AB0175 ALTERATIONS IN JAK-STAT SIGNALING PATHWAY ARE FOUND IN PERIPHERAL BLOOD LEUKOCYTES FROM UNTREATED EARLY ARTHRITIS PATIENTS

Background:

Early inflammatory arthritis is a condition that may evolve to several known rheumatic diseases, such as rheumatoid arthritis (RA). Alterations in JAK-STAT signaling pathway have been documented in several immune-mediated disorders such as RA. We hypothesize that JAK- STAT pathway is key to chronic arthritis onset and its early inhibition might have a major effect on allowing lasting disease control.

Objectives:

We aimed to characterize peripheral blood leukocyte populations of untreated early arthritis patients (with <1 year of symptom duration) and evaluate the effect of conventional treatment with methotrexate (MTX) on JAK-STAT signaling pathway. Moreover, a group of refractory established RA patients was recruited and the effect of upadacitinib (UPA), a JAK inhibitor approved for RA treatment, was assessed.

Methods:

Blood samples from untreated early arthritis and established refractory RA patients were collected at baseline and after 6 months of treatment with MTX and UPA, respectively. Peripheral blood mononuclear cells (PBMC) were isolated by density-gradient centrifugation and the frequency, phenotype and STAT phosphorylation (pSTAT) levels were evaluated on peripheral blood leukocytes [B cells, T cells, monocytes and dendritic cells (DC)] by flow cytometry. A group of age and gender matched healthy controls was also included for comparison.

Results:

We included 46 early arthritis patients (67% female, age 59.0±16.1 years, symptom duration 6.1±2.0 months). We found significant differences in both frequency and phenotype of immune cell populations in early arthritis patients, particularly in seropositive RA, when compared to controls (Figure 1). Treatment with MTX restored some of these alterations, increasing the frequency of total B cells, the percentages of pre-SM, post-SM and DN B cells and decreasing transitional and naïve B cell subsets. Cytotoxic T cells were also affected by treatment, with an increase in frequency when compared to baseline. No alterations were observed in monocytes and in the main DC populations. However, CD1c+ mDCs were significantly increased in percentage, whereas CD141+ mDCs became severely reduced after treatment. The measurement of pSTAT levels by median fluorescence intensity (MFI) showed decreased STAT activation in early disease in comparison with healthy controls (Figure 2), which was maintained after conventional treatment with MTX. In addition, 10 established refractory RA patients (80% female, age 54.0±9.5 years, disease duration 15.4±9.1 years) were included. After 6 months of treatment, UPA mainly affected the frequency of DC subpopulations and T cell phenotype, but did not significantly impact pSTAT levels in peripheral blood leukocytes.

Conclusion:

Our data supports the immunomodulatory effects of both MTX and UPA in peripheral blood leukocytes from early and established arthritis patients and reinforce the role of JAK-STAT signaling pathway since early disease onset.

REFERENCES:

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Acknowledgements:

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Disclosure of Interests:

None declared.