There are also important advantages to screening for immunogens in a system that is outside the context of normal viral expression of Env: Screening in the yeast system allows exploration of a wider range of sequence space of Env variants than would be possible in the context of a viable virus since variant forms of Env that bind to BNAb UCAs do not need to retain their functions in viral infection and propagation in order to elicit the desired immune responses. This evidence concerns the gene ERVW-1 and viral infectious disease.