Characterization of memory B cells from thymus and its impact for DLBCL classification

A multiple myeloma classification system that associates normal B-cell subset phenotypes with prognosis

Despite the recent progress in treatment of multiple myeloma (MM), it is still an incurable malignant disease, and we are therefore in need of new risk stratification tools that can help us to understand the disease and optimize therapy. Here we propose a new subtyping of myeloma plasma cells (PCs) from diagnostic samples, assigned by normal B-cell subset associated gene signatures (BAGS). For this purpose, we combined fluorescence-activated cell sorting and gene expression profiles from normal bone marrow (BM) Pre-BI, Pre-BII, immature, naïve, memory, and PC subsets to generate BAGS for assignment of normal BM subtypes in diagnostic samples. The impact of the subtypes was analyzed in 8 available data sets from 1772 patients' myeloma PC samples. The resulting tumor assignments in available clinical data sets exhibited similar BAGS subtype frequencies in 4 cohorts from de novo MM patients across 1296 individual cases. The BAGS subtypes were significantly associated with progression-free and overall survival in a meta-analysis of 916 patients from 3 prospective clinical trials. The major impact was observed within the Pre-BII and memory subtypes, which had a significantly inferior prognosis compared with other subtypes. A multiple Cox proportional hazard analysis documented that BAGS subtypes added significant, independent prognostic information to the translocations and cyclin D classification. BAGS subtype analysis of patient cases identified transcriptional differences, including a number of differentially spliced genes. We identified subtype differences in myeloma at diagnosis, with prognostic impact and predictive potential, supporting an acquired B-cell trait and phenotypic plasticity as a pathogenetic hallmark of MM.

[Thymic B cells: not simple bystanders of T cell lymphopoiesis]

The thymus is the central site for the differentiation and selection of T cells. It has been known for decades that B lymphocytes reside in the thymus, but little attention has been paid to this unique population. Thymic B cells are mainly located in the medulla and at the cortico-medullary junction. They develop intrathymically, do not recirculate and harbor a distinct phenotype in comparison to peripheral B cells. Furthermore, because of their activated phenotype and their precise histological localization, they have been suspected to play a role in the selection of self-reactive T cells. But it is only during this last decade that murine and human studies have highlighted their functions, such as antigen-presenting cells shaping the T cell repertoire. These works have demonstrated the major role of thymic B cells in the immune system.