Targeting AEBP1 to Mitigate Protumor Activity of Cancer-Associated Fibroblasts and Increase Therapeutic Efficacy of Anti–PD-1

Cancer-associated fibroblasts (CAF) are key components of the tumor microenvironment (TME) that promote tumor progression either directly through tumor-CAF interactions or indirectly by influencing tumor-infiltrating immune cells, thereby creating an immunosuppressive TME. High stromal signatures have been associated with reduced therapeutic efficacy and resistance to immune checkpoint blockades. Adipocyte enhancer-binding protein 1 (AEBP1) is predominantly expressed in myofibroblasts, and its expression is further increased in CAFs that produce the extracellular matrix. It has two isoforms: The extracellular isoform binds to collagen and promotes collagen remodeling, whereas the intracellular isoform modulates transcription and signaling. We observed the expression of both isoforms in primary human CAFs. Our data showed that the combined knockout (KO) of both AEBP1 isoforms via gene editing decreased CAF proliferation, collagen gel contractility, and CAF-mediated tumor cell proliferation in vitro. AEBP1 KO mouse fibroblasts demonstrated reduced activity in both in vitro assays and in vivo within a coimplantation mouse model. RNA sequencing revealed that AEBP1 KO downregulated the collagen biosynthesis and extracellular matrix organization-related pathways in mouse fibroblasts and human CAFs. Importantly, AEBP1 loss in fibroblasts led to significant alterations in tumor cell phenotypes, including a marked reduction of tumor cells exhibiting an epithelial-mesenchymal transition signature in vivo. Furthermore, AEBP1 KO in CAFs enhanced the anti-PD-1-induced effector T-cell function and the anti-PD-1 efficacy. Our findings indicate that AEBP1 plays a crucial role in regulating the function of CAFs within the TME. Targeting AEBP1 could be a promising strategy to inhibit the tumor-promoting activities of CAFs and to overcome resistance to anti-PD-1 immunotherapy.