Modified Vaccinia virus Ankara: innate immune activation and induction of cellular signalling

Attenuated poxviruses are currently under development as vaccine vectors against a number of diseases including, influenza, HIV, malaria and tuberculosis. Modified Vaccinia virus Ankara (MVA) is an attenuated, replication deficient vaccinia virus (VACV) strain which, similar to replication competent VACV, is highly immunogenic. The lack of productive viral replication further improves the safety profile of MVA as a vector, minimizing the potential for reversion to virulent forms particularly if used in immunocompromised individuals. Despite its inability to replicate in most mammalian cells, MVA still efficiently expresses viral and recombinant genes making it a potent antigen delivery platform. Moreover, due to the loss of various immunomodulatory factors MVA infection leads to rapid local immune responses, fulfilling a requirement of an adjuvant. In this review we take a look at the immunostimulatory properties of MVA, paying particular attention to the signalling of the innate immune system in response to MVA and VACV infection. Understanding the cellular and molecular mechanisms modulated by VACV will help in the future design and engineering of new vaccines and may provide insight into previously unknown mechanisms of dominant virus-host interactions.