Prospective Evaluation Of Spatial Heterogeneity At Single Cell Resolution In Multiple Myeloma.

8524 Background: Osteolytic lesions (OL) characterize symptomatic multiple myeloma (MM). It is still unclear why plasma cells (PC) cause OL in certain regions of the body while other areas show no signs of bone destruction despite significant bone marrow infiltration. We conducted the first study of single cell RNA sequencing (scRNA-seq) and whole-exome sequencing (WES) of PC obtained from random bone marrow samples (RS) and paired OL. Methods: As part of a prospective clinical trial, patients consented to an imaging-guided biopsy of new OL identified by PET/CT in addition to the RS from the iliac crest. Both samples were acquired in the same session. On the same day PC were isolated using a CD138 positive selection kit and single cell gene expression libraries were generated for scRNA-seq. Frozen PC were subjected to DNA extraction and WES. Results: We sequenced 93569 purified, viable PC from paired samples from 15 different locations in the first 7 consecutive patients (median PC from location: 7203; range 1121-10279). Quality assessment of scRNA-seq data revealed no differences between PC in OL and RS. Based on scRNA-seq, 9-24 different subpopulations of PC in individual patients were identified. Over 90% of clusters found in the RS were also present in corresponding OL suggesting a common ancestor. This was true for patients with overlapping as well as divergent mutational profiles in RS and OL as shown by WES. In each patient we found PC clusters that were predominantly present in OL. Respective clusters were characterized by expression of Wnt-signaling inhibitors like DKK-1, Frzb and sFRP-2 and other genes linked to MM bone disease (HGF, CXCL-12, CCL3). Lysosome-associated membrane protein-like molecule 5 (LAMP5) and J-chain were overexpressed in OL clusters. Analysis of genes (IKZF1 and IKZF3) associated with response to treatment and outcome revealed vast heterogeneity and differences in risk scores (UAMS70 and IFM15) on a single cell level from different locations in individual patients. Conclusions: Our study provides the first evidence that PC from OL have distinct transcriptomic profiles that link site-specific gene expression to development of bone disease and adverse outcome.