TLR-9 and B-Cell Antigen Receptor Triggering of Primary B Cells From Mantle Cell Lymphoma Induce Cell Proliferation and Telomerase Activity,

Abstract 3690

Mantle cell lymphoma (MCL), a less common non-Hodgkin's lymphoma (NHL), often has a poor prognosis and a median survival time of 3–5 years. Historically, MCLs were believed to originate from mature but naive B cells; this notion has now changed based on the demonstration of somatically mutated IgHV sequences in the lymphoma cells from a subset of cases. Indirect evidence suggesting that the B-cell receptor (BCR) pathway may be at the base of the observed activation in the disease exists; however, that extent that this activation results from Toll-like receptor (TLR), B-cell antigen receptor (BCR), or a combination of signaling from both has not been adequately addressed. In this study, the responsiveness of purified primary B cells isolated from peripheral blood (PB) and/or bone marrow (BM) of MCL patients in the leukemic phase of the disease to triggering via the BCR or via TLR-9 alone or in context with selected chemokines – CCL17, CCL22, or CXCL12 - was assessed using various early and late cell signaling readouts.

Phosphoflow analysis revealed that within 5 minutes of stimulation both PB and BM B cells significantly increased levels of pAkt and pNFkB in response to BCR crosslinking by an anti-IgM monoclonal antibody (mAb). When PB B cells were cultured for 3 days in the presence of various stimuli to evaluate their proliferative response (uptake of 3H-thymidine), anti-BCR triggering stimulated 2 to 5.5 fold increases in DNA synthesis, whereas the TLR-9 agonist ODN2006 elicited 55 to 235 fold increases. In addition, conditions simulating T-cell help (anti-CD40 mAb + IL-4 in the presence of CD32-transfected fibroblasts) stimulated significant (40–65 fold) proliferative responses in MCL B cells. Simultaneously, a significant increase in HLA-DR (anti-BCR: 49%; ODN2006: 61%; T-cell help: 20%) and Bcl-2 expression (anti-BCR: 21%; ODN2006: 36%; T-cell help: 25%) was induced by these stimuli. Furthermore, B cells from the BM of the same cases differed in their proliferative responses based on the agonist. Thus, in response to BCR triggering, B cells from BM proliferated to a greater extent compared with PB B cells, whereas in response to TLR-9 stimulation PB B cells proliferated to a greater extent than those from BM. In independent experiments, B cells were incubated with various stimuli including those simulating T-cell help and chemokines for 3 days. Cells were harvested and extracts prepared from viable cells to determine telomerase activity using the telomere repeat amplification protocol (TRAP). Anti-BCR stimulation and anti-TLR-9 stimulation independently increased telomerase activity 1.7 and 1.9 fold, respectively, whereas in combination with CCL17 and CCL22, anti-TLR-9 stimulation further increased telomerase activity to 2.28 and 2.36 fold, respectively.

In summary, these findings suggest an important role for commonly encountered microenvironmental influences interacting with TLR9 and to a lesser extent the BCR in promoting the aggressiveness of MCL. They also suggest that responses to these stimuli differ between MCL cells residing in the BM and those circulating in the blood. Finally, the data suggest that ligands for CCR4 may play an enhancing role for signals transduced by the BCR and TLR-9 in this disease. If documented in a larger number of cases, treatment regimens that target these signaling pathways might be of therapeutic value.