Development of immunocompetent melanoma brain metastases organoids - Abstract Immune checkpoint inhibition (ICI) can control intracranial disease in approximately 50% of patients with melanoma brain metastases (MBM), which is the leading cause of death for these cancer patients - implicating that immune microenvironment (IM) modulation can be therapeutic in the brain. There has been a paradigm shift in clinical management wherein immunotherapy can be considered rather than traditional surgery and/or radiation. However, there is a lack of preclinical models available that model the IM in patient MBM, which are needed to test and improve immune therapies (IT). Our goal for this R03 proposal is to develop and test a patient derived organoid model that mimics the IM found in patient MBM, which will have future applications in the development and optimization of IT strategies. The development of this model will provide foundational data to study cellular cross-talk in the IM of MBM, which will be the focus of a larger NCI R01. Our laboratory has experience using ex vivo patient derived brain organoids from surgical samples for precision medicine assays and drug screening. Our preliminary data derived from single cell RNA sequencing (scRNA-seq) of patient MBM samples demonstrates that CD8+ T cells in the parent tumor express exhaustion markers (i.e., PDCD1, CTLA4, LAG3, and TIGIT) – supporting therapeutic strategies targeting T cell activation. Further, cell-cell communication analyses of our scRNA-seq data suggests that cancer associated fibroblasts (CAFs) are the dominant cells receiving T cell crosstalk in MBM - indicating that T cells modulate the extracellular matrix. We hypothesize that patient derived organoid models need ECM to retain T cell characteristics of patient MBM and that an organoid with ECM will provide an optimal model for testing IT strategies. The aims of this study are: 1.) To identify the T cell phenotype in immunocompetent MBM organoids with and without ECM. 2.) To identify T cell phenotype following ICI treatment in MBM organoids. The development of a preclinical, immunocompetent, ex vivo model of MBM has yet to be accomplished and will facilitate the following innovations: i) establishment of biospecimen workflow that will allow for preservation of tumor stroma and immune cells in brain metastasis organoids, ii) identification of T cell-tumor cell interactions that can be targeted in the future, and iii) identification of biomarkers of ICI efficacy in the brain. The innovations gained by this R03study will contribute to the lives of patients with end stage melanoma as brain metastases is the leading cause of death in these patients. Our data will provide a basis for a future NCI R01 application.
