Purchase H G
Cancer Res. 1976 Feb;36(2 pt 2):696-700.
Marek's disease (MD) is a highly infectious neoplastic condition of chickens caused by a herpesvirus. The virus is cell associated in tumors and in all organs except in the feather follicle where enveloped infectious virions egress from the body. From this source, infection is spread horizontally by the airborne route to the environment and to other chickens. Vertical transmission from dam to offspring does not occur or at best is very rare. The nonpathogenic herpesvirus of turkeys (HTV) is ubiquitous in turkeys and is probably spread horizontally by the airborne route. When chickens are inoculated with this virus, they do not subsequently develop MD even after infection with virulent Marek's disease virus. The Marek's disease virus, not the HVT, will spread horizontally from dually infected birds. The HVT vaccine is safe and highly effective in preventing MD under field conditions, and most chickens throughout the world are vaccinated with this vaccine. Other vaccines that have been used but have disadvantages over HVT include the following: (a) the highly pathogenic HPRS 16 strain of Marek's disease virus was attenuated by passage in cell culture. The attenuated virus protects against MD and does not spread, but "over-attenuated" virus does not protect; (b) naturally apathogenic strains virologically, immunologically, and epizootiologically similar to pathogenic strains will protect when adminstered before infection with the virulent strains; (c) virus preparations that have been chemically treated to inactivate infectivity protect only slightly. When a candidate vaccine virus for the prevention of herpesvirus-induced cancer in humans is developed, the purity of the vaccine preparations will be easily determined by modern techniques. However, measurements of safety and effectiveness are a significant problem. If, analogous to the MD model, the vaccine will have to be administered shortly after birth and the incubation period to development of neoplasms is long, then pathogenicity tests in nonhuman primates and other animals may be of limited valued. However, biochemical demonstration that the segment of the nucleic acid responsible for oncogenesis is absent from the vaccine virus may be the major indication that the vaccine is nonocogenic and therefore safe. Because of the low incidence of neoplasia and long incubation period, the effectiveness of the vaccine will be difficult to test. The vaccine possibly will protect against an acute manifestation of viral infection. Future research on MD will be directed to determining the mechanism of protection against disease, i.e., whether immunity is mediated by thymus- or bursa-dependent systems, and to identifying the protective antigen, i.e., which cell surface or an interior antigen induces the protective immunity. The prevention of MD by vaccination may become a very fruitful area for model studies on prevention of human cancer by vaccination.
马立克氏病（MD）是一种由疱疹病毒引起的鸡的高度传染性肿瘤性疾病。该病毒与肿瘤细胞以及除毛囊外的所有器官相关联，在毛囊中，包膜感染性病毒粒子从体内释放出来。由此，感染通过空气传播途径在环境中水平传播并传染给其他鸡。从母鸡到后代的垂直传播不会发生，或者充其量非常罕见。火鸡的非致病性疱疹病毒（HTV）在火鸡中普遍存在，可能通过空气传播途径水平传播。当用这种病毒接种鸡时，即使在感染强毒马立克氏病病毒后，它们随后也不会患上MD。马立克氏病病毒而非HVT会从双重感染的禽类中水平传播。HVT疫苗在田间条件下预防MD安全且高效，全世界大多数鸡都接种这种疫苗。其他已使用但相对于HVT有缺点的疫苗包括：（a）马立克氏病病毒的高致病性HPRS 16株通过在细胞培养中传代而减毒。减毒病毒可预防MD且不会传播，但“过度减毒”的病毒则无保护作用；（b）在病毒学、免疫学和流行病学上与致病株相似的天然无致病性毒株，在感染强毒株之前接种时可提供保护；（c）经过化学处理以灭活传染性的病毒制剂仅有轻微保护作用。当开发用于预防人类疱疹病毒诱导癌症的候选疫苗病毒时，疫苗制剂的纯度可通过现代技术轻松测定。然而，安全性和有效性的测定是一个重大问题。如果类似于MD模型，疫苗必须在出生后不久接种，并且肿瘤发生的潜伏期很长，那么在非人类灵长类动物和其他动物中进行的致病性测试可能价值有限。然而，从生化角度证明疫苗病毒中不存在负责肿瘤发生的核酸片段可能是疫苗无致癌性因而安全的主要指标。由于肿瘤发生率低且潜伏期长，疫苗的有效性将难以测试。该疫苗可能会预防病毒感染的急性表现。未来对MD的研究将致力于确定预防疾病的机制，即免疫是否由胸腺依赖性或法氏囊依赖性系统介导，以及确定保护性抗原，即哪种细胞表面或内部抗原诱导保护性免疫。通过接种疫苗预防MD可能会成为通过接种疫苗预防人类癌症的模型研究的一个非常富有成果的领域。
