The primary purpose of this study is to characterize changes in gluten-specific T cells and pathology in the small intestine with specific focus on biomarkers likely to change with therapeutic celiac disease (CeD) treatment.

Gluten challenge studies are used to test the effectiveness of therapies designed to prevent immune response to gluten in participants with CeD. The study will enroll approximately 20 participants. Participants will be randomly assigned (by chance, like flipping a coin) in a 1:1 ratio to one of the two treatment groups:

• Group A: Gluten 3 gm
• Group B: Gluten 10 gm

All participants will be asked to take an oral dose of gluten at the same time on Days 1 to 14 throughout the study. This multi-center trial will be conducted in the United States. The overall time to participate in this study is 10 weeks. Participants will visit to the clinic on Day -45 and will be contacted for follow-up assessment on Days 15 to 42.

Inclusion Criteria:

1. Be a non-smoker who has not used tobacco- or nicotine-containing products (example, nicotine patch) for at least 6 months before Day 1 gluten administration.
2. Have well-controlled biopsy-proven CeD, compliant with a gluten-free diet (GFD) for greater than or equal to (>=) 6 months preceding screening, with resolution of CeD symptoms, normalization of CeD serology, and in the judgment of the investigator, have inactive or minimally-active disease.
3. Be HLA-DQ2.5 and/or HLA-DQ8 positive, assessed at screening. If participants have already been genotyped, results from previous testing may be used in lieu of genotyping at screening.
4. Be willing to delay a planned procedure involving the use of powerful electromagnetic fields (example, magnetic resonance imaging), until the PillCam SB 3 capsule is excreted.
5. Not undergo VCE or optical coherence tomography (OCT) if has an implanted electromedical device or a swallowing disorder.
6. Not undergo OCT if has a contraindication to the device or procedure as per reference information.

Exclusion Criteria:

1. Had major surgery and/or donated or lost 1 unit of blood (approximately 500 milliliter [mL]) within 8 weeks before the first dose of gluten.
2. Are unable to refrain from or anticipate the use of any unapproved medication, including prescription drugs, nonprescription drugs, and herbal remedies, beginning approximately 7 days before administration of the initial dose of gluten and continuing throughout the trial until the follow-up visit.
3. Consume excessive amounts of coffee, tea, cola, energy drinks, or other caffeinated beverages per day. An excessive amount is defined as greater than 6 servings (1 serving is approximately equivalent to 120 mg of caffeine).
4. Have positive IgA anti-tissue transglutaminase (tTG), IgA anti-deamidated gliadin peptide (DGP), and IgG DGP serologies at Screening.
5. Have inflammatory gastrointestinal disorders or autoimmune diseases other than CeD or autoimmune thyroid disease.
6. Have known or suspected gastrointestinal obstructions, strictures, or fistulas based on the clinical picture or pre-procedure testing and profile of the PillCam SB 3 capsule.
7. Endoscopy and intestinal biopsy are contraindicated.

Takeda makes patient-level, de-identified data sets and associated documents available for all interventional studies after applicable marketing approvals and commercial availability have been received (or program is completely terminated), an opportunity for the primary publication of the research and final report development has been allowed, and other criteria have been met as set forth in Takeda's Data Sharing Policy (see www.TakedaClinicalTrials.com for details). To obtain access, researchers must submit a legitimate academic research proposal for adjudication by an independent review panel, who will review the scientific merit of the research and the requestor's qualifications and conflict of interest that can result in potential bias. Once approved, qualified researchers who sign a data sharing agreement are provided access to these data in a secure research environment.

The safety set consisted of all participants who were enrolled and received at least 1 dose of gluten.

Treatment emergent adverse events (TEAEs) are adverse events that started after the first dose of gluten up to Day 43

At each visit the investigator had to document any occurrence of adverse events and abnormal laboratory findings. Any event spontaneously reported by the participant or observed by the investigator was recorded, irrespective of the relation to study treatment.