Abstract CT215: Frontline vaccination with the B-cell peptide compound HER-Vaxx (IMU-131), combined with standard-of-care chemotherapy induces high levels of HER2-specific antibodies mediating ADCC and intracellular phosphorylation inhibition resulting in overall survival benefit in patients with HER2+ metastatic or advanced gastric/GEJ adenocarcinoma - Final results from Phase II/HERIZON study
Authors: Tobias Joshua , Kundi Michael , Garner-Spitzer Erika , Zielinski Christoph , Maglakelidze Marina , Andric Zoran , Petrovic Zoran , Nagarkar Rajnish , Chawla Tanuj , Chong Leslie Mi Ok , Nixon Bonnie , Yavrom Sharon , Ede Nicholas J. , Wiedermann Ursula 
Published: April 2024

Background: HER2, a member of the epidermal growth factor receptor (EGFR) family, is overexpressed in approximately 30% of gastric cancers. HER-Vaxx is a B cell peptide-based anti-HER2 vaccine (IMU-131) comprising trastuzumab’s binding site. Here, we present the results of the randomized open-label, multicenter phase 2 HERIZON trial (NCT02795988), which compared HER-Vaxx plus chemotherapy to chemotherapy alone. The study aimed to evaluate clinical (primary endpoint) and antibody (secondary endpoint) responses in patients with HER2-overexpressing gastric/gastro-esophageal junction (GC) cancer naïve to anti HER2 therapy.

Methods: Patients were randomized to chemotherapy alone (n=17) or HER-Vaxx (50µg, recommended phase 2 dose) plus chemotherapy (n=19). In the HER-Vaxx group, patients received the vaccine at days 0, 14, 35, and 77, then every 63 days until disease progression. Chemotherapy consisted of oxaliplatin plus capecitabine and was started at day 0, repeated every 21 days for a maximum of 6 cycles. The clinical responses were assessed by RECIST 1.1 criteria. FACS analysis of PBMCs for immunophenotyping was carried out, as well as in vitro phosphorylation inhibition assays of HER2 and the signaling pathway kinases Akt and MAPK, and mediation of ADCC to characterize the vaccine-induced IgG antibodies.

Results: A 42% survival benefit for patients treated with HER-Vaxx plus chemotherapy [median overall survival: 13.9 months (7.5, 14.3)] compared to chemotherapy alone [mOS: 8.3 months (6.0, 9.6)] was shown, which translated into an OS HR of 0.580 (80% 2-sided CI: 0.362, 0.927). A highly significant HER2-specific IgG and IgG1 antibody response at all time points, particularly after 3 or more doses of HER-Vaxx were induced (P&lt;0.001). The HER-Vaxx antibody response correlated well with mediating ADCC (IgG, P=0.003; IgG1, P=0.05) and the anti-tumor effect (IgG, P=0.001; IgG1, P=0.016). Moreover, the HER-Vaxx-induced IgG antibodies exhibited binding to the gastric cancer cell line N87, with capacity to inhibit HER2 signaling pathway kinases Akt and MAPK phosphorylation. It also demonstrated decreased levels of Foxp3+ Tregs (P=0.0013).

Conclusions: The previously shown safety profile of HER-Vaxx, along with the improved clinical and antibody responses in HER2-overexpressing GC patients shown here, validate the proof of concept for a first-in-class B-cell immunotherapy based on HER2 B-cell peptides. Clinical trials evaluating further treatment with HER-Vaxx in HER2+ GC are ongoing.

Citation Format: Joshua Tobias, Michael Kundi, Erika Garner-Spitzer, Christoph Zielinski, Marina Maglakelidze, Zoran Andric, Zoran Petrovic, Rajnish Nagarkar, Tanuj Chawla, Leslie Mi Ok Chong, Bonnie Nixon, Sharon Yavrom, Nicholas J. Ede, Ursula Wiedermann. Frontline vaccination with the B-cell peptide compound HER-Vaxx (IMU-131), combined with standard-of-care chemotherapy induces high levels of HER2-specific antibodies mediating ADCC and intracellular phosphorylation inhibition resulting in overall survival benefit in patients with HER2+ metastatic or advanced gastric/GEJ adenocarcinoma - Final results from Phase II/HERIZON study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT215.