T-cell number and subtype influence the disease course of primary chronic lymphocytic leukaemia xenografts in alymphoid mice.

Chronic lymphocytic leukaemia (CLL) cells require microenvironmental support for their proliferation. This can be recapitulated in highly immunocompromised hosts in the presence of T cells and other supporting cells. Current primary CLL xenograft models suffer from limited duration of tumour cell engraftment coupled with gradual T-cell outgrowth. Thus, a greater understanding of the interaction between CLL and T cells could improve their utility. In this study, using two distinct mouse xenograft models, we investigated whether xenografts recapitulate CLL biology, including natural environmental interactions with B-cell receptors and T cells, and whether manipulation of autologous T cells can expand the duration of CLL engraftment. We observed that primary CLL xenografts recapitulated both the tumour phenotype and T-cell repertoire observed in patients and that engraftment was significantly shorter for progressive tumours. A reduction in the number of patient T cells that were injected into the mice to 2-5% of the initial number or specific depletion of CD8+ cells extended the limited xenograft duration of progressive cases to that characteristic of indolent disease. We conclude that manipulation of T cells can enhance current CLL xenograft models and thus expand their utility for investigation of tumour biology and pre-clinical drug assessment

Prolonged Exposure to a Mer Ligand in Leukemia: Gas6 Favors Expression of a Partial Mer Glycoform and Reveals a Novel Role for Mer in the Nucleus

Mer tyrosine kinase is ectopically expressed in acute lymphoblastic leukemia and associated with enhanced chemoresistance and disease progression. While such effects are generally ascribed to increased engagement of oncogenic pathways downstream of Mer stimulation by its ligand, Gas6, Mer has not been characterized beyond the scope of its signaling activity. The present study explores Mer behavior following prolonged exposure to Gas6, a context similar to the Gas6-enriched microenvironment of the bone marrow, where a steady supply of ligand facilitates continuous engagement of Mer and likely sustains the presence of leukemic cells. Long-term Gas6 exposure induced production of a partially N-glycosylated form of Mer from newly synthesized stores of protein. Preferential expression of the partial Mer glycoform was associated with diminished levels of Mer on the cell surface and altered Mer localization within the nuclear-soluble and chromatin-bound fractions. The presence of Mer in the nucleus is a novel finding for this receptor, and the glycoform-specific preferences observed in each nuclear compartment suggest that glycosylation may influence Mer function within particular subcellular locales. Previous studies have established Mer as an attractive cancer biologic target, and understanding the complexity of its activity has important implications for potential strategies of Mer inhibition in leukemia therapy. Our results identify several novel features of Mer that expand the breadth of its functions and impact the development of therapeutic modalities designed to target Mer

Radiation therapy with tositumomab (B1) anti-CD20 monoclonal antibody initiates extracellular signal-regulated kinase/mitogen-activated protein kinase-dependent cell death that overcomes resistance to apoptosis

Purpose: the use of targeted radiation therapy (RT) in conjunction with anti-CD20 monoclonal antibodies (mAb) delivers high clinical response rates in B-cell lymphomas as part of radioimmunotherapy. The mechanisms underlying these impressive responses, particularly in patients whose lymphomas have become refractory to chemotherapy, are poorly understood. Experimental design: in this study, we have investigated the signaling pathways and mode of cell death induced in B-cell lymphoma cells after the combination of RT and either type I (rituximab) or type II (tositumomab/B1) anti-CD20 mAb. Results: increased tumor cell death was observed when RT was combined with tositumomab, but not rituximab. This additive cell death was found to be mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK)–dependent and could be reversed with mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK) inhibitors, as well as small interfering RNA targeting MEK1/2. Furthermore, we found that this increased death was associated with ERK1/2 nuclear accumulation after tositumomab treatment, which was enhanced in combination with RT. Importantly, although Bcl-2 overexpression resulted in resistance to RT-induced apoptosis, it had no effect on the tumor cell death induced by tositumomab plus RT, indicating a nonapoptotic form of cell death. Conclusions: these findings indicate that RT and type II anti-CD20 mAb combine to stimulate a prodeath function of the MEK-ERK1/2 pathway, which is able to overcome apoptotic resistance potentially explaining the efficacy of this modality in treating patients with chemoresistant disease

Expression patterns of CD180 in the lymph nodes of patients with chronic lymphocytic leukaemia

There is strong evidence implicating microenvironmental sensors, including toll-like receptors (TLRs), in the pathobiology of chronic lymphocytic leukaemia (CLL).1,2We have previously demonstrated that the orphan TLR CD180 is heterogeneously expressed on peripheral blood (PB) CLL cells in~60%of cases.3Ligation of CD180 with monoclonal antibody (mAb)resulted in the activation, cycling and proliferation of PB CLLc ells. We further demonstrated that CD180 engagement utilised two, often alternative signalling pathways mediated by protein kinase B (AKT) or p38 mitogen-activated protein kinase (p38MAPK), which corresponded with CLL cell survival and apoptosis, respectively. Moreover, in our hands, ligation of CD180 rewired immunoglobulin M (IgM)-mediated signalling from AKT to p38MAPK pathway.