Phase II trial of HER-Vaxx, a B cell peptide-based vaccine, in HER2-overexpressing advanced gastric cancer patients under platinum-based chemotherapy (HERIZON)

Abstract Purpose: A multicenter, randomized, open-label, Phase II study (HERIZON; NCT02795988) was conducted to evaluate the clinical and immunological efficacy of HER-Vaxx (IMU-131), a B-cell, peptide-based vaccine targeting HER2 overexpressed in 6%-30% of gastroesophageal adenocarcinomas (GEAs). Patients and Methods: Patients (n=36) with GEA were treated with standard-of-care chemotherapy (n=17) or HER-Vaxx plus chemotherapy (n=19), using the recommended Phase 2 dose for the vaccine. Overall survival (OS; primary endpoint), safety, progression-free survival (PFS), and clinical response (secondary endpoints), and vaccine-induced HER2-specific antibody levels in serum and correlation with tumor response rates (exploratory endpoints) were investigated. Results: A 40% OS benefit (hazard ratio [HR]: 0.60; median OS: 13.9 months; 80% CI:7.52-14.32) for patients treated with HER-Vaxx plus chemotherapy compared with OS of 8.31 months (80% CI:6.01-9.59) in patients that received chemotherapy-alone. Along with this, a 20% PFS difference was obtained for the vaccination arm (HR: 0.80; 80% CI:0.47, 1.38). No additional toxicity due to HER-Vaxx was observed. The vaccine induced high levels of HER2-specific total IgG and IgG1 antibodies (P<0.001 vs. controls), that significantly correlated with tumor reduction (IgG, P=0.001; IgG1, P=0.016), had a significant capacity in inhibiting phosphorylation of the intracellular HER2-signalling pathways, mediated antibody-dependent cellular cytotoxicity, and decreased immunosuppressive FOXP3+ Tregs. Conclusions: HER-Vaxx plus standard chemotherapy exhibits an excellent safety profile and improves OS. Furthermore, vaccine-induced immune response was significantly associated with reduced tumor size compared to standard-of-care chemotherapy. The presented vaccination approach may substitute for treatment with trastuzumab, upon unavailability or toxicity, based on further evidence of equivalent treatment efficacy.