Background: Conditions such as trauma, autoimmunity or infection can lead to devastating arthropathies with enormous socioeconomic impact due to their high frequency and chronic nature. Developing new treatments continues to pose a major clinical challenge. Additionally, the aetiology of these diseases, their progression, and patients’ responsiveness to treatment are highly individualised, highlighting the necessity for tailored therapeutic approaches. While 2D in vitro cultures and animal models have contributed to understanding the pathological processes involved in arthritis, they remain inadequate for predicting individual treatment responses because of the intricate nature of the affected synovium. We hypothesised that a 3D organoid model using patient cells may give insight into individual pathogenetic mechanisms in arthritis development relevant to personalised treatment choices.

Objectives: To develop and validate a reliable and reproducible advanced organoid model toolbox that reflects the intricate biological interactions in the human synovium, simulating the disease states of the inflamed joint.

Methods: To establish 2D and 3D cell cultures, native synovial fibroblasts and THP1 macrophages were utilised. The collection of patient samples and their storage at the Rheumatology and Orthopedics Departments USB Biobank received approval from the ethics review board EKNZ (2019-01391). Organoids were assembled by integrating biocompatible magnetic nanoshuttles followed by bioprinting, enabling the self-assembly of cells into 3D structures by forming autologous ECM. This method is highly scalable and reproducible, relying on no artificial scaffolds, and it fosters a native microenvironment that maintains the endogenous tissue phenotypes. Optimal setup parameters, including growth status, cell number, size, culture conditions, organoid maturation, and medium formulation, were further tested. Organoids were exposed to disease-relevant stimuli, cytokines were measured in the supernatants using ELISA, and the expression of cellular phenotypes was assessed by IHC.

Results: Biological samples from six OA patients, encompassing synovial tissue, plasma, serum, and synovial fluid, were gathered and preserved. This facilitated the successful creation of both 2D and 3D in vitro synovial fibroblasts and THP1 macrophage cultures, cocultures and organoids. The integration of macrophages into the synovial organoid was verified in different coculture setups. Data from a limited set of RA-related markers, including IL6, IL8, TNFα and RANKL, revealed a synergistic impact of the coculture environment on the secretion of proinflammatory cytokines following different stimulations. Furthermore, preliminary comparisons between the 2D cultures and 3D organoids post-inflammatory stimulation indicated that macrophages serve as the primary source of TNFα.

Conclusion: The establishment of an engineered human 3D synovial tissue model, emulating the physiology of the human synovium by utilising targeted tissue material, serves to functionally test essential aspects of synovial inflammation. The ability to induce inflammatory responses in the organoids provides a proof of concept for cytokine-driven inflammation in autoimmunity. This will substantially improve the drug development process and tackle the limited predictive value of existing in vitro and in vivo animal models.

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Acknowledgements: NIL.

Disclosure of Interests: None declared.

© The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.