PDCD1 and rheumatoid arthritis: In contrast, PCA of CD8+PD-1+ and CD8+PD-1− cells did not reveal separate clusters (Fig. 1g) and differential gene expression analysis of CD8+ cells demonstrated no significantly differentially expressed genes when comparing CD8+PD-1+ versus CD8+PD-1− cells (Fig. 1h), suggesting that peripheral blood CD8+ PD-1+ cells are not a true cell subtype present in the periphery of early RA patients.