Replication-incompetent viral vaccine vectors ChAdOx1 and MVA as tools for evaluating T-cell responses to naturally processed antigens in vitro.

Assessing T-cell responses is critical for vaccine development. In vitro methods using SARS-CoV-2 or recombinant vaccinia virus with B cells effectively activate T-cells but require stringent biosafety conditions. As an alternative, we explored attenuated, replication-incompetent viral vectors, such as modified vaccinia Ankara (MVA) and chimpanzee adenoviral vectors (ChAdOx1 and ChAdOx2). These vectors successfully transduced B cells, as confirmed by GFP expression. B cells transduced with ChAdOx1 nCoV-19 (encoding SARS-CoV-2 Spike) activated autologous CD8⁺ and CD4⁺ T-cells. Similarly, B cells transduced with MVA encoding Spike activated autologous CD4⁺ T-cells. Our findings provide proof-of-concept support for the use of these safer viral vectors in vitro studies of vaccine-induced cellular immunity.