Endothelial, pericyte and tumor cell expression in glioblastoma identifies fibroblast activation protein (FAP) as an excellent target for immunotherapy

Abstract

Objectives. Targeted immunotherapies such as chimeric antigen receptor (CAR)-T cells are emerging as attractive treatment options for glioblastoma, but rely on identification of a suitable tumor antigen. We validated a new target antigen for glioblastoma, fibroblast activation protein (FAP), by undertaking a detailed expression study of human samples. Methods. Glioblastoma and normal tissues were assessed using immunostaining, supported by analyses of published transcriptomic datasets. Short-term cultures of glioma neural stem (GNS) cells were compared to cultures of healthy astrocytes and neurons using flow cytometry. Glioblastoma tissues were dissociated and analysed by highparameter flow cytometry and single-cell transcriptomics (scRNAseq). Results. Compared to normal brain, FAP was overexpressed at the gene and protein level in a large percentage of glioblastoma tissues, with highest levels of expression associated with poorer prognosis. FAP was also overexpressed in several paediatric brain cancers. FAP was commonly expressed by cultured GNS cells but absent from normal neurons and astrocytes. Within glioblastoma tissues, the strongest expression of FAP was around blood vessels. In fact, almost every tumor vessel was highlighted by FAP expression, whereas normal tissue vessels and cultured endothelial cells (ECs) lacked expression. Single-cell

The Role of Cytokines and Chemokines in Shaping the Immune Microenvironment of Glioblastoma: Implications for Immunotherapy

“…In common with other solid tumours, the glioblastoma microenvironment harbours an array of non-malignant (stromal) cell types in addition to the cancer cells themselves [ 18 , 19 ]. The main stromal cell types in glioblastoma are cells of the immune system—discussed in detail below—and cells associated with the structure and function of blood vessels (endothelial cells and pericytes) [ 20 ]. In contrast to most other tumour types, fibroblasts are not known to be a significant component of the glioblastoma TME.…”

“…Cells of the myeloid lineage are a major component of the glioblastoma TME [ 20 , 24 , 25 , 26 ]. In fact, these cells are reported to constitute a remarkable 30–50% of the glioblastoma tumour mass.…”

Oncogenesis, Microenvironment Modulation and Clinical Potentiality of FAP in Glioblastoma: Lessons Learned from Other Solid Tumors

“…In GBM, increased FAP expression has been detected mainly in mesenchymal stromal cells, astrocytes, glioma neural stem cells and sporadic CD45-positive cells [ 9 , 12 ]. These scattered CD45-positive cells might be fibrocytes or possibly a subset of macrophages originating in the bone marrow [ 8 ].…”

“…In various malignant tumors, FAP is overexpressed and has been demonstrated to participate in tumor growth and progression; therefore, efforts in the clinical translation of FAP have been made, including imaging biomarkers, prognostic value and FAP-targeted therapies [ 8 ]. Recent studies discovered upregulated FAP expression within the GBM microenvironment [ 9 ] and associated FAP expression with tumorigenesis, immunosuppression and chemoresistance in GBM [ 10 , 11 , 12 ]. As an identifying surface marker of cancer-associated fibroblasts (CAFs) in other solid tumors, FAP also assists CAFs in suppressing antitumor immunity, promoting tumor growth and driving epithelial–mesenchymal transition (EMT) [ 13 , 14 , 15 ].…”

Tumor Immune Microenvironment and Its Related miRNAs in Tumor Progression

“…TME contains a variety of cells, including fibroblasts, endothelial cells, mast cells, and immune cells ( 1 ). Fibroblasts are predominantly related to vascular development and tumor cell proliferation ( 2 ), while endothelial cells are deemed to be an important source of cytokines that can boost TME homeostasis ( 3 ). Immune cells in the TME include T lymphocytes (CD4+ T lymphocytes and CD8+ T lymphocytes), natural killer (NK) cells, tumor-associated macrophages (TAM), dendritic cells (DC), myeloid-derived suppressor cells (MDSC), regulatory T cells (Treg), and neutrophils ( 4 ).…”