Gene Therapy for Urea Cycle Disorders

描述（由申请人提供）：这是一份来自宾夕法尼亚大学和国家儿童医学中心的申请，申请更新现有的P01项目“尿素循环障碍的基因治疗”的资金。我们完成了本计划当前4年周期的主要目标。建立了一种临床候选载体：AAVS，表达来自肝脏特异性TBG启动子的鸟氨酸转氨基甲酰基酶（OTC）密码子优化cDNA。在与伦理咨询委员会密切磋商后，我们决定在迟发但严重OTC缺乏症（OTCD）婴儿的I期临床试验中对临床候选药物进行初步评估。我们将使用独立于P01竞争更新的机制来资助临床试验。在我们的临床前研究中，我们确定了在考虑对新生儿出现危及生命的高氨血症发作的严重OTCD患者进行临床试验之前应该解决的几个问题。在新生小鼠和猴子中，高水平的基因转移是可以实现的，然而，由于在发育中的新生肝脏环境中稀释，它会减少到低水平。我们也担心T细胞对一些新生儿发病受试者的反应，因为他们可能有无效的等位基因，不能删除对正常OTC有反应的T细胞。最后，由于母体抗体的被动转移，一些新生儿将对AAVS具有预先存在的免疫力。项目一将解决与T细胞对转基因编码OTC的反应相关的问题，并将尝试设计载体基因组，以便在目标细胞群增殖时进行复制。项目二将评估新的药物干预措施，以提高基因治疗的疗效。项目III将对AAVS衣壳进行改造，使其能够逃脱某种程度的预先存在的中和抗体。这些项目将由专门研究载体、细胞形态学和动物模型的核心实验室提供支持。在续期申请结束时，可交付的是第二代临床候选药物，在辅助药物治疗的设置下，适用于新生儿发病OTCD患者的评估。

DESCRIPTION (provided by applicant): This is an application from the University of Pennsylvania and the Children's National MedicalCenter to renew funding of an existing P01 entitled "Gene Therapy of Urea Cycle Disorders." We achieved the primary objectives of the current 4 year cycle of this P01. A Clinical Candidate vector was established: AAVS expressing a codon-optimized cDNA for ornithine transcarbamylase (OTC) from the liver-specific TBG promoter. In close consultation with our Ethics Advisory Board, it was decided to initially evaluate the Clinical Candidate in a phase I clinical trial in infants with late onset but severe OTC deficiency (OTCD). We will be using mechanisms to fund the clinical trial separate from this P01 competing renewal. In the conduct of our preclinical studies, we identified several issues that should be addressed before considering clinical trials in those with severe OTCD who present with life-threatening episodes of hyperammonemia as neonates. High level gene transfer in newborn mice and monkeys is acheivable, however, it diminishes to low levels due to dilution in the setting of the developing newborn liver. We also have concerns about T cell responses to some neonatal onset subjects since they may have null alleles that fail to delete T cells reactive to the normal version of OTC. Finally, some newborns will have pre-existing immunity to AAVS due to passive transfer of maternal antibodies. Project I will address issues related to T cell responses to transgene-encoded OTC and will attempt to engineer the vector genome to allow for replication when the target cell population is proliferating. Project II will evaluate novel pharmacologic interventions that could augment the efficacy of gene therapy that is less than curative. Project III will engineer the AAVS capsid to escape some level of pre-existing neutralizing antibodies. These Projects will be supported by Core laboratories that specialize in Vector, Cell Morphology and Animal Models. The deliverable at the end of the renewal application is a second generation Clinical Candidate which, in the setting of adjuvant pharmacologic therapy, is suitable for evaluation in humans with neonatal onset OTCD.