Primary human pulmonary artery endothelial cells cryopreserved at the end of the tertiary culture. • Viability at least 70% • ≥500,000 viable cells/vial • Capable of at least 16 population doublings • Mycoplasma: Not Detected • Hepatitis B: Not Detected • Hepatitis C: Not Detected • HIV-1: Not Detected • Bacteria, yeast, and other fungi: Not Detected • Positive for von Willebrand factor (vWf) • Positive for CD31 • Negative for α-actin • Positive for diI-Ac-LDL uptake