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In recent years, fowl adenovirus (FAdV)-induced diseases became a global problem with considerable impact on chicken health and welfare. This has prompted numerous studies to focus on experimental immunization strategies using whole virus formulations (live or killed vaccines), some of them modified as recombinantly constructed vector vaccines. In addition, FAdV capsid proteins were frequently reported as immunizing antigens (subunit vaccines), with fiber proteins being amongst the most successful candidates. To date, there is no standardized protocol to assess vaccine efficacy in experimental FAdV protection studies, with the consequence that the experimental settings present several degrees of variations even when sharing similar premises. Differences in formulation preparations, route of inoculation, antigen dose, vaccination scheme, choice of challenge strain, or type and age of the birds are capable to greatly influence the magnitude of the immune response and the consequent protective efficacy, altogether addressing remaining challenges. Beyond the antigen composition of a vaccine, the epidemiology of FAdVs with the potential of vertical transmission of virus and/or antibodies from breeders to progenies has a substantial impact on protection strategies. The goal of this review is to outline a broad overview of the findings made thus far regarding immunization strategies against diseases associated to FAdV infections, considering the literature published since the appearance of hepatitis-hydropericardium syndrome (HHS) in the late Eighties, in order to emphasize the current knowledge on FAdV vaccines and highlight fields of future research and intervention., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The continuous emergence of highly immune-evasive SARS-CoV-2 variants has challenged vaccine efficacy. A vaccine that can provide broad protection is desirable. We evaluated the immunogenicity of a series of monovalent and bivalent adenovirus-vectored vaccines containing the spikes of Wildtype (WT), Beta, Delta, Omicron subvariants BA.1, BA.2, BA.2.12.1, BA.2.13, BA.3, BA.5, BQ.1.1, and XBB. Vaccination in mice using monovalent vaccines elicited the highest neutralizing titers against each self-matched strain, but against other variants were reduced 2- to 73-fold. A bivalent vaccine consisting of WT and BA.5 broadened the neutralizing breadth against pre-Omicron and Omicron subvariants except XBB. Among bivalent vaccines based on the strains before the emergence of XBB, a bivalent vaccine consisting of BA.2 and BA.5 elicited the most potent neutralizing antibodies against Omicron subvariants, including XBB. In mice primed with injected WT vaccine, intranasal booster with a bivalent vaccine containing XBB and BA.5 could elicit broad serum and respiratory mucosal neutralizing antibodies against all late Omicron subvariants, including XBB. In mice that had been sequentially vaccinated with WT and BA.5, intranasal booster with a monovalent XBB vaccine elicited greater serum and mucosal XBB neutralizing antibodies than bivalent vaccines containing XBB. Both monovalent and bivalent XBB vaccines induced neutralizing antibodies against EG.5. Unlike the antibody response, which is highly variant-specific, mice receiving either monovalent or bivalent vaccines elicited comparable T-cell responses against all variants. Furthermore, intranasal but not intramuscular booster induced antigen-specific lung resident T cells. This study provides insights into the design of the COVID-19 vaccine and vaccination strategies.

Background: We describe the epidemiological and clinical characteristics of thrombosis with thrombocytopenia syndrome (TTS) cases reported in Spain., Methods: We included all cases of venous or arterial thrombosis with thrombocytopenia following administration of adenoviral vector vaccines (AstraZeneca or Janssen) against COVID-19 disease between 1 February and 26 September 2021. We describe the crude rate and the standardised morbidity ratio. We assessed the predictors of mortality., Results: Sixty-one cases were reported and 45 fulfilled eligibility criteria; 82% of patients were women. The crude TTS rate was 4 cases/1 000 000 doses, and 14-15 cases/1 000 000 doses among patients aged 30-49 years. The number of observed cases of cerebral venous thrombosis was 6-18 times higher than that expected in patients younger than 49 years. Symptoms started a median (quartiles 1 and 3 [Q 1 -Q 3 ]) of 10 (7-14) days after vaccination. Eighty percent (95% confidence interval [CI]: 65%-90%) had thrombocytopenia at the time of the emergency department visit, and 65% (49%-78%) had D-dimer levels > 2000 ng/mL. Patients had thromboses affecting multiple locations in 36% of cases and fatal outcomea in 24%. Platelet nadir < 50 000/μL (odds ratio [OR]: 7.4; 95% CI: 1.2-47.5) and intracranial hemorrhage (OR: 7.9; 95% CI: 1.3-47.0) were associated with fatal outcomes., Conclusion: TTS must be suspected in patients with symptoms 10 days after vaccination and thrombocytopenia and/or elevated D-dimer levels., (Copyright © 2022 Sociedad Española de Neurología. Published by Elsevier España, S.L.U. All rights reserved.)

Background: Human adenoviruses (HAdVs) frequently cause common respiratory or gastrointestinal infections among children, adults, individuals with immune deficiencies, and other vulnerable populations with varying degree of symptoms, ranging from mild to server, and in some cases, even fatalities. Despite the significant clinical impact of HAdVs, there is currently no approved vaccine available., Methods: This study explores the potential of the adenovirus type 5 fiber knob (Ad5-FK) to stimulate the production of Ad-specific neutralizing antibodies and T-cell responses in mice. Based on structure predictions, we first expressed Ad5-FK in E. coli and confirmed the assembly of FK into its trimeric form. After testing the binding capability of the trimeric FK to susceptible cells, the immunogenicity of the protein in combination with the c-di-AMP adjuvant was assessed in BALB/c mice., Results: The purified Ad5-FK exhibited self-trimerization and maintained correct conformation akin to the authentic FK structure. This facilitated effective binding to susceptible HEK293 cells. Notably, the protein demonstrated significant inhibition of HEK293 cells infection by rAd5-GFP. Immunization of BALB/c mice with Ad5-FK, or Ad5-FK mixed with c-di-AMP yielded FK-specific antibodies with potent neutralization capacity. Significantly, Ad5-FK was found to elicit a vigorous CD4 + T-cell response in the immunized mice., Conclusion: Our findings underscore the efficacy of FK-based vaccine in eliciting anti-Ad humoral immune response and CD4 T-cell immune reactions essential for protection against viral infections., (© 2024. The Author(s).)

A mucosal route of vaccination could prevent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replication at the site of infection and limit transmission. We compared protection against heterologous XBB.1.16 challenge in nonhuman primates (NHPs) ~5 months following intramuscular boosting with bivalent mRNA encoding WA1 and BA.5 spike proteins or mucosal boosting with a WA1-BA.5 bivalent chimpanzee adenoviral-vectored vaccine delivered by intranasal or aerosol device. NHPs boosted by either mucosal route had minimal virus replication in the nose and lungs, respectively. By contrast, protection by intramuscular mRNA was limited to the lower airways. The mucosally delivered vaccine elicited durable airway IgG and IgA responses and, unlike the intramuscular mRNA vaccine, induced spike-specific B cells in the lungs. IgG, IgA and T cell responses correlated with protection in the lungs, whereas mucosal IgA alone correlated with upper airway protection. This study highlights differential mucosal and serum correlates of protection and how mucosal vaccines can durably prevent infection against SARS-CoV-2., (© 2024. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.)

Background: Human adenovirus (HAdV) is a prevalent causative agent of acute respiratory disease (ARD) and is frequently responsible for outbreaks, particularly in military environments. Current vaccines do not effectively cover HAdV subtypes commonly found among Korean military personnel, highlighting the need for a new targeted vaccine. This study presents a cost-benefit analysis to evaluate the economic viability of developing and implementing such a vaccine within a military context., Methods: We adopted a societal perspective for this cost-benefit analysis, which included estimating costs associated with vaccine development, production, and distribution over a projected timeline. We assumed a development period of five years, after which vaccine production and administration were initiated in the sixth year. The cost associated with vaccine development, production, and dispensation was considered. The benefits were calculated based on both direct and indirect cost savings from preventing HAdV infections through vaccination. All financial figures were expressed in 2023 US dollars. A sensitivity analysis was conducted to explore the impact of varying factors such as vaccination rate, incidence of infection, vaccine efficacy, and discount rate., Results: For the base case scenario, we assumed a vaccination rate of 100 %, an incidence rate of 0.02, and a vaccine efficacy of 95 %, applying a 3 % discount rate. Initially, in the sixth year, the benefit-cost ratio stood at 0.71, suggesting a cost disadvantage at the onset of vaccination. However, this ratio improved to 1.32 in the following years, indicating a cost benefit from the seventh year onward. The cumulative benefit-cost ratio over a decade reached 2.72. The outcomes from the sensitivity analysis were consistent with these findings., Conclusion: Our cost-benefit analysis demonstrates that the introduction of an HAdV vaccine for the Korean military is economically advantageous, with substantial cost benefits accruing from the seventh year after the commencement of vaccination., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Background: Human adenovirus type 55 (hAd55) infection can lead to acute respiratory diseases that often present with severe symptoms. Despite its persistent prevalence in military camps and communities, there are no commercially available vaccines or vaccine candidates undergoing clinical evaluation; therefore, there is an urgent need to address this. In this study, we evaluated the immunogenicity of inactivated hAd55 isolates and investigated the effects of adjuvants and various immunization intervals., Methods and Results: To select a vaccine candidate, four hAd55 strains (6-9, 6-15 (AFMRI 41014), 28-48 (AFMRI 41013), and 12-164 (AFMRI 41012)) were isolated from infected patients in military camps. Sequence analysis revealed no variation in the coding regions of structural proteins, including pentons, hexons, and fibers. Immunization with inactivated hAd55 isolates elicited robust hAd55-specific binding and neutralizing antibody responses in mice, with adjuvants, particularly alum hydroxide (AH), enhancing antibody titers. Co-immunization with AH also induced hAd14-specific neutralizing antibody responses but did not induce hAd11-specific neutralizing antibody responses. Notably, booster immunization administered at a four-week interval resulted in superior immune responses compared with shorter immunization intervals., Conclusions: Prime-boost immunization with the inactivated hAd55 isolate and an AH adjuvant shows promise as a potential approach for preventing hAd55-induced respiratory disease. Further research is needed to evaluate the efficacy and safety of these vaccine candidates in preventing hAd55-associated respiratory illnesses., (© 2024. The Author(s).)

