B-cell malignancy-derived immunoglobulin (idiotype) and survivin, a member of the inhibitor of apoptosis gene family and a shared tumor-associated antigen, are expressed by B-CLL cells. Idiotype- and ...survivin-specific cytotoxic T cells (CTLs), capable of lysing primary autologous B-CLL cells, can be induced in patients with B-CLL. However, the leukemia cell microenvironment was shown to protect B-CLL cells from apoptosis. The protective effects of stromal cells can be reversed by CXCR4 antagonists in vitro and resensitize CLL cells to spontaneous and chemotherapy-induced apoptosis. The aim of the present study is to investigate whether stromal cell contact impairs CLL killing by CTLs raised against immunoglobulin- or survivin-derived peptides and whether the addition of CXCR4 inhibitors enhances T cell mediated cytotoxicity. To analyze the T cell response, we isolated CD8+ T cells and PBMCs from HLA-A2+ healthy donors. PBMCs were differentiated into dendritic cells (DCs) and CD40-activated B cells. CD8+ T cells were primarily stimulated with peptide-pulsed DCs and then restimulated weekly with peptide-pulsed CD40-activated B cells. Heteroclitic framework region (FR−), heteroclitic complementarity-determining region (CD−) derived peptides, and native and heteroclitic survivin-derived peptides were used for CTL induction. As expected, heteroclitic peptide modifications increased the binding affinity to HLA-A*0201 compared to the native peptide as predicted by the Parker Score (Median change of predicted half-time of dissociation to HLA class I molecules 1429 minutes) and measured by the T2 binding assay (Fluorescence Index (FI) native 0.2; FI heteroclitic 0.9). Cytotoxicity of T cells was assessed by chromium release assay and by flow cytometry against CFSE-labelled CLL cells alone and in co-culture with unlabelled stromal cells in the absence or presence of CXCR4 blocking agents. The induced CTLs efficiently lysed allogenic HLA-A2+ CLL cells (mean cytotoxicity at 30:1, 10:1, 3:1 effector-to-target (E:T) ratio: 15,5%+/−2,8; 7,5%+/−2,8; and 1,9%+/− 0,6), but not HLA-A2 negative CLL cells. Co-culture of CLL cells with the murine stromal cell line M2-10B4 resulted in protection of CLL cells from lysis by antigen-specific cytotoxic T cells in vitro, indeed suggesting a protective role of the microenvironment (mean cytotoxicity at 30:1, 10:1, 3:1 E:T ratio: 5,2%+/−4,1; 0,4%+/−1,6; 1,2%+/−2,0). In contrast to apoptosis induced by fludarabine, CXCR4 blocking agents did not reverse the protective effects of the stromal cell line on T cell mediated cytotoxicity (mean cytotoxicity 30:1, 10:1, 3:1 E:T ratio: 3,1%+/−2,4; 0,8%+/−2,5; 2,3%+/−1,6). These data indicate that the microenvironment may exert protective effects against immunotherapeutic strategies in CLL. However, the protective interaction is not entirely mediated by the CXCR4 - CXCL12 axis. Additional cell-cell interactions appear to play a role and need to be identified as therapeutic targets in order to effectively interrupt the protective effect of the microenvironment on T cell mediated cytotoxicity of B-CLL cells.
In recent years, the demand of train-commuting nomadic users for the Internet has been a huge challenge for train and mobile operators. Consequently, train operators have started to deploy in-train ...repeater systems to increase mobile users' service quality. These systems generally follow the structure of static deployments. However, in contrast to a static deployment where the system is set up once using constant parameters that are based on an initial measurement, the train will commute in dense urban city centers and sparsely populated rural areas. We propose a holistic model that helps to understand the role of each system component, namely, cabin pathloss, repeater model, window penetration loss, and outdoor pathloss, in which each individual element can be measured independently. We parametrize the model by measuring an existing in-train repeater deployment of a high-speed train. Finally, we have analyzed the operation of the complete system for two extreme cases of deployment strategy: simple rural and optimized track side. We show that the main benefit of the tested system is visible in the nonoptimized rural deployment. However, the optimized deployment also benefits from the repeater setup.
