Development of a Novel Nipah Virus Pre-Fusion Protein Recombinant Vaccine.

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Abstract Nipah virus (NiV) is a member of the Henipavirus genus (family Paramyxoviridae) and is the causative agent of sporadic outbreaks of respiratory and encephalitic disease in Southeast Asia. During the initial NiV outbreaks in Malaysia and Singapore, most human NiV cases were caused by close contact with pigs. In subsequent outbreaks during 2001 to 2012 in Bangladesh and India, drinking fresh date palm sap, which was contaminated by fruit bat’s droppings, urine and saliva, and close contact with infected humans were found to be the major source of NiV infection. However, pigs are highly susceptible to NiV and generally serve as an amplifying host of the virus. Due to the lethal nature of disease and potential risk of reversion of a live attenuated vaccine to wild-type is not advisable. Therefore, many candidate vaccine for NiV are 'recombinant', where NiV proteins are produced from inserted genes in another safer virus (referred to as the vector). The fusion (F) and (G) proteins of NiV are commonly chosen as they provide an effective immune response in the body. The G protein allows the virus to attach to the cell and the F protein causes fusion of the virus envelope with the cell membrane so that the virus nucelic acid can enter the cell. Recently it has been discovered for several other paramyxovirus that the form of the F protein in the mature virus (post fusion form) is not as good at inducing an immune response as the form of F which occurs when the virus is entering cells (pre-fusion form). The pre-fusion F protein is unstable but we are able to stabilise this by making slight sequence changes. We will use another ‘safe’ member of the Paramyxovirdae, Sendai virus (SeV, a rodent virus) as the vector. We will compare the immune response of the SeV vaccines which produce one of the 2 types of F protein alone or each in combination with the G protein. Increasing evidence indicates that SeV has substantial potential as a vaccine vector in part because the virus uses common sialic acid receptors for cell entry, which facilitates infection of a wide range of cell types from different species including pigs and humans. Although SeV biosafety risks are minimal, we will also develop the system to generate replication-incompetent SeV NiV vaccines that infect host cells and produce the NiV F and G proteins but removes any residual biosafety concerns of a live SeV vector spreading between animals or humans. We hypothesise that novel vaccine approach based on replication-competent and incompetent SeV vectors expressing pre-fusion NiV F protein will provide a significant breakthrough in the generation of highly successful NiV vaccines. We further hypothesise that NiV vaccines based on rSeV expressing pre-fusion NiV F will induce more robust and longer lasting protective immunity than post fusion F vaccines. Used as a pig vaccine these systems will greatly reduce porcine to human transmission. Futhermore, production of non-replicating SeV vaccines addresses biosafety. As Sev also infects human cells, these vaccines could be subsequently trialled for human use.