Recombinant rabies virus expressing IL-21 enhances immunogenicity through activation of T follicular helper cells and germinal centre B cells

Over-expression of IL-33 enhances rabies virus early antigen presentations and cellular immune responses in mice

Human inactivated rabies virus (RABV) vaccines have been widely used worldwide over 30 years. The mechanisms of humoral immunity elicited by previously reported rabies candidate vaccines have been fully investigated, but little is known about the cellular immunity profiles. Herein, the recombinant RABV rLBNSE-IL-33 overexpressing the mouse interleukin-33 (IL-33) proliferated well in Neuro-2a cells and had no effects with the parent virus on growth kinetic in vitro and viral pathogenicity in mice. The rLBNSE-IL-33 experienced more antigen presentations by MHC-II on DCs and activated more CD4+ T cells which helped recruit more CD19+CD40+ B cells in blood and promote rapid and robust IgG1 antibodies responses at initial infection stage compared with the parent rLBNSE strain. Simultaneously, the rLBNSE-IL-33 were also presented by MHC-I to CD8+ T cells which contributed to produce high levels of IgG2a. The rLBNSE-IL-33 elicited significantly high levels of RABV-specific IFN-γ secreting memory CD4+ T cells, more RABV-specific IL-4 and IFN-γ secreting memory CD8+ T cells in spleens at early infection stage in mice. Altogether, overexpression of IL-33 in rLBNSE-IL-33 enhanced early antigen presentation, markedly promote CD4+, memory CD4+ and CD8+ T cells-mediated responses and provided a 100 % protection from lethal RABV challenge in mice. These findings provided an alternative novel therapy and vaccine strategy in future.

A recombinant rabies virus chimera expressing the DC-targeting molecular MAB2560 shows enhanced vaccine immunogenicity through activation of dendritic cells

BACKGROUND

Rabies, caused by the rabies virus (RABV), is an ancient and neglected zoonotic disease posing a large public health threat to humans and animals in developing countries. Immunization of animals with a rabies vaccine is the most effective way to control the epidemic and the occurrence of the disease in humans. Therefore, the development of cost-effective and efficient rabies vaccines is urgently needed. The activation of dendritic cells (DCs) is known to play an important role in improving the host immune response induced by rabies vaccines.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we constructed a recombinant virus, rCVS11-MAB2560, based on the reverse genetic system of the RABV CVS11 strain. The MAB2560 protein (a DC-targeting molecular) was chimeric expressed on the surface of the viral particles to help target and activate the DCs when this virus was used as inactivated vaccine. Our results demonstrated that inactivated rCVS11-MAB2560 was able to promote the recruitment and/or proliferation of DC cells, T cells and B cells in mice, and induce good immune memory after two immunizations. Moreover, the inactivated recombinant virus rCVS11-MAB2560 could produce higher levels of virus-neutralizing antibodies (VNAs) in both mice and dogs more quickly than rCVS11 post immunization.

CONCLUSIONS/SIGNIFICANCE

In summary, the recombinant virus rCVS11-MAB2560 chimeric-expressing the molecular adjuvant MAB2560 can stimulate high levels of humoral and cellular immune responses in vivo and can be used as an effective inactivated rabies vaccine candidate.

Interleukin-25 enhances humoral immune responses caused by the rabies virus

Rabies is an important zoonotic disease caused by the rabies virus (RABV). Currently, no effective treatment is available for this condition. The prevention and control of rabies mainly depend on effective vaccination. Therefore, it is crucial to enhance the immune responses induced by the rabies vaccine. Virus neutralizing antibodies (VNA) induced by rabies vaccines are important for the clearance of RABV. Interleukin-25 (IL-25) has been demonstrated to activate T helper type 2 cells that contribute to humoral immune responses. The IL-25 gene was inserted into the genome of RABV, and the immunogenicity of recombinant RABV with IL-25 gene was investigated to develop more efficient rabies vaccines. Here, we found that the expression of IL-25 did not affect RABV production in vitro and pathogenicity in vivo. However, recombinant RABV expression of IL-25 induced a better VNA level than the parental virus in mice. In addition, expression of IL-25 enhanced the IgG1 level induced by RABV. Furthermore, mice immunized with recombinant RABV showed a higher survival rate and milder clinical signs than those immunized with the parent strain after challenge with CVS-11. Thus, these results showed that IL-25 could enhance the humoral immune responses induced by RABV, suggesting that IL-25 can be used as a viral vaccine adjuvant.

