A recombinant fowlpox virus expressing the envelope antigen of subgroup A avian leukosis/sarcoma virus.

A recombinant fowlpox virus (FPV) was constructed by inserting cloned sequences from Schmidt-Ruppin subgroup A avian sarcoma virus coding for the viral envelope (env) antigen into a nonessential region of FPV DNA downstream from a synthetic promoter. Sera from chickens hyperimmunized with the recombinant FPV neutralized the infectivity of the homologous subgroup A virus (RCASBP/AP) but only weakly neutralized the infectivity of Rous sarcoma virus, another subgroup A avian leukosis virus. Similarly, vaccination of 1-day-old chicks with this recombinant FPV protected against infection with RCASBP/AP virus but not against infection with another subgroup A Rous-associated virus (RAV-1). These results show that such a recombinant FPV can be used to protect chickens against avian leukosis virus and confirm previous observations that a type-specific antigenic variability existed within the subgroup A avian leukosis/sarcoma virus group.