Figure 5.

The Immune Landscape and Intercellular Communication Network in the Tumor Microenvironment (TME)

The TME consists of a complex and heterogeneous population of multiple cell types of different origins that are divided into two major groups: tumor cells and stromal cells. The stromal cells comprise cancer-associated fibroblasts (CAFs), endothelial cells, and immune cells. The immune cells are also heterogeneous and participate in pro- or anti-tumorigenic activities that are influenced by the surrounding signaling. For instance, Treg cells, myeloid-derived suppressor cells (MDSCs), and tumor-associated macrophages (TAMs) are immunosuppressive and pro-tumorigenic, whereas CD8⁺ T cells, Th1 cells (facilitated by dendritic cell [DC]-mediated generation), and natural killer (NK) cells increase anti-tumor responses. Moreover, the implications of tumor and immune cell intercellular interactions, such as those involving PD-L1/PD1, have led to the development of immune therapies such as targeting PD1 on CD8⁺ T cells, thus inducing activation and clonal expansion of tumor-reactive CD8⁺ T cells.