Increased circulating CD39+FoxP3+CD4+ regulatory T cells in Early Rheumatoid Arthritis facilitate the antiinflammatory action of methotrexate and associate with the clinical response

OBJECTIVES FoxP3+ regulatory T cells (Tregs) are key to the immune system homeostasis; their CD39+ subset (Treg39+) hydrolises adenine nucleotides released by stressed cells, rendering the antiinflammatory adenosine. Methotrexate (MTX), inhibiting AICAR transformylase (ATIC), enhances the extrusion of adenine nucleotides and hence may help Treg39+ cells control inflammation. Therefore, we examined the relation of CD39 expression on Tregs of early RA (ERA) patients with the effect of MTX. METHODS Freshly isolated lymphocytes from 72 untreated ERA patients (duration <24 weeks) and 72 healthy controls (HCs) were examined by cytometry. Treg cell potency was assessed in cocultures of CD4+CD25+CD127- Treg with CD4+CD25- CD127+ responder T cells (Tresp). RESULTS ERA patients demonstrated a superior frequency of circulating Tregs containing increased proportions of Treg39+ cells. Total ERA Tregs were more potent than HC Tregs and MTX further heightened their potency, with greater amplification in ERA vs HC; differences were reduced by adenosine pathway blockade. The potency of isolated Treg39+ and its enhancement by MTX were comparable for ERA and HC suggesting that the differences seen with total Tregs are due to the increased ERA Treg39+ frequency. Basal Treg39+ cell proportions > 39.3 associated with a good 12 month EULAR response [RR 13.4 (2.9-75.6)]. At 12 months, the ERA Treg39+ frequency had decreased to HC levels but its association with the clinical response remained. CONCLUSION MTX cooperates with Treg39+ cells and the basal Treg39+ frequency is a predictor of clinical response. The increased circulating Treg39+ cells in untreated ERA would further facilitate the action of MTX thereby providing a slot for prompt MTX initiation. ### Competing Interest Statement Unrestricted Research Grant from Gebro Pharma