Researcher Dhruv Sareen's own stem cells are now orbiting the Earth. The mission? To test whether they'll grow better in zero gravity.

Scientists at Cedars-Sinai Medical Center in Los Angeles are trying to find new ways to produce huge batches of a type of stem cell that can generate nearly any other type of cell in the body — and potentially be used to make treatments for many diseases. The cells arrived over the weekend at the International Space Station on a supply ship.

"I don't think I would be able to pay whatever it costs now" to take a private ride to space, Sareen said. "At least a pa...