Heritable diversity in the human antigen inexperienced B cell repertoire

Human transitional B cells and naïve B cells are each variable beyond the widely discussed diversity in their B cell receptor repertoire, because whilst remaining within their subset definition, the phenotypes and transcriptomes of individual cells occur within a range of values. Cells can therefore have different functional biases. Here we have taken advantage of small clones of transitional and naïve B cells that exist within different tissue sites in pre-existing dataset to ask whether the transcriptomes of individual clone members are more similar to each other than to the transcriptomes of unrelated cells. We observe that cells that are clonally related are more similar to each other in terms of gene expression than they are to the remainder of cells in clones. This demonstrates that differences are shared between clone members and are therefore heritable. We suggest further that diversity in the transitional and naïve B cell populations has the potential to be propagated and thus sustained.

IL-4 receptor blockade is a global repressor of naïve B cell development and responses in a dupilumab-treated patient

Here, we report a case of atopic dermatitis (AD) in a patient who received biweekly doses of dupilumab, an antibody against the IL-4 receptor α chain (IL-4Rα). Single cell RNA-sequencing showed that naïve B cells expressed the highest levels of IL4R compared to other B cell subpopulations. Compared to controls, the dupilumab-treated patient exhibited diminished percentages of IL4R+IGHD+ naïve B cells and down-regulation of IL4R, FCER2 (CD23), and IGHD. Dupilumab treatment resulted in upregulation of genes associated with apoptosis and inhibition of B cell receptor signaling and down-regulation of class-switch and memory B cell development genes. The dupilumab-treated patient exhibited a rapid decline in COVID-19 anti-spike and anti-receptor binding domain antibodies between 4 and 8 and 11 months post COVID-19 vaccination. Our data suggest that intact and persistent IL-4 signaling is necessary for maintaining robust survival and development of naïve B cells, and maintaining a long term vaccine response.

Improving naive B cell isolation by absence of CD45RB glycosylation and CD27 expression in combination with BCR isotype

In past years ex vivo and in vivo experimental approaches involving human naive B cells have proven fundamental for elucidation of mechanisms promoting B cell differentiation in both health and disease. For such studies, it is paramount that isolation strategies yield a population of bona fide naive B cells, i.e., B cells that are phenotypically and functionally naive, clonally non-expanded, and have non-mutated BCR variable regions. In this study different combinations of common as well as recently identified B cell markers were compared to isolate naive B cells from human peripheral blood. High-throughput BCR sequencing was performed to analyze levels of somatic hypermutation and clonal expansion. Additionally, contamination from mature mutated B cells intrinsic to each cell-sorting strategy was evaluated and how this impacts the purity of obtained populations. Our results show that current naive B cell isolation strategies harbor contamination from non-naive B cells, and use of CD27-IgD⁺ is adequate but can be improved by including markers for CD45RB glycosylation and IgM. The finetuning of naive B cell classification provided herein will harmonize research lines using naive B cells, and will improve B cell profiling during health and disease, e.g. during diagnosis, treatment, and vaccination strategies.

Proportion versus absolute counts of B cell populations in the assessment of immunological profiles of kidney transplant recipients

Immunophenotyping lymphocytes in kidney transplant recipients often raises questions as to whether proportions or absolute counts should be considered, especially for longitudinal assessment. Several studies conclude the pathophysiology of rejection based on proportions of naive and memory B cells. We compared the two analytical methods for B cells sampled from 82 clinically stable, adult kidney transplant recipients. Time post-transplant was analyzed both as a continuous variable and as tertiles (<1.5 years, 1.5-8 years, and > 8 years). B cells were stained for CD38 and IgD and were classified according to mature B cells (Bm) classification. The proportion of cells in the naive Bm2 compartment decreased by more than half in the late versus the early tertile, whereas the percentages of memory early Bm5 tripled and that of memory Bm5 cells doubled. In contrast, we observed a substantial reduction in naive B cell counts, but very stable memory B cell counts. Linear regressions showed that the absolute reduction in the Bm2 cell compartment was independent of age, sex, graft function, immunosuppression scheme, and rejection occurrence. In conclusion, the physiological reservoir of naive cells decreases over time post-transplant in kidney recipients, whereas that of memory B cells remains stable. Peripheral B subset percentages should be interpreted cautiously when analyzing pathophysiological processes.

miR-29b directly targets activation-induced cytidine deaminase in human B cells and can limit its inappropriate expression in naïve B cells

Class-switch recombination (CSR) is an essential B cell process that alters the isotype of antibody produced by the B cell, tailoring the immune response to the nature of the invading pathogen. CSR requires the activity of the mutagenic enzyme AID (encoded by AICDA) to generate chromosomal lesions within the immunoglobulin genes that initiate the class switching recombination event. These AID-mediated mutations also participate in somatic-hypermutation of the immunoglobulin variable region, driving affinity maturation. As such, AID poses a significant oncogenic threat if it functions outside of the immunoglobulin locus. We found that expression of the microRNA, miR-29b, was repressed in B cells isolated from tonsil tissue, relative to circulating naïve B cells. Further investigation revealed that miR-29b was able to directly initiate the degradation of AID mRNA. Enforced overexpression of miR-29b in human B cells precipitated a reduction in overall AID protein and a corresponding diminution in CSR to IgE. Given miR-29b's ability to potently target AID, a mutagenic molecule that can initiate chromosomal translocations and "off-target" mutations, we propose that miR-29b acts to silence premature AID expression in naïve B cells, thus reducing the likelihood of inappropriate and potentially dangerous deamination activity.