Enhancement of live vaccines by co-delivery of immune modulating proteins

Vaccines are very effective in providing protection against many infectious diseases. However, it has proven difficult to develop highly efficacious vaccines against some pathogens and so there is a continuing need to improve vaccine technologies. The first successful and widely used vaccines were based on attenuated pathogens (e.g., laboratory passaged Pasteurella multocida to vaccinate against fowl cholera) or closely related non-pathogenic organisms (e.g., cowpox to vaccinate against smallpox). Subsequently, live vaccines, either attenuated pathogens or non-pathogenic microorganisms modified to deliver heterologous antigens, have been successfully used to induce protective immune responses against many pathogens. Unlike conventional killed and subunit vaccines, live vaccines can deliver antigens to mucosal surfaces in a similar manner and context as the natural infection and hence can often produce a more appropriate and protective immune response. Despite these advantages, there is still a need to improve the immunogenicity of some live vaccines. The efficacy of injectable killed and subunit vaccines is usually enhanced using adjuvants such mineral salts, oils, and saponin, but such adjuvants cannot be used with live vaccines. Instead, live vaccines can be engineered to produce immunomodulatory molecules that can stimulate the immune system to induce more robust and long-lasting adaptive immune responses. This review focuses on research that has been undertaken to engineer live vaccines to produce immunomodulatory molecules that act as adjuvants to increase immunogenicity. Adjuvant strategies with varying mechanisms of action (inflammatory, antibody-mediated, cell-mediated) and delivery modes (oral, intramuscular, intranasal) have been investigated, with varying degrees of success. The goal of such research is to define adjuvant strategies that can be adapted to enhance live vaccine efficacy by triggering strong innate and adaptive immune responses and produce vaccines against a wider range of pathogens.

Overexpression of Interleukin-33 in Recombinant Rabies Virus Enhances Innate and Humoral Immune Responses through Activation of Dendritic Cell-Germinal Center Reactions

Rabies is a zoonotic infectious disease caused by rabies virus (RABV), and its mortality rate is as high as 100%. Globally, an average of 60,000 people die from rabies each year. The most effective method to prevent and limit rabies is vaccination, but it is currently expensive and inefficient, consisting of a 3-dose series of injections and requiring to be immunized annually. Therefore, it is urgent to develop a single dose of long-acting rabies vaccine. In this study, recombinant rabies virus (rRABV) overexpressing interleukin-33 (IL-33) was constructed and designated as rLBNSE-IL33, and its effect was evaluated in a mouse model. The results showed that rLBNSE-IL33 could enhance the quick production of RABV-induced immune antibodies as early as three days post immunization (dpi) through the activation of dendritic cells (DCs), a component of the innate immune system. Furthermore, rLBNSE-IL33 induced high-level virus-neutralizing antibodies (VNA) production that persisted for 8 weeks by regulating the T cell-dependent germinal center (GC) reaction, thus resulting in better protection against rabies. Our data suggest the IL-33 is a novel adjuvant that could be used to enhance innate and humoral immune responses by activating the DC-GC reaction, and thus, rLBNSE-IL33 could be developed as a safe and effective vaccine for animals.

