Non-replicating Adenoviral Vector Research Articles

The Evolution of Nadofaragene Firadenovec: A Review and the Path Forward

BACKGROUND: The intravesical gene therapy nadofaragene firadenovec (rAd-IFNα/Syn3) was FDA approved in 2022 for non-muscle invasive bladder cancer (NMIBC) unresponsive to frontline treatment with BCG, and the first gene therapy developed for bladder cancer. This non-replicating recombinant adenovirus vector delivers a copy of the human interferon alpha-2b gene into urothelial and tumor cells, causing them to express this pleotropic cytokine with potent antitumor effects. OBJECTIVE: To provide a historical overview describing how several decades of preclinical and clinical studies investigating the role of interferon in the treatment of bladder cancer ultimately led to the development of gene therapy with nadofaragene for NMIBC. METHODS: We conducted a review of the literature using PubMed, Google Scholar, and ClinicalTrials.gov to summarize our knowledge of the evolution of interferon-based therapy in NMIBC. RESULTS: The FDA approval of this therapy represents an important landmark in urologic oncology and several decades of research dedicated to the study of interferon’s direct and indirect antitumor properties in NMIBC. The data gathered from the phase 1, 2, and 3 clinical trials continue to provide additional insights into the precise mechanisms underlying both the efficacy of and resistance to nadofaragene. CONCLUSIONS: Nadofaragene leverages the cytotoxic, anti-angiogenic, and immune-modulatory roles of interferon to effectively treat NMIBC that is resistant to BCG. Ongoing studies of resistance mechanisms and prognostic biomarkers have been promising; these will ultimately improve patient selection and allow for the modulation of factors in the tumor or immune microenvironment to further increase therapeutic response.

The Equal Neutralizing Effectiveness of BNT162b2, ChAdOx1 nCoV-19, and Sputnik V Vaccines in the Palestinian Population.

Since the beginning of the COVID-19 pandemic, different viral vector-based and mRNA vaccines directed against the SARS-CoV-2 "S" spike glycoprotein have been developed and have shown a good profile in terms of safety and efficacy. Nevertheless, an unbiased comparison of vaccination efficiency, including post-vaccination neutralizing activity, between the different vaccines remains largely unavailable. This study aimed to compare the efficacy of one mRNA (BNT162b2) and two non-replicating adenoviral vector vaccines (ChAdOx1 nCoV-19 and Sputnik V) in a cohort of 1120 vaccinated Palestinian individuals who received vaccines on an availability basis and which displayed a unique diversity of genetic characteristics. We assessed the level of anti-S antibodies and further determined the antibody neutralizing activity in 261 of those individuals vaccinated with BNT162b2a (121), ChAdOx1 (72) or Sputnik V (68). Our results showed no significant difference in the distribution of serum-neutralizing activity or S-antibody serum levels for the three groups of vaccines, proving equivalence in efficacy for the three vaccines under real-life conditions. In addition, none of the eight demographic parameters tested had an influence on vaccination efficacy. Regardless of the vaccine type, the vaccination campaign ultimately played a pivotal role in significantly reducing the morbidity and mortality associated with COVID-19 in Palestine.

The varying extent of humoral and cellular immune responses to either vector- or RNA-based SARS-CoV-2 vaccines persists for at least 18 months and is independent of infection.

The corona virus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome corona-virus 2 (SARS-CoV-2) spurred a worldwide race for the development of an efficient vaccine. Various strategies were pursued; however, the first vaccines to be licensed presented the SARS-CoV-2 spike protein either in the context of a non-replicating adenoviral vector or as an mRNA construct. While short-term efficacies have extensively been characterized, the duration of protection, the need for repeated boosting, and reasonable vaccination intervals have yet to be defined. We here describe the adaptive immune response resulting from homologous and heterologous vaccination regimen at 18 months after primary vaccination. To that extent, we monitored 176 healthcare workers, the majority of whom had recovered from previous SARS-CoV-2 infection. In summary, we find that differences depending on primary immunization continue to exist 18 months after the first vaccination and these findings hold true irrespective of previous infection with the virus. Homologous primary immunization with BNT162b2 was repeatedly shown to produce higher antibody levels and slower antibody decline, leading to more effective in vitro neutralization capacities. Likewise, cellular responses resulting from in vitro re-stimulation were more pronounced after primary immunization involving BNT162b2. In contrast, IL-2 producing memory T helper and cytotoxic T cells appeared independent from the primary vaccination regimen. Despite these differences, comparable infection rates among all vaccination groups suggest comparable real-life protection.IMPORTANCEVaccination against the severe acute respiratory syndrome corona-virus 2 (SARS-CoV-2) was shown to avert severe courses of corona virus disease 2019 (COVID-19) and to mitigate spreading of the virus. However, the duration of protection and need for repeated boosting have yet to be defined. Monitoring and comparing the immune responses resulting from various vaccine strategies are therefore important to fill knowledge gaps and prepare for future pandemics.

