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，人们一直在寻求一种能够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的巨细胞病毒疫苗，但这一努力仍未实现。评估任何疫苗效力的主要客观衡量标准是疫苗接种者是否产生并维持了保护性免疫水平。对巨细胞病毒来说，一个重要的问题是什么是保护性免疫的定义。使用严格的阈值，只有当接种者在反复接触病毒后获得绝对保护而不受感染时，免疫反应才被认为是保护性的。或者，如果挑战病毒的感染过程发生了极大的变化，以至于基本上消除了挑战病毒的传播(水平和垂直)和致病机制，疫苗仍可被认为是保护性的。两者之间的差异涉及主要挑战地点的病毒复制水平和以外的传播程度。前一种定义要求产生和维持灭菌免疫，而不会传播病毒。后者没有，但它确实要求免疫系统对具有免疫能力的宿主中具有复杂自然持久性历史的病毒的复制保持终身限制。提出的假设是，针对CMV的免疫可以产生保护性免疫反应，尽管保护的程度(灭菌与有限传播)将取决于挑战病毒的滴度和暴露的频率。根据这一假设，免疫可以完全防止罕见地接触到低滴度的CMV挑战。随着病毒滴度和/或暴露于挑战病毒的频率的增加，保护措施将变得更加可变。疫苗接种应该使病毒-宿主的平衡明显有利于宿主，从而显著减少病毒的重新激活和脱落。这一假说将在巨细胞病毒感染的恒河猴模型中通过以下目的进行验证。(I)用RhCMV gB、pp65和IE1基因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免疫。(Ii)通过实验接种高滴度或低滴度的重组人巨细胞病毒，对接种者和对照组进行皮下挑战。(Iii)对猕猴进行免疫接种，然后通过自然途径挑战接种者和控制组，使其与血清阳性、排毒的猕猴共居，从而获得自然滴度的人巨细胞病毒。(4)改变RhCMV基因表达模式以诱导新的保护性免疫反应。如果巨细胞病毒疫苗导致死胡同感染，则可被认为是保护性的。这项建议将严格测试基因免疫和福尔马林灭活病毒的组合是否可以有效地消除实验性或自然感染后的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.