ScRNA-seq reveals tumor microenvironment remodeling induced by local intervention-based immunotherapy

Laser immunotherapy (LIT) combines local photothermal therapy (PTT), to disrupt tumor homeostasis and release tumor antigens, and an intratumorally administered immunostimulant, N-dihydrogalactochitosan (GC), to induce antitumor immune responses. We performed single-cell RNA sequencing on tumor-infiltrating leukocytes of MMTV-PyMT mouse mammary tumors to characterize LIT-induced myeloid and lymphoid compartment remodeling. Analysis of 49,380 single cell transcriptomes from different treatment groups revealed that proinflammatory IFN, IFN{gamma}, and TNF cytokine signaling pathways were enriched in both lymphoid and myeloid cells isolated from LIT-treated tumors. The CD4+ and CD8+ T cells in LIT treated tumors resided in an activated state while immune cells in untreated and PTT-treated tumors remained in a neutral/resting state. Additionally, monocytes recruited into the LIT-treated tumors were driven towards proinflammatory M1-like macrophage phenotypes or monocyte-derived dendritic cells. Our results reveal that LIT prompts immunological remodeling of the tumor microenvironment by initiating broad proinflammatory responses to drive antitumor immunity. STATEMENT OF SIGNIFICANCETranscriptome profiling of tumor infiltrating leukocytes revealed that localized laser immunotherapy (LIT) greatly enhanced antitumor T cell activity by promoting proinflammatory myeloid cell responses within the tumor microenvironment. This manuscript demonstrates that LIT broadly stimulates antitumor immunity and has great potential to synergize with current immunotherapies to increase their efficacy.