Poultry vaccines of the future.

Current poultry vaccines are based either on live attenuated organisms or on killed organisms. Future vaccines also may be based on deletion mutants, live viral or bacterial vectors that express foreign genes, and naked DNA. Vaccines have different purposes, depending on the disease, which govern their intrinsic characteristics. Improvement of vaccine efficacy can be addressed by modifications of the vaccine and its administration, modifications in the capacity of the host to mount an immune response, and modifications of environmental factors. The concept of "designer vaccines" for matching vaccines that deliver specific antigenic peptides to chickens with the MHC haplotype that best presents those peptides to T cells is discussed.