On the Lyssarian homeworld, there was a creature called a Lyssarian Desert Larvae. When it was injected with genetic material from another species, it created a mimetic simbiot, or a clone. The Lyssarian Prime Conclave deemed doing this illegal.
A rogue group who called themselves the Velandran Circle experimented with an enzyme which would slow the aging process of such a genetic clone. As of 2153, it was still experimental. (ENT: "Similitude")