TRANSGENIC APPROACHES TO THE INCREASE OF DISEASE RESISTANCE IN FARM-ANIMALS

Molecular genetics and reproductive biology techniques enable the tran sfer of foreign DNA into mammals. Novel approaches to modify disease r esistance or susceptibility in livestock are justified by economic and animal welfare concerns. Current research on the improvement of disea se resistance by gene transfer focuses an three main strategies, as fo llows: a) somatic gene transfer, i.e., nucleic acid vaccines b) deleti ve germ-line gene transfer, i.e., gene knockout c) additive germ-line gene transfer. These strategies aim at either the transient or stable expression of components known to influence non-specific or specific h ost defence mechanisms, or the disruption of genes known to cause susc eptibility to disease. Referring to the source of the effective agent and the site and mode of action, the strategies are termed 'genetic', 'congenital', 'intracellular' and 'extracellular' immunisation. Each g ene transfer experiment has to be evaluated carefully with respect to the potential to create novel cases of pathogen resistance or to lose species barriers or cell-type restrictions.