Mixed infection with multiple strains of murine cytomegalovirus occurs following simultaneous or sequential infection of immunocompetent mice

Abstract

As with human cytomegalovirus (HCMV) infection of humans, murine CMV (MCMV) infection is widespread in its natural host, the house mouse Mus domesticus, and may consist of mixed infection with different CMV isolates. The incidence and mechanisms by which mixed infection occurs in free-living mice are unknown. This study used two approaches to determine whether mixed infection with MCMV could be established in laboratory mice. The first utilized two naturally occurring MCMV strains, N1 and G4, into which the lacZ gene was inserted by homologous recombination. The lacZ gene was used to track recombinant and parental viruses in simultaneously coinfected mice. In the second approach, a real-time quantitative PCR (qPCR) assay was used to detect viral immediate-early 1 (ie1) gene sequences in mice successively coinfected with G4 and then with the K181 MCMV strain. In both systems, mixed infection was detected in the salivary glands and lungs of experimentally infected mice. MCMV-specific antibody in sera and G4 IE1-specific cytotoxic lymphocyte responses in the spleens of twice-infected mice did not prevent reinfection. Finally, the prevalence of mixed infection in free-living mice trapped in four Australian locations was investigated using real-time qPCR to detect ie1 DNA sequences of N1, G4 and K181. Mixed infection with MCMVs containing the G4 and K181 ie1 sequences was detected in the salivary glands of 34?2 % of trapped mice. The observations that mixed infections are common in free-living M. domesticus and are acquired by immunocompetent mice through simultaneous or successive infections are important for vaccine development. INTRODUCTIONThe prevalence of human cytomegalovirus (HCMV) is widespread in many human populations (Britt & Alford, 1996) where primary infection is asymptomatic for most individuals (Sissons & Carmichael, 2002). In principle, new viral genotypes may appear in the infected host either through mutation or reinfection with a different viral strain. Infection of individuals with more than one HCMV genotype was first thought to occur only in those with altered immunity such as AIDS patients (Drew et al., 1984;Gerna et al., 1992;Spector et al., 1984), transplant recipients (Chou, 1986) and pregnant women (Arav-Boger et al., 2002;Huang et al., 1980;Shen et al., 1993). However, mixed infection of healthy individuals may frequently occur. Multiple genotypes of the glycoprotein B (gB) gene were detected in organ and blood samples collected from 25 people at necropsy (Meyer-König et al., 1998), and also in women who regularly attended clinics for sexually transmitted disease (Chandler et al., 1987). The mechanism by which mixed CMV infection occurs in healthy individuals is unknown. The presence of multiple strains of a virus in the infected host has significant implications for the design of vaccines where numerous immunologically distinct viral strains may confound vaccination attempts.To understand further the phenomenon of mixed infection with multiple CMV variants, we have utilized murine CMV (M...

Cytomegalovirus-Based Vaccine Expressing a Modified Tumor Antigen Induces Potent Tumor-Specific CD8+ T-cell Response and Protects Mice from Melanoma

“…However, superinfection has been observed in mice, rhesus macaques, and humans (23)(24)(25). Widespread use of CMV vectors as tumor vaccines would largely depend on the ability to induce a superinfection in already infected individuals.…”

“…CMV belongs to the Herpesviridae family, and the following unique characteristics make CMV a promising cancer vaccine vector: (i) CMV establishes a lifelong, asymptomatic infection in immunocompetent hosts; (ii) a remarkable characteristic of CMV infections is that a robust superinfection is observed despite the presence of preexisting CMV-specific immunity, and thus individuals who may already harbor latent CMV can be reimmunized with CMV-based vaccines (23)(24)(25); (iii) cloning of the CMV genome as a bacterial artificial chromosome makes it possible to introduce multiple tumor antigens into the CMV vector; (iv) CMV infection induces a strong inflammatory innate immune response followed by a robust polyfunctional CD8 T-cell expansion, which makes CMV a potentially ideal T-cell-based cancer vaccine vector; (v) in mice and in humans, a process called memory inflation continues long after the establishment of latency, in which CMV-specific CD8 T-cell populations proliferate for the life of the host (26)(27)(28)(29), and a large percentage of these "inflationary" CD8 T cells are functional as exhibited by their ability to secrete multiple cytokines; and (vi) the CMV-specific CD8 þ T cells are distributed widely in lymphoid and nonlymphoid organs, such as the lung, liver, and brain; therefore, CMV vaccines could be used to target metastases in different organs.…”

Murine Cytomegalovirus Is Not Restricted to the House Mouse Mus musculus domesticus: Prevalence and Genetic Diversity in the European House Mouse Hybrid Zone

“…MCMV infection in wild M. m. domesticus mice is dependent on mouse population density (9,10) and is positively correlated with the age of the individuals, suggesting cumulative exposure over time (11). Multistrain MCMV infections are common in free-living mice (5,12). The strains are acquired by immunocompetent mice through simultaneous or successive infections (12).…”

“…Multistrain MCMV infections are common in free-living mice (5,12). The strains are acquired by immunocompetent mice through simultaneous or successive infections (12). A study on enclosure populations of M. m. domesticus has shown that MCMV had minimal or no impact on mouse survival or breeding when individuals were infected with a single strain but that young males infected with two viral strains had a 20% reduction in survival (13).…”

Socioeconomic Impact of HIV/AIDS on Households under Free Antiretroviral Therapy in Preah Sihanouk Province, Cambodia

“…Indeed, a onetime exposure to various viruses besides HIV-1 seem to confer no or only partial protection, allowing a secondary infection to occur in the presence of another viral strain against which an adaptive immune response has been mounted. Members of the herpes virus family, such as herpes simplex virus 1 [78] or 2 [79], Epstein-Barr virus [80], varicella zoster virus (reviewed in [81]), human herpes virus 8 [82], and notably cytomegalovirus (CMV) [83][84][85][86][87][88], provide remarkable examples of secondary infections in previously chronically infected hosts. For the scope of this review, we will limit the discussion to a few viruses that have a major impact on global health.…”