The spatial organization of cDC1 with CD8+ T cells is critical for the response to immune checkpoint inhibitors in melanoma patients

Dendritic cells (DCs) are promising targets for cancer immunotherapies because of their central role in the initiation and control of immune responses. The type 1 conventional DC (cDC1) population is of particular interest because of its ability to cross-present antigens to CD8+ T cells, to promote Th1 cell polarization and NK cell activation and recruitment. However, the spatial organization and specific functions of cDC1s in response to immunotherapy remain to be clearly characterized in human tumors. In this study, we used a multiplexed immunofluorescence analysis pipeline coupled with computational image analysis to determine the spatial organization of cDC1s in skin lesions from a cohort of advanced melanoma patients treated with immune checkpoint inhibitors (ICI). For this, we performed a whole-slide image analysis of cDC1 infiltration, distribution, and spatial interaction with key immune partners such as CD8+ T cells and plasmacytoid DCs (pDC). We also analyzed LAMP3+-DC, which correspond to a mature subset of tumor-infiltrating DCs. Distance and cell network analyses demonstrated that cDC1s exhibited a scattered distribution compared to tumor-infiltrating pDCs and LAMP3+-DCs, which were preferentially organized in dense areas with high homotypic connections. The proximity and interactions between CD8+ T cells and cDC1s were positively associated with the response to ICI. In conclusion, our study unravels the complex spatial organization of cDC1s and their interactions with CD8+ T cells in melanoma patient lesions, shedding light on the pivotal role of these cells in shaping the response to ICI. NanoString GeoMx Digital Spatial Profiler (Human Immuno-Oncology Protein Assay) was used on FFPE tissues from eight representative patients. Tissue sections were incubated with a cocktail of oligonucleotide-conjugated antibodies (immuno-oncology panel kit) and counterstained with a nuclear stain.