Thirteen down, eight to go.

As part of its initiative to house all 21 federally approved human embryonic stem-cell lines, the National Stem Cell Bank at the WiCell Research Institute in Madison added two stem-cell lines Tuesday from the University of California-San Francisco, bringing its total to 13.

"We're very excited about this, because it means we're more than halfway to getting all the lines," WiCell Executive Director Beth Donley said. "It'll provide a great resource to the stem cell community here, as well as nationally."

Next stop: Sweden, where Donley said she hopes to obtain another federally approved stem-cell line from biotechnology company Cellartis.

Donley said Cellartis "expressed interest" in providing WiCell another federally approved stem-cell line when she visited the company in Sweden last November.

Like many international biotechnology companies, the one concern Cellartis representatives expressed, according to Donley, was ensuring the stem-cell lines would be cultured and maintained in conditions similar to those in their home country.

But, having resolved those issues, Donley said she is confident WiCell will reach an agreement with Cellartis by the end of the year.

In the meantime, Derek Hei, a WiCell researcher and leader of the National Stem Cell Bank, said the stem-cell lines obtained from UCSF will add valuable diversity to the lines already housed by the bank.

"By having more diverse cell lines, the more we can understand the subtle differences between them," Hei said, "which helps in determining which cell lines are better for certain applications."

Donley said she hopes to obtain the remaining federally approved lines from Novocell, a stem-cell engineering company in San Diego and Technion, the Israel Institute of Technology located in Haifa.

However, Donley said licensing issues still have to be resolved with Novocell before an agreement could be reached.

As for Technion, Donley said discussions have been delayed since the Israel-Lebanon conflict erupted in July.

"We haven't even approached them as of now," Donley said.

Despite the potential hold-ups, Donley said she is "97 percent" confident the National Stem Cell Bank will eventually obtain all 21 federally approved stem-cell lines.

"We can only accommodate new stem-cell lines one at a time," Donley said. "But as people gain confidence in our culture methods, I think they will see the benefits of depositing their stem-cell lines here."

Established in September 2005 and funded by the National Institutes of Health, the National Stem Cell Bank is the first and only repository of federally approved stem-cell lines in the U.S., housing and distributing stem-cell lines to researchers in academic and non-profit institutions across the nation.