Effect of PD1/PD-L1 checkpoint blockade on efficacy of anti-GD2 antibody ch14.18/CHO in neuroblastoma.

Abstract

10548 Background: Immunotherapy (IT) with anti-GD2 antibody (Ab) ch14.18/CHO is effective for treatment of high-risk neuroblastoma (NB) patients mainly due to induction of GD2-specific Ab-dependent cellular cytotoxicity (ADCC). Methods to further enhance the effect are important and currently explored in prospective clinical trials randomizing ch14.18/CHO ± scIL-2. Programmed death-1 (PD-1) is an inhibitory receptor expressed by activated T- and NK-cells, and cancer cells express PD-1 ligand. Here, we report for the first time effect and mechanism of PD-1/PD-L1 blockade in the context of ch14.18/CHO-based IT in preclinical models. Methods: Expression of PD-L1 and PD-1 on NB cells and leukocytes was analyzed by RT-PCR and flow cytometry in the presence of ch14.18/CHO or IL-2. Mechanism of PD-L1 induction was analyzed with anti-CD11b Ab. The effect of PD-1/PD-L1 blockade on ch14.18/CHO-mediated anti-NB immune response was evaluated using anti-PD-1 Ab both in vitro (Nivolumab) and in the syngeneic GD2+ NB NXS2 mouse model (anti-mouse PD-1). Mice (n = 10) were treated with ch14.18/CHO (5x300 µg, i.p.) in combination with anti-PD-1 (8x250 µg, i.p.), and compared to controls. Results: Culture of LA-N-1 (low PD-L1 baseline expression) in the presence of leukocytes and subtherapeutic ch14.18/CHO concentrations for 24h induced strong upregulation of PD-L1 resulting in complete inhibition of ADCC mediated by ch14.18/CHO. Co-incubation with anti-CD11b Ab abrogated this PD-L1 upregulation. Importantly, blockade with Nivolumab reversed the PD-L1-dependent inhibition of ADCC. Mice treated with ch14.18/CHO in combination with PD-1 blockade showed a strong reduction of tumor growth and prolonged survival as well as the highest level of NB cell lysis mediated by serum and leukocytes compared to controls. Conclusions: Ch14.18/CHO-mediated effects upregulate the inhibitory checkpoint PD-1/PD-L1 and combination of ch14.18/CHO with PD-1/PD-L1 blockade results in synergistic treatment effects in mice. This concept will be evaluated in a clinical trial.