Isolation of a novel insect-specific flavivirus with immunomodulatory effects in vertebrate systems

A Chimeric Classical Insect-Specific Flavivirus Provides Complete Protection Against West Nile Virus Lethal Challenge in Mice

West Nile virus (WNV), an arthropod-borne flavivirus, can cause severe symptoms, including encephalitis, and death, posing a threat to public health and the economy. However, there is still no approved treatment or vaccine available for humans. Here, we developed a novel vaccine platform based on a classical insect-specific flavivirus (cISF) YN15-283-02, which was derived from Culicoides. The cISF-WNV chimera was constructed by replacing prME structural genes of the infectious YN15-283-02 cDNA clone with those of WNV and successfully rescued in Aedes albopictus cells. cISF-WNV was nonreplicable in vertebrate cells and nonpathogenic in type I interferon receptor (IFNAR)-deficient mice. A single-dose immunization of cISF-WNV elicited considerable Th1-biased antibody responses in C57BL/6 mice, which was sufficient to offer complete protection against lethal WNV challenge with no symptoms. Our studies demonstrated the potential of the insect-specific cISF-WNV as a prophylactic vaccine candidate to prevent infection with WNV.

Development of flavivirus subviral particles with low cross-reactivity by mutations of a distinct antigenic domain

The most conserved fusion loop (FL) domain present in the flavivirus envelope protein has been reported as a dominant epitope for cross-reactive antibodies to mosquito-borne flaviviruses (MBFVs). As a result, establishing accurate serodiagnosis for MBFV infections has been difficult as anti-FL antibodies are induced by both natural infection and following vaccination. In this study, we modified the most conserved FL domain to overcome this cross-reactivity. We showed that the FL domain of lineage I insect-specific flavivirus (ISFV) has differences in antigenicity from those of MBFVs and lineage II ISFV and determined the key amino acid residues (G106, L107, or F108), which contribute to the antigenic difference. These mutations were subsequently introduced into subviral particles (SVPs) of dengue virus type 2 (DENV2), Zika virus (ZIKV), Japanese encephalitis virus (JEV), and West Nile virus (WNV). In indirect enzyme-linked immunosorbent assays (ELISAs), these SVP mutants when used as antigens reduced the binding of cross-reactive IgG and total Ig induced by infection of ZIKV, JEV, and WNV in mice and enabled the sensitive detection of virus-specific antibodies. Furthermore, immunization of ZIKV or JEV SVP mutants provoked the production of antibodies with lower cross-reactivity to heterologous MBFV antigens compared to immunization with the wild-type SVPs in mice. This study highlights the effectiveness of introducing mutations in the FL domain in MBFV SVPs with lineage I ISFV-derived amino acids to produce SVP antigens with low cross-reactivity and demonstrates an improvement in the accuracy of indirect ELISA-based serodiagnosis for MBFV infections. KEY POINTS: • The FL domain of Lineage I ISFV has a different antigenicity from that of MBFVs. • Mutated SVPs reduce the binding of cross-reactive antibodies in indirect ELISAs. • Inoculation of mutated SVPs induces antibodies with low cross-reactivity.

Exploring the immunogenicity of an insect-specific virus vectored Zika vaccine candidate

Zika virus (ZIKV) is an important re-emerging flavivirus that presents a significant threat to human health worldwide. Despite its importance, no vaccines are approved for use in humans. Insect-specific flaviviruses (ISFVs) have recently garnered attention as an antigen presentation platform for vaccine development and diagnostic applications. Here, we further explore the safety, immunogenicity, and efficacy of a chimeric ISFV-Zika vaccine candidate, designated Aripo-Zika (ARPV/ZIKV). Our results show a near-linear relationship between increased dose and immunogenicity, with 1011 genome copies (i.e., 108 focus forming units) being the minimum dose required for protection from ZIKV-induced morbidity and mortality in mice. Including boosters did not significantly increase the short-term efficacy of ARPV/ZIKV-vaccinated mice. We also show that weanling mice derived from ARPV/ZIKV-vaccinated dams were completely protected from ZIKV-induced morbidity and mortality upon challenge, suggesting efficient transfer of maternally-derived protective antibodies. Finally, in vitro coinfection studies of ZIKV with Aripo virus (ARPV) and ARPV/ZIKV in African green monkey kidney cells (i.e., Vero-76) showed that ARPV and ARPV/ZIKV remain incapable of replication in vertebrate cells, despite the presence of active ZIKV replication. Altogether, our data continue to support ISFV-based vaccines, and specifically the ARPV backbone is a safe, immunogenic and effective vaccine strategy for flaviviruses.

