Understanding of Rare Inflammatory Arthritis in Comparison to Classical Inflammatory Arthritis : Tissular Observations and Immune Infiltrate Characterization : the UTOPIC Project

The pathophysiology of certain inflammatory arthritides remains poorly understood, particularly when associated with rare systemic autoimmune diseases such as systemic sclerosis (SSc), or when emerging in the context of immune-related adverse events from cancer immunotherapies. These immunotherapy-induced arthritides represent a new and increasingly encountered clinical entity in rheumatology. A deeper understanding of the mechanisms underlying joint inflammation in these settings is essential for identifying specific therapeutic targets, especially given the limitations of current treatment options and the risks associated with broad immunosuppressive strategies such as prolonged corticosteroid use, which may impair anti-tumor immune responses.

Synovial biopsy analysis provides a powerful tool for dissecting the cellular and molecular components of joint inflammation, including immune cell infiltration, cytokine profiles, and cell-cell interactions. Advances in high-dimensional techniques such as multiplex immunofluorescence and mass cytometry now allow for the identification and spatial localization of numerous protein markers at the subcellular level. Additionally, spatial transcriptomics offers complementary insight into gene expression profiles within the tissue microenvironment, providing a comprehensive understanding of inflammatory processes.

The investigators propose a prospective, proof-of-concept study to characterize and compare rare and emerging inflammatory arthritides-including those linked to SSc and immunotherapy-related immune toxicity-with classical inflammatory rheumatic diseases such as rheumatoid arthritis (RA), psoriatic arthritis (PsA), spondyloarthritis (SpA), polymyalgia rheumatica (PMR), and reactive arthritis. Through detailed immunological and molecular profiling, this study aims to identify disease-specific signatures and novel therapeutic targets. These findings could pave the way for precision medicine approaches and inform the development of targeted therapies in both rare and common forms of inflammatory arthritis.