Comparative analysis of ChAdOx1 nCoV-19 and Ad26.COV2.S SARS-CoV-2 vector vaccines

Vector-based SARS-CoV-2 vaccines have been associated with vaccine-induced thrombosis with thrombocytopenia syndrome (VITT/TTS), but the causative factors are still unresolved. We comprehensively analyzed ChAdOx1 nCov-19 (AstraZeneca) and Ad26.COV2.S (Johnson & Johnson). ChAdOx1 nCoV-19 contains significant amounts of host cell protein impurities, including functionally active proteasomes, and adenoviral proteins. In Ad26.COV2.S much less impurities were found. Platelet-factor 4 (PF4) formed complexes with ChAdOx1 nCoV-19 constituents, but not with purified virions from ChAdOx1 nCoV-19 or with Ad26.COV2.S. Vascular hyperpermeability was induced by ChAdOx nCoV-19 but not by Ad26.COV2.S.These differences in impurities together with EDTA-induced capillary leakage might contribute to the higher incidence rate of VITT associated with ChAdOx1 nCoV-19 compared to Ad26.COV2.S.

Thrombotic Thrombocytopenia after COVID-19 Vaccination: In Search of the Underlying Mechanism

The rollout of COVID-19 vaccines brings hope for successful pandemic mitigation and getting the transmission of SARS-CoV-2 under control. The vaccines authorized in Europe displayed a good safety profile in the clinical trials. However, during their post-authorization use, unusual thrombotic events associated with thrombocytopenia have rarely been reported for vector vaccines. This led to the temporary suspension of the AZD1222 vaccine (Oxford/AstraZeneca) in various European countries and the Ad26.COV2 vaccine (Janssen/Johnson&Johnson) in the United States, with regulatory bodies launching investigations into potential causal associations. The thromboembolic reactions were also rarely reported after mRNA vaccines. The exact cause of these adverse effects remains to be elucidated. The present paper outlines the hypotheses on the mechanisms behind the very rare thrombotic thrombocytopenia reported after the COVID-19 vaccination, along with currently existing evidence and future research prospects. The following are discussed: (i) the role of antibodies against platelet factor 4 (PF4), (ii) the direct interaction between adenoviral vector and platelets, (iii) the cross-reactivity of antibodies against SARS-CoV-2 spike protein with PF4, (iv) cross-reactivity of anti-adenovirus antibodies and PF4, (v) interaction between spike protein and platelets, (vi) the platelet expression of spike protein and subsequent immune response, and (vii) the platelet expression of other adenoviral proteins and subsequent reactions. It is also plausible that thrombotic thrombocytopenia after the COVID-19 vaccine is multifactorial. The elucidation of the causes of these adverse events is pivotal in taking precautionary measures and managing vaccine hesitancy. It needs to be stressed, however, that the reported cases are currently sporadic and that the benefits of COVID-19 vaccines vastly outweigh their potential risks.

