Monocytes and the 38kDa-antigen of mycobacterium tuberculosis modulate natural killer cell activity and their cytolysis directed against ovarian cancer cell lines
1 Department of Otorhinolaryngology, University of Duisburg-Essen, Essen, 45147, Germany
2 Department of Gynecology and Obstetrics, University of Duisburg-Essen, Essen, 45147, Germany
3 LIONEX Diagnostics and Therapeutics GmbH, Salzdahlumer Straße 196, Braunschweig, 38126, Germany
BMC Cancer 2012, 12:451 doi:10.1186/1471-2407-12-451Published: 4 October 2012
Despite strong efforts to improve clinical outcome of ovarian cancer patients by conventional and targeted immuno-based therapies, the prognosis of advanced ovarian cancer is still poor. Natural killer (NK) cells mediate antibody-dependent cellular cytotoxicity (ADCC), release immunostimulatory cytokines and thus function as potent anti-tumour effector cells. However, tumour cells developed mechanisms to escape from an effective immune response. So highly immunogenic substances, like the 38 kDa-preparation of M. tuberculosis, PstS-1, are explored for their potential to enhance cancer-targeted immune responses. In this study we examined the modulation of different NK cell functions by accessory monocytes and PstS-1. We focussed on NK cell activation as well as natural and antibody-dependent cellular cytotoxicity directed against epidermal-growth-factor-receptor (EGFR)-positive ovarian cancer cell lines.
Activation, cytokine release and cytotoxicity of NK cells stimulated by monocytes and PstS-1 were determined by FACS-analysis, ELISA, Bioplex assay and quantitative polymerase-chain reaction (qPCR). Transwell assays were used to discriminate cell-cell contact-dependent from contact-independent mechanisms. Five ovarian cancer cell lines (A2780, IGROV-1, OVCAR-3, OVCAR-4 and SKOV-3) with different EGFR-expression were used as target cells for natural and antibody-dependent cellular cytotoxicity assays. Cetuximab (anti-EGFR-antibody) was used for ADCC studies.
Our data show that monocytes effectively enhance activation as well natural and antibody-dependent cytolytic activity of NK cells. PstS-1 directly stimulated monocytes and further activated monocyte-NK-co-cultures. However, PstS-1 did not directly influence purified NK cells and did also not affect natural and antibody-dependent cellular cytotoxicity directed against EGFR-positive ovarian cancer cells, even in presence of monocytes. Direct cell-cell contact between NK cells and monocytes was required for NK activation, while released cytokines seemed to play a minor role.
Our data suggest that monocytes enhance natural and antibody-dependent cytotoxic activity of NK cells in a cell-cell contact dependent manner. The TLR-agonist PstS-1 provides additional monocyte activation and induces NK activation markers, while NK cytotoxicity remains unaffected. We conclude that monocytes provide accessory function for ADCC exerted by NK during antibody-based cancer immunotherapy directed against EGFR-positive ovarian cancer cells.