T-negative

From Memory Alpha, the free Star Trek reference.

T-negative is a rare Vulcan blood type. Both Ambassador Sarek and his son Commander Spock share this type. For this reason, in 2268, when Sarek underwent emergency heart surgery aboard the USS Enterprise, Spock served as his blood donor. (TOS: "Journey to Babel")

"T-Negative" was also the name of a fanzine published in the 1960s and 70s.