Adjuvant effects of interleukin-2 co-expression with VP60 in an oral vaccine delivered by attenuated Salmonella typhimurium against rabbit hemorrhagic disease

Recent Advances in Oral Vaccines for Animals

Compared to traditional injected vaccines, oral vaccines offer significant advantages for the immunization of livestock and wildlife due to their ease of use, high compliance, improved safety, and potential to stimulate mucosal immune responses and induce systemic immunity against pathogens. This review provides an overview of the delivery methods for oral vaccines, and the factors that influence their immunogenicity. We also highlight the global progress and achievements in the development and use of oral vaccines for animals, shedding light on potential future applications in this field.

Characterisation of Lagovirus europaeus GI-RHDVs (Rabbit Haemorrhagic Disease Viruses) in Terms of Their Pathogenicity and Immunogenicity

Rabbit haemorrhagic disease viruses (RHDV) belong to the family Caliciviridae, genus Lagovirus europaeus, genogroup GI, comprising four genotypes GI.1-GI.4, of which the genotypes GI.1 and GI.2 are pathogenic RHD viruses, while the genotypes GI.3 and GI.4 are non-pathogenic RCV (Rabbit calicivirus) viruses. Among the pathogenic genotypes GI.1 and GI.2 of RHD viruses, an antigenic variant of RHDV, named RHDVa-now GI.1a-RHDVa, was distinguished in 1996; and in 2010, a variant of RHDV-named RHDVb, later RHDV2 and now GI.2-RHDV2/b-was described; and recombinants of these viruses were registered. Pathogenic viruses of the genotype GI.1 were the cause of a disease described in 1984 in China in domestic (Oryctolagus (O.) cuniculus domesticus) and wild (O. cuniculus) rabbits, characterised by a very rapid course and a mortality rate of 90-100%, which spread in countries all over the world and which has been defined since 1989 as rabbit haemorrhagic disease. It is now accepted that GI.1-RHDV, including GI.1a-RHDVa, cause the predetermined primary haemorrhagic disease in domestic and wild rabbits, while GI.2-RHDV2/b cause it not only in rabbits, including domestic rabbits' young up to 4 weeks and rabbits immunised with rabbit haemorrhagic disease vaccine, but also in five various species of wild rabbits and seven different species of hares, as well as wild ruminants: mountain muskoxen and European badger. Among these viruses, haemagglutination-positive, doubtful and harmful viruses have been recorded and described and have been shown to form phylogenogroups, immunotypes, haematotypes and pathotypes, which, together with traits that alter and expand their infectious spectrum (rabbit, hare, wild ruminant, badger and various rabbit and hare species), are the determinants of their pathogenicity (infectivity) and immunogenicity and thus shape their virulence. These relationships are the aim of our consideration in this article.

Promising Cytokine Adjuvants for Enhancing Tuberculosis Vaccine Immunity

Tuberculosis, caused by Mycobacterium tuberculosis (M. tuberculosis), remains a formidable global health challenge, affecting a substantial portion of the world's population. The current tuberculosis vaccine, bacille Calmette-Guérin (BCG), offers limited protection against pulmonary tuberculosis in adults, underscoring the critical need for innovative vaccination strategies. Cytokines are pivotal in modulating immune responses and have been explored as potential adjuvants to enhance vaccine efficacy. The strategic inclusion of cytokines as adjuvants in tuberculosis vaccines holds significant promise for augmenting vaccine-induced immune responses and strengthening protection against M. tuberculosis. This review delves into promising cytokines, such as Type I interferons (IFNs), Type II IFN, interleukins such as IL-2, IL-7, IL-15, IL-12, and IL-21, alongside the use of a granulocyte-macrophage colony-stimulating factor (GM-CSF) as an adjuvant, which has shown effectiveness in boosting immune responses and enhancing vaccine efficacy in tuberculosis models.