Strategy to develop broadly effective multivalent COVID-19 vaccines against emerging variants based on Ad5/35 platform

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron strain has evolved into highly divergent variants with several sub-lineages. These newly emerging variants threaten the efficacy of available COVID-19 vaccines. To mitigate the occurrence of breakthrough infections and re-infections, and more importantly, to reduce the disease burden, it is essential to develop a strategy for producing updated multivalent vaccines that can provide broad neutralization against both currently circulating and emerging variants. We developed bivalent vaccine AdCLD-CoV19-1 BA.5/BA.2.75 and trivalent vaccines AdCLD-CoV19-1 XBB/BN.1/BQ.1.1 and AdCLD-CoV19-1 XBB.1.5/BN.1/BQ.1.1 using an Ad5/35 platform-based non-replicating recombinant adenoviral vector. We compared immune responses elicited by the monovalent and multivalent vaccines in mice and macaques. We found that the BA.5/BA.2.75 bivalent and the XBB/BN.1/BQ.1.1 and XBB.1.5/BN.1/BQ.1.1 trivalent vaccines exhibited improved cross-neutralization ability compared to their respective monovalent vaccines. These data suggest that the developed multivalent vaccines enhance immunity against circulating Omicron subvariants and effectively elicit neutralizing antibodies across a broad spectrum of SARS-CoV-2 variants.

Boosting with variant-matched adenovirus-based vaccines promotes neutralizing antibody responses against SARS-CoV-2 Omicron sublineages in mice

Global spreading of SARS-CoV-2 Omicron subvariants, such as BA.4, BA.5, and XBB.1.5, has been leading the recent wave of COVID-19. Unique mutations in the spike proteins in these emerging Omicron subvariants caused immune evasion from the pre-existing protective immunity induced by vaccination or natural infection. We previously developed AdCLD-CoV19-1, a non-replicating recombinant adenoviral vector that encode receptor binding domain of spike protein of ancestral SARS-CoV-2 strain. Based on the same recombinant adenoviral vector platform, we constructed updated vaccines that cover unique mutations found in each Omicron subvariants including BA.1, BA.2, BA.4.1, and BA.5. Preclinical studies reveal that each updated vaccine as a booster shot following primary vaccination targeting ancestral strain most effectively improved neutralizing antibody responses against pseudo-virus of its respective strain. Of note, boosting with a vaccine targeting the BA.1 or BA.2 Omicron subvariant was most effective in neutralization against the pseudo-virus of BA.2.75 strain, whereas BA.4.1/5-adapted booster shots were most effective in neutralization against BQ.1, BQ1.1, and BF.7. Therefore, it is imperative to develop a vaccination strategy that can cover the unique spike mutations of currently circulating Omicron subvariants to prevent the next wave of COVID-19.

Pre-Clinical Development of an Adenovirus Vector Based RSV and Shingles Vaccine Candidate.

Respiratory syncytial virus (RSV) infection and shingles are two viral diseases that affect older adults, and a combined vaccine to protect against both could be beneficial. RSV infection causes hospitalisations and significant morbidity in both children and adults and can be fatal in the elderly. The RSV fusion (F) envelope glycoprotein induces a strong RSV-neutralising antibody response and is the target of protective immunity in the first RSV vaccine for older adults, recently approved by the FDA. An initial childhood infection with the varicella zoster virus (VZV) results in chickenpox disease, but reactivation in older adults can cause shingles. This reactivation in sensory and autonomic neurons is characterized by a skin-blistering rash that can be accompanied by prolonged pain. The approved protein-in-adjuvant shingles vaccine induces VZV glycoprotein E (gE)-fspecific antibody and CD4+ T cell responses and is highly effective. Here we report the evaluation of RSV/shingles combination vaccine candidates based on non-replicating chimpanzee adenovirus (ChAd) vectors. We confirmed the cellular and humoral immunogenicity of the vaccine vectors in mice using T cell and antibody assays. We also carried out an RSV challenge study in cotton rats which demonstrated protective efficacy following a homologous prime-boost regimen with our preferred vaccine candidate.

