The main aim is to see how DONQ52 works to improve small intestinal damage and reduce celiac-related symptoms due to gluten exposure, in participants with celiac disease (CeD) attempting to maintain a gluten-free diet (GFD) in treated participants versus placebo controls.

Inclusion Criteria:

• Body mass index (BMI) of 18 to 40 (kg/m2) at screening.

• Willingness to ingest a gluten-free product and Simulated Inadvertent Gluten Exposure (SIGE) products as per the study protocol.

• History of medically diagnosed, and adequately documented (i.e., included in the participant's medical records), CeD

• Attempting a GFD for at least 12 months prior to the screening visit.

  - The participants should be instructed not to alter dietary habits including a GFD during the study period.

• Valid results from central testing of blood documenting a positive result for the HLA DQ2.5 genotype (HLA-DQA1*05 and HLA-DQB1*02) (homozygous or heterozygous).

• Experienced at least 2 gluten-related symptom events (i.e., 2 different gluten-related symptoms which are diarrhea, abdominal pain, bloating, nausea, tiredness or 1 gluten-related symptom occurred twice) within a month before the screening.

• Willingness to undergo 2 on-study upper gastrointestinal endoscopies with duodenal biopsies.

• Presence of ongoing duodenal mucosal damage defined as Vh:Cd of 2.5 or less

Exclusion Criteria:

• Participants with documented history (i.e., included in the participant's medical records) of medically diagnosed Refractory Celiac Disease (RCD) or suspected RCD by the investigator.
• History of IgE-mediated reactions to wheat, barley, rye, or other ingredients in gluten-free and SIGE products used in this study (i.e., methylcellulose, and gelatin).
• History of cancer, including hematological malignancy and solid tumors, within 5 years prior to the screening visit, or history of T cell lymphoma or B cell lymphoma ever.
• History of hypersensitivity reactions including anaphylaxis to a biological medical product or any of the excipients.
• Participants who carry the HLA-DQ8 (HLA-DQA1*03 and DQB1*0302) genotype (homozygous or heterozygous).
• Any other chronic, active gastrointestinal disease (e.g., inflammatory bowel disease, microscopic colitis, eosinophilic esophagitis, peptic ulcer, gastroesophageal reflux disease, functional dyspepsia, or irritable bowel syndrome) that might in the investigator's opinion, interfere with the assessment of GI symptoms or small intestinal histology.
• Helicobacter pylori tests that indicate current infection.
• Positive either human immunodeficiency virus (HIV) antigen or antibody test at screening.
• Positive hepatitis B surface antigen (HBsAg) test or total hepatitis B core (HBc) antibody test at screening.
• Positive hepatitis C virus (HCV) antibody test at screening, except in participants who have negative results for HCV ribonucleic acid (RNA) test at screening.
• Positive for QuantiFERON-TB Gold test at screening that indicates active tuberculosis (TB) at screening.

Qualified researchers may request access to individual patient level data through the clinical study data request platform. For further details on Chugai's Data Sharing Policy and how to request access to related clinical study documents, see here (www.chugai-pharm.co.jp/english/profile/rd/ctds\_request.html).