Xenocite

The Xenocytes are alien "leeches" that are mass produced and attached to a human host, which create what they are commonly known as the DNAliens. As they attach to their host, they take over the personalities of the people they possess and control them (forcibly hacking their DNA). Within hours, the Xenocyte will completely cover the host's bodies transforming him into a DNAlien. Xenocytes eggs were created from an egg-laying machine. The eggs were hatched underwater in large artificial rivers (that look similar to the pools used to store radioactive material). After hatching, the Xenocytes are stored in boxes filled with DNAlien slime, probably to keep them fresh, considering that in the end of Max Out they were seen living in open air and many were shoved into wooden crates with seemingly no DNAlien slime it suggests that Xenocytes are amphibious lifeforms. Kenneth Tennyson, Gwen's older brother, was near to transforming into a DNAlien from a Xenocyte in Max Out. Towards the beginning of the episode, a Xenocyte was close to attaching itself to Max Tennyson, until he crushed it. The Xenocyte eggs were going to ship out all throughout the country, but the Tennysons and Kevin Levin managed to stop that from happening. Towards the end of the episode, DNAliens, disguised as humans, were shown collecting the remains of the Xenocytes from the Highbreed base and throwing them in trash cans.

It is revealed in the video game, Ben 10: Alien Force The Game, Xenocytes can mutate more than just humans. These examples include DNAliens of a Pyronite, a Vulpimancer, a Florauna, and a Null Guardian. However they seem incapable of mutating Crystalsapiens as Ben (as Chromastone) was able to remove one from himself with no problem, even commenting "Indestructible super-dense silicon guys.... Nice try though.".

It's possible they originate from Xenon due to the similarity between their names.

Video Games
Ben 10: Alien Force
 * DNAliens appear in the game as villain who you have to defeat.

Toys
Ben 10: Alien Force
 * 4 inch Alien Collection DNAlien
 * 4 inch Alien Collection 3-pack - includes: DNAlien (clear), Swampfire & Alan as Heatblast.

Trivia

 * The idea of Xenocytes may have been originated from the baby aliens in the "Aliens VS Predator" series.