Adenoviral-vectored universal influenza vaccines administered intranasally reduce lung inflammatory responses upon viral challenge 15 months post-vaccination.

Vaccines targeting highly conserved proteins can protect broadly against diverse viral strains. When a vaccine is administered to the respiratory tract, protection against disease is especially powerful. However, it is important to establish that this approach is safe. When vaccinated animals later encounter viruses, does reactivation of powerful local immunity, including T cell responses, damage the lungs? This study investigates the safety of mucosal vaccination of the respiratory tract. Non-replicating adenoviral vaccine vectors expressing conserved influenza virus proteins were given intranasally. This vaccine-induced protection persists for at least 15 months. Vaccination did not exacerbate inflammatory responses or tissue damage upon influenza virus infection. Instead, vaccination with nucleoprotein reduced cytokine responses and histopathology, while neutrophil and T cell responses resolved earlier. The results are promising for safe vaccination at the site of infection and thus have implications for the control of influenza and other respiratory viruses.

Randomized controlled phase III trial of weekly paclitaxel ± ofranergene obadenovec (VB-111) for platinum-resistant ovarian cancer (OVAL Study/GOG 3018).

5505 Background: Ofranergene obadenovec (ofra-vec, VB-111) is a nonreplicating adenoviral vector with a murine pro-endothelin 1 (PPE-1-3X) promoter and pro-apoptotic Fas-tumor necrosis factor receptor 1 (TNFR1) chimeric transgene thought to have a dual mechanism of action: vascular disruption and immune activation. Methods: This is a randomized, placebo-controlled, double-blind, multi-center randomized phase III trial (ClinicalTrials.gov identifier: NCT03398655) of ofranergene obadenovec combined with paclitaxel vs paclitaxel with placebo for the treatment of patients with recurrent platinum resistant ovarian cancer (PROC). Patients were randomly assigned 1:1 to receive IV VB-111 1x1013 viral particles (VPs) every 8 weeks with weekly IV paclitaxel 80 mg/m2 or placebo with paclitaxel until disease progression. The dual primary endpoints were overall survival (OS) and progression free survival (PFS) as assessed by Blinded Independent Central Review (BICR). Results: Between December 2017 and March 2022, 409 patients were randomized at 86 clinical sites in US, Israel, Spain, Poland and Japan. The median PFS was 5.29 months in the VB-111 arm and 5.36 months in the control arm; hazard ratio (HR) 1.03 (CI: 0.83-1.29, p = 0.7823), and median OS with was 13.37 months vs. 13.14 months HR 0.97 (CI: 0.75–1.27 p = 0.8440). Objective response rates (ORR) were similar in both arms: RECIST 1.1 ORR was 28.9% with VB-111 vs. 29.6% with control (CA-125 ORR 41.1% vs 49.4%). In both treatment arms response to CA-125 was a substantial prognostic factor for both PFS and OS. In the VB-111 arm, the HR in CA-125 responders compared to non-responders was for PFS HR 0.2428 (CI: 0.1642-0.3588), and for OS HR 0.3343 (CI: 0.2134-0.5238). Safety profile was consistent with the known safety profile of ofra-vec and was characterized by common transient flu like symptoms such as fever and chills. Conclusions: The addition of ofranergene obadenovec to paclitaxel did not improve PFS or OS. Clinical trial information: NCT03398655 .

Vaccine-induced immune thrombotic thrombocytopenia: what do we know hitherto?

Vaccine-induced immune thrombotic thrombocytopenia (VITT), also known as thrombosis with thrombocytopenia syndrome, is a catastrophic and life-threatening reaction to coronavirus disease 2019 (COVID-19) vaccines, which occurs disproportionately in response to vaccination with non-replicating adenovirus vector (AV) vaccines. The mechanism of VITT is not well defined and it has not been resolved why cases of VITT are predominated by vaccination with AV vaccines. However, virtually all VITT patients have positive platelet-activating anti-platelet factor 4 (PF4) antibody titers. Subsequently, platelets are activated and depleted in an Fcγ-receptor IIa (FcγRIIa or CD32a)-dependent manner, but it is not clear why or how the anti-PF4 response is mounted. This review describes the pathogenesis of VITT and provides insight into possible mechanisms that prompt the formation of a PF4/polyanion complex, which drives VITT pathology, as an amalgam of current experimental data or hypotheses.

Expanding Opportunities in Viral Oncolysis.

Expanding Opportunities in Viral Oncolysis.