Adenovirus (Ad) vectors based on human adenovirus serotype 5 (Ad5) have attracted significant attention as vaccine vectors for infectious diseases. However, the effectiveness of Ad5 vectors as vaccines is often inhibited by the anti-Ad5 neutralizing antibodies retained by many adults. To overcome this drawback, we focused on human adenovirus serotype 35 (Ad35) vectors with low seroprevalence in adults. Although Ad35 vectors can circumvent anti-Ad5 neutralizing antibodies, vector yields of Ad35 vectors are often inferior to those of Ad5 vectors. In this study, we developed novel Ad35 vectors containing the Ad5 E4 orf 4, 6, and 6/7 or the Ad5 E4 orf 6 and 6/7 for efficient vector production, and compared their properties. These E4-modified Ad35 vectors efficiently propagated to a similar extent at virus titers comparable to those of Ad5 vectors. An Ad35 vector containing the Ad5 E4 orf 4, 6, and 6/7 mediated more efficient transduction than that containing the Ad5 E4 orf 6 and 6/7 in human cultured cells. Furthermore, insertion of an arginine-glycine-aspartate (RGD) peptide in the fiber region of an Ad35 vector containing the Ad5 E4 orf 4, 6, and 6/7 significantly improved the transgene product-specific antibody production following intramuscular administration in mice. The Ad35 vector containing the RGD peptide mediated efficient vaccine effects even in the mice pre-immunized with an Ad5., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Hiroyuki Mizuguchi reports financial support was provided by Ministry of Education, Culture, Sports, Sciences, and Technology of Japan. Hiroyuki Mizuguchi reports financial support was provided by Japanese Agency for Medical Research and Development. Hiroyuki Mizuguchi reports financial support was provided by BIKEN Foundation. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

Background: Targeting kinases presents a potential strategy for treating solid tumors; however, the therapeutic potential of vaccines targeting kinases remains uncertain., Methods: Adenovirus (Ad) vaccines encoding Aurora kinase A (AURKA) or cyclin-dependent kinase 7 (CDK7) were developed, and their therapeutic potentials were investigated by various methods including western blot, flow cytometry, cytotoxic T lymphocyte assay, and enzyme-linked immunospot (ELISpot), in mouse and humanized solid tumor models., Results: Co-immunization with Ad-AURKA/CDK7 effectively prevented subcutaneous tumor growth in the Renca, RM-1, MC38, and Hepa1-6 tumor models. In therapeutic tumor models, Ad-AURKA/CDK7 treatment impeded tumor growth and increased immune cell infiltration. Administration of Ad-AURKA/CDK7 promoted the induction and maturation of dendritic cell subsets and augmented multifunctional CD8 + T-cell antitumor immunity. Furthermore, the vaccine induced a long-lasting antitumor effect by promoting the generation of memory CD8 + T cells. Tumor recovery on CD8 + T-cell depletion underscored the indispensable role of these cells in the observed therapeutic effects. The potent efficacy of the Ad-AURKA/CDK7 vaccine was consistently demonstrated in lung metastasis, orthotopic, and humanized tumor models by inducing multifunctional CD8 + T-cell antitumor immune responses., Conclusions: Our findings illustrate that the Ad-AURKA/CDK7 vaccine targeting dual kinases AURKA and CDK7 emerges as a promising and effective therapeutic approach for the treatment of solid tumors., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Adenoviral and mRNA vaccines encoding the viral spike (S) protein have been deployed globally to contain severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Older individuals are particularly vulnerable to severe infection, probably reflecting age-related changes in the immune system, which can also compromise vaccine efficacy. It is nonetheless unclear to what extent different vaccine platforms are impacted by immunosenescence. Here, we evaluated S protein-specific immune responses elicited by vaccination with two doses of BNT162b2 or ChAdOx1-S and subsequently boosted with a single dose of BNT162b2 or mRNA-1273, comparing age-stratified participants with no evidence of previous infection with SARS-CoV-2. We found that aging profoundly compromised S protein-specific IgG titers and further limited S protein-specific CD4 + and CD8 + T cell immunity as a probable function of progressive erosion of the naive lymphocyte pool in individuals vaccinated initially with BNT162b2. Our results demonstrate that primary vaccination with ChAdOx1-S and subsequent boosting with BNT162b2 or mRNA-1273 promotes sustained immunological memory in older adults and potentially confers optimal protection against coronavirus disease 2019., (© 2024. The Author(s), under exclusive licence to Springer Nature America, Inc.)

Introduction: Human adenovirus type 7 (HAdv-7) infection is the main cause of upper respiratory tract infection, bronchitis and pneumonia in children. At present, there are no anti- adenovirus drugs or preventive vaccines in the market. Therefore, it is necessary to develop a safe and effective anti-adenovirus type 7 vaccine., Methods: In this study, In this study, we used the baculovirus-insect cell expression system to design a recombinant subunit vaccine expressing adenovirus type 7 hexon protein (rBV-hexon) to induce high-level humoral and cellular immune responses. To evaluate the effectiveness of the vaccine, we first detected the expression of molecular markers on the surface of antigen presenting cells and the secretion of proinflammatory cytokines in vitro . We then measured the levels of neutralizing antibodies and T cell activation in vivo ., Results: The results showed that the rBV-hexon recombinant subunit vaccine could promote DC maturation and improve its antigen uptake capability, including the TLR4/NF-κB pathway which upregulated the expression of MHCI, CD80, CD86 and cytokines. The vaccine also triggered a strong neutralizing antibody and cellular immune response, and activated T lymphocytes., Discussion: Therefore, the recombinant subunit vaccine rBV-hexon promoted promotes humoral and cellular immune responses, thereby has the potential to become a vaccine against HAdv-7., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Li, Yang, Zhao, Xiu, Li, Li, Song, Ge, Fang, Han, Zhu and Li.)

Intramuscular delivery of human adenovirus (HAdV)-based vaccines leads to rapid recruitment of neutrophils, which then release antimicrobial peptides/proteins (AMPs). How these AMPs influence vaccine efficacy over the subsequent 24 h is poorly understood. In this study, we asked if human neutrophil protein 1 (HNP-1), an α-defensin that influences direct and indirect innate immune responses to a range of pathogens, impacts the response of human phagocytes to three HAdV species/types (HAdV-C5, -D26, -B35). We show that HNP-1 binds to the capsids and redirects HAdV-C5, -D26, and -B35 to Toll-like receptor 4 (TLR4), which leads to internalization, an NLRP3-mediated inflammasome response, and interleukin 1 beta (IL-1β) release. Surprisingly, IL-1β release was not associated with notable disruption of plasma membrane integrity. These data further our understanding of HAdV vaccine immunogenicity and may provide pathways to extend the efficacy. IMPORTANCE This study examines the interactions between danger-associated molecular patterns and human adenoviruses, and their impact on vaccines. HAdVs and HNP-1 can interact, and these interactions will modify the response of antigen-presenting cells, which will influence vaccine efficacy.

Recent reports of rare ChAdOx1-S vaccine-related venous thrombosis led to the suspension of its usage in several countries. Vaccine-induced thrombotic thrombocytopenia (VITT) is characterized by thrombocytopenia and thrombosis in association with anti-platelet factor 4 (PF4) antibodies. Herein, we propose five potential anionic substances of the ChAdOx1-S vaccine that can combine with PF4 and trigger VITT, including (1) the proteins on the surface of adenovirus, e.g., negative charged glycoprotein, (2) the adjuvant components of the vaccine, e.g., Tween 80, (3) the DNA of adenovirus, (4) the S protein antigen expressed by the vaccine, and (5) the negatively charged impurity proteins expressed by the vaccine, e.g., adenovirus skeleton proteins. After analysis of each case, we consider the most possible trigger to be the negatively charged impurity proteins expressed by the vaccine. Then, we display the possible extravascular route and intravascular route of the formation of PF4 autoantibodies triggered by the negatively charged impurity proteins, which is accordant with the clinical situation. Accordingly, the susceptible individuals of VITT after ChAdOx1-S vaccination may be people who express negatively charged impurity proteins and reach a certain high titer., Competing Interests: HL and TJ are employed by Tigermed Consulting Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Pang, Liu, He, Ji, Zhu and Cui.)

