Immunoreactive domains and integrin-binding motifs in adenovirus penton base capsomer

A humanized anti-human adenovirus 55 monoclonal antibody with good neutralization ability

Background

Human adenovirus type 55 (HAdV55) has a re-emerged as pathogen causing an acute respiratory disease presenting as a severe lower respiratory illness that can cause death. To date, there is no HAdV55 vaccine or treatment available for general use.

Methods

Herein, a monoclonal antibody specific for HAdV55, mAb 9-8, was isolated from an scFv-phage display library derived from mice immunized with the purified inactived-HAdV55 virions. By using ELISA and a virus micro-neutralization assay, we evaluated the binding and neutralizing activity of mAb 9-8 following humanization. Western blotting analysis and antigen-antibody molecular docking analysis were used to identify the antigenic epitopes that the humanized monoclonal antibody 9-8-h2 recognized. After that, their thermal stability was determined.

Results

MAb 9-8 showed potent neutralization activity against HAdV55. After humanization, the humanized neutralizing monoclonal antibody (9-8-h2) was identified to neutralize HAdV55 infection with an IC50 of 0.6050 nM. The mAb 9-8-h2 recognized HAdV55 and HAdV7 virus particles, but not HAdV4 particles. Although mAb 9-8-h2 could recognize HAdV7, it could not neutralize HAdV7. Furthermore, mAb 9-8-h2 recognized a conformational neutralization epitope of the fiber protein and the crucial amino acid residues (Arg 288, Asp 157, and Asn 200) were identified. MAb 9-8-h2 also showed favorable general physicochemical properties, including good thermostability and pH stability.

Conclusions

Overall, mAb 9-8-h2 might be a promising molecule for the prevention and treatment of HAdV55.

Directed evolution of mutator adenoviruses resistant to antibody neutralization

We incorporated a previously identified mutation that reduces the fidelity of the DNA polymerase into a human adenovirus vector. Using this mutator vector, we demonstrate rapid selection of resistance to a neutralizing anti-hexon monoclonal antibody due to a G434D mutation in hexon that precludes antibody binding. Since mutator adenoviruses can accumulate compound mutations that are unattainable using traditional random mutagenesis techniques, this approach will be valuable to the study of antivirals and host factor interactions.

Neutralizing antibody blocks adenovirus infection by arresting microtubule-dependent cytoplasmic transport

Neutralizing antibodies are commonly elicited by viral infection. Most antibodies that have been characterized block early stages of virus entry that occur before membrane penetration, whereas inhibition of late stages in entry that occurs after membrane penetration has been poorly characterized. Here we provide evidence that the neutralizing antihexon monoclonal antibody 9C12 inhibits adenovirus infection by blocking microtubule-dependent translocation of the virus to the microtubule-organizing center following endosome penetration. These studies identify a previously undescribed mechanism by which neutralizing antibodies block virus infection, a situation that may be relevant for other nonenveloped viruses that use microtubule-dependent transport during cell entry.

Epitopes expressed in different adenovirus capsid proteins induce different levels of epitope-specific immunity

On the basis of the concept that the capsid proteins of adenovirus (Ad) gene transfer vectors can be genetically manipulated to enhance the immunogenicity of Ad-based vaccines, the present study compared the antiantigen immunogenicity of Ad vectors with a common epitope of the hemagglutinin (HA) protein of the influenza A virus incorporated into the outer Ad capsid protein hexon, penton base, fiber knob, or protein IX. Incorporation of the same epitope into the different capsid proteins provided insights into the correlation between epitope position and antiepitope immunity. Following immunization of three different strains of mice (C57BL/6, BALB/c, and CBA) with either an equal number of Ad particles (resulting in a different total HA copy number) or different Ad particle numbers (to achieve the same HA copy number), the highest primary (immunoglobulin M [IgM]) and secondary (IgG) anti-HA humoral and cellular CD4 gamma interferon and interleukin-4 responses against HA were always achieved with the Ad vector carrying the HA epitope in fiber knob. These observations suggest that the immune response against an epitope inserted into Ad capsid proteins is not necessarily dependent on the capsid protein number and imply that the choice of incorporation site in Ad capsid proteins in their use as vaccines needs to be compared in vivo.

