Inclusion Criteria:

• Adults aged 18 to 80 years, inclusive.
• Diagnosed with celiac disease based on positive serology (eg, tissue transglutaminase IgA antibody and/or deamidated gliadin peptide IgG) and intestinal histology consistent with ≥ Marsh Type II or with evidence of villous atrophy.
• Has HLA-DQ2.5 genotype (HLA-DQA1*05 and HLA-DQB1*02) (homozygotes or heterozygotes).
• Has followed a GFD for > 12 months immediately prior to study entry.
• Negative for tTG and negative or weak positive for DGP-IgA/IgG during screening.
• Male or female, and using at least 2 acceptable birth control methods or who are sterile or postmenopausal.
• Capable of understanding and complying with protocol requirements.
• Patient understands and has signed the informed consent form.

Exclusion Criteria:

• Refractory celiac disease.
• Selective IgA deficiency.
• Positive for HLA-DQ8 (DQA1*03, DQB1*0302).
• Previous treatment with tolerance-inducing therapies for celiac disease.
• Known wheat allergy.
• Part B only: History of hyperacute or prolonged symptoms following gluten exposure.
• Uncontrolled or significant medical conditions (including active infections or chronic hepatitis) which, in the opinion of the Investigator, preclude participation.
• History of dermatitis herpetiformis.
• Pregnant or breastfeeding.