Abstract B70: Universal adapter CAR-engineered NK-92 cells target patient-derived glioblastoma cancer stem cells

Glioblastoma multiforme (GBM) is the most common and aggressive primary malignant brain tumor in adults. The current standard-of-care treatment, which includes surgical resection, radiation, and chemotherapy, extends the survival of patients to merely 14.6 months. GBM is virtually incurable due to its heterogeneity, which is represented by tumor cells with different patterns of gene expression (proneural, neural, classical, and mesenchymal GBM), the presence of GBM cancer stem (like) cells (CSC), and immune evasion. Thus, new therapeutic strategies directed at eliminating GBM CSC in particular are urgently needed. Utilizing fresh patient material from surgical resections, GBM CSC were successfully enriched and cultivated in serum-free medium and subsequently differentiated by switching to medium containing FBS. The gene expression pattern of both, GBM CSC and differentiated cells, was characterized. Furthermore, a screening platform was tailored for flow-cytometric characterization of patient-specific antigen expression of all newly established glioblastoma cell lines. In this work we present a promising immunotherapeutic approach towards eradication of GBM CSC by combining the universal targeting and controllability of our recently developed adapter chimeric antigen receptor (AdCAR) system with the “off-the-shelf” properties of the continuously expandable and well-characterized NK cell line NK-92. The AdCAR system is based on the unique properties of a novel scFv targeting a “neo”-epitope-like structure derived from the endogenous vitamin biotin, which can be linked to monoclonal antibodies (mAb). Utilizing these biotinylated mAb as adapter molecules, the system allows precise quantitative (on-/off switch) as well as qualitative (change and combination of target antigen) regulation of immune cell function. AdCAR-transduced NK-92 cells demonstrated significant target cell lysis, which, importantly, is largely independent from activation of endogenously expressed NK receptors and the presence of their ligands on target cells but mainly mediated by AdCAR activation through binding to the respective tumor antigen. In the presence of the respective antigen, first and foremost biotinylated antibodies directed at CD9, CD146, CD276, and EGFR were capable of inducing significant AdCAR NK-92-mediated lysis of GBM cells after 2 hours. Interestingly, due to overexpression of various target antigens on GBM cancer stem cells, CSC lysis was noticeably higher as compared