Improved gene delivery to intestinal mucosa by adenoviral vectors bearing subgroup B and d fibers

A major obstacle to successful oral vaccination is the lack of antigen delivery systems that are both safe and highly efficient. Conventional replication-incompetent adenoviral vectors, derived from human adenoviruses of subgroup C, are poorly efficient in delivering genetic material to differentiated intestinal epithelia. To date, 51 human adenovirus serotypes have been identified and shown to recognize different cellular receptors with different tissue distributions. This natural diversity was exploited in the present study to identify suitable adenoviral vectors for efficient gene delivery to the human intestinal epithelium. In particular, we compared the capacities of a library of adenovirus type 5-based vectors pseudotyped with fibers of several human serotypes for transduction, binding, and translocation toward the basolateral pole in human and murine tissue culture models of differentiated intestinal epithelia. In addition, antibody-based inhibition was used to gain insight into the molecular interactions needed for efficient attachment. We found that vectors differing merely in their fiber proteins displayed vastly different capacities for gene transfer to differentiated human intestinal epithelium. Notably, vectors bearing fibers derived from subgroup B and subgroup D serotypes transduced the apical pole of human epithelium with considerably greater efficiency than a subgroup C vector. Such efficiency was correlated with the capacity to use CD46 or sialic acid-containing glycoconjugates as opposed to CAR as attachment receptors. These results suggest that substantial gains could be made in gene transfer to digestive epithelium by exploiting the tropism of existing serotypes of human adenoviruses.

Postentry neutralization of adenovirus type 5 by an antihexon antibody

Antibodies against hexon, the major coat protein of adenovirus (Ad), are an important component of the neutralizing activity in serum from naturally infected humans and experimentally infected animals. The mechanisms by which antihexon antibodies neutralize the virus have not been defined. As a model system, murine monoclonal antibodies raised against Ad type 5 (Ad5) were screened for antihexon binding and neutralization activity; one monoclonal antibody, designated 9C12, was selected for further characterization. The minimum ratio of 9C12 to Ad5 required for neutralization was 240 antibody molecules per virus particle, or 1 antibody per hexon trimer. Analysis of antibody-virus complexes by dynamic light scattering and negative-stain electron microscopy (EM) showed that the virus particles were coated with electron-dense material but not aggregated at neutralizing ratios. Cryo-EM image reconstruction of the antibody-virus complex showed that the surface of the virus particle was covered by a meshwork of 9C12 antibody density, consistent with bivalent binding at multiple sites. Confocal analysis revealed that viral attachment, cell entry, and intracellular transport to the nuclear periphery still occur in the presence of neutralizing levels of 9C12. A model is presented for neutralization of Ad by an antihexon antibody in which the hexon capsid is cross-linked by antibodies, thus preventing virus uncoating and nuclear entry of viral DNA.

Increased adenoviral transduction efficacy in human laryngeal carcinoma cells resistant to cisplatin is associated with increased expression of integrin alphavbeta3 and coxsackie adenovirus receptor

In our study, we investigated molecular mechanisms of increased adenoviral transduction efficacy in cisplatin-resistant human laryngeal carcinoma cells CA3ST as compared to parental cells HEp2. Using reverse transcription-PCR, the genes potentially implicated in adenoviral entry were screened. In cisplatin-resistant cells, only upregulation of alphavbeta3 integrin was detected, which was additionally confirmed by flow cytometry. Moderately increased expression of CAR was determined in cisplatin-resistant CA3ST cells using flow cytometry and measurement of wild-type adenovirus Ad5CMVbetagal attachment. In order to test the implication of alphavbeta3 integrin in transduction efficacy, 6 HEp2-derived alphavbeta3-expressing clones with graded expression of alphavbeta3 were isolated. To a certain degree of density, expression of alphavbeta3 positively correlated with Ad5CMVbetagal transduction efficacy (i.e., increased viral transduction), suggesting a role of alphavbeta3 in transduction efficacy. However, HEp2 clones with the highest alphavbeta3) expression were negatively correlated with transduction efficacy (i.e., decreased viral transduction). This was shown to be associated with downregulation of alphavbeta5 integrin, also involved in viral transduction, in clones with the highest alphavbeta3 expression. The implication of CAR in increased adenoviral transduction efficacy in cisplatin resistant CA3ST cells was further assessed by transduction experiments using adenoviral mutant Ad5FbDelta639 whose entry is only to a very small extent dependent on the presence of CAR. Indeed, Ad5FbDelta639 infected 2.5-fold more, in comparison to wild-type adenovirus, which infected 5-fold more efficiently resistant CA3ST cells than parental HEp2 cells, indicating that increased expression of CAR contributes to increased efficacy of adenoviral transduction. Thus, the data presented provide evidence that both alphavbeta3 integrin and CAR are involved in increased adenoviral transduction efficacy in cisplatin resistant CA3ST cells. These findings may have significant implications in human gene therapy using adenoviruses, especially in patients after unsuccessful cisplatin treatment.

