Inclusion Criteria:

• Participant must be 18 to 70 years of age, inclusive, at the time of signing the informed consent.
• Participants must be diagnosed with type 1 or type 2 diabetes.
• Participants must be diagnosed with diabetic gastroparesis, defined by the presence of the following criteria:
  • At least a 3-month past or current history of symptoms of gastroparesis (e.g., postprandial fullness, early satiety, bloating, postprandial nausea/vomiting, and epigastric or abdominal pain);
  • Screening or documented historical scintigraphy (within 3 years prior to screening) with approximately 10% or greater of solid contents retained at 4 hours.
• BMI ≥ 20.0 and ≤  50.0 (kg/m2) (inclusive).
• Male and/or female participants.
• Contraception use by men or women should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies.
• Participant and their opposite sex partner(s), if they are of childbearing potential, should use highly effective, double barrier contraception during the study and 90 days following last dose of nimacimab. Participants must agree not to donate sperm or oocytes during study participation through 90 days after dosing.
  • Note: Abstinence is acceptable if this is the usual lifestyle and preferred contraception for the participant. Periodic abstinence, the rhythm method, and the withdrawal method are not acceptable.
• Females must have a negative serum pregnancy test at Screening and a negative urine pregnancy test on Day 1.
• Participants are capable of giving signed informed consent which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in this protocol.

Exclusion Criteria: 

• Participants have a known malignancy that is progressing or has required active treatment within the past 3 years.
  • Note: Participants with basal cell carcinoma of the skin, squamous cell carcinoma of the skin, or carcinoma in situ (e.g., breast carcinoma, cervical cancer in situ) that have undergone potentially curative therapy are not excluded.
• Participants have a known history of Human Immunodeficiency Virus (HIV) infection (HIV 1/2 antibodies).
• Participants have a known active Hepatitis B (defined as Hepatitis B surface antigen [HBsAg] reactive) or known active Hepatitis C virus (defined as HCV RNA [qualitative] is detected) infection.
• Participants with uncontrolled diabetes. Participants with controlled diabetes and stable blood glucose levels are allowed (insulin is allowed). HbA1c > 9.9% at screening are excluded.
• Participants with history of seizures, major depression, or suicidality.
• Participants with uncontrolled hypertension SBP >165 mmHg or DBP >110mmHg.
• Participants with end stage renal disease on hemodialysis or Stage 4 or greater CKD.
• Participants have a history of myocardial infarction or arterial thromboembolic events within 6 months prior to enrollment or severe or unstable angina, New York Heart Association (NYHA) Class III or IV disease, or a QTc interval > 470 msec.
• Participants have an active infection requiring systemic therapy.
• Participants have a history or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the study, interfere with the participants’ participation for the full duration of the study, or is not in the best interest of the participants to participate in the opinion of the treating Investigator.
• Participants have known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the study
• Participants who had surgery within the past 3 months prior to the first study intervention administration determined by the Investigator to be clinically relevant.
• Women participants who are pregnant or breastfeeding, or expecting to conceive or father children within the projected duration of the study.
• Participants have an active autoimmune disease that has required systemic treatment within 3 months (i.e., with use of disease modifying agents, corticosteroids or immunosuppressive drugs). Replacement therapy (e.g., thyroxine, insulin, or physiologic corticosteroid [stable / low doses of ≤ 10 mg/day prednisone or equivalent dose]) for adrenal or pituitary insufficiency is not considered a form of systemic treatment and is allowed.
• Aspartate aminotransferase (AST) or alanine transaminase (ALT) > 3 x upper limit of normal (ULN). One repeat test may be allowed within 7 days at the discretion of the Investigator.
• A "yes" response to any one of the suicidal ideation or suicidal behavior questions in the C-SSRS at the screening or baseline visit.
• Participants on prokinetic (investigational agents, non-approved agents, and metoclopramide) therapy and/or opiates should have these medications withdrawn at least 7 days prior to any study scintigraphy exam and at least 7 days prior to placebo run-in (Day 1) and through study Day 15 of treatment.
• Participants must be on a stable medication dose for diabetes for at least 4 weeks prior to baseline.
• Participants with any active prokinetic device (including gastric electrical stimulator, transpyloric stent, gastro-jejunal feeding tube, jejunal feeding tube, gastrostomy tube for feeding) are excluded, unless device is turned off for at least 7 days prior to any study scintigraphy exam and at least 7 days prior to placebo run-in (Day 1) and through study Day 15 of treatment.
• Participants who have had bariatric surgery, or laparoscopic or endoscopic pyloroplasty, or esophageal surgery, or fundoplication.
• Participants who are currently or have participated in a study of an investigational product or used an investigational device within 4 weeks prior to the first dose of study intervention.
• Participants who have had previous exposure to nimacimab or have an allergy to nimacimab or inactive components of nimacimab.