2 BCR or NOT 2 BCR - receptor dilution: a unique mechanism for preventing the development of holes in the protective B cell repertoire

scRNA+TCR+BCR-seq revealed the proportions and gene expression patterns of dual receptor T and B lymphocytes in NPC and NLH

While the relationship between single receptor lymphocytes and cancer has been deeply researched, the origin and biological roles of dual receptor lymphocytes in tumor microenvironment (TME) remain largely unknown. And since nasopharyngeal carcinoma (NPC) is a type of cancer closely associated with immune infiltration, studying the TME of NPC holds particular significance. Utilizing single-cell RNA sequencing combined with T cell receptor (TCR) and B cell receptor (BCR) sequencing (scRNA + TCR + BCR-seq), we analyzed data from 7 patients with NPC and 3 patients with nasopharyngeal lymphatic hyperplasia (NLH). In our research, it was firstly found that the presence of dual receptor lymphocytes in both the TME of NPC and the inflammatory environment of NLH. We also confirmed their clonal expansion, suggesting their potential involvement in the immune response. Subsequently, we further discovered the lineage and the pairing characteristics. It was found that the dual receptor lymphocytes in NPC and NLH mainly originate from memory cells, and the predominant pairing type for dual TCR was β+α1+α2 and dual BCR was heavy+κ+λ. By further analyzing their gene expression, we compared the function of dual receptor cells with single receptor cells in the context of both NPC and NLH. This groundbreaking research has enhanced our comprehension of the features of dual-receptor cells and has contributed to a better understanding of the TME in NPC. By comparing with NLH, it illuminates part of the alterations in the process of malignant transformation in NPC. These findings present the potential to acquire improved diagnostic markers and treatment modalities.

scBCR-seq revealed a special and novel IG H&L V(D)J allelic inclusion rearrangement and the high proportion dual BCR expressing B cells

Since the initial report of V (D) J "allelic exclusion/inclusion" (allelic exclusion rearrangement or allelic inclusion rearrangement) and the concept of the "dual B cell receptor (BCR)" in 1961, despite ongoing discoveries, the precise proportion and source mechanism of dual BCR under physiological conditions have been puzzling immuologists. This study takes advantage of the single cell B cell receptor sequencing (scBCR-seq) technology, which can perfectly match the heavy and light chains of BCR at the level of a single B cell, and obtain the full length mRNA sequence of the complementary determining region 3 (CDR3). Through analyzing the pairing of functional IGH (immunoglobulin heavy chain) and IGL (immunoglobulin light chain) in single B cell from both human and mouse bone marrow and peripheral blood, it was observed that dual BCR B cells exhibit stable and high levels of expression. Among them, the human bone marrow and peripheral blood contain about 10% dual (or multiple) BCR B cells, while in mouse peripheral blood and bone marrow memory B cells, this proportion reaches around 20%. At the same time, we innovatively found that in each research sample of humans and mice, there are three (or more) functional rearrangements (mRNA level) of a single chain in a single B cell. By analyzing the position, direction and other compositional characteristics of the V(D)J gene family, we found that at least two (or more) of them are derived from over two (or more) specific allelic inclusion rearrangements of a single chromosome (mRNA molecular level evidence), our findings also highlighted the necessity of classified single cell sequencing data based on single, dual (or multiple) and cannot be assembled into BCR when analyzing the B cell repertoire. The results of this article provides new methods and modeling references for evaluating the proportion and source mechanisms of dual BCR B cells, as well as potential significance of allelic inclusion (exclusion escape) of V(D)J rearrangement.

Light chain skewing in autoantibodies and B-cell receptors of the citrullinated antigen-binding B-cell response in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease affecting 1% of the world population. RA is associated with the presence of autoantibodies, of which anti-citrullinated protein antibodies (ACPA) are most prominent. ACPA are produced by citrullinated antigen-binding B cells that have presumably survived tolerance checkpoints. So far, it is unclear how and when such autoreactive B cells emerge. Light chain (LC) rearrangement and mutation rates can be informative with regard to selection steps during B-cell development. Therefore, we studied LC characteristics of ACPA-expressing B cells and secreted ACPA with the aim to better understand the development of this disease-specific, autoreactive B-cell response. Paired ACPA-IgG and ACPA-depleted IgG were isolated from serum (n = 87) and synovial fluid (SF, n = 21) of patients with established RA. We determined the LC composition for each fraction by ELISA using kappa(Igκ)- and lambda(Igλ) LC-specific antibodies. Cellular LC expression was determined using flow cytometry. In addition, we used a B-cell receptor (BCR)-specific PCR to obtain LC variable region sequences of citrullinated antigen- and tetanus toxoid (TT)-binding B cells. In serum, we observed an increased frequency of lambda LC in ACPA-IgG (1.64:1) compared to control IgG (2.03:1) and to the κ/λ ratio reported for healthy individuals (2:1). A similar trend towards higher frequencies of lambda LCs was observed for ACPA-IgG in SF (1.84:1). Additionally, the percentage of Igλ-expressing B cells was higher for citrullinated antigen-binding B cells (51%) compared to TT-specific (43%) and total CD19+CD20+ B cells (36%). Moreover, an increased Igλ percentage was observed in BCR-sequences derived from ACPA-expressing (49%) compared to TT-specific B cells (34%). Taken together, we report an enhanced frequency of lambda LCs in the secreted ACPA-IgG repertoire and, on the cellular level, in BCR sequences of ACPA-expressing B cells compared to control. This skewing in the autoreactive B-cell repertoire could reflect a process of active selection.