Single-cell profiling uncovers extracellular vesicle-associated malignant plasma cell subpopulations driving multiple myeloma progression.

Background: Multiple myeloma (MM) is a heterogeneous hematological malignancy characterized by the clonal proliferation of plasma cells in the bone marrow, with distinct subtypes including smoldering MM (SMM), newly diagnosed MM (NDMM), and relapsed/refractory MM (RRMM). Despite therapeutic advances, outcomes remain unsatisfactory, especially for RRMM, due to unclear heterogeneity, progression mechanisms, and crosstalk between tumor cells and the bone marrow microenvironment (BMME) via direct interactions or extracellular vesicles (EVs). Methods: Single-cell RNA sequencing (scRNA-seq) was performed on bone marrow samples from 12 MM patients, and major cell types were identified. Plasma cells were subjected to re-clustering to explore subpopulation heterogeneity. Functional enrichment analysis of differentially expressed genes (DEGs) was conducted. Cellular stemness was evaluated by CytoTRACE, and developmental trajectories were inferred via Monocle and Slingshot. Cell-cell communication was analyzed by CellChat, while transcription factor (TF) regulatory networks were identified through SCENIC analysis. Metabolic pathway activity was also assessed. Finally, loss-of-function experiments (siRNA-mediated ASS1 knockdown) were conducted to validate its functional role. Results: The analysis identified 7 major cell types. Plasma cells were further stratified into 6 subpopulations (C0- Conclusion: Our study delineates MM heterogeneity, developmental dynamics, and regulatory networks at the single-cell level.