Two of the three patients have reported a positive outcome after receiving injections of neural stem cells, doctors at the Zurich University said.
Doctors say the ultimate aim is to help those paralysed by injury to walk again, 'The Telgraph' reported.
The trial worked on the theory that injected adult stem cells would transform themselves into spinal cord nerves, reconnecting brain and lower body.
Professor Armin Curt, who lead the study, described the result as "fundamental".
"To find something that can repair the spinal cord is a huge breakthrough. If we can show that something has changed for the better [as a result of stem cell therapy] that's fundamental," he said.
He presented the findings at the annual conference of the International Spinal Cord Society in London yesterday.
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"We think these stem cells are one of the first tools we have for actually repairing the central nervous system. To see this kind of change in patients who truly have the worst-of-the-worst type of injury to the spinal cord is very exciting," Dr Stephen Huhn, from the firm, said.
The three patients, who all had complete spinal injury and could feel nothing below their nipples, were each given a dose of 20 million 'adult neural stem cells about six months ago.
This was primarily a safety trial, and Curt said monitoring had shown "a very good safety profile".
Detailed questioning and objective tests also showed signals were passing up the injured spine to the brain, when they had not before.
One of the patients, a 46-year-old Norwegian financial consultant, said: "I