Tumors invade the surrounding tissues to progress, but the heterogeneity of cell types at the tumor-stroma interface and the complexity of their potential interactions hampered mechanistic insight required for efficient therapeutic targeting. Here, combining single-cell and spatial transcriptomics on human basal cell carcinomas, we define the cellular contributors of tumor progression. In the invasive niche, tumor cells exhibit a collective migration phenotype, characterized by the expression of cell-cell junction complexes. In physical proximity, we identify cancer-associated fibroblasts with extracellular matrix-remodeling features. Tumor cells strongly express the cytokine Activin A, and increased Activin A-induced gene signature is found in adjacent cancer-associated fibroblast subpopulations. Altogether, our data identify the cell populations and their transcriptional reprogramming contributing to the spatial organization of the basal cell carcinoma invasive niche. They also demonstrate the power of integrated spatial and single-cell multi-omics to decipher cancer-specific invasive properties and develop targeted therapies.

SUMMARY While squamous transdifferentiation within subpopulations of adenocarcinomas represents an important drug resistance problem, its underlying mechanism remains poorly understood. Here, using surface markers of resistant basal cell carcinomas (BCCs) and patient single-cell and bulk transcriptomic data, we uncover the dynamic roadmap of basal to squamous cell carcinoma transition (BST). Experimentally induced BST identifies activator protein 1 (AP-1) family members in regulating tumor plasticity, and we show that c-FOS plays a central role in BST by regulating the accessibility of distinct AP-1 regulatory elements. Remarkably, despite prominent changes in cell morphology and BST marker expression, we show using inducible model systems that c-FOS-mediated BST demonstrates reversibility. Blocking EGFR pathway activation after c-FOS induction partially reverts BST in vitro and prevents BST features in both mouse models and human tumors. Thus, by identifying the molecular basis of BST, our work reveals a therapeutic opportunity targeting plasticity as a mechanism of tumor resistance.

Purpose: Cemiplimab is approved for the treatment of locally advanced basal cell carcinomas (BCCs), however with mitigated results. We sought to interrogate the cellular and molecular transcriptional reprogramming underlying BCC resistance to immunotherapy. Experimental Design: Here, we combined spatial and single-cell transcriptomics to deconvolute the spatial heterogeneity of the tumor microenvironment in regard with response to immunotherapy, in a cohort of both naive and resistant BCCs. Results: We identified subsets of intermingled cancer-associated fibroblasts (CAFs) and macrophages contributing the most to CD8 T cells exclusion and immunosuppression. Within this spatially-resolved peritumoral immunosuppressive niche, CAFs and adjacent macrophages were found to display Activin A-mediated transcriptional reprogramming towards extracellular matrix remodeling, suggesting active participation to CD8 T cells exclusion. In independent datasets of human skin cancers, Activin A-conditioned CAFs and macrophages were associated with resistance to immune checkpoint inhibitors (ICI). Conclusions: Altogether, our data identify the cellular and molecular plasticity of TME and the pivotal role of Activin A in polarizing the TME towards immune suppression and ICI resistance.

CRISPR/Cas9 technology has revolutionized genetic engineering of primary cells. Although its use is gaining momentum in studies on CD8+ T cell biology, it remains elusive to what extent CRISPR/Cas9 affects in vivo function of CD8+ T cells. Here, we optimized nucleofection-based CRISPR/Cas9 genetic engineering of naïve and in vitro-activated primary mouse CD8+ T cells and tested their in vivo immune responses. Nucleofection of naïve CD8+ T cells preserved their in vivo antiviral immune responsiveness to an extent that is indistinguishable from non-nucleofected cells, whereas nucleofection of in vitro-activated CD8+ T cells led to slightly impaired expansion/survival at early time point after adoptive transfer and more pronounced contraction. Of note, different target proteins displayed distinct decay rates after gene editing. This is in stark contrast to a comparable period of time required to complete gene inactivation. Thus, for optimal experimental design, it is crucial to determine the kinetics of the loss of target gene product to adapt incubation period after gene editing. In sum, nucleofection-based CRISPR/Cas9 genome editing achieves efficient and rapid generation of mutant CD8+ T cells without imposing detrimental constraints on their in vivo functions.

<div>AbstractPurpose:<p>Cemiplimab is approved for the treatment of locally advanced basal cell carcinomas (BCC), although with mitigated results. We sought to interrogate the cellular and molecular transcriptional reprogramming underlying BCC resistance to immunotherapy.</p>Experimental Design:<p>Here, we combined spatial and single-cell transcriptomics to deconvolute the spatial heterogeneity of the tumor microenvironment in regard with response to immunotherapy, in a cohort of both naïve and resistant BCCs.</p>Results:<p>We identified subsets of intermingled cancer-associated fibroblasts (CAF) and macrophages contributing the most to CD8 T-cell exclusion and immunosuppression. Within this spatially resolved peritumoral immunosuppressive niche, CAFs and adjacent macrophages were found to display Activin A–mediated transcriptional reprogramming towards extracellular matrix remodeling, suggesting active participation to CD8 T-cell exclusion. In independent datasets of human skin cancers, Activin A–conditioned CAFs and macrophages were associated with resistance to immune checkpoint inhibitors (ICI).</p>Conclusions:<p>Altogether, our data identify the cellular and molecular plasticity of tumor microenvironment (TME) and the pivotal role of Activin A in polarizing the TME towards immune suppression and ICI resistance.</p></div>