Evaluation of Protective CMV Vaccines in Rhesus Macaques

描述（由申请方提供）：由于人巨细胞病毒（HCMV）首次被认为是对发育中胎儿的威胁，因此一直呼吁开发一种疫苗，以保护有HCMV疾病风险的人群免受HCMV感染的破坏性影响。长期以来，人们一直在寻找一种可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的HCMV疫苗，但这一目标仍未实现。评价任何疫苗效力的主要客观指标是接种者是否产生和维持保护性免疫水平。HCMV的一个重要问题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暴露于病毒后绝对免受感染时，免疫应答才能被认为是保护性的。或者，如果攻毒病毒感染过程发生显著改变，基本消除了攻毒病毒传播（水平和垂直）和致病的可能性，则疫苗仍可被视为具有保护性。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范围。前一种定义要求产生和维持绝育免疫力，而不传播病毒。后者不需要，但它确实需要免疫系统维持对病毒复制的终身限制，该病毒具有在免疫活性宿主中持续存在的复杂自然历史。提出的假设是，针对CMV的免疫接种可以产生保护性免疫应答，尽管保护的程度（灭菌与有限的传播）将取决于挑战病毒的滴度和暴露的频率。根据这一假设，免疫接种可以完全保护不频繁暴露于低滴度CMV攻击。随着滴度和/或暴露于攻毒病毒的频率增加，保护作用将变得更加可变。疫苗接种应该明显改变病毒与宿主的平衡，有利于宿主，从而显着减少再激活和脱落。将通过以下目的在HCMV感染的恒河猴模型中检验该假设。(I)用RhCMV gB、pp 65和IE 1的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)通过实验性接种高或低滴度的RhCMV对疫苗接种者和对照进行皮下攻毒。(III)猕猴免疫接种，然后通过自然途径用自然滴度的RhCMV对接种者和对照组进行攻毒，方法是将接种者与血清阳性的病毒分泌猕猴共同饲养。(IV)RhCMV基因表达模式的改变诱导新的保护性免疫应答。CMV疫苗可以被认为是保护性的，如果它导致死端感染。该提案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.