Redundancy complicates the definition of essential genes for vaccinia virus.

Vaccinia virus (VACV) genes are characterized as either essential or non-essential for growth in culture. It seems intuitively obvious that if a gene can be deleted without imparting a growth defect in vitro it does not have a function related to basic replication or spread. However, this interpretation relies on the untested assumption that there is no redundancy across the genes that have roles in growth in cell culture.

Vaccinia virus F5 is required for normal plaque morphology in multiple cell lines but not replication in culture or virulence in mice.

Vaccinia virus (VACV) gene F5L was recently identified as a determinant of plaque morphology that is truncated in Modified Vaccinia virus Ankara (MVA). Here we show that F5L also affects plaque morphology of the virulent VACV strain Western Reserve (WR) in some, but not all cell lines, and not via previously described mechanisms. Further, despite a reduction in plaque size for VACV WR lacking F5L there was no evidence of reduced virus replication or spread in vitro or in vivo.

Truncation of gene F5L partially masks rescue of vaccinia virus strain MVA growth on mammalian cells by restricting plaque size.

Modified vaccinia virus Ankara (MVA) is a candidate vaccine vector that is severely attenuated due to mutations acquired during several hundred rounds of serial passage in vitro. A previous study used marker rescue to produce a set of MVA recombinants with improved replication on mammalian cells. Here, we extended the characterization of these rescued MVA strains and identified vaccinia virus (VACV) gene F5L as a determinant of plaque morphology but not replication in vitro.

Analysis of A47, an immunoprevalent protein of vaccinia virus, leads to a reevaluation of the total antiviral CD8+ T cell response.

Vaccinia virus (VACV) is the prototypic orthopoxvirus and was the live vaccine used to eradicate smallpox. In addition, VACV is a possible vector for recombinant vaccines. Despite these reasons for study, the roles of many VACV genes are unknown, and some fundamental aspects, such as the total size of immune responses, remain poorly characterized.