Human transitional and IgMlow mature naïve B cells preserve permissive B-cell receptors

Self-reactive B cells are increased in all major stages of peripheral development in Sjögren's disease

Sjögren's disease (SjD) is a chronic autoimmune disorder characterized by increased circulating self-reactive B cells. While many of these self-reactive B cells emerge from the bone marrow, it is not known whether they are excluded from or enriched in specific developmental stages in the periphery. The aim of this study was to determine the immunophenotype of circulating self-reactive B cells in SjD to inform more precise therapeutic targeting. Five major B cell populations: transitional, mature naïve, switched memory, double negative and plasmablasts were single-cell sorted and cultured to produce IgG. Self-reactive IgG was identified by ELISA, flow cytometry of permeabilized HEK293 cells and HEp-2 indirect immunofluorescence. Immunoglobulin heavy chains were sequenced by Sanger and next-generation sequencing. Compared with healthy donor controls (HCs), SjD patients had higher frequencies of naïve and CD21low atypical memory B cell subsets, while antigen-experienced B cells expressed more Ki67 and CD86. B cells recognizing intracellular self-antigens were identified in all stages of peripheral B cell development for SjD and HCs, but frequencies of autoreactive B cells were up to 10-fold higher in SjD. Self-reactive transitional B cells expressed higher surface CD38 and lower surface IgM. An increase in self-reactive B cells throughout peripheral development in SjD compared with HCs suggests that counterselection of autoantibody-bearing B cells during central and peripheral tolerance checkpoints are reduced in SjD. Therapeutic strategies focused on depleting B cells based on B cell receptor specificity rather than the developmental stage would be more efficient to target self-reactive B cells in SjD.

Profiling the broad antibody diversity of lymphatic filariasis immune antibody repertoire by deep sequencing

Lymphatic filariasis is caused by infections of thread-like filarial worms, namely Wuchereria bancrofti, Brugia Malayi and Brugia timori. However, in-depth analysis of the antibody repertoire against Lymphatic filariasis is lacking. Using high-throughput sequencing of antibody repertoires, immunome analysis of IgG (LG) and IgM (LM) repertoires were studied. Despite significant differences between LG and LM in V(D)J gene usage, IGHV4-34, IGHV6-1, IGHD3-10 and IGHJ4 were preferred in both repertoires. The CDR3 in the LG repertoire showed a longer length than LM. Higher SHM level were observed in LG sequences and presence of oligoclonal sequences indicates the extent of clonal expansion. The prevalence of rare clonotypes in LM repertoire depicts the high clonal diversity when compared to LG repertoire. Monoclonal antibodies against closely related parasitic infections were present within the LG repertoire suggesting that immune repertoires may not be as exclusive and biased against the target infection as initially thought. The characterization of the immune repertoire can provide critical insight into the antibody response patterns in disease state, antibody generation process during infections and future antibody designs.

Isolation and characterisation of PR3-specific B cells and their immunoglobulin sequences

BACKGROUND

PR3 autoantibodies are essential to the diagnosis and monitoring of granulomatosus with polyangiitis, but to date no PR3 autoantibody sequences have been published.

OBJECTIVES

To identify and characterise PR3-specific B cells from the peripheral blood of patients with PR3 autoantibodies.

METHODS

Peripheral blood mononuclear cells from seven patients with PR3 autoantibodies were stained with PR3. B cells that bound PR3 underwent single cell sorting, transcriptome sequencing, and their immunoglobulin sequences expressed as antibodies and tested for PR3-specificity by ELISA.

RESULTS

We identified 19 PR3-specific B cells from only one PR3-seropositive patient at a low frequency (0.0075 % of B cells) in the peripheral blood. These were polyclonal, IgG+ and enriched for IgG4, lambda pairing, IGHJ6 gene usage, CDRH3 length, IGHE and CD71 expression. They demonstrated relatively low levels of somatic hypermutation and variably reduced PR3 binding when reverted to germline.

CONCLUSIONS

Identifying PR3-specific B cells in the peripheral blood is possible but challenging and those we did identify exhibited features suggesting that PR3-self reactivity may occur early in B-cell development.

IgD shapes the pre-immune naïve B cell compartment in humans

B cell maturation and immunoglobulin (Ig) repertoire selection are governed by expression of a functional B cell receptor (BCR). Naïve B cells co-express their BCR as IgM and IgD isotype. However, the role of the additionally expressed IgD on naïve B cells is not known. Here we assessed the impact of IgD on naïve B cell maturation and Ig repertoire selection in 8 individuals from 3 different families with heterozygous loss-of-function or loss-of expression mutations in IGHD. Although naïve B cells from these individuals expressed IgM on their surface, the IGHD variant in heterozygous state entailed a chimeric situation by allelic exclusion with almost half of the naïve B cell population lacking surface IgD expression. Flow cytometric analyses revealed a distinct phenotype of IgD-negative naïve B cells with decreased expression of CD19, CD20 and CD21 as well as lower BAFF-R and integrin-β7 expression. IgD-negative B cells were less responsive in vitro after engaging the IgM-BCR, TLR7/9 or CD40 pathway. Additionally, a selective disadvantage of IgD-negative B cells within the T2 transitional and mature naïve B cell compartment as well as reduced frequencies of IgM^lo/- B cells within the mature naïve B cell compartment lacking IgD were evident. RNA-Ig-seq of bulk sorted B cell populations showed an altered selection of distinct V_H segments in the IgD-negative mature naïve B cell population. We conclude that IgD expression on human naïve B cells is redundant for generation of naïve B cells in general, but further shapes the naive B cell compartment starting from T2 transitional B cells. Our observations suggest an unexpected role of IgD expression to be critical for selection of distinct Ig V_H segments into the pre-immune Ig repertoire and for the survival of IgM^lo/- naïve B cells known to be enriched in poly-/autoreactive B cell clones.

Immunizations with diverse sarbecovirus receptor-binding domains elicit SARS-CoV-2 neutralizing antibodies against a conserved site of vulnerability

Viral mutations are an emerging concern in reducing SARS-CoV-2 vaccination efficacy. Second-generation vaccines will need to elicit neutralizing antibodies against sites that are evolutionarily conserved across the sarbecovirus subgenus. Here, we immunized mice containing a human antibody repertoire with diverse sarbecovirus receptor-binding domains (RBDs) to identify antibodies targeting conserved sites of vulnerability. Antibodies with broad reactivity against diverse clade B RBDs targeting the conserved class 4 epitope, with recurring IGHV/IGKV pairs, were readily elicited but were non-neutralizing. However, rare class 4 antibodies binding this conserved RBD supersite showed potent neutralization of SARS-CoV-2 and all variants of concern. Structural analysis revealed that the neutralizing ability of cross-reactive antibodies was reserved only for those with an elongated CDRH3 that extends the antiparallel beta-sheet RBD core and orients the antibody light chain to obstruct ACE2-RBD interactions. These results identify a structurally defined pathway for vaccine strategies eliciting escape-resistant SARS-CoV-2 neutralizing antibodies.