ORLANDO, Fla - A stem cell therapy for treating patients experiencing moderate to severe heart failure showed real promise in preventing serious consequences or death, according to data from a small mid-stage clinical trial.The treatment from Australia's Mesoblast Ltd, known as revascor, appeared to be safe and reduced by 78 percent the rate of major adverse events -- heart attacks, cardiac death and need for artery clearing procedures -- after one year compared with patients who received the standard of care.Closer to treatment?Researchers have been studying stem cells from numerous sources for more than a decade with the hope that their ability to transform into a wide variety of other types of cells would help treat many types of illness and injuries, from spinal injuries to heart disease. Several companies appear to be closing in on turning therapeutic promise into viable treatments.The Mesoblast therapy uses adult stem cells derived from bone marrow known as mesenchymal precursor cells. The cells are delivered by catheter directly to the heart on the theory that they will help stimulate growth of blood vessels.The cells are provided by a healthy, unrelated donor. As a result, the first hurdle is to make sure patients do not develop significant antibodies to the cells.None of the heart failure patients who received the cells became overly sensitized or made significant antibodies to the cells, so no significant immune response was seen, researchers said.Patients in the study had moderate to severe heart failure, a condition in which the heart muscle shows diminished capacity to pump blood. The study subjects had an ejection fraction, or fraction of blood pumped out of the left and right ventricles, of less that 40 percent. For a healthy person it should be greater than 55 percent.There was no significant improvement in ejection fraction seen in patients who received the stem cell therapy, but there was a trend toward improvement in a six-minute walking test, which can be an indication that patients are feeling better.The study tested three doses, or concentrations, of cells -- 25 million cells, 75 million cells and 150 million cells -- with 15 patients in each group and 15 additional patients receiving optimal standard of care. Based on findings from this Phase II study, the companies said they expect to move into the pivotal human trials with the 150 million cell dose."The high dose had no heart failure hospitalization and no cardiac deaths," Perin said.The findings from the 60-patient trial were presented on Monday at the American Heart Association scientific meeting in Orlando and were deemed to be statistically significant, despite the small size of the study."It is extremely surprising and really incredible to see that there are less cardiac deaths and less MACE (major adverse cardiac events) events in the treated population and that is over a long period of follow-up, in some patients close to three years, so that's very impressive," said Dr Emerson Perin, the study's lead investigator."If we have the same findings in a larger study, we think we've got something that will be an approvable therapy," Perin, from the Texas Heart Institute in Houston, said in an interview.Mesoblast and its partner Teva Pharmaceutical Industries, which recently acquired original partner Cephalon, said they plan to start enrolling patients in a much larger Phase III trial in the first half of next year.Safety was the primary goal of the Mesoblast study and there were no cases of adverse events attributed to the Mesoblast stem cells, researchers said.