592 Enhancing the therapeutic potential of oncolytic adenoviruses with vSENS™ technology

BackgroundOncolytic viro-therapeutics is a promising treatment for cancer. Among the different strains of oncolytic viruses currently being developed, potent cytolytic activity, manageable safety profiles, large genomic capacity for addition of transgenes and available advanced manufacture processes make adenovirus (Ad) a great choice.1 However, the delivery of Ad for clinical application is limited due to 1) neutralization by pre-existing neutralizing antibodies (nAb) in bloodstream and 2) receptor restricted tumor-cellular entry.2 To overcome these limitations, we developed a novel proprietary polymer nanoparticle delivery system, so called Stability Enhanced Nano Shells (SENS™) for the delivery of Virus (vSENS).MethodsSENS™ employs proprietary an ionizable cationic lipid and biodegradable and biocompatible polymers. Following complexation with replication-incompetent adenovirus serotype 5 (Ad-vSENS) or replication-competent oncolytic adenovirus serotype 5 (OAd-vSENS), the physicochemical properties of the complexes were characterized by dynamic light scattering (DLS) and electron microscopy. The benefit of vSENS in coxsackievirus and adenovirus receptor (CAR) restricted cellular transduction of adenovirus was evaluated with Ad-vSENS in CAR negative cancer cells. Pharmacokinetic profile of OAd-vSENS was examined in mice following systemic administration to assess the protective effect of vSENS in the presence of pre-existing immunity to Adenoviral proteins. Anti-tumor efficacy was evaluated in syngeneic subcutaneous tumor mice models. The serum level of alanine aminotransferase (ALT) in mice was evaluated by blood chemistry analyzer.ResultsAd-vSENS effectively infected cancer cells in CAR-independent manner, where cancer cell-killing effects of OAd-vSENS were significantly enhanced in CAR negative cancer cells compare with those of naked OAd. When vSENS is complexed with an adenovirus, it encapsulates the virus like a shell shielding the adenovirus. Consistently, in syngeneic tumor bearing mice with pre-existing Ad immunity, longer virus blood half-life and longer survival of the mice were observed when administered with OAd-vSENS compared to naked OAd. The hepatotoxicity of OAd was greatly reduced by vSENS formulation as evidenced by the absence of acute spike in serum ALT levels typically seen after systemic administration of OAd.ConclusionsThe results show the potential of vSENS as a novel platform technology for delivery of Ad to overcome challenges adeno-virotherapies face in the clinic. vSENS platform is expected to expand the efficacy of the virus from cancer patients with high CAR expression to patients with limited CAR expression often associated as the cancer progresses. The platform is likely to facilitate treatment in patients with high levels of antibodies to adenovirus by shielding the virus from neutralization and increasing the bioavailability.Ethics ApprovalThe study was approved by Samyang Biopharmaceuticals Institution’s Ethics Board, approval number SYAU2009.ReferencesTwumasi-Boateng K, Pettigrew JL, Kwok YYE, Bell JC, Nelson BH, Oncolytic viruses as engineering platforms for combination immunotherapy. Nat Rev Cancer 2018;18:419–322.Zheng M, Huang J, Tong A, Yang H, Oncolytic viruses for cancer therapy: barriers and recent advances. Mol Ther Oncolytics 2019;15:234–247.

Using the E4orf6-Based E3 Ubiquitin Ligase as a Tool To Analyze the Evolution of Adenoviruses

ABSTRACTE4orf6 proteins from all human adenoviruses form Cullin-based ubiquitin ligase complexes that, in association with E1B55K, target cellular proteins for degradation. While most are assembled with Cul5, a few utilize Cul2. BC-box motifs enable all these E4orf6 proteins to assemble ligase complexes with Elongins B and C. We also identified a Cul2-box motif used for Cul2 selection in all Cul2-based complexes. With this information, we set out to determine if other adenoviruses also possess the ability to form the ligase complex and, if so, to predict their Cullin usage. Here we report that all adenoviruses known to encode an E4orf6-like protein (mastadenoviruses and atadenoviruses) maintain the potential to form the ligase complex. We could accurately predict Cullin usage for E4orf6 products of mastadenoviruses and all but one atadenovirus. Interestingly, in nonhuman primate adenoviruses, we found a clear segregation of Cullin binding, with Cul5 utilized by viruses infecting great apes and Cul2 by Old/New World monkey viruses, suggesting that a switch from Cul2 to Cul5 binding occurred during the period when great apes diverged from monkeys. Based on the analysis of Cullin selection, we also suggest that the majority of human adenoviruses, which exhibit a broader tropism for the eye and the respiratory tract, exhibit Cul5 specificity and resemble viruses infecting great apes, whereas those that infect the gastrointestinal tract may have originated from monkey viruses that share Cul2 specificity. Finally, aviadenoviruses also appear to contain E4orf6 genes that encode proteins with a conserved XCXC motif followed by, in most cases, a BC-box motif.IMPORTANCETwo early adenoviral proteins, E4orf6 and E1B55K, form a ubiquitin ligase complex with cellular proteins to ubiquitinate specific substrates, leading to their degradation by the proteasome. In studies with representatives of each human adenovirus species, we (and others) previously discovered that some viruses use Cul2 to form the complex, while others use Cul5. In the present study, we expanded our analyses to all sequenced adenoviruses and found that E4orf6 genes from all mast- and atadenoviruses encode proteins containing the motifs necessary to form the ligase complex. We found a clear separation in Cullin specificity between adenoviruses of great apes and Old/New World monkeys, lending support for a monkey origin for human viruses of theHuman mastadenovirus A,F, andGspecies. We also identified previously unrecognized E4orf6 genes in the aviadenoviruses that encode proteins containing motifs permitting formation of the ubiquitin ligase.

