KS05.7.A Characterization of the immune composition of extreme long-term survivors with malignant glioma at single-cell level

Abstract Background Glioblastoma Multiforme (GBM) remains the most common malignant primary brain tumor with a dismal prognosis that rarely exceeds beyond two years despite extensive therapy, which consists of maximal safe surgical resection, radiotherapy and/or chemotherapy. Recently, it has become clear that GBM is not one homogeneous entity and that both intra-and intertumoral heterogeneity contribute significantly to differences in tumoral behavior which may consequently be responsible for differences in survival. Strikingly and in spite of its dismal prognosis, small fractions of GBM patients seem to display extended survival compared to the large majority of patients. The underlying mechanisms for this peculiarity remain largely unknown however, even though emerging data suggest that both cancer cell-autonomous and microenvironmental factors and their interplay probably play an important role. Material and Methods We used high-dimensional, multiplexed immunohistochemistry to spatially, and cytometry by time-of-flight to quantitively characterize the cell constitution and interactions within the tumor microenvironment (TME) in 21 extreme long-term survivors (living over ten years since primary diagnosis or five years after recurrence) and 42 deeply matched short-term controls (living under 1.5 year) on a single cell level. For all tumors (epi-)genetic data was also collected. Results We identified a high level of both inter-and intrapatient heterogeneity defined by several distinct tumor niches, as well as described interactions within these niches and with the surrounding infiltrating immune cells of the TME. By linking patient characteristics with the heterogeneous immune composition we are building an immune stratification that can be linked to patient survival in GBM. Conclusion Generating an immune stratification for GBM will allow us to identify immune characteristics responsible for longer or even exceptional survival, as well as thoroughly identify tumor components that may serve as a potential target for personalized treatment strategies. Therefore, this study is also an essential initial step towards such clinical trials which alter the TME in a favorable way with a personalized modulation strategy.