Generation of a recombinant chimeric Newcastle disease virus vaccine that allows serological differentiation between vaccinated and infected animals

Using a recently developed reverse genetics system, we have generated a rec ombinant Newcastle disease virus (NDV) vaccine in which the gene encoding t he hemagglutinin-neuraminidase (HN) has been replaced by a hybrid HN gene c onsisting of the cytoplasmic domain, transmembrane region, and stalk region of HN of NDV, and the immunogenic globular domain of HN of avian paramyxov irus type 4 (APMV4). The objective was to generate a chimeric live vaccine that induces a protective immune response against NDV by eliciting neutrali zing antibodies against the fusion (F) protein, but which can be differenti ated from wild-type NDV on the basis of different antibodies elicited by th eir HN proteins. Pathogenicity tests in day-old chickens showed that the re combinant was non-virulent (intracerebral pathogenicity index [ICPI] = 0.00 ). A vaccination-challenge experiment in 4-week-old specific pathogen free chickens demonstrated that the recombinant was completely safe and was able to protect chickens from challenge with a lethal dose of virulent NDV. By using a secreted form of HN produced in Pichia pastoris, a test was develop ed that allowed serological differentiation between animals vaccinated with the recombinant vaccine and animals infected with NDV. These results demon strate that genetically modified marker vaccines can be generated from smal l RNA viruses that lack non-essential genes. (C) 2001 Elsevier Science Ltd. All rights reserved.