A Phase 1 Dose Escalation Trial of Ex-Vivo Expanded Allogeneic Cord Blood-Derived Natural Killer Cell Immunotherapy for Pediatric Solid Tumor Malignancies

2546 Background: Despite aggressive multimodality therapy, survival outcomes of most patients with recurrent/refractory solid tumors remain dismal. Preclinical data have shown that natural killer (NK) cells play a significant role in controlling cancer progression, metastasis, and survival. In this phase I dose escalation trial, we evaluated the safety and phase 2 recommended dose of cord blood derived NK cells in children and young adults with recurrent/refractory pediatric solid tumors. Methods: Eligible patients were 1-40 years old. Cord blood donors were 4, 5, or 6/6 HLA matched. Ex-vivo, antigen presenting cell-mediated expansion of human cord blood derived NK cells was performed over 14 days. All patients received lymphodepleting regimen with cyclophosphamide (500 mg/m 2 /day) and etoposide (100 mg/m 2 /day) for 5 days (days -7 to -3) followed by 2 days rest and a single infusion of NK cells on Day 0. The study evaluated two dose levels using a standard 3+3 phase I trial design with an expansion cohort at the maximum tolerated dose. Results: Twelve patients (median age 16 years) received NK cells infusions. Tumor types included osteosarcoma (n = 7), Ewing sarcoma (n = 4), and synovial sarcoma (n = 1). Three patients received NK cells at dose level 1 (5 X 10 7 /Kg), and nine patients at dose level 2 (1 X10 8 /Kg), which was determined to be the recommended Phase 2 dose. No dose-limiting toxicities were observed. Most adverse events were grade 1 and 2 (fatigue, dizziness, nausea and vomiting). Most frequently observed grade 3 and 4 adverse events were leukopenia, neutropenia, lymphopenia, and thrombocytopenia. No cytokine release syndrome or neurotoxicity was observed. Allogeneic NK cells were detected in recipients’ peripheral blood as high as 100% of all NK cell populations and as late as 9 days post infusion. Of the 9 patients evaluable for tumor response, 3 patients (with osteosarcoma) had stable disease and 6 had progressive disease. Conclusions: Allogeneic ex-vivo expanded NK cells immunotherapy demonstrated favorable safety profile in patients with advanced pediatric solid tumors. Strategies to improve efficacy are warranted including using adjuvant therapy to increase persistence, more stringent selection strategies and gene editing approaches to increase alloreactivity against recipient tumor cells. Clinical trial information: NCT03420963 .