Ebola virus (EBOV) causes severe hemorrhagic fever in humans, with a case fatality rate of up to 90% [
1,
2]. Its high fatality rate and human-to-human spread renders the virus a potential bioterrorism weapon. Currently, there are no licensed vaccines or therapeutic regimens for the disease. A safe and efficient vaccine for EBOV is yet to be developed. EBOV is an enveloped single-stranded negative-sense RNA virus belonging to the family
Filoviridae[
3]. The envelope glycoprotein (GP) of EBOV is an important virulence factor and mediates cell receptor binding and virus–cell membrane fusion [
2,
4‐
10]. GP protein also plays a central role in inducing protective neutralizing antibodies in the host [
11,
12]. Several recombinant GP-expressing viruses have been developed, including replication-defective adenovirus-5 (rAd5) [
13,
14], replication-competent vesicular stomatitis virus (VSV) [
15,
16], Newcastle diseases virus (NDV)[
17], rabies virus (RV) [
18] and human parainfluenza virus type 3 (HPAIV) (Bukreyev et al., 2007).
Newcastle disease virus (NDV) is a member of the genus
Avulavirus of the family
Paramyxoviridae. NDV strains are classified as nonvirulent (lentogenic), moderately virulent (mesogenic), or highly virulent (velogenic) in poultry [
19]. NDV has two envelope glycoproteins, hemagglutinin-neuramidinase (HN) and fusion protein (F). HN functions sialic acid receptor binding and F induces fusion during cell entry of NDV [
20]. Viral virulence is mainly determined by the amino acid sequence at the protease cleavage site of theF precursor [
20]. Lentogenic strains contain fewer basic amino acids at this site and can only be cleaved by trypsin-like extracellular proteases, which are largely confined to the respiratory tract, whereas highly virulent strains are cleaved by ubiquitous intracellular proteases, potentially resulting in systemic infections [
21]. The attractions of NDV as a vaccine vector for emerging human infectious diseases include: preexisting immunity and maternal antibodies to mammalian paramyxoviruses do not interfere with the infection or replication of NDV because NDV is antigenically distinct from the mammalian paramyxoviruses [
22,
23]; lentogenic NDV usually shows limited replication in mammalian host cells because it requires a trypsin-like proteinase for the cleavage of the F glycoprotein [
20,
21,
24,
25]. Currently, lentogenic NDV strains, such as the LaSota strain, are used as live attenuated vaccines against NDV in poultry [
26] and have been actively developed and evaluated as vaccine vectors for the control of human and animal infectious diseases, including influenza [
27,
28], severe acute respiratory syndrome [
29], human parainfluenza [
30], highly pathogenic H5N1 [
13,
31,
32], human immunodeficiency virus [
33,
34], rabies [
35], Nipah disease [
36], and Rift Valley fever [
37]. The safety and efficacy of NDV has been demonstrated in mice [
32,
36], dogs [
35], pigs [
36], cattle [
38,
39], sheep [
37], African green and rhesus monkeys [
17,
30], and humans [
40‐
43]. Recently, a study by DiNapoli et al. showed that a recombinant NDV expressing EBOV GP was immunogenic and caused no abnormalities or disease symptoms after its inoculation into rhesus monkeys [
17]. Their study also showed that EBOV GP was incorporated into the recombinant NDV particles, which raised a serious question. Does EBOV GP function biologically normally in the virus particle during cell entry? If so, this entails biosafety concerns regarding the candidate vaccine vector.
In this study, we generated a recombinant lentogenic NDV, based on the LaSota strain, that expresses the EBOV GP protein. Its safety for poultry and mice in vivo, its infection and spreadability among cells in vitro, its sensitivity to anti-NDV and anti-EBOV neutralizing antibodies, and the internalization pathway of this recombinant virus were characterized.