Spatial immune landscape of cutaneous squamous cell carcinomas (cSCC) prior to immune checkpoint blockade

Summary: Abstract Body: This project aimed to elucidate the spatial relationships and chemokine networks among key immune cells in cSCCs before immune checkpoint inhibition (ICI) therapy. Spatial analyses of baseline tumors (FFPE samples) from patients treated with anti-PD1 therapy was performed, correlating these findings with documented clinical responses to ICI (n=10). Spatial transcriptomics platforms (Merscope and Xenium) were used, targeting over 400 genes focused on immuno-oncology. Probes were selected to investigate immune cell phenotypes, cell-cell communication, and tumor-intrinsic proteins. In responder patients, a significant upregulation of key chemokines, including CCL19, CXCL9-11, and CXCL13 was observed, compared to non-responders. CCL19 and CXCR3 ligands (CXCL9-11) can be secreted by dendritic cells or macrophages, while CXCL13 can be produced by T cells. CCL19 interacts with CCR7, and CXCL9-11 with CXCR3 on T cells. CXCL13, on the other hand, potentially recruits B cells from circulation into the tumor microenvironment. In responder cSCC patients, T cells and APCs were co-localized within the tumor microenvironment. In these cellular neighborhoods, elevated expression of markers associated with tissue-resident memory T cells, such as ITGAE (CD103) and ITGA1 (CD49a), was observed (p < 0.05). Additionally, markers such as LAMP3 (a dendritic cell marker) and Flt3-Ligand are were upregulated (p < 0.05). Flt3-Ligand can enhance dendritic cell proliferation. In contrast, non-responder patients exhibited upregulation of markers such as TREM2, which has been linked with macrophages and poor prognosis in other cancer cohorts. Overall, these findings suggest a critical role for antigen-presenting cell–T cell interactions in the tumor microenvironment of cSCC responder tissues. The effective recruitment of T cells into the tissue, along with the activation of resident T cells already present within the tissue, may serve as key determinants of therapeutic success. Robin Reschke^{1, 2} 1. Department of Dermatology and National Center for Tumor Diseases, Universitat Heidelberg, Heidelberg, BW, Germany. 2. German Cancer Consortium (DKTK), DKFZ Core Center Heidelberg, Universitat Heidelberg, Heidelberg, BW, Germany. UV Biology/Injury and Non-melanoma Cancers