However, CTLA-4 Ig treatment was also shown to be effective in treating established arthritis in collagen-induced arthritis (CIA) mouse model4 and human RA patients, in whom memory T cells predominate over naïve T cells in the inflamed synovium5; these memory T cells are much less dependent on costimulatory pathways compared to naïve T cells. Here, CTLA4 is linked to arthritic joint disease.