Abstract 3815: Investigating the role of bone marrow microenvironment dysregulation at remission in disease outlook of multiple myeloma
Authors: Wang Julia T. , Fiala Mark , Fortier Julie , Liu Ruiyang , Jayasinghe Reyka , Vij Ravi , Ding Li 
Published: June 2022

Abstract
Multiple myeloma (MM) is a cancer characterized by the unchecked proliferation of antibody-secreting plasma cells (PCs), which to date remains incurable despite therapeutic advancements. The idea that deeper tumor clearance leads to better outcomes is widely accepted in MM treatment: minimal residual disease (MRD) testing, whereby ultra-sensitive sequencing or fluorescence-based cytometric detection of the clonal immunoglobulin secreted by tumor PCs, has been found to be the strongest independent prognostic factor when predicting survival. However, MRD status remains an imperfect predictor. As PCs have a well-defined physiological niche within the bone marrow (BM), and patients often exhibit immunosuppressive BM dysregulation, we investigate the presence of BM microenvironment signatures present at remission that may influence clinical outcomes insufficiently explained by tumor risk strata or MRD status. We conducted 3’ single-cell RNA sequencing of 36 remission, 8 primary diagnosis, and 3 relapse whole BM aspirates taken from 35 patients enrolled in an ongoing clinical trial evaluating a treatment regimen consisting of ixazomib, lenalidomide, and dexamethasone (IRD). 19 of 35 patients were MRD+ at remission; among these, 6 have been reported as having poor outcome (PO; progression-free survival &lt;2.5yrs post sample collection), 12 have had average outcomes (AO; PFS &gt;2.5yrs), and 1 is awaiting assessment. The remaining 16 patients were MRD- at remission, 6 of whom had poor outcome, 7 average, and 3 awaiting assessment. Preliminary analysis of 43 samples have yielded an average capture of 8,620 cells per sample with 1,247 median genes per cell. In comparing 3 PO to 8 AO MRD- remission samples, we see clear polarity between PO and AO cells in every major immune lineage, with a majority of clusters being predominantly (&gt;80%) made of either PO or AO cells. Surprisingly, T, NK, and B cells from AO samples exhibit FOS/JUN upregulation relative to those from PO samples, indicative of AP-1 transcription factor activity that is typically associated with cell proliferation. PO samples also exhibited signs of active cytotoxicity, including upregulated granzymes H and B and IL7R in T and NK cells. Sizeable PC populations were detected in several MRD- remission samples with subpopulation heterogeneity in the expression of MM marker genes; comparison against PCs isolated from healthy donor BM suggests possible persistence of disease phenotypes not captured by MRD testing. We further investigate BM microenvironment evolution between primary diagnosis, remission, and relapse timepoints to elucidate changes in response to tumor clearance. Overall, this study enhances our understanding of how immune surveillance and interaction may influence treatment response in MM.
Citation Format: Julia T. Wang, Mark Fiala, Julie Fortier, Ruiyang Liu, Reyka Jayasinghe, Ravi Vij, Li Ding. Investigating the role of bone marrow microenvironment dysregulation at remission in disease outlook of multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3815.