Abstract CT147: Phase 1 study of recombinant interleukin 15 (rhIL-15) in combination with checkpoint inhibitors nivolumab and ipilimumab in subjects with refractory cancers

Abstract Introduction: Recombinant human interleukin 15 (rhIL-15) has been shown to stimulate the activation and expansion in the number of effector T lymphocytes and natural killer cells in patients. The addition of the immune checkpoint inhibitors (ICI) CTLA-4 and PD-1 has shown increased antitumor efficacy in preclinical models, and the triplet is hypothesized to enhance anti-tumor immune response by augmenting effector cell expansion, differentiation, cytotoxic activity, and immune checkpoint inhibition. Results of the lead-in safety arms of rhIL-15/ipilimumab (Ipi) or rhIL-15/nivolumab (N) doublets were previously reported (O’Sullivan et al. AACR. 2019) and we now report results for the dose escalation phase of the triplet combination (NCT03388632). Methods: This phase 1, open-label, 3+3 dose escalation trial enrolled adult patients (pts) with measurable metastatic or refractory solid tumors and ECOG performance status ≤2. Prior therapy with 2 of the 3 study agents was permitted. Pts were treated on three dose levels (DL 1-3) of rhIL-15 (0.5, 1, or 2 mcg/kg/day) administered subcutaneously on days (D)1-8 and D22-29 of a 6-week cycle for the first 4 cycles only. Nivolumab (240mg IV) was administered on D8, 22, 36 and ipilimumab (1mg/kg IV) on D8 of every cycle. Response was assessed by RECIST 1.1. Upon progression, pts could continue for response assessment utilizing iRECIST if clinically stable and without toxicity. Treatment-induced changes in circulating and tumor T cell activation, signaling, and the PD-L1 checkpoint will be assessed with validated pharmacodynamic biomarker assays. Results: A total of 17 pts were enrolled on the triplet dose escalation phase; 15 pts were evaluable for response and 6 pts had received prior treatment with a PD-1/PD-L1 inhibitor. Median time on treatment (MTT) was 12 weeks (range 3-101). A confirmed partial response (PR) was observed in a pt with intrahepatic cholangiocarcinoma (MSI-H) after 3 cycles (total time on treatment 101 weeks). Across all dose levels, 7 pts (46.7%) had stable disease (SD) that prolonged their time on treatment with MTT of 20.4 weeks; 7 pts (46.7%) experienced progressive disease (PD) with MTT of 6.4 weeks. To better profile toxicity, 5 pts were replaced due to incomplete dosing of C1. Dose limiting toxicities at DL 3 (rhIL-15 at 2 mcg/kg/day) were photosensitivity and rash. Main drug-related adverse events included grade 4 lymphopenia (n=1) and grade 3 colitis, hyperthyroidism, hyponatremia, myocarditis, neutropenia, and photosensitivity (n=1, each). No pts discontinued therapy due to toxicity events. No deaths occurred on study. Conclusions: The recommended phase 2 dose (RP2D) of rhIL-15 is 1 mcg/kg/day when administered in combination with N+Ipi. The triplet dose expansion phase with the RP2D is currently accruing and includes biomarker studies in blood and tumor biopsies to assess the tumor microenvironment. This study was funded in part by NCI Contract HHSN261200800001E. *In memorium: Dr. Thomas Waldmann7. Citation Format: Sarah J. Shin, Geraldine O'Sullivan Coyne, Howard Streicher, Naoko Takebe, Ashley Bruns, Elad Sharon, Richard Piekarz, Lamin Juwara, Larry Rubinstein, Ralph Parchment, Kristin Fino, King L. Fung, Katherine Ferry-Galow, Arjun Mittra, Abdul Rafeh Naqash, Kevin Conlon, James H. Doroshow, Alice P. Chen. Phase 1 study of recombinant interleukin 15 (rhIL-15) in combination with checkpoint inhibitors nivolumab and ipilimumab in subjects with refractory cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT147.