Baseline Numbers of Circulating CD28-negative T Cells May Predict Clinical Response to Abatacept in Patients with Rheumatoid Arthritis

OBJECTIVE: To evaluate the number of circulating CD28-negative (CD28-) T cells as a predictor of clinical response to abatacept in patients with rheumatoid arthritis (RA). METHODS: Peripheral blood CD28- T cell subsets were evaluated by flow cytometry at baseline in 32 patients with RA treated with abatacept. Receiver-operator curves were applied to examine the predictive value of T cell populations and to choose the cutoff for the best performance of the test. Remission was defined using the Disease Activity Score 28 based on C-reactive protein. RESULTS: The overall predictive values of the CD8+CD28- and CD4+CD28- cells for remission after 6 months of abatacept therapy were 0.802 (SE 0.078) and 0.743 (SE 0.089), respectively. Cutoff values of < 87 CD8+CD28- cells/μl and < 28 CD4+CD28- cells/μl had 80.0% sensitivity and 81.8% specificity (Fisher test: p = 0.001), and 60.0% sensitivity and 77.3% specificity (p = 0.043), respectively, for prediction of remission at 6 months. Patients having low baseline numbers of CD8+CD28- T cells had a more than 4-fold higher probability of achieving remission within 6 months than patients with higher levels of these cells. CONCLUSION: A simple laboratory measure, the baseline number of circulating CD28- T cells, predicted remission after 6 months of abatacept treatment in patients with RA.