Effects of vaccination on cytomegalovirus-associated interstitial pneumonia in strain 2 guinea pigs

Using Hysterectomy Rederivation to Produce Guinea Pigs (Cavia porcellus) Free of Guinea Pig Cytomegalovirus

Due to similarities in placentation, guinea pigs can be used as models of human cytomegalovirus infection, but they mustbe free of guinea pig cytomegalovirus. Many commercial guinea pig colonies are enzootically infected with guinea pigcytomegalovirus, which can be transmitted vertically as well as horizontally through saliva, vaginal secretions, and milk.These characteristics make its eradication in a commercial setting challenging. Because embryo transfer technology in guineapigs is in its infancy, it is not generally a viable option for obtaining animals free of guinea pig cytomegalovirus. However,a combination of hysterectomy rederivation and testing by PCR assay and serology of both dams and offspring from anenzootically infected colony produced offspring free of guinea pig cytomegalovirus.

Developing a Vaccine against Congenital Cytomegalovirus (CMV) Infection: What Have We Learned from Animal Models? Where Should We Go Next?

Congenital human cytomegalovirus (HCMV) infection can lead to long-term neurodevelopmental sequelae, including mental retardation and sensorineural hearing loss. Unfortunately, CMVs are highly adapted to their specific species, precluding the evaluation of HCMV vaccines in animal models prior to clinical trials. Several species-specific CMVs have been characterized and developed in models of pathogenesis and vaccine-mediated protection against disease. These include the murine CMV (MCMV), the porcine CMV (PCMV), the rhesus macaque CMV (RhCMV), the rat CMV (RCMV), and the guinea pig CMV (GPCMV). Because of the propensity of the GPCMV to cross the placenta, infecting the fetus in utero, it has emerged as a model of particular interest in studying vaccine-mediated protection of the fetus. In this paper, a review of these various models, with particular emphasis on the value of the model in the testing and evaluation of vaccines against congenital CMV, is provided. Recent exciting developments and advances in these various models are summarized, and recommendations offered for high-priority areas for future study.

Guinea Pig Cytomegalovirus (GPCMV): A Model for the Study of the Prevention and Treatment of Maternal-Fetal Transmission

A major public health challenge today is the problem of congenital cytomegalovirus (CMV) transmission. Maternal-fetal CMV infections are common, occurring in 0.5-2% of pregnancies, and these infections often lead to long-term injury of the newborn infant. In spite of the well-recognized burden that these infections place on society, there are as yet no clearly established interventions available to prevent transmission of CMV. In order to study potential interventions, such as vaccines or antiviral therapies, an animal model of congenital CMV transmission is required. The best small animal model of CMV transmission is the guinea pig cytomegalovirus (GPCMV) model. This article summarizes the GPCMV model, putting it into the larger context of how studies in this system have relevance to human health. An emphasis is placed on how the vertical transmission of GPCMV recapitulates the pathogenesis of congenital CMV in infants, making this a uniquely well-suited model for the study of potential CMV vaccines.

Progress toward an elusive goal: current status of cytomegalovirus vaccines

Although infection with human cytomegalovirus (CMV) is ubiquitous and generally asymptomatic in most individuals, certain patient populations are at high risk for CMV-associated disease. These include HIV-infected individuals with AIDS, transplant patients, and newborn infants with congenital CMV infection. Immunity to CMV infection, both in the transplant setting and among women of childbearing age, plays a vital role in the control of CMV-induced injury and disease. Although immunity induced by CMV infection is not completely protective against reinfection, there is nevertheless a sound basis on which to believe that vaccination could help control CMV disease in high-risk patient populations. Evidence from several animal models of CMV infection indicates that a variety of vaccine strategies are capable of inducing immune responses sufficient to protect against CMV-associated illness following viral challenge. Vaccination has also proven effective in improving pregnancy outcomes following CMV challenge of pregnant guinea pigs, providing a 'proof-of-principle' relevant to human clinical trials of CMV vaccines. Although there are no licensed vaccines currently available for human CMV, progress toward this goal has been made, as evidenced by ongoing clinical trial testing of a number of immunization strategies. CMV vaccines currently in various stages of preclinical and clinical testing include: protein subunit vaccines; DNA vaccines; vectored vaccines using viral vectors, such as attenuated pox- and alphaviruses; peptide vaccines; and live attenuated vaccines. This review summarizes some of the obstacles that must be overcome in development of a CMV vaccine, and provides an overview of the current state of preclinical and clinical trial evaluation of vaccines for this important public health problem.

