a Schematic representation of vector construction. S and N antigen sequences (red spheres and green triangles) were inserted into sMVA fragments F2 and F3 by bacterial recombination methods in E. coli. The modified sMVA fragments of F2 and F3 with inserted antigen sequences and the unmodified sMVA fragment F1 were isolated from E. coli and co-transfected into FPV-infected BHK cells to initiate virus reconstitution. b Schematics of single (sMVA-S, sMVA-N) and double (sMVA-N/S, sMVA-S/N) recombinant sMVA-CoV2 vectors with S and N antigen sequences inserted into commonly used MVA insertion sites (Del2, IGR69/70, Del3) as indicated. All antigens were expressed via the Vaccinia mH5 promoter. ITR inverted terminal repeat. c PCR analysis. CEFs infected with the single and double recombinant sMVA-CoV2 vectors derived with FPV HP1.441 (sMVA-S/N hp, sMVA-N/S hp) or TROVAC (sMVA-S/N tv, sMVA-N/S tv, sMVA-S tv, sMVA-N tv) were evaluated by PCR with primers specific for the Del2 and Del3 insertion sites harboring the N and S antigen sequences or primers specific for the F1/F2 and F2/F3 recombination sites. d Western Blot. BHK cells infected with the sMVA-CoV2 vectors were evaluated for antigen expression by Western Blot using anti-S1 and anti-N antibodies (αS1 and αN). Vaccinia B5R protein was verified as infection control. Higher and lower molecular weight bands may represent mature and immature protein species. e Flow cytometry staining. HeLa cells infected with the vaccine vectors were evaluated by cell surface and intracellular flow staining using anti-S1, S2, and N antibodies (αS1, αS2, and αN). Live cells were used to evaluate cell surface antigen expression. Fixed and permeabilized cells were used to evaluate intracellular antigen expression. Anti-Vaccinia virus antibody (αVAC) was used as staining control to verify MVA protein expression. Cells infected with sMVA or wtMVA or uninfected cells were used as controls for experiments in c, d, and e as indicated. The experiments in c, d, and e were performed twice with similar results.