Siba K. Samal

[This corrects the article DOI: 10.1371/journal.pone.0052751.].

Avian paramyxoviruses (APMVs) have gained a great attention to be developed as vaccine vectors against human and veterinary pathogens. Avirulent APMVs are highly safe to be used as vaccine vectors for avian and non-avian species. APMV vectored vaccines induce robust cellular and humoral immune responses in a broad range of hosts. APMV vectors can be a good platform by facilitating rapid generation of vaccines against emerging pathogens. In this chapter, we discuss application of reverse genetics of APMVs for vaccine development, design of APMV vectored vaccines, cloning of protective antigen(s) into a vector, recovery of vectored vaccines and characterization of generated vaccine viruses.

Fc effector functions and antibody specificity, rather than IgG or neutralizing titers, may serve as protective correlates for Ebola vaccines.

A reverse genetic system for avian paramyxovirus type-3 (APMV-3) strain Wisconsin was created and the infectious virus was recovered from a plasmid-based viral antigenomic cDNA. Green fluorescent protein (GFP) gene was cloned into the recombinant APMV-3 genome as a foreign gene. Stable expression of GFP by the recovered virus was confirmed for at least 10 consecutive passages. APMV-3 strain Wisconsin was evaluated against APMV-3 strain Netherlands and APMV-1 strain LaSota as a vaccine vector. The three viral vectors expressing GFP as a foreign protein were compared for level of GFP expression level, growth rate in chicken embryo fibroblast (DF-1) cells, and tissue distribution and immunogenicity in specific pathogen-free (SPF) day-old chickens. APMV-3 strain Netherlands showed highest growth rate and GFP expression level among the three APMV vectors in vitro. APMV-3 strain Wisconsin and APMV-1 strain LaSota vectors were mainly confined to the trachea after vaccination of day-old SPF chickens without any observable pathogenicity, whereas APMV-3 strain Netherlands showed wide tissue distribution in different body organs (brain, lungs, trachea, and spleen) with mild observable pathogenicity. In terms of immunogenicity, both APMV-3 strain-vaccinated groups showed HI titers two to three fold higher than that induced by APMV-1 strain LaSota vaccinated group. This study offers a novel paramyxovirus vector (APMV-3 strain Wisconsin) which can be used safely for vaccination of young chickens as an alternative for APMV-1 strain LaSota vector.

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in more than 16 million infections and more than 600,000 deaths worldwide. There is an urgent need to develop a safe and effective vaccine against SARS-CoV-2. Currently, several strategies are being pursued to develop a safe and effective SARS-CoV-2 vaccine. However, each vaccine strategy has distinct advantages and disadvantages. Therefore, it is important to evaluate multiple vaccine platforms to select the most efficient vaccine platform for SARS-CoV-2. In this regard, Newcastle disease virus (NDV), an avian virus, has several well-suited properties for development of a vector vaccine against SARS-CoV-2. Here, we elaborate on the idea of considering NDV as a vaccine vector for SARS-CoV-2.

Viral vectored vaccines are desirable alternatives for conventional infectious bronchitis virus (IBV) vaccines. We have recently shown that a recombinant Newcastle disease virus (rNDV) strain LaSota expressing the spike (S) protein of IBV strain Mass-41 (rLaSota/IBV-S) was a promising vaccine candidate for IBV. Here we evaluated a novel chimeric rNDV/avian paramyxovirus serotype 2 (rNDV/APMV-2) as a vaccine vector against IBV. The rNDV/APMV-2 vector was chosen because it is much safer than the rNDV strain LaSota vector, particularly for young chicks and chicken embryos. In order to determine the effectiveness of this vector, a recombinant rNDV/APMV-2 expressing the S protein of IBV strain Mass-41 (rNDV/APMV-2/IBV-S) was constructed. The protective efficacy of this vector vaccine was compared to that of the rNDV vector vaccine. In one study, groups of one-day-old specific-pathogenic-free (SPF) chickens were immunized with rLaSota/IBV-S and rNDV/APMV-2/IBV-S and challenged four weeks later with the homologous highly virulent IBV strain Mass-41. In another study, groups of broiler chickens were single (at day one or three weeks of age) or prime-boost (prime at day one and boost at three weeks of age) immunized with rLaSota/IBV-S and/or rNDV-APMV-2/IBV-S. At weeks six of age, chickens were challenged with a highly virulent IBV strain Mass-41. Our challenge study showed that novel rNDV/APMV-2/IBV-S provided similar protection as rLaSota/IBV-S in SPF chickens. However, compared to prime-boost immunization of chickens with chimeric rNDV/APMV-2, rLaSota/IBV-S and/or a live IBV vaccine, single immunization of chickens with rLaSota/IBV-S, or live IBV vaccine provided better protection against IBV. In conclusion, we have developed the novel rNDV/APMV-2 vector expressing S protein of IBV that can be a safer vaccine against IB in chickens. Our results also suggest a single immunization with a LaSota vectored IBV vaccine candidate provides better protection than prime-boost immunization regimens.

Highly pathogenic avian influenza virus (HPAIV) subtype H5N1 causes a devastating disease in poultry. Vaccination is an effective method of controlling avian influenza virus (AIV) infection in poultry. The hemagglutinin (HA) protein is the major determinant recognized by the immune system of the host. Cleavage of the HA precursor HA0 into HA1 and HA2 subunits is required for infectivity of the AIV. We evaluated the individual contributions of HA1 and HA2 subunits to the induction of HPAIV serum neutralizing antibodies and protective immunity in chickens. Using reverse genetics, recombinant Newcastle disease viruses (rNDVs) were generated, each expressing HA1, HA2, or HA protein of H5N1 HPAIV. Chickens were immunized with rNDVs expressing HA1, HA2, or HA. Immunization with HA induced high titers of serum neutralizing antibodies and prevented death following challenge. Immunization with HA1 or HA2 alone neither induced serum neutralizing antibodies nor prevented death following challenge. Our results suggest that interaction of HA1 and HA2 subunits is necessary for the display of epitopes on HA protein involved in the induction of neutralizing antibodies and protection. These epitopes are lost when the two subunits are separated. Therefore, vaccination with either a HA1 or HA2 subunit may not provide protection against HPAIV.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.