Immune synergistic mechanism of recombinant plasmid adjuvant containing chicken IL-4 and IL-2 fusion genes on chicken coccidia live vaccine

The recombinant plasmid pCI-IL-4-IL-2-EGFP containing fusion genes of chicken IL-4 and IL-2 can be used as an adjuvant to enhance the anticoccidiosis effect of the chicken coccidia live vaccine. The chickens were divided into 3 groups: blank control group, vaccine + pCI-IL-4-IL-2-EGFP adjuvant coimmunization group, and vaccine-only group to investigate the immune synergy mechanism of recombinant plasmid adjuvant pCI-IL-4-IL-2-EGFP. The expressions of IL-2, IL-4, TNF-α, and IFN-γ in chicken sera and tissues were detected by ELISA and RT-qPCR, and the proliferation of T and B lymphocytes and antigen presenting cells (APC) in chicken immune organs and intestines were detected by acid alpha-naphthalase (ANAE) staining, methyl green pyronine (MGP) staining, and immunofluorescence (IF) staining, respectively. Results showed that the mRNA expression of IL-2, IL-4, IFN-γ and the number of activated T and B lymphocytes were significantly upregulated in the spleen and cecum tonsils of chickens in vaccine + pCI-IL-4-IL-2-EGFP group compared with the vaccine-only group on 7 d after vaccination (P < 0.05). Protein contents of IL-2, IL-4 and TNF-α in vaccine + pCI-IL-4-IL-2-EGFP group were significantly increased compared to vaccine-only group on 28 d of inoculation (P < 0.05). The number of T and B lymphocytes and APC in chickens of the vaccine+ pCI-IL-4-IL-2-EGFP group was significantly higher than that of the vaccine-only group in cecum tonsils, thymus and spleen after 14 and 28 d of inoculation (P < 0.05). All results revealed that pCI-IL-4-IL-2-EGFP adjuvant enhanced the immune response of chicken coccidia live vaccine by upregulating the expression of IL-2, IL-4, TNF-α, and IFN-γ and promoting the proliferation of T, B lymphocytes and APCs in chicken intestines and immune organ sites. Moreover, our study provides a theoretical basis for the clinical application of cytogenic plasmids as adjuvants.

Oral Administration of Cancer Vaccines: Challenges and Future Perspectives

Cancer vaccines, a burgeoning strategy in cancer treatment, are exploring innovative administration routes to enhance patient and medical staff experiences, as well as immunological outcomes. Among these, oral administration has surfaced as a particularly noteworthy approach, which is attributed to its capacity to ignite both humoral and cellular immune responses at systemic and mucosal tiers, thereby potentially bolstering vaccine efficacy comprehensively and durably. Notwithstanding this, the deployment of vaccines through the oral route in a clinical context is impeded by multifaceted challenges, predominantly stemming from the intricacy of orchestrating effective oral immunogenicity and necessitating strategic navigation through gastrointestinal barriers. Based on the immunogenicity of the gastrointestinal tract, this review critically analyses the challenges and recent advances and provides insights into the future development of oral cancer vaccines.

A DNA vaccine (EG95-PT1/2/3-IL2) encoding multi-epitope antigen and IL-2 provokes efficient and long-term immunity to echinococcosis

Echinococcosis is a highly prevalent global zoonosis, and vaccines are required. The commercial vaccine based on a protein-based subunit (EG95), however, is limited by its insufficient cellular immunity, a short protection period, and limited prevention against novel mutant strains. Herein, we applied bioinformatics to develop a DNA vaccine (pEG95-IL2) expressing both multi-epitope-based antigens (EG95-PT1/2/3) and an IL-2 adjuvant to regulate T cell differentiation and memory cell response. EG95-PT1/2/3 was screened with hierarchical structure prediction from the epitope conformation of B cells with high confidence across various species to guarantee immunogenicity. Importantly, cationic arginine-rich lipid nanoparticles (RNP) were utilized as a delivery vehicle to form lipoplexes that had a transfection efficiency of nearly two orders of magnitude greater than that of commercial reagents (Lipofectamine 2000 and polyethyleneimine) with both immune and nonimmune cells (DC2.4 and L929 cells, respectively). RNP/pEG95-IL2 lipoplexes displayed a robust and long-term antigen expression, as well as adjuvant effects during the immunization. Consequently, intramuscular injection of RNP/pEG95-IL2 elicited similar humoral immune responses and significantly greater cellular responses in mice when compared with those of the commercial vaccine. In addition, the inoculation protocol of RNP/pEG95-IL2 with sequential booster further strengthens cellular immunity in comparison with the homologous booster. Those findings provide a promising strategy for improving plasmid vaccine efficacy.

