LANDSCAPE ANALYSIS OF SINGLE-CELL RNA SEQUENCING IN FCΓRIIB DEFICIENCY AGAINST BRAIN CANCER

Abstract

Glioblastoma multiforme (GBM) is the most common and fatal malignant cancer in the central nerve system. Standard treatment for patients with GBM is surgical tumor resection followed by combined radio-chemotherapy. Although this standardized treatment shows improved patient survival, the prognosis for patients still remains extremely poor with 15 months of median survival. The immune checkpoint blocker (ICB) is effective on hematological tumors though the application of the ICB is still not optimistic on GBM patients. These limitations of the treatments originate from the lack of comprehensive understanding of the tumor microenvironment (TME). TME consists of not only the heterogeneous glioblastoma stem cells but also the various types of immune cells with pro-tumoral properties. Thus, understanding of this tumor infiltrating immune cells and functional status in GBM can provide a better approach to treatment strategies. To collect the accurate and broad spectrum of the information about the tumor infiltrating immune cells, we performed single-cell RNA sequencing on immune cells of GL261 injected GBM mouse model. From the results, we identified that the GBM up-regulated inhibitory FcγR gene, Fcgr2b, on tumor infiltrating immune cells, and this inhibitory receptor quantitatively and qualitatively suppressed the antitumor response. FcγRIIb is commonly mediates immune homeostasis through the binding of the immune complex. Broad types of immune cells express FcγRIIb and reversely blocking or deletion of the receptor induces proinflammatory response. For the adequate understanding of the function of the FcγRIIB in GBM condition, we used the FcγRIIb-KO mouse and analyzed the landscape of tumor infiltrating immune cells. At the early time point of GBM, 10 days, tumor associated microglia are polarized from pro- to anti-tumoral states in FcγRIIb-KO mouse. The microglia enhanced the TNF-alpha signaling pathway and upregulated adaptive immune cell recruiting chemokines such as Ccl3 and Ccl4. Furthermore, at a late stage of tumor progress, 20 days of GBM, total immune cell number was increased in FcγRIIb-KO mouse. Especially cytotoxic CD8 T cells increased in tumor site infiltration with enhanced cytotoxicity with enriched gene expression of Prf1 and Gzmb. Based on these analyses, FcγRIIb plays critical roles in GBM infiltrating immune cells particularly microglia and cytotoxic CD8 T cells. This work is worth investigating since the understanding of the role of FcγRIIb in GBM and provides a detailed dataset for heterogeneity of GBM-associated immune cells.