Recombinant measles virus incorporating heterologous viral membrane proteins for use as vaccines

La Sota-vectored recombinant vaccine with chimeric hemagglutinin-neuraminidase for enhanced protection against highly pathogenic pigeon paramyxovirus type 1

Pigeon Paramyxovirus Type 1 (PPMV-1), an antigenic and host variant of the Newcastle Disease Virus (NDV), can infect pigeons of all ages and cause severe economic losses in the poultry industry. The existing commercial vaccines are not capable of providing complete protection against the prevalent PPMV-1 strains. To address this issue, reverse genetic technology was employed to create a recombinant 167DM strain by incorporating the chimeric genotype Ⅵ hemagglutinin-neuraminidase (HN) with La Sota as the backbone. The optimal anti-PPMV-1 vaccine candidate was identified through a systematical comparison of biological characteristics and immune efficacy of the predominant PPMV-1 epidemic strain, the 167DM strain, and the La Sota strain. Results indicated that the 167DM strain exhibited the highest culture titers in allantoic fluid and the strongest heat resistance. The antibody titers in the 167DM vaccine group consistently surpassed those in other groups tested. Cross-hemagglutination inhibition (HI) tests revealed no detectable antigenic differences between the 167DM and the prevalent PPMV-1 strain. Furthermore, the 167DM strain conferred 100% protection by preventing PPMV-1 infection and completely inhibiting virus shedding. These findings provide valuable insights for the development of a novel vaccine targeting ND in pigeons, thus laying a foundation for further advancements in vaccine development within this avian population.

A protective measles virus-derived vaccine inducing long-lasting immune responses against influenza A virus H7N9

A novel Influenza A virus (subtype H7N9) emerged in spring 2013 and caused considerable mortality in zoonotically infected patients. To be prepared for potential pandemics, broadly effective and safe vaccines are crucial. Recombinant measles virus (MeV) encoding antigens of foreign pathogens constitutes a promising vector platform to generate novel vaccines. To characterize the efficacy of H7N9 antigens in a prototypic vaccine platform technology, we generated MeVs encoding either neuraminidase (N9) or hemagglutinin (H7). Moraten vaccine strain-derived vaccine candidates were rescued; they replicated with efficiency comparable to that of the measles vaccine, robustly expressed H7 and N9, and were genetically stable over 10 passages. Immunization of MeV-susceptible mice triggered the production of antibodies against H7 and N9, including hemagglutination-inhibiting and neutralizing antibodies induced by MV_vac2-H7(P) and neuraminidase-inhibiting antibodies by MV_vac2-N9(P). Vaccinated mice also developed long-lasting H7- and N9-specific T cells. Both MV_vac2-H7(P) and MV_vac2-N9(P)-vaccinated mice were protected from lethal H7N9 challenge.

Versatility of live-attenuated measles viruses as platform technology for recombinant vaccines

Live-attenuated measles virus (MeV) has been extraordinarily effective in preventing measles infections and their often deadly sequelae, accompanied by remarkable safety and stability since their first licensing in 1963. The advent of recombinant DNA technologies, combined with systems to generate infectious negative-strand RNA viruses on the basis of viral genomes encoded on plasmid DNA in the 1990s, paved the way to generate recombinant, vaccine strain-derived MeVs. These live-attenuated vaccine constructs can encode and express additional foreign antigens during transient virus replication following immunization. Effective humoral and cellular immune responses are induced not only against the MeV vector, but also against the foreign antigen cargo in immunized individuals, which can protect against the associated pathogen. This review aims to present an overview of the versatility of this vaccine vector as platform technology to target various diseases, as well as current research and developmental stages, with one vaccine candidate ready to enter phase III clinical trials to gain marketing authorization, MV-CHIK.

A safe and highly efficacious measles virus-based vaccine expressing SARS-CoV-2 stabilized prefusion spike

Measles virus (MeV) vaccine is one of the safest and most efficient vaccines with a track record in children. Here, we generated a panel of rMeV-based vaccines with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) S antigens inserted near 3′ of the MeV genome. The rMeV expressing a soluble stabilized, prefusion spike (preS) is much more potent in triggering SARS-CoV-2–specific neutralizing antibody than rMeV-based full-length S vaccine candidate. A single dose of rMeV-preS is sufficient to induce high levels of SARS-CoV-2 antibody in animals. Furthermore, rMeV-preS induces high levels of Th1-biased immunity. Hamsters immunized with rMeV-preS were completely protected against SARS-CoV-2 challenge. Our results demonstrate rMeV-preS is a safe and highly efficacious bivalent vaccine candidate for SARS-CoV-2 and MeV.

