The role of hematopoietic progenitor cells in immunotherapy resistance

In the last decade, immune checkpoint inhibitors (ICI) have made a paradigm shift in clinical oncology. However, the main obstacle is the development of tumor resistance. The Shaked lab previously suggested a mechanism for ICI resistance, showing that in response to immunotherapy, the host generates pro-tumorigenic effects which is associated with increased levels of IL-6. In another study, the Shaked lab demonstrated that high metastatic tumors are enriched with monocyte-dendritic progenitors (MDPs). This effect is mediated by IL-6 signaling, which further differentiates MDPs into immunosuppressive macrophages (M2), supports metastasis and tumor cell aggressiveness. Taken together, we hypothesize that MDPs accumulate in tumors treated with ICI therapy in order to support resistance by differentiating into immunosuppressive cells. 4T1 breast carcinoma models were generated in our lab, demonstrating response or lack of response to anti-PD1 therapy. GR1+ cells were then isolated and underwent a single cell RNA sequencing (scRNAseq). The transcriptomic data generated is the basis of the bioinformatic analysis. Two main clusters were observed and their classification was broadly verified by using known monocytic (Cd45,Cd11b,Ly6c1) and granulocytic (Cd45,Cd11b,Ly6g) marker genes. Then, focusing specifically on the monocyte derived cluster, a few sub-clusters were identified: MDP-like (Cx3cr1,Csf1r,Ly86,Spi1,Irf8); monocyte progenitors (Batf3,Nr4a1,Klf4,Cebpa); M1-like (Il6,Thbs1,Inhba,Ptgs2) and M2-like (Cd163,Il10,Cbr2,Lyve1). Our initial analysis demonstrated that MDPs accumulate in anti-PD1 treated tumors. Our next goals are to study whether the MDPs can differentiate in M2 macrophages and examine their abundance in tumors that are either resistance or sensitive to immunotherapy.