Single-cell profiling reveals MIF-mediated immune evasion and CD8 + T cell exhaustion in relapsed multiple myeloma.

Multiple myeloma (MM) is a heterogeneous hematologic cancer marked by clonal plasma cell expansion in the bone marrow. Although treatments have improved, relapse remains common due to clonal evolution, tumor microenvironment changes, ultimately leading to drug resistance. This study utilized single-cell RNA sequencing data analysis to explore immune microenvironment dynamics during MM progression and relapse, aiming to uncover key pathways and cellular interactions correlated with disease relapse. ScRNA-seq data from 20 MM patients (10 primary, 2 remission, 8 relapsed) from the GEO dataset GSE223060 were analyzed. After quality control and batch correction, cells were clustered and annotated. Differential gene expression and functional enrichment analyses were conducted to explore cellular functions. Pseudotime analysis was used to trace plasma cell differentiation, and cell-cell communication was analyzed. Immunohistochemistry and flow cytometry were used for validation.60,234 high-quality single cells were classified into 12 distinct populations. Relapsed MM showed increased T cell infiltration and decreased plasma cells. Relapsed samples had more regulatory T cells (Tregs) and impaired CD8 + T cells. MIF was identified as a key regulator in plasma cell evolution, linked to B cell receptor and interferon-alpha signaling. Enhanced MIF pathway activity was noted between plasma cells and CD8 + T cells in relapsed MM. Increased MIF expression was confirmed in relapsed tissues. Our findings reveal profound immune microenvironment remodeling in relapsed MM, characterized by MIF-mediated signaling, NF-κB suppression, and CD8⁺ T cell dysfunction. These results provide new insights into the mechanisms of MM relapse and highlight potential therapeutic targets for preventing disease relapse.