China-based Forlong Biotechnology has announced approval to initiate a Phase I clinical trial of FL115, an IL-15/IL-15Rα-Fbody fusion protein, in patients with advanced solid tumors in Australia. The trial will dose FL115 once every three weeks, a schedule designed to exploit the pharmacokinetic advantages of subcutaneous delivery over the intravenous route used in prior studies.
FL115 activates NK and CD8+ T cells through IL-15-mediated signaling, promoting anti-tumor cytotoxicity, while its engineered Fbody domain preserves FcRn-mediated half-life extension without triggering Fcγ receptor or complement activation. Preclinical studies showed more than 20-fold lower peak drug exposure while maintaining ≥60% bioavailability, a profile intended to reduce cytokine-related toxicity while sustaining immune activation.
The Australian trial follows completion of two Phase I IV monotherapy studies — one conducted in the US (FL115-101, 11 patients) and one in China (FL115-102, 23 patients) — in heavily pretreated patients with advanced solid tumors. Across both studies, Forlong reported a favorable safety profile and preliminary efficacy: three patients achieved durable disease control beyond 12 months, including two confirmed partial responses and one stable disease. A disease control rate of 41% with a 7% partial response rate was reported from the combined Phase I data. Those results were presented as a late-breaking abstract at the Society for Immunotherapy of Cancer (SITC) 2025 annual meeting and at the 2026 American Society of Clinical Oncology (ASCO) annual meeting.
The only approved IL-15 agonist is ImmunityBio's Anktiva (nogapendekin alfa inbakicept), approved with BCG for BCG-unresponsive NMIBC. Unlike Anktiva, FL115 is being developed across solid tumors and bladder cancer, with Forlong arguing that its engineered Fbody design may improve the therapeutic window. No comparative clinical data are available.