Bronchopulmonary Dysplasia (BPD) is the most frequent disease related to a premature birth, 15-50% of very low birth newborns (<1500 gr.) will develop BPD. The prevalence of BPD is increasing due to the advances in neonatology, with a rise in the survival of smaller and more premature babies. The etiology of BPD is multifactorial, in which oxygen, maternal chorioamnionitis, insufficient pulmonary maturation etc. have an important role. These factors lead to a pathological development of the lung and pulmonary vessels, developing secondary Pulmonary Hypertension (PH). Nowadays there is no efficient treatment; this generates a important sanitary burden and a decrease in life quality. Multiple experimental models in mice have studied Mesenchymal Stem Cell (MSC) therapy as prevention of BPD, also recently some clinical trials have tried this therapy on premature newborns with promising results. Hypothesis: MSC therapy in patients at high risk of BPD prevents pulmonary lesions. Methods: The investigators have designed a clinical trial to evaluate the feasibility and security of MSC therapy in patients at high risk of developing BPD.

Inclusion Criteria:

• Preterm newborns ≤ 28 weeks gestational age
• Birth Weight <1250 gr.
• Still on of mechanical ventilation FiO2 > 0,3 at day + 14

Exclusion Criteria:

• Other congenital pathology (pulmonary malformations, active pulmonary bleeding, renal malformations, CHD, malformative syndromes, chromosomopathies)
• Severe neurological lesion.
• HIV infection
• Cardiovascular instability due to any cause
• 72 hours after mayor surgery
• Necrotizing enterocolitis grades II or higher, according to Bell classification, at the time of inclusion.