Immunization with Hexon modified adenoviral vectors integrated with gp83 epitope provides protection against Trypanosoma cruzi infection

Recent Advances in the Development of Adenovirus-Vectored Vaccines for Parasitic Infections

Vaccines against parasites have lagged centuries behind those against viral and bacterial infections, despite the devastating morbidity and widespread effects of parasitic diseases across the globe. One of the greatest hurdles to parasite vaccine development has been the lack of vaccine strategies able to elicit the complex and multifaceted immune responses needed to abrogate parasitic persistence. Viral vectors, especially adenovirus (AdV) vectors, have emerged as a potential solution for complex disease targets, including HIV, tuberculosis, and parasitic diseases, to name a few. AdVs are highly immunogenic and are uniquely able to drive CD8+ T cell responses, which are known to be correlates of immunity in infections with most protozoan and some helminthic parasites. This review presents recent developments in AdV-vectored vaccines targeting five major human parasitic diseases: malaria, Chagas disease, schistosomiasis, leishmaniasis, and toxoplasmosis. Many AdV-vectored vaccines have been developed for these diseases, utilizing a wide variety of vectors, antigens, and modes of delivery. AdV-vectored vaccines are a promising approach for the historically challenging target of human parasitic diseases.

Immunoinformatic construction of an adenovirus-based modular vaccine platform and its application in the design of a SARS-CoV-2 vaccine

The current SARS-CoV-2 pandemic has imposed new challenges and demands for health systems, especially in the development of new vaccine strategies. Vaccines for many pathogens were developed based on the display of foreign epitopes in the variable regions of the human adenovirus (HAdV) major capsid proteins (hexon, penton and fiber). The humoral immune response against the HAdV major capsid proteins was demonstrated to play a role in the development of an immune response against the epitopes in display. Through the immunoinformatic profiling of the major capsid proteins of HAdVs from different species, we developed a modular concept that can be used in the development of vaccines based on HAdV vectors. Our data suggests that different immunomodulatory potentials can be observed in the conserved regions, present in the hexon and penton proteins, from different species. Using this modular approach, we developed a HAdV-5 based vaccine strategy for SARS-CoV-2, constructed through the display of SARS-CoV-2 epitopes indicated by our prediction analysis as immunologically relevant. The sequences of the HAdV vector major capsid proteins were also edited to enhance the IFN-gamma induction and antigen presenting cells activation. This is the first study proposing a modular HAdV platform developed to aid the design of new vaccines by inducing an immune response more suited for the epitopes in display.

Capsid-Incorporation Strategy To Display Antigens for an Alternative Adenoviral Vector Vaccine Approach

The adenovirus (Ad) is widely used as a vaccine because of its ability to induce a cellular and humoral immune response. In addition, human clinical trials have validated the safety and efficacy of Ad as a vaccine vector. The traditional approach for employing the adenovirus as vaccine is to configure the antigen genes into the expression cassette of the Ad genome. An alternative method for inducing an immune response is the "capsid-incorporation" strategy. This strategy is based upon the incorporation of proteins or peptides into the capsid proteins. This review will focus on the established uses of this approach as well as highlighting the new developments regarding the capsid-incorporation strategy.

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.

Development of novel vaccine vectors: Chimpanzee adenoviral vectors

Adenoviral vector has been employed as one of the most efficient means against infectious diseases and cancer. It can be genetically modified and armed with foreign antigens to elicit specific antibody responses and T cell responses in hosts as well as engineered to induce apoptosis in cancer cells. The chimpanzee adenovirus-based vector is one kind of novel vaccine carriers whose unique features and non-reactivity to pre-existing human adenovirus neutralizing antibodies makes it an outstanding candidate for vaccine research and development. Here, we review the different strategies for constructing chimpanzee adenoviral vectors and their applications in recent clinical trials and also discuss the oncolytic virotherapy and immunotherapy based on chimpanzee adenoviral vectors.

