David was a male genetically engineered Human born in 2353. His birth was part of a research project on the Darwin Genetic Research Station that developed aggressive immune systems capable of destroying disease organisms. However, the antibodies of the children were capable of attacking other Humans and hyper-accelerating the aging process, killing them within days due to old age.
David was beamed aboard the USS Enterprise-D in suspended animation in 2365, so Doctor Katherine Pulaski could scan for the disease, unaware at the time that David was a carrier. She became infected with the disease, but was cured by using the bio-filters of the transporter. After this event, David stayed isolated on the station. (TNG: "Unnatural Selection")