Using a variant of the Wraith retrovirus, normal Humans were placed in chambers where they were genetically altered. As part of this conversion, they were provided all the strengths of the Wraith but lacked their one true weakness, namely the need to feed on life energy. This resulted in the artificial creation of the Hybrid race in the Pegasus galaxy.
The subjects of the conversion process were placed in rectangular chambers where they appeared to be unconscious. Machinery was required to maintain the genetic changes. If shut down, the humans inside died as a result. (SGA: "The Kindred, Part 2")
After the discovery of Michael's database, Dr. Jennifer Keller of the Atlantis expedition was able to reverse the changes on the Hybrids making many of them human once again. (SGA: "Search and Rescue")