Phase Ib/II study of imprime PGG and pembrolizumab in patients with previously treated advanced non-small cell lung cancer (NSCLC): BTCRC LUN 15-017.

Background: Therapeutic strategies to engage anti-tumor innate immunity are still underdeveloped. Imprime PGG (imprime), a pathogen-associated molecular pattern (PAMP), through pattern recognition receptors, successfully illicit a broad-based innate immune response in preclinical models against various cancers. We aimed to study safety and efficacy of imprime in combination with pembrolizumab in advanced stage non-small cell lung cancer (NSCLC).

Methods: We conducted an investigator-initiated, multi-institutional, single-arm, phase Ib/II trial in previously treated, advanced stage NSCLC patients. Primary endpoints were maximum-tolerated dose (MTD) of imprime for the phase Ib, and progression-free survival (PFS) for the phase II study (NCT03003468).

Results: All 33 eligible patients were included in the safety analysis. No dose-limiting toxicity was observed and the imprime dose of 4 mg/kg was determined as the MTD. Thirty patients treated at the MTD (phase Ib, 6; phase II, 24) were included in the efficacy analysis. Median length of follow-up was 10.8 months. Confirmed objective response rate was 10% [95% confidence interval (CI): 2-27%], with one complete and two partial responses. Median PFS was 2.6 months (95% CI: 1.4-7.0), and 6- and 12-month PFS rates were 37% and 17%, respectively. Median overall survival (OS) was 11.1 months, and 6- and 12-month OS rates were 75% and 46%. Univariate analysis was performed to assess the impact of age, sex, race, disease-stage, programmed death-ligand 1 (PD-L1) expression levels, and prior immunotherapy on PFS and OS. Of these, prior immunotherapy negatively influenced OS [hazard ratio (HR): 2.95, 95% CI: 1.21-7.24]. Overall, the combination was safe and tolerable.

Conclusions: The combination of imprime and pembrolizumab is tolerable but did not improve the outcome of advanced stage NSCLC patients who previously progressed on anti-programmed death 1 (PD-1)/PD-L1 immunotherapies. Further investigation is needed to understand the effects of therapeutic PAMPs to mount a strong innate immune response against cancer.