Eligibility Criteria:
1.1 Inclusion Criteria
* Ability to provide informed consent
* Age between 18 and 65 years
* Confirmed diagnosis of UC for at least 3 months with the extent defined within the previous year
* Moderate to severe UC as defined by a Mayo score of 6-12
* Concomitant medications: Can be on 5-amino salicylate (5-ASA) medications and stable doses (same dose \> 4 weeks) of oral steroids
* Concomitant medications cannot include Infliximab, Adalimumab, Certolizumab or Natalizumab for 4 weeks; rectal steroids, 6-mercaptopurine (6-MP), Azathioprine, Tacrolimus, Methotrexate, Thalidomide, Cellcept for 4 weeks; Theophylline, sulfonylureas, non-steroidal anti-inflammatory drug (NSAIDs) or aspirin for 10 days
* Negative serum pregnancy test within 2 weeks prior to receiving the first dose of study drug in female participants of child-bearing potential
* Female participants of child-bearing potential must be willing to use birth control during the study and for 4 weeks following the last dose of study drug.
1.2 Exclusion Criteria
* Crohn's disease or indeterminate colitis
* Mayo score of \<6 (mild UC)
* Hospitalized or exhibiting signs of toxicity (abdominal distension, severe abdominal tenderness, fever, nausea, vomiting, or tachycardia)
* A history of colorectal cancer or colorectal dysplasia
* Pregnant or breastfeeding females or females wishing to become pregnant within the next 6 months or unwilling to use birth control
* Serum creatinine ≥ 2.0 milligrams per deciliter (mg/dL)
* Alkaline phosphatase, aspartate aminotransferase (AST), alanine aminotransferase (ALT), or direct bilirubin \>1.5x normal: elevated indirect bilirubin related to likely Gilbert's disease permissible
* Use of any of the following medications: Azathioprine, 6-MP, Methotrexate, Mycophenolate Mofetil, Tacrolimus, Cyclosporine, Thalidomide, Adalimumab, Infliximab, Certolizumab, Natalizumab, rectal steroids. Theophylline, sulfonylureas, NSAIDs or aspirin within 10 days of study enrollment
* Psychiatric illness or substance abuse that would interfere with ability to comply with protocol requirements or give informed consent
* Surgery within the last 3 months
* Prior gastrointestinal surgery
* Clinically significant infectious, immune mediated or malignant disease
* Receiving an elemental diet or parenteral nutrition
* History of coagulopathy
* Human immunodeficiency virus (HIV) positive
* Hepatitis B surface antigen (HBsAg) positive
* Active cytomegalovirus (CMV)
* Anemia: hemoglobin (Hb) \< 8 grams/deciliter (g/dL). If the subject has known significant cardiac disease, subjects with Hb \< 10.5 g/dL will be excluded.
* Thrombocytopenia (platelets \< 100,000 per microliter \[100K/mcL\])
* Lymphopenia (absolute lymphocyte count \<0.7)
* Immunoglobulin G (IgG) anti-cardiolipin antibody positive \>16 International Units (IU)
* Prior exposure to OKT3
* Positive quantiferon gold, tuberculosis (TB) spot test, or purified protein derivative (PPD) test
* Known sensitivity to any ingredients in the study drug
* Anti-mouse antibody titer \>1:1000
* Any known autoimmune disease except for ulcerative colitis
* Allergy or hypersensitivity to Omeprazole
* Participated in another clinical trial within 30 days of screening for this trial