Myeloma Genomics and Microenvironment and immune profiling
Category: Myeloma Genomics and Microenvironment and immune profiling
Stromal cell dysfunction and chronic inflammation characterize the Multiple Myeloma induced vertebral fracture
Mette B. Levring, MD (she/her/hers)
PhD student
Univeristy of Southern Denmark
Vertebral fractures are common complications in benign osteoporosis (OP) and multiple myeloma (MM). Following fracture and tissue injury, there is an orchestrated balance of initial inflammation, followed by resolution of inflammation and secondary bone healing. In MM, malignant plasma cells induce chronic bone marrow inflammation and deregulation of immune and bone remodeling cell interactions. However, there is a lack of knowledge regarding the abnormal microenvironment’s response to fracture. Thus, we explored the immune response, stromal cell function, and bone-forming capacity directly at the fracture site in MM-induced vertebral fractures.
Methods: Bone marrow aspirates and bone biopsies were collected from the fracture site of 38 MM and 12 OP patients undergoing vertebroplasty. Explant cultures of osteoblastic cells were established from fresh bone biopsies and characterized by their proliferation capacity, and ability to form mineralized matrix. Formalin-fixed, decalcified, paraffin-embedded, sectioned bone biopsies were Masson’s Trichrome stained, and analyzed for signs of sclerotic bone formation. RNA was extracted from CD138+ depleted bone marrow cells, and whole mRNA transcripts sequenced. Bone marrow cells from 3 MM and 3 OP patients underwent single-cell sequencing using the 10X Chromium Next GEM 3' protocol.
Results: Cultured osteoblastic cells from MM patients had reduced proliferation capacity (p = 0.013), and ability to form mineralized matrix (p = 0.044) in comparison to OP. Histomorphometric analysis revealed high variation in sclerotic bone formation in the fracture between patients (range 0-92% of total bone area), but with no significant difference between MM and OP. Gene set enrichment analysis of CD138-depleted bulk transcriptomic data revealed enriched pathways of innate immunity and cytokine signaling such as Interferon Gamma Response ([STRING], p < 10-21), TNFα signaling via NF-κB (p < 10-18), Interferon Alpha Response (p < 10-17), and Complement System (p < 10-15) in MM. Single-cell data supported differential expression of inflammatory cytokines, with a two to threefold increase in CD14+ and CD16+ monocytes, and upregulation of complement components 1q A, B, and C (10-9 < p < 10-4). Likewise, TNFα and IFN-inducible response genes were particularly enriched in cytotoxic CD8+ T-cells, e.g, TNF, NFKB1, IFIT1–3, and IFIH1 (Hallmark_TNFα_Signaling_via_NFKB [MSigDB], p < 10-11, Hallmark Interferon Gamma Response [MSigDB], p < 10-16, Interferon Signaling [Reactome Pathways, STRING], p < 10-9).
Conclusions: Our findings reveal a dysregulated bone marrow microenvironment in MM vertebral fractures, characterized by chronic inflammatory activity and reduced osteoblast function. Despite this, new bone formation is present in the majority of patients, indicating preserved bone formation capacity. Ongoing studies and in-depth analysis will further explore regulators of immune and bone activity in MM-induced fractures.