Development of broadly protective COVID-19 vaccine against up-to-date variants based on adenovirus type 5/35 vector platform.

Abstract The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) omicron strain has evolved into a highly divergent variant with several sub-lineages. These new emerging variants could impair the protective efficacy of COVID-19 vaccines based on the ancestral spike, causing breakthrough infections and re-infections. Therefore, it is imperative to develop new multivalent vaccines that can provide broad protection against currently prevalent new variants. We previously developed AdCLD-CoV19-1 OMI, an Ad5/35 platform based non-replicating recombinant adenoviral vector that encodes the spike protein of BA.1, and currently performing clinical studies. We also constructed vaccines against emerging subvariants such as BA.5, BA.2.75, XBB, BQ.1.1, and BN.1 using the Ad5/35 platform and evaluated their immunogenicity by sera from vaccinated mice. To develop the bivalent vaccine, we selected a combination of BA.5 and BA.2.75 vaccines by antigenic cartography map based on cross-neutralizing activities. We found that a bivalent vaccine could induce broadly neutralizing antibodies against the predominant circulating strains and improved cross-neutralization capacity. These data suggest that the bivalent vaccine broadens immunity against current prevalent omicron subvariants. We further investigate combinations of next-generation multivalent vaccines to confer broad protection against new subvariants. Based on the results of preclinical studies, clinical trials of the polyvalent vaccines will be conducted. Supported by grant from the Bio & Medical Technology Development Program of the National Research Foundation (NRF) funded by the Korean government (MSIT) (2020M3A9I2107463)

Adenoviral Vector-Based Vaccine Platform for COVID-19: Current Status.

The coronavirus disease (COVID-19) breakout had an unimaginable worldwide effect in the 21st century, claiming millions of lives and putting a huge burden on the global economy. The potential developments in vaccine technologies following the determination of the genetic sequence of SARS-CoV-2 and the increasing global efforts to bring potential vaccines and therapeutics into the market for emergency use have provided a small bright spot to this tragic event. Several intriguing vaccine candidates have been developed using recombinant technology, genetic engineering, and other vaccine development technologies. In the last decade, a vast amount of the vaccine development process has diversified towards the usage of viral vector-based vaccines. The immune response elicited by such vaccines is comparatively higher than other approved vaccine candidates that require a booster dose to provide sufficient immune protection. The non-replicating adenoviral vectors are promising vaccine carriers for infectious diseases due to better yield, cGMP-friendly manufacturing processes, safety, better efficacy, manageable shipping, and storage procedures. As of April 2022, the WHO has approved a total of 10 vaccines around the world for COVID-19 (33 vaccines approved by at least one country), among which three candidates are adenoviral vector-based vaccines. This review sheds light on the developmental summary of all the adenoviral vector-based vaccines that are under emergency use authorization (EUA) or in the different stages of development for COVID-19 management.

1960. Mucosal rAd5 Immunization against SARS-CoV-2 Spike Elicits Cross-Reactive Nasal and Serum Neutralizing Antibodies and Protects Against Beta Variant Challenge in African Green Monkeys

Abstract Background Mucosal vaccination may offer increased protection against SARS-CoV-2 compared to parental immunization. Here, we describe immunogenicity and efficacy following viral challenge in non-human primates after intranasal delivery of three unique non-replicating adenoviral vector vaccine (rAd5) candidates. Methods African green monkeys (AMG) were prime boost immunized 29 days apart with vaccine candidates either expressing the parental spike protein alone (Wuhan-S), spike plus nucleocapsid (Wuhan-S-N), or the spike protein from the beta variant (beta-S). Serum and nasal swabs were collected every 14 days and humoral responses to full length spike (S) and receptor binding domain (RBD) were assessed. All AMGs were challenged with SARS-CoV-2 B.1.351 (beta variant) on day 56. Viral loads measured every two days by TCID50 in nasal washes and bronchial lavage fluid post challenge. Results Mucosal immunization with Wuhan-S induced significant increases in serum IgG and IgA responses against the homologous parental lineage, as well as beta, delta, and omicron variants. In nasal samples, Wuhan-S immunization elicited over 500-fold increases in in cross-reactive IgA against multiple variants of concern including delta and omicron. While the beta-S rAd5 vaccine candidate induced enhanced serum IgG responses to homologous S and RBD proteins, this approach resulted in less cross-reactive antibodies to other variants compared to Wuhan-S rAd5 vaccine. Despite the differences in the ability to elicit cross-reactive antibody responses, all vaccinated AMGs challenged with SARS-CoV-2 B.1.351 (beta variant), had a significant reduction in viral titers by TCID50 in the nasal passages and reduced viral load in bronchial lavage fluid compared to unvaccinated controls. Conclusion These results demonstrate mucosal administration of rAd5 clinical candidate vaccine, Wuhan-S, is immunogenic and offers cross-protective humoral responses in both serum and nasal compartments against a mismatched SARS-CoV-2 challenge virus. Disclosures Becca A. Flitter, PhD, MPH, Vaxart Inc: Stocks/Bonds Sarah N. Tedjakusuma, n/a, Vaxart Inc: Stocks/Bonds Colin A. Lester, n/a, Vaxart Inc: Stocks/Bonds Elena D. Neuhaus, n/a, Vaxart Inc: Stocks/Bonds Susan Johnson, PhD, Vaxart Inc: Stocks/Bonds Emery G. Dora, n/a, Vaxart Inc: Stocks/Bonds Nadine Peinovich, MPH, Vaxart Inc: Stocks/Bonds Clara B. Jegede, n/a, Vaxart Inc: Stocks/Bonds Sean N. Tucker, PhD, Vaxart Inc: Stocks/Bonds.

