Evaluation of Protective CMV Vaccines in Rhesus Macaques

描述（由申请人提供）：自从人类巨细胞病毒（HCMV）首次被认为是对发育中的胎儿的威胁以来，人们一再呼吁开发一种疫苗，以保护那些有HCMV疾病风险的人免受HCMV感染的破坏性影响。长期以来，人们一直在寻找一种HCMV疫苗，以预防先天性感染和胎儿后遗症，以及免疫受损个体的终末器官疾病。评价任何一种疫苗有效性的主要客观指标是接种者是否产生并维持保护性免疫水平。HCMV的一个重要问题是什么构成保护性免疫的定义。使用严格的阈值，只有当疫苗接种者在反复接触病毒后完全免受感染时，才能认为免疫反应具有保护作用。或者，如果攻毒病毒感染的过程发生显著改变，从而基本上消除了攻毒病毒传播（水平和垂直）和发病机制的可能性，那么疫苗仍可被认为具有保护作用。两者之间的差异涉及病毒在主要攻击部位的复制水平和传播程度。前一定义要求产生和维持绝育免疫而不传播病毒。后者没有，但它确实要求免疫系统对病毒的复制保持终身限制，这种病毒具有在免疫能力强的宿主中持续存在的复杂自然历史。假设针对巨细胞病毒的免疫接种可以产生保护性免疫反应，尽管保护程度（灭菌还是有限传播）将取决于攻击病毒的滴度和暴露频率。根据这一假设，免疫可以完全防止不经常暴露于低滴度巨细胞病毒攻击。随着攻击病毒滴度和/或接触频率的增加，保护将变得更加多变。接种疫苗应使病毒与宿主的平衡明显地向有利于宿主的方向转变，从而使病毒的再激活和脱落都显著减少。该假设将通过以下目的在恒河猴HCMV感染模型中进行验证。(1)用RhCMV gB、pp65和IE1质粒表达载体对血清阴性猕猴进行遗传免疫，然后用福尔马林灭活病毒进行免疫。（II）实验性接种高滴度或低滴度RhCMV，对接种者和对照组进行皮下攻击。（III）对猕猴进行免疫，然后将疫苗接种者与血清阳性、病毒分泌的猕猴共同安置，通过具有自然RhCMV滴度的自然途径对疫苗接种者和对照者进行攻击。（四）改变RhCMV基因表达模式诱导新的保护性免疫反应。如果巨细胞病毒疫苗导致死角感染，则可被认为具有保护作用。本研究将严格检验遗传免疫与福尔马林灭活病毒结合是否能有效消除实验性或自然感染后RhCMV的水平传播。

DESCRIPTION (provided by applicant): Since human cytomegalovirus (HCMV) was first recognized as a threat to the developing fetus, there have been repeated calls for a vaccine that could protect from the damaging effects of HCMV infection in those at risk for HCMV disease. The long quest for a HCMV vaccine that could prevent congenital infection and fetal sequelae, as well as end-organ disease in immune compromised individuals, remains unfulfilled. The primary objective measure for evaluating the efficiency of any vaccine is whether protective levels of immunity are generated and sustained in the vaccinees. An important issue for HCMV is the definition of what constitutes protective immunity. Using a stringent threshold, an immune response can be considered protective only if the vaccinees are absolutely protected from infection following repeated exposure to virus. Alternatively, a vaccine could still be considered protective if the course of challenge virus infection was so dramatically altered that the potential for transmission (horizontal and vertical) and pathogenesis of challenge virus was essentially eliminated. The difference between the two involves the level of virus replication at the primary site of challenge and the extent of dissemination beyond. The former definition requires the generation and maintenance of sterilizing immunity with no spread of the virus. The latter does not, but it does require that the immune system maintain a lifelong restriction on replication of a virus with a complex natural history of persistence in immune competent hosts. The hypothesis is presented that immunization against CMV can generate protective immune responses, although the degree of protection (sterilizing versus limited dissemination) will be dependent on both the titer of challenge virus and the frequency of exposure. According to this hypothesis, immunization can protect completely against infrequent exposure to a low titer CMV challenge. Protection will become more variable as the titer and/or the frequency of exposure to challenge virus increases. Vaccination should shift the virus-host balance decidedly in favor of the host such that both reactivation and shedding are significantly diminished. The hypothesis will be tested in the rhesus macaque model of HCMV infection through the following Aims. (I) Genetic immunization of seronegative macaques with plasmid expression vectors for RhCMV gB, pp65, and IE1, followed by immunization with formalin-inactivated virus. (II) Subcutaneous challenge of vaccinees and controls by experimental inoculation with either high or low titers of RhCMV. (III) Immunization of macaques followed by challenge of vaccinees and controls by natural routes with natural titers of RhCMV by co-housing vaccinees with seropositive, virus-excreting macaques. (IV) Alterations of RhCMV gene expression patterns to induce novel protective immune responses. A CMV vaccine can be considered protective if it results in a dead-end infection. This proposal will stringently test whether a combination of genetic immunization and formalin-inactivated virus can effectively eliminate horizontal spread of RhCMV following either experimental or natural infection.