The treatment with CD19-specific chimeric antigen receptor T-cells (CAR-Ts) has shown remarkable antitumor activity in patients with B-cell malignancies. However, the clinical benefits of CAR-Ts in solid tumors remain unclear. A compelling concern is that in patients with solid tumors CAR-Ts do not immediately encounter their cognate antigen in the circulation and thus lack the appropriate costimulatory signals necessary for full activation. We here sought to explore if expressing IL-15 in CAR-Ts would provide them with sufficient sustained survival until they engage the cognate antigen. Using the GD2-specific CAR and neuroblastoma (NB) as a tumor model, we explored the benefits of incorporating the IL-15 cytokine (and the iCaspase9 suicide gene for safety) within the CAR molecule. CAR-Ts from 12 healthy donors were transduced with an optimized GD2.CAR (encoding the CD28 endodomain) without (GD2-Ts) or with the IL15 (GD2.15.iC9-Ts) and expanded ex vivo with IL-7/IL-15 for 14 days. CAR transduction (82% ± 8% and 82% ± 12%, respectively) and ex vivo antitumor activity in 4 days co-culture at different E:T ratios were comparable. However, upon repetitive stimulation with GD2+ NB tumors (CHLA-255 and LAN-1), only GD2.15.iC9-Ts showed significantly superior expansion and antitumor activity (p<0.05). In vivo in a NB metastatic model in NSG mice engrafted with FireflyLuciferase+ CHLA-255 or LAN-1, IL-15 producing CAR-Ts showed superior antitumor activity at low T-cell doses. Tumor rechallenge experiments clearly highlighted the superior survival of mice receiving GD2.15.iC9-Ts, which was paralleled by higher detection of IL-15 in the circulation and frequency of CAR-Ts in vivo. Remarkably, although CAR-Ts were expanded in the presence of the same amount of exogenous IL-7/IL-15, we observed a significantly higher frequency of “stem-like cells” in GD2.15.iC9-Ts (25% ± 11%, CD45RA+CCR7+) compared to GD2-Ts (6% ± 2%, CD45RA+CCR7+, p<0.001), suggesting that transgenic IL-15 expression favors the preservation of T-cell “stem-ness.” Importantly, CAR-Ts were controllable as the dimerizing drug AP20187 induced cell death of GD2.15.iC9-Ts both in vitro and in vivo. Overall, our data suggest that transgenic IL-15 within the CAR construct can increase the persistence of CAR-Ts targeting NB tumors and preserve more stem-ness. Our results will not only guide therapeutic options for patient with NB, but also CAR-T developmental research for a broad range of solid tumors.

Citation Format: Yuhui Chen, Chuang Sun, Leonid Metelitsa, Gianpietro Dotti, Barbara Savoldo. Eradication of neuroblastoma by T-cells redirected with an optimized GD2-specific chimeric antigen receptor and IL-15 [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A025.