Single-cell transcriptomics reveals erbb-driven clonal evolution and immune evasion in plasma cell leukemia

Abstract

Abstract Introduction:Plasma cell leukemia (PCL) is a rare yet highly aggressive form of plasma cell dyscrasia, defined by high tumor burden, frequent extramedullary dissemination, and rapid clinical progression. Compared with multiple myeloma (MM), PCL exhibits greater genomic instability, immune escape, and a more hostile bone marrow microenvironment, resulting in poor therapeutic responses and short survival. While prior bulk sequencing and cytogenetic studies have revealed select features of PCL biology, a high-resolution, single-cell dissection of its malignant and immune landscape remains lacking. In particular, how PCL reshapes its tumor microenvironment (TME) to support immune evasion and systemic dissemination has not been fully elucidated. Aim: This study aims to characterize the transcriptional, genomic, and immunologic features of PCL at single-cell resolution. We sought to identify PCL-specific oncogenic drivers, immune evasion mechanisms, and intercellular communication circuits that differentiate PCL from MM and healthy bone marrow, with a particular focus on the ERBB signaling axis and T/NK cell dysfunction. Methods:Bone marrow samples were collected from three newly diagnosed primary PCL patients and one MM patient from our center, These specimens were subjected to 10x Genomics 3' single-cell sequencing. Additionally, three normal bone marrow and three MM bone marrow samples retrieved from the Gene Expression Omnibus (GEO) database were incorporated for integrative analysis. Comparative analyses were conducted to assess clonal architecture, transcriptional programs, and immune landscape. Key findings were validated using qPCR and publicly available clinical and transcriptomic datasets. Results:After quality control filtering, we obtained single-cell transcriptome data from 49,059 high-quality mononuclear cells. Based on canonical marker gene expression, we identified eight major cell populations: plasma cells, myeloid cells, T cells, NK cells, NKT cells , B cells , dendritic cells, and megakaryocytes. This included 11,485 PCs, 3,466 B cells, and 33,603 other immune cells. PCL plasma cells demonstrated significantly higher CNV burden than MM, with recurrent gains on chr3q, chr9q, chr15q, and chr18q. Amplification of oncogenes including BCL2, MCL1, PIK3CA, KRAS, and BRAF suggested enhanced apoptotic resistance, proliferative signaling, and immune evasion. Transcriptomic profiling revealed PCL-specific upregulation of the ERBB signaling axis, including ERBB4, EPHA6, and downstream effectors KRAS, SOS1/2, and MAPK1/8. ERBB pathway enrichment was confirmed by GSEA and pseudotime analysis revealed persistent upregulation along the malignant differentiation trajectory. High expression of ERBB pathway genes correlated with significantly worse overall survival in the CoMMpass cohort. qRT-PCR validation in patient samples confirmed significant overexpression of ERBB-related genes in PCL. Analysis of over 23,000 T/NK lineage cells identified 21 subtypes. In PCL, cytotoxic subsets such as CD8⁺ naive, CD56dim NK, and NKT cells were notably reduced or exhibited elevated exhaustion scores. NKT cells showed elevated IFN-response genes but downregulation of cytotoxic effectors, indicating a paradoxical “hyperactivated-yet-dysfunctional” state. CellChat analysis revealed extensive reprogramming of ligand-receptor interactions in PCL. Compared to ND and MM, PCL plasma cells engaged in enriched immunosuppressive and adhesive signaling via MIF, TGF-β, CD86, NOTCH, and APRIL axes. Enhanced communication with CD8⁺ T and NKT cells may promote chronic stimulation and immune exhaustion, supporting tumor immune escape and dissemination. Conclusion: This study presents the first high-resolution single-cell atlas of primary PCL, revealing that enhanced ERBB signaling, elevated CNV burden, and profound immune dysfunction collectively drive its aggressive clinical behavior. Malignant plasma cells in PCL not only acquire stem-like features and oncogenic pathway activation but also actively remodel the immune microenvironment via suppressive signaling, leading to T/NK cell exhaustion and impaired surveillance. These findings uncover actionable targets such as ERBB4/PI3K/MAPK and immune exhaustion pathways, offering a molecular framework for future precision therapy in PCL. Further functional validation and clinical translation of these discoveries are warranted.