Dose-finding Study of MT-1303 in Subjects With Moderate to Severe Chronic Plaque Psoriasis

Inclusion Criteria: * Have been diagnosed with plaque psoriasis for at least 6 months prior to screening * Have moderate to severe chronic plaque psoriasis as defined by PASI score ≥ 12 and BSA ≥ 10% at baseline * In the investigator's opinion is a candidate for systemic therapy Exclusion Criteria: * Non-plaque forms of psoriasis (e.g., guttate, erythrodermic or pustular) * Current drug-induced or aggravated psoriasis (e.g., a new onset of psoriasis or an exacerbation of psoriasis from beta-blockers, calcium-channel blockers, or lithium carbonate) * History of any of a list of pre-defined cardiovascular diseases * History or known presence of any significant infectious, metabolic, oncological, ophthalmological or respiratory system disease or illness likely to render the subject unsuitable for the study. * Previous exposure to any other S1P receptor modulator * Receipt of a live vaccine within 28 days prior to randomisation * Need, or likely need for, treatment with Class I or III anti-arrhythmic drugs or with heart-rate-lowering beta-blockers or calcium-channel blockers, or with any other drugs which can reduce the heart rate * Clinically significant findings electrocardiogram (ECG) findings.