Abstract 6848: Analysis of the bone microenvironment cells by single cell transcriptomics reveals altered features in multiple myeloma patients compared to pre-malignant monoclonal gammopathies

Abstract Multiple myeloma (MM) is a malignant plasma cell dyscrasia that can be preceded by monoclonal gammopathy of undetermined significance (MGUS) and smoldering MM (SMM). How the bone microenvironment (BME) changes and contributes to tumoral progression in MM remains unresolved. Published data on BME are mainly produced in vitro and few data are on MGUS/SMM patients. Up to date, no single-cell RNA sequencing database of the BME cells has been described in MM. The aim of this project was to characterize for the first time at single cell level, the BME in patients with newly diagnosed MM (MMD) and MGUS/SMM to identify alterations involved in tumoral progression. From 15 bone biopsies of MMD, MGUS and SMM patients, we depleted CD235a+, CD45+, CD31+, and CD138+ cells to enrich the rare BME non-hemopoietic cells. The CD45-CD31-CD235a-CD138- cells were analyzed by scRNAseq. Data were generated on Chromium 10X Genomics. Cellranger and Seurat pipeline in R software has been used. Cell identities were assigned by manual curation. The trajectory analysis has been made by Monocle3. Decouple R and FindMarkers were used to compare pathways, and differential gene expression (DGE) of the samples throughout the different conditions. A total of 35723 cells were profiled. We identified 13 BME cell type clusters: 7 mesenchymal stromal cells (MSCs) clusters (proliferating MSC, MSC DDK-OPG-, MSC DKK+, MSC RUNX2-, MSC OPG+, MSC Osteogenic, Perivascular MSC) and 6 osteoblasts (OBs) clusters (OB precursor, OB precursor LEPR+, OB BGLAP+, OB SPP1+, OB NFkB+, OB late). Psdeudotime analyses highlighted a complex trajectory of differentiation from more immature cell clusters (proliferating MSC) to late OB cluster, confirming the ability of the dataset to snapshot the in vivo complexity of BME and we highlighted an alteration of the MSCs clusters trajectories starting in SMM samples till a disruption in MM. Pathway analyses, in MMD compared to MGUS/SMM, revealed an upregulation of VEGF and PI3K activity in proliferating MSC, perivascular MSC and OB clusters. TRAIL pathway activity, known to suppress MM cell proliferation, was upregulated in MSC osteogenic and OB BGLAP+ in MGUS. Finally, DGE analyses revealed the modulation of different genes, many not yet described in MM. MGUS MSCs clusters showed an upregulation of FBLN1, SERPNF1 and MMD MSCs clusters dramatically downregulated WISP2 and upregulated SRGN, involved in MM cell proliferation. Interestingly, in SMM samples, we reported an upregulation of genes involved both in the promotion of osteoblastogenesis (SCARA3, SPON2) and inhibition (GREM1), likely underling the attempt to contrast the establishment of altered BME, characteristic of MM. Our approach is able to dissect the complex organization of the BME and to highlight at single cells level the alterations of the BME in patients with MM compared to MGUS and SMM. Citation Format: Paola Storti, Tommaso Torelli, Cristina Manferdini, Denise Toscani, Alessandro Guidi, Rosanna Vescovini, Nicolas Thomas Iannozzi, Benedetta Dalla Palma, Matteo Scita, Federica Librale, Stefania Ricci, Vincenzo Raimondi, Oxana Lungu, Giannalisa Todaro, Gabriella Sammarelli, Emanuela Aleo, Gina Lisignoli, Luca Agnelli, Nicola Giuliani. Analysis of the bone microenvironment cells by single cell transcriptomics reveals altered features in multiple myeloma patients compared to pre-malignant monoclonal gammopathies abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6848.