K cell
From Memory Alpha, the free Star Trek reference.
The K cell is the primary component of the humanoid immune system that kill infected cells in the body.
In 2153, the DNA of the Human crewmembers of Enterprise became mutated by a mutagenic virus on the Loque'eque homeworld, transforming them into another species.
T'Pol, who was also a member of the landing party was not drastically affected by the virus thanks to her Vulcan K cells, which were determined by Doctor Phlox to have a neutralizing effect on the virus. Based on this information, Phlox was able to synthesize an antivirus using T'Pol's genetic profile and an active sample of her DNA. (ENT: "Extinction")
