TLR9 Ligand (CpG Oligodeoxynucleotide) Induces CLL B-Cells to Differentiate into CD20(+) Antibody-Secreting Cells.

Hussein Ghamlouch,Jean-Pierre Marolleau,Aline Regnier,Aude Guyart,Jean-Franã§Ois Claisse,Hakim Ouled-Haddou,Stã©Phanie Trudel,Brigitte Gubler,Vincent Fuentes,Bruno Royer

doi:10.3389/fimmu.2014.00292

Abstract

B-cell chronic lymphocytic leukemia (CLL) is the most frequent adult leukemia in the Western world. It is a heterogeneous disease characterized by clonal proliferation and the accumulation of CD5+ mature B lymphocytes. However, the normal counterpart from which the latter cells arise has not yet been identified. CD27 expression and gene expression profiling data suggest that CLL cells are related to memory B-cells. In vitro, memory B-cells differentiate into plasma cells when stimulated with CpG oligodeoxynucleotide (CpG). The objective of the present study was therefore to investigate the ability of CpG, in the context of CD40 ligation, to induce the differentiation of CLL B-cells into antibody-secreting cells (ASCs). CD20+CD38− CLL B-cells were stimulated with a combination of CpG, CD40 ligand and cytokines (CpG/CD40L/c) in a two-step, 7-day culture system. We found that the CpG/CD40L/c culture system prompted CLL B-cells to differentiate into CD19+CD20+CD27+CD38−ASCs. These cells secreted large amounts of IgM and had the same shape as plasma cells. However, only IgMs secreted by ASCs that had differentiated from unmutated CLL B-cells were poly/autoreactive. Class-switch recombination (CSR) to IgG and IgA was detected in cells expressing the activation-induced cytidine deaminase gene (AICDA). Although these ASCs expressed high levels of the transcription factors PRDM1 (BLIMP1), IRF4, and XBP1s, they did not downregulate expression of PAX5. Our results suggest that CLL B-cells can differentiate into ASCs, undergo CSR and produce poly/autoreactive antibodies. Furthermore, our findings may be relevant for (i) identifying the normal counterpart of CLL B-cells and (ii) developing novel treatment strategies in CLL.

Highlights

B-cell chronic lymphocytic leukemia (CLL) is a heterogeneous disease characterized by clonal proliferation and the accumulation of mature CD5+ B lymphocytes in the bone marrow, peripheral blood, and lymphoid tissues [1]
Our data show that when stimulated with CpG/CD40 ligand (CD40L)/c, CLL B-cells differentiated into CD20+CD27+CD38− antibody-secreting cells (ASCs), which were able to produce large amounts of IgM
It was suggested that the differential expression of human CD38, CD138, HLADR, and CD20 may correspond to alternative or additional ASC subsets derived from independent differentiation pathways in blood, bone marrow, and possibly other tissues [33]

Summary

Introduction

B-cell chronic lymphocytic leukemia (CLL) is a heterogeneous disease characterized by clonal proliferation and the accumulation of mature CD5+ B lymphocytes in the bone marrow, peripheral blood, and lymphoid tissues [1]. Gene expression profiling shows that only a relatively small set of genes [20–100] can discriminate between mutated and unmutated CLL clones [3, 4]. Mutated and unmutated CLL B-cells display a common, characteristic gene expression profile that is largely independent of their IgV genotype and is more strongly reminiscent of memory B-cells than of cells derived from naive B-cells, CD5+ B-cells, or germinal center centroblasts/centrocytes [3]. The researchers controversially reported that (i) unmutated CLL clones were derived from mature, unmutated CD5+CD27− B-cells and (ii) mutated CLL clones were derived from a distinct, previously unrecognized, CD5+CD27+ post-germinal-center (memory) B-cell subset [6]. To address the question of the CLL B-cells’ normal counterpart, most literature studies have used immunophenotypic, molecular, and gene expressing profiling to look for similarities between CLL B-cells and normal B-cells isolated ex vivo.

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