Candied Cells Have Longer Shelf Life

Microbes called tardigrades can survive for decades without water.

You can buy them in any toy store: dried sea monkeys that spring to life in a dish of water. Now researchers have borrowed a chemical trick from these tiny animals to revive dried or frozen human cells. The technique could lead to off-the-shelf human cells and tissue for blood transfusions, skin grafts, and a variety of other medical treatments, two teams report in the February Nature Biotechnology.

Organisms as diverse as sea monkeys (they are tiny shrimp, in fact), yeast, and microbes called tardigrades can survive decades without water. But cultured human cells quickly die unless they are coddled. To help human cells survive cold storage, explains biomedical engineer Mehmet Toner of Harvard Medical School in Boston, researchers coat them with protectants, freeze them slowly so damaging ice crystals don't form, and store them in expensive tanks cooled by liquid nitrogen.

To find a better way to keep cells on ice, Toner's team loaded cells with trehalose, a sugar that protects cells in some organisms from ice crystals and desiccation. Trehalose can take the place of water in the cell, forming a protective coat around enzymes, membranes, and DNA. Our bodies don't make trehalose, and it is too big to cross the cell membrane, so they snuck it into cells via a-hemolysin, a bacterial toxin that pokes holes in the membrane large enough to let the sugar in. Without trehalose, less than 1% of cells survived freezing; when laced with the sugar, 72% of the cells revived after thawing.

Trehalose also preserves human cells that are dried, reports a second team led by geneticist Fred Levine of the University of California, San Diego. The researchers engineered cells called fibroblasts to produce the bacterial enzymes that make trehalose. Normal cells die within 1 day after being dried out, but the altered cells were fine for up to 5 days without water.

It's "remarkable" that simply adding a sugar is enough to preserve both frozen and dried cells, says biochemist John Crowe of the University of California, Davis. The method might make it possible to store dried human tissue on a shelf indefinitely. "It's been a dream of a lot of people to do that for a long time," says Crowe.

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