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Editorial: Lymphocyte Highs and Lows With Baricitinib

The advent of JAK inhibitors has provided a powerful new set of immunomodulatory agents to treat rheumatoid arthritis (RA). JAK inhibitors bind to and interfere with the function of Janus kinases (JAKs), which mediate signaling downstream of multiple cytokine and growth factor receptors(1). Given the wide range of cytokines that JAK inhibition can potentially influence, it is important to establish the dominant immunologic effects that these molecules exert in patients. In this issue of Arthritis and Rheumatology, Tanaka and colleagues describe the changes in circulating lymphocyte populations induced by baricitinib using data from 3 Phase 3 randomized controlled trials(2). By examining alterations in lymphocyte populations in over 2000 patients, with some patients followed for 2 years, the authors provide a robust set of observations that can be compared to experience with other JAK inhibitors and can yield insights into the effects of baricitinib on immune cell homeostasis. This article is protected by copyright. All rights reserved.