"If the temperature is just deep enough, we can store cells for decades and then bring them back to life, " explains Heiko Zimmermann, cryoscientist at IBMT. The critical brand is below minus 130 degrees Celsius. In this cold icy silence reigns between and in the cells in every respect. Neither substances crystallize nor does any form of exchange take place between the cells. "You can not compare this condition with a three-star freezer, " quips Zimmermann. The cold chain must never be interrupted, otherwise the frozen cells will perish.
While, for example, eggs and sperm can easily be preserved, larger objects are causing difficulties: "The freezing of entire organs or even living things belongs to the realm of fairy tales, " explains Andreas Sputtek, a cryo-researcher at the University of Hamburg. Veins and blood vessels could already be frozen and used for bypass surgery. But the size of these grafts is always limited to a few millimeters to centimeters.
Zimmermann has now succeeded in reviving tissue pieces in the case of the pancreas. The 8, 000 cells each produced insulin again after thawing. "The rate was not quite as high as for fresh cells, but reached at least about 60 percent, " says Zimmermann. display
The hormone insulin is needed by the body to digest sugar. Many diabetics lack this substance. Against this background, the thawed tissue samples were tested by Mainz doctors on diabetes mice. To the delight of the researchers, the animals showed no signs of the disease for a year. The cells from the cryotank had taken over the task of the defective pancreas.
"We now have permission to freeze even human pancreatic cells, " reveals Zimmermann. One day, these could be stored for transplants and later given to diabetics. "The road to application is still long and we still have many technical hurdles to take. But I'm very confident, "commented Zimmermann on this vision. He expects the thawed mini-tissue pieces to be first demanded by the pharmaceutical industry. She could test new diabetes medications on the cells.
The freezing of tissue samples from the pancreas, however, is extremely demanding: "The association of pancreatic cells is a functional unit that must not be destroyed, " explains Zimmermann. Ice crystals could injure the walls and break the contacts between the cells. When freezing, the cells also lose water and can thus shrink to death.
These difficulties are further potentiated by the size of the cell structure. It is simply impossible to guarantee ideal conditions for freezing at any point. "From a fabric diameter of five millimeters upwards, this problem has not yet been satisfactorily solved", explains Andreas Sputtek.
Zimmermann achieves the best survival rates when he very gently puts the cells into a cold sleep. One degree per minute decreases the temperature in his experiments. In addition to this trick, the researchers help chemicals to bring the cells to death rigor. So-called cryoprotectants prevent the ice crystals from growing. To date, the Fraunhofer researchers have used dimethylsulfoxide. However, this chemical alters the genome. "We can not use that on humans, " explains Zimmermann.
Another adversity for a future therapy from the cold is that the immune system recognizes the cells as foreign. Only if the recipients and donors were identical could this problem be eliminated. "Theoretically, pancreatic cells could be taken from the neonate and then stored as a precautionary measure, " Sputtek thinks aloud. "But who wants to be ethical?"
Zimmermann's researchers hope to find another answer to this question: In animal experiments, they have sheathed the cells with alginate, the skeletal substance of algae. Thanks to the invisibility cloak, the mouse's immune system does not notice the foreign cells. The insulin, however, migrates through the hell. Thus, every tissue donation would be suitable for the patient. The researchers now have to reduce the volume of alginate, as otherwise a human graft would be too large.ddp / science.de Susanne Donner