The developed humanoid physiology is not normally conducive to cryogenic preservation in a way that allows for the subject to be successfully revived. For one thing, when living cells freeze over, they tend to burst as a result of the expansion of water and the formation of sharp ice crystals. At the same time, being able to freeze the crew members of a starship on a long voyage to a distant star system is highly desireable, as this drastically reduces the resources consumed over the course of the journey; even if active crew are required, such as in the aftermath of the Armoa Incident, they can operate on a 'hot bunk' basis with the sleepers to conserve space and resources. To solve the issues of cryopreservation, scientists with the Lepidosian corporation White Mountain Laboratories, in cooperation with Evermornan scientists connected to the Evermorn Strategic Colony Initiative, developed a gene therapy regimen that grants a recipient the resistence to extreme cold similar to that found in some varieties of arctic fish.
Transmission & Vectors
Cryoprotectant therapy vectors are viruses which have been genetically altered to contain the desired cryoprotectant genes. These genes have multiple effects. First, they cause altered cells to produce a substance which drastically lowers the freezing point of water, thus preventing the subject's cells from bursting even when exposed to temperatures at which metabolic processes are nearly halted. Second, the genes re-enable latent hibernation abilities, further reducing the upkeep requirements of cryopreserved individuals. Lastly, the genes amplify the mammalian dive reflex of the subject, allowing for extended immersion in cryogenic solutions.
The treatment itself causes increased body temperature and a slightly fishy odor in the sweat in most recipients. These symptoms last for the duration of the treatment, but are generally mild. In the event that a patient becomes immunocompromised in the course of their treatment, the treatment must be halted until the underlying issue is resolved to prevent severe secondary infection.
Because it is important for the cryoprotectant gene therapy vector to reach as many cells in the body as possible, treatment is generally pursued over the course of an entire year. Multiple injections are administered during this period, with different viral vectors used over the course of treatment to prevent the body from developing a resistance to any one vector in particular. This has the welcome secondary effect of vaccinating the patient against several rare Evermornan diseases in the process, as the protiens on the outside of some vectors are associated with these diseases; should the recipient show prior immunity against a given strain, the vector must be changed in response. Finally, to ensure that the treatment has been successful, upon completing the full regiment of injections, the recipient is subjected to a 'trial chilling.' This involves immersing the patient in an ice bath and checking to ensure that the required autonomic responses are exhibited in response to the lack of air and heat. A full freeze is not implemented at this juncture, however, as each freeze carries a small risk of fatality even with cryoprotectant therapy (see Prognosis).
Despite the best efforts of medical science, being cryofrozen and flown across known space is not without certain inherent risks. For every 5 years spent in a freeze, there is a roughly 1% chance that a traveler will simply not wake up after being frozen. That means that, for example, a Lepidosian emigrating to Evermorn has an almost 1 in 25 chance of dying during the seven light-year journey. Because the body cannot repair itself easily unless thawed, a sleeper must be woken at least once every 10 years to recover from injuries sustained from posture, background radiation, and the occasional cell death due to incomplete gene therapy saturation. Usually, this means passengers and crew aboard a spacecraft will take turns spending a few months awake during a journey; coupled with the limited resources of an interstellar journey, this puts a cap on the largest practical cryopreserved population aboard a starship.
Recipients of cryoprotectant therapy retain their uncanny resistance to cold-related injury and illness for life - though this doesn't necessarily mean that they will suddenly start enjoying the cold or ignoring the discomfort it brings. For example, Midori Milan famously yearns for the summer warmth of her desert homeland despite her near-perfect preservation. For Ms. Milan, the ESCI Revelation feels chilly, as its mostly Evermornan and Lepidosian-Evermornan crew is well-adapted to the damp, cool environment of Planet Evermorn and keeps the ship operating under similar atmospheric conditions. At the same time, she likes entertaining guests with a few parlour tricks she knows involving dry ice, as the cold won't hurt her except on very long exposure.