By: Adam Feuerstein | 11/18/14 - 10:16 AM EST

Inject a cocktail of undifferentiated stem cellsinto a patient who has suffered a heart attack, and days or even weekslater, the stem cells transform into cardiac cells and rebuild the damaged heart muscle. Months later, the patient has a "new" healthy heart.It's a great story. But so far, the proof remains elusive though not for a lack of trying.

The latest company to fulfill this ambitious scenario is NeoStem (NBS) which presented disappointing (but not surprising) results from a small study of its proprietary cardiac stem-cell therapy NBS10 at the American Heart Association annual meeting Monday. NeoStem tried to put some positive spin on the bad news but shares are down 25% to $5.10.

NBS10, formerly known as AMR-001, is an autologous stem-cell therapy derived from a patient's own bone marrow. When injected back into patients following a heart attack, the stem cells are supposed torestore blood flow, rebuild damaged cardiac muscle and improve function.

Except in NeoStem's study, NBS10 fell short on two primary endpoints designed to assess the therapy's efficacy. The study used non-invasive imaging to assess blood flow through the heart, six months after a single infusion of NBS10 or a placebo. There was no difference between NBS and placebo, NeoStem said.

The study's other co-primary efficacy endpoint was a measurement of adverse cardiac "MACE" events --defined as cardiovascular death, a repeatheart attack, heart failure hospitalization and coronary revascularization. To date, 17% of patientstreated with NBS10 have suffered a MACE event compared to 19% of patients in the placebo arm -- a difference which was not statistically significant.

NeoStem said NBS10 therapy was safe relative to placebo and that no patients treated with the stem cells have died compared to three deaths in the placebo patients. But with only one year of follow up on a small number of patients, any claims about a mortality benefit are clinically meaningless.

More:
NeoStem's Stem Cell Therapy Fails Mid-Stage Heart Attack Study