Nature Medicine

Genetically engineered stem cells can restore heart performance and repair the damage caused by a heart attack, according to a study published in the September issue of Nature Medicine.

Researchers have tried for years to repair damaged hearts with mesenchymal stem cells-a type of stem cell derived from bone marrow. But they achieved only limited success, in part because most of the stem cells die shortly after being transplanted. Victor Dzau and colleagues engineered the stem cells to express Akt, a protein that prevents cell death. After growing the stem cells in culture and introducing the Akt gene, the investigators injected the cells into the hearts of rats induced to have a heart attack or myocardial infarction.

They found that the Akt-expressing cells incorporated into the damaged heart tissue and, compared to cells that did not express Akt, were impervious to cell death. The treatment restored 80-90% of lost myocardial volume, and brought cardiac performance up to near normal. The approach has potential as an effective treatment for human cardiac disease, the researchers say.

Nature Medicine

More than 90% of people vaccinated for smallpox might retain lifetime immunity to vaccinia, the virus used to vaccinate against the disease, Mark Slifka and colleagues report in the September issue of Nature Medicine.

The researchers examined the levels and duration of antiviral immunity-both by virus-specific antibodies and by 'memory' T-cells-after smallpox vaccination. While vaccinia-specific T-cell memory declined slowly over decades, most people maintained stable antibody responses for up to 75 years after vaccination, suggesting essentially a lifelong immunity, the researchers report.

Based on their evidence, the risks of an intentional smallpox outbreak would be significantly lesser, the researchers suggest. However, those born after the mid-1970s, when routine vaccination in the US was halted, would still be at risk. There are insufficient amounts of the existing smallpox vaccine to protect all those who would be at risk of infection in the event of a large-scale outbreak. The Dryvax vaccine was also grown in the skin of calves or other large animals, a method that is now obsolete.

In the same issue of Nature Medicine, Richard Weltzin and colleagues describe a new vaccine adapted from the existing Dryvax samples. In animal models and a human clinical study, the researchers report, the new vaccine is at least as effective at inducing immunity against the vaccinia virus and might represent an advance in terms of its safety.

Nature Medicine

The September issue of Nature Medicine includes the retraction of a paper, first published in March 2000, which reported the results of a small clinical trial with metastatic kidney cancer patients. An editorial in the same issue addresses the retraction.