Inclusion Criteria:
1. 18 years or older
2. Moderate to severe Crohn's disease (Crohn's disease activity index 220 to 450)
3. Ileocolonic Crohn's disease (CD) with Simple Endoscopic Score for Crohn Disease ≥6 or ileal or colonic CD with with Simple Endoscopic Score for Crohn Disease ≥4 and ulcer score ≥1 in at least one segment
4. Fecal calprotectin ≥250 µg/g or C-reactive protein≥0.5 mg/dL
5. Patients who have never been to exposed to any biologic agent
6. Patients who are non-responsive or intolerance to conventional therapy (corticosteroids, immunomodulators, or antibiotics, etc.) or contraindicated to conventional therapy
7. Patients who gave a voluntary informed consent
Exclusion Criteria:
1. Patients who have a history of hypersensitivity to humanized proteins
2. Patients ever treated with corticosteroids within 8 weeks of screening date
3. a) Symptomatic intestinal stricture, b) Symptomatic anal stricture, c) Untreated intra-abdominal abscess, d) Untreated perianal abscess, e) Abdominal surgery within 6 months, f) Patients who are expected to require intestinal surgeries during study period
\- However, the following patients can be included: from baseline, 4 weeks or more after proper drainage of perianal abscess and from baseline, 8 weeks or more after proper drainage of intra-abdominal abscess
4. Active tuberculosis. However, the following patients can be included: Patients who were diagnosed with tuberculosis, but were properly treated with anti-tuberculosis therapy according to the standard guidelines and who were confirmed to be cured.
5. Latent tuberculosis infection (LTBI): Patients confirmed as having latent tuberculosis through medical history, physical examination, chest X-ray, PPD (Purified Protein Derivative) skin test or interferon gamma release assay (IGRA) by a pulmonology specialist. However, patients with LTBI who finished proper treatment for LTBI for 4 weks and who are going to complete LTBI treatment.
6. HBsAg (Hepatitis B virus surface antigen)-positivity. Patients with negative HBsAg, but positive IgG anti-HBc (Immunoglobulin G anti-Hepatitis B core antibody) should be tested for HBV (hepatitis B virus) DNA real time quantitative PCR (polymerase chain reaction). If HBV DNA real time quantitative PCR ≥10 IU/mL should be excluded.
7. Anti-HCV (hepatitis C virus) antibody-positivity
8. History of HIV (human immunodeficiency virus) infection of positivity for anti-HIV
9. Heart disease of NYHA (New York Heart Association) Class III/IV
10. Active infection
11. Malignancy (excluding skin basal cell carcinoma, skin squamous cell carcinoma, and uterine cervix cancer) or history of colonic or small bowel dysplasia within 5 years
12. Pregnancy or lactating woman
13. Patients who are not applying proper contraceptive measures and patients who do not have a plan for proper contraceptive measures for at least 6 months after the last dose of infliximab (oral, parenteral, or implantable hormonal contraceptives, diaphragm, condom, intra-uterine device, or abstinence are accepted as proper contraceptive methods.
14. Patients who are decided to be not proper to be enrolled into the study by investigators.
