It was an element of an Ultimate storyline in which Wolverines and Magda Maximoff (aka the Witch of Wundagore) have a secret love child name Jimmy that has an agent called Mothervine that activates mutant genetics in folks that was part of a plan to weaponize sleeper cell assassins via sudden mutation. Ultimate Quicksilver tries to use it to put mutants back on top but it goes off the rails as so many of Pietro’s plans to help mutant kind do just as the universe is ending. Anywho, that somehow got over here in the 616, as covered by the lost great scribe Cullen Bunn in his run of Uncanny X-Men. Magneto and the 05 meet Jimmy who comes here as one of many refugees from the Ultimate verse, and Havok (still evil from Axis) and the Hellfire Club want to capture him so they can use Mothervine to turn a whole lot of inactive or non mutants into mutants.
And I swear on the dingy rag that use to be my soul that is as simple and straightforward as I could summarize it.