Patient description: A 17 year old boy complains of vomiting, non-bloody diarrhea, abdominal pain, fever, chills and loss of appetite for the past 3 days. He ate a salad at a restaurant prior to his diarrhea onset. Physical exam was remarkable for pallor, jaundice, and diffuse abdominal tenderness. Lab results were as follows: Hemoglobin: 9.7 g/dL Platelet: 110,000 /cu.mm Creatinine: 3.6 mg/dL blood urea nitrogen (BUN): 73 mg/dL direct bilirubin: 2.4 mg/dL lactate dehydrogenase (LDH): 881 IU/L (normal: 110-265 IU/L) Peripheral blood smear showed a moderate number of schistocytes and helmet cells. Shiga-like toxin-producing E. coli (STEC) stx1/stx2 were found in stools. He has no other underlying disease and he is not on any medications.

Clinical trial eligibility criteria: eligible ages (years): 18.0-80.0,  Stroke An individual is eligible for if all of the following apply: 1. Is 18-80 years old 2. Has had a recent (within the past 9 days), acute, cortical, hemispheric, ischemic stroke in the middle cerebral artery (MCA) distribution without a midline shift as detected by magnetic resonance imaging (MRI) as a diffusion-weighted image (DWI) abnormality 3. Has a National Institutes of Health Stroke Scale (NIHSS) score of 8-15 (R) and 8-18 (L) at the time of enrollment with no more than a 4 point increase (worsening of score) from the baseline score compared to 24 hours prior to infusion 4. Subjects must have a platelet count >100,000/uL, hemoglobin >8gm/dl, and white blood cell count (wbc) >2,500/uL. 5. Subjects who received tissue plasminogen activator (tPA) or underwent mechanical reperfusion may be included in the study. 6. Is able to provide consent to study or consent is obtained from the subject's legally authorized representative 7. Subjects of childbearing potential must practice effective contraception during the study, and be willing to continue contraception for at least 6 months after intervention so that, in the opinion of the investigator, they will not become pregnant during the course of the study 8. Is a good candidate for the trial, in the opinion of the investigator 9. Agrees to participate in follow up visits 10. Has an ABO/Rh matched umbilical cord blood unit with a minimum of 0.5 x 10^7 total nucleated cells (TNCC)/kg based on the pre-cryopreservation TNCC  An individual is ineligible to participate if any of the following apply. Medical Conditions: 1. Has a medical history of neurological or orthopedic pathology with a deficit as a consequence that results in a modified Rankin Scale >1 before stroke or has a pre-existing cognitive deficit 2. Has clinically significant and/or symptomatic hemorrhage associated with stroke 3. Has new intracranial hemorrhage, edema, or mass effect that may place patient at increased risk for secondary deterioration when assessed prior to infusion 4. Has hypotension as defined as the need for IV pressor support of systolic blood pressure <90 5. Has isolated brain stem stroke 6. Has pure lacunar stroke 7. Requires mechanical ventilation 8. Requires a craniotomy 9. Has a serious psychiatric or neurological disease which could alter evaluation on functional or cognitive scales 10. Has an active systemic infection or is HIV positive 11. Has had an active malignancy within 3 years prior to the start of screening excluding skin cancers other than melanoma 12. Has known coagulopathy such as Factor V Leyden, AntiPhospholipid Syndrome (APC), Protein C, Protein S deficiency, sickle cell, anticardiolipin antibody, or phospholipid syndrome 13. Has any concurrent illness or condition that in the opinion of the investigator might interfere with treatment or evaluation of safety 14. Has current or recent history of alcohol or drug abuse, or stroke associated with drug abuse 15. Pregnant as documented by urine or blood test Concomitant or Prior Therapies: 1. Subjects currently receiving immunosuppressant drugs 2. History of prior transfusion reaction 3. Currently on dialysis 4. Recipient of bone marrow or organ transplant 5. Renal insufficiency with serum creatinine >2.0 mg/dL 6. Hepatic insufficiency (bilirubin >2.5mg/dL or transaminases >5x the upper limit of normal). Patients with Gilberts syndrome are eligible for study enrollment if other liver function tests are normal, regardless of bilirubin level. 7. Any previous or current treatment with angiogenic growth factors, cytokines, gene or stem cell therapy 8. Subjects participating in another interventional clinical trial of an investigational therapy within 30 days of screening Other: 1. Pregnant or lactating women 2. Unable to be evaluated for follow up visits