Subjects will be randomly assigned to Group A (ponesimod treatment group) or Group B (placebo treatment group) in a 1:1 ratio. Subjects in Group B will be further randomized in a 1:1 ratio to one of the following sequences: 400 mg moxifloxacin followed by moxifloxacin-matching placebo or moxifloxacin matching placebo followed by 400 mg moxifloxacin.