Construction Of Cytomegalovirus DNA Vaccines And Evaluation Of Their Immunoprotective Effects In BALB/c Mice

This article consists of brief introduction of cytomegalovirus (CMV) and CMV vaccines, construction of plasmid DNA vaccines, and evaluation of protection provided by MCMV DNA vaccines.CMV belongs to the Betaherpesvirinae subfamily of Herpesviridae, which has a high infection rate in common people and causes opportunistic infection. Infection with CMV has been associated with severe diseases in newborns and immunologically impaired patients. Thus it is important to reveal the immune mechanisms of the virus control and to develop a safe and effective vaccine. Development of a vaccine for prevention of CMV infection was listed as a top priority in the United States in 2001. Although the first clinical trials of a CMV vaccine took place 30 years ago, an effective vaccine for the prevention of CMV infection and diseases remains elusive. At present, researches on CMV vaccines are mainly focused on subunit vaccines and DNA vaccines.Because of the strict species specificity of the herpesviruses, animal models of CMV immunity have used MCMV, which is similar to HCMV with regard to virion structure, genome organization, tissue tropism, and latency. In the paper, the genes M04, M54, M55, M84, M105 and immediate-early 1 (IE-1) from the MCMV Smith strain were first obtained by PCR, and then separately cloned into expressing vector pcDNA3.1/myc-His B to form a series of DNA vaccines. The above genes encode MCMV gp34, DNA polymerase, glycoprotein B(gB), p65, DNA helicase and pp89 proteins, respectively. Correct construction of the plasmids was confirmed DNA sequencing.The abilities of the constructed plasmids to provide protective immunity were explored in BALB/c mice. Mice were administered with the plasmid DNAs by electroporation (100μg per administration for 5 times, at an interval of 2 weeks), and were then challenged with a lethal dose (3×LD50) of homologous virus (salivary gland virus, SGV), which was prepared by 14 serial passages of salivary gland homogenates in BALB/c mice. The protection of DNA vaccines was evaluated by the serum antibody titers, the number of IFN-y-secreting splenocytes, weight loss, residual salivary gland virus titers and survival rates of mice. The results showed that the mice vaccinated with pM55 plasmid had a high level of specific antibody response, and those with pM04,pM84,pM105 or pIE-1 plasmid produced significantly high number of IFN-y-secreting splenocytes. The mice immunized five times with pM04, pM84 or pIE-1 survived 100%, and those with pM54, pM55 or pM105 showed 56-67% survival rate. Those results suggested that MCMV-DNA vaccines could provide effective protection against lethal SGV challenge.