High Dimensional Immune Profiling in Smoldering Multiple Myeloma Identifies Novel Organizing Features of the Tumor Microenvironment

Multiple myeloma (MM) is a malignancy of plasma cells that arises from premalignant Monoclonal Gammopathy of Undetermined Significance (MGUS) and often progresses through an asymptomatic Smoldering (SMM) phase lasting months or years before manifesting clinical symptoms warranting therapy. Current research indicates that the tumor microenvironment (TME) in the bone marrow may play a significant role in governing progression to symptomatic disease. Therefore, understanding of the interactions between malignant plasma cells and the TME in early disease states is critical in the pursuit of therapies that will prevent progression to symptomatic disease. We performed high dimensional genomic and immunologic analysis of bone marrow specimens from 73 subjects with SMM. We performed RNA-seq on the malignant plasma cells isolated by anti-CD138 magnetic bead positive selection, mass cytometry (CyTOF) and T cell receptor sequencing (TCR Seq) of CD138-depleted bone marrow mononuclear cells, and proteomics, seromic, and grand serology analysis of bone marrow plasma. These samples and assays provided a broad view of the tumor cells and the cellular and soluble components of the TME. Each of these assays identified self-organizing clusters of subjects, indicating that subgroups of SMM patients shared common characteristics in the tumor or TME populations. We then applied novel bioinformatic methods to compare data from pairs, trios, quartets, and quintets of assays to identify communities of subjects with similar immunologic and genomic characteristics. Integrated analysis of CyTOF, proteomic, and TCR Seq resolved three distinct communities with a high degree of significance. These communities shared distinct cellular and proteomic features that suggested early adaptive, activated adaptive, or innate immune characteristics. These results suggest that the continuum from MGUS to MM does not consist of a single pathway in either the tumor cells or the TME, and that complex interactions ultimately determine progression. This suite of assays (CyTOF, proteomics, and TCR Seq) may be applicable in translational and clinical studies to understand key tumor and immune determinants of SMM and lead to rationally designed therapy to replicate these conditions to prevent progression to symptomatic disease.