DNA immunization confers protection against murine cytomegalovirus infection

Abstract

The murine cytomegalovirus (MCMV) immediate-early gene 1 (IE1) encodes an 89-kDa phosphoprotein (pp89) which plays a key role in protecting BALB/c mice against the lethal effects of the MCMV infection. In this report, we have addressed the question of whether "naked DNA" vaccination with a eukaryotic expression vector (pcDNA-89) that contains the MCMV IE1 gene driven by a strong enhancer/promoter can confer protection. BALB/c mice were immunized intradermally with pcDNA-89 or with the plasmid backbone pcDNAI/Amp (pcDNA) and then challenged 2 weeks later with either a lethal or a sublethal intraperitoneal dose of the K181 strain of MCMV. Variable results were obtained for the individual experiments in which mice received a lethal challenge. In four separate trials, an average of 63% of the mice immunized with pcDNA-89 survived, compared with 18% of the mice immunized with pcDNA. However, in two other trials there was no specific protection. The results of experiments in which mice were injected with a sublethal dose of MCMV were more consistent, and significant decreases in viral titer in the spleen and salivary glands of pcDNA-89-immunized mice were observed, relative to controls. At the time of peak viral replication, titers in the spleens of immunized mice were reduced 18-to >63-fold, while those in the salivary gland were reduced approximately 24-to 48-fold. Although DNA immunization elicited only a low level of seroconversion in these mice, by 7 weeks postimmunization the mice had generated a cytotoxic T-lymphocyte response against pp89. These results suggest that DNA vaccination with selected CMV genes may provide a safe and efficient means of immunizing against CMV disease.

Modulating the immune response to genetic immunization

“…These early studies had several important features: they showed that DNA vaccines could induce immunity in several different disease models; that antibody, Th, and CTL responses could all be generated; that a response could be induced by different routes of immunization (e.g., intramuscular, epidermal, or mucosal); and, in the case of influenza, that these vaccines could protect animals from subsequent challenge with pathogenic virus. Since then, genetic immunization has been investigated in numerous infectious disease models in addition to those mentioned above, with vaccines currently in various stages of development for HIV-2 (7,8), herpes simplex virus 1 (HSV-1) (9), HSV-2 (10), rabies (11), hepatitis C (12), tuberculosis (13), malaria (14), mycoplasma (15), Leishmania major (16), cytomegalovirus (17), Toxoplasma gondii (18), rotavirus (19), and, most recently, Ebola (20). In addition to infectious diseases applications, genetic immunization may have potential as a means of cancer immunotherapy.…”

Nasal Peptide Vaccination Elicits CD8 Responses and Reduces Viral Burden after Challenge with Virulent Murine Cytomegalovirus

“…Acute MCMV infection by IP injection leads to a peak viral burden in spleen at 3-6 days, and in salivary gland at 10-14 days (11). After 1 month, mice have recovered from the acute phase of the infection, and have low MCMV titers in the salivary gland and other organs (11,30). In previous studies, we have demonstrated that mice develop persistent MCMV infection after recovery from the acute infection (13,32,39).…”

“…Mice with chronic MCMV infection had consistent immune responses to the peptide YPHFMPTNL as measured by IFN-γ ELISPOT. Acute MCMV infection by IP injection leads to a peak viral burden in spleen at 3-6 days, and in salivary gland at 10-14 days (11). After 1 month, mice have recovered from the acute phase of the infection, and have low MCMV titers in the salivary gland and other organs (11,30).…”

“…Nasal vaccination with YPHFMPTNL generated cell-mediated immune responses as determined by IFNγ ELISPOT. Previous studies have demonstrated that this peptide induces CD8 cell-mediated cytotoxicity (4,8,11,26). The ELISPOT assay provides a direct enumeration of responding cells without in vivo expansion (1).…”

“…Adoptive transfer of antiviral CD8 cells prevents MCMV disease and accelerates the resolution of productive infection (23,37). An immediate-early phase MCMV protein, pp89 (phosphoprotein 89, synonym IE1), has been identified as immunodominant (4,11). A specific pp89 peptide, YPHFMPTNL, elicits partially protective responses against MCMV infections in BALB/c mice (4,8,28).…”