CD4 and secondary progressive multiple sclerosis: Flow cytometric analyses showed that, within the remaining lymphocyte subsets, the incidences of CD4+ and CD8+ naive T cells were reduced, while anti-inflammatory Th2 and T regulatory cells (Tregs) were enriched [120], indicating a shift towards an anti-inflammatory and suppressive homeostatic immune system that can contribute to the clinical effectiveness of siponimod in SPMS.