Postnatal ontogeny of HCMV-specific CD4 T cell immunity

人类巨细胞病毒（HCMV）是美国先天性出生缺陷的主要感染性原因，也是免疫功能低下者发病率和死亡率的重要来源。由于相当大比例的HCMV传播发生在围产期和婴儿期早期，理想的HCMV疫苗将对这一年龄组有效。在这个年龄接种疫苗的一个潜在限制是CD4 T细胞效应分子的表达明显不成熟，特别是分泌的细胞因子，如干扰素γ (ifn - γ)和肿瘤坏死因子（TNF），表面分子，如cd40 -配体（CD40-L）。出生后获得性HCMV感染未显示出这种限制。本项目的第一个目的是确定hcmv特异性CD4 T细胞效应分子的表达，特别是分泌的细胞因子，如干扰素- γ (ifn - γ)和肿瘤坏死因子（TNF），表面分子，如cd40 -配体（CD40-L）。出生后获得性HCMV感染未显示出这种限制。本项目的首要目的是确定婴儿和成人原发性HCMV感染后HCMV特异性CD4 T细胞记忆/效应功能及其与其他HCMV特异性免疫反应、病毒清除和病毒潜伏期建立的关系。据推测，与成人相比，幼儿的HCMV抗原特异性记忆/效应CD4 T细胞的积累会减少，这些细胞可以分泌细胞因子或表达CD40-L。我们进一步预测，婴儿hcmv特异性CD4 T细胞将优先产生缺乏抗病毒活性或许多抑制这种活性的Th2细胞因子。对HCMV的总体反应和pp65基质蛋白（似乎是CD4 T细胞反应的主要靶点）的反应将被检查。将确定婴儿CD4 T细胞反应的降低和/或改变是否与血清中和性HCMV抗体水平的降低、病毒血症的延长、尿病毒排出的延长（全部由临床研究中心确定）、HCMV特异性CD8 T细胞功能的降低（项目2）和抗原呈递功能（APC）的降低（项目3）并行。第二个目标是开发含有pp65肽的荧光标记HLA-DR四聚体分子，以鉴定具有pp65特异性的婴儿和成人CD4 T细胞。这将验证一个假设，即婴儿而非成人有相当一部分CD4 T细胞具有pp65特异性，但对pp65抗原的反应性降低或不存在。这些研究将深入了解正常婴儿和成人原发性HCMV感染后的人类CD4记忆/效应T细胞反应，APC功能。由于HCMV疫苗的新试验即将进行，这些研究也可能为疫苗效力提供有用的未成熟反应预测因子，例如预防HCMV感染和/或改善潜伏期的维持。他们还可能指出通过免疫疗法增强保护性反应的策略，特别是在婴儿期。

Human cytomegalovirus (HCMV) is the leading infectious cause of congenital birth defects in the United States, and is an important source of morbidity and mortality for those who are immunocompromised. Since a substantial proportion of HCMV transmission occurs perinatally and in early infancy, an ideal HCMV vaccine would be effective in this age group. A potential limitation of vaccination at this age is the apparent immaturity of CD4 T cell expression of effector molecular, particularly secreted cytokines, e.g., interferon-gamma (IFN-gamma) and tumor necrosis factor (TNF), surface molecules, such as CD40-ligand (CD40-L). Such limitations have not been shown for postnatally acquired HCMV infection. The first aim of this project is to determine HCMV-specific CD4 T cell expression of effector molecules, particularly secreted cytokines, e.g., interferon-gamma (IFN-gamma) and tumor necrosis factor (TNF), surface molecules, such as CD40-ligand (CD40-L). Such limitations have not been shown for postnatally acquired HCMV infection. The first aim of this project is to determine HCMV-specific CD4 T cell memory/effector function following primary HCMV infection of infants and adults, and its relationship with other HCMV-specific immune responses, viral clearance, and the establishment of viral latency. It is hypothesized that young infants will have a decreased accumulation of HCMV antigen-specific memory/effector CD4 T cells that can secrete cytokines or express CD40-L compared to adults. We further predict that infant HCMV-specific CD4 T cells will preferentially produce Th2 cytokines that lack anti-viral activity or many inhibit this activity. Responses to HCMV overall, and to the pp65 matrix protein, which appears to be a major target of the CD4 T cell response, will be examined. It will be determined if decreased and/or altered infant CD4 T cell responses are paralleled by decreased serum levels of neutralizing HCMV antibody, prolonged viremia, prolonged urinary viral shedding (all determined by the Clinical Research Core), decreased HCMV-specific CD8 T cell function (Project 2), and decreased antigen-presenting function (APC) (Project 3). The second aim is to develop fluorochrome- labeled HLA-DR tetramer molecules containing ppo65 peptides to identify CD4 T cells in infants and adults with specificity for pp65. This will test the hypothesis that infants but not adults have a substantial fraction of CD4 T cells with specificity for pp65 but reduced or absent responsiveness to pp65 antigen. These studies will provide insight into the human CD4 memory/effector T cell response following primary HCMV infection in normal infants and adults, APC function. Since new trials of HCMV vaccines are imminent, these studies may also provide useful immature response predictors for vaccine efficacy, such as prevention of HCMV infection and/or improved maintenance of latency. They may also point out strategies by which protective responses might be augmented by immunotherapy, particularly during infancy.