Improved Killing of Ovarian Cancer Stem Cells by Combining a Novel Chimeric Antigen Receptor-Based Immunotherapy and Chemotherapy

Ovarian cancer represents the most lethal gynecological cancer. Although cytoreductive chemotherapy and surgery lead to complete macroscopic tumor removal, most of the patients in advanced stages suffer from recurrent disease and subsequently die. This may be explained by the activity of cancer stem cells (CSC), which are a subpopulation of cells with an elevated chemoresistance and an increased capacity for self-renewal and metastatic spread. Specifically targeting these cells by adoptive immunotherapy represents a promising strategy to reduce the risk for recurrent disease. This study selected the widely accepted CSC marker CD133 as a target for a chimeric antigen receptor (CAR)-based immunotherapeutic approach to treat ovarian cancer. A lentiviral vector was generated encoding a third-generation anti-CD133-CAR, and clinically used NK92 cells were transduced. These engineered natural killer (NK) cells showed specific killing against CD133-positive ovarian cancer cell lines and primary ovarian cancer cells cultured from sequential ascites harvests. Additionally, specific activation of these engineered NK cells was demonstrated via interferon-gamma secretion assays. To improve clinical efficacy of ovarian cancer treatment, the effect of the chemotherapeutic agent cisplatin was evaluated together with CAR-transduced NK cell treatment. It was demonstrated that NK cells remain cytotoxic and active under cisplatin treatment and, importantly, that sequential treatment with cisplatin followed by CAR-NK cells led to the strongest killing effect. The specific eradication of ovarian CSCs by anti-CD133-CAR expressing NK92 cells represents a promising strategy and, when confirmed in vivo, shall be the basis of future clinical studies with the aim to prevent recurrent disease.