CD28 and rheumatoid arthritis: Furthermore, an accumulation of CD28− CD4+ and CD28− CD8+ T cells has been described in RA patients [68,69] and, notably, therapy with abatacept, a CD80/86-CD28 T cell co-stimulation modulator, was able to reduce these T cell subsets with an improvement of the disease, as measured by DAS28 score and CRP levels [70].