Recombination-Mediated Genetic Engineering of a Bacterial Artificial Chromosome Clone of Modified Vaccinia Virus Ankara (MVA) - Genetic Engineering: Recent Developments in Applications - page 46

Immunogenicity of MVA-BACs
The principal utility of MVA is as a vaccine vector, particularly for eliciting T cell
responses. The immunogenicity of the viruses derived from the four MVA-BAC
clones was therefore assessed in mice by determining CD8 + T cell responses to
viral antigens following intradermal inoculation. Tscharke et al. have described
in detail the immunodominance hierarchy of CD8+ T cell “determinants” (i.e.,
epitopes) following infection of BALB/c and C57BL/6 mice with Vaccinia virus,
MVA and other poxviruses [61], [62]. We used the described synthetic peptides
to stimulate splenocytes from immunised BALB/c or C57BL/6 mice and quanti-
fied antigen-specific T cell responses by IFN- γ ELIspot assay (Figure 2).
Figure 2. Immunogenicity of four MVA-BAC clones (21, 22, 26, 48) in C57BL/6 and BALB/c mice compared
to parent virus (containing the BAC cassette) and MVA (lacking the BAC cassette). Mice were immunised with
106 pfu i.d. and the specific T cell responses to the indicated endogenous synthetic peptide epitopes [61], [62]
were measured 14 days later by IFN- γ ELIspot assay. Data are means and SEM from groups of four mice.
Mice were immunised intradermally with the four MVA-BAC clones, the
MVA-BAC-parent (from which the BAC clones were derived), or MVA (i.e. virus
lacking the BAC cassette). In C57BL/6 mice, all were immunogenic and there
was no statistically significant difference by one-way ANoVA between the T cell
responses to any of these viruses for each of the five available determinants. In
BALB/c mice, the same was true for the immunodominant determinant E3, but
there were significant differences in the subdominant determinant specific F2(G)
responses (p<0.01, one-way ANoVA), and a post-hoc test revealed that the sta-
tistically significant pairwise comparisons are clone #26 versus parent or MVA
(p<0.05, Newman-Keuls multiple comparison test). Despite the lack of conven-
tional significance for other clones, there is a trend towards higher responses to
BAC-derived MVA in BALB/c mice, but this is not an effect of the presence
of the BAC cassette at deletion III, since MVA-BAC-parent also contains this
insertion.
The inability to distinguish the MVA-BAC clones by restriction map, viral
growth yield or murine immunogenicity suggests that they are likely to be identical,