• Pneumonia severity index• Oxygenation index (PaO2/FiO2)• Side effects in the UC-MSCs treatment group• 28-days survival• Sequential organ failure assessment• C-reactive protein• Procalcitonin• Lymphocyte count• CD3+, CD4+ and CD8+ T celll count• CD4+/CD8+ratio. The gene discussed is CD4; the disease is susceptibility to pneumonia measurement.