearing animals were treated with ex vivo expanded tumor-specific lymphocytes and tumor antigen-specific RNA-loaded dendritic cell (tsRNA-DC) vaccines. In a different approach, animals were treated with a combination of tsRNA-DC vaccines and anti-PD-1 checkpoint-blockade therapy. Tumor progression and survival outcomes were determined. The immune cell response was evaluated using flow cytometry, TCR sequencing, and single-cell RNAseq. RESULTS Our results demonstrate the effectiveness of tsRNA-DC vaccines in eliciting robust anti-tumor immune responses in combination with adoptive cellular therapy and checkpoint blockade therapy. Additionally, our findings substantiate a robust increase in tumor-infiltrating lymphocytes characterized by enhanced effector function both intratumorally and systemically after tumor antigen-specific RNA-directed immunotherapies. CONCLUSION This powerful approach to generating immunotherapy recognizing a plurality of tumor antigens uniquely addresses the challenge of dealing with tumor antigenic heterogeneity and confronting the reality of patient-to-patient variation in antigen expression in the development of antigen targeting strategies.