Poxvirus viruses have been utilized for many years as vaccine vectors. Recent years have seen an increase in efforts to identify safer pox vectors to express heterologous antigens, in this case HIV antigens.
Safer pox vectors have included MVA, ALVAC and NYVAC, which are all replication deficient in human cells. However, the loss of replication competence has also reduced antigen expression, and therefore, immunologic response to the vaccination. We have constructed vectors in a NYVAC background that are replication competent but attenuated for virulence.