These observations contrast with studies in mammalian hosts since expression of the V129 PrP variant in humans is associated with resistance to clinical vCJD after exposure to BSE prions (54), and mice transgenic for Val129 human PrP are severely resistant to classical BSE infection and are sufficiently restricted to infection with vCJD prions to allow emergence of a distinct prion strain (52). This evidence concerns the gene PRNP and variant Creutzfeldt-Jakob disease.