The gD ORF was placed under the control of NDV transcriptional signals and inserted at the PmeI site between the P and M genes in the NDV vector (Fig. 1). The transcription cassette was designed to maintain the rule of six, whereby the genome nucleotide length must be an even multiple of six in order to be efficiently

replicated [35] and [36]. A Kozak sequence was inserted before the start codon of the gD gene ORF to provide for efficient translation [37]. The resulting plasmid, designated BIBW2992 supplier as pLaSota/gDFL, encoded an antigenome of 16,476 nt, which is increased by 1290 nt compared to the parental NDV strain LaSota. As a potential strategy to increase the efficiency of incorporation of gD into the NDV vector virion, we made another construct in which the ectodomain of gD was fused with the transmembrane domain and cytoplasmic tail of the NDV F protein. This chimeric gene, flanked by NDV transcription signals, was inserted into the NDV antigenomic cDNA in the same way as described above (Fig. 1). The resulting plasmid, designated pLaSota/gDF, encoded an antigenome of the same nt length as pLaSota/gDFL

and also conformed to the rule of six. Both of the recombinant viruses, designated as rLaSota/gDFL and rLaSota/gDF, were recovered using the reverse genetics method described previously [30]. The structure of each gD insert in the genome of these viruses was confirmed by RT-PCR and nucleotide sequence analysis (data Epacadostat price not shown). Both of the recombinant viruses were propagated in embryonated chicken eggs and the titers were determined by HA assay. The HA titers of rLaSota/gDFL and rLaSota/gDF viruses were 1–2 log2 lower than that of the parental rLaSota virus. This result is consistent with previous findings that a moderate attenuation of replication can result from the insertion of a foreign gene [30] and [34]. To determine the stability of the gD gene in the rLaSota/gDFL and rLaSota/gDF viruses, the recovered

viruses were passaged five times in embryonated chicken eggs and five times in chicken embryo fibroblast DF-1 cells. Sequence analysis of the gD gene of the resulting virus preparations showed that the integrity of the gD gene was preserved and stably maintained even after 10 passages. The expression Mannose-binding protein-associated serine protease of the two versions of gD in DF1 and MDBK cells infected with rLaSota/gDFL and rLaSota/gDF viruses was analyzed by indirect immunofluorescence using a pool of gD-specific monoclonal antibodies. Intracellular expression was investigated in cells that were fixed and permeabilized with Triton X-100 detergent. This showed that gD was expressed efficiently in the cytoplasm of both of the cell lines by rLaSota/gDFL and rLaSota/gDF viruses at 24 h post-infection (Fig. 2, panels b, c, e and f). We were not able to perform Western blot analysis with the gD specific monoclonal antibodies as these antibodies recognize only conformationally dependent epitopes.