CD4+ T cells taken from CD30L- or CD30-deficient mice showed a reduced ability to differentiate into Th17 cells [31]. In vivo experiments showed that transfection of CD30L−/− CD4+ T cells in severe combined immunodeficiency (SCID) CD30L-deficient mice leads to an altered Th17 differentiation, while transferring CD30L+/+ CD4+ T cells causes a normal Th17 differentiation. The gene discussed is CD4; the disease is severe combined immunodeficiency.