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

Platform and asset

• 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 and VLP projects, including programs reaching Phase III; partnered programs include malaria, Nipah and influenza.

• 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.

• Designed to complement established HER2 therapies with a broad, potentially durable, patient-generated antibody response; immune memory remains to be evaluated.

• The HER2 treatment market was estimated at ~€15B in annual global sales; the clinical test is improved disease control with acceptable safety.

Phase I evidence

• Open-label Phase I evaluates safety, tolerability and immunogenicity in advanced HER2-positive or HER2-low breast cancer; tested doses are 50, 150 and 450 μg.

• 12/13 evaluable patients had at least twofold anti-HER2 antibody-titre rises; responses occurred across dose levels, titres increased during induction and remained elevated in available follow-up samples.

• No dose-limiting toxicities have been reported across the dose levels; the small, uncontrolled study cannot establish added clinical efficacy, and antibody durability remains under evaluation.