Genetic Adjuvantation of a Cell-Based Therapeutic Vaccine for Amelioration of Chagasic Cardiomyopathy

Chagas disease, caused by infection with the protozoan parasite Trypanosoma cruzi, is a leading cause of heart disease ("chagasic cardiomyopathy") in Latin America, disproportionately affecting people in resource-poor areas. The efficacy of currently approved pharmaceutical treatments is limited mainly to acute infection, and there are no effective treatments for the chronic phase of the disease. Preclinical models of Chagas disease have demonstrated that antigen-specific CD8⁺ gamma interferon (IFN-γ)-positive T-cell responses are essential for reducing parasite burdens, increasing survival, and decreasing cardiac pathology in both the acute and chronic phases of Chagas disease. In the present study, we developed a genetically adjuvanted, dendritic cell-based immunotherapeutic for acute Chagas disease in an attempt to delay or prevent the cardiac complications that eventually result from chronic T. cruzi infection. Dendritic cells transduced with the adjuvant, an adenoviral vector encoding a dominant negative isoform of Src homology region 2 domain-containing tyrosine phosphatase 1 (SHP-1) along with the T. cruzi Tc24 antigen and trans-sialidase antigen 1 (TSA1), induced significant numbers of antigen-specific CD8⁺ IFN-γ-positive cells following injection into BALB/c mice. A vaccine platform transduced with the adenoviral vector and loaded in tandem with the recombinant protein reduced parasite burdens by 76% to >99% in comparison to a variety of different controls and significantly reduced cardiac pathology in a BALB/c mouse model of live Chagas disease. Although no statistical differences in overall survival rates among cohorts were observed, the data suggest that immunotherapeutic strategies for the treatment of acute Chagas disease are feasible and that this approach may warrant further study.

Epitope Capsid-Incorporation: New Effective Approach for Vaccine Development for Chagas Disease

Background:

Previously we reported that a hexon-modified adenovirus (Ad) vector containing the invasive neutralizing epitope of Trypanosoma cruzi (T. cruzi) trypomastigote gp83 (Ad5-gp83) provided immunoprotection against T. cruzi infection. The purpose of this work was to design an improved vaccine for T. cruzi using a novel epitope capsid incorporation strategy. Thus, we evaluated the immunoprotection raised by co-immunization with Ad5-gp83 and an Ad vector containing an epitope (ASP-M) of the T. cruzi amastigote surface protein 2.

Methods:

Protein IX (pIX)-modified Ad vector (Ad5-pIX-ASP-M) was generated, characterized, and validated. C3H/He mice were immunized with Ad5-pIX-ASP-M and Ad5-gp83 and the cell-mediated responses were evaluated by enzyme-linked immunospot (ELISPOT) assay and intracellular staining. Immunized mice were challenged with T. cruzi to evaluate the vaccine efficacy.

Results:

Our findings indicate that Ad5-pIX-ASP-M was viable. Specific CD8⁺ T-cell mediated responses prior to the challenge show an increase in IFNγ and TNFα production. A single immunization with Ad5-pIX-ASP-M provided protection from T. cruzi infection, but co-immunizations with Ad5-pIX-ASP-M and Ad5-gp83 provided a higher immunoprotection and increased survival rate of mice.

Conclusions:

Overall, these results suggest that the combination of gp83 and ASP-M specific epitopes onto the capsid-incorporated adenoviruses would provide superior protection against Chagas disease as compared with Ad5-gp83 alone.

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.

Development of an Ad5H3 Chimera Using the "Antigen Capsid-Incorporation" Strategy for an Alternative Vaccination Approach

BACKGROUND

Adenovirus type 5 (Ad5) achieved success as a conventional transgene vaccine vector in preclinical trials, however; achieved poor efficiency in some of the clinical trials, due to the major hurdle associated with Ad5 pre-existing immunity (PEI) in the majority of the human population.

OBJECTIVE

We sought to generate Ad5-based chimeras to assess their capabilities to bypass this bottleneck and to induce antigen-specific humoral immune response.

