BackgroundChronic lymphocytic leukemia B-cells display prolonged survival in vivo, but when cultured in vitro rapidly undergo spontaneous apoptosis. We hypothesize that interaction with endothelial cells in infiltrated tissues and during recirculation may have a pathogenetic role in chronic lymphocytic leukemia.Design and MethodsWe evaluated apoptosis of leukemic cells after co-culture on HUVEC monolayer with addition of Fludarabine and blocking adhesion antibodies. Then, we compared microarray-based expression profiles between leukemic cells at baseline and after co-culture.ResultsWe found that endothelial layer protected leukemic cells from apoptosis inducing a 2-fold mean decrement in apoptotic cells after 2 days co-culture. Moreover, endothelial layer decreased sensitivity of chronic lymphocytic leukemia B-cells to Fludarabine-induced apoptosis. Physical contact with endothelium mediated by both β1- and β2- integrins is essential for survival advantage. In particular, blocking CD106 on endothelial cells or CD18 on leukemic B-cells determined the almost complete abrogation of survival advantage (>70% inhibition of viability). Conversely, a reduction of apoptosis was also measured in leukemic cells cultured in conditioned medium collected after 2 days of co-culture, implying that survival is partially mediated by soluble factors. Overall, the contact with endothelial cells modulated 1,944 genes on chronic lymphocytic leukemia B-cells, establishing a peculiar gene expression profile: up-regulation of angiogenesis-related genes, increase of genes involved in TGFβ and Wnt signalling pathways, secretion of cytokines recruiting stromal cells and macrophages and increase in anti-apoptotic molecules such as Bcl2 and Survivin. ConclusionOur study supports the notion that endothelial cells are major players in chronic lymphocytic leukemia microenvironment. Adhesion to endothelium strongly sustains survival, protects from drug-induced apoptosis and widely modifies gene expression profile of leukemic cells.
Physical contact with endothelial cells through β1- and β2- integrins rescues chronic lymphocytic leukemia from spontaneous and drug-induced apoptosis and induces a peculiar gene expression profile on leukemic cells.
DEAGLIO, Silvia;
2012-01-01
Abstract
BackgroundChronic lymphocytic leukemia B-cells display prolonged survival in vivo, but when cultured in vitro rapidly undergo spontaneous apoptosis. We hypothesize that interaction with endothelial cells in infiltrated tissues and during recirculation may have a pathogenetic role in chronic lymphocytic leukemia.Design and MethodsWe evaluated apoptosis of leukemic cells after co-culture on HUVEC monolayer with addition of Fludarabine and blocking adhesion antibodies. Then, we compared microarray-based expression profiles between leukemic cells at baseline and after co-culture.ResultsWe found that endothelial layer protected leukemic cells from apoptosis inducing a 2-fold mean decrement in apoptotic cells after 2 days co-culture. Moreover, endothelial layer decreased sensitivity of chronic lymphocytic leukemia B-cells to Fludarabine-induced apoptosis. Physical contact with endothelium mediated by both β1- and β2- integrins is essential for survival advantage. In particular, blocking CD106 on endothelial cells or CD18 on leukemic B-cells determined the almost complete abrogation of survival advantage (>70% inhibition of viability). Conversely, a reduction of apoptosis was also measured in leukemic cells cultured in conditioned medium collected after 2 days of co-culture, implying that survival is partially mediated by soluble factors. Overall, the contact with endothelial cells modulated 1,944 genes on chronic lymphocytic leukemia B-cells, establishing a peculiar gene expression profile: up-regulation of angiogenesis-related genes, increase of genes involved in TGFβ and Wnt signalling pathways, secretion of cytokines recruiting stromal cells and macrophages and increase in anti-apoptotic molecules such as Bcl2 and Survivin. ConclusionOur study supports the notion that endothelial cells are major players in chronic lymphocytic leukemia microenvironment. Adhesion to endothelium strongly sustains survival, protects from drug-induced apoptosis and widely modifies gene expression profile of leukemic cells.
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