# Single‐Cell Sequencing Reveals the Immunosuppressive Trajectory in the Tumor Microenvironment of Human Giant Cell Tumor of Bone

## TL;DR

This study uses single-cell sequencing to map the immune cell landscape in bone tumors, revealing how immune suppression helps the tumor evade treatment.

## Contribution

The study identifies immunosuppressive cell subtypes and interactions in GCTB using single-cell RNA sequencing.

## Key findings

- Tumor-associated macrophages (TAMs) are the main infiltrating cells and show multiple subtypes with distinct markers.
- Exhausted T cells and regulatory T cells contribute to the immunosuppressive environment in GCTB.
- Strong interactions between TAMs and tumor cells suggest a role in immune evasion.

## Abstract

Giant cell tumor of bone (GCTB) presents considerable complexity in tumor microenvironment (TME) because of its intricate intercellular heterogeneity and the presence of an immunosuppressive milieu. In order to understand the complex gene expression patterns and cell interactions in GCTB, we carried out a thorough investigation using single‐cell RNA sequencing (scRNA‐seq).

We examined scRNA‐seq data from 7091 cells that were collected after surgical removal of GCTB. Following the initial quality control process, 10 separate groups of cells were distinguished, which consisted of dendritic cells, endothelial cells, macrophage cells, mast cells, monocyte cells, neutrophil cells, tumor cells, osteoclast cells, pericyte cells, and T cells. Additional analysis uncovered distinct categories within tumor‐associated macrophages (TAMs), CD8+ T cells, and CD4+ T cells. The differentiation mechanisms of TAMs, CD8+ T cells, and CD4+ T cells were explored using pseudo‐time trajectory analysis. The CellPhoneDB study revealed the interactions between various cell types within the TME of GCTB.

TAMs have been identified as the main infiltrating cells in GCTB. These TAMs exhibit several subtypes that are characterized by specific marker genes and functional states. The identification of several subgroups within CD8+ T cells that are involved in regulating immunological checkpoints underscores the difficulties encountered when attempting to employ immune checkpoint blockade therapy for GCTB. T cell exhaustion poses a major barrier to the efficacy of antitumor immune responses. Research suggests a strong correlation between TAMs and exhausted T cells (Texs) in the TME. The high number of regulatory T cells (Tregs) highlights the immunosuppressive nature of the immunological environment in GCTB. Significant interactions have been observed between TAMs and tumor cells, highlighting their crucial involvement in immune evasion strategies.

This scRNA‐seq study provides a general overview of the different cellular compositions and immune interactions within GCTB. The identified subtypes and communication networks provide valuable information about the immunosuppressive environment of GCTB, laying the foundation for prospective therapeutic approaches targeting specific cell types or interactions.