Background Adoptive cell therapy of malignant diseases takes advantages of the cellular immune system to recognize and destroy cancer cells. Despite the remarkable success in B cell malignancies after adoptive transfer of CD19 CAR T cells, CAR T cell therapy in solid tumors has shown less encouraging clinical results, above all caused by tumor escape mechanisms.In order to overcome such limitations, NK-92, a permanent and IL-2-dependent cell line with a high cytotoxicity in vitro, has been engineered in preclinical models with CAR. In this project, we exploited a CAR directed against the human antigen hPSMA that is overexpressed in prostate tumors. This project aimed at transducing NK-92 cell line to obtain a hPSMA-specific CAR NK-92 cell population, to be thereafter characterized in vitro and in vivo for antigen-specific functional activity.

Materials and Methods NK-92 cell line was transduced with a lentiviral vector (LV) carrying a CAR anti-hPSMA. The cell population obtained was then sorted and analyzed for degranulation capacity, IFNγ production and lytic activity against hPSMA⁺ (PC3-hPSMA, LNCaP) or hPSMA^-tumor cell lines. In vivo therapeutic efficacy of CAR-transduced NK-92 was evaluated initially using Winn-Assay and than in subcutaneous and orthotopic tumor models.

Results CAR-expressing LV efficiently transduced NK-92 cells, which in turn produced cytokines, degranulated and exerted a relevant cytotoxic upon challenge with PSMA+ prostate tumor cells, irrespective of 10 Gy γ-irradiation. In all the in vivo, tumor models CAR-transduced NK-92 shown a statistically significant inhibition of tumor growth.

Conclusions Chimeric antigen receptor-engineered NK-92 could offer a valid and cost-effective alternative to primary CAR NK or T cells, in particular in cases, where a suitable donor is not available or the sophisticated infrastructure needed for cell isolation, expansion and genetic modification is missing. This work demonstrates that CAR-engineered NK-92 cells display a high and specific recognition of hPSMA+ PC both in vitro as is in vivo, and could represent an efficient strategy as a new therapeutic intervention against prostate carcinoma, thus paving the way to an Off-The-Shelf cellular therapeutic for targeted elimination of cancer cells and induction of protective antitumor immunity.

Disclosure Information G. Zuccolotto: None. A. Penna: None. I.M. Montagner: None. D. Carpanese: None. A. Rosato: None.