Research Advances on the Interactions between Rabies Virus Structural Proteins and Host Target Cells: Accrued Knowledge from the Application of Reverse Genetics Systems

Rabies is a lethal zoonotic disease caused by lyssaviruses, such as rabies virus (RABV), that results in nearly 100% mortality once clinical symptoms appear. There are no curable drugs available yet. RABV contains five structural proteins that play an important role in viral replication, transcription, infection, and immune escape mechanisms. In the past decade, progress has been made in research on the pathogenicity of RABV, which plays an important role in the creation of new recombinant RABV vaccines by reverse genetic manipulation. Here, we review the latest advances on the interaction between RABV proteins in the infected host and the applied development of rabies vaccines by using a fully operational RABV reverse genetics system. This article provides a background for more in-depth research on the pathogenic mechanism of RABV and the development of therapeutic drugs and new biologics.

Lactobacillus plantarum surface-displayed ASFV (p54) with porcine IL-21 generally stimulates protective immune responses in mice

African classical swine fever virus (ASFV) has spread seriously around the world and has dealt with a heavy blow to the pig breeding industry due to the lack of vaccines. In this study, we produced recombinant Lactobacillus plantarum (L. plantarum) expressing an ASFV p54 and porcine IL-21 (pIL-21) fusion protein and evaluated the immune effect of NC8-pSIP409-pgsA'-p54-pIL-21 in a mouse model. First, we verified that the ASFV p54 protein and p54-pIL-21 fusion protein were anchored on the surface of L. plantarum NC8 by flow cytometry, immunofluorescence and Western blotting. Then, the results were verified by flow cytometry, ELISA and MTT assays. Mouse-specific humoral immunity and mucosal and T cell-mediated immune responses were induced by recombinant L. plantarum. The results of feeding mice recombinant L. plantarum showed that the levels of serum IgG and mucosal secreted IgA (SIgA), the number of CD4 and CD8 T cells, and the expression of IFN-γ in CD4 and CD8 T cells increased significantly, and lymphocyte proliferation occurred under stimulation with the ASFV p54 protein. Our data lay a foundation for the development of oral vaccines against ASFV in the future.

Composition of the murine gut microbiome impacts humoral immunity induced by rabies vaccines

BACKGROUND

Gut microbiome plays a crucial role in modulating human and animal immune responses. Rabies is a fatal zoonosis causing encephalitis in mammals and vaccination is the most effective method to control and eliminate rabies. The relationship between the gut microbiome and humoral immunity post rabies vaccination has not been investigated yet.

METHODS

Mice orally administrated with a cocktail of broad-spectrum antibiotics were inoculated with rabies vaccines, and humoral immune response was analyzed at indicated time points. The 16S ribosomal RNA (16S rRNA) gene sequencing was performed on fecal samples from groups in vancomycin-treated and untreated mice. Mice were immunized with rabies vaccines and virus-neutralizing antibody (VNA) levels were measured, resulting in VNA high (H) and low (L) groups. Then 16S rRNA gene sequencing was performed on fecal samples from H and L group mice.

RESULTS

After antibiotic (Abx) treatment, mice had decreased levels of rabies virus (RABV)-specific IgM, IgG, and virus-neutralizing antibody compared with untreated mice. Abx-treated mice had fewer T follicular helper cells, germinal center B cells, and antibody secreting cells (ASCs) in lymph nodes than did untreated mice. Gut microbiome facilitated secondary immune responses by increasing the generation of ASCs. Treatment with vancomycin alone had a similarly impaired effect on the humoral immune responses compared with Abx-treated mice. From the natural population group of mice received rabies vaccines, VNA titers vary significantly and the abundance of Clostridiales and Lachnospiraceae was positively associated with the antibody titers in mice.

CONCLUSIONS

Our results provide the evidence that the gut microbiome impacts humoral immunity post rabies vaccination, and further investigation of the mechanism will help the development of novel adjuvants and vaccines.

Trying to treat the untreatable: experimental approaches to clear rabies virus infection from the CNS

Rabies virus causes an invariably fatal encephalitis following the onset of clinical disease. Despite the availability of safe and effective vaccines, the clinical stages of rabies encephalitis remain untreatable, with few survivors being documented. A principal obstacle to the treatment of rabies is the neurotropic nature of the virus, with the blood-brain barrier size exclusion limit rendering the delivery of antiviral drugs and molecules to the central nervous system inherently problematic. This review focuses on efforts to try and overcome barriers to molecule delivery to treat clinical rabies and overviews current progress in the development of experimental live rabies virus vaccines that may have future applications in the treatment of clinical rabies, including the attenuation of rabies virus vectors through either the duplication or mutation of existing genes or the incorporation of non-viral elements within the genome. Rabies post-infection treatment (PIT) remains the holy grail of rabies research.