Background: Vaccines that are shelf stable and easy to administer are crucial to improve vaccine access and reduce severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission around the world., Methods: In this study, we demonstrate that an oral, adenovirus-based vaccine candidate protects against SARS-CoV-2 in a Syrian hamster challenge model., Results: Hamsters administered 2 doses of VXA-CoV2-1 showed a reduction in weight loss and lung pathology and had completely eliminated infectious virus 5 days postchallenge. Oral immunization induced antispike immunoglobulin G, and neutralizing antibodies were induced upon oral immunization with the sera, demonstrating neutralizing activity., Conclusions: Overall, these data demonstrate the ability of oral vaccine candidate VXA-CoV2-1 to provide protection against SARS-CoV-2 disease., (© The Author(s) 2021. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Human adenovirus types 4 (HAdV4) and 7 (HAdV7) often lead to severe respiratory diseases and occur epidemically in children, adults, immune deficiency patients, and other groups, leading to mild or severe symptoms and even death. However, no licensed adenovirus vaccine has been approved in the market for general use. E3 genes of adenovirus are generally considered nonessential for virulence and replication; however, a few studies have demonstrated that the products of these genes are also functional. In this study, most of the E3 genes were deleted, and two E3-deleted recombinant adenoviruses (ΔE3-rAdVs) were constructed as components of the vaccine. After E3 deletion, the replication efficiencies and cytopathogenicity of ΔE3-rAdVs were reduced, indicating that ΔE3-rAdVs were attenuated after E3 genes deletion. Furthermore, single immunization with live-attenuated bivalent vaccine candidate protects mice against challenge with wild-type human adenovirus types 4 and 7, respectively. Vaccinated mice demonstrated remarkably decreased viral loads in the lungs and less lung pathology compared to the control animals. Taken together, our study confirms the possibility of the two live-attenuated viruses as a vaccine for clinic use and illustrates a novel strategy for the construction of an adenovirus vaccine.

Objective: To systematically evaluate the effectiveness and safety of the SARS-CoV-2 vaccines currently undergoing clinical trials., Methods: PubMed, EMBASE, and Cochrane Library databases were searched to collect open human COVID-19 vaccines randomized controlled trials, without limiting the search time and language. The research papers collected in the above-mentioned databases were initially screened according to the title and abstract content and merged, and the repeated ones were removed. After reading the full text of the remaining research, the studies that did not meet the inclusion criteria were excluded, and finally, nine studies were obtained. After extracting the statistical data of adverse events in the study, load them into Review Manager for heterogeneity analysis., Results: The incidence of adverse reactions of inactivated virus vaccines, RNA vaccines, and adenovirus vector vaccines was higher than that of placebo. Common adverse reactions included pain, swelling, and fever at the injection site., Conclusion: From the perspective of effectiveness, RNA vaccine > adenovirus vector vaccine > inactivated virus vaccine. From the perspective of safety, the incidence of adverse reactions of the three vaccines is higher than that of a placebo, and the incidence of adverse reactions of the adenovirus vector vaccine is higher., (© 2021 Wiley Periodicals LLC.)

COVID-19 vaccines emerging from different platforms differ in efficacy, duration of protection, and side effects. To maximize the benefits of vaccination, we explored the utility of employing a heterologous prime-boost strategy in which different combinations of the four types of leading COVID-19 vaccine candidates that are undergoing clinical trials in China were tested in a mouse model. Our results showed that sequential immunization with adenovirus vectored vaccine followed by inactivated/recombinant subunit/mRNA vaccine administration specifically increased levels of neutralizing antibodies and promoted the modulation of antibody responses to predominantly neutralizing antibodies. Moreover, a heterologous prime-boost regimen with an adenovirus vector vaccine also improved Th1-biased T cell responses. Our results provide new ideas for the development and application of COVID-19 vaccines to control the SARS-CoV-2 pandemic.

Fowl adenoviruses (FAdVs) have long been recognized as critical viral pathogens within the poultry industry, associated with severe economic implications worldwide. This specific group of viruses is responsible for a broad spectrum of diseases in birds, and an increasing occurrence of outbreaks was observed in the last ten years. Since their first discovery forty years ago in South Korea, twelve antigenically distinct serotypes of fowl adenoviruses have been described. This comprehensive review covers the history of fowl adenovirus outbreaks in South Korea and updates the current epidemiological landscape of serotype diversity and replacement as well as challenges in developing effective broadly protective vaccines. In addition, transitions in the prevalence of dominant fowl adenovirus serotypes from 2007 to 2021, alongside the history of intervention strategies, are brought into focus. Finally, future aspects are also discussed.

The global COVID-19 pandemic has sparked intense interest in the rapid development of vaccines as well as animal models to evaluate vaccine candidates and to define immune correlates of protection. We recently reported a mouse-adapted SARS-CoV-2 virus strain (MA10) with the potential to infect wild-type laboratory mice, driving high levels of viral replication in respiratory tract tissues as well as severe clinical and respiratory symptoms, aspects of COVID-19 disease in humans that are important to capture in model systems. We evaluated the immunogenicity and protective efficacy of novel rhesus adenovirus serotype 52 (RhAd52) vaccines against MA10 challenge in mice. Baseline seroprevalence is lower for rhesus adenovirus vectors than for human or chimpanzee adenovirus vectors, making these vectors attractive candidates for vaccine development. We observed that RhAd52 vaccines elicited robust binding and neutralizing antibody titers, which inversely correlated with viral replication after challenge. These data support the development of RhAd52 vaccines and the use of the MA10 challenge virus to screen novel vaccine candidates and to study the immunologic mechanisms that underscore protection from SARS-CoV-2 challenge in wild-type mice. IMPORTANCE We have developed a series of SARS-CoV-2 vaccines using rhesus adenovirus serotype 52 (RhAd52) vectors, which exhibit a lower seroprevalence than human and chimpanzee vectors, supporting their development as novel vaccine vectors or as an alternative adenovirus (Ad) vector for boosting. We sought to test these vaccines using a recently reported mouse-adapted SARS-CoV-2 (MA10) virus to (i) evaluate the protective efficacy of RhAd52 vaccines and (ii) further characterize this mouse-adapted challenge model and probe immune correlates of protection. We demonstrate that RhAd52 vaccines elicit robust SARS-CoV-2-specific antibody responses and protect against clinical disease and viral replication in the lungs. Further, binding and neutralizing antibody titers correlated with protective efficacy. These data validate the MA10 mouse model as a useful tool to screen and study novel vaccine candidates, as well as the development of RhAd52 vaccines for COVID-19.

Background: A DNA-prime/human adenovirus serotype 5 (HuAd5) boost vaccine encoding Plasmodium falciparum (Pf) circumsporozoite protein (PfCSP) and Pf apical membrane antigen-1 (PfAMA1), elicited protection in 4/15 (27%) of subjects against controlled human malaria infection (CHMI) that was statistically associated with CD8+ T cell responses. Subjects with high level pre-existing immunity to HuAd5 were not protected, suggesting an adverse effect on vaccine efficacy (VE). We replaced HuAd5 with chimpanzee adenovirus 63 (ChAd63), and repeated the study, assessing both the two-antigen (CSP, AMA1 = CA) vaccine, and a novel three-antigen (CSP, AMA1, ME-TRAP = CAT) vaccine that included a third pre-erythrocytic stage antigen [malaria multiple epitopes (ME) fused to the Pf thrombospondin-related adhesive protein (TRAP)] to potentially enhance protection., Methodology: This was an open label, randomized Phase 1 trial, assessing safety, tolerability, and VE against CHMI in healthy, malaria naïve adults. Forty subjects (20 each group) were to receive three monthly CA or CAT DNA priming immunizations, followed by corresponding ChAd63 boost four months later. Four weeks after the boost, immunized subjects and 12 infectivity controls underwent CHMI by mosquito bite using the Pf3D7 strain. VE was assessed by determining the differences in time to parasitemia as detected by thick blood smears up to 28-days post CHMI and utilizing the log rank test, and by calculating the risk ratio of each treatment group and subtracting from 1, with significance calculated by the Cochran-Mantel-Haenszel method., Results: In both groups, systemic adverse events (AEs) were significantly higher after the ChAd63 boost than DNA immunizations. Eleven of 12 infectivity controls developed parasitemia (mean 11.7 days). In the CA group, 15 of 16 (93.8%) immunized subjects developed parasitemia (mean 12.0 days). In the CAT group, 11 of 16 (63.8%) immunized subjects developed parasitemia (mean 13.0 days), indicating significant protection by log rank test compared to infectivity controls (p = 0.0406) and the CA group (p = 0.0229). VE (1 minus the risk ratio) in the CAT group was 25% compared to -2% in the CA group. The CA and CAT vaccines induced robust humoral (ELISA antibodies against CSP, AMA1 and TRAP, and IFA responses against sporozoites and Pf3D7 blood stages), and cellular responses (IFN-γ FluoroSpot responses to CSP, AMA1 and TRAP) that were not associated with protection., Conclusions: This study demonstrated that the ChAd63 CAT vaccine exhibited significant protective efficacy, and confirmed protection was afforded by adding a third antigen (T) to a two-antigen (CA) formulation to achieve increased VE. Although the ChAd63-CAT vaccine was associated with increased frequencies of systemic AEs compared to the CA vaccine and, historically, compared to the HuAd5 vectored malaria vaccine encoding CSP and AMA1, they were transient and associated with increased vector dosing., Competing Interests: The authors have declared that no competing interests exist. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

