Genome sequence and comparative virulence of raccoonpox virus: the first North American poxvirus sequence

Abstract

We report here the complete genome sequence of raccoonpox virus (RCNV), a naturally occurring North American poxvirus. This is the first such North American sequence to the best of our knowledge, and the data showed that RCNV forms a new phylogenetic branch between orthopoxviruses and Yoka poxvirus. RCNV shared overall similarity in genome organization with orthopoxviruses, and the proteins in the central conserved region shared approximately 90 % amino acid identity with orthopoxviruses. RCNV proteins shared approximately 81 % amino acid identity with Yokapox virus proteins. RCNV is missing 10 genes normally conserved in orthopoxviruses, most of which are implicated in virulence. These gene deletions may explain the attenuated phenotype of RCNV in mammals. RCNV contained one unique genome region containing approximately 1 kb of DNA sequence that is not present in any reported poxvirus. It contained a unique ORF predicted to encode a protein with a transmembrane domain. RCNV replicates well in mammalian cells, is naturally attenuated and has been shown to be effective as a vaccine vector platform, so we further tested its safety. We showed here that RCNV is substantially more attenuated than even the highly attenuated VACV-A35Del mutant virus in pregnant, nude and severe combined immunodeficient (SCID) mouse models. RCNV was much safer in pregnant mice and was cleared rapidly from tissues, even in immunocompromised animals, whereas the VACV-A35Del mutant retains virulence and persists in tissues. Thus, RCNV is expected to be a superior vaccine vector for infectious diseases and cancer due to its excellent safety profile, reported vaccine efficacy and ability to replicate in mammalian cells.

Oncolytic properties of non-vaccinia poxviruses

“…It was recently reported that RCNV Herman strain is less virulent and much safer than VACV in immunocompromised or pregnant mouse models [ 54 ]. Although the wild type Herman strain was highly attenuated, deletion of TK gene attenuated it further [ 29 ], as is the case in VACV [ 63 ].…”

“…Raccoonpox virus (RCNV) is a member of the Orthopoxvirus genus and is closely related to the Vaccinia and Cowpox viruses [ 29 ]. RCNV was first isolated in 1961 from a naturally occurring infection from the respiratory tract of raccoons [ 30 ].…”

Hazard Characterization of Modified Vaccinia Virus Ankara Vector: What Are the Knowledge Gaps?

“…In case of MVA, this will require knowledge of the occurrence, distribution and characteristics of naturally circulating OPVs in locations and ecosystems in which recombinant MVA vaccines are to be deployed, especially for the vaccination of domesticated animals and wildlife. With the exception of Germany [ 112 , 113 , 114 , 115 , 116 ], United Kingdom [ 115 , 117 , 118 ], Fennoscandia [ 119 , 120 , 121 , 122 , 123 , 124 ], USA [ 125 , 126 , 127 , 128 ], Brazil [ 129 , 130 , 131 , 132 ] and India [ 133 , 134 , 135 ], data on the occurrence and characteristics of wild-type OPVs in remaining regions of the globe are limited or non-existent. MVA-vectored vaccines against malaria [ 136 , 137 ], HIV/AIDS [ 138 ], tuberculosis [ 68 ], Middle East respiratory syndrome coronavirus (MERS-CoV) [ 83 ], Ebola [ 73 ] and several other human and animal diseases [ 26 , 86 ] are in trials in Africa, Asia and Middle East, but knowledge of the characteristics and reservoir animal species for wild-type OPVs in these regions are largely non-existent.…”

Development of improved therapeutic mesothelin-based vaccines for pancreatic cancer

“…Several poxviruses are used as recombinant vectors to develop vaccines for a wide range of infectious diseases including bacterial, viral and parasitic pathogens, as well as for cancer therapies, and several are approved or currently in clinical trials [ 19 – 26 ]. The only HIV vaccine with demonstrated efficacy in humans to date employs an avian poxvirus vector, and it entered NIH-sponsored Phase 2b/3 trials in 2016 [ 27 ].…”

“…Vaccinia virus is the most commonly used poxvirus vaccine vector; however, its use is limited by its potential virulence, especially in immunocompromised hosts [ 19 , 21 , 29 , 30 ]. Raccoonpox virus provides a safer vector compared to vaccinia virus [ 19 , 21 , 26 , 30 ], and the Modified Vaccinia virus Ankara (MVA) strain is even more attenuated, because it cannot replicate in most mammalian cells [ 31 ]. However MVA immunogenicity has been limiting, requiring high doses and boost vaccinations [ 28 , 31 – 38 ].…”