Cytomegalovirus (CMV) latency is associated with severity of joint destruction in rheumatoid arthritis (RA). A prospective observational cohort study (n = 71 at baseline, n = 43 at 21–24 week follow-up) of patients beginning DMARD therapy for early RA found a correlation between the change in 28-joint disease activity score (DAS28) and peripheral blood mononuclear cell (PBMC) cytokine production profiles in response to incubation with human CMV and Epstein–Barr virus. The study validates the idea that immune response profiling could be used to predict patient treatment outcome.