The coronavirus disease 2019 (COVID-19) pandemic caused by the emergent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) threatens global public health, and there is an urgent need to develop safe and effective vaccines. Here, we report the generation and the preclinical evaluation of a novel replication-defective gorilla adenovirus-vectored vaccine encoding the pre-fusion stabilized Spike (S) protein of SARS-CoV-2. We show that our vaccine candidate, GRAd-COV2, is highly immunogenic both in mice and macaques, eliciting both functional antibodies that neutralize SARS-CoV-2 infection and block Spike protein binding to the ACE2 receptor, and a robust, T helper (Th)1-dominated cellular response. We show here that the pre-fusion stabilized Spike antigen is superior to the wild type in inducing ACE2-interfering, SARS-CoV-2-neutralizing antibodies. To face the unprecedented need for vaccine manufacturing at a massive scale, different GRAd genome deletions were compared to select the vector backbone showing the highest productivity in stirred tank bioreactors. This preliminary dataset identified GRAd-COV2 as a potential COVID-19 vaccine candidate, supporting the translation of the GRAd-COV2 vaccine in a currently ongoing phase I clinical trial (ClinicalTrials.gov: NCT04528641)., Competing Interests: Declaration of interests S. Capone, A.R., M.G., S.B., A.S., A.M.C., R.S., F.B., A. Leuzzi, E.L., G. Miselli, A.N., M.F., F.T., M.S., A.F., S. Colloca, and A.V. are employees of ReiThera Srl. A.F. and S. Colloca are also shareholders of Keires AG. A. Lahm is a consultant for ReiThera Srl. S. Colloca, A. Lahm, A.R., and A.V. are inventors of the patent application number 20183515.4, titled “Gorilla Adenovirus Nucleic Acid- and Amino Acid-Sequences, Vectors Containing Same, and Uses Thereof.” The other authors declare no competing interests., (Copyright © 2021 The American Society of Gene and Cell Therapy. All rights reserved.)

The development of a safe and effective vaccine against SARS-CoV-2, the causative agent of pandemic coronavirus disease-2019 (COVID-19), is a global priority. Here, we aim to develop novel SARS-CoV-2 vaccines based on a derivative of less commonly used rare adenovirus serotype AdC68 vector. Three vaccine candidates were constructed expressing either the full-length spike (AdC68-19S) or receptor-binding domain (RBD) with two different signal sequences (AdC68-19RBD and AdC68-19RBDs). Single-dose intramuscular immunization induced robust and sustained binding and neutralizing antibody responses in BALB/c mice up to 40 weeks after immunization, with AdC68-19S being superior to AdC68-19RBD and AdC68-19RBDs. Importantly, immunization with AdC68-19S induced protective immunity against high-dose challenge with live SARS-CoV-2 in a golden Syrian hamster model of SARS-CoV-2 infection. Vaccinated animals demonstrated dramatic decreases in viral RNA copies and infectious virus in the lungs, as well as reduced lung pathology compared to the control animals. Similar protective effects were also found in rhesus macaques. Taken together, these results confirm that AdC68-19S can induce protective immune responses in experimental animals, meriting further development toward a human vaccine against SARS-CoV-2., Competing Interests: The authors declare that LZ, DZ, ML, and XS are co-inventors on pending patent applications related to the AdC68-19S, AdC68-19RBD, and AdC68-19RBDs vaccine candidates. ZH, XT, and LY are employees of Walvax Biotechnology Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Li, Guo, Lu, Zhou, Shi, Shi, Cheng, Liang, Liu, Wang, Wang, Wang, Fu, Xing, Wang, Ju, Liu, Lau, Jia, Tong, Yuan, Guo, Qi, Zhang, Huang, Chen, Zhang, Chen, Peng, Zhou and Zhang.)

Hepatocyte infection by malaria sporozoites is a bottleneck in the life-cycle of Plasmodium spp. including P. falciparum , which causes the most lethal form of malaria. Therefore, developing an effective vaccine capable of inducing the strong humoral and cellular immune responses necessary to block the pre-erythrocytic stage has potential to overcome the spatiotemporal hindrances pertaining to parasite biology and hepatic microanatomy. We recently showed that when combined with a human adenovirus type 5 (AdHu5)-priming vaccine, adeno-associated virus serotype 1 (AAV1) is a potent booster malaria vaccine vector capable of inducing strong and long-lasting protective immune responses in a rodent malaria model. Here, we evaluated the protective efficacy of a hepatotropic virus, adeno-associated virus serotype 8 (AAV8), as a booster vector because it can deliver a transgene potently and rapidly to the liver, the organ malaria sporozoites initially infect and multiply in following sporozoite injection by the bite of an infected mosquito. We first generated an AAV8-vectored vaccine expressing P. falciparum circumsporozoite protein (PfCSP). Intravenous (i.v.) administration of AAV8-PfCSP to mice initially primed with AdHu5-PfCSP resulted in a hepatocyte transduction rate ~2.5 times above that seen with intramuscular (i.m.) administration. This immunization regimen provided a better protection rate (100% sterile protection) than that of the i.m. AdHu5-prime/i.m. AAV8-boost regimen (60%, p < 0.05), i.m. AdHu5-prime/i.v. AAV1-boost (78%), or i.m. AdHu5-prime/i.m. AAV1-boost (80%) against challenge with transgenic PfCSP-expressing P. berghei sporozoites. Compared with the i.m. AdHu5-prime/i.v. AAV1-boost regimen, three other regimens induced higher levels of PfCSP-specific humoral immune responses. Importantly, a single i.v. dose of AAV8-PfCSP recruited CD8 + T cells, especially resident memory CD8 + T cells, in the liver. These data suggest that boost with i.v. AAV8-PfCSP can improve humoral and cellular immune responses in BALB/c mice. Therefore, this regimen holds great promise as a next-generation platform for the development of an effective malaria vaccine., Competing Interests: SY, MI, and HM are named inventors on filed patents related to immunization with the AAV anti-malarial vaccines. These products have not been commercialized. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Shahnaij, Iyori, Mizukami, Kajino, Yamagoshi, Syafira, Yusuf, Fujiwara, Yamamoto, Kato, Ohno and Yoshida.)

Hemorrhagic enteritis virus (HEV) is an immunosuppressive adenovirus that causes an acute clinical disease characterized by hemorrhagic gastroenteritis in 4-week-old turkeys and older. Recurrent incidence of secondary infections (e.g., systemic bacterial infections, cellulitis, and elevated mortality), may be associated with the presence of field-type HEV in Canadian turkey farms. We speculate that field-type HEV and vaccine/vaccine-like strains can be differentiated through analysis of the viral genomes, hexon genes, and the specific virulence factors (e.g., ORF1, E3, and fib knob domain). Nine out of sixteen spleens obtained from cases suspected of immunosuppression by HEV were analyzed. The limited data obtained showed that: (1) field-type HEV circulates in many non-vaccinated western Canadian flocks; (2) field-type HEV circulates in vaccinated flocks with increased recurrent bacterial infections; and (3) the existence of novel point mutations in hexon, ORF1, E3, and specially fib knob domains. This is the first publication showing the circulation of wild-type HEV in HEV-vaccinated flocks in Western Canada, and the usefulness of a novel procedure that allows whole genome sequencing of HEV directly from spleens, without passaging in cell culture or passaging in vivo. Further studies focusing more samples are required to confirm our observations and investigate possible vaccination failure.

Cancer is a major challenge in our societies, according to the World Health Organization (WHO) about 1/6 deaths were cancer related in 2018 and it is considered the second leading cause of death globally. Immunotherapies have changed the paradigm of oncologic treatment for several cancers where the field had fallen short in providing competent therapies. Despite the improvement, broadly acting and highly effective therapies capable of eliminating or preventing human cancers with insufficient mutated antigens are still missing. Adenoviral vector-based vaccines are a successful tool in the treatment of various diseases including cancer; however, their success has been limited. In this review we discuss the potential of adenovirus as therapeutic tools and the current developments to use them against cancer. More specifically, we examine how to use them to target endogenous retroviruses (ERVs). ERVs, comprising 8% of the human genome, have been detected in several cancers, while they remain silent in healthy tissues. Their low immunogenicity together with their immunosuppressive capacity aid cancer to escape immunosurveillance. In that regard, virus-like-vaccine (VLV) technology, combining adenoviral vectors and virus-like-particles (VLPs), can be ideal to target ERVs and elicit B-cell responses, as well as CD8 + and CD4 + T-cells responses.

