Oncologic Trogocytosis Figure 3. Specific interaction between OVCAR3 cells and Hospicells. A. Adhesion of eGFP-OVCAR3 to Hospicells compared to that of fibroblasts and HBMEC (Human Bone Marrow Endothelial Cells). B and C. Hospicells were seeded on Matrigel coated culture plates allowing them to form a network. eGFP-OVCAR3 cells were then added. eGFP-OVCAR3 cells developed on the Hospicells network. doi:10.1371/journal.pone.0003894.g003 Moreover when seeded on Matrigel pre-coated plates contain- ing Hospicells, eGFP-OVCAR3 were mainly growing on the network previously formed by the stromal cells (Figure 3B and C). peritoneal carcinosis. As displayed in Figure 5, when treated by carboplatin or paclitaxel ECOA managed to survive compared to isolated cancer cells. Chemoresistance assays We were able to demonstrate that co-culture of the two cellular sub-types gave a significant proliferative advantage to the cancer cells. The proliferative advantage was also demonstrated in an in- vivo model of peritoneal carcinosis (Supplementary Figure S1). To investigate their potential role in chemoresistance we conducted a chemoresistance assay. Firstly we demonstrated as displayed in Figure 4A that the co-culture of Hospicells and OVCAR3 cells induced a chemo-resistant profile with differences of 2.2 to 2.5 fold between the co-culture and the eGFP-OVCAR3 cells alone depending the chemotherapeutic agents used, (p,0.05). This effect was Hospicells specific, HBMEC and fibroblasts being unable to confer chemoresistance, and was mediated by direct cell contact as shown by transwell experiments (Figure 4B). We then investigated the role of Multi Drug Resistance (MDR) proteins by conducting a chemoresistance assay in the presence of the selective drug-efflux pump inhibitor, Verapamil [18,19]. Verapamil abrogated the acquisition of chemoresistance (Figure 4C), thus establishing the involvement of MDR proteins. The effect of Hospicells among ECOA was assessed by treating freshly isolated ECOA form non-previously treated patients with ovarian Membrane exchange Intercellular communication by mechanisms such as peptide transfer through gap-junctions, ligand-receptor interactions and membrane protein transfer can lead to the acquisition of complex phenotypes [20]. Most lymphoid cells actively capture membrane pieces from antigen-presenting cells to which they are bound during antigen recognition or from target cells such as cancer cells [21–23]. This phenomenon, called trogocytosis, can also occur between certain cancer cells in the absence of an exogenous stimulus. To test this hypothesis, we adapted the trogocytosis assay to the capture of Hospicell membranes by co-incubated OVCAR3 cells. Hospicells’ membrane were stained with a lipophylic fluorescent dye PKH67; after three hours of incubation, OVCAR3 cells acquired strong green fluorescence as a result of the capture of labelled Hospicells’ membrane fragments (an increase in mean fluorescence intensity (mfi) from 196 to 4315, Figure 6A). When the OVCAR3 cells were labelled instead, the Hospicells also acquired green fluroescence, but to a lesser extent (an increase in mfi from 92 to 658, Figure 6B). Massive Hospicells’ membrane acquisition by bound OVCAR3 cells was confirmed by confocal microscopy (Figure 6C and D). We have thus demonstrated that PLoS ONE | www.plosone.org 4 December 2008 | Volume 3 | Issue 12 | e3894