A replicating adenovirus capsid display recombinant elicits antibodies against Plasmodium falciparum sporozoites in Aotus nancymaae monkeys

Progress in Adenoviral Capsid-Display Vaccines

Adenoviral vectored vaccines against infectious diseases are currently in clinical trials due to their capacity to induce potent antigen-specific B- and T-cell immune responses. Heterologous prime-boost vaccination with adenoviral vector and, for example, adjuvanted protein-based vaccines can further enhance antigen-specific immune responses. Although leading to potent immune responses, these heterologous prime-boost regimens may be complex and impact manufacturing costs limiting efficient implementation. Typically, adenoviral vectors are engineered to genetically encode a transgene in the E1 region and utilize the host cell machinery to express the encoded antigen and thereby induce immune responses. Similarly, adenoviral vectors can be engineered to display foreign immunogenic peptides on the capsid-surface by insertion of antigens in capsid proteins hexon, fiber and protein IX. The ability to use adenoviral vectors as antigen-display particles, with or without using the genetic vaccine function, greatly increases the versatility of the adenoviral vector for vaccine development. This review describes the application of adenoviral capsid antigen-display vaccine vectors by focusing on their distinct advantages and possible limitations in vaccine development.

Novel viral vectors in infectious diseases

Since the development of vaccinia virus as a vaccine vector in 1984, the utility of numerous viruses in vaccination strategies has been explored. In recent years, key improvements to existing vectors such as those based on adenovirus have led to significant improvements in immunogenicity and efficacy. Furthermore, exciting new vectors that exploit viruses such as cytomegalovirus (CMV) and vesicular stomatitis virus (VSV) have emerged. Herein, we summarize these recent developments in viral vector technologies, focusing on novel vectors based on CMV, VSV, measles and modified adenovirus. We discuss the potential utility of these exciting approaches in eliciting protection against infectious diseases.

A potent malaria vaccine based on adenovirus with dual modifications at Hexon and pVII

Adenovirus (Ad) is thought to be one of the most promising platforms for a malaria vaccine targeted against its liver stages, because of its ability to induce a strong T-cell response against a transgene. However, a further improvement of this platform is needed in order to elicit another arm of the immunity, i.e. humoral response, against malaria. In order to augment immunogenicity and protective efficacy of Ad-based malaria vaccine, we inserted B-cell, as well as CD4+ T-cell, epitopes of Plasmodium falciparum circumsporozoite protein (PfCSP) into the capsid protein, Hexon, and the core protein, VII (pVII), of Ad, respectively, in addition to the PfCSP transgene. Insertion of PfCSP-derived B cell epitope to Hexon significantly enhanced the epitope-specific antibody response compared to AdPfCSP, an Ad vaccine expressing only PfCSP transgene. PfCSP-derived CD4+ T-cell epitope insertion into pVII augmented not only PfCSP-specific CD4+ T-cell response but also anti-PfCSP antibody response. Finally, mice immunized with AdPfCSP having both Hexon and pVII modifications were more protected than AdPfCSP or Hexon-modified AdPfCSP against challenge with transgenic rodent malaria parasites expressing the PfCSP. Overall, this study has demonstrated that Hexon and pVII-modified AdPfCSP vaccine is a promising malaria vaccine which induces strong PfCSP-specific humoral, CD4+ T-cell, and CD8+ T-cell responses and protects against infection with transgenic malaria parasites expressing the PfCSP.

Vaccination with recombinant adenovirus expressing multi-stage antigens of Toxoplasma gondii by the mucosal route induces higher systemic cellular and local mucosal immune responses than with other vaccination routes

