First derivation in Spain of human embryonic stem cell lines: use of long-term cryopreserved embryos and animal-free conditions.

The first two human embryonic stem cell lines (VAL-1 and VAL-2) have been derived in Spain with long-term cryopreserved embryos under animal-free conditions. In the first series, 40 human embryos that had been cryopreserved at day 2 of development were thawed after >5 years. A derivation efficiency of 5% per frozen embryo or 12.5% per blastocyst was obtained.