An animal model of neonatal cytomegalovirus infection

Cytomegalovirus (CMV) is the most common cause of congenital infection in the developed world and can lead to a life-threatening disease. We therefore developed an animal model to evaluate candidate anti-CMV drugs and to further define the pathogenesis of CMV infections. Newborn guinea pigs were infected by intraperitoneal administration of 10(6) pfu of a virulent salivary gland (SG) passaged guinea pig CMV (gpCMV) within 48 h of birth. Inoculation of animals produced 50% overall mortality. A lack of weight gain was also a hallmark of infection. By day 14 after inoculation the weight of gpCMV-infected animals was significantly less than controls (152.9+/-45 g versus 254.7+/-38.5 g, P<0.0001). The most consistent isolation and highest titers of virus were found in the liver and spleen early while lung titers were maximal at day 10. A quantitative competitive PCR (qcPCR) assay confirmed the presence of a high CMV viral load in infected organs. Antiviral treatment with cyclic HPMPC (cHPMPC) for 7 days significantly reduced mortality (1/20 versus 14/20, P<0.001) and viral replication but did not improve weight gain. This model should be useful for further evaluations of the pathogenesis of CMV infections and for evaluation of antiviral drugs and vaccines.

Down-regulation of surface major histocompatibility complex class I by guinea pig cytomegalovirus

Live attenuated strains of human cytomegalovirus are under development as vaccines to prevent birth defects resulting from congenital infections. These strains encode four proteins that inhibit surface expression of MHC class I, presumably to evade cytotoxic T-cell recognition and, perhaps, attenuate induction of immunity. To initiate studies of the role of class I down-regulation on congenital infection and vaccine efficacy, the ability of guinea pig cytomegalovirus to down-regulate class I was examined. Surface class I was specifically down-regulated on infected cells up to 8-fold. Sensitivity to UV irradiation and insensitivity to a viral DNA synthesis inhibitor revealed that immediate early or early viral gene(s) are responsible. Identification of these genes will permit future experiments to evaluate the role of class I down-regulation in congenital cytomegalovirus disease and its impact on vaccine efficacy. These findings should be pertinent to understanding human cytomegalovirus disease and may help guide the design of candidate vaccines.

Animal cytomegaloviruses

Cytomegaloviruses are agents that infect a variety of animals. Human cytomegalovirus is associated with infections that may be inapparent or may result in severe body malformation. More recently, human cytomegalovirus infections have been recognized as causing severe complications in immunosuppressed individuals. In other animals, cytomegaloviruses are often associated with infections having relatively mild sequelae. Many of these sequelae parallel symptoms associated with human cytomegalovirus infections. Recent advances in biotechnology have permitted the study of many of the animal cytomegaloviruses in vitro. Consequently, animal cytomegaloviruses can be used as model systems for studying the pathogenesis, immunobiology, and molecular biology of cytomegalovirus-host and cytomegalovirus-cell interactions.

Evaluation of new antiviral agents: II. The use of animal models

Antiviral chemotherapy has become a reality in the 1980s. Since the use of animal models in the testing of new antiviral agents is an inevitable step prior to clinical trial in human patients, it is important to understand the basic principles of using model systems. Briefly reviewed in this paper are the heterologous and homologous animal models which have been used for studies of various herpesvirus infections in humans. Discussions of the use of the guinea pig models mainly, for members of the Herpesviridae are presented in more detail. Precautions needed for the development of new animal models, and suggestions proposed for the use of animal models for testing new antiviral agents are outlined. It is hoped that new animal models will be developed in the foreseeable future for evaluating the much needed effective but less toxic antiviral agents for a variety of human viral diseases.

