1212PComprehensive results of a phase Ib study with a HER2/neu B-cell peptide vaccine administered with cisplatin and 5-fluorouracil or capecitabine chemotherapy show safety, immunogenicity and clinical response in patients with HER2/Neu overexpressing advanced gastric cancer

Abstract Background HER2/neu is overexpressed in 15-25% of gastric cancer patients and associated with poor prognosis. Treatment with recombinant monoclonal Abs against HER2/neu is effective yet alternatives are needed due to cost and global availability issues. Thus a peptide vaccine (IMU-131) was developed, consisting of 3 fused B-cell epitopes (p467) from the HER2/neu extracellular domain coupled to CRM197 and administered with the adjuvant Montanide. The present study evaluated the optimal/safe vaccine dose leading to immunogenicity and clinical responses. Methods In an open-label multicenter Phase Ib trial (SE-Asia & Eastern Europe), 14 patients with HER2/neu overexpressing ( ++/ +++) gastric adenocarcinoma were recruited to receive 3 injections of IMU-131 (days 0, 14, 35) in combination with chemotherapy (CT). Dose escalation (10, 30 and 50 µg) was performed in 3 cohorts (C) to evaluate safety, immunogenicity and clinical responses. Results No SAEs related to IMU-131 administration were reported. Eleven patients were evaluable for vaccine-specific immune responses and RECIST assessment. Higher HER2-specific IgG levels were observed in C2 (30 µg) vs. C1 (10 µg). 3/5 patients in C2 showed moderate or little increase in HER2-specific Abs, while all C3 patients (50µg) responded with moderate to high Ab levels. According to RECIST, 1 patient showed complete response, 5 partial response and 4 stable disease. Strong correlation between high Ab levels and clinical responses was observed in C3, while this was only moderate in C2. Capacity to inhibit HER2 phosphorylation was tested in patient sera and could be detected in association with strong tumor reduction. Furthermore, patients with good clinical responses, but low Ab titers featured cellular responses with high IFNγ and TNFα/IL-10 ratios. Conclusions The vaccine was well tolerated and safe with Ab responses at the highest dose showing strong correlation with clinical responses. Currently, the 50 µg dose is being evaluated in a Phase II trial with two arms (IMU 131 + CT and CT only). Clinical trial identification NCT02795988. Legal entity responsible for the study Imugene Ltd. Funding Imugene Ltd. Disclosure U. Wiedermann: Research grant / Funding (institution), Officer / Board of Directors, CSO until September 2018: Imugene; Research grant / Funding (institution): GSK; Research grant / Funding (institution): Pfizer; Research grant / Funding (institution): Themis. I. Bulat: Advisory / Consultancy, Research grant / Funding (self), Full / Part-time employment: Arensia Exploratory Medicine . T. Yau: Honoraria (self), Advisory / Consultancy: Bristol-Myers Squibb. M. Maglakelidzde: Advisory / Consultancy, Research grant / Funding (self), Full / Part-time employment: ARENSIA Exploratory Medicine . T. Ungtrakul: Travel / Accommodation / Expenses: AstraZeneca. C.C. Zielinski: Honoraria (self), Advisory / Consultancy: Roche; Honoraria (self), Advisory / Consultancy: Novartis; Honoraria (self), Advisory / Consultancy, Research grant / Funding (institution): BMS; Honoraria (self), Advisory / Consultancy, Research grant / Funding (institution): MSD; Honoraria (self), Advisory / Consultancy, Officer / Board of Directors, Scientific Advisory Board Member until June 2018: Imugene; Honoraria (self), Advisory / Consultancy: Ariad; Honoraria (self), Advisory / Consultancy, Research grant / Funding (institution): Pfizer; Honoraria (self), Advisory / Consultancy: Merrimack; Honoraria (self), Advisory / Consultancy: Merck; Honoraria (self), Advisory / Consultancy: KGaA; Honoraria (self), Advisory / Consultancy: Fibrogen; Honoraria (self), Advisory / Consultancy, Research grant / Funding (institution): AstraZeneca; Honoraria (self), Advisory / Consultancy: Tesaro; Honoraria (self), Advisory / Consultancy: Gilead; Honoraria (self), Advisory / Consultancy: Servier; Honoraria (self), Advisory / Consultancy: Shire; Honoraria (self), Advisory / Consultancy: Eli Lilly; Honoraria (self), Advisory / Consultancy: Athenex. L. Chong: Honoraria (self), Advisory / Consultancy, Leadership role, Travel / Accommodation / Expenses, Shareholder / Stockholder / Stock options, Full / Part-time employment: Imugene Ltd. N. Ede: Leadership role, Research grant / Funding (institution), Travel / Accommodation / Expenses, Shareholder / Stockholder / Stock options, Licensing / Royalties, Full / Part-time employment: Imugene Ltd. A. Good: Advisory / Consultancy, Leadership role, Shareholder / Stockholder / Stock options, Full / Part-time employment: Imugene Ltd; Advisory / Consultancy, Shareholder / Stockholder / Stock options: Kazia Therapeutics; Shareholder / Stockholder / Stock options: Living Cell Technologies. All other authors have declared no conflicts of interest.