FIRST PATIENT DOSED IN CITRYLL’S IMAGING STUDY EVALUATING DISTRIBUTION AND TARGET ENGAGEMENT OF CIT-013

• PET-based imaging study designed to assess the biodistribution of CIT-013 and associate disease activity with CIT-013 target disposition in participants with rheumatoid arthritis and hidradenitis suppurativa
• Findings will be additive to outcomes of ongoing Phase IIa studies in both indications, which launched in 2025

Oss, Netherlands – 17 February 2026 – Citryll, a biotech company pioneering a transformative approach to treating immune-mediated inflammatory diseases by targeting Extracellular Traps (ETs), today announces that the first patient has been successfully dosed in its imaging study, ‘Cityview’, evaluating the distribution of radiolabeled CIT-013 in participants with rheumatoid arthritis (RA) and hidradenitis suppurativa (HS).

Cityview has been designed to assess the biodistribution of CIT-013 in the body using PET-CT imaging in participants with RA and HS. The study will evaluate the antibody’s target engagement and disposition as well as the link between disease activity and CIT-013 distribution – the presence at specific sites of inflammation. Cityview follows a preclinical study in mice which showed congruence between PET-CT based imaging of radiolabelled-CIT-013 and clinically inflamed joints and stands as a critical step in validating CIT-013’s mechanisms of action.

Cityview is a Phase IIa, open-label, single-center study planned to enroll 12 participants in two sequential groups starting with participants with active RA, followed by participants with RA in remission and participants with active HS. Following a single dose of radiolabeled CIT-013, participants will undergo PET-CT imaging at intervals over a week follow-up period. The study will also explore the effect on immune system response, pharmacokinetics, and safety, with optional lymph node biopsies offering deeper insight into CIT-013’s mechanism of action in affected tissue.

Maarten Kraan, Chief Medical Officer of Citryll, said, “This is a crucial study that will deepen our understanding on CIT-013’s biodistribution and target engagement, while informing the ongoing Phase IIa and future Phase IIb studies in rheumatoid arthritis and hidradenitis suppurativa. Beyond applying these insights in our own clinical development, we look forward to sharing findings with the wider inflammatory disease community as milestones are reached. We remain convinced that an ET-targeting approach has the potential to be transformative for these underserved patient groups"

This imaging study comes alongside two ongoing Phase IIa trials: Citydream in RA, and Citylights in HS, assessing the efficacy, safety, and tolerability of CIT-013.

-ENDS-

About CIT-013

CIT-013 is Citryll’s first-in-class monoclonal antibody targeting Extracellular Traps (ETs), a key driver of inflammation in RA and other immune-mediated diseases, which has yet to be addressed therapeutically. It has a unique dual mechanism of action, which enhances the clearance of existing ETs and inhibits the formation of new ETs. CIT-013 is highly selective for its epitope, minimizing off-target effects and representing a potentially transformative therapeutic strategy, going beyond individual pathway management and symptom treatment.

About Citryll

Citryll is pioneering a transformative approach to treating inflammatory diseases by targeting Extracellular Traps (ETs), a fundamental component of the inflammatory process that has yet to be addressed therapeutically.

Citryll is developing the first ET-targeting therapy and potentially creating a new class of therapeutics with broad applications across immune-mediated inflammatory diseases.

Our lead asset, CIT-013, is a first-in-class monoclonal antibody with a unique dual mechanism of action: it enhances the clearance of existing ETs and inhibits the formation of new ETs.

By addressing this key driver of inflammation, CIT-013 has the potential to offer a differentiated and comprehensive treatment option for conditions such as rheumatoid arthritis and hidradenitis suppurativa, where current therapies often fall short of providing adequate disease control.

Contacts

Citryll
Sjoerd van Gorp, COO / CFO
Email: info@citryll.com

Citryll Media Contacts
ICR Healthcare
Amber Fennell, Stephanie Cuthbert, Lucy Featherstone
Email: citryll@icrinc.com

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