 The primary goal of this study is to evaluate the effects of BAF312 siponimod on select immune and neuronal nerve cells by examining laboratory specimens blood andor spinal fluid at multiple time points, prior to, and following the initiation of BAF312 or placebo treatment, in patients with Secondary Progressive Multiple Sclerosis SPMS who are enrolled in a clinical trial NCT01665144 to evaluate the effectiveness and safety of BAF312. 