CD4 and CD8 PD-1 T-cell expression in responders (R) and nonresponders (NR). Peripheral blood samples were collected before each dose of abatacept and 1 month after the administration of 6 doses of abatacept. Peripheral blood mononuclear cells were stained for CD4 (A) or CD8 (B) and PD-1 cell surface expression. Results were analyzed using flow cytometry. At baseline, there was no difference in CD4 PD-1 expression in responders vs nonresponders (P = .34). One month after 6 doses of abatacept, a significant increase in CD4 PD-1 expression was observed in clinical responders (P = .009) (A), with a representative example shown (C). Similarly, there was no difference at baseline in CD8 PD-1 expression when comparing responders with nonresponders (P = .27). One month after 6 doses of abatacept, a significant increase in CD8 PD-1 expression was noted (P = .007) in clinical responders (B), with a representative example shown (C). A representative example of CD4 and CD8 PD-1 expression in a nonresponder is shown in (D).