Duck IL-7 as a novel adjuvant improves the humoral immune response to an inactivated duck tembusu virus vaccine

Duck tembusu virus (DTMUV), belonging to the Flavivirus genus, Flaviviridae family, has caused huge economic losses in the duck industry. However, the inactivated DTMUV vaccine requires multiple immunizations and has incomplete effectiveness. The humoral immune response is a key factor in the control of DTMUV infection. IL-7 derived from mammals has the ability to enhance antibody production. Whether duck IL-7 (duIL-7) possesses the ability to improve the humoral immunity of inactivated DTMUV vaccine has not yet been declared. Here, a beta-propiolactone (BPL)-inactivated DTMUV vaccine was employed to characterize the adjuvant property of duIL-7 in humoral immune responses. Intramuscular injection of DTMUV inactivated vaccine with or without duIL-7 was administered twice to the ducks. The results showed that duIL-7 was able to promote rapid antibody responses and enhance DTMUV-specific IgG and neutralizing antibody production to the vaccine. T follicular helper (Tfh) cells play a key role in assisting long humoral immunity. It was found that duIL-7 upregulated duIl-6 and duIl-21 gene expression at 3 w post first vaccination, which encode Tfh cell differentiation-related cytokines duIL-6 and duIL-21, respectively. This may be the reason that duIL-7 could prolong the humoral immune response to the inactivated DTMUV vaccine. Next, the ability of duIL-7 to simplify the immunization procedure of the inactivated DTMUV vaccine was tested. When ducks were immunized once, the titers of neutralizing antibodies in ducks from the inactivated DTMUV vaccine supplemented with duIL-7 group were significantly higher than those of ducks from the inactivated DTMUV vaccine group (P < 0.05). In addition, duIL-7 could assist the inactivated DTMUV vaccine in maintaining neutralizing antibodies at high levels during the whole experimental period. The viral titers in the ducks immunized with the inactivated DTMUV vaccine and duIL-7 were lower than those in the ducks immunized with the inactivated DTMUV vaccine alone at 3 days post infection (3 dpi, P < 0.05). Overall, duIL-7 possessed the ability to promote and prolong humoral immune responses to the inactivated DTMUV vaccine, even at one dose. This study provides a new efficient adjuvant for inactivated DTMUV vaccine development.

Current Progress and Challenges in the Study of Adjuvants for Oral Vaccines

Over the past 20 years, a variety of potential adjuvants have been studied to enhance the effect of oral vaccines in the intestinal mucosal immune system; however, no licensed adjuvant for clinical application in oral vaccines is available. In this review, we systematically updated the research progress of oral vaccine adjuvants over the past 2 decades, including biogenic adjuvants, non-biogenic adjuvants, and their multi-type composite adjuvant materials, and introduced their immune mechanisms of adjuvanticity, aiming at providing theoretical basis for developing feasible and effective adjuvants for oral vaccines. Based on these insights, we briefly discussed the challenges in the development of oral vaccine adjuvants and prospects for their future development.

Interleukin-2 shows high adjuvanticity for an inactivated vaccine against duck Tembusu virus disease

