Characterization of a Novel Third-Generation Anti-CD24-CAR against Ovarian Cancer

Novel therapeutic approaches against ovarian cancer (OC) are urgently needed because of its high rate of recurrence even after extensive surgery and multi-agent chemotherapy. We aimed to develop a novel anti-CD24 chimeric antigen receptor (CAR) as an immunotherapeutic approach against OC cells and cancer stem cells (CSC). CSC represents a subpopulation of the tumor characterized by enhanced chemoresistance as well as the increased capability of self-renewal and metastasis. We designed a codon-optimized third-generation CAR containing the highly active single chain variable fragment (scFv) "SWA11" against CD24. We equipped the human NK-cell line NK-92 with the anti-CD24 CAR and an anti-CD19 control CAR using lentiviral transduction. Engineered NK-92 cells showed high cytotoxic activity against CD24-positive OC cell lines (SKOV3, OVCAR3). This effect was restricted to CD24-expressing cells as shown after lentiviral transduction of CD24-negative cell lines (A2780, HEK-293T) with CD24 transmembrane proteins. Additionally, NK-92 cells equipped with our novel anti-CD24 CAR were highly effective against patient-derived primary ovarian cancer cells. The activation of NK cells was shown by specific IFNγ secretion upon antigen stimulation. To further reduce possible off-target effects in vivo, we applied a dual-CAR approach using an anti-CD24-CD28-41BB fusion protein linked via a 2A sequence to an anti-mesothelin-CD3ζ-CAR. The dual-CAR was simultaneously active against CD24 and mesothelin expressing cells. Our novel anti-CD24-CAR showed a highly cytotoxic effect against OC cell lines and primary OC cells and will be evaluated in future in vivo trials as a promising immunotherapeutic approach against OC.