The Poxvirus A35 Protein Is an Immunoregulator

Abstract

It was shown previously that the highly conserved vaccinia virus A35 gene is an important virulence factor in respiratory infection of mice. We show here that A35 is also required for full virulence by the intraperitoneal route of infection. A virus mutant in which the A35 gene has been removed replicated normally and elicited improved antibody, gamma interferon-secreting cell, and cytotoxic T-lymphocyte responses compared to wild-type virus, suggesting that A35 increases poxvirus virulence by immunomodulation. The enhanced immune response correlated with an improved control of viral titers in target organs after the development of the specific immune response. Finally, the A35 deletion mutant virus also provided protection from lethal challenge (1,000 50% lethal doses) equal to that of the wild-type virus. Together, these data suggest that A35 deletion viruses will make safer and more efficacious vaccines for poxviruses. In addition, the A35 deletion viruses will serve as improved platform vectors for other infectious diseases and cancer and will be superior vaccine choices for postexposure poxvirus vaccination, as they also provide improved kinetics of the immune response.

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

“…RCNV has been shown to be less virulent in immunocompetent and immunodeficient mouse models, and we showed here that RCNV was highly attenuated, even compared with VACV-A35Del, which is 100-1000-fold less virulent than the parental VACV-WR (Roper, 2006;Rehm et al, 2010a). Whilst VACV-A35Del persists in SCID mouse tissues 10 days after infection, RCNV was almost completely cleared.…”

“…Mice were weighed daily for 10 days and sacrificed. Organs were placed in 1 ml ice-cold RPMI medium, frozen and thawed three times, homogenized (Omni Tissue Master 125) and sonicated as described previously (Rehm et al, 2010a). Virus replication was evaluated by titration of the organ on BS-C-1 monolayers and staining with 0.1% crystal violet in 20% ethanol after 40-48 h. VACV and RCNV formed similar-sized plaques.…”

“…RCNV contains a full-length A35 orthologue (RCNV ORF151). In vaccinia, the A35R gene has been shown to block MHC class II antigen presentation in vitro and antibody and T-lymphocyte responses in vivo (Rehm & Roper, 2011;Rehm et al, 2010a, b) suggesting that the use of A35Del virus as a vaccine platform or oncolytic virus would improve both safety and efficacy. Here, we directly compared these two potential oncolytic and vaccine candidates.…”

“…Although the RCNV genome is larger than the VACV-WR genome, the latter causes much higher morbidity and mortality in mice. As RCNV is a safe and effective vaccine in normal mice (Lodmell et al, 1991;Osorio et al, 2003b), we further tested RCNV in immunodeficient mice and compared it with virulent VACV-WR and with an A35 deletion mutant virus (A35Del), which is attenuated 100-1000-fold compared with VACV-WR although it replicates equally well (Rehm et al, 2010a;Roper, 2006). RCNV contains a full-length A35 orthologue (RCNV ORF151).…”

“…Here we provide the genome sequence of RCNV to provide insight into its attenuation and facilitate diagnostics, recombinant DNA strategies, and drug and vaccine design. In addition, we compared the virulence of RCNV and the highly attenuated VACV-A35Del mutant, which is missing the immunoregulatory A35R gene (Rehm et al, 2010a, b;Roper, 2006). We employed two commonly used immunocompromised mouse models.…”