Background: Neutrophil extracellular traps (NETs) contribute to the pathophysiology of many immune-mediated inflammatory diseases (IMIDs). Though NETosis-targeting therapeutics have shown potential as effective treatments, currently there are no NET-specific therapies available. We have developed CIT-013, a first-in-class monoclonal antibody specifically targeting citrullinated histones H2A and H4 in NETs, having a unique dual mode of action by inhibiting NET release and enhancing macrophage-mediated NET clearance. CIT-013 has shown safety, tolerability, and target engagement in phase 1 clinical trials. Here we show that CIT-013 targets NETs in inflamed joints and halts the progression of bone and cartilage erosion in a mouse model of collagen-induced arthritis (CIA). Furthermore, we provide evidence for CIT-013’s potential application in rheumatoid arthritis (RA) patients by showing presence of its target in human RA serum and inflamed synovial tissue.

Objectives: The objectives of the study were to test the therapeutic and diagnostic potential of CIT-013 in a mouse model of CIA and to test presence of its target in RA patient material. Questions that we wanted to answer were: 1) Can therapeutic administration of CIT-013 block the progression of bone and cartilage erosion? 2) Can radiolabeled CIT-013 be used to identify inflamed joints or tissues with NET associated disease? 3) Is CIT-013’s target present in RA patient serum and inflamed synovial tissue?

Methods: To assess the efficacy of CIT-013 in the mouse CIA model, a mouse variant of CIT-013 was used (mACHA). Disease progression was monitored by visual arthritis scoring, and paw sections were used to study the histological features of bone and cartilage erosion. In a separate CIA study, a radiolabeled mouse variant of CIT-013 (mACHA) was administered to study the biodistribution of the antibody. CIT-013’s target was determined in human RA synovial tissue and serum samples with the use of standard histological staining techniques as well as an in-house CIT-013 epitope detection ELISA.

Results: We found that mouse variant of radiolabeled CIT-013 (mACHA) specifically localizes to the inflamed joints in CIA mice. Therapeutic treatment of CIA mice with mACHA halted progression of pannus formation, cartilage damage and bone resorption. In human RA serum significantly enhanced level of CIT-013’s target was detected compared to healthy volunteer samples, and in human RA synovial tissue CIT-013 staining correlated positively with the observed histological severity.

Conclusion: Together, this demonstrates that CIT-013 can target its epitopes in inflamed joints, suppresses the proinflammatory properties of NETs, and thereby has therapeutic potential for IMIDs like RA. This reinforces the position of CIT-013 as a unique therapeutic approach for NET-associated diseases with unmet therapeutic needs.

CIT-013 will enter phase 2 proof-of-concept clinical trials in RA and Hidradenitis suppurativa during 2024.

REFERENCES: [1] Chirivi et al, Cellular & Molecular Immunology 18: p1528-1554, 2021. DOI: 10.1038/s41423-020-0381-3

[2] Van der Linden et al, MAbs 2023, VOL. 15, NO. 1, 2281763. DOI: 10.1080/19420862.2023.2281763

Acknowledgements: NIL.

Disclosure of Interests: Sangeeta Kumari Shareholder of stock options, Employee of Citryll BV, Annemarie Kip Shareholder of stock options, Employee of Citryll BV, Maarten van der Linden Shareholder of stock options, Employee of Citryll BV, Josephine Stein Shareholder of stock options, Employee of Citryll BV

, Tirza Bruurmijn Shareholder of stock options, Employee of Citryll BV

, Martyn Foster consultant to Citryll BV, Peter van Zandvoort Shareholder of stock options, Employee of Citryll BV, Stephanie van Dalen Shareholder of stock options, Employee of Citryll BV

, Helmuth van Es Shareholder of Stock options and shares, Citryll BV

, Eric Meldrum Shareholder of stock options

, Employee of Citryll BV, Renato Chirivi Shareholder of stock options and share

, Employee of Citryll BV