Adenovirus Replaces Mitotic Checkpoint Controls

ABSTRACTInfection with adenovirus triggers the cellular DNA damage response, elements of which include cell death and cell cycle arrest. Early adenoviral proteins, including the E1B-55K and E4orf3 proteins, inhibit signaling in response to DNA damage. A fraction of cells infected with an adenovirus mutant unable to express the E1B-55K and E4orf3 genes appeared to arrest in a mitotic-like state. Cells infected early in G1of the cell cycle were predisposed to arrest in this state at late times of infection. This arrested state, which displays hallmarks of mitotic catastrophe, was prevented by expression of either the E1B-55K or the E4orf3 genes. However, E1B-55K mutant virus-infected cells became trapped in a mitotic-like state in the presence of the microtubule poison colcemid, suggesting that the two viral proteins restrict entry into mitosis or facilitate exit from mitosis in order to prevent infected cells from arresting in mitosis. The E1B-55K protein appeared to prevent inappropriate entry into mitosis through its interaction with the cellular tumor suppressor protein p53. The E4orf3 protein facilitated exit from mitosis by possibly mislocalizing and functionally inactivating cyclin B1. When expressed in noninfected cells, E4orf3 overcame the mitotic arrest caused by the degradation-resistant R42A cyclin B1 variant.IMPORTANCECells that are infected with adenovirus type 5 early in G1of the cell cycle are predisposed to arrest in a mitotic-like state in a p53-dependent manner. The adenoviral E1B-55K protein prevents entry into mitosis. This newly described activity for the E1B-55K protein appears to depend on the interaction between the E1B-55K protein and the tumor suppressor p53. The adenoviral E4orf3 protein facilitates exit from mitosis, possibly by altering the intracellular distribution of cyclin B1. By preventing entry into mitosis and by promoting exit from mitosis, these adenoviral proteins act to prevent the infected cell from arresting in a mitotic-like state.

The Mre11/Rad50/Nbs1 Complex Limits Adeno-Associated Virus Transduction and Replication

ABSTRACT Adeno-associated virus (AAV) is a parvovirus with a small single-stranded DNA genome that relies on cellular replication machinery together with functions supplied by coinfecting helper viruses. The impact of host factors on AAV infection is not well understood. We explored the connection between AAV helper functions supplied by adenovirus and cellular DNA repair proteins. The adenoviral E1b55K/E4orf6 proteins induce degradation of the cellular Mre11 repair complex (MRN) to promote productive adenovirus infection. These viral proteins also augment recombinant AAV transduction and provide crucial helper functions for wild-type AAV replication. Here, we show that MRN poses a barrier to AAV and that the helper function provided by E1b55K/E4orf6 involves MRN degradation. Using a fluorescent method to visualize the viral genome, we show an effect at the viral DNA level. MRN components accumulate at AAV replication centers and recognize the viral inverted terminal repeats. Together, our data suggest that AAV is targeted by MRN and has evolved to exploit adenoviral proteins that degrade these cellular factors.