gms | German Medical Science

Objective: NK cells represent an important component of the innate immune system and are characterized by simultaneous expression of various inhibitory and activating receptors. They have been emerging as new effectors for immunotherapy of cancer. In particular the engraftment of chimeric antigen receptors (CARs) consisting of a single chain antibody fragment (scFv) fused to the CD3 zeta signaling adapter revealed promising results in preclinical studies. In our study we sought to develop a new NK cell CAR based on the activating NKp46 receptor, which is an essential activating NK cell receptor for controlling Influenza infection and which signals via an associated CD3 zeta chain. The aim of the study was to generate and evaluate an alphaPSCA-NKp46 CAR for redirecting NK cells to glioma cells expressing the prostate stem cell antigen (PSCA).

Method: The NK cell line YTS was subsequently transduced with lentiviral vectors encoding for novel chimeric antigen receptor alphaPSCA-NKp46 and the CD3 zeta chain, a signaling adapter protein of NK cells containing three immunoreceptor tyrosine-based activation motifs. As negative controls for the experiments we included YTS cells transduced with wild type NKp46 and CD3 zeta, respectively. Efficient transduction of cells and surface expression of receptors and the signaling adapter protein was assessed by FACS-staining. The efficacy of alphaPSCA-NKp46 to redirect NK cells to PSCA-positive targets was tested in a chromium release assay.

Results: YTS cells were efficiently transduced with alphaPSCA-NKp46 and the CD3 zeta chain by using a lentiviral vector system. After antibiotic selection of transduced cells FACS analysis revealed that 90-100% of YTS cells were positive for CD3 zeta and alphaPSCA-NKp46 expression. YTS cells engrafted with the chimeric alphaPSCA-NKp46 receptor and the CD3 zeta chain conferred a selective cytotoxicity against PSCA-positive target cells, whereas controls showed no effect.

Conclusions: Our results suggest that the NKp46-based CAR format efficiently redirects YTS NK cells to tumor cells in an antigen-dependent manner and therefore might be suitable for NK-cell based immunotherapy of tumors, in particular PSCA-positive gliomas.