Expression of retroviral genes in transgenic chickens.

The development of transgenic technology in poultry has lagged behind that in mammals because of the unique reproductive system of birds. Therefore, we chose to use wild-type and recombinant replication-competent avian leukosis viruses to determine whether these retroviruses could be artificially introduced into the germ line by injecting them near the blastoderm of fertile eggs just before incubation. We generated 23 proviral inserts that were stably inherited through two generations. Twenty-one inserts coded for complete avian leukosis virus. Two interesting inserts failed to produce complete virus. One coded for envelope glycoprotein only and the other coded for the group-specific antigen and envelope glycoprotein. Cell culture and animal studies showed that one of these inserts was very resistant to infection and oncogenesis by subgroup A field strains of avian leukosis virus. Therefore, this represents a model system for introducing genes from the pathogen into the host to induce host resistance to the pathogen. Future studies should be aimed at developing more efficient systems for introducing replication-defective retroviral vectors or cloned DNA into the germ line of poultry so that the regulation of gene expression can be studied and transgenic technology can be applied to the improvement of this highly reproductive group of farm animals.