ExpreS2ion Biotech (EXPRS2) 26th Annual Biotech in Europe Forum summary

Asset and platform

• ES2B-C001 is a clinical-stage active immunotherapy for HER2-expressing cancers, built on the ExpreS2 Drosophila S2 protein platform.

• The platform has supported 500+ protein/VLP projects; a COVID-19 vaccine programme met its Phase I primary endpoint and was out-licensed to Bavarian Nordic before Phase I.

HER2 immunotherapy approach

• ES2B-C001 displays all four extracellular HER2 domains at high density on a non-infectious VLP, designed to induce polyclonal antibodies against multiple HER2 epitopes.

• Proposed as an add-on to established HER2 therapies in a market estimated at ~€15B annual global sales; the clinical test is improved disease control with acceptable safety.

Phase I observations

• Preliminary exploratory data: 12/13 evaluable patients had ≥2-fold rises in anti-HER2 antibody titres; titres increased during induction and remained elevated in available follow-up samples.

• No dose-limiting toxicities reported to date across 50, 150 and 450 μg dose levels; an integrated Phase I package was targeted for year-end 2026.

• NHP antibody assays showed complement-mediated tumour damage, higher maximum phagocytosis than trastuzumab in the same assay, and maximum cytotoxic response comparable to trastuzumab.

• Phase I patient-serum functional assays were underway, with results expected in the end-2026 translational package to inform dose selection and Phase II planning.