SAT0019 CONDITIONED MEDIUM FROM ADIPOSE MESENCHYMAL STEM CELL EXERT IMMUNOSUPPRESSIVE EFFECT ON TH17/TREG AXIS IN RHEUMATOID ARTHRITIS IN VITRO
Authors: Georgi Vasilev, Mariana Ivanova Goycheva, Ekaterina Ivanova-Todorova, Kalina Tumangelova-Yuzeir, Ekaterina Kurteva, Rumen Stoilov, Dobroslav Kyurkchiev
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background:</h3> Emerging data have demonstrated that mesenchymal stem cells (MSC) are well endowed with a broad repertoire of immunosuppressive tools and they could modulate the immune response on several levels via production of a plethora of soluble factors and contact-dependent mechanisms. For these reasons, mesenchymal stem cells-based protocols were spotlighted as promising multiple-hit treatment candidates for therapeutic intervention in a multitude of autoimmune diseases and debilitating conditions such as rheumatoid arthritis (RA). <h3>Objectives:</h3> In line with aforementioned and taking in mind the current shift in Th1/Th2 paradigm suggesting a key role of Th17/Treg axis dysregulations in RA pathogenesis, we aimed to appraise the immunoregulatory effects of secretory factors produced by adipose-derived MSC (AT-MSC) on Th17 and Tregs subsets and also pro-inflammatory cytokines production in patients with RA. <h3>Methods:</h3> The study encompasses 17 patients matching the ACR/EULAR 2010 criteria for RA. AT-MSC were isolated and cultured according to well-established protocols. Peripheral blood mononuclear cells (PBMCs) isolated from RA patients' samples were cultured in AT-MSC conditioned media and in control media. Flow cytometry was used for detection of Th17 and Treg markers (of CD3, CD4, CD161, CD196 and CD25 and intracellular expression of FoxP3). ELISA was performed for testing the cytokines produced by PBMC (TGF-β1, TNF-α, IL-17A, IL-21). <h3>Results:</h3> We found significant elevation in percentage of CD4<sup>+</sup>CD25<sup>+</sup>FoxP3<sup>+</sup>Treg cell in the pool of PBMC cultured with AT-MSC as opposed to control medium, 4.22 ± 2% (mean ± SD) vs. 6.04 ± 3.6% (p = 0.001). Paired sample analysis of Th17 cells percentage values from all CD4<sup>+</sup> in PBMC cultured with control media (mean ± SD) 10.13 ± 3.88% in contrast to Th17 percentage in PBMC cultured with AT-MSC supernatants 8.98 ± 3.58% showed significant decrease in Th17 numbers (p = 0.02) under the influence of AT-MSC secretory factors. Cultivation of RA patient`s PBMCs with AT-MSC supernatants led to significant up-regulation of TGF-β1 levels, (median [IQR]) 8.318 ng/ml (6.327 – 11.686 ng/ml) vs. 6.227 ng/ml; (1.681 – 10.148 ng/ml) (p = 0.013) and decrease in levels of TNF-α, IL-17A, and IL-21 respectively: 5 pg/ml (1.75 – 11.65 pg/ml) vs. 1 pg/ml (0.7 – 1.9 pg/ml) (p = 0.001); 4.2 pg/ml (3.1 – 6.1pg/ml) vs. 2.3 pg/ml (0.75 – 5.42 pg/ml) (p = 0.017); 75.1 ± 35.95 pg/ml vs. 52.09 ± 30.8 pg/ml (p = 0.022). The reduction in IL-17 levels positively correlated with the decrease of TNF-α (r = 0.921, p = 0.001). <h3>Conclusion:</h3> Our study unambiguously demonstrated that secretory factors produced by AT-MSC exert an immunoregulatory effect on Th17 and Treg cells and also could inhibit major effector cytokine pathways: TNF-α, IL-17, IL-21 production in RA <i>in vitro.</i> The study of mechanisms of immunoregulation induced by MSCs provide us better insight into the pathogenesis of rheumatoid arthritis and could be a potential therapeutic approach. <h3>Disclosure of Interests:</h3> Georgi Vasilev: None declared, Mariana Ivanova Goycheva Speakers bureau: Abbvie, Pfizer, UCB, Novartis, Ekaterina Ivanova-Todorova: None declared, Kalina Tumangelova-Yuzeir: None declared, Ekaterina Kurteva: None declared, Rumen Stoilov Speakers bureau: Abbvie, Pfizer, Amgen, UCB, Novartis, Dobroslav Kyurkchiev: None declared