HBsAg-vectored vaccines simultaneously deliver CTL responses to protective epitopes from multiple viral pathogens.

We have previously demonstrated that the potent immunogenicity of hepatitis B surface antigen (HBsAg) may be exploited to deliver foreign antigens for cytotoxic T-lymphocyte (CTL) induction. Here we demonstrate that a single low-dose immunization with rHBsAg DNA is sufficient to prime for CTL responses against encoded foreign epitope and that the responses may be recalled many months after immunization. We show that simultaneous disease-protective CTL responses restricted through a diversity of MHC class I haplotypes are elicited by recombinant (r) HBsAg DNA containing multiple viral epitopes appended as a C'-terminal polyepitope or encoded individually within the HBsAg polypeptide. CTL responses delivered by rHBsAg DNA were elicited in the presence of HBsAg-directed antibody. These studies vindicate the use of HBsAg as a powerful vector to deliver CTL responses to foreign antigen and have implications for a multidisease vaccine applicable to an MHC-polymorphic population.

Sequence variation in the Newcastle disease virus genome.

Full-length genome sequences of five virulent and five avirulent strains of Newcastle disease virus isolated between 1998 and 2002 in Victoria and New South Wales, Australia were determined. Comparisons between these strains revealed that coding sequence variability in the haemagglutinin-neuraminidase (HN), matrix (M) and phosphoprotein (P) gene sequences appeared to be more variable than in the fusion (F), nucleocapsid (N) and RNA dependent-RNA replicase (L) genes. Sequence analysis of a number of other isolates made during the recent virulent NDV outbreaks, also identified the presence of a number of variants with altered F gene cleavage sites, which resulted in altered biological properties of those viruses. Quasispecies analysis of a number of field isolates indicated the presence of virulent virus in one particular isolate. Gene sequence analysis of the progenitor virus isolated in 1998 showed very little sequence variation when compared to that of a progenitor-like virus isolated in 2001, demonstrating that in the field, viral genome sequence variation appears to be biologically restricted to that of a consensus sequence.