Immunoglobulin light chain amyloidosis (AL amyloidosis) is characterized by the presence of B cells producing amyloidogenic immunoglobulin light chains (LCs). The low frequency of aberrant B cells in AL is often masked by a polyclonal B cell background, making it difficult for treatment. We analyzed the single-cell RNA sequencing data from GEO database to compare the plasma cell (PCs) in four individuals with AL amyloidosis, one AL subject after treatment, and six healthy controls. High interindividual variability in AL-derived PCs in their expression pattern of known overexpressed genes in multiple myeloma and their usage of V regions in LCs was demonstrated. We also found overexpression of MHC class I molecules as one of the common features of clonal PCs in individuals with AL amyloidosis. Significantly reduced frequencies of circulating natural killer (NK) cells were also observed in a small cohort of AL patients when compared to healthy controls. These data demonstrate that aberrant PCs in AL has a highly diverse transcriptome, an upregulation of MHC, and a dampened capability of immunosurveillance by reduction of circulating NK frequencies. The analysis of clonal PCs at single cell level may provide a better approach for precise molecular profiling and diagnosis of AL amyloidosis. Keywords Immunoglobulin light chain amyloidosis • Single-cell RNA sequencing • Plasma cells • Natural killer cells Abbreviations AL Immunoglobulin light chain BM Bone marrow DEG Differentially expressed gene ER Endoplasmic reticulum LC Light chain MGUS Monoclonal gammopathy of undetermined significance MM Multiple myeloma NK Natural killer PC Plasma cell scRNA-seq Single-cell RNA sequencing UMAP Uniform manifold approximation and projection Yujia Wang and Lushuang Xu have contributed equally to this work.
Amyloid light‐chain (AL) is characterized by the presence of small, poorly proliferating plasma cell clones with the production and deposition of light chains into tissues. T cell changes within the tumour microenvironment in AL are poorly understood. By sequencing at a single‐cell level of CD3 + T cells purified from bone marrow (BM) and blood of newly diagnosed AL patients before and after a combination of daratumumab with cyclophosphamide, bortezomib, and dexamethasone (Dara‐BCD), we analysed the transcriptomic features of T cells and found an expansion, activation and type I cytokine upregulation in BM and circulating T cells after the treatment. More prominent changes were shown in CD8 + T cells. In particular, we found the presence of CD8 + BM resident memory T cells (T RM ) with high expression of inhibitory molecules in AL patients at diagnosis. After Dara‐BCD, these T RM cells were quickly activated with downregulation of suppressive molecules and upregulation of IFNG expression. These data collectively demonstrate that Dara‐based therapy in patients with AL amyloidosis promotes anti‐tumour T cell responses. The similar transcriptomic features of BM and circulating T cells before and after therapy further provide a less invasive approach for molecular monitoring of T cell response in AL amyloidosis.
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