Drop the Needle; A Temperature Stable Oral Tablet Vaccine Is Protective against Respiratory Viral Pathogens

To effectively combat emerging infections and prevent future pandemics, next generation vaccines must be developed quickly, manufactured rapidly, and most critically, administered easily. Next generation vaccines need innovative approaches that prevent infection, severe disease, and reduce community transmission of respiratory pathogens such as influenza and SARS-CoV-2. Here we review an oral vaccine tablet that can be manufactured and released in less than 16 weeks of antigen design and deployed without the need for cold chain. The oral Ad5 modular vaccine platform utilizes a non-replicating adenoviral vector (rAd5) containing a novel molecular TLR3 adjuvant that is delivered by tablet, not by needle. This enterically coated, room temperature-stable vaccine tablet elicits robust antigen-specific IgA in the gastrointestinal and respiratory tracts and upregulates mucosal homing adhesion molecules on circulating B and T cells. Several influenza antigens have been tested using this novel vaccine approach and demonstrated efficacy in both preclinical animal models and in phase I/II clinical trials, including in a human challenge study. This oral rAd5 vaccine platform technology offers a promising new avenue for aiding in rapid pandemic preparedness and equitable worldwide vaccine distribution.

A single-shot adenoviral vaccine provides hemagglutinin stalk-mediated protection against heterosubtypic influenza challenge in mice

Conventional influenza vaccines fail to confer broad protection against diverse influenza A viruses with pandemic potential. Efforts to develop a universal influenza virus vaccine include refocusing immunity towards the highly conserved stalk domain of the influenza virus surface glycoprotein, hemagglutinin (HA). We constructed a non-replicating adenoviral (Ad) vector, encoding a secreted form of H1 HA, to evaluate HA stalk-focused immunity. The Ad5_H1 vaccine was tested in mice for its ability to elicit broad, cross-reactive protection against homologous, heterologous, and heterosubtypic lethal challenge in a single-shot immunization regimen. Ad5_H1 elicited hemagglutination inhibition (HI+) active antibodies (Abs), which conferred 100% sterilizing protection from homologous H1N1 challenge. Furthermore, Ad5_H1 rapidly induced H1-stalk-specific Abs with Fc-mediated effector function activity, in addition to stimulating both CD4+ and CD8+ stalk-specific Tcell responses. This phenotype of immunity provided 100% protection from lethal challenge with a head-mismatched, reassortant influenza virus bearing a chimeric HA, cH6/1, in a stalk-mediated manner. Most importantly, 100% protection from mortality following lethal challenge with a heterosubtypic avian influenza virus, H5N1, was observed following a single immunization with Ad5_H1. In conclusion, Ad-based influenza vaccines can elicit significant breadth of protection in naive animals and could be considered for pandemic preparedness and stockpiling.

A qPCR-Based Method for Quantification of Replication Competent Adenovirus (RCA) in Conditionally Replicating Oncolytic Adenoviruses.