Follicular helper T (Tfh) cells regulate high-affinity antibody production. Some findings have indicated that Tfh cells could be differentiated into memory cells. Here we have investigated the effects of IFN-α, as an adjuvant, on the generation of memory Tfh cell and memory B cell responses. The data showed that adenoviral vectors expressing: (i) foot-and-mouth disease virus (FMDV) VP1 proteins and porcine IFN-α, or (ii) porcine IFN-α alone, potently enhanced the generation of memory Tfh cells, especially the CCR7 l o memory Tfh subset. Upon rechallenge with FMD recombinant adenoviral vaccines, IFN-α enhances Tfh cells activity, rapidly upregulating their signature Bcl-6, CXCR5, and IL-21 markers. The results suggest that IFN-α enhances the levels of the transcription factor Bcl-6 within Tfh cells, potentially by regulating STAT1. Additionally, IFN-α substantially increased the number of IgG1 + and CD86 + memory B cells, which are responsible for inducing the rapid effector functions of memory Tfh cells after vaccine reactivation, establishing the close relationship between memory B cell and memory Tfh cell subsets. In brief, IFN-α enhances the potency of FMD recombinant adenoviral vaccines to induce memory Tfh and memory B cell responses, thus elevating serum antibody titers. IFN-α administration therefore represents an attractive strategy for enhancing responses to vaccination., (Copyright © 2020 Duan, Sun, Lan, Shen, Zhang, Hou, Chen, Ma, Xia and Su.)

Adenoviral vectors are being developed as vaccines against infectious agents and tumour-associated antigens, because of their ability to induce cellular immunity. However, the protection afforded in animal models has not easily translated into primates and clinical trials, underlying the need for improving adenoviral vaccines-induced immunogenicity. A Toll-like receptor signalling molecule, TRAM, was assessed for its ability to modify the immune responses induced by an adenovirus-based vaccine. Different adenovirus vectors either expressing TRAM alone or co-expressing TRAM along with a model antigen were constructed. The modification of T-cell and antibody responses induced by TRAM was assessed in vivo in mice and in primates. Co-expression of TRAM and an antigen from adenoviruses increased the transgene-specific CD8+ T cell responses in mice. Similar effects were seen when a TRAM expressing virus was co-administered with the antigen-expressing adenovirus. However, in primate studies, co-administration of a TRAM expressing adenovirus with a vaccine expressing the ME-TRAP malaria antigen had no significant effect on the immune responses. While these results support the idea that modification of innate immune signalling by genetic vectors modifies immunogenicity, they also emphasise the difficulty in generalising results from rodents into primates, where the regulatory pathway may be different to that in mice.

A respiratory outbreak associated with human adenovirus type 7 (HAdV-7) occurred among unvaccinated officer candidates attending initial military training. Respiratory infections associated with HAdV-7 can be severe, resulting in significant morbidity. Genomic sequencing revealed HAdV-7d, a genome type recently remerging in the United States as a significant respiratory pathogen, following reports from Southeast Asia. Twenty-nine outbreak cases were identified; this likely represents an underestimate. Although the HAdV type 4 and 7 vaccine is currently given to US military enlisted recruit trainees, it is not routinely given to officer candidates. Administration of the HAdV type 4 and 7 vaccine may benefit this cohort., (Published by Oxford University Press for the Infectious Diseases Society of America 2019.)

Background: A number of serious human adenovirus (HAdV) outbreaks have been recently reported: HAdV-B7 (Israel, Singapore, and USA), HAdV-B7d (USA and China), HAdV-D8, -D54, and -C2 (Japan), HAdV-B14p1 (USA, Europe, and China), and HAdV-B55 (China, Singapore, and France)., Methods: To understand the epidemiology of HAdV infections in Singapore, we studied 533 HAdV-positive clinical samples collected from 396 pediatric and 137 adult patients in Singapore from 2012 to 2018. Genome sequencing and phylogenetic analyses were performed to identify HAdV genotypes, clonal clusters, and recombinant or novel HAdVs., Results: The most prevalent genotypes identified were HAdV-B3 (35.6%), HAdV-B7 (15.4%), and HAdV-E4 (15.2%). We detected 4 new HAdV-C strains and detected incursions with HAdV-B7 (odds ratio [OR], 14.6; 95% confidence interval [CI], 4.1-52.0) and HAdV-E4 (OR, 13.6; 95% CI, 3.9-46.7) among pediatric patients over time. In addition, immunocompromised patients (adjusted OR [aOR], 11.4; 95% CI, 3.8-34.8) and patients infected with HAdV-C2 (aOR, 8.5; 95% CI, 1.5-48.0), HAdV-B7 (aOR, 3.7; 95% CI, 1.2-10.9), or HAdV-E4 (aOR, 3.2; 95% CI, 1.1-8.9) were at increased risk for severe disease., Conclusions: Singapore would benefit from more frequent studies of clinical HAdV genotypes to identify patients at risk for severe disease and help guide the use of new antiviral therapies, such as brincidofovir, and potential administration of HAdV 4 and 7 vaccine., (© The Author(s) 2019. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Background: For the purpose of studying functional human dendritic cells (DCs) in a humanized mouse model that mimics the human immune system (HIS), a model referred to as HIS mice was established., Methods: Human immune system mice were made by engrafting NOD/SCID/IL2Rgammanull (NSG) mice with human hematopoietic stem cells (HSCs) following the transduction of genes encoding human cytokines and human leukocyte antigen (HLA)-A2.1 by adeno-associated virus serotype 9 (AAV9) vectors., Results: Our results indicate that human DC subsets, such as CD141+CD11c+ and CD1c+CD11c+ myeloid DCs, distribute throughout several organs in HIS mice including blood, bone marrow, spleen, and draining lymph nodes. The CD141+CD11c+ and CD1c+CD11c+ human DCs isolated from HIS mice immunized with adenoviruses expressing malaria/human immunodeficiency virus (HIV) epitopes were able to induce the proliferation of malaria/HIV epitopes-specific human CD8+ T cells in vitro. Upregulation of CD1c was also observed in human CD141+ DCs 1 day after immunization with the adenovirus-based vaccines., Conclusions: Establishment of such a humanized mouse model that mounts functional human DCs enables preclinical assessment of the immunogenicity of human vaccines in vivo., (© The Author(s) 2019. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Porcine reproductive and respiratory syndrome virus (PRRSV) keeps causing economic damages in the swine sector across the globe. There has been emergence of the European (EU) genotype of porcine reproductive and respiratory syndrome virus (Genotype-I PRRSV) in China in recent years. The presently available vaccines cannot unable to provide safeguard against PRRSV infection completely. This study was aimed to construct recombinant adenovirus expressing the ORF3 and ORF5 genes of the EU-type PRRSV strain. Then, the recombinant adenovirus vaccines for EU-type PRRSV (rAd-E3518, rAd-E35, rAd-E3 and rAd-E5) which we constructed and evaluated were constructed and identified by western blot and PCR. All recombinant adenovirus vaccines were evaluated for humoral and cellular responses and EU-type PRRSV challenge in pigs. The results showed that the group of rAd-E3518+Quil A developed higher GP3 and GP5 specific antibody responses compared to the group of rAd-E3518. The majority of the neutralizing antibody titers were higher than 1:16 (P<0.05), the fusion of IL-18 has increased significantly PRRSV-stimulated secretion of IFN-γ and IL-4 in porcine serum, the group of rAd-E3518+Quil A produced highest T-lymphocytes (CD3 + CD4 + and CD3 + CD8 + T cells) proliferative in peripheral blood of pigs. The animals were challenged with the EU-type PRRSV strain and the viral load was detected in the several tissues, the viral load of rAd-E3518 and rAd-E3518+Quil A were lower than the wild-type adenovirus group. Our findings provide evidence to confirm that the recombinant adenovirus vaccine can protect pigs from EU-PRRSV infection.

