A single-cell atlas of bone marrow B cells reveals defective central B-cell tolerance in immune thrombocytopenia.

Immune thrombocytopenia (ITP) is characterized by the overproduction of antiplatelet autoantibodies. Although B-cell depletion therapies show promise in ITP, their high relapse rates suggest a potential de novo breakdown of tolerance during an early stage of B-cell development. Here, we investigated how central B-cell tolerance mechanisms affect autoantibody production in ITP. Paired single-cell RNA/B-cell receptor (BCR) sequencing and bulk BCR sequencing revealed reduced V-J genomic distances in immunoglobulin kappa-chain (IGK) genes within bone marrow and peripheral B cells from patients with ITP, along with decreased expression of recombination-activating gene in the immature B cells, suggesting insufficient receptor editing. Single-cell antibody cloning demonstrated increased autoreactive and polyreactive naïve B cells in ITP, indicating defective central B-cell tolerance. Through an in vivo study, we established a causal link between receptor editing defects and antiplatelet antibody production, validating the immature B-cell stage as the key phase of dysregulation. These findings suggest that insufficient receptor editing of immature B cells triggers central B-cell tolerance deficiency and autoantibody accumulation in ITP.