CD4 and Huntington disease: Although there was no significant difference in the frequency of conventional CD4 and CD8 T cells between HD and untreated subjects, and between untreated and IFNβ-treated subjects, FTY720 induced a decline in the frequency of CD4 T cells concomitant with an increase in CD8 T cells compared with that in untreated subjects (Additional file 3: Figure S1).