Cryobiologists propose nine milestones for testing reversible biostasis

Cryobiologists propose nine milestones for testing reversible biostasis

On July 23, fifteen cryobiologists and biostasis practitioners published the Berkeley Biostasis Classification. Their framework links the preserved part of the organism, the animal's size, and the test used to assess recovery.

Biostasis studies operate at different scales. A brain slice may conduct neural signals, a kidney may remain viable after storage, and neural tissue may retain its structure. Each result answers a different question. The authors propose describing every such experiment along three dimensions: which biological system was preserved, the size of the animal, and the observation used to confirm that the system still functioned.

The classification divides the task into nine milestones, from A1 to C3. Level A concerns the central nervous system, which must show normal or minimally impaired electrical activity after rewarming. Level B includes the brain, spinal cord, peripheral nerves, and muscles. The animal must be able to sense and move, and it must pass a behavioral test. Level C covers the entire organism. The number indicates the scale: a small rodent, a large mammal, or a human.

The authors identify B1 as the nearest shared goal. After cryopreservation and rewarming, a small rodent must complete a behavioral task and survive for a long time. Its vital functions may be restored through transplantation or a life support system. Such an experiment tests the entire pathway from the sensory organs to the brain and from the brain to the muscles.

In a March study by Alexander German and colleagues, vitrification, in which water in tissue enters a glasslike state without forming ice crystals, allowed the researchers to restore neuronal excitability, signal transmission between neurons, and plasticity in the hippocampus of adult mice for a short period. The researchers studied both brain slices and the brain within the organism. B1 moves the assessment to the level of animal behavior after cryopreservation.

Brain slice preservation, nerve function, and recovery of the whole organism now have separate, measurable tests. This framework will make it possible to compare experiments that were previously difficult to evaluate on the same scale.