Single cell sequencing of mouse syngeneic tumor models

Tumor ecosystems are composed of multiple cell types that communicate by ligand-receptor interactions. Targeting ligand-receptor interactions, for instance with immune check-point inhibitors, can provide significant benefit for patients. However, our knowledge of which interactions occur in a tumor and how these interactions affect outcome is still limited. We present an approach to characterize communication by ligand-receptor interactions across all cell types in a microenvironment using single-cell RNA sequencing. We apply this approach to identify and compare ligand-receptor interactions present in six syngeneic mouse tumor models. To identify interactions potentially associated with outcome, we regress interactions against phenotypic measurements of tumor growth rate. In addition, we quantify ligand-receptor interactions between T-cell subsets and their relation to immune infiltration using a publicly available human melanoma data-set. Overall, this approach provides a tool for studying cell-cell interactions, their variability across tumors, and their relationship to outcome. Overall design: We used three different types of immuno-competent inbred mouse strains: BALB/c, and A/J z. All animals enrolled in our study were 6-8 weeks old female mice that were housed in vivarium under specific pathogen free conditions in cages of up to 5 animals and receiving special rodent diet (Teklad). We implanted two mice for each syngeneic model resulting in a total of 12 samples. Each mouse tumor was harvested when the tumor size reached 100 – 200 mm3. Each sample was minced and digested with reagents from Mouse Tumor Dissociation Kit (Miltenyi) according to the manufacturer's instructions. Cells were resuspended at 2x105 cells/mL in PBS-0.04% BSA. Each sample was processed individually and run in technical duplicates. For each sample (except CT26 and MC-38) one replicate was enriched for CD45 positive cells. Live CD45 positive cells were sorted with BD Aria after staining with FITC-CD45 (Biolegend) and 7-AAD. Single cell suspensions of all samples were resuspended in PBS-0.04% BSA at 5x105 cells/mL and barcoded with a 10x Chromium Controller (10x Genomics). In total, this procedure resulted in 24 samples.

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Kumar MP, Du J, Lagoudas G, Jiao Y, Sawyer A, Drummond DC, Lauffenburger DA, Raue A