This study is to evaluate the efficacy and safety of PNEUMOSTEM® for the Prevention and Treatment of Severe Bronchopulmonary Dysplasia (Severe BPD) in Premature Infants. Half of subjects will receive PNEUMOSTEM, while the other half will receive a placebo.

Bronchopulmonary dysplasia (BPD) is a chronic lung disease in which premature infants and it results in significant morbidity and mortality. PNEUMOSTEM is intended to prevent and treat BPD by modulating inflammation and repairing damaged lung tissue in premature infants through paracrine effects.

Inclusion Criteria:

at screening and randomization

1. 23 weeks to < 25 weeks of gestational age
2. 500g to 1,250g body weight at birth
3. premature infant within postnatal 13 days of age
4. use ventilator with ventilation rate >12 breaths/min or oxygen supply > 25%, or use high frequency ventilator (HFV)

at IP administration

1. premature infant within postnatal 5 to 14 days of age
2. No improvement in ventilator setting 24 hours prior to administration of IP

Exclusion Criteria:

1. subject with cyanotic congenital heart disease or non-cyanotic congenital heart disease that can cause heart failure
2. subject with pulmonary hypoplasia, congenital diaphragmatic hernia, or serious lung malformation such as congenital cystic lung disease
3. subject with chromosome disorder with serious malformation (i.e. Edward syndrome, patau syndrome, Down syndrome, etc.), severe congenital malformation (i.e. hydrocephalus, encephalocele, etc.), or severe congenital infection (i.e., herpes, toxoplasmosis, rubella, syphilis, AIDS, etc.)
4. subject with serious sepsis as active infection or shock due to sepsis
5. subject with grade 3 or 4 of bilateral intraventricular hemorrhage
6. at screening, subject with active pulmonary hemorrhage or active air leak syndrome
7. subject who underwent/will undergo surgery within 72 hours before/after investigational product (IP) administration
8. subject who is expected to be treated with surfactant within 24 hours prior to IP administration
9. subject who is expected to be allergic to gentamicin (Birth mother's allergy for gentamicin will be confirmed).
10. subject who have previously participated in other clinical trials
11. subject who is considered ineligible by investigator due to other medical reasons