B cell-targeted therapies, such as CD20-targeting mAbs, deplete B cells but do not target the autoantibody-producing plasma cells (PCs). PC-targeting therapies such as daratumumab (anti-CD38) form an attractive approach to treat PC-mediated diseases. CD38 possesses enzymatic and receptor capabilities, which may impact a range of cellular processes including proliferation and differentiation. However, very little is known whether and how CD38 targeting affects B-cell differentiation, in particular for humans beyond cancer settings. Using in-depth in vitro B-cell differentiation assays and signaling pathway analysis, we show that CD38 targeting with daratumumab demonstrated a significant decrease in proliferation, differentiation, and IgG production upon T cell-dependent B-cell stimulation. We found no effect on T-cell activation or proliferation. Furthermore, we demonstrate that daratumumab attenuated the activation of NF-κB in B cells and the transcription of NF-κB-targeted genes. When culturing sorted B-cell subsets with daratumumab, the switched memory B-cell subset was primarily affected. Overall, these in vitro data elucidate novel non-depleting mechanisms by which daratumumab can disturb humoral immune responses. Affecting memory B cells, daratumumab may be used as a therapeutic approach in B cell-mediated diseases other than the currently targeted malignancies.
© 2023 Verhoeven et al.

Chronic lymphocytic leukemia (CLL) is considered a clonal B cell malignancy. Sporadically, CLL cases with multiple productive heavy and light-chain rearrangements were detected, thus leading to a bi- or oligoclonal CLL disease with leukemic cells originating either from different B cells or otherwise descending from secondary immunoglobulin rearrangement events. This suggests a potential role of clonal hematopoiesis or germline predisposition in these cases. During the screening of 75 CLL cases for kappa and lambda light-chain rearrangements, we could detect a single case with CLL cells expressing two distinct kappa and lambda light chains paired with two separate immunoglobulin heavy-chain variable regions. Furthermore, this patient also developed a prostate carcinoma. Targeted genome sequencing of highly purified light-chain specific CLL clones from this patient and from the prostate carcinoma revealed the presence of a rare germline polymorphism in the POLE gene. Hence, our data suggest that the detected SNP may predispose for cancer, particularly for CLL.

Cerebrospinal fluid (CSF) flow cytometry has a crucial role in the diagnosis of leptomeningeal disease in onco-hematology. This report describes the flow cytometry characterization of 138 CSF samples from patients affected by non-Hodgkin lymphoma, negative for disease infiltration. The aim was to focus on the CSF non-neoplastic population, to compare the cellular composition of the CSF with paired peripheral blood samples and to document the feasibility of flow cytometry in hypocellular samples. Despite the extremely low cell count (1 cell/µl, range 1.0-35) the study was successfully conducted in 95% of the samples. T lymphocytes were the most abundant subset in CSF (77%; range 20-100%) with a predominance of CD4-positive over CD8-positive T cells (CD4/CD8 ratio = 2) together with a minority of monocytes (15%; range 0-70%). No B cells were identified in 90% of samples. Of relevance, a normal, non-clonal B-cell population was documented in 5/7 (71%) patients with primary central nervous system lymphoma at diagnosis (p<0.0001), suggesting a possible involvement of blood-brain barrier cell permeability in the pathogenesis of cerebral B-cell lymphomas. The highly significant differences between CSF and paired peripheral blood lymphoid phenotype (p<0.0001) confirms the existence of an active mechanism of lymphoid migration through the meninges.
Copyright © 2021 Cordone, Masi, Giannarelli, Pasquale, Conti, Telera, Pace, Papa, Marino, de Fabritiis and Mengarelli.

Bortezomib is a potent inhibitor of proteasomes currently used to eliminate malignant plasma cells in multiple myeloma patients. It is also effective in depleting both alloreactive plasma cells in acute Ab-mediated transplant rejection and their autoreactive counterparts in animal models of lupus and myasthenia gravis (MG). In this study, we demonstrate that bortezomib at 10 nM or higher concentrations killed long-lived plasma cells in cultured thymus cells from nine early-onset MG patients and consistently halted their spontaneous production not only of autoantibodies against the acetylcholine receptor but also of total IgG. Surprisingly, lenalidomide and dexamethasone had little effect on plasma cells. After bortezomib treatment, they showed ultrastructural changes characteristic of endoplasmic reticulum stress after 8 h and were no longer detectable at 24 h. Bortezomib therefore appears promising for treating MG and possibly other Ab-mediated autoimmune or allergic disorders, especially when given in short courses at modest doses before the standard immunosuppressive drugs have taken effect.
Copyright © 2014 by The American Association of Immunologists, Inc.

The aim of this study was to screen for cell surface markers that could discriminate CLL-type MBL from CLL or identify CLL cases likely to have stable disease.
Six color flow cytometry was performed on CLL-type MBL (n = 94) and CLL (n = 387) at diagnosis or relapse; 39 cases had poor-risk chromosomal abnormalities (17p and/or 11q deletion). Expression of 30 markers was analysed: CCR6, CD10, CD103, CD11c, CD138, CD200, CD22, CD23, CD24, CD25, CD27, CD31, CD38, CD39, CD43, CD49d, CD5, CD52, CD62L, CD63, CD79b, CD81, CD86, CD95, CXCR5, HLADR, IgD, IgG, IgM, LAIR1.
There was no difference in expression between CLL-type MBL and CLL for the majority of markers. Differential expression was observed for several markers, mainly between MBL and CLL cases with adverse-risk chromosomal abnormalities. These differences included lower expression of CD38 (9.4-fold lower, P = 0.007) and CD49d (3.2-fold lower, P = 0.008) and higher expression of LAIR-1 (3.7-fold higher, P = 0.003), CXCR5 (1.25-fold higher, P = 0.002), and CCR6 (1.9-fold higher P < 0.001) on CLL-type MBL compared to CLL with adverse chromosomal abnormalities. CD62L (L-selectin) which mediates lymphocyte adhesion to endothelial venules of lymphoid tissue, was expressed at a significantly different level between CLL-type MBL and both CLL sub-groups, with 1.3-fold lower (P = 0.04) expression levels on the MBL cases. However, there was broad overlap in expression levels.
CLL-type MBL is phenotypically identical to CLL for a very broad range of markers. Differential expression is predominantly related to known prognostic markers and proteins involved in homing to lymphoid tissue.
© 2010 International Clinical Cytometry Society.