Genomic sequence of chorioallantois vaccinia virus Ankara, the ancestor of modified vaccinia virus Ankara

Abstract

Chorioallantois vaccinia virus Ankara (CVA) is the parental virus of modified vaccinia virus Ankara (MVA), which was derived from CVA by more than 570 passages in chicken embryo fibroblasts (CEF). MVA became severely host-cell-restricted to avian cells and has strongly diminished virulence in mammalian hosts, while maintaining good immunogenicity. We determined the complete coding sequence of the parental CVA and mapped the exact positions of the six major deletions that emerged in the MVA genome. All six major deletions occurred in regions of the CVA genome where one or more truncated or fragmented open reading frames (ORFs) pre-existed. The CVA genome contains 229 ORFs of which 51 are fragments of full-length orthopoxvirus (OPV) genes, including fragmented orthologues of C9L and M1L (encoding two well-conserved ankyrin-like proteins), A39R (encoding a semaphorin-like protein) and A55R (encoding a kelch-like protein). Phylogenetic analysis demonstrated that MVA was most closely related to CVA, followed by the vaccinia virus (VACV) strain DUKE, a patient-derived isolate of the Dryvax vaccine virus. Loss or mutation of genes outside the six major deletions are assumed to contribute to the restricted host range phenotype of MVA. In support of this notion, deletions, insertions and non-synonymous mutations were found in 122 of the 195 ORFs remaining in MVA when compared with their CVA counterparts. Thus, detailed knowledge of the CVA genomic sequence is a prerequisite to further dissect the genetic basis of the MVA host range phenotype as well as the particular immunological properties of MVA.

Survival of lethal poxvirus infection in mice depends on TLR9, and therapeutic vaccination provides protection

“…The stimulation of DCs in response to ECTV and particularly CVA and CPXV was greatly increased when these viruses were first UV inactivated, suggesting that these active viruses harbor mechanisms that inhibit DC recognition. Although MVA is a direct descendant of CVA (27), it was able to activate DCs and did not activate DCs more in a UV-inactivated state, suggesting that this virus has lost at least some of the inhibitory mechanisms of its CVA ancestor.…”

Deletion of the Vaccinia Virus N2L Gene Encoding an Inhibitor of IRF3 Improves the Immunogenicity of Modified Vaccinia Virus Ankara Expressing HIV-1 Antigens

“…This could be due to the difference between the two vectors in the number of immunomodulatory genes (90)(91)(92).…”

Recombinant Modified Vaccinia Virus Ankara Generating Excess Early Double-Stranded RNA Transiently Activates Protein Kinase R and Triggers Enhanced Innate Immune Responses

“…This discrepancy might have been caused by genetic differences between the two VACV strains. In contrast to the VACV WR strain, CVA lacks functional versions of several known (A39R, A55R) and potential (M1L, C9L) virulence factors (45) and is not mouse adapted, providing a rationale for potentially stronger effects of deletions of innate immune inhibitors on CVA virulence.…”

“…For the 0-h time point, cells were kept on ice after the 60-min adsorption period, washed with ice-cold DMEM, supplemented with 2 ml ice-cold DMEM-2% FCS, and immediately frozen. MVA titers were determined on CEF cells, and CVA titers were determined on CV-1 cells using the TCID 50 method as described previously (45).…”

“…Wild-type MVA (MVA) and MVA mutants were propagated on secondary CEF or DF-1 cells and titrated on CEF cells using the 50% tissue culture infective dose (TCID 50 ) method as described previously (45). Wild-type CVA (CVA) and CVA mutants were propagated on Vero cells and titrated by the TCID 50 method on CV-1 cells.…”