Background: Enthesitis is a hallmark feature of psoriatic arthritis (PsA) course. So far, most of the data on enthesitis in PsA are based on clinical assessment as well as MRI or ultrasound examinations, due to the challenge in retrieving good quality entheseal tissue for molecular analysis. However, pre-clinical studies as well as surgical invasive approaches on spondyloarthritis patients showed that interleukin-17 (IL-17) is a key molecule in enthesitis pathogenesis, as also confirmed by the clinical efficacy of IL-17 inhibitors in patients with enthesitis. To date, there are no molecular data assessing how IL-17 blockade ameliorates enthesitis in humans. Therefore, deep omics analysis of these ultra-specialized tissues might expand our insights on PsA pathogenesis as well as provide information on treatment response.

Objectives: To investigate the immune and the non-immune compartment in active enthesitis of PsA patients and their changes upon IL-17A inhibition.

Methods: Minimal-invasive ultrasound (US)-guided biopsies of the lateral epicondyle (technology described previously[1]) were performed in 10 PsA patients with active elbow enthesitis before and after 3 months of treatment with 150mg/month s.c. secukinumab. All patients were biologicDMARD naïve at time of inclusion. Only one patient did not receive the second biopsy. Once harvested, the samples were fixed and conventional histology staining as well as second harmonic generation (SHG) were performed for morphologic evaluation and entheseal region identification[1]. Further slides were used for protein expression, through Hyperion imaging mass cytometry (IMC) and for RNA expression, through GeoMx spatial transcriptomic technology.

Results: 40% of the patients included into the study were female with an average age of 54 (± 9 SD). At the time of screening DAPSA, LEI and SPARCC were (mean ± SD) 23 ± 12, 2 ± 1 and 4 ± 3, respectively, decreasing to 11 ± 10, 1 ± 1, 1 ± 1, respectively, after secukinumab. Entheseal regions within the biopsies was identified by SHG. Neutrophils (CD66b+), CD4+T cells (CD3+ CD4+) and ILC (Lineage-, CD127+) significantly decreased upon IL-17 blockade (p=0.017, 0.017, 0.021, respectively), particular with respect to the IL-17A-positive fractions of each cell type. Beside quantitative reduction of IL-17-producing immune cells, specific effects on transcriptional states of resident entheseal cells were observed. Spatial deconvolution analysis revealed a significant increase in the abundance of pro-resolving CD200+ fibroblasts[2] and ILC2 cells following treatment (p=0.055, 0.049, respectively). Moreover, these cells were found to spatially colocalize together and with MERTK+ macrophages (CD200+ R=0.57 p=0.0041, ILC2 R=0.39 p=0.063), while dissociating with CD4+ T cells (CD200+ R=-0.74 p=0.000, ILC2 R=-0.64 p=0.001).

Conclusion: Here we show for the first time a full picture of cellular changes in the microarchitecture of inflamed human entheses upon anti-IL-17 treatment. Resolving enthesial inflammation was not only associated with a reduction of the cellular load of IL-17-producing cells but also with tissue intrinsic modulations towards a pro-resolving microenvironment upon treatment with IL-17 inhibitors.

REFERENCES: [1] Pachowsky ML, Raimondo MG, et al. Ann Rheum Dis. 2022; 81(8):1131-1135.

[2] Rauber et al., Nat Immunol. 2024, in press.

Acknowledgements: NIL.

Disclosure of Interests: Maria Gabriella Raimondo: None declared, Hashem Mohammadian: None declared, Stefano Alivernini: None declared, Vladyslav Fedorchenko: None declared, Simon Rauber: None declared, Hannah Labinsky: None declared, Mario Angeli: None declared, Filippo Fagni: None declared, Giulia Corte: None declared, Koray Tascilar: None declared, Lars Bräuer: None declared, Maria Antonietta D’ Agostino: None declared, Georg Schett: None declared, Arnd Kleyer: None declared, Milena Pachowsky: None declared, Andreas Ramming Novartis, Novartis.