Production of conditionally replicating adenoviruses may unfortunately generate undesired replication-competent adenovirus (RCA) which raises safety concerns in clinical usage. Cell-based assays can detect RCA in batches of nonreplicating adenoviral vectors but cannot distinguish RCA from conditionally replicating oncolytic adenoviruses. Considering the great potential in using oncolytic viruses for cancer treatment, there is a need for comprehensive RCA-detection and -quantification methods. Here, we present a quantitative polymerase chain reaction (qPCR)-based assay that can be used to detect RCA particles in batches of conditionally replicating oncolytic adenoviruses. The assay is quantifying RCA by detection of the specific DNA sequence generated after a recombination event. Results showed that the method can successfully detect low levels of RCA, with a low limit of detection of ten viral particles.

Efficacy of the Vaccines, Their Safety, and Immune Responses against SARS-CoV-2 Infections

The search for vaccines has been a high priority since the worldwide COVID-19 pandemic was declared. Currently, mRNA-based vaccines, adenovirus-based vaccines, inactivated virus vaccines, and other vaccine platforms are all employed to combat the SARS-CoV-2 virus. BNT162b2 and mRNA-1273 are mRNA-based vaccines. The vaccination appears to be effective against SARS-CoV-2 strains that have emerged since the first study. They have primarily minor side effects, and there are no major safety concerns. Adenovirus-based vaccines are delivered by genetic cargo that is based on non-replicating adenovirus vectors that can increase immune response without the need of adjuvants. This is the case for Ad26.CoV2.S, ChAdOx1 nCoV-19/AZD1222, Gam-COVID-Vac/Sputnik V andAd5-based COVID-19 vaccine. There have been no known incidences of allergy to adenovirus vaccines, unlike mRNA vaccines. Inactivated virus vaccines are a common form of vaccine that has been used for decades. The goal is to render the virus non-infectious while preserving immunogenicity with high-quality antigens in order to trigger an immune response. The researched formaldehyde-inactivated whole-virus SARS-CoV2 vaccine (CoronaVac), as well as WIV04 and HB02, utilize this sort of vaccine formulation. A recombinant protein nanoparticle vaccine named NVX-CoV2373 is made up of trimeric spike glycoproteins with a potent Matrix-M1 adjuvant. Against the variant B.1.1.7 (Alpha), the vaccine appeared to be very effective. Vaccine efficacy against the B.1.351 (Beta) strain, on the other hand, proved to be lower.

Comment on ‘Vitiligo in a COVID‐19‐vaccinated patient with ulcerative colitis: coincidence?’: Type I interferons as possible link between COVID‐19 vaccine and vitiligo

We read with interest the article entitled "Vitiligo in a COVID-19-vaccinated patient with ulcerative colitis: coincidence?" by Aktas et al.1 The authors describe a 58-year-old man with ulcerative colitis who developed symmetrically distributed vitiligo facial patches around one week after receiving first dose of mRNA vaccine.1 the authors then ponder on the possible underlying immunological mechanism.

Immunization Update 2021

Immunization Update 2021

Nonreplicating Adenoviral Vectors: Improving Tropism and Delivery of Cancer Gene Therapy.

Simple SummaryThe treatment of cancer has progressed greatly with the advent of immunotherapy and gene therapy, including the use of nonreplicating adenoviral vectors to deliver genes with antitumor activity for cancer gene therapy. Even so, the successful application of these vectors may benefit from modifications in their design, including their molecular structure, so that specificity for the target cell is increased and off-target effects are minimized. With such improvements, we may find new opportunities for systemic administration of adenoviral vectors as well as the delivery of strategic antigen targets of an antitumor immune response. We propose that the improvement of nonreplicating adenoviral vectors will allow them to continue to hold a key position in cancer gene therapy and immunotherapy.Recent preclinical and clinical studies have used viral vectors in gene therapy research, especially nonreplicating adenovirus encoding strategic therapeutic genes for cancer treatment. Adenoviruses were the first DNA viruses to go into therapeutic development, mainly due to well-known biological features: stability in vivo, ease of manufacture, and efficient gene delivery to dividing and nondividing cells. However, there are some limitations for gene therapy using adenoviral vectors, such as nonspecific transduction of normal cells and liver sequestration and neutralization by antibodies, especially when administered systemically. On the other hand, adenoviral vectors are amenable to strategies for the modification of their biological structures, including genetic manipulation of viral proteins, pseudotyping, and conjugation with polymers or biological membranes. Such modifications provide greater specificity to the target cell and better safety in systemic administration; thus, a reduction of antiviral host responses would favor the use of adenoviral vectors in cancer immunotherapy. In this review, we describe the structural and molecular features of nonreplicating adenoviral vectors, the current limitations to their use, and strategies to modify adenoviral tropism, highlighting the approaches that may allow for the systemic administration of gene therapy.