Currently, the widely used vaccine against duck Tembusu virus (DTMUV) disease is inactivated vaccine which, however, facing the limits of large inoculation dose, short immunization period, and incomplete effectiveness. Access to efficient adjuvants aiding for DTMUV inactivated vaccine seems to be of critical importance. Interleukin-2 (IL-2) was reported to induce a persistent expansion of effector T cells and could be a promising molecular adjuvant for many kinds of vaccines. In this study, the efficacy of duck interleukin (dIL)-2 as an adjuvant for a DTMUV inactivated vaccine was evaluated. Fifty-five Pekin ducks were divided into 5 groups and intramuscularly administered with 5 batches of vaccines at 42 D (A: DTUMV + dIL-2; B: 1/2DTUMV + dIL-2; C: DTUMV; D: 1/2DTUMV and E: PBS), respectively, and received the second vaccination 2 wk later. Fifty-six days after immunization, 6 ducks from each group were randomly selected to conduct a challenge protection test. Antibody titers and cytokine responses were detected to assess humoral and cellular immune responses in serum of inoculated ducks by hemagglutination inhibition and ELISA, respectively; virus isolation and RT-PCR method were used in immunity protective test. Our results showed that dIL-2 exerted an enhanced effect on the vaccine while reducing the dose of inoculated antigen highlighting high adjuvanticity of IL-2. The vaccines supplemented with IL-2 induced a higher level of antibodies and higher percentage of inhibition values than inactivated vaccines without IL-2 to a significant extent. The production level of IFN-α, IFN-γ, and IL-6 genes were elevated, enhancing both humoral and cellular responses. Furthermore, it provided higher protection after virus challenge. Therefore, IL-2 can be considered as a potential adjuvant for inactivated vaccine against DTMUV disease.

Strict Assembly Restriction of Peptides from Rabbit Hemorrhagic Disease Virus Presented by Rabbit Major Histocompatibility Complex Class I Molecule RLA-A1

Rabbits are pivotal domestic animals for both the economy and as an animal model for human diseases. A large number of rabbits have been infected by rabbit hemorrhagic disease virus (RHDV) in natural and artificial pandemics in the past. Differences in presentation of antigenic peptides by polymorphic major histocompatibility complex (MHC) molecules to T-cell receptors (TCR) on T lymphocytes are associated with viral clearance in mammals. Here, we screened and identified a series of peptides derived from RHDV binding to the rabbit MHC class I molecule, RLA-A1. The small, hydrophobic B and F pockets of RLA-A1 capture a peptide motif analogous to that recognized by human class I molecule HLA-A*0201, with more restricted aliphatic anchors at P2 and PΩ positions. Moreover, the rabbit molecule is characterized by an uncommon residue combination of Gly53, Val55, and Glu56, making the 3₁₀ helix and the loop between the 3₁₀ and α1 helices closer to the α2 helix. A wider A pocket in RLA-A1 can induce a special conformation of the P1 anchor and may play a pivotal role in peptide assembly and TCR recognition. Our study broadens the knowledge of T-cell immunity in domestic animals and also provides useful insights for vaccine development to prevent infectious diseases in rabbits.IMPORTANCE We screened rabbit MHC class I RLA-A1-restricted peptides from the capsid protein VP60 of rabbit hemorrhagic disease virus (RHDV) and determined the structures of RLA-A1 complexed with three peptides, VP60-1, VP60-2, and VP60-10. From the structures, we found that the peptide binding motifs of RLA-A1 are extremely constraining. Thus, there is a generally restricted peptide selection for RLA-A1 compared to that for human HLA-A*0201. In addition, uncommon residues Gly53, Val55, and Glu56 of RLA-A1 are located between the 3₁₀ helix and α1 helix, which makes the steric position of the 3₁₀ helix in RLA-A1 much closer to the α2 helix than that found in other mammalian MHC class I molecules. This special conformation between the 3₁₀ helix and α1 helix plays a pivotal role in rabbit MHC class I assembly. Our results provide new insights into MHC class I molecule assembly and peptide presentation of domestic mammals. Furthermore, these data also broaden our knowledge on T-cell immunity in rabbits and may also provide useful information for vaccine development to prevent infectious diseases in rabbits.

Emerging Infectious Diseases of Rabbits

Recently, multiple infectious organisms have been identified as the cause of emerging diseases in lagomorphs. The most important of these emerging diseases is rabbit hemorrhagic disease virus (RHDV) type 2, a new variant with differences in pathogenicity to classical RHDV. Hepatitis E is considered an emerging zoonotic infectious disease, with widespread prevalence in many different rabbit populations. Mycobacteriosis has been recently reported in other captive domestic rabbit populations. This article provides a recent review of the published literature on emerging infectious diseases in rabbits, including farmed, laboratory, and pet rabbits, some of which have zoonotic potential.