Employing Oxford Nanopore Technologies (ONT) for understanding the ecology and transmission dynamics of flaviviruses in mosquitoes (Diptera: Culicidae) from eastern Colombia

Studies focused on identifying the viral species of Flavivirus in vectors are scarce in Latin America and particularly in Colombia. Therefore, the frequency of infection of the Flavivirus genus and its feeding preferences were identified in the mosquito species circulating in the municipality of Puerto Carreño-Vichada, located in the Eastern Plains of Colombia. This was done by sequencing the viral NS5 and vertebrate 12S rRNA genes, respectively, using Oxford Nanopore Technologies (ONT). A total of 1,159 mosquitoes were captured, with the most abundant species being Aedes serratus at 73.6% (n=853). All the mosquitoes were processed in 230 pools (2-6 individuals) and 51 individuals, where 37.01% (n=104) were found to be infected with Flavivirus. In these samples, infection by arboviruses of epidemiological importance, such as dengue virus (DENV), Zika virus (ZIKV), and chikungunya virus (CHIKV), was ruled out by PCR. However, through sequencing, infection by different insect-specific viruses (ISFVs) and a medically important virus, West Nile virus (WNV), were identified in a mosquito of the Culex browni species. Additionally, the feeding patterns showed that most species present a generalist behavior. Given the above, conducting entomovirological surveillance studies is crucial, especially in areas of low anthropogenic intervention, due to the high probability that potentially pathogenic viruses could generate spillover events under deforestation scenarios.

Humoral and T-cell-mediated responses to a pre-clinical Zika vaccine candidate that utilizes a unique insect-specific flavivirus platform

Vaccination is critical for the control and prevention of viral outbreaks, yet conventional vaccine platforms may involve trade-offs between immunogenicity and safety. Insect-specific viruses have emerged as a novel vaccine platform to overcome this challenge. Detailed studies of humoral and T-cell responses induced by new insect-specific flavivirus (ISFV)-based vaccine platforms are needed to better understand correlates of protection and improve vaccine efficacy. Previously, we used a novel ISFV called Aripo virus (ARPV) to create a Zika virus (ZIKV) vaccine candidate (designated ARPV/ZIKV). ARPV/ZIKV demonstrated exceptional safety and single-dose efficacy, completely protecting mice from a lethal ZIKV challenge. Here, we explore the development of immune responses induced by ARPV/ZIKV immunization and evaluate its correlates of protection. Passive transfer of ARPV/ZIKV-induced immune sera to naïve mice prior to challenge emphasized the importance of neutralizing antibodies as a correlate of protection. Depletion of T-cells in vaccinated mice and adoptive transfer of ARPV/ZIKV-primed T-cells to naïve mice prior to challenge indicated that ARPV/ZIKV-induced CD4 + and CD8 + T-cell responses contribute to the observed protection but may not be essential for protection during ZIKV challenge. However, vaccination of Rag1 KO, Tcra KO, and muMt - mice demonstrated the critical role for ARPV/ZIKV-induced T-cells in developing protective immune responses following vaccination. Overall, both humoral and T-cell-mediated responses induced by ISFV-based vaccines are important for comprehensive immunity, and ISFV platforms continue to be a promising method for future vaccine development.

Phylogenetic characterization of Orthobunyaviruses isolated from Trinidad shows evidence of natural reassortment

The genus Orthobunyavirus is a diverse group of viruses in the family Peribunyaviridae, recently classified into 20 serogroups, and 103 virus species. Although most viruses within these serogroups are phylogenetically distinct, the absence of complete genome sequences has left several viruses incompletely characterized. Here we report the complete genome sequences for 11 orthobunyaviruses isolated from Trinidad, French Guiana, Guatemala, and Panama that were serologically classified into six serogroups and 10 species. Phylogenetic analyses of these 11 newly derived sequences indicate that viruses belonging to the Patois, Capim, Guama, and Group C serocomplexes all have a close genetic origin. We show that three of the 11 orthobunyaviruses characterized (belonging to the Group C and Bunyamwera serogroups) have evidence of histories of natural reassortment through the M genome segment. Our data also suggests that two distinct lineages of Group C viruses concurrently circulate in Trinidad and are transmitted by the same mosquito vectors. This study also highlights the importance of complementing serological identification with nucleotide sequencing when characterizing orthobunyaviruses.

