Scientists in the UK say they have grown tiny sections of human liver.
The Newcastle team is hoping to use their work in drug testing
The sections of liver were created using stem cells from umbilical cords by a team at Newcastle University.
It is hoped the "mini-livers" will be used to test drugs, avoiding incidents like the Northwick Park trial in which six patients became seriously ill.
But other experts warned, because the work was unpublished, it was not possible to assess its worth and that cells made in this way were unreliable.
Researchers Dr Nico Forraz and Professor Colin McGuckin have started a company called ConoStem in an effort to market their stem cell work.
They believe it will be decades before a grown liver can be used in a human transplant operation.
But they say the use of small sections of liver, which are less than the size of a penny, could be used to treat patients within 10-15 years.
A more realistic short-term use would be to replace some of the testing on humans and animals of pharmaceuticals.
The extent of the team's work emerged after publicity following a local business award.
The tissue is grown using a microgravity bioreactor, a piece of equipment derived from Nasa technology, which aids the creation of cells by mimicking weightlessness.
Professor McGuckin said if human testing could be reduced by using organ cells grown from stem cells an incident like that at Northwick Park Hospital could be avoided.
"We take the stem cells from the umbilical cord blood and make small mini-livers," he said.
"We then give them to pharmaceutical companies and they can use them to test new drugs on.
"It could prevent the situation that happened earlier this year when those six patients had a massive reaction to the drugs they were testing."
The news was welcomed by the British Union for the Abolition of Vivisection which said the government should pump money into the creation of "ethically-sourced human tissue".
But Professor Malcolm Alison, from the Centre for Diabetes and Metabolic Medicine at Queen Mary's School of Medicine and Dentistry, said the use of the term "mini-liver" constituted a bold claim.
"Many groups, including the Newcastle one, have been able to turn stem cells from the blood into cells that look like liver cells [hepatocytes], but these have been difficult to expand in culture into a mass of cells that was therapeutically useful."
And Dr Stephen Minger, director of the Stem Cell Biology Laboratory, Kings College London, said: "This research hasn't been through the proper scientific channels yet - it hasn't been peer reviewed. It is impossible to know whether this work is meaningful or not."
Dr Mike Nicholds, acting chief executive of ConoStem, said peer-reviewed papers would be in the pipeline, and that it was hoped the first liver cells would be used in a drugs test within 12 months.
Professor Ian Gilmore, a liver specialist at the Royal Liverpool Hospital, told BBC News the team's work was significant.
"Firstly that they are able to do it from umbilical cord blood and not requiring embryos. That's quite a big ethical leap forward.
Up to 10% of people in the UK have liver problems
"And they are producing such a significant amount of tissue."
But he said: "We're a long way from producing a whole liver. The liver has its own blood supply, its own fibrous skeleton, they are just producing the individual liver cells.
"But nonetheless it is exciting because there is a real dearth of treatments available for people with liver disease."
It is estimated that up to 10% of the UK population have problems with their liver - most are linked to lifestyle factors, such as heavy drinking and obesity.