Monocyte-mediated metabolic rewiring via CD31-CD38 interactions promotes growth and drug-resistance in multiple myeloma.

Multiple myeloma (MM) cells interact with different components of the bone marrow (BM) microenvironment, which plays a critical role in MM progression and confers resistance to therapy. Here, we report that monocytes actively control MM cell metabolism by transferring mitochondria to MM cells, thereby increasing their mitochondrial content. Transfer of mitochondria required the expression of CD38 on the surface of MM cells and its ligand CD31 (PECAM-1) on monocytes. The mitochondrial increase in MM cells induced a boost in oxidative phosphorylation (OXPHOS). This monocyte-mediated metabolic adjustment promoted growth, motility, and drug-resistance in both MM cell lines and primary MM cells. Notably, the CD38-targeting monoclonal antibody daratumumab prevented mitochondrial transfer via blocking CD38 on MM cells. Furthermore, in the presence of daratumumab, monocytes acquired a divergent role and obtained mitochondria from MM cells through the process of trogocytosis. Daratumumab-mediated disruption of mitochondrial transfer reduced the mitochondrial content in MM cells, prevented the boost in OXPHOS, significantly impaired MM cell growth and migration, and mitigated drug-resistance. In conclusion, we reveal a crucial metabolic interplay between monocytes and MM cells within the BM microenvironment that promotes tumor growth and induces therapy resistance, providing the rationale for treatment strategies that combine targeting tumor metabolism with existing anti-MM agents.