Rational Development of Live-Attenuated Zika Virus Vaccines

Zika virus (ZIKV), a re-emerging mosquito-borne flavivirus, has caused outbreaks in Africa, Asia, the Pacific, and, more recently, in the Americas. ZIKV has been associated with the neurological autoimmune disorder Guillain-Barre syndrome in adults and congenital Zika syndrome in fetuses and infants, including microcephaly, spontaneous abortion, and intrauterine growth restriction. It is considered to be a major threat to global public health due to its unprecedented clinical impact on humans. Currently, there are no specific prophylactics or therapeutics available to prevent or treat ZIKV infection. The development of a safe and efficacious ZIKV vaccine remains a global health priority. Since the recent outbreak, multiple platforms have been used in the development of candidate ZIKV vaccines. The candidate vaccines have been shown to elicit strong T cell and neutralization antibody responses and protect against ZIKV infection in animal models. Some candidates have progressed successfully to clinical trials. Live-attenuated vaccines, which induce rapid and durable protective immunity, are one of the most important strategies for controlling flavivirus diseases. In this review, we discuss recent progress in the development of candidate live-attenuated ZIKV vaccines.

Jingmenviruses: Ubiquitous, understudied, segmented flavi-like viruses

Jingmenviruses are a group of viruses identified recently, in 2014, and currently classified by the International Committee on Taxonomy of Viruses as unclassified Flaviviridae. These viruses closely related to flaviviruses are unique due to the segmented nature of their genome. The prototype jingmenvirus, Jingmen tick virus (JMTV), was discovered in Rhipicephalus microplus ticks collected from China in 2010. Jingmenviruses genomes are composed of four to five segments, encoding for up to seven structural proteins and two non-structural proteins, both of which display strong similarities with flaviviral non-structural proteins (NS2B/NS3 and NS5). Jingmenviruses are currently separated into two phylogenetic clades. One clade includes tick- and vertebrate-associated jingmenviruses, which have been detected in ticks and mosquitoes, as well as in humans, cattle, monkeys, bats, rodents, sheep, and tortoises. In addition to these molecular and serological detections, over a hundred human patients tested positive for jingmenviruses after developing febrile illness and flu-like symptoms in China and Serbia. The second phylogenetic clade includes insect-associated jingmenvirus sequences, which have been detected in a wide range of insect species, as well as in crustaceans, plants, and fungi. In addition to being found in various types of hosts, jingmenviruses are endemic, as they have been detected in a wide range of environments, all over the world. Taken together, all of these elements show that jingmenviruses correspond exactly to the definition of emerging viruses at risk of causing a pandemic, since they are already endemic, have a close association with arthropods, are found in animals in close contact with humans, and have caused sporadic cases of febrile illness in multiple patients. Despite these arguments, the vast majority of published data is from metagenomics studies and many aspects of jingmenvirus replication remain to be elucidated, such as their tropism, cycle of transmission, structure, and mechanisms of replication and restriction or epidemiology. It is therefore crucial to prioritize jingmenvirus research in the years to come, to be prepared for their emergence as human or veterinary pathogens.

NLRX1 Deficiency Alters the Gut Microbiome and Is Further Exacerbated by Adherence to a Gluten-Free Diet

Patients with gluten sensitivities present with dysbiosis of the gut microbiome that is further exacerbated by a strict adherence to a gluten-free diet (GFD). A subtype of patients genetically susceptible to gluten sensitivities are Celiac Disease (CeD) patients, who are carriers of the HLA DR3/DQ2 or HLA DR4/DQ8 haplotypes. Although 85-95% of all CeD patients carry HLA DQ2, up to 25-50% of the world population carry this haplotype with only a minority developing CeD. This suggests that CeD and other gluten sensitivities are mediated by factors beyond genetics. The contribution of innate immune system signaling has been generally understudied in the context of gluten sensitivities. Thus, here we examined the role of NOD-like receptors (NLRs), a subtype of pattern recognition receptors, in maintaining the composition of the gut microbiome in animals maintained on a GFD. Human transcriptomics data revealed significant increases in the gene expression of multiple NLR family members, across functional groups, in patients with active CeD compared to control specimens. However, NLRX1 was uniquely down-regulated during active disease. NLRX1 is a negative regulatory NLR that functions to suppress inflammatory signaling and has been postulate to prevent inflammation-induced dysbiosis. Using Nlrx1^-/- mice maintained on either a normal or gluten-free diet, we show that loss of NLRX1 alters the microbiome composition, and a distinctive shift further ensues following adherence to a GFD, including a reciprocal loss of beneficial microbes and increase in opportunistic bacterial populations. Finally, we evaluated the functional impact of an altered gut microbiome by assessing short- and medium-chain fatty acid production. These studies revealed significant differences in a selection of metabolic markers that when paired with 16S rRNA sequencing data could reflect an overall imbalance and loss of immune system homeostasis in the gastrointestinal system.

