MODL-24. NEUROIMMUNE-COMPETENT HUMAN BRAIN ORGANOID MODEL FOR STUDYING BRAIN TUMOR INVASION

Abstract INTRODUCTION Diffuse intrinsic pontine glioma (DIPG) is a highly aggressive pediatric brain tumor with a very poor prognosis (< 12 months survival). There is currently no effective treatment for DIPG. Complete surgical resection of DIPG is difficult due to its skull base location and infiltrative growth pattern. Gaining insights into the invasion process of the DIPG cells and their interaction with brain cells in the tumor microenvironment, such as microglia - the brain's primary immune cells, may guide the development of effective treatment strategies to halt or even reverse disease progression. To build a clinically relevant model for studying the microglia/tumor interaction in a 3D human tissue context, we developed a neuroimmune-competent brain organoid/DIPG fusion model system. METHODS Human embryonic stem cell derived-neural progenitor cells (NPCs) and -GFP-labelled human myeloid precursor cells were combined to form microglia-containing organoids (MiCBOs) through self-assembly and co-development over two months. Using two-photon live imaging, we characterized the distribution and motility of microglia in MiCBOs and corroborated these results with immunofluorescence staining and single-cell RNA-Sequencing (scRNA-Seq). Tumor cell invasion and interaction with microglia in the brain organoids were assessed by confocal microscopy as well as immunofluorescence stainings. RESULTS The human microglia in MiCBOs are viable, widely distributed, actively motile, and highly resemble those in the human brain. Confrontation experiments of the MiCBO with DIPG spheroids enable quantitative characterization of the invasion patterns for different cell lines under various conditions. CONCLUSION Our MiCBOs represent a valuable model for studying tumor cell invasion within a neuroimmune-competent human tissue context. Ongoing experiments with different primary DIPG cell lines as well as genetically engineered microglia will deliver more detailed insights into the invasion patterns of tumor cells into brain tissue and shed light on tumor cell/microglia interplay during the DIPG invasion process.