Citryll, a Netherlands-based biotech company, has achieved a significant milestone by dosing the first patient in its Phase IIa clinical trial evaluating CIT-013, a first-in-class monoclonal antibody targeting Neutrophil Extracellular Traps (NETs) in patients with moderately active rheumatoid arthritis. The announcement on September 2, 2025, marks a critical advancement in the company's mission to transform treatment for immune-mediated inflammatory diseases.
Novel Therapeutic Approach Targets Previously Unaddressed Mechanism
CIT-013 represents a fundamentally different approach to treating rheumatoid arthritis by targeting NETs, a key driver of inflammation that has yet to be addressed therapeutically. The monoclonal antibody features a unique dual mechanism of action that enhances the clearance of existing NETs while simultaneously inhibiting the formation of new NETs.
"By targeting NETs, CIT-013 represents a novel and potentially disease-modifying approach to RA as well as other immune mediated conditions," said Rogier Thurlings, MD, PhD, Lead Investigator of the Citydream trial. "This mechanism offers a fundamentally different mode of action from current therapies, which often fail to achieve sustained disease control in patients."
Phase IIa Trial Design and Patient Population
The Citydream study is designed as a Phase IIa, randomized, double-blind, placebo-controlled, multi-center trial conducted across multiple sites in Europe. The study will assess the efficacy, safety, and tolerability of CIT-013 in patients with moderately active rheumatoid arthritis. The trial will enroll 88 patients who will undergo a 6-week treatment period, followed by an open-label extension phase to further assess safety and efficacy.
Addressing Significant Unmet Medical Need
Rheumatoid arthritis is a chronic autoimmune disease characterized by inflammation of the joints, with hallmark symptoms including joint pain, stiffness and swelling that result in reduced mobility and loss of joint integrity, severely impacting quality of life. Despite significant advances in treatment options, there remains a high medical unmet need, with a high proportion of patients unable to maintain adequate disease control through current therapies.
"The dosing of the first patient in our Phase IIa trial marks a significant milestone in Citryll's mission to transform the treatment landscape for patients suffering from immune-mediated inflammatory conditions such as rheumatoid arthritis," said Maarten Kraan, Chief Medical Officer of Citryll. "With a compelling preclinical and clinical data set together with strong backing from a top-tier investor syndicate we are proud to advance our lead programme into Phase 2 trials."
Clinical Development Progress and Future Plans
The Phase IIa trial follows the successful completion of Citryll's first-in-human Phase 1 study, which included successful repeat dosing of rheumatoid arthritis patients. The company has also secured significant financial backing through an €85 million Series B fundraise to support its clinical development programs.
To support the advancement of clinical investigations and broader strategy, Citryll has established a Rheumatoid Arthritis Clinical Advisory Board, comprising leading experts in the field to provide strategic and scientific guidance throughout the clinical development of CIT-013 in RA and other autoimmune diseases.
Beyond rheumatoid arthritis, Citryll plans to expand CIT-013's clinical evaluation to other immune-mediated inflammatory diseases. An additional Phase IIa trial is planned in hidradenitis suppurativa starting later this year, demonstrating the potential broad applicability of NET-targeting therapy across multiple inflammatory conditions.
CIT-013's highly selective targeting of its epitope is designed to minimize off-target effects, representing a potentially transformative therapeutic strategy that goes beyond individual pathway management and symptom treatment to address a fundamental component of the inflammatory process.
