Inclusion Criteria:

1. Males and females 18 to 65 years of age
2. Signed fully informed consent provided as per this protocol
3. Diagnosis of Crohn's Disease confirmed by endoscopy or radiography and/or histology at least 6 months prior to randomization into the study
4. CD involving the ileum and/or colon
5. Moderately to severely active CD (Crohn's Disease Activity Index (CDAI) score of ≥ 220 and ≤450) at baseline
6. Subject must be intolerant or have insufficient response to conventional therapy
7. Subjects must meet concomitant medication criteria described below:

   Oral 5-acetyl salicylic acid (5-ASA) compounds

   • If currently being taken, dose must be stable for at least 4 weeks
   • If discontinued due to lack of response or lack of tolerance, the stop-date must have been at least 4 weeks prior to baseline

   Corticosteroid therapy

   • If currently being taken, dose must be stable for at least 2 weeks
   • If discontinued due to lack of a response or lack of tolerance, stop date must have been at least 2 weeks prior to baseline

   Azathioprine or 6-mercaptopurine (6-MP) or methotrexate

   • If currently being used, dose must be stable for at least 8 weeks
   • If discontinued due to a lack of response or lack of tolerance, stop date must have been at least 4 weeks prior to baseline
8. White blood cell count ≥ 3.5x109 at screening
9. C-reactive protein > Upper Limit of Normal (ULN)
10. Subject agrees to use barrier contraceptive methods (i.e. diaphragm, cervical cap, contraceptive sponge or condom) with spermicidal foam/gel/cream/suppository, or intrauterine device (IUD) throughout the study and for at least 6 weeks after last study drug administration, unless subject is post-menopausal or otherwise incapable of becoming pregnant by reason of surgery or tubal ligation, or has had a vasectomy.

Exclusion criteria

1. Crohn's Disease involvement isolated to the mouth, upper gastrointestinal tract, or anus
2. History of total colectomy with ileorectal anastomosis or a proctocolectomy.
3. History of fistulizing Crohn's Disease
4. Subject has postoperative stoma, ostomy, or ileoanal pouch
5. Subject has short bowel syndrome
6. Subject is scheduled for surgical bowel resection
7. Subject has known symptomatic obstructive strictures or bowel perforation in the 6 months prior to screening
8. Treatment with anti-Tumor Necrosis Factor (TNF) biologic agents (e.g. monoclonal antibody therapies), other agents intended to reduce TNF, or other biological therapies < 8 weeks prior to baseline or within 5 half-lives of agent prior to baseline, whichever is longer
9. Previous treatment with rifabutin and/or clofazimine
10. Oral or parenteral antibiotics in the 4 weeks prior to baseline (topical antibiotics are permitted)
11. Treatment with probiotics (excluding yogurt and yogurt-derived products) in the 4 weeks prior to screening
12. Females who have a positive pregnancy test or are lactating