Certain strains of fowl adenovirus serotype 4 (FAdV-4) of the family Adenoviridae are recognized to be the causative agents of Hydropericardium Syndrome (HPS) in broiler chicken. Despite the significantly spiking mortality in broilers due to HPS, not much effort has been made to design an effective vaccine against FAdV-4. The combination of immuno- and bioinformatics tools for immunogenic epitope prediction is the most recent concept of vaccine design. It reduces the time and effort required for hunting a potent vaccine candidate and is economical. Previously, we have reported the penton base protein of FAdV-4 to be a candidate for subunit vaccine against HPS. In the present study, we have computationally pre-screened promising B- and T-cell epitopes of the penton base. Multiple methods were employed for linear B-cell epitope identification; BepiPred and five other methods based on physicochemical properties of the amino acids. The penton base was homology modeled by means of Modeller 9.17 and after refinement of the model (by GalaxyRefine web server) ElliPro web tool was used to predict the discontinuous epitopes. NetMHCcons 1.1 and NetMHCIIpan 3.1 servers were used for the likelihood of peptide binding to Major Histocompatibility Complex (MHC) class I & II molecules respectively for T-cell epitope forecast. As a result, we identified the peptide stretch of 1-225  as the most promiscuous B- and T-cell epitope region in penton base Full Length (FL) protein sequence. Escherichia coli based expression vectors were generated containing cloned peptide stretch 1-225 (penton base 1-225 ) and penton base FL gene sequence. The recombinant penton base 1-225 and penton base FL proteins were expressed and purified using Escherichia coli-based expression system. Purification yield of penton base 1-225 was 3-fold higher compared to penton base FL. These proteins were injected in chickens to determine their competence in protection against HPS. The results showed equal protection level of the two proteins and the commercial inactivated vaccine against FAdV-4 infection. The results suggest the peptide stretch 1-225 of penton base as a valuable candidate for developing an epitope-driven vaccine to combat HPS., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Background: In March 2011, the U.S. Food and Drug Administration licensed adenovirus type 4 and type 7 vaccine, live, oral (Barr Labs, Inc.) (adenovirus vaccine) for use in military personnel 17 through 50 years of age. The vaccine was first universally administered to U.S. military recruits in October 2011. We investigated adverse event (AE) reports following the adenovirus vaccine submitted to the Vaccine Adverse Event Reporting System (VAERS)., Methods: We searched the VAERS database for U.S. reports among persons who received adenovirus vaccine during October 2011 through July 2018 including participants in a military observational study. We reviewed all serious reports and accompanying medical records. We compared the proportion of serious reports in a proxy military recruit population and reviewed all reports of suspected allergic reactions following adenovirus vaccination., Results: During the analytic period, VAERS received 100 reports following adenovirus vaccination; 39 (39%) were classified as serious and of these, 17 (44%) were from the observational study. One death was reported. Males accounted for 72% of reports. Median age of vaccinees was 19 years (range 17-32). The most frequently reported serious AEs were Guillain Barré syndrome (GBS) (n = 12) and anaphylaxis (n = 8); of these, two GBS and all the anaphylaxis reports were reported in the observational study. Reports documented concurrent receipt of multiple other vaccines (95%) and penicillin G (IM Pen G) or other antibiotics (50%)., Conclusions: The reporting rate for serious AEs was higher than with other vaccines administered in the comparison military recruit population (39% vs 18%); however, we identified no unexpected or concerning pattern of adenovirus vaccine AEs. Co-administration of vaccines and IM Pen G was commonly reported in this military population. These exposures may have contributed to the GBS and anaphylaxis outcomes observed with the adenovirus vaccine. Future adenovirus vaccine safety studies in a population without these co-administrations would be helpful in clarifying the vaccine's safety profile., (Published by Elsevier Ltd.)

Adenovirus (AdV)-based vectors are popular experimental vaccine vectors, but despite their ability to induce strong immune responses, their application is impeded by widespread preexisting immunity against many AdV types that can impair or even abrogate the induction of transgene-specific immune responses. Therefore, the development of vectors based on AdV types with a low seroprevalence is important for effective AdV-based immunization in humans. We investigated the immunization efficacy of vectors based on AdV type 48 (Ad48) and Ad50 in the ovalbumin (ova) model as well as the Friend retrovirus (FV) model, which allows testing of the protective effect of vaccine-induced immunity. Using ova-encoding vectors, we found a significantly lower induction of ova-specific CD8 + T cells and antibody responses by Ad48- and Ad50-based vectors than by Ad5-based vectors. Similarly, we found a reduced induction of FV-specific CD8 + T cell responses in Ad48- and Ad50.Leader-Gag-immunized mice compared with that in Ad5-immunized mice; however, some of those mice were able to control the FV infection, and protection correlated with the level of neutralizing antibodies 10 days after FV challenge. Analyses of the AdV-specific antibodies and CD8 + T cells induced by the individual AdV types revealed a high level of cross-reactivity, and the efficacy of Ad48-based immunization was impaired in Ad5-preimmune mice. Our results show that the immunity induced by Ad48- and Ad50-based vectors is reduced compared to that induced by Ad5 and is sufficient to control FV infection in only some of the immunized mice. A high level of cross-reactivity suggests that AdV preimmunity must be considered even when applying rare AdV-based vectors. IMPORTANCE AdV-based vectors are important tools for the development of vaccines against a wide range of pathogens. While AdV vectors are generally considered safe and highly effective, their application can be severely impaired by preexisting immunity due to the widespread seroprevalence of some AdV types. The characterization of different AdV types with regard to immunogenicity and efficacy in challenge models is of great importance for the development of improved AdV-based vectors that allow for efficient immunization despite anti-AdV immunity. We show that the immunity induced by an Ad48-based vector is inferior to that induced by an Ad5-based vector but can still mediate the control of an FV infection in highly FV-susceptible mice. However, the efficacy of Ad48-based immunization was impaired in Ad5-preimmune mice. Importantly, we found cross-reactivity of both the humoral and cellular immune responses raised by the individual AdV types, suggesting that switching to a different AdV type may not be sufficient to circumvent preexisting anti-AdV immunity., (Copyright © 2019 American Society for Microbiology.)

Human adenovirus type 4 (HAdV4) is an etiological agent of acute respiratory disease (ARD) in pediatric and adult patients. HAdV4 strains can be divided into two major genomic clusters, namely prototype (p)-like viruses and a-like viruses. Here, the complete genome sequence of HAdV4 strain GZ01, isolated from a child with ARD in southern China, is first reported and analyzed. This strain was determined to be of the 4a1 genome-type based on in silico restriction profiles. Then, a replication-competent rAd4DsRed virus, containing the HAdV4 GZ01 infectious genome and expressing the reporter molecule DsRed, was generated and characterized. Recombinant rAd4DsRed can infect AD293, hamster, and mouse cells in which DsRed protein was expressed. No changes in antigenicity and genome replication were detected for rAd4DsRed and wild-type HAdV4. Mice immunized with rAd4DsRed was elicited a marked antibody response to DsRed. A rapid method of testing neutralizing antibodies against HAdV3 and HAdV4 was also established using a mixture of rAd4DsRed and rAd3EGFP. Our results provide the foundation to develop HAdV4 vaccines, potential vector platforms for vaccine and gene therapy, and rapid methods for serological and antiviral screening., (Copyright © 2019 Elsevier B.V. All rights reserved.)

CD8+ T lymphocytes play an important role in controlling infections by intracellular pathogens. Chemokines and their receptors are crucial for the migration of CD8+ T-lymphocytes, which are the main IFNγ producers and cytotoxic effectors cells. Although the participation of chemokine ligands and receptors has been largely explored in viral infection, much less is known in infection by Trypanosoma cruzi, the causative agent of Chagas disease. After T. cruzi infection, CXCR3 chemokine receptor is highly expressed on the surface of CD8+ T-lymphocytes. Here, we hypothesized that CXCR3 is a key molecule for migration of parasite-specific CD8+ T-cells towards infected tissues, where they may play their effector activities. Using a model of induction of resistance to highly susceptible A/Sn mice using an ASP2-carrying DNA/adenovirus prime-boost strategy, we showed that CXCR3 expression was upregulated on CD8+ T-cells, which selectively migrated towards its ligands CXCL9 and CXCL10. Anti-CXCR3 administration reversed the vaccine-induced resistance to T. cruzi infection in a way associated with hampered cytotoxic activity and increased proapoptotic markers on the H2KK-restricted TEWETGQI-specific CD8+ T-cells. Furthermore, CXCR3 receptor critically guided TEWETGQI-specific effector CD8+ T-cells to the infected heart tissue that express CXCL9 and CXCL10. Overall, our study pointed CXCR3 and its ligands as key molecules to drive T. cruzi-specific effector CD8+ T-cells into the infected heart tissue. The unveiling of the process driving cell migration and colonization of infected tissues by pathogen-specific effector T-cells is a crucial requirement to the development of vaccine strategies., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Since the 1970s, replication-competent human adenoviruses 4 and 7 have been used as oral vaccines to protect U.S. soldiers against the severe respiratory diseases caused by these viruses. These vaccines are thought to establish a digestive tract infection conferring protection against respiratory challenge through antibodies. The success of these vaccines makes replication-competent adenoviruses attractive candidates for use as oral vaccine vectors. However, the inability of human adenoviruses to replicate efficiently in laboratory animals has hampered the study of such vectors. Here, we used mouse adenovirus type 1 (MAV-1) in mice to study oral replication-competent adenovirus-based vaccines. We show that MAV-1 oral administration provides protection that recapitulates the protection against homologous respiratory challenge observed with adenovirus 4 and 7 vaccines. Moreover, live oral MAV-1 vaccine better protected against a respiratory challenge than inactivated vaccines. This protection was linked not only with the presence of MAV-1-specific antibodies but also with a better recruitment of effector CD8 T cells. However, unexpectedly, we found that such oral replication-competent vaccine systemically spread all over the body. Our results therefore support the use of MAV-1 to study replication-competent oral adenovirus-based vaccines but also highlight the fact that those vaccines can disseminate widely in the body. IMPORTANCE Replication-competent adenoviruses appear to be promising vectors for the development of oral vaccines in humans. However, the study and development of these vaccines suffer from the lack of any reliable animal model. In this study, mouse adenovirus type 1 was used to develop a small-animal model for oral replication-competent adenovirus vaccines. While this model reproduced in mice what is observed with human adenovirus oral vaccines, it also highlighted that oral immunization with such a replication-competent vaccine is associated with the systemic spread of the virus. This study is therefore of major importance for the future development of such vaccine platforms and their use in large human populations., (Copyright © 2019 American Society for Microbiology.)

