ExpreS2ion: ES2B-C001 clears another hurdle: consistent immune responses and green light to escalate

ExpreS2ion today reported updated Phase I data from its ongoing Phase I trial of ES2B, showing eight of nine evaluable patients meeting the predefined responder criterion, up from five of six in February. Antibody titres increase with successive dosing and remain elevated at follow-up, with the longest observation at approximately five months post-final dose. The independent DSMB recommends escalation to the 450 µg dose level and expansion of the 150 µg cohort, with no safety concerns identified.

Data from its ongoing Phase I trial of ES2B-C001, showed that eight of nine evaluable patients have met the predefined responder criterion of a ≥2-fold increase in anti-HER2-specific antibody titres versus baseline. The dataset now spans both the 50 µg and 150 µg dose cohorts, with antibody titres increasing over successive dosing visits and remaining elevated at later follow-up points. In the first treated patient, titres remained elevated approximately five months after the final dose, providing the longest durability observation reported to date.

Separately, the independent Data Safety Monitoring Board (DSMB) has reviewed accumulated safety data and recommended both expansion of the 150 µg cohort and escalation to the next dose level of 450 µg, with no safety signals of concern identified.

Compared with the February update, where five of six evaluable patients had demonstrated a vaccine-specific immune response, today's release meaningfully expands both the breadth and consistency of the dataset. The responder rate has increased from five of six to eight of nine patients, maintaining a high response rate as the evaluable population grows and as data mature across dose levels.

Importantly, the definition of response has also been tightened relative to earlier communications — now based on a predefined ≥2-fold increase in anti-HER2 titres rather than a more general increase from baseline — which adds rigour to the interpretation.

The DSMB recommendation to escalate to 450 µg is a notable new element, as it introduces a third dose level and signals that the safety and tolerability profile observed to date is considered acceptable for further clinical exploration.

Together, these developments represent continued incremental progress and are broadly consistent with the clinical timeline communicated by management, who have guided for Phase Ia dose escalation completion around mid-2026 and Phase Ib expansion toward year-end.

From an investment perspective, the update arrives at a particularly relevant time. On 2 March, ExpreS2ion announced a planned fully pre-emptive rights issue of approximately SEK 53m, with proceeds primarily earmarked for completing the Phase I programme (~55% of proceeds) alongside strengthening R&D and manufacturing capabilities and growing the CRO business. The issue, which is subject to EGM approval on 1 April, is covered to approximately 60% through subscription and guarantee commitments and includes attached warrants (TO13) exercisable in September 2026.

In this context, today's clinical update is constructive, as continued positive data flow supports the investment thesis underpinning the capital raise and reduces the risk that the rights issue proceeds are deployed against a programme with weakening clinical signals.

 In our current investment-case (one-pager), the share price at the time of the one-pager publication (25 February) implied a probability of success of approximately 1.7% in our base case — well below the ~7% historical benchmark for Phase I candidates and also below Redeye's 9% likelihood of approval assumed in its base case valuation of SEK 28 per share. We have previously noted that the low implied probability likely reflects funding risk and limited cash runway as much as doubts about the underlying science. If the rights issue is successfully completed, the resulting extension of runway through Phase I completion could begin to alleviate one of the two principal discount factors — although dilution from the issue itself, including the discount of at least 35% to TERP, will mechanically affect per-share metrics and must be weighed against the operational benefit.

Overall, today's update further strengthens the qualitative investment case for ES2B-C001. The consistency of immune responses across a growing patient population, the early but encouraging durability signal, the introduction of a tighter responder criterion, and the DSMB's endorsement of escalation to a third dose level all contribute to a progressively more robust Phase I dataset.

With the rights issue process now underway and key catalysts ahead — including further dose-escalation data, the 450 µg cohort, and eventually Phase Ib expansion results — 2026 remains a defining year for ExpreS2ion. For now, however, the data remain preliminary and based on a limited number of patients in a heterogeneous population, and material revaluation will likely require more mature read-outs across additional patients and dose levels before the market is willing to reassign the probability of success it prices into the share.

Disclaimer: HC Andersen Capital receives payment from ExpreS2ion Biotechnologies for a Digital IR/Corporate Visibility subscription agreement. /Michael Friis, 11:16, 25/03-2026