ExpreS2ion today announced an update to the Phase I program for ES2B-C001 alongside additional preliminary observations and study design changes. Anti-HER2 antibody responses have now been observed in 9 of 9 evaluable patients, up from 8 of 9 in March, with titres maintained at later follow-up.

On the clinical side, all 9 of 9 evaluable patients across the 50 µg and 150 µg cohorts have now demonstrated anti-HER2 antibody responses, extending the consistent immunogenicity signal first reported in February (5/6) and broadened in March (8/9). Titres have continued to increase across dosing visits and to remain elevated at later follow-up. The first patient in the 450 µg cohort, the third and highest planned dose level, has now been dosed following DSMB approval in March, and no safety signals of concern have been identified to date, including at the new dose level.

Importantly, the headline timelines are unchanged: Phase I primary readout is reiterated for end-2026 and Phase II initiation for mid-2027. This is reassuring against the backdrop of an expanded translational program and the addition of a maintenance phase, both of which could in principle have introduced timeline risk. Management's reiteration of the existing schedule, and the explicit statement that the maintenance phase runs concurrently with Phase II initiation, suggests confidence that the broader program can be delivered within the existing budget envelope.

The more substantive element of today's release, in our view, is the programme update itself. Management has incorporated three notable refinements.

First, an enriched translational analysis program has been added, designed to generate deeper insights into immune response quality and durability, mechanism of action, and preliminary efficacy signals. The company explicitly frames this as a response to feedback from potential development partners and investors, a useful signal that partnering discussions are sufficiently advanced for prospective partner input to be incorporated into trial design.

Second, the program now incorporates a maintenance phase of up to 18 months following the primary induction phase, subject to regulatory approval, designed to assess booster dosing potential and longer-term immune durability. The maintenance phase runs concurrently with Phase II initiation and does not affect the mid-2027 start target.

Third, the Phase II design has been revised toward a more targeted and focused approach that management expects to be more capital-efficient. This is a meaningful framing, as Phase II capital intensity has been one of the central concerns surrounding the investment case.

A more capital-efficient Phase II would, all else equal, reduce the gap between currently available resources and the funding required to advance the program independently, and could improve negotiating leverage in any licensing or co-development discussions.

Details on the revised Phase II design however remains limited, with management indicating that a more detailed preliminary design will likely be communicated around the time of the end-2026 Phase I readout.

From an investment perspective, today's update is constructive but largely qualitative. The 9/9 responder rate reinforces the immunogenicity narrative without materially changing it, while the programme refinements, particularly the framing around partner-driven translational depth and a more capital-efficient Phase II, are best understood as incremental de-risking

Material revaluation of the share price will likely require more mature read-outs across additional patients and dose levels, including data from the 450 µg cohort, before the market is willing to meaningfully reassign the probability of success it prices into the share.

Further details on the dataset could come in focus, when we the 28th. May 2026 is hosting an event with management presenting the Q1-2026 results.

Sign up here: https://www.inderes.dk/videos/expres2ion-biotech-presentation-of-q1-2026-interim-report

Disclaimer: HC Andersen Capital receives payment from ExpreS2ion Biotechnologies for a Digital IR/Corporate Visibility subscription agreement. /Michael Friis, 15:25 19/05-2026