Single-cell RNA sequencing reveals the evolution of the immune response in GBM progression

Alan Yeo et al.
of Harvard Medical School in the United States used single-cell transcriptomics and flow cytometry to reveal large-scale comprehensive longitudinal changes
in immune cell composition throughout tumor progression in a genetic mouse GBM model driven by epidermal growth factor receptors.

The results were published online in the May 2022 issue of Nature Immunology
.

——Excerpt from the article chapter

【Ref: Yeo AT, et al.
Nat Immunol.
2022 Jun; 23(6):971-984.
doi: 10.
1038/s41590-022-01215-0.
Epub 2022 May 27】

Research background

Glioblastoma (GBM) is an incurable primary malignant brain tumor characterized by a large number of immune components
that promote tumor development.

But little is known about changes in the GBM immune microenvironment during tumor progression
.

Alan Yeo et al.
of Harvard Medical School in the United States used single-cell transcriptomics and flow cytology to reveal large-scale comprehensive longitudinal changes
in immune cell composition throughout tumor progression in a genetic mouse GBM model driven by epidermal growth factor receptors (EGFR).

The results were published online in the May 2022 issue of Nature Immunology
.

Research Methods

To determine cell interactions in GBM progression, the authors used gene editing to create a GBM mouse model in which tumors are initiated
by in situ deletion of human EGFR overexpression binding CDKN2A and PTEN.

The authors performed uniform UMAP dimensionality reduction on 27633 CD45-cells and 36304 CD45+ cells, generating 17 and 20 subsets
from CD45- and CD45+ samples, respectively.

Four dendritic cell (DC) subsets, four macrophage subsets, and four T cell/natural killer (NK) cell subsets
were detected.

Subpopulation 3 are CD4 T cells (Cd4+); Subpopulation 7 consists of CD8 T cells (Cd8+) and NK cells (Gzma+); Subsets 3 and 32 contain regulatory T cells (Tregs, Cd4+ Il2ra+) as well as 3 microglia subsets
.

Subsets of 19S stage cells of early and late GBM mice were significantly increased with normal brain tissue controls; A 5-fold increase in EdU+ microglia in GBM mouse models (10.
07±2.
21%: 2.
22±1.
92%) demonstrated microglial proliferation
in GBM tissues.

EdU+ GBM microglia contain upregulated genes
related to mitosis, cytoplasmic division, cell division and cell cycle.

In the GBM tumor microenvironment (TME), microglia subsets respond
to tumors through proliferation and less participation in polarization procedures.

Through signaling pathway analysis, the authors found that one microglial subpopulation can respond to tumors by supporting pro-inflammatory procedures, while another microglial subset lacks this function
.

The authors then analyzed 32 cytokines and found that most (22/32) cytokines were enriched in CD45+ cells, indicating that most intratumor cytokines and their receptors were expressed more in the CD45+ cell population than in cancer cells
.

The authors also analyzed the expression of immune checkpoints in CD45+ cells and found that most checkpoint transcripts were expressed in CD45+ cells, mainly in T cells and bone marrow cells
.

By performing a temporal longitudinal evolution analysis of GBM, the authors found that EGFR+ cells are absent in normal brain tissue and increase
significantly in early and late GBM.

Early GBM is mainly composed of microglia, and late GBM shows increased
macrophage infiltration.

Results of the study

Conclusion of the study

In summary, the authors performed single-cell RNA sequencing studies on the immune and non-immune composition of mouse GBMs at single-cell resolution, and performed longitudinal analysis
of cell populations during initiation and progression.

The authors observed that the innate immune population underwent dramatic changes
in the high infiltration of immunosuppressive macrophages and neutrophils from the early stages of GBM development to the GBM end-stage.