The purpose of this study is to determine the safety and efficacy of ALD518 in three different doses in patients who have not had an adequate response to methotrexate.

This will be a phase II, parallel-group, double-blind, randomized, placebo-controlled study of ALD518 in patients with active RA with an inadequate response to methotrexate.

Enrolled patients will be screened within a 4-week period (Day -35 to -7). within a 12-day period (Day-14 to -3) before initial dosing on Day 1 patients will be randomized to one of the following four treatment groups:

Group A: 2x ALD518 80 mg Group B: 2x ALD518 160 mg Group C: 2x ALD518 320 mg Group D: 2x placebo

In all treatment groups patients will continue to take a stable dose of methotrexate.

There will be a total of 11 visits. The total duration of the patient study participation will be approximately 16 weeks (excluding the screening period).

Inclusion Criteria:

• Active Rheumatoid Arthritis for at least 16 weeks duration
• Have a C-reactive protein (CRP) of ≥ 10mg/L
• Have a stable dose of methotrexate (≥ 10mg/week) for at least 3 months

Exclusion Criteria:

• Arthritis onset prior to 16 years old
• Received any biologic therapy in the previous 12 months
• A history of or currently have active tuberculosis
• Any clinically significant concurrent medical condition