Abstract LB-382: Engineered NK92MICD64 cell docking platform as a combination therapy approach for prostate cancer

Natural killer (NK) cells are cytotoxic lymphocytes that detect and kill virally infected or malignant cells. Targeting NK cells to solid tumors can be improved by engineering NK cells to express CD64 (FcγR1), a high affinity receptor for human IgG Fc, in combination with therapeutic monoclonal antibodies (mAbs). CD64 can capture soluble mAbs with two to three orders of magnitude higher affinity than CD16A (FcγIIIA) and mediates tumor cell killing when anti-tumor mAb is bound. This docking platform allows for switchable targeting elements to effectively direct the NK cells to multiple tumor antigens. We are targeting several relevant prostate cancer (PCa) antigens including TROP2, a transmembrane glycoprotein that is overexpressed in metastatic PCa, and FAP, a membrane bound serine protease expressed by cancer-associated fibroblasts in the tumor microenvironment. For all cytotoxicity experiments, we used an immortalized human PCa stromal cell line that highly expresses FAP (hPrCSC-44) and a human PCa cell line that highly expresses TROP2 (DU145). Cell killing was measured using the Delfia EuTDA cytotoxicity assay. First, we tested for mediation of NK92MICD64 cell antibody dependent cell cytotoxicity (ADCC) using a titration of anti-FAP or anti-TROP2 mAb (5 to 0 µg/mL) and saw a concentration dependent effect on cell killing. Next, CD64 capture of soluble anti-FAP or anti-TROP2 mAb was tested by flow cytometry. Over 98% of the NK92MICD64 cells incubated with the therapeutic mAbs were positively stained, indicating that the mAbs dock to CD64 and could direct tumor cell killing. Therapeutic efficacy of anti-FAP or anti-TROP2 mAb bound to NK92MICD64 cells (αFAP-NK92MICD64 and αTROP2-NK92MICD64) was tested by incubating the effector cells with hPrCSC-44 or DU145 cells at several effector:target (E:T) ratios. Potent cytotoxicity was observed and the % specific release was significantly higher than the NK92MICD64 cells alone. Cytotoxicity dropped to baseline levels when the anti-tumor mAb was switched to an isotype control, indicating that the mAb-directed cell killing occurs by an antigen-selective mechanism. After seeing the success of the monotherapies, we wanted to evaluate αFAP-NK92MICD64 and αTROP2-NK92MICD64 cells as a combination therapy. Previous studies have reported a synergistic effect of combination therapies that target both the tumor stroma and malignant cells. To test our approach, hPrCSC-44 and DU145 cells were co-incubated with αFAP-NK92MICD64 and αTROP2-NK92MICD64 cells at several E:T ratios. We observed potent cytotoxicity and % specific release was significantly higher than the NK92MICD64 cells alone. In conclusion, CD64 on NK92MI cells facilitated ADCC and cytokine production demonstrating functional activity in our prostate cancer models. The use of CD64 as a docking platform for therapeutic mAbs was shown to effectively mediate tumor cell killing. Together, these data suggest the potential for our combination cell therapy to be developed as a new therapeutic approach for PCa. Citation Format: Hallie M. Hintz, Aaron M. LeBeau. Engineered NK92MICD64 cell docking platform as a combination therapy approach for prostate cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-382.