Replication is the key barrier during the dual-host adaptation of mosquito-borne flaviviruses

Most viruses have a relatively narrow host range. In contrast, vector-borne flaviviruses, such as dengue virus and Zika virus, maintain their transmission cycle between arthropods and vertebrates, belonging to different phyla. How do these viruses adapt to the distinct cellular environments of two phyla? By comparing the single-host insect--specific flavivirus and dual-host Zika virus, we identified three key molecular factors that determine MBF host tropism. This study will greatly increase the understanding of entry, replication, and cross-species evolution of mosquito-borne flaviviruses.

Mosquito-borne flaviviruses (MBFs) adapt to a dual-host transmission circle between mosquitoes and vertebrates. Dual-host affiliated insect-specific flaviviruses (dISFs), discovered from mosquitoes, are phylogenetically similar to MBFs but do not infect vertebrates. Thus, dISF–MBF chimeras could be an ideal model to study the dual-host adaptation of MBFs. Using the pseudoinfectious reporter virus particle and reverse genetics systems, we found dISFs entered vertebrate cells as efficiently as the MBFs but failed to initiate replication. Exchange of the untranslational regions (UTRs) of Donggang virus (DONV), a dISF, with those from Zika virus (ZIKV) rescued DONV replication in vertebrate cells, and critical secondary RNA structures were further mapped. Essential UTR-binding host factors were screened for ZIKV replication in vertebrate cells, displaying different binding patterns. Therefore, our data demonstrate a post-entry cross-species transmission mechanism of MBFs, while UTR-host interaction is critical for dual-host adaptation.

The Chimeric Binjari-Zika Vaccine Provides Long-Term Protection against ZIKA Virus Challenge

We recently developed a chimeric flavivirus vaccine technology based on the novel insect-specific Binjari virus (BinJV) and used this to generate a chimeric ZIKV vaccine (BinJ/ZIKA-prME) that protected IFNAR-/- dams and fetuses from infection. Herein, we show that a single vaccination of IFNAR-/- mice with unadjuvanted BinJ/ZIKA-prME generated neutralizing antibody responses that were retained for 14 months. At 15 months post vaccination, mice were also completely protected against detectable viremia and substantial body weight loss after challenge with ZIKVPRVABC59. BinJ/ZIKA-prME vaccination thus provided long-term protective immunity without the need for adjuvant or replication of the vaccine in the vaccine recipient, both attractive features for a ZIKV vaccine.

Enemy of My Enemy: A Novel Insect-Specific Flavivirus Offers a Promising Platform for a Zika Virus Vaccine

Vaccination remains critical for viral disease outbreak prevention and control, but conventional vaccine development typically involves trade-offs between safety and immunogenicity. We used a recently discovered insect-specific flavivirus as a vector in order to develop an exceptionally safe, flavivirus vaccine candidate with single-dose efficacy. To evaluate the safety and efficacy of this platform, we created a chimeric Zika virus (ZIKV) vaccine candidate, designated Aripo/Zika virus (ARPV/ZIKV). ZIKV has caused immense economic and public health impacts throughout the Americas and remains a significant public health threat. ARPV/ZIKV vaccination showed exceptional safety due to ARPV/ZIKV’s inherent vertebrate host-restriction. ARPV/ZIKV showed no evidence of replication or translation in vitro and showed no hematological, histological or pathogenic effects in vivo. A single-dose immunization with ARPV/ZIKV induced rapid and robust neutralizing antibody and cellular responses, which offered complete protection against ZIKV-induced morbidity, mortality and in utero transmission in immune-competent and -compromised murine models. Splenocytes derived from vaccinated mice demonstrated significant CD4⁺ and CD8⁺ responses and significant cytokine production post-antigen exposure. Altogether, our results further support that chimeric insect-specific flaviviruses are a promising strategy to restrict flavivirus emergence via vaccine development.