postgraduate Institute of Hematology & Blood Diseases Hospital, Chinese Academy of Medical Science & Peking Union Medical College Tianjin, Tianjin, China (People's Republic)
Introduction: A growing body of evidence has indicated impaired function or compositional changes of monocytes in inflammatory disorders, such as acute respiratory syndrome and covid-19. In multiple myeloma (MM) tumor microenvironment, activation of type I interferon pathway and dysregulated expression of major histocompatibility complex type II genes are observed in classical monocytes, which result in loss of antigen presentation of monocytes. The proportions of BAFF+PD-L1+ monocytes in the bone marrow also correlate with survival of myeloma patients following chimeric antigen-receptor T cell therapy. Nevertheless, the mechanisms underlying monocytes defects in MM remain poorly addressed, at least in part by the lack of large scale scRNA-seq studies.
Methods: To resolve the heterogeneous bone marrow (BM) and peripheral blood (PB) monocyte subpopulations and their transcriptional factors between healthy donors (HD) and MM patients. We performed scRNA-seq on monocytes of 7 newly diagnosed MM (NDMM) patients and 12 HD. Specifically, 3 and 5 BM samples and 9 and 7 PB samples of 12 HD and 7 NDMM patients were obtained and sequenced.
Results: Here, we employed scRNA-seq technology to systematically analyze 26,683 BM and 82,328 circulating monocytes, and genetically defined their subpopulations. We constructed a precise atlas of human PB and BM monocytes, identified seven subpopulations in both BM and PB—including S100A12, HLA, ISG15, CD16, proinflammatory, and intermediate in both BM and PB; megakaryocyte-like in PB; and proliferating subset in BM. Differential expression analysis on the BM and PB monocytes showed that a large number of type I interferon (IFN) signaling pathway genes (e.g. IFI27, IFI6, ISG15) were overexpressed in MM compared with HD. Genes encoding major complement system components and class II major histocompatibility complex molecules (MHC class II) were more highly expressed in MM compared to HD, indicating higher inflammatory and phagocytic potential of MM monocytes. However, relative to HD, T-cell attraction-related genes (e.g. CCL3 and CCL4) were markedly downregulated in MM, and T-cell suppression-related genes (e.g. IDO1, CD274 and PDCD1LG2) were markedly upregulated in MM. Furthermore, we identified two monocyte differentiation pathways in both BM and PB, and discovered that BM monocyte feature type I IFN-associated alterations in differentiation in patients with MM as well as dysregulated patterns at transcriptome. Finally, we included 10 MM patients as a validation cohort, by tracking the alterations in transcriptome and differentiation during treatment using scRNA-seq. Our results indicated that type I IFN signaling pathway activation and alterations in differentiation was partially alleviated for BM monocytes in MM by antitumor therapy.
Conclusions: Our results provided further insight into transcriptional and differentiation alterations occurring in the BM and PB monocytes from patients with MM and explored mechanisms of immune evasion associated with monocytes.
