Close Spatial Interactions between Cancer Cells and Cancer-Associated Fibroblasts Suppress Antitumor Immunity

Cancer-associated fibroblasts (CAF) play immunosuppressive roles in the tumor microenvironment. Specifically, they reportedly act as physical barriers preventing immune cell infiltration. However, the spatial relationships between CAFs and cancer cells in antitumor immunity remain unknown. In this study, we established three-dimensional (3D) constructs, in which the spatial relationships were controlled using a 3D bioprinter. Using these models, we found that the mixed distribution of fibroblasts (FB) and cancer cells suppressed the antitumor immunity more than the surrounding distribution of FBs as physical barriers. The 3D construct with mixed distribution promoted TGFβ and periostin (encoded by Postn gene) cross-talk, resulting in immunosuppression. Postn knockdown in FBs decreased the TGFβ production in the mixed 3D construct and activated antitumor immunity both in vitro and in vivo. Clinically, patients with head and neck cancer or lung cancer showing a mixed distribution of α-smooth muscle actin⁺ myofibroblast-like CAFs exhibited worse prognosis after PD-1 blockade therapies, and lower CD8⁺ T-cell infiltration than those that had CAFs surrounding cancer cells. Overall, our findings suggest that the close interactions of CAFs and cancer cells facilitate immunosuppression, rather than the physical barriers created by CAFs, highlighting their potential as biomarkers and therapeutic targets for cancer immunotherapies based on spatial relationships. Furthermore, this study highlights the beneficial applications of 3D bioprinters.