Citryll's Novel Antibody Aims to Visualize and Neutralize Inflammation

OSS, NETHERLANDS – February 17, 2026 – Dutch biotech firm Citryll has initiated a pivotal imaging study for its first-in-class drug, CIT-013, dosing the first patient in a trial designed to visualize the drug's activity at the source of inflammation. The study, named 'Cityview', will use advanced PET-CT imaging to track the antibody in patients with rheumatoid arthritis (RA) and hidradenitis suppurativa (HS), two debilitating inflammatory diseases with significant unmet medical needs.

This milestone represents a critical step in validating a novel therapeutic strategy that targets a fundamental, yet previously unaddressed, driver of autoimmune disease: Extracellular Traps (ETs).

A New Strategy Against an Old Foe: Targeting Extracellular Traps

For decades, treatments for inflammatory diseases like RA have focused on suppressing downstream immune responses, often with broad immunosuppressive effects and limited efficacy for a large subset of patients. Citryll is pioneering a different approach by targeting the root cause. Their strategy centers on Extracellular Traps, web-like structures of DNA and toxic proteins released by immune cells, most notably neutrophils, in a process called NETosis.

While ETs are a vital part of the body's defense against pathogens, their overproduction or improper clearance is a key driver of pathology in many autoimmune diseases. In rheumatoid arthritis, these NETs accumulate in the joints, releasing autoantigens—specifically citrullinated proteins—that trigger the production of autoantibodies (ACPAs) characteristic of the disease. This perpetuates a vicious cycle of inflammation, leading to synovial damage and joint destruction.

Similarly, in hidradenitis suppurativa, a painful and chronic skin condition, NETs are found in high concentrations within skin lesions. Their presence correlates with disease severity, contributing to chronic inflammation and tissue damage. For both conditions, current therapies often fail to provide lasting remission, leaving a significant number of patients searching for better options.

Citryll's lead candidate, CIT-013, is a monoclonal antibody engineered with a unique dual mechanism. It is designed to not only enhance the body's ability to clear existing ETs but also to inhibit the formation of new ones. By targeting citrullinated histones, a core component of these traps, CIT-013 aims to dismantle the inflammatory scaffold directly, offering a potentially transformative approach that goes beyond managing symptoms.

Illuminating the Path Forward with Advanced Imaging

The 'Cityview' study is more than just a standard clinical trial; it is an exercise in precision pharmacology. By radiolabeling CIT-013 and using Positron Emission Tomography-Computed Tomography (PET-CT), researchers can non-invasively watch the drug travel through the body in real-time. The goal is to confirm that the antibody reaches and binds to its intended targets within the inflamed joints of RA patients and the skin lesions of those with HS.

This type of imaging study is invaluable in modern drug development. It provides definitive proof of mechanism, showing that a drug engages its target as designed. The findings will be crucial for understanding the antibody's biodistribution and for establishing a clear link between drug concentration, target engagement, and disease activity.

"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," said Maarten Kraan, Chief Medical Officer of Citryll, in a statement. "We remain convinced that an ET-targeting approach has the potential to be transformative for these underserved patient groups."

The open-label study will enroll 12 participants who will receive a single dose of radiolabeled CIT-013 and undergo imaging over a one-week period. The data gathered will provide critical insights to optimize dosing for two larger, ongoing Phase IIa efficacy trials: 'Citydream' in RA and 'Citylights' in HS.

Addressing a Vast Unmet Need in Inflammatory Disease

The launch of the 'Cityview' study offers a new ray of hope for millions of patients grappling with the limitations of current treatments. For rheumatoid arthritis, despite a multi-billion dollar market of biologic drugs and JAK inhibitors, up to 40% of patients fail to respond adequately to existing therapies. Many cycle through different treatments, enduring significant side effects, including an increased risk of serious infections, without achieving sustained remission.

The situation is even more challenging for patients with hidradenitis suppurativa. This painful, chronic skin disease has historically had few effective options. While newer biologics targeting TNF-alpha and IL-17 have provided some relief, response rates remain modest, with many patients experiencing persistent symptoms and a profound impact on their quality of life. The unmet need for novel, highly effective, and well-tolerated therapies in both diseases is immense.

By targeting the foundational role of ETs, CIT-013 has the potential to offer a differentiated treatment that could benefit patients who are refractory to current standards of care. If successful, it would not only provide a new option but could establish an entirely new class of therapeutics for a broad spectrum of immune-mediated inflammatory diseases.

Citryll's Strategic Ascent in a Competitive Market

Citryll's ambitious clinical program is backed by significant financial and strategic support. In late 2024, the company secured an oversubscribed €85 million Series B financing round co-led by a syndicate of top-tier global life sciences investors, including Johnson & Johnson Innovation – JJDC, Inc., Forbion, and the Novartis Venture Fund. This robust funding underscores the high level of confidence in the company's novel scientific platform and its potential to disrupt the inflammatory disease market.

While Citryll is a pioneer, it is not alone in recognizing the potential of targeting Extracellular Traps. Competitors like US-based Neutrolis are also in clinical development with therapies designed to clear NETs, while others are developing small molecule inhibitors of PAD4, a key enzyme in the NET formation pathway. This emerging competitive landscape highlights the growing scientific consensus around the importance of ETs as a therapeutic target.

The 'Cityview' imaging study serves as a key strategic move for Citryll. Positive data would provide early human validation of its platform, significantly de-risking the development of CIT-013 and strengthening its position in the field. The visual confirmation of target engagement would be a powerful asset in guiding the ongoing Phase II trials and in future discussions with regulators and potential partners. By demonstrating that its antibody can precisely target the inflammatory source, Citryll is laying the groundwork for what it hopes will be a new paradigm in treating autoimmune disease.