Safety, Tolerability, Pharmacokinetics and Pharmacodynamics of AMG 139 in Healthy Subjects and Subjects With Moderate to Severe Psoriasis

Inclusion Criteria: Part A - Healthy Volunteers: * Healthy male or female of non-reproductive potential subjects between 18 to 45 years-of-age * Body mass index (BMI) between 18 and 32 kg/m2 * Normal or clinically acceptable physical examination, clinical laboratory values, and ECG * Additional inclusion criteria apply Part B - Psoriasis Subjects: * Male or female of non-reproductive potential subjects with PsO between 18 to 55 years-of-age * Body mass index (BMI) between 18 and 32 kg/m2 * Normal or clinically acceptable physical examination (PE), clinical laboratory values, and ECG; clinically acceptable PE includes evidence of moderate to severe plaque PsO * Diagnosis of plaque PsO for at least 6 months * Moderate to severe plaque PsO defined by: * A minimum PASI score of ≥ 10 * Psoriasis involving ≥ 10% of the Body Surface Area (BSA) * Additional inclusion criteria apply Exclusion Criteria: Parts A - Healthy Volunteers: * History or evidence of a clinically significant disorder (including psychiatric), condition or disease that would pose a risk to subject safety or interfere with the study evaluation, procedures or completion; * Recent or on-going infection(s) * Underlying condition(s) that predisposes the subject to infections * History of malignancy of any type, other than in situ cervical cancer or surgically excised non-melanomatous skin cancers in past 5 years * Additional exclusion criteria apply Part B - Psoriasis Subjects: * History or evidence of a clinically significant disorder (including psychiatric), condition or disease that would pose a risk to subject safety or interfere with the study evaluation, procedures or completion; * Recent or on-going infection(s) * Underlying condition(s) that predisposes the subject to infections * Guttate, pustular, or other non-plaque forms of PsO * Evidence of skin conditions other than PsO (eg, eczema) that would interfere with evaluations of the effect of investigational product on psoriasis * History of malignancy of any type, other than in situ cervical cancer or surgically excised non-melanomatous skin cancers in past 5 years * Additional exclusion criteria apply