Transcriptomic Characterization of Locally Derived Microglial-like Macrophages That Drive Tumor Volume in Vestibular Schwannomas

Introduction: The origin and role of macrophages within vestibular schwannomas (VS) remain largely unknown. Tumor-associated macrophages (TAMs) polarized to a pro-tumorigenic M2 phenotype may drive sporadic and neurofibromatosis type 2 (NF2) related VS.

Methods: We performed an integrated analysis of the macrophage fraction in sporadic and NF2-related VS. We created parallel single cell (n = 2 sporadic; 2 NF2)/single nucleus transcriptomic maps (n = 6 sporadic; 6 NF2). We used reference-based (SingleR) and marker-based (custom) classifications to identify macrophages and their transcriptomic profiles. We then validated the canonical cell classes with multiplexed immunohistochemistry (n = 8).

Results: Macrophages were identified based on referenced-based and marker-based classifications. We found differences in macrophage fractions and clusters depending on the sequencing technique used (single-cell RNA and single-nucleus RNA). We found predominant M2 phenotype macrophages that expressed CD163 (40-75%) and CD204 (30-59%) in NF2 and sporadic schwannoma. In our analysis, 30% and 15% of macrophages expressed the colony-stimulating-factor 1 receptor (CSF1R) and VEGFA respectively. On average, macrophages had a higher percent and average expression of the P2Y12 marker (10-50%) than peripheral blood monocyte markers such as CD44 (1-20%) and CD206 (1-5%). Macrophage fractions were validated using multiplex immunohistochemistry and had a range of 30-67%. We found that VS macrophage fractions trended positively with tumor volume but negatively with specific growth rate.

Conclusion : In this integrated sequenced analysis of sporadic and NF2-related schwannomas, we found that macrophages comprised up to 70% of canonical cell fractions. We found that these macrophages were predominantly microglial derived and were polarized to a pro-tumorigenic M2 phenotype. The association between volume and macrophage fraction suggests potential therapeutic strategies targeting macrophages in abrogating VS mass effect in the posterior fossa.