Combined Inhibition of Dipeptidyl Peptidase IV (DPIV/CD26) and Aminopeptidase N (APN/CD13) in the Treatment of Psoriasis

Inclusion Criteria: 1. Age 18 years of age at pre-study and 2. Diagnosis of plaque type psoriasis at least 3 month prior to enrolment 3. Mild to moderate plaque type psoriasis with at least 2 plaques of approximately 15cm2 for which topical treatment is indicated 4. Patients must be able to give written informed consent before any trial-specific procedures are performed (see Section 12.2 Exclusion Criteria: 1. Other type of psoriasis (e.g. erythrodermic, guttate or pustular) at enrolment 2. Drug induced psoriasis at enrolment (e.g. lithium) 3. Pregnant or lactating women, patients (men or women) planning a pregnancy during the duration of the study 4. Systemic therapy affecting PASI or phototherapy for a period of 4 weeks prior to enrolment 5. Topical therapy affecting PASI for a period of 2 weeks prior to enrolment 6. Treatment with biologic agents affecting PASI for a period of 3 months prior to enrolment 7. Systemic treatment with immunosuppressive agents (e.g. methotrexate, cyclosporin) or treatment with lithium, anti-malaria medication, or intramuscular gold application for a period of 4 weeks prior to enrolment 8. Having a history of or an ongoing uncontrolled serious or recurring bacterial, viral, fungal, or atypical mycobacterial infection 9. Having a severe medical condition that, in the judgment of the investigator, would jeopardize in any way the subject's safety following exposure to study drug 10. Having the presence or history of malignancy, including lymphoproliferative disorders. Subjects with a history of fully resolved basal or squamous cell skin cancer may be enrolled