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Objectives: Paediatric Burkitt's lymphoma (pBL) is the most common childhood non‐Hodgkin B‐cell lymphoma. Despite the encouraging survival rates for most children, treating cases with relapse/resistance to current therapies remains challenging. CD38 is a transmembrane protein highly expressed in pBL. This study investigates the effectiveness of CD38‐targeting monoclonal antibodies (mAbs), daratumumab and isatuximab, in impairing crucial cellular processes and survival pathways in pBL malignant cells. Methods: In silico analyses of patient samples, combined with in vitro experiments using the Ramos cell line, were conducted to assess the impact of daratumumab and isatuximab on cellular proliferation, apoptosis and the phosphoinositide 3‐kinase (PI3K) pathway. Results: Isatuximab was found to be more effective than daratumumab in disrupting B‐cell receptor signalling, reducing cellular proliferation and inducing apoptosis. Additionally, isatuximab caused a significant impairment of the PI3K pathway and induced metabolic reprogramming in pBL cells. The study also revealed a correlation between CD38 and MYC expression levels in pBL patient samples, suggesting CD38 involvement in key oncogenic processes. Conclusion: The study emphasises the therapeutic potential of CD38‐targeting mAbs, particularly isatuximab, in pBL. [ABSTRACT FROM AUTHOR]

Objective: Subsets of CD21−/low memory B cells (MBCs), including double‐negative (DN, CD27−IgD−) and Tbet+CD11c+ cells, are expanded in chronic inflammatory diseases. In rheumatoid arthritis (RA), CD21−/low MBCs correlate with joint destruction. However, whether this is due to the Tbet+CD11c+ subset, its function and pathogenic contribution to RA are unknown. This study aims to investigate the association between CD21−/lowTbet+CD11c+ MBCs and joint destruction as well as other clinical parameters and to elucidate their functional properties in patients with untreated RA (uRA). Methods: Clinical observations were combined with flow cytometry (n = 36) and single‐cell RNA sequencing (scRNA‐seq) and V(D)J sequencing (n = 4) of peripheral blood (PB) MBCs from patients with uRA. The transcriptome of circulating Tbet+CD11c+ MBCs was compared with scRNA‐seq data of synovial B cells. In vitro coculture of Tbet+CD11c+ B cells with T cells was used to assess costimulatory capacity. Results: CD21−/lowTbet+CD11c+ MBCs in PB correlated with bone destruction but no other clinical parameters analyzed. The Tbet+CD11c+ MBCs have undergone clonal expansion and express somatically mutated V genes. Gene expression analysis of these cells identified a unique signature of more than 150 up‐regulated genes associated with antigen presentation functions, including B cell receptor activation and clathrin‐mediated antigen internalization; regulation of actin filaments, endosomes, and lysosomes; antigen processing, loading, presentation, and costimulation; a transcriptome mirrored in their synovial tissue counterparts. In vitro, Tbet+CD11c+ B cells induced retinoic acid receptor–related orphan nuclear receptor γT expression in CD4+ T cells, thereby polarizing to Th17 cells, a T cell subset critical for osteoclastogenesis and associated with bone destruction. Conclusion: This study suggests that Tbet+CD11c+ MBCs contribute to the pathogenesis of RA by promoting bone destruction through antigen presentation, T cell activation, and Th17 polarization. [ABSTRACT FROM AUTHOR]

Switched and IgM memory B cells execute different and noninterchangeable functions. We studied memory B cells in children of different ages, in peripheral blood and spleen and compared them with those of children born asplenic or unable to build germinal centers. We show that, whereas switched memory B cells are mostly generated in the germinal centers at all ages, IgM memory B cells can be distinct in three types with different developmental history. Innate IgM memory B cells, the largest pool in infants, are generated in the spleen by a germinal center-independent mechanism. With age, if the spleen is present and germinal centers are functional, innate IgM memory B cells are remodelled and accumulate somatic mutations. The third type of IgM memory B cell is a by-product of the germinal center reaction. Our data suggest that the B-cell memory developmental program is implemented during the first 5-6 years of life. [ABSTRACT FROM AUTHOR]

Objective: Subsets of CD21 -/low memory B cells (MBCs), including double-negative (DN, CD27 - IgD - ) and Tbet + CD11c + cells, are expanded in chronic inflammatory diseases. In rheumatoid arthritis (RA), CD21 -/low MBCs correlate with joint destruction. However, whether this is due to the Tbet + CD11c + subset, its function and pathogenic contribution to RA are unknown. This study aims to investigate the association between CD21 -/low Tbet + CD11c + MBCs and joint destruction as well as other clinical parameters and to elucidate their functional properties in patients with untreated RA (uRA)., Methods: Clinical observations were combined with flow cytometry (n = 36) and single-cell RNA sequencing (scRNA-seq) and V(D)J sequencing (n = 4) of peripheral blood (PB) MBCs from patients with uRA. The transcriptome of circulating Tbet + CD11c + MBCs was compared with scRNA-seq data of synovial B cells. In vitro coculture of Tbet + CD11c + B cells with T cells was used to assess costimulatory capacity., Results: CD21 -/low Tbet + CD11c + MBCs in PB correlated with bone destruction but no other clinical parameters analyzed. The Tbet + CD11c + MBCs have undergone clonal expansion and express somatically mutated V genes. Gene expression analysis of these cells identified a unique signature of more than 150 up-regulated genes associated with antigen presentation functions, including B cell receptor activation and clathrin-mediated antigen internalization; regulation of actin filaments, endosomes, and lysosomes; antigen processing, loading, presentation, and costimulation; a transcriptome mirrored in their synovial tissue counterparts. In vitro, Tbet + CD11c + B cells induced retinoic acid receptor-related orphan nuclear receptor γT expression in CD4 + T cells, thereby polarizing to Th17 cells, a T cell subset critical for osteoclastogenesis and associated with bone destruction., Conclusion: This study suggests that Tbet + CD11c + MBCs contribute to the pathogenesis of RA by promoting bone destruction through antigen presentation, T cell activation, and Th17 polarization., (© 2024 The Authors. Arthritis & Rheumatology published by Wiley Periodicals LLC on behalf of American College of Rheumatology.)

The spleen is the second major reservoir of B cells in the adult. In the spleen, cells, generated in the bone marrow, are selected, mature, and become part of the peripheral B-cell pool. Murine spleen comprises several B-cell subsets representing various maturation stages and/or cell functions. The spleen is a complex lymphoid organ organized into two main structures with different functions: the red and white pulp. The red pulp is flowed with blood while the white pulp is organized in primary follicles, with a B-cell area composed of follicular B cells and a T-cell area surrounding a periarterial lymphatic sheath. The frontier between the red and white pulp is defined as the marginal zone (MZ) and contains the MZ B cells. Because B cells, localized in different areas, are characterized by distinct expression levels of B-cell receptor (BCR) and of other surface markers, splenic B-cell subsets can be easily identified and purified by flow cytometry analyses and fluorescence-activated cell sorting (FACS).Here, we will focus on MZ B cells and on their precursors, giving some experimental hints to identify, generate, and isolate these cells. We will combine the use of FACS analysis and confocal microscopy to visualize MZ B cells in cell suspensions and in tissue sections, respectively. We will also give some clues to analyze B-cell repertoire on isolated MZ-B cells.