PRTN3 and rheumatoid arthritis: Amazingly, the frequencies of AE-specific CD8+ T cells (as detected by dextramers) were significantly higher in Rs than in NRs at time 0 (before the start of therapy), as indicated by the significant ROC sensitivity and specificity, and correlated with the disease activity only in Rs. This, together with the finding that no clinical criterion (including DAS28-ESR, DAS28-CRP, and ACPA) was capable of discriminating Rs and NRs, suggests that the frequency of AE-specific CD8+ T cells represents a unique biomarker predicting the response to TNF-α inhibitor therapy in RA patients.