Institute for Memory Impairments and Neurological Disorders, University of California, Irvine, 92697-4540, USA.
CNS Neurol Disord Drug Targets. 2010 Apr;9(2):207-16. doi: 10.2174/187152710791012080.
Pre-clinical and clinical data suggest that the development of a safe and effective anti-amyloid-beta (Abeta) immunotherapy for Alzheimer's disease (AD) will require therapeutic levels of anti-Abeta antibodies, while avoiding proinflammatory adjuvants and autoreactive T cells which may increase the incidence of adverse events in the elderly population targeted to receive immunotherapy. The first active immunization clinical trial with AN1792 in AD patients was halted when a subset of patients developed meningoencephalitis. The first passive immunotherapy trial with bapineuzumab, a humanized monoclonal antibody against the end terminus of Abeta, also encountered some dose dependent adverse events during the Phase II portion of the study, vasogenic edema in 12 cases, which were significantly over represented in ApoE4 carriers. The proposed remedy is to treat future patients with lower doses, particularly in the ApoE4 carriers. Currently there are at least five ongoing anti-Abeta immunotherapy clinical trials. Three of the clinical trials use humanized monoclonal antibodies, which are expensive and require repeated dosing to maintain therapeutic levels of the antibodies in the patient. However in the event of an adverse response to the passive therapy antibody delivery can simply be halted, which may provide a resolution to the problem. Because at this point we cannot readily identify individuals in the preclinical or prodromal stages of AD pathogenesis, passive immunotherapy is reserved for those that already have clinical symptoms. Unfortunately those individuals have by that point accumulated substantial neuropathology in affected regions of the brain. Moreover, if Abeta pathology drives tau pathology as reported in several transgenic animal models, and once established if tau pathology can become self propagating, then early intervention with anti-Abeta immunotherapy may be critical for favorable clinical outcomes. On the other hand, active immunization has several significant advantages, including lower cost and the typical immunization protocol should be much less intrusive to the patient relative to passive therapy, in the advent of Abeta-antibody immune complex-induced adverse events the patients will have to receive immuno-supperssive therapy for an extended period until the anti Abeta antibody levels drop naturally as the effects of the vaccine decays over time. Obviously, improvements in vaccine design are needed to improve both the safety, as well as the efficacy of anti-Abeta immunotherapy. The focus of this review is on the advantages of DNA vaccination for anti-Abeta immunotherapy, and the major hurdles, such as immunosenescence, selection of appropriate molecular adjuvants, universal T cell epitopes, and possibly a polyepitope design based on utilizing existing memory T cells in the general population that were generated in response to childhood or seasonal vaccines, as well as various infections. Ultimately, we believe that the further refinement of our AD DNA epitope vaccines, possibly combined with a prime boost regime will facilitate translation to human clinical trials in either very early AD, or preferably in preclinical stage individuals identified by validated AD biomarkers.
临床前和临床数据表明,为了开发治疗阿尔茨海默病(AD)的安全有效的抗β淀粉样蛋白(Abeta)免疫疗法,需要治疗水平的抗 Abeta 抗体,同时避免使用可能增加针对接受免疫疗法的老年人群不良反应发生率的促炎佐剂和自身反应性 T 细胞。在 AD 患者中首次进行的针对 AN1792 的主动免疫临床试验因一部分患者发生脑膜炎脑炎而停止。针对 Abeta 末端的人源化单克隆抗体 bapineuzumab 的首次被动免疫疗法试验也在研究的二期部分遇到了一些与剂量相关的不良反应,12 例血管源性水肿,在 ApoE4 携带者中显著过度表达。提出的补救方法是用较低剂量治疗未来的患者,特别是在 ApoE4 携带者中。目前,至少有五项正在进行的抗 Abeta 免疫疗法临床试验。其中三项临床试验使用人源化单克隆抗体,这些抗体价格昂贵,需要重复给药以维持患者体内抗体的治疗水平。但是,如果对被动治疗抗体的输送产生不良反应,可以简单地停止输送,这可能会解决这个问题。由于目前我们无法在 AD 发病机制的临床前或前驱期轻易识别个体,因此被动免疫疗法仅适用于已经出现临床症状的个体。不幸的是,这些个体在受影响的大脑区域已经积累了大量的神经病理学。此外,如果 Abeta 病理学如几个转基因动物模型所报告的那样驱动 tau 病理学,并且一旦 tau 病理学能够自我传播,那么早期使用抗 Abeta 免疫疗法可能对临床结果有利。另一方面,主动免疫具有几个显著的优势,包括成本较低,相对于被动治疗,典型的免疫接种方案对患者的侵入性较小,在 Abeta-抗体免疫复合物诱导的不良反应发生的情况下,患者将不得不接受免疫抑制治疗延长一段时间,直到抗 Abeta 抗体水平自然下降,因为疫苗随着时间的推移而失效。显然,需要改进疫苗设计,以提高抗 Abeta 免疫疗法的安全性和有效性。本综述的重点是 DNA 疫苗在抗 Abeta 免疫疗法中的优势,以及主要障碍,如免疫衰老、选择合适的分子佐剂、通用 T 细胞表位,以及可能基于利用针对儿童或季节性疫苗以及各种感染产生的现有记忆 T 细胞的多表位设计。最终,我们相信,进一步完善我们的 AD DNA 表位疫苗,可能结合初级增强方案,将有助于将其转化为针对早期 AD 或最好是针对通过验证的 AD 生物标志物识别的临床前个体的人类临床试验。
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