The purpose of the HARMONY study is to assess the safety and efficacy of an investigational drug called HuZAF, in patients with moderate to severe Crohn's disease (CD). HuZAF is a humanized anti-Interferon-gamma (anti-IFN-γ) monoclonal antibody, which binds and blocks IFN-γ, a protein in the immune system that is involved in inflammation. Antibodies are proteins normally produced by our immune system to help fight off foreign substances. Scientists have been able to make therapeutic humanized monoclonal antibodies, similar to the antibodies in our bodies, to target diseases.