Chimeric subgroup A respiratory syncytial virus with the glycoproteins substituted by those of subgroup B and RSV without the M2-2 gene are attenuated in African green monkeys

Using the existing reverse genetics system developed for the subgroup A respiratory syncytial virus (RSV), a chimeric virus (designated rA-G(B)F(B)) that expresses subgroup B-specific antigens was constructed by replacing the G and F genes of the A2 strain with those of the 9320 strain of subgroup B RSV. rA-G(B)F(B) grew well in tissue culture, but it was attenuated in the respiratory tracts of cotton rats and African green monkeys. To further attenuate this chimeric RSV, the M2-2 open reading frame was removed from rA-G(B)F(B). rA-G(B)F(B)Delta M2-2 was highly attenuated in replication in the respiratory tracts of the infected monkeys, but it provided complete protection against wild-type subgroup B RSV challenge following two doses of infection. In this study, rA2 Delta M2-2 (a recombinant A2 RSV that lacks the M2-2 gene) was also evaluated in African green monkeys. The replication of rA2 Delta M2-2 was highly restricted in both the upper and lower respiratory tracts of the infected monkeys and it induced titers of serum anti-RSV neutralizing antibody that were slightly lower than those induced by wild-type rA2. When rA2 Delta M2-2-infected monkeys were challenged with wild-type A2 virus, the replication of the challenge virus was reduced by approximately 100-fold in the upper respiratory tract and 45,000-fold in the lower respiratory tracts. rA2 Delta M2-2 and rA-G(B)F(B)Delta M2-2 could represent a bivalent RSV vaccine composition for protection against multiple strains from the two RSV subgroups. (C) 2001 Academic Press.