In humans, CD39 expression on CD4+T cells is largely restricted to a Treg population with little CD73 co-expression.26 As such, production of adenosine requires interaction with CD73 expressing cells or exosomes.10 Given the multiple cell types present in the inflammatory pannus in RA this could be achieved by distinct CD73 expressing CD4+T cells or B cells. This evidence concerns the gene ENTPD1 and rheumatoid arthritis.