Distinct mechanisms of dysfunctional antigen-presenting DCs and monocytes by single-cell sequencing in multiple
Jinxing Jiang1, Jing Xiang1, Mengping Chen1
1Department of Hematology, Ren Ji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
Abstract:
Multiple myeloma (MM) is an incurable plasma cell malignancy with the hallmark of immunodeficiency, including dysfunction of T cells, NK cells, and APCs. Dysfunctional APCs have been reported to play a key role in promoting MM progression. However, the molecular mechanisms remain elusive. Here, single-cell transcriptome analysis of dendritic cells (DC) and monocytes from 10 MM patients and three healthy volunteers was performed. Both DCs and monocytes were divided into five distinct clusters, respectively. Among them, monocyte-derived DCs (mono-DC) were shown to develop from intermediate monocytes (IM) via trajectory analysis. Functional analysis showed that, compared with healthy controls, conventional DC2 (cDC2), mono-DC, and IM of MM patients exhibited impaired antigen processing and presentation capacity. Moreover, reduced regulon activity of interferon regulatory factor 1 (IRF1) was found in cDC2, mono-DC and IM of MM patients according to single-cell regulatory network inference and clustering (SCENIC) analysis, while the downstream mechanisms were distinct. Specifically in MM patients, cathepsin S (CTSS) was markedly downregulated in cDC2, major histocompatibility complex (MHC) class II transactivator (CIITA) was significantly decreased in IM, in addition both CTSS and CIITA were downregulated in mono-DC based on differentially expressed genes analysis. In vitro study validated that knockdown of Irf1 downregulated Ctss and Ciita respectively in mouse DC cell line DC2.4 and mouse monocyte/macrophage cell line RAW264.7, which ultimately inhibited proliferation of CD4+ T cells after being cocultured with DC2.4 or RAW264.7 cells. This current study unveils the distinct mechanisms of cDC2, IM, and mono-DC function impairment in MM, offering new insight into the pathogenesis of immunodeficiency.
Insights
Multiple myeloma impairs antigen-presenting cells, including dendritic cells (DCs) and monocytes. Reduced interferon regulatory factor 1 (IRF1) activity in these cells hinders T-cell proliferation, contributing to immunodeficiency in multiple myeloma.
Area of Science:
- Immunology
- Oncology
- Cell Biology
Background:
- Multiple myeloma (MM) is an incurable cancer characterized by immunodeficiency, particularly involving dysfunctional antigen-presenting cells (APCs).
- The precise molecular mechanisms underlying APC dysfunction in MM remain largely unknown, hindering the development of targeted therapies.
Purpose of the Study:
- To investigate the molecular mechanisms of dendritic cell (DC) and monocyte dysfunction in multiple myeloma (MM) patients using single-cell transcriptome analysis.
- To identify specific molecular pathways and regulatory networks responsible for impaired antigen processing and presentation in MM-associated APCs.
Main Methods:
- Single-cell transcriptome analysis was performed on dendritic cells (DCs) and monocytes from 10 MM patients and 3 healthy volunteers.
- Trajectory analysis was used to determine developmental relationships between cell types, such as monocyte-derived DCs (mono-DCs) from intermediate monocytes (IMs).
- Single-cell regulatory network inference and clustering (SCENIC) analysis was employed to assess regulon activity, specifically for interferon regulatory factor 1 (IRF1).
Main Results:
- MM patients exhibited impaired antigen processing and presentation capacity in conventional DC2 (cDC2), mono-DCs, and IMs compared to healthy controls.
- Reduced IRF1 regulon activity was observed in cDC2, mono-DCs, and IMs from MM patients, with distinct downstream effects.
- Key genes involved in antigen presentation, cathepsin S (CTSS) and major histocompatibility complex (MHC) class II transactivator (CIITA), were downregulated in specific cell populations of MM patients.
- In vitro studies confirmed that IRF1 knockdown reduced CTSS and CIITA expression and subsequently inhibited CD4+ T-cell proliferation.
Conclusions:
- This study reveals distinct molecular mechanisms underlying the functional impairment of cDC2, IM, and mono-DC populations in multiple myeloma.
- The findings highlight the critical role of IRF1 signaling in APC function and T-cell responses within the MM microenvironment.
- Understanding these mechanisms provides novel insights into MM pathogenesis and suggests potential therapeutic targets for restoring immune function.
