Researchers at biotech firm PPL Therapeutics have managed to convert skin cells back into stem cells - the body's master cells, capable of growing into a wide range of tissues - and then into working heart cells. The experiments were carried out using cow cells grown in the laboratory, but PPL's UK research team hope to repeat the process using human cells.

The findings were presented by managing director Dr Ron James at a meeting of the British Fertility Society last Friday, although for commercial reasons, he did not reveal any details of the procedure. But he believes that the new method of producing stem cells will be 'equally applicable' to human cells. PPL's initial research focus will be on producing a supply of insulin-producing cells for the treatment of diabetes.

The PPL scientists are the first to completely reprogramme a fully differentiated (developed) cell, though several groups have managed to grow different tissues from partly-specialised adult stem cells. If successful, reprogrammed adult cells may provide an alternative to early embryo cells for developing treatments for a wide range of diseases. But PPL's research director Dr Alan Colman stressed that all options should be kept open, and it was too early to rule out so-called 'therapeutic cloning' approaches.

PPL's shares rose by 11 per cent up to 176p in response to the announcement, though analysts warned that it would take several years before any new treatments reached the market.