The Iron Maidens were mutant humans created through Dr. Luis Sera's continued experimentation with "Leech-like Plagas", and so were a variation of the Regeneradores.
When Los Iluminados gained their coveted Plaga parasites, they began a series of experiments to change the parasites and make them more fit to their plans. One of the experiments resulted in "leech-like Plagas" that lived as colonies around human bodies, as opposed to a single parasite in the neck. The human hosts mutated from their parasitism and became Regeneradores, slender grey humans with sharp teeth and immense regenerative abilities thanks to their Plagas. The Iron Maidens were also derived from continued experimentation, resulting in Regeneradores that could grow sharp spikes from their bodies. The Iron Maidens were destroyed in late 2004 when the island lab they lived on was destroyed by a series of charges.