High-Dimensional Single-Cell Analysis Delineates Radiofrequency Ablation Induced Immune Microenvironmental Remodeling in Pancreatic Cancer

Radiofrequency ablation (RFA) is a local therapy that accepted to the treatment of cancer patients with liver metastases. RFA treatment of liver metastases in pancreatic cancer could reduce tumor volume and induce anti-tumor immune responses on distant non-RFA tumors. However, these immune responses transformed into exhausting in a few days after RFA treatment. So far, the alterations of tumor immune microenvironment in distant non-RFA tumor after RFA treatment are still unclear. In this study, by using syngeneic tumor models and single-cell RNA and TCR sequencing, we investigated the alterations of tumor-infiltrating immune cells in distant non-RFA tumor on day 3 after RFA treatment. Single-cell RNA sequencing identified six distinct lymphoid clusters, five distinct monocyte/macrophage clusters, three dendritic cells clusters, and one cluster of neutrophils. We found that RFA treatment could reduce the proportions of immunosuppressive cells including regulatory T cells, tumor-associated macrophages and tumor-associated neutrophils, whereas increase the percentages of functional T cells in distant non-RFA tumor. Moreover, RFA treatment also altered gene expression on a per cell in each cell cluster. And by using pseudo-time analysis, we described the biological processes of tumor-infiltrating CD8+ T cells and monocytes/macrophages based on transcriptional profiles. In addition, the immune checkpoints including PD-1, TIM3, LAG3 and CTLA4 were upregulated in T cells in distant non-RFA tumor after RFA treatment. In conclusion, our data indicated that RFA treatment induced tumor immune microenvironmental remodeling in non-RFA tumors in pancreatic cancer mouse model and provided an evidence for combination of RFA and immune checkpoint inhibitors.