Introduction : Human adenovirus (HAdV)-derived vectors have been used in numerous pre-clinical and clinical trials during the last 40 years. Current research in HAdV-based vaccines focuses on improving transgene immunogenicity and safety. Because pre-existing humoral immunity against HAdV types correlate with reduced vaccine efficacy and safety, many groups are exploring the development of HAdV types vectors with lower seroprevalence. However, global seroepidemiological data are incomplete. Areas covered : The goal of this review is to centralize 65 years of research on (primarily) HAdV epidemiology. After briefly addressing adenovirus biology, we chronical HAdV seroprevalence studies and highlight major milestones. Finally, we analyze data from about 50 studies with respect to HAdVs types that are currently used in the clinic, or are in the developmental pipeline. Expert opinion : Vaccination is among the most efficient tools to prevent infectious disease. HAdV-based vaccines have undeniable potential, but optimization is needed and antivector immunity remains a challenge if the same vectors are to be administrated to different populations. Here, we identify gaps in our knowledge and the need for updated worldwide epidemiological data.

Host immune responses play an important role in the outcome of infection with hepatitis C virus (HCV). They can lead to viral clearance and a positive outcome, or progression and severity of chronic disease. Extensive research in the past >25 years into understanding the immune responses against HCV have still resulted in many unanswered questions implicating a role for unknown factors and events. In our earlier studies, we made a surprising discovery that peptides derived from structural and non-structural proteins of HCV have substantial amino acid sequence homologies with various proteins of adenoviruses and that immunizing mice with a non-replicating, non-recombinant adenovirus vector leads to induction of a robust cross-reactive cellular and humoral response against various HCV antigens. In this work, we further demonstrate antibody cross-reactivity between Ad and HCV in vivo. We also extend this observation to show that recombinant adenoviruses containing antigens from unrelated pathogens also possess the ability to induce cross-reactive immune responses against HCV antigens along with the induction of transgene antigen-specific immunity. This cross-reactive immunity can (a) accommodate the making of dual-pathogen vaccines, (b) play an important role in the natural course of HCV infection and (c) provide a plausible answer to many unexplained questions regarding immunity to HCV.

Adenovirus type 7 (Ad7) infection is associated with acute respiratory disease (ARD), especially in military recruits living in close quarters. Recently, several outbreaks of Ad7 infections have occurred in civilian populations, with some cases leading to death. However, the current Ad7 vaccine is licensed for use only in military recruits because it utilizes an orally delivered wild type virus which is shed in the stool for 28 days after immunization. This poses a safety risk due to the possibility of virus spread to vulnerable populations. To address the need for a safer Ad7 vaccine for use in civilian populations, we developed a single-cycle Ad7 virus (scAd7). This scAd7 virus is deleted for the Ad7 fiber protein, so that viruses produced outside of complementing cells lines lack this essential structural protein and have severely reduced infectivity. In vitro studies in noncomplementing A549 cells showed that the scAd7 virus has genomic DNA replication kinetics and Ad7 hexon expression similar to a replication-competent virus; however, virus progeny produced after infection has impaired infectivity. Therefore, this scAd7 virus combines the safety advantages of a replication-defective virus with the increased Ad7 gene expression of a replication-competent virus. Due to these advantages, we believe that scAd7 viruses should be further studied as an alternative, safer Adenovirus 7 vaccine.

In some serotypes of adenovirus (Ad), the penton base and attached trimeric fiber assemble into dodecameric virus-like particles called penton-dodecahedron (Pt-Dd), which can be internalized and used to deliver the vaccine antigens and drugs. Fowl adenovirus serotype 4 (FAdV-4) is an important pathogen, causing seriously economic loss to poultry industry in China and other counties. Pt-Dd particles from FAdV-4 infected cells, as well as in those infected with recombinant human Ad expressing fiber-1, fiber-2, and penton base of FAdV-4, were visualized by transmission electron microscopy. For the first time, we proved that FAdV-4 produced Pt-Dd in infected cells. Pt-Dd can also be assembled by the overexpressed recombinant proteins fiber-1, fiber-2, and penton base. Pt-Dd, as well as the recombinant proteins fiber-1, fiber-2, and penton base, were then used to immunize chickens. The humoral immune response, expression of selected immune molecules and challenge results were used to evaluate the immune efficacy of the vaccine candidates. Pt-Dd induced the highest level of enzyme-linked immunosorbent assay antibodies and significant high levels (p < 0.05) of interferonγ, interleukin-4, and major histocompatibility complex II expression in peripheral blood mononuclear cells at 48 h post-infection. The challenge results showed that Pt-Dd, inactivated FAdV-4 vaccine, and fiber-1 induced the best protection (100%), followed by fiber-2 (80%) and penton base (67%). The present study showed that FAdV-4 -Pt-Dd and recombinant fiber-1 are promising FAdV-4 vaccine candidates and could be used to replace the tissue-sourced inactivated FAdV-4 vaccine., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Cytomegalovirus (CMV) and non-replicating adenoviral vectors can induce expanded, sustained effector-memory CD8 + T-cell responses, termed "memory inflation". During murine CMV (MCMV) infection, CD4 + Tcells maintain inflationary virus-specific CD8 + T-cell responses via IL-2 but not IL-21. Adenovirus vector vaccination can induce phenotypically, functionally and transcriptionally similar inflationary responses, but it is not known how IL-21 influences the inflating memory response to adenoviral vaccination. Here, we show that IL-21 is an absolute requirement for induction and maintenance of vaccine-derived inflationary CD8 + T-cell responses. These data indicate that the induction pathway of inflationary Ad-LacZ T-cells is distinct from inflationary MCMV-specific T-cells and is highly dependent on IL-21. Our observations highlight a fundamental difference in the mechanism by which adenovirus vectors and MCMV drive inflationary T-cell responses., (Copyright © 2018. Published by Elsevier Ltd.)

Background: Agonists of TLR3 and TLR4 are effective immunoadjuvants for different types of vaccines. The mechanisms of their immunostimulatory action differ significantly; these differences are particularly critical for immunization with non-replicating adenovirus vectors (rAds) based vaccines. Unlike traditional vaccines, rAd based vaccines are not designed to capture vaccine antigens from the external environment by antigen presenting cells (APCs), but rather they are targeted to the de novo synthesis of vaccine antigens in APCs transfected with rAd. To date, there is no clear understanding about approaches to improve the efficacy of rAd vaccinations with immunoadjuvants. In this study, we investigated the immunoadjuvant effect of TLR3 and TLR4 agonists on the level of activation of APCs during vaccination with rAds., Results: We demonstrated that TLR3 and TLR4 agonists confer different effects on the molecular processes in APCs that determine the efficacy of antigen delivery and activation of antigen-specific CD4 + and CD8 + T cells. APCs activated with agonists of TLR4 were characterized by up-regulated production of target antigen mRNA and protein encoded in rAd, as well as enhanced expression of the co-activation receptors CD80, CD86 and CD40, and pro-inflammatory cytokines TNF-α, IL6 and IL12. These effects of TLR4 agonists have provided a significant increase in the number of antigen-specific CD4 + and CD8 + T cells. TLR3 agonist, on the contrary, inhibited transcription and synthesis of rAd-encoded antigens, but improved expression of CD40 and IFN-β in APCs. The cumulative effect of TLR3 agonist have resulted in only a slight improvement in the activation of antigen-specific T cells. Also, we demonstrated that IFN-β and TNF-α, secreted by APCs in response to TLR3 and TLR4 agonists, respectively, have an opposite effect on the transcription of the targeted gene encoded in rAd. Specifically, IFN-β inhibited, and TNF-α stimulated the expression of target vaccine antigens in APCs., Conclusions: Our data demonstrate that agonists of TLR4 but not TLR3 merit further study as adjuvants for development of vaccines based on recombinant adenoviral vectors.