Toxoplasmosis caused by Toxoplasma gondii, an obligate intracellular protozoan, is a cause of congenital disease and abortion in humans and animals. Various vaccination strategies against toxoplasmosis in rodent models have been used in the past few decades; however, effective vaccines remain a challenge. A recombinant adenovirus vaccine expressing ubiquitin-conjugated multi-stage antigen segments (Ad-UMAS) derived from different life-cycle stages of T. gondii was constructed previously. Here, we compared the immune responses and protection effects in vaccination of mice with Ad-UMAS by five vaccination routes including intramuscular (i.m.), intravenous (i.v.), subcutaneous (s.c.), intraoral (i.o.), and intranasal (i.n.). Much higher levels of T. gondii-specific IgG and IgA antibodies were detected in the sera of the intraoral and intranasal vaccination groups on day 49 compared with controls (p < 0.05). The percentages of CD8⁺ T-cells in mice immunized intranasally and intraorally were larger than in mice immunized intramuscularly (p < 0.05). The highest level of IL-2 and IFN-γ was detected in the group with nasal immunization, and splenocyte proliferation activity was significantly enhanced in mice immunized via the oral and nasal routes. Furthermore, the higher survival rate (50%) and lower cyst numbers observed in the intraoral and intranasal groups all indicate that Ad-UMAS is far more effective in protecting mice against T. gondii infection via the mucosal route. Ad-UMAS could be an effective and safe mucosal candidate vaccine to protect animals and humans against T. gondii infection.

Future Prospects for the Development of Cost-Effective Adenovirus Vaccines

Vaccination is one of the most efficient tools for disease prevention, and a continuously growing field of research. However, despite progress, we still need more efficient and cost-effective vaccines that would improve access to those in need. In this review, we will describe the status of virus-vectored vaccine technology with a focus on adenoviral-based vaccines. Adenovirus (Ad) vaccines have proven to be efficient in military vaccinations against Ad4 and Ad7 and as highly efficient vectored vaccines against rabies. The question of how other adenovirus-based vaccines can become as efficient as the rabies vaccine is the underlying theme in this review. Here, we will first give an overview of the basic properties of vectored vaccines, followed by an introduction to the characteristics of adenoviral vectors and previously tested modifications of the vector backbone and expression cassettes, with a focus on how they can contribute to increased vaccine cost-effectiveness. Finally, we will highlight a few successful examples of research that have attempted to improve the use of adenoviral-based vaccines by improving the transgene immunogenicity.

A Plasmodium Promiscuous T Cell Epitope Delivered within the Ad5 Hexon Protein Enhances the Protective Efficacy of a Protein Based Malaria Vaccine

A malaria vaccine is a public health priority. In order to produce an effective vaccine, a multistage approach targeting both the blood and the liver stage infection is desirable. The vaccine candidates also need to induce balanced immune responses including antibodies, CD4+ and CD8+ T cells. Protein-based subunit vaccines like RTS,S are able to induce strong antibody response but poor cellular reactivity. Adenoviral vectors have been effective inducing protective CD8+ T cell responses in several models including malaria; nonetheless this vaccine platform exhibits a limited induction of humoral immune responses. Two approaches have been used to improve the humoral immunogenicity of recombinant adenovirus vectors, the use of heterologous prime-boost regimens with recombinant proteins or the genetic modification of the hypervariable regions (HVR) of the capsid protein hexon to express B cell epitopes of interest. In this study, we describe the development of capsid modified Ad5 vectors that express a promiscuous Plasmodium yoelii T helper epitope denominated PyT53 within the hexon HVR2 region. Several regimens were tested in mice to determine the relevance of the hexon modification in enhancing protective immune responses induced by the previously described protein-based multi-stage experimental vaccine PyCMP. A heterologous prime-boost immunization regime that combines a hexon modified vector with transgenic expression of PyCMP followed by protein immunizations resulted in the induction of robust antibody and cellular immune responses in comparison to a similar regimen that includes a vector with unmodified hexon. These differences in immunogenicity translated into a better protective efficacy against both the hepatic and red blood cell stages of P. yoelii. To our knowledge, this is the first time that a hexon modification is used to deliver a promiscuous T cell epitope. Our data support the use of such modification to enhance the immunogenicity and protective efficacy of adenoviral based malaria vaccines.

Adenoviral vector-based strategies against infectious disease and cancer

Adenoviral vectors are widely employed against infectious diseases or cancers, as they can elicit specific antibody responses and T cell responses when they are armed with foreign genes as vaccine carriers, and induce apoptosis of the cancer cells when they are genetically modified for cancer therapy. In this review, we summarize the biological characteristics of adenovirus (Ad) and the latest development of Ad vector-based strategies for the prevention and control of emerging infectious diseases or cancers. Strategies to circumvent the pre-existing neutralizing antibodies which dampen the immunogenicity of Ad-based vaccines are also discussed.

