Maeda S, Osaga S, Maeda T, et al. - Given high pathogenicity of T-helper (Th)17.1 cells in inflammatory diseases, researchers examined the changes in the proportions of Th subsets, including Th17.1, which are correlated with abatacept (ABA) treatment response in Japanese patients with rheumatoid arthritis. On the basis of the results, they assessed the potential utility of Th17.1 as a cellular biomarker. Forty patients with rheumatoid arthritis were assessed for the circulating Th subsets among CD4+ T lymphocytes before abatacept treatment using multicolor flow cytometry. Following abatacept treatment for 24 weeks, the patients were assessed for changes in disease activity score, including 28-joint count C-reactive protein, and responsiveness indicated by other indices to abatacept treatment according to the European League Against Rheumatism criteria (good and moderate responders and nonresponders). Patients categorized as good responders had a significantly lower proportion of baseline Th17.1 cells than those categorized as non-good responders (moderate responders and nonresponders). After 24 weeks of abatacept therapy, there was a significant negative correlation of a decrease in 28-joint count C-reactive protein with the proportion of Th17.1 cells. Findings suggest a possible value of baseline Th17.1 levels as a prognostic predictor of ABA treatment in patients with rheumatoid arthritis. Moreover, although there is a correlation between Th17 and therapeutic response to ABA, Th17.1 exhibited a stronger correlation. In this study, the most novel finding is the identification of cells that are associated with ABA therapeutic response among Th cells that induce antigen-specific responses.