Abstract 1777: Examining dendritic cell heterogeneity in the tumor microenvironment

Abstract Dendritic cells (DCs) are key regulators of anti-tumor immunity with critical roles in priming and stimulating anti-tumor T cells. DCs have heterogeneous phenotype, ontogeny, activation status, and function. However, the distribution of DC subsets within solid tumors remains unclear. Moreover, the study of intratumoral DCs is hampered by their rarity and difficulties associated with distinguishing DCs from other similar cell types in the tumor microenvironment. Using genetically engineered DC reporter mice (ZBTB46-GFP), we performed single-cell RNA-sequencing (scRNA-seq) on DCs from tumors and normal tissue as an unbiased approach for examining DC heterogeneity. Within our scRNA-seq analysis, we identified the major ontological DC subsets (cDC1s and cDC2s) along with two activated DC subsets: one that expressed a migratory signature (mDC) and the other that expressed an interferon-signaling signature (IFN-DC). By comparing DCs in different tumor models and healthy lung tissue, we found that mDCs were present in both tumor and normal tissue, while IFN-DCs were specific to tumors. IFN-DCs were Sca-1high and were selectively enriched for key anti-tumor interferon-stimulated genes such as Cxcl9 and Cxcl10. Additionally, IFN-DCs were further separated into a type I IFN-enriched subcluster (IFN-DC1) and a type II IFN-enriched subcluster (IFN-DC2). IFN-DC2s were lost in tumors of cDC1-deficient Batf3-KO mice as revealed by scRNA-seq of tumor DCs in Batf3-KO mice. Further experiments suggested that this loss of IFN-DC2 was a cell-extrinsic effect due to the dramatic decrease in IFNy in the tumor microenvironment. Specifically, the decrease in IFNy was associated with the absence of cDC1-primed IFNy-producing CD8 T cells in Batf3-KO tumors. In summary, our analysis of tumor DCs using scRNA-seq and DC reporter mice reveals heterogeneous activated DC subsets, including DCs enriched for distinct type I and type II IFN signaling. Further elucidation of the functional relevance of each subset to the tumor immune response can enable more specific targeting of DCs for cancer immunotherapy. Citation Format: Tsun Ki Jerrick To, Samir Devalajara, Ian W. Folket, Malay Haldar. Examining dendritic cell heterogeneity in the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1777.