This Phase II clinical study is to test safety and efficacy of BT061 against psoriasis given as repeated doses.

Patients are enrolled into escalating dose levels. Improvement of PASI, physician's global assessment and itching score is evaluated after administration of BT061 or placebo. Safety data are assessed by an independent data and safety monitoring board (DSMB).

Inclusion Criteria:

• Male and female patients with moderate, moderate to severe or severe chronic plaque psoriasis diagnosed ≥ 12 months prior to Screening.
• BSA (Body surface area) involvement > 10% for more than 6 months.
• PASI ≥10.
• Age ≥ 18 to ≤ 75 years.
• Body mass index (BMI) of 18-30 kg/m2 with a body weight between 50 and 130 kg.

Exclusion Criteria:

• Erythrodermic, guttate or palmar pustular psoriasis (mixed forms may be admissible if chronic plaque psoriasis clearly remains the predominant diagnosis
• Treatment with a biological within less than 30 days or within less than 5 half-lives of the respective compound prior to administration of BT061/placebo.
• Serious local (e.g. abscess) or systemic infection (e.g. pneumonia, septicaemia) within 3 months prior to the administration of BT061 or placebo.
• Presence or history of clinically significant immune deficiency or autoimmune disease (except psoriasis).
• Positive diagnosis for acute or chronic infections (i.e. Hepatitis C Virus [HCV], Hepatitis B Virus [HBV], Human Immunodeficiency Virus [HIV]) at Screening visit.