ExpreS2ion Biotech Holding AB has submitted a protocol amendment to Austrian regulatory authorities that will enable testing of its breast cancer vaccine candidate ES2B-C001 in combination with antibody-drug conjugates (ADCs), the company announced on May 13, 2025. The amendment also seeks to expand the number of clinical trial sites to accelerate patient recruitment for the ongoing Phase I study.
The protocol modification aims to evaluate ES2B-C001 alongside established treatment regimens for advanced-stage breast cancer, particularly Enhertu® (trastuzumab deruxtecan), which recently received reimbursement approval from Austrian health authorities for HER2-positive metastatic breast cancer patients.
Strategic Acceleration of Combination Testing
While ExpreS2ion had initially planned to conduct combination trials during later clinical development phases, the recent reimbursement approval for Enhertu® in Austria presents an opportunity to generate valuable combination data earlier than anticipated.
"Demonstrating that ES2B-C001 is safe — and potentially adds efficacy — when combined with ESMO guideline recommended treatment regimens for advanced-stage breast cancer could significantly enhance the commercial and licensing potential of ExpreS2ion's breast cancer program," the company stated in its announcement.
HER2-targeting therapies are typically administered in combination regimens for metastatic breast cancer. The protocol amendment aligns the trial with current treatment standards and supports broader patient eligibility criteria.
Enhanced Recruitment Strategy
To support patient enrollment, ExpreS2ion has established referral agreements with five clinics in Vienna that will directly refer eligible patients to the active study site. The company has also requested an increase in the number of clinical trial sites throughout Austria.
ExpreS2ion anticipates regulatory approval of these amendments by mid-Q3 2025 and expects the modifications to substantially accelerate recruitment for the ongoing Phase I trial. Importantly, the company emphasized that patients will continue to be recruited under the current protocol until the amendment is approved, and these changes are not expected to affect existing timelines.
The company remains on track to report interim safety and tolerability data from the first patient cohort in the ES2B-C001 Phase I study and has committed to providing timeline updates once the first patient has been dosed.
ES2B-C001: A Novel Approach to HER2-Expressing Cancers
ES2B-C001 represents an innovative therapeutic vaccine specifically developed for HER2-expressing cancers. The vaccine combines ExpreS2ion's ExpreS2 production platform with AdaptVac's virus-like particle (VLP) technology, both of which have demonstrated efficacy in Phase III clinical trials.
The HER2-VLP vaccine is designed to stimulate a robust and durable polyclonal immune response against HER2-expressing tumors, offering a complementary approach to existing treatments. Preclinical studies published by Ruzzi et al. (2022) demonstrated the vaccine's safety and efficacy across multiple animal models, showing significant inhibition of tumor growth and improved survival rates.
By leveraging the patient's own immune system, ES2B-C001 addresses the complexities of HER2-expressing breast cancers in a novel way. This approach could potentially offer enhanced therapeutic options for patients and fill critical gaps in the current treatment landscape for HER2-positive breast cancer.
Market Implications
The strategic amendment to include combination testing with established ADCs like Enhertu® could significantly enhance the commercial prospects of ES2B-C001. Combination therapies have become the standard of care in advanced oncology treatment paradigms, and demonstrating compatibility and potential synergy with approved therapies could position ES2B-C001 more favorably for future licensing deals and market adoption.
The breast cancer vaccine market represents a significant opportunity, particularly for innovative approaches that can complement existing treatment modalities. By accelerating the evaluation of ES2B-C001 in combination with standard-of-care treatments, ExpreS2ion is positioning its candidate to potentially address unmet needs in the HER2-positive breast cancer treatment landscape more rapidly.
