Toxicity of L19-Interleukin 2 Combined with Stereotactic Body Radiation Therapy: A Phase 1 Study

The immunocytokine L19-IL2 delivers interleukin-2 to the tumor by exploiting the selective L19-dependent binding of extradomain B of fibronectin on tumor blood vessels. In preclinical models, L19-IL2 has been shown to enhance the local and abscopal effects of radiation therapy. The clinical safety of L19-IL2 monotherapy has been established previously. In this study, the safety and tolerability of L19-IL2 after stereotactic body radiation therapy (SBRT) was assessed.

Patients with oligometastatic solid tumors received radical SBRT to all visible metastases. Within 1 week after SBRT, intravenous L19-IL2 using a 3 + 3 dose escalation design was administered. Safety and tolerability were analyzed as the primary endpoint using the Common Terminology Criteria for Adverse Events 4.03 scoring system, with progression-free and overall survival as secondary endpoints.

A total of 6 patients in 2 L19-IL2 dose levels were included. The 15 million International Units (Mio IU) dose level was well tolerated with no dose-limiting toxicity. The most frequently reported adverse events were chills, noninfectious fever, fatigue, edema, erythema, pruritus, nausea/vomiting, and cough and dyspnea. Blood analysis revealed abnormalities in liver function tests, anemia, hypoalbuminemia, and hypokalemia. At the second dose level (ie, 22.5 Mio IU), which is the recommended dose for L19-IL2 monotherapy, all 3 included patients experienced dose-limiting toxicity but recovered without sequelae. We documented 2 long-term progression-free responders, both having non-small cell lung cancer as primary tumor.

Based on the results of this phase 1 clinical trial, the recommended phase 2 dose for SBRT combined with L19-IL2 is 15 Mio IU. The therapeutic efficacy of this combination is currently being evaluated in the multicentric EU-funded phase 2 clinical trial, ImmunoSABR.