Stage 1 type 1 diabetes memory B lymphocytes transcriptionally differ from healthy controls and harbor insulin-binding specificities

Autoreactive B cell activity defines the earliest detectable stage (Stage 1) of type 1 diabetes (T1D) but is incompletely understood, particularly for B cells reactive against the key T1D autoantigen, insulin. To test whether Stage 1 T1D B cells are transcriptionally rewired compared to healthy individuals, we performed single-cell transcriptional, phenotypic, and immune repertoire profiling of CD19+ cells isolated from the peripheral blood of Stage 1 T1D individuals, identified via Type 1 Diabetes TrialNet as being positive for ≥ 2/5 islet autoantibodies, and healthy controls. Stage 1 T1D memory B cells upregulated n = 122 genes compared to healthy controls, including genes involved in actin cytoskeleton rearrangement, B cell receptor (BCR) signaling, and antigen presentation, and exhibited reduced BCR somatic hypermutation, particularly in atypical-like memory B cells. Clonally expanded B cells in the atypical-like memory subset of Stage 1 T1D individuals exhibited avidity driven insulin-binding specificities, without polyreactivity to HEp-2 cell autoantigens. Insulin-binding B cells showed non-significant upregulation of genes involved in key B cell functions. Our findings highlight transcriptional and BCR-repertoire differences in Stage 1 T1D B cells with potential for optimization as future screening tools to identify rare, autoreactive B cells and biomarkers of T1D progression.