A Phase 2a Safety and Efficacy Open-Label Study of PRA023 in Subjects With Moderately to Severely Active Crohn's Disease

Inclusion Criteria:

• Confirmed diagnosis of Crohn's disease

• Moderately to severely active CD as defined by Crohn's disease activity index (CDAI)score and centrally read endoscopy

• Must have corticosteroid dependence or have had no response, insufficient response,loss of response and/or intolerance to at least one of the following therapies:corticosteroid, immunosuppressants, or an approved anti-tumor necrosis factor (TNF),anti-integrin, or anti-interleukin (IL)12/23

• Able to provide written informed consent and understand and comply with therequirements of the study

Exclusion Criteria:

• Women of child bearing potential (WOCBP) and men with female partner of childbearingpotential who are unwilling to use two highly effective methods of contraception toavoid pregnancy for the entire study period and up to 12 weeks after the last doseof study drug

• Diagnosis of ulcerative colitis (UC) or indeterminate colitis

• CD isolated to the stomach, duodenum, jejunum, or perianal region, without colonicand/or illeal involvement

• Suspected or diagnosed intra-abdominal or perianal abscess at screening

• Current stoma or need for colostomy or ileostomy

• Previous small bowel resection with a combined resected length of >100 cm orprevious colonic resection of > 2 segments

• Surgical bowel resection within 3 months before screening

• Past or current evidence of definite low-grade or high-grade colonic dysplasia notcompletely removed

• Subjects in the opinion of the investigator are at an unacceptable risk forparticipation in the study

• Subjects who meet the protocol criteria for important laboratory exclusion criteria