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

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.

Factors involved in CLL pathogenesis and cell survival are disrupted by differentiation of CLL B-cells into antibody-secreting cells

“…The concept whereby malignant B-cells are induced to differentiate into a more mature, non-malignant or less malignant state is clinically plausible and can be a promising strategy as differentiation therapy in CLL [ 14 , 29 , 33 – 35 ]. To the best of our knowledge, the present report is the first to demonstrate the modulatory effects of differentiation on factors that have an important role in physiopathology of CLL, including LEF1, TCL1, ROR1, FMOD, TNFRSF13B , PI3K, BTK, p27, BCL2, BCLXL, PUMA and MCL1.…”

“…In addition to differentiation-dependent apoptosis, differentiation therapy in CLL could potentially be combined with other targeted therapies or immunotherapy [ 35 ]. Indeed, terminal differentiation confers exquisite apoptotic sensitivity to proteasome inhibitors, inhibitors of the ER stress-associated pathway (IRE1/XBP1) [ 59 , 60 ], inhibitors of HSP90 [ 61 ], BCL2, BCLxL (e.g.…”

“…However, there is now renewed interest in studying the differentiation capacity of CLL B-cells [ 14 , 33 – 36 ]. Recent research has shown that CLL B-cells display a strong tendency to differentiate into ASCs and may thus be amenable to differentiation therapy [ 14 , 29 , 33 – 35 ]. In a two-step, 7-day culture system, our laboratory recently demonstrated that phorbol myristate acetate (PMA) and CpG oligodeoxynucleotide induces differentiation of CLL B-cells to an intermediate stage in the plasma cell differentiation process [ 34 , 35 ].…”

“…Recent research has shown that CLL B-cells display a strong tendency to differentiate into ASCs and may thus be amenable to differentiation therapy [ 14 , 29 , 33 – 35 ]. In a two-step, 7-day culture system, our laboratory recently demonstrated that phorbol myristate acetate (PMA) and CpG oligodeoxynucleotide induces differentiation of CLL B-cells to an intermediate stage in the plasma cell differentiation process [ 34 , 35 ]. Using a similar culture systems, in this study we sought to investigate the impact of B-cell differentiation on the expression of factors that contribute to the physiopathology of CLL and/or are known to be deregulated in CLL B-cells (including LEF1, TCL1, ROR1, FMOD, TACI, PI3K, BTK and p27).…”

The Importance of an In-depth Study of Immunoglobulin Gene Rearrangements When Ascertaining the Clonal Relationship between Concomitant Chronic Lymphocytic Leukemia and Multiple Myeloma

“…It has been shown that CLL B-cells can differentiate spontaneously into antibody-secreting plasma cells in vivo (9, 10) and in vitro , when exposed to various stimuli and can produce IgM, IgG, and IgA (11, 12). It is thus possible that the malignant plasma cells are differentiated or transformed CLL B-cells (hypothesis 1, H1) .…”