Study to Assess the Safety, Tolerability, and Preliminary Efficacy of ST266 in Infants With Necrotizing Enterocolitis (NEC)

Inclusion Criteria: 1. Infants born from ≥22 weeks gestational age up to and including 40 weeks gestational age; up to 40 weeks postmenstrual age (gestational age plus chronological age in terms of weeks) with current weight at diagnosis of NEC between ≥500g and ≤3000g, as a result of prematurity and/or IUGR. Parent(s)/legal medical representative(s) voluntarily provides written consent prior to study enrollment. 2. Bell's Stage IIA or higher medical NEC (Stages IIA - IIIA only) diagnosis by radiologic confirmed pneumatosis intestinalis and may include intestinal dilation and ileus. The clinician confirms NEC diagnosis by evaluation of the radiologic imaging for confirmed pneumatosis intestinalis. If X-ray is used and is equivocal, an ultrasound (US) may be used, if available, to confirm pneumatosis. If the clinician (Neonatologist and/or Pediatric Surgeon) has differing interpretation from that of the Radiologist, that should be documented in both the medical and research records for accuracy of NEC diagnosis. Exclusion Criteria: 1. Infants with abdominal perforation. 2. Not expected to survive ≥2 weeks or born with a lethal condition requiring hospice or palliative care (e.g., disease has progressed to NEC totalis, or patient has multi-organ system failure). 3. Born with major congenital anomalies such as cardiac defects (e.g., Tetralogy of Fallot) or chromosomal disorders/anomalies (e.g., neural tube defect). 4. Mother's receipt of any investigational product during pregnancy. 5. Infants with malignancies (e.g., neoplastic cell growth as a solid tumor or a blood neoplasm, such as congenital leukemia). 6. Infants with hypercoagulability disorders (any active thrombosis, diagnosis of disseminated intravascular coagulation or other acquired/inherited disorders (i.e., hemophilia) of coagulation. 7. Infants with a known immunodeficiency (such as galactosemia or agranulocytosis). 8. Infants with anatomic defects that require surgical intervention. 9. Infants with persistent pulmonary hypertension of newborn. 10. Infants with any congenital or acquired gastrointestinal pathology that preclude feeds within 7 days after birth (e.g., duodenal atresia). 11. Infants who have hypoxic ischemic injury (perinatal asphyxia). 12. Infants with polycythemia (at time of treatment) (\>22 g/dL). 13. Positive maternal human immunodeficiency virus status. 14. History of maternal drug abuse (such as amphetamines, opiates, cocaine). This does not include marijuana, or prescription medications for treatment of drug abuse. 15. Considered by the Investigator, for any reason, to be an unsuitable candidate for the study. 16. Infants diagnosed with NEC who will require immediate surgical intervention.