Cytomegalovirus (CMV) is a ubiquitous pathogen that causes significant morbidity and mortality in immunocompromised populations. Currently, there is no effective vaccine against CMV. Development of a vaccine, particularly for women of child-bearing age, is considered to be a major public health priority because of the risk of congenital infection to the fetus. This application proposes the use of a replication-impaired live CMV vaccine lacking an essential gene. The mutant viruses will be capable of infecting non-complementing cells in an abortive single cycle of virus replication but incapable of producing infectious virus. We hypothesize that a disabled infectious single cycle (DISC) vaccine against CMV would be non-pathogenic, regardless of virus dosage used, but highly immunogenic inducing antibody and T-cell responses to an array of viral antigens. Additionally, we propose that the effectiveness of such a DISC vaccine against CMV will be further augmented by introducing a second copy of the major neutralizing antigen, glycoprotein gB, into the viral genome. We also hypothesize that the co-administration of the vaccine strain with a pro-inflammatory cytokine (IL-12) adjuvant will polarize the T cell helper type 1 (Th1) immune response against the virus creating a bias towards a cell mediated immune response. Human CMV, as with all CMV, is a species specific virus and consequently animal CMVs in their respective hosts must be studied to test any proposed vaccine or antiviral strategy. Among the small animal models of CMV only the guinea pig model allows the study of congenital infection. Our long-term goal is the continued development of this model to test intervention strategies against congenital infection in particular pre-conception vaccines. As proof of principle for the CMV DISC vaccine strategy these studies will be carried out in the guinea pig model. The proposed research will define the antibody and cellular immune responses to a series of vaccine candidate CMV DISC strains. Additionally, the research will determine the ability of candidate DISC vaccines to protect against congenital CMV infection in comparison to a recombinant gB subunit vaccine strategy that has previously been tested in this model. PUBLIC HEALTH RELEVANCE: HCMV is a ubiquitous pathogen that causes significant morbidity and mortality in immunocompromised populations. Primary HCMV infection in immunocompetent individuals is usually benign but establishes a lifelong latent infection. Solid organ transplant recipients or AIDS patients are particularly susceptible to reactivation of the virus, which can lead to life-threatening end-organ disease. Congenital infection of newborns by HCMV (approximately 1% of live births in the US) can lead to serious symptomatic disease including mental retardation and hearing loss. Indeed it is estimated that congenital HCMV related sensorineural hearing loss (SNHL) occurs at a greater frequency than SNHL related to Hemophilus influenza infection in the pre-HIB vaccine era. Furthermore, congenital HCMV infection is the second most common cause of mental retardation next to Down's syndrome in newborns. Although antivirals are available for treatment of AIDS and transplant patients these drugs cannot be used to prevent congenital infection because of the risk of toxic side effects on the fetus. Additionally, antivirals act at late stages of virus infection and can result in the development of resistant strains with prolonged therapy. Consequently, a vaccine against HCMV is probably the most effective method of preventing or lowering the incidence of disease. Additionally, a vaccine would save considerably in the resources currently employed for the long term treatment/ care of congenitally infected newborns with severe hearing loss and mental retardation.