A Toxoplasma gondii vaccine encoding multistage antigens in conjunction with ubiquitin confers protective immunity to BALB/c mice against parasite infection

BACKGROUND

Toxoplasma gondii is a widely prevalent intracellular parasite which infects almost all warm-blooded animals including humans and causes serious zoonotic toxoplasmosis. DNA vaccines have proved effective in the protection against parasites. However, the problems of weak immunity and inefficient delivery of DNA vaccine remain major issues. Therefore, comprehensive antigens derived from all stages of the parasite, effective adjuvants and delivery systems should be considered in the vaccine construction.

METHODS

SAG3101-144,ROP18347-396, MIC6288-347, GRA7182-224, MAG158-125, BAG1156-211 and SPA142-200, derived from antigens in tachyzoite, bradyzoite and sporozoite stages of T. gondii were screened based on CD8(+) T cell epitope binding affinity to HLA and H-2. We constructed a recombinant DNA vaccine and an adenovirus vaccine encoding multi-stage antigen of T. gondii linked to ubiquitin molecules and vaccinated BALB/c mice with different strategies. Antibodies, cytokines, splenocytes proliferation, as well as the percentage of CD4(+) and CD8(+) T cells in immunized mouse were analyzed by the Enzyme-Linked Immunosorbent Assays (ELISA), Flow Cytometry (FCM). Protective efficacy was evaluated by challenging immunized mice with type I and type II parasite.

RESULTS

Our results indicated that the DNA vaccine had the advantage of inducing a stronger humoral response, whereas the adenovirus-vectored vaccine effectively improved the cellular immune response. Priming with DNA vaccine and boosting with adenovirus-vectored vaccine induced Th1-type immune responses with highest levels of IgG2a and secretion of cytokines IL-2 and IFN-γ. Effective protection against type I and type II parasite with an increase in survival rate and a decrease in brain cyst burden was achieved in immunized mice.

CONCLUSIONS

Priming vaccination with DNA vaccine and boosting with the recombinant adenovirus vaccine encoding ubiquitin conjugated multi-stage antigens of T. gondii was proved to be a potential strategy against the infection of type I and type II parasite.

Capsid display of a conserved human papillomavirus L2 peptide in the adenovirus 5 hexon protein: a candidate prophylactic hpv vaccine approach

Background

Infection by any one of 15 high risk human papillomavirus (hrHPV) types causes most invasive cervical cancers. Their oncogenic genome is encapsidated by L1 (major) and L2 (minor) coat proteins. Current HPV prophylactic vaccines are composed of L1 virus-like particles (VLP) that elicit type restricted immunity. An N-terminal region of L2 protein identified by neutralizing monoclonal antibodies comprises a protective epitope conserved among HPV types, but it is weakly immunogenic compared to L1 VLP. The major antigenic capsid protein of adenovirus type 5 (Ad5) is hexon which contains 9 hypervariable regions (HVRs) that form the immunodominant neutralizing epitopes. Insertion of weakly antigenic foreign B cell epitopes into these HVRs has shown promise in eliciting robust neutralizing antibody responses. Thus here we sought to generate a broadly protective prophylactic HPV vaccine candidate by inserting a conserved protective L2 epitope into the Ad5 hexon protein for VLP-like display.

Methods

Four recombinant adenoviruses were generated without significant compromise of viral replication by introduction of HPV16 amino acids L2 12–41 into Ad5 hexon, either by insertion into, or substitution of, either hexon HVR1 or HVR5.

Results

Vaccination of mice three times with each of these L2-recombinant adenoviruses induced similarly robust adenovirus-specific serum antibody but weak titers against L2. These L2-specific responses were enhanced by vaccination in the presence of alum and monophoryl lipid A adjuvant. Sera obtained after the third immunization exhibited low neutralizing antibody titers against HPV16 and HPV73. L2-recombinant adenovirus vaccination without adjuvant provided partial protection of mice against HPV16 challenge to either the vagina or skin. In contrast, vaccination with each L2-recombinant adenovirus formulated in adjuvant provided robust protection against vaginal challenge with HPV16, but not against HPV56.

Conclusion

We conclude that introduction of HPV16 L2 12–41 epitope into Ad5 hexon HVR1 or HVR5 is a feasible method of generating a protective HPV vaccine, but further optimization is required to strengthen the L2-specific response and broaden protection to the more diverse hrHPV.