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 fo r the viral envelope (env) antigen into a nonessential region of FPV D NA downstream from a synthetic promoter. Sera from chickens hyperimmun ized with the recombinant FPV neutralized the infectivity of the homol ogous subgroup A virus (RCASBP/AP) but only weakly neutralized the inf ectivity of Rous sarcoma virus, another subgroup A avian leukosis viru s. Similarly, vaccination of 1-day-old chicks with this recombinant FP V protected against infection with RCASBP/AP virus but not against inf ection with another subgroup A Rous-associated virus (RAV-1). These re sults 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 avi an leukosis/sarcoma virus group.