CD39 positive regulatory T cell frequency as a biomarker of treatment response to methotrexate in rheumatoid arthritis

Abstract

Aim: Nearly one-third of patients with rheumatoid arthritis (RA) do not respond to Methotrexate (MTX), the first-line therapy in RA. CD39, an ectonucleotidase highly expressed on regulatory T cells (Tregs), is responsible for production of adenosine, an important anti-inflammatory mediator of MTX action. Higher expression of CD39 on Tregs improves their suppressive capacity. Therefore, we aimed to study the role of CD39+ Treg frequency as a biomarker for MTX treatment response in RA. Methods: Patients with active RA who were naive to disease-modifying anti-rheumatic drugs were enrolled. Frequencies of CD39+ Tregs (CD4+ CD25+ FoxP3+ CD39+ cells) and CD4+ CD25+ CD39+ cells were determined by flow cytometry in peripheral blood before the start of therapy. After 4 months of MTX monotherapy, patients were classified into responders (European League Against Rheumatism [EULAR] good/moderate response) and non-responders (EULAR no response). All samples were genotyped for single nucleotide polymorphisms (SNPs) rs11188513 and rs7071836 in the ENTPD1 (CD39) gene. Results: After 4 months of MTX monotherapy, 54 patients were classified as responders and 16 as non-responders. The baseline CD39+ Treg and CD4+ CD25+ CD39+ cell frequencies were significantly higher in the responder group as compared with the non-responder group (P < 0.05 and P < 0.01, respectively). AA genotype at SNP rs7071836 was associated with poor response to MTX (P < 0.05; odds ratio = 5.67; 95% CI = 1.12-28.75). Conclusion: Higher frequencies of CD39+ Tregs and CD4+ CD25+ CD39+ cells in the peripheral blood are associated with response to MTX in RA and hence, these could be considered as potential biomarkers for prediction of response to MTX treatment.