Adenovirus fibre exchange alters cell tropism in vitro but not transgene-specific T CD8+ immune responses in vivo

Gene transfer with recombinant adenoviruses (rAds) is a powerful means of inducing an immune response against a transgene product. However, little is known about the mechanisms that underlie the induction of the immune response after intramuscular inoculation of adenovirus and, in particular, the relative role of the different cell types transduced. Several studies have suggested that CD8+ cytotoxic T lymphocyte responses elicited after inoculation of adenoviruses (Ads) are induced both by direct transduction of antigen presenting cells (APCs) and by cross-priming. In the present study, a library of fibre-chimeric rAds was screened in order to identify rAds with distinct capacities to express transgene product in murine cell types naturally found in muscle, i.e. myoblasts, endothelial cells (both representing non-APCs) and dendritic cells (representing APCs). Four selected pseudotypes, differing in their ability to infect muscular cells were used to immunize C57BL/6 mice. The relationship between the capacity to transduce non-APC or APC in vitro and the ability to induce humoral and cellular responses against the beta-galactosidase antigen after intramuscular inoculation were studied. Results indicate that CD8+ T cell responses against the beta-galactosidase antigen were similar after inoculation of the four viruses, thus revealing no direct relationship with their ability to transduce myoblasts, endothelial cells or dendritic cells in vitro.

Specific antibodies modulate the interactions of adenovirus type 5 with dendritic cells

Adenovirus type 5 (Ad5) is able to induce an efficient CD8+ T lymphocyte (CTL) response against a transgene product, a property thought to be linked to its ability to transduce dendritic cells (DCs). Little, however, is known about the capacity of Ad5 to interact with DCs in the presence of specific antibodies, although most people test positive for antibodies directed against Ad5. In the present study, we found that in the presence of Ad5 antibodies, a large fraction of Ad5 binds very efficiently to DCs, and that this binding is FcgammaRII/FcgammaRIII dependent. Nevertheless, in the presence of high levels of antibodies against the whole virion, Ad5 entry was inhibited. Increased binding led to increased entry in DCs in the presence of fiber-specific antibodies or in the presence of low amounts of a whole antiserum raised against whole virions, showing that the relative concentration of antibodies directed against fiber and penton base plays a major role in entry efficacy. Nevertheless, mice previously immunized with virions or purified fiber developed a lower transgene-specific CD8+ T cell response than naive mice, although their serum appeared to increase virus entry into DCs in vitro.

Identification of adenovirus (ad) penton base neutralizing epitopes by use of sera from patients who had received conditionally replicative ad (addl1520) for treatment of liver tumors

Sera from 17 patients with primary and secondary liver tumors who had been administered oncolytic adenovirus (Ad) mutant Addl1520 were analyzed for anti-Ad neutralization titers and antibodies to the Ad major capsid proteins hexon, penton base (Pb), and fiber. The antibodies recognized mainly conformational epitopes in hexon and both linear and conformational epitopes in Pb and fiber. Pb-specific antibodies were isolated from serum samples that had been obtained prior to and during the course of the treatment of four of these patients. We found that the Pb antibodies had a significant contribution toward anti-Ad neutralization, and this mainly occurred at the step of virus internalization. The Pb antigenic epitopes were determined by phage biopanning and were