METHODS

A His6 tag was incorporated into the hypervariable region 2 (HVR2) of hexon3 (H3) capsid protein using the "Antigen Capsid-Incorporation" strategy. This lead to the construction of a viral chimera, Ad5H3-HVR2-His. Ad5H3 was generated previously by substituting the hexon of Ad5 (hexon5) with the hexon from adenovirus type 3 (Ad3).

RESULTS

His6 was presented on the viral capsid surface and recognized by a His6 antibody. An in vitro neutralization assay with Ad5 sera indicated the ability of Ad5 chimeras to partially escape Ad5 immunity. Immunization with Ad5H3-HVR2-His generated significant humoral response to the incorporated tagged peptide, when compared to the immunizations with controls.

CONCLUSION

Based on our in vitro studies the data suggested that Ad5H3 as a novel chimeric vaccine platform yields the possibility to escape Ad5 neutralization, and the potential to generate robust humoral immunity against incorporated antigens using the "Antigen Capsid-Incorporation" strategy.

A Novel Vaccine Approach for Chagas Disease Using Rare Adenovirus Serotype 48 Vectors

Due to the increasing amount of people afflicted worldwide with Chagas disease and an increasing prevalence in the United States, there is a greater need to develop a safe and effective vaccine for this neglected disease. Adenovirus serotype 5 (Ad5) is the most common adenovirus vector used for gene therapy and vaccine approaches, but its efficacy is limited by preexisting vector immunity in humans resulting from natural infections. Therefore, we have employed rare serotype adenovirus 48 (Ad48) as an alternative choice for adenovirus/Chagas vaccine therapy. In this study, we modified Ad5 and Ad48 vectors to contain T. cruzi’s amastigote surface protein 2 (ASP-2) in the adenoviral early gene. We also modified Ad5 and Ad48 vectors to utilize the “Antigen Capsid-Incorporation” strategy by adding T. cruzi epitopes to protein IX (pIX). Mice that were immunized with the modified vectors were able to elicit T. cruzi-specific humoral and cellular responses. This study indicates that Ad48-modified vectors function comparable to or even premium to Ad5-modified vectors. This study provides novel data demonstrating that Ad48 can be used as a potential adenovirus vaccine vector against Chagas disease.

Progress on adenovirus-vectored universal influenza vaccines

Influenza virus (IFV) infection causes serious health problems and heavy financial burdens each year worldwide. The classical inactivated influenza virus vaccine (IIVV) and live attenuated influenza vaccine (LAIV) must be updated regularly to match the new strains that evolve due to antigenic drift and antigenic shift. However, with the discovery of broadly neutralizing antibodies that recognize conserved antigens, and the CD8(+) T cell responses targeting viral internal proteins nucleoprotein (NP), matrix protein 1 (M1) and polymerase basic 1 (PB1), it is possible to develop a universal influenza vaccine based on the conserved hemagglutinin (HA) stem, NP, and matrix proteins. Recombinant adenovirus (rAd) is an ideal influenza vaccine vector because it has an ideal stability and safety profile, induces balanced humoral and cell-mediated immune responses due to activation of innate immunity, provides 'self-adjuvanting' activity, can mimic natural IFV infection, and confers seamless protection against mucosal pathogens. Moreover, this vector can be developed as a low-cost, rapid-response vaccine that can be quickly manufactured. Therefore, an adenovirus vector encoding conserved influenza antigens holds promise in the development of a universal influenza vaccine. This review will summarize the progress in adenovirus-vectored universal flu vaccines and discuss future novel approaches.

