Abstract
Purpose: This study explored the combination of fibroblast activation protein (FAP) IL2 variant (FAP-IL2v), a novel immune-cytokine, with pembrolizumab in patients with advanced and/or metastatic melanoma. Patients and methods: This open-label, multicenter, phase Ib clinical study (NCT03875079) evaluated the safety, tolerability, pharmacodynamics, pharmacokinetics, and antitumor activity of FAP-IL2v (simlukafusp alfa, RO6874281) in combination with pembrolizumab. Patients with advanced and/or metastatic melanoma were either checkpoint inhibitor (CPI)-naïve or CPI-experienced. Patients received 10 mg FAP-IL2v either continuously once every 3 weeks (Q3W) or in an induction/maintenance setting consisting of a 3-week induction phase with weekly (QW) dosing followed by continuous Q3W dosing. Pembrolizumab was dosed Q3W at 200 mg. Results: Eighty-three patients were treated: 16 patients in two safety run-in cohorts and 67 patients in two extension cohorts; 75 (90.4%) patients were CPI-experienced. The pharmacokinetics of FAP-IL2v in combination with pembrolizumab was similar to that after administration as monotherapy. Consistent with the proposed mode of action, FAP-IL2v preferentially expanded NK and CD8 T cells. The most common FAP-IL2v-related grade 3/4 adverse events were lymphopenia (23%), elevated γ-glutamyltransferase (8%), elevated alanine aminotransferase (6%), and infusion-related reaction (6%). A response was observed in 5 of 75 (6.7%) CPI-experienced patients (all partial responses) and 2 of 8 CPI-naïve patients (one complete response and one partial response). The median progression-free survival was 3.1 months. Conclusions: The safety profile of FAP-IL2v in combination with pembrolizumab was manageable and consistent with the known safety profile. However, further exploration of FAP-IL2v and pembrolizumab was precluded in patients with melanoma with prior CPI due to the lack of clinical activity. Significance: In this phase Ib study, the combination of FAP-IL2v, an immune-cytokine developed to overcome the limitations of wild-type IL2, with the CPI pembrolizumab did not show meaningful antitumor activity in patients who had progressed on prior CPI therapy, suggesting that FAP-IL2v alone cannot overcome CPI resistance or unresponsiveness.