Single‐cell atlas of the immune microenvironment reveals macrophage reprogramming and the potential dual macrophage‐targeted strategy in multiple myeloma

The tumour microenvironment (TME) plays a critical role in disease progression in multiple myeloma (MM). This study aimed to present an atlas of MM-TME in disease progression and explore TME-directed therapeutic strategies. We performed single-cell RNA sequencing (scRNAseq) in samples from different disease stages. We validated the findings by bulk RNAseq, flow cytometry (FCM) and in vitro and in vivo functional experiments. We delineated a compromised TME during disease progression, characterized by enrichment of exhausted NK cells and CD8+ T cells and reprogramming of macrophages (MPs). The reprogrammed tumour-associated MPs (TAMs) displayed a mixed phenotype showing both M1 and M2 features, with two TAM clusters exclusively present in the MM stage showing higher M2 scores. We validated the mixed M1/M2 phenotype in TAMs in a clinical cohort and verified phagocytic dysfunction in reprogrammed TAMs. Cellular interaction analysis identified two enriched ligand-receptor pairs between MPs and malignant plasma cells (PCs), including the SIRPA-CD47 pathway suppressing phagocytosis and the CD74-MIF (macrophage inhibitory factor) reshaping the phenotype of MPs. The expression of CD47 and MIF correlated with disease progression and adverse outcomes. We designed a dual-MP-targeted strategy by combining an anti-CD47 antibody and MIF inhibitor to activate phagocytosis and repolarize MP to a functional phenotype and proved its potent antitumour effect in vitro and in vivo. We drafted alterations in MM-TME during disease progression and unravelled TAM's reprogramming. The dual MP-targeted approach blocking both CD47 and MIF showed potent antitumour effects.