Study to Compare Efficacy and Safety of ABP 501 and Adalimumab (HUMIRA®) in Adults With Moderate to Severe Plaque Psoriasis

Percent Improvement From Baseline in PASI at Week 32

The PASI measures the average redness (erythema), thickness (induration), and scaliness (each graded on a 0 to 4 scale) of psoriasis lesions, weighted by the area of involvement in the four main body areas (i.e., head and neck, trunk, upper extremities, and lower extremities). PASI scores can range from 0.0 to 72.0, with higher scores indicating greater severity and/or more extensive psoriasis. Percent improvement from baseline is calculated as (value at baseline - value at post-baseline visit) × 100 / (value at baseline).

Time frame: Baseline and week 32

Percent Improvement From Baseline in PASI at Week 50

The PASI measures the average redness (erythema), thickness (induration), and scaliness (each graded on a 0 to 4 scale) of psoriasis lesions, weighted by the area of involvement in the four main body areas (i.e., head and neck, trunk, upper extremities, and lower extremities). PASI scores can range from 0.0 to 72.0, with higher scores indicating greater severity and/or more extensive psoriasis. Percent improvement from baseline is calculated as (value at baseline - value at post-baseline visit) × 100 / (value at baseline).

Time frame: Baseline and week 50

Percentage of Participants With a Static Physician's Global Assessment (sPGA) Response at Week 16

The sPGA is a 6-point scale ranging from 0 (clear) to 5 (very severe) used to measure the severity of disease (induration, scaling, and erythema). A sPGA response is defined as a sPGA value of clear (score 0) or almost clear (score 1).

Time frame: Week 16

Percentage of Participants With a sPGA Response at Week 32

The sPGA is a 6-point scale ranging from 0 (clear) to 5 (very severe) used to measure the severity of disease (induration, scaling, and erythema). A sPGA response is defined as a sPGA value of clear (score 0) or almost clear (score 1).

Time frame: Week 32

Percentage of Participants With a sPGA Response at Week 50

The sPGA is a 6-point scale ranging from 0 (clear) to 5 (very severe) used to measure the severity of disease (induration, scaling, and erythema). A sPGA response is defined as a sPGA value of clear (score 0) or almost clear (score 1).

Time frame: Week 50

Change From Baseline in the Percentage of Body Surface Area (BSA) Involved With Psoriasis at Week 16

A measurement of psoriasis involvement, given as the physician's assessment of the percentage of the participant's total body surface area (BSA) involved with psoriasis. The percent of BSA affected was estimated by assuming that the subject's palm, excluding the fingers and thumb, represented roughly 1% of the body's surface. Change from baseline is calculated as (value at post-baseline visit - value at baseline). A decrease from baseline (negative value) indicates improvement.

Time frame: Baseline and Week 16

Change From Baseline in the Percentage of BSA Involved With Psoriasis at Week 32

A measurement of psoriasis involvement, given as the physician's assessment of the percentage of the participant's total body surface area (BSA) involved with psoriasis. The percent of BSA affected was estimated by assuming that the subject's palm, excluding the fingers and thumb, represented roughly 1% of the body's surface. Change from baseline is calculated as (value at post-baseline visit - value at baseline). A decrease from Baseline (negative value) indicates improvement.

Time frame: Baseline and week 32

Change From Baseline in the Percentage of BSA Involved With Psoriasis at Week 50

A measurement of psoriasis involvement, given as the physician's assessment of the percentage of the participant's total body surface area (BSA) involved with psoriasis. The percent of BSA affected was estimated by assuming that the subject's palm, excluding the fingers and thumb, represented roughly 1% of the body's surface. Change from baseline is calculated as (value at post-baseline visit - value at baseline). A decrease from Baseline (negative value) indicates improvement.

Time frame: Baseline and week 50

Number of Participants With Adverse Events

The Investigator assessed whether each adverse event (AE) was possibly related to the investigational product. AEs were graded for severity according to the Common Toxicity Criteria for Adverse Events (CTCAE) version 4.03. A serious AE is defined as an AE that meets at least 1 of the following serious criteria: * fatal * life threatening * requires inpatient hospitalization or prolongation of existing hospitalization * results in persistent or significant disability/incapacity * congenital anomaly/birth defect * other medically important serious event. Results are reported from Day 1 to week 16 for the Part 1 ABP 501 and Adalimumab groups, and from post week 16 to the end of study (week 52) for the Part 2 ABP 501/ABP 501, Adalimumab/Adalimumab and Adalimumab/ABP 501 groups.

Time frame: From first dose of study drug until 28 days after the last dose. Treatment was for 16 weeks in Part 1 and 32 weeks in Part 2.

Percentage of Participants Developing Antibodies to ABP 501 or Adalimumab

Two validated assays were used to detect the presence of anti-drug antibodies. Samples were first tested in an electrochemiluminescence (ECL)-based bridging immunoassay to detect anti-drug antibodies (ADA) against ABP 501 and adalimumab (Binding Antibody Assay). Samples confirmed to be positive for binding antibodies were subsequently tested in a non-cell based bioassay to determine neutralizing activity against ABP 501 or adalimumab (Neutralizing Antibody Assay). Developing antibody incidence is defined as a negative or no antibody result at baseline and a positive antibody result at a post-baseline time point.

Time frame: For 16 weeks in Part 1 and for 52 weeks for participants who were re-randomized in Part 2.