TUMOUR-ASSOCIATED MACROPHAGE INfiLTRATION DIFFERS IN MENINGIOMA GENOTYPES, AND IS IMPORTANT IN TUMOUR DYNAMICS

Abstract AIMS Meningiomas, the most common intracranial brain tumours, are classified by the World Health Organisation (WHO) into WHO grades for prognostic purposes. Some clinically aggressive grade 1 meningiomas, as well as grade 2, 3, and recurrent cases necessitate the exploration of new therapeutic strategies. Recent clinical trials suggest initial promising results for immunotherapy in meningioma patients. The tumour microenvironment (TME), particularly tumour-associated macrophages (TAMs), plays a pivotal role in tumour progression. How- ever, the link between the TME and genomic driver mutations remains underexplored METHODS We used multiplex immunohistochemistry (mIHC) and bulk RNA sequencing (RNA-seq) to analyse TME in ge- netically stratified meningioma tissues and matched 3D spheroid models. RNA-seq enabled comparative anal- ysis of immune infiltration across parental tissues, 2D monolayer cultures, and 3D models was carried out. In co-culture experiments, M2 polarised macrophages from peripheral blood mononuclear cells (PBMCs) were introduced to study tumour-immune interactions. RESULTS Our results revealed TME differences associated with specific genotypes and methylation classes (MCs). This study is the first to show significant differences in both M2-like TAM populations across genotypes and MCs. Notably, the 3D models more closely replicated the TME of parental tissues than 2D, offering a superior plat- form for immune infiltration studies. The 3D co-culture models revealed that M2 polarised macrophages could effectively infiltrate tumour cells, promote their proliferation while inhibiting invasion. CONCLUSION Our findings suggest potential biological mechanisms that may influence meningioma behaviour. Understand- ing the TME based on genotypes and MCs can provide valuable insights into tumour progression and therapeutic targets. These findings underscore the potential of 3D co-culture models to elucidate interactions between genet- ically defined tumour cells and immune components, offering insights that could guide novel immunotherapy strategies for improving therapeutic outcomes and quality of life in meningioma patients.