Maternal cell-mediated cytolysis of CMV-infected fetal cells and the outcome of pregnancy in the guinea pig

Cytolytic recognition of CMV-infected syngeneic fetal guinea pig cells by maternal peripheral blood mononuclear cells (PBMC) was suppressed late in pregnancies of uninfected guinea pig breeders with less than 25% conceptus loss. A small subset of less successful uninfected pregnancies with greater than or equal to 50% fetal wastage exhibited only partial suppression of cytolytic activity against CMV-infected fetal cells. Primary CMV infection of dams extending into early pregnancy induced augmented cytolysis of CMV-infected fetal cells, but not MA104 NK cell targets, throughout gestation and resulted in 70% loss of conceptus. Decreased suppression of cytolytic activity against CMV-infected fetal cells in uninfected pregnancy was also associated with runting of newborn pups, which was not as severe as that observed in congenitally CMV-exposed or CMV-infected pups. Congenitally infected pups were affected more than their exposed but uninfected litter mates. Lack of suppression of cytolysis of CMV-infected syngeneic fetal cells, whether spontaneous or CMV-infection-induced, appears to be associated with poor pregnancy outcome.

Detection of guinea pig cytomegalovirus nucleic acids in cultured cells with biotin-labelled hybridization probes

Biotin labelled hybridization probes prepared from recombinant plasmids containing segments of the guinea pig cytomegalovirus (GPCMV) genome were used to detect GPCMV nucleic acids in guinea pig cells by in situ hybridization. The time course of GPCMV infection was assessed in two cultured cell types, guinea pig embryo (GPE) cells and 104C1 cells, a transformed and cloned guinea pig cell line. Detection of GPCMV nucleic acids was accomplished in both cell types with individual GPCMV DNA fragments and with mixtures of GPCMV DNA fragments. When compared to other established methods of GPCMV detection, the method of in situ hybridization enabled the detection of a higher percentage of positive cells early during the course of the infection. In addition, differences in the replication cycle of GPCMV in the two cultured cell lines could be demonstrated. These findings will facilitate future studies of GPCMV tissue tropism in vivo.

Pulmonary macrophage function during experimental cytomegalovirus interstitial pneumonia

Since cytomegalovirus (CMV) infections may alter host defense against a variety of pathogens, phagocytosis, oxygen uptake, and H2O2 release by pulmonary macrophages obtained from guinea pigs with acute CMV interstitial pneumonia were evaluated. Experimental animals were inoculated subcutaneously on day zero with 10(7.5) 50% tissue culture infective doses of virulent guinea pig CMV. Control animals received an uninfected salivary gland suspension. The animals were sacrificed on day 7; the tissues were cocultivated for virus isolation, and the lungs were lavaged to obtain pulmonary macrophages. CMV was isolated from buffy coat cells (96%), bone marrow cells (71%), whole lungs (77%), pulmonary macrophages (60%), and pulmonary granulocytes (49%). There was no significant difference between groups at sacrifice in the total number of macrophages obtained by pulmonary lavage or in the phagocytic activity of the macrophages in vitro. However, in CMV-infected animals, the maximum rates of O2 consumption in response to the soluble stimulus, phorbol myristate acetate, and the particulate stimulus, Staphylococcus aureus, were 47 and 55%, respectively, of the rates in uninfected controls. Total macrophage O2 consumption in CMV-infected animals was 32 and 37%, respectively, of control values in response to the same stimuli. In CMV-infected animals, the maximum rates of H2O2 release were 22% of those in simultaneous controls for both stimuli, and total H2O2 release was 30 and 25%, respectively, of that in controls in response to these stimuli. Such alterations in macrophage oxidative function may contribute to superinfection during CMV pneumonia.