Toll-Like Receptor 7 Enhances Rabies Virus-Induced Humoral Immunity by Facilitating the Formation of Germinal Centers

Rabies virus (RABV) causes fatal encephalitis in mammals and poses a public health threat in many parts of the world. Vaccination remains the most effective means for prevention and control of rabies. Studies focusing on the mechanism of RABV immunogenicity are necessary for improvement of rabies vaccines. Toll-like receptor 7 (TLR7), an innate receptor sensing single-stranded viral RNA, is important for the induction of innate and adaptive immunity. Our studies revealed that the absence of TLR7 led to a lower antibody production in mice immunized with RABV. It is further found that TLR7 deficiency affected the recruitment of germinal center (GC) B cells and led to lessened GCs formation. Consistently, there were less plasma cells (PCs) and antibody secreting cells (ASC) in TLR7^-/- mice than those in wild type (WT) mice, resulting in impaired production of RABV-neutralizing antibodies (VNA). TLR7 deficiency also impaired the generation of memory B cells (MBCs) and the induction of secondary immune responses. Moreover, TLR7 deficiency down-regulated the induction of some cytokines/chemokines, especially IFN-γ, resulting in a Th2-biased antibody production. Overall, our results suggest that TLR7 facilitates the induction of the humoral immunity in response to RABV.

Recombinant rabies virus expressing IL-15 enhances immunogenicity through promoting the activation of dendritic cells in mice

Rabies remains a public health threat that kills approximately 59,000 people worldwide each year, most of which are from the developing countries of Africa and Asia where dog rabies are endemic. Therefore, developing an affordable and efficacious vaccine is crucial for rabies control in these countries. Interleukin (IL)-15, an immunoregulatory cytokine, is a pluripotent molecule with therapeutic potential, which targets many cell types and links the innate and adaptive immune system. In this study, IL-15 gene was cloned and inserted into the genome of a recombinant rabies virus (RABV) strain LBNSE (designated as LBNSE-IL15), and the effect of over-expression of IL-15 on the immunogenicity of RABV was investigated. It was found that mice vaccinated with LBNSE-IL15 could induce significantly higher level of virus-neutralizing antibody (VNA) than those immunized with LBNSE, resulting in the higher protection after challenge. Further investigation was performed to find out the possible role of IL-15 plays in the process of antibody induction, and it was found that LBNSE-IL15 could enhance the maturation of dendritic cells (DCs) in immunized mice. Furthermore, the mice immunized with LBNSE-IL15 could promote the T_FH cells differentiation and the generation of germinal center B cells and plasma cells. Together, these data indicated that IL-15 could be a potential adjuvant in enhancing the immunogenicity of RABV, contributing to the development of more-efficacious rabies vaccines.

Immunological aspects of rabies: a literature review

Rabies is a lethal disease caused by the neurotropic virus rabies virus (RABV), and it remains an important public health problem globally. It is known that the host immune response is important for control of viral infection and promoting viral clearance. In this context, it is well documented that, in addition to RABV neutralizing antibody, interferons and cell-mediated immunity also have an important role in preventing the establishment of disease. On the other hand, RABV suppresses host immunity through different mechanisms, for example, direct inhibition of host gene expression, sequestration of pathogen-associated molecular patterns, or modification of cytokine signalling pathways, which hinder the protective host immune responses to RABV infection. Here, we review the immunological aspects of rabies, highlighting innate and adaptive immunity, as well as the host evasion immune mechanisms used by the virus. Finally, we briefly discuss how this knowledge can direct new research and be harnessed for future therapeutic strategies.