Human adenoviruses (AdVs) have been extensively studied as vectors for gene therapy and vaccination. However, little attention has been paid to AdV vaccine development and treatment. Currently, there is a lack of information concerning the immunogenicity of AdV major capsid proteins. Here, using AdV7 as a model, we compared the immunogenicity and protection efficacy of its three major capsid proteins in DNA forms, pFiber, pHexon and pPenton, on a mouse model. Quantification of antigen-specific antibodies showed that pHexon induced highest IgG in sera while pPenton induced highest IgA in respiratory mucosae. A neutralization assay revealed that pPenton elicited the highest neutralizing activity against the homologous AdV7 in both sera and bronchoalveolar lavages (BALs). In addition, sera and BALs from mice immunized with either of the three constructs had cross-neutralizing activities against the heterologous AdV3. Furthermore, pHexon and pPenton induced Th1/2- and Th1/17-biased cellular responses, respectively, with pFiber being the weakest in the induction of cellular responses. Virus challenge assay showed that, pPenton group had the fastest virus clearance rate, followed by pFiber and pHexon groups. Likewise, the inflammation in the lung was well controlled in pPenton group against virus challenge. Taken together, our data demonstrate that penton base is better than fiber and hexon as a vaccine candidate against AdVs. Our findings provide important information for the development of subunit vaccines against AdVs., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Human adenovirus (Ad) species B contains several of the most important types associated with acute respiratory diseases, Ad3, -7, -14 and -55, which often lead to severe lower respiratory tract diseases and epidemic outbreaks. However, there is currently no Ad vaccine approved for general use. The major capsid protein, hexon, is the primary determinant recognized by neutralizing antibodies (NAbs). In this study, four recombinant Ads that have the same genome sequence as Ad3 with the exception of the hexon genes, rAd3EGFP, rAd3H7, rAd3H14 and rAd3H55, were combined as a tetravalent Ad candidate vaccine against Ad3, -7, -14 and -55. The replication efficiencies of chimeric rAd3H14, rAd3H7 and rAd3H55 were similar to that of rAd3EGFP. Recombinant rAd3EGFP, rAd3H7, rAd3H14 and rAd3H55 induced high titers of NAbs against Ad3, -7, -14 and -55, respectively, which were comparable to those induced by wild-type Ads. The mixture of the four recombinant Ads in equal proportions, rAdMix, or rAdMix inactivated by β-propiolactone, induced balanced NAb responses against Ad3, -7, -14 and -55 in mice without reciprocal immunological interference. In co-culture the four recombinant Ads replicated with a similar efficiency without reciprocal inhibition, and the progeny virions may be chimeric. Purified co-culture, rAdMix-C, also elicited balanced immune responses, suggesting a simple method for multivalent vaccine production. These results indicate the possible advantage of the four Ads as a live combined vaccine. Importantly, pre-immunization with rAdMix conferred protection against Ad3, -7, -14 or -55 challenge in mice in vivo. Thus, this research provides a novel tetravalent Ad vaccine candidate against Ad3, -7, -14 and -55., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Human adenoviruses types 3 (HAdV-3), 7 (HAdV-7) and 55 (HAdV-55) are major pathogens of acute respiratory infections (ARI) in children and adults. More than one type of HAdV can infect patients simultaneously, and the infections are sometimes fatal. However, there is currently no vaccine approved for general use in children and adults. Thus, development of a multivalent HAdV vaccine to combat HAdV infection becomes imperative. In this study, we constructed a new recombinant trivalent human adenovirus vaccine (rAdMHE3-h55), which expresses the hexon protein of HAdV-55 in the E3 region of rAdMHE3, a previously prepared bivalent vaccine candidate against HAdV-3 and HAdV-7. The results of in vitro neutralization assays indicate that rAdMHE3-h55 can induce the production of neutralizing antibodies against HAdV-3, HAdV-7, and HAdV-55 in mice. Furthermore, immunization with the recombinant trivalent vaccine candidate completely protected the mice challenged with HAdV-3, HAdV-7, orHAdV-55, respectively, showing lower lung viral loads and less lung Pathological changes was compared with those in unvaccinated mice. The current findings contribute to the development of a new adenovirus vaccine candidate and also advance this construction method for the generation of recombinant adenovirus vaccines. In conclusion, our recombinant trivalent vaccine rAdMHE3-h55 can provides protection against challenge with HAdV-3, HAdV-7, or HAdV-55 in mice. Future work of optimizing this vaccine candidate may lead to a more effective way of preventing respiratory diseases caused by common human adenoviruses., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Human and chimpanzee adenovirus vectors are being developed to circumvent preexisting antibodies against common adenovirus vectors such as Ad5. However, baseline immunity to these vectors still exists in human populations. Traditional cloning of new adenovirus vaccine vectors is a long and cumbersome process that takes 2 months or more and that requires rare unique restriction enzyme sites. Here we describe a novel, restriction enzyme-independent method for rapid cloning of new adenovirus vaccine vectors that reduces the total cloning procedure to 1 week. We developed 14 novel adenovirus vectors from rhesus monkeys that can be grown to high titers and that are immunogenic in mice. All vectors grouped with the unusual adenovirus species G and show extremely low seroprevalence in humans. Rapid cloning of novel adenovirus vectors is a promising approach for the development of new vector platforms. Rhesus adenovirus vectors may prove useful for clinical development. IMPORTANCE To overcome baseline immunity to human and chimpanzee adenovirus vectors, we developed 14 novel adenovirus vectors from rhesus monkeys. These vectors are immunogenic in mice and show extremely low seroprevalence in humans. Rhesus adenovirus vectors may prove useful for clinical development., (Copyright © 2018 Abbink et al.)

Since a novel hyper-virulent fowl adenovirus serotype 4 (FAdV-4) infection occurred in 2015, the novel FAdV-4 has been widely spreading across China, causing significant economic losses to the poultry industry. As the urgency of the issue calls for effective and efficient solutions, the present study investigated the possibility of the fiber-2 protein of the FAdV-4 to serve as a vaccine candidate against the novel FAdV-4. In the research, fiber-2 proteins were expressed in Escherichia coli, and then purified. To evaluate the immunogenicity of the recombinant fiber-2 protein, we investigated both the humoral and cellular immune responses in chickens immunized with fiber-2. The humoral immunity was assessed by detecting IgY antibodies and virus-neutralizing antibodies in chicken serum at 7, 14, 21 days post-immunization (dpi). We examined cellular immune responses by detecting CD3+CD4+ and CD3+CD8+ changes in chickens' peripheral blood through using flow cytometry at 7, 14, 21 dpi. The cytokine production in the serum of the immunized chickens was detected by ELISA at 7, 14, 21 dpi to further explore the impact of the recombinant protein on the regulation of cytokines. The protective efficacy was determined by the survival rate of the immunized chickens challenged with the novel FAdV-4. The results show that the level of IgY antibodies of the chickens immunized with fiber-2 protein was significantly higher than that of the chickens immunized with an inactivated vaccine against FAdV-4. Moreover, 7 days after immunization, the CD4+ T-cell proliferative response of the chickens immunized with fiber-2 was significantly higher than that of the chickens immunized with the inactivated vaccine. Challenge experiment showed that the fiber-2 protein could provide full protection and the inactivated vaccine could provide 90 percent protection against the FAdV-4. These results suggest that the recombinant fiber-2 protein can be an ideal candidate for subunit vaccines against the disease., (Copyright © 2018 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

The spread of hydropericardium syndrome has recently become serious in China since 2015. There is, therefore, an urgent need for new, safe and effective vaccines that prevent the disease. Here, the immune protection induced by Escherichia coli-expressed capsid proteins of fowl adenovirus serotype 4, including fiber-1, fiber-2, penton base and hexon (loop-1 region) were compared in chickens at different inoculation amounts. According to challenge mortalities and tissue gross/micro lesion results, fiber-2 induced the best protection, followed by fiber-1 and hexon. Fiber-1 and fiber-2 provided complete protection against 10 5.5 TCID 50 viral load challenge with 100 or 50μg doses per chicken, respectively. Penton could induce effective protection only at the high dosage of 200μg per chicken. The immunoprotective characteristics of these FAdV-4 capsid proteins may prove useful for developing subunit vaccines to control hydropericardium syndrome., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Adenovirus (Ad)-based immunization is a popular approach in vaccine development, and Ad-based vectors are renowned for their potential to induce strong CD8 + T cell responses to the encoded transgene. Surprisingly, we previously found in the mouse Friend retrovirus (FV) model that Ad-based immunization did not induce CD8 + T cell responses to the FV Leader-Gag-derived immunodominant epitope GagL 85-93 We show now that induction of GagL 85-93 -specific CD8 + T cells was highly effective when leader-Gag was delivered by plasmid DNA immunization, implying a role for Ad-derived epitopes in mediating unresponsiveness. By immunizing with DNA constructs encoding strings of GagL 85-93 and the two Ad-derived epitopes DNA-binding protein 418-426 (DBP 418-426 ) and hexon 486-494 , we confirmed that Ad epitopes prevent induction of GagL 85-93 -specific CD8 + T cells. Interestingly, while DBP 418-426 did not interfere with GagL 85-93 -specific CD8 + T cell induction, the H-2D d -restricted hexon 486-494 suppressed the CD8 + T cell response to the H-2D b -restricted GagL 85-93 strongly in H-2 b/d mice but not in H-2 b/b mice. This finding indicates that competition occurs at the level of responding CD8 + T cells, and we could indeed demonstrate that coimmunization with an interleukin 2 (IL-2)-encoding plasmid restored GagL 85-93 -specific CD8 + T cell responses to epitope strings in the presence of hexon 486-494 IL-2 codelivery did not restore GagL 85-93 responsiveness in Ad-based immunization, however, likely due to the presence of further epitopes in the Ad vector. Our findings show that seemingly immunodominant transgene epitopes can be dominated by Ad-derived epitopes. These findings underline the importance of thorough characterization of vaccine vectors, and modifications of vectors or immunogens may be required to prevent impaired transgene-specific immune responses. IMPORTANCE Ad-based vectors are widely used in experimental preclinical and clinical immunization studies against numerous infectious agents, such as human immunodeficiency virus, Ebola virus, Plasmodium falciparum , or Mycobacterium tuberculosis Preexisting immunity to Ad-based vectors is widely recognized as a hindrance to the widespread use of Ad-based vectors for immunizations in humans; however, our data show that an immune response to Ad-derived T cell epitopes can also result in loss or impairment of transgene-specific immune responses in prenaive vaccinees due to immune competition. Our results highlight that seemingly immunodominant epitopes may be affected by dominance of vector-derived epitopes, and modifications of the vector design or the immunogens employed in immunization may lead to more effective vaccines., (Copyright © 2017 American Society for Microbiology.)