Purified CD4+ T cells were CFSE-labeled and then activated by anti-CD3 or anti-CD3/CD28 antibodies in presence of cell culture supernatants from CD46-costimulated T cells for 5 days in presence or absence of calcitriol from either one healthy donor or one untreated patient with RRMS. This evidence concerns the gene CD28 and relapsing-remitting multiple sclerosis.