Neutralizing epitopes mapping of human adenovirus type 14 hexon

Human adenoviruses 14 (HAdV-14) caused several clusters of acute respiratory disease (ARD) outbreaks in both civilian and military settings. The identification of the neutralizing epitopes of HAdV-14 is important for the surveillance and control of infection. Since the previous studies had indicated that the adenoviruses neutralizing epitopes were likely to be exposed on the surface of the hexon, four epitope peptides, A14R1 (residues 141-157), A14R2 (residues 181-189), A14R4 (residues 252-260) and A14R7 (residues 430-442) were predicted and mapped onto the 3D structures of hexon by homology modeling approach. Then the four peptides were synthesized, and all the four putative epitopes were identified as neutralizing epitopes by enzyme-linked immunosorbent assay (ELISA) and neutralization tests (NT). Finally we incorporated the four epitopes into human adenoviruses 3 (HAdV-3) vectors using the "antigen capsid-incorporation" strategy, and two chimeric adenoviruses, A14R2A3 and A14R4A3, were successfully obtained which displayed A14R2 and A14R4 respectively on the hexon surface of HAdV-3 virions. Further analysis showed that the two chimeric viruses antiserum could neutralize both HAdV-14 and HAdV-3 infection. The neutralization titers of anti-A14R4A3 group were significantly higher than the anti-KLH-A14R4 group (P=0.0442). These findings have important implications for the development of peptide-based broadly protective HAdV-14 and HAdV-3 bivalent vaccine.

Development of Novel Adenoviral Vectors to Overcome Challenges Observed With HAdV-5-based Constructs

Recombinant vectors based on human adenovirus serotype 5 (HAdV-5) have been extensively studied in preclinical models and clinical trials over the past two decades. However, the thorough understanding of the HAdV-5 interaction with human subjects has uncovered major concerns about its product applicability. High vector-associated toxicity and widespread preexisting immunity have been shown to significantly impede the effectiveness of HAdV-5–mediated gene transfer. It is therefore that the in-depth knowledge attained working on HAdV-5 is currently being used to develop alternative vectors. Here, we provide a comprehensive overview of data obtained in recent years disqualifying the HAdV-5 vector for systemic gene delivery as well as novel strategies being pursued to overcome the limitations observed with particular emphasis on the ongoing vectorization efforts to obtain vectors based on alternative serotypes.

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.

Utilizing the antigen capsid-incorporation strategy for the development of adenovirus serotype 5-vectored vaccine approaches

Adenovirus serotype 5 (Ad5) has been extensively modified with traditional transgene methods for the vaccine development. The reduced efficacies of these traditionally modified Ad5 vectors in clinical trials could be primarily correlated with Ad5 pre-existing immunity (PEI) among the majority of the population. To promote Ad5-vectored vaccine development by solving the concern of Ad5 PEI, the innovative Antigen Capsid-Incorporation strategy has been employed. By merit of this strategy, Ad5-vectored we first constructed the hexon shuttle plasmid HVR1-KWAS-HVR5-His6/pH5S by subcloning the hypervariable region (HVR) 1 of hexon into a previously constructed shuttle plasmid HVR5-His6/pH5S, which had His6 tag incorporated into the HVR5. This HVR1 DNA fragment containing a HIV epitope ELDKWAS was synthesized. HVR1-KWAS-HVR5-His6/pH5S was then linearized and co-transformed with linearized backbone plasmid pAd5/∆H5 (GL) , for homologous recombination. This recombined plasmid pAd5/H5-HVR1-KWAS-HVR5-His6 was transfected into cells to generate the viral vector Ad5/H5-HVR1-KWAS-HVR5-His6. This vector was validated to have qualitative fitness indicated by viral physical titer (VP/ml), infectious titer (IP/ml) and corresponding VP/IP ratio. Both the HIV epitope and His6 tag were surface-exposed on the Ad5 capsid, and retained epitope-specific antigenicity of their own. A neutralization assay indicated the ability of this divalent vector to circumvent neutralization by Ad5-positive sera in vitro. Mice immunization demonstrated the generation of robust humoral immunity specific to the HIV epitope and His6. This proof-of-principle study suggested that the protocol associated with the Antigen Capsid-Incorporation strategy could be feasibly utilized for the generation of Ad5-vectored vaccines by modifying different capsid proteins. This protocol could even be further modified for the generation of rare-serotype adenovirus-vectored vaccines.