The current pandemic of COVID-19 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) highlights an urgent need to develop a safe, efficacious, and durable vaccine. Using a measles virus (rMeV) vaccine strain as the backbone, we developed a series of recombinant attenuated vaccine candidates expressing various forms of the SARS-CoV-2 spike (S) protein and its receptor binding domain (RBD) and evaluated their efficacy in cotton rat, IFNAR^−/−mice, IFNAR^−/−-hCD46 mice, and golden Syrian hamsters. We found that rMeV expressing stabilized prefusion S protein (rMeV-preS) was more potent in inducing SARS-CoV-2–specific neutralizing antibodies than rMeV expressing full-length S protein (rMeV-S), while the rMeVs expressing different lengths of RBD (rMeV-RBD) were the least potent. Animals immunized with rMeV-preS produced higher levels of neutralizing antibody than found in convalescent sera from COVID-19 patients and a strong Th1-biased T cell response. The rMeV-preS also provided complete protection of hamsters from challenge with SARS-CoV-2, preventing replication in lungs and nasal turbinates, body weight loss, cytokine storm, and lung pathology. These data demonstrate that rMeV-preS is a safe and highly efficacious vaccine candidate, supporting its further development as a SARS-CoV-2 vaccine.

Chimeric Measles Virus (MV/RSV), Having Ectodomains of Respiratory Syncytial Virus (RSV) F and G Proteins Instead of Measles Envelope Proteins, Induced Protective Antibodies against RSV

In our previous study, fusion (F) or glyco (G) protein coding sequence of respiratory syncytial virus (RSV) was inserted at the P/M junction of the measles AIK-C vector (MVAIK), and the recombinant measles virus induced protective immune responses. In the present study, the ectodomains of measles fusion (F) and hemagglutinin (HA) proteins were replaced with those of RSV F and G proteins, and a chimeric MV/RSV vaccine was developed. It expressed F and G proteins of RSV and induced cytopathic effect (CPE) in epithelial cell lines (Vero, A549, and HEp-2 cells), but not in lymphoid cell lines (B95a, Jurkat, and U937 cells). A chimeric MV/RSV grew similarly to AIK-C with no virus growth at 39 °C. It induced NT antibodies against RSV in cotton rats three weeks after immunization through intramuscular route and enhanced response was observed after the second dose at eight weeks. After the RSV challenge with 10⁶ PFU, significantly lower virus (10^1.4±0.1 PFU of RSV) was recovered from lung tissue in the chimeric MV/RSV vaccine group than in the MVAIK control group with 10^4.6±0.2 PFU (p < 0.001) and no obvious inflammatory pathological finding was noted. The strategy of ectodomain replacement in the measles virus vector is expected to lead to the development of safe and effective vaccines for other enveloped viruses.

Tricistronic Plasmid Expressing the T7 RNA Polymerase and Measles Virus N and P Proteins for Rescue of Measles Virus AIK-C Strain

: Up to now, several attenuated measles virus vaccine strains derived from the Edmonston B vaccine consisting of Schwarz/Moraten, Zagreb, and AIK-C have been introduced for the rescue of their relative viruses through reverse genetics. In most studies, the measles virus rescue was done by supplying a cell line that expresses T7 RNA polymerase and measles virus N and P proteins as accessory proteins. The present study aimed to evaluate the rescue efficiency of the recombinant measles virus AIK-C vaccine strain by using a tricistronic expression plasmid. In this study, the rescue of the recombinant measles virus AIK-C vaccine strain was performed by co-transfection of three plasmids, including the cloned antigenomic cDNA of measles virus, a tricistronic expression plasmid that contained T7 RNA polymerase and measles virus N and P genes, and measles virus L polymerase expression plasmid. To increase the rescue efficiency, the transfected HEK-293 cells were co-cultured with Vero cells. As a result, the use of tricistronic expression plasmid that concomitantly encoded three necessary genes for the rescue of the measles virus led to the viral cytopathic effect with high efficacy five days post-transfection. Finally, the co-culture of transfected HEK-293 cells with Vero cells showed a relatively fast induction of viral cytopathic effect.

Measles-vectored vaccine approaches against viral infections: a focus on Chikungunya

INTRODUCTION

The large global burden of viral infections and especially the rapidly spreading vector-borne diseases and other emerging viral diseases show the need for new approaches in vaccine development. Several new vaccine technology platforms have been developed and are under evaluation. Areas covered: This article discusses the measles vector platform technology derived from the safe and highly efficacious measles virus vaccine. The pipeline of measles-vectored vaccine candidates against viral diseases is reviewed. Particular focus is given to the Chikungunya vaccine candidate as the first measles-vectored vaccine that demonstrated safety, immunogenicity, and functionality of the technology in humans even in the presence of pre-existing anti-measles immunity and thus achieved proof of concept for the technology. Expert commentary: Demonstrating no impact of pre-existing anti-measles immunity in humans on the response to the transgene was fundamental for the technology and indicates that the technology is suitable for large-scale immunization in measles pre-immune populations. The proof of concept in humans combined with a large preclinical track record of safety, immunogenicity, and efficacy for a variety of pathogens suggest the measles vector platform as promising plug-and-play vaccine platform technology for rapid development of effective preventive vaccines against viral and other infectious diseases.

Vaccine platform recombinant measles virus

The classic development of vaccines is lengthy, tedious, and may not necessarily be successful as demonstrated by the case of HIV. This is especially a problem for emerging pathogens that are newly introduced into the human population and carry the inherent risk of pandemic spread in a naïve population. For such situations, a considerable number of different platform technologies are under development. These are also under development for pathogens, where directly derived vaccines are regarded as too complicated or even dangerous due to the induction of inefficient or unwanted immune responses causing considerable side-effects as for dengue virus. Among platform technologies are plasmid-based DNA vaccines, RNA replicons, single-round infectious vector particles, or replicating vaccine-based vectors encoding (a) critical antigen(s) of the target pathogens. Among the latter, recombinant measles viruses derived from vaccine strains have been tested. Measles vaccines are among the most effective and safest life-attenuated vaccines known. Therefore, the development of Schwarz-, Moraten-, or AIK-C-strain derived recombinant vaccines against a wide range of mostly viral, but also bacterial pathogens was quite straightforward. These vaccines generally induce powerful humoral and cellular immune responses in appropriate animal models, i.e., transgenic mice or non-human primates. Also in the recent first clinical phase I trial, the results have been quite encouraging. The trial indicated the expected safety and efficacy also in human patients, interestingly independent from the level of prevalent anti-measles immunity before the trial. Thereby, recombinant measles vaccines expressing additional antigens are a promising platform for future vaccines.

Avian Paramyxovirus Type-3 as a Vaccine Vector: Identification of a Genome Location for High Level Expression of a Foreign Gene

Avian paramyxovirus serotype 3 (APMV-3) causes infection in a wide variety of avian species, but it does not cause apparent diseases in chickens. On the contrary, APMV-1, also known as Newcastle disease virus (NDV), can cause severe disease in chickens. Currently, natural low virulence strains of NDV are used as live-attenuated vaccines throughout the world. NDV is also being evaluated as a vaccine vector against poultry pathogens. However, due to routine vaccination programs, chickens often possess pre-existing antibodies against NDV, which may cause the chickens to be less sensitive to recombinant NDV vaccines expressing antigens of other avian pathogens. Therefore, it may be possible for an APMV-3 vector vaccine to circumvent this issue. In this study, we determined the optimal insertion site in the genome of APMV-3 for high level expression of a foreign gene. We generated recombinant APMV-3 viruses expressing the green fluorescent protein (GFP) by inserting the GFP gene at five different intergenic regions in the genome. The levels of GFP transcription and translation were evaluated. Interestingly, the levels of GFP transcription and translation did not follow the 3′-to-5′ attenuation mechanism of non-segmented, negative-sense RNA viruses. The insertion of GFP gene into the P-M gene junction resulted in higher level of expression of GFP than when the gene was inserted into the upstream N-P gene junction. Unlike NDV, insertion of GFP did not attenuate the growth efficiency of AMPV-3. Thus, APMV-3 could be a more useful vaccine vector for avian pathogens than NDV.

Development of Recombinant Measles Virus-Based Vaccines

This chapter describes the development of recombinant measles virus (MV)-based vaccines starting from plasmid DNA. Live-attenuated measles vaccines are very efficient and safe. Since the availability of a reverse genetic system to manipulate MV genomes and to generate respective recombinant viruses, a considerable number of recombinant viruses has been generated that present antigens of foreign pathogens during MV replication. Thereby, robust humoral and cellular immune responses can be induced, which have shown protective capacity in a substantial number of experiments.For this purpose, the foreign antigen-encoding genes are cloned into additional transcription units of plasmid based full-length MV vaccine strain genomes, which in turn are used to rescue recombinant MV by providing both full-length viral RNA genomes respective anti-genomes together with all protein components of the viral ribonucleoprotein complex after transient transfection of the so-called rescue cells. Infectious centers form among these transfected cells, which allow clonal isolation of single recombinant viruses that are subsequently amplified, characterized in vitro, and then evaluated for their immunogenicity in appropriate preclinical animal models.

Replicon RNA Viral Vectors as Vaccines

Single-stranded RNA viruses of both positive and negative polarity have been used as vectors for vaccine development. In this context, alphaviruses, flaviviruses, measles virus and rhabdoviruses have been engineered for expression of surface protein genes and antigens. Administration of replicon RNA vectors has resulted in strong immune responses and generation of neutralizing antibodies in various animal models. Immunization of mice, chicken, pigs and primates with virus-like particles, naked RNA or layered DNA/RNA plasmids has provided protection against challenges with lethal doses of infectious agents and administered tumor cells. Both prophylactic and therapeutic efficacy has been achieved in cancer immunotherapy. Moreover, recombinant particles and replicon RNAs have been encapsulated by liposomes to improve delivery and targeting. Replicon RNA vectors have also been subjected to clinical trials. Overall, immunization with self-replicating RNA viruses provides high transient expression levels of antigens resulting in generation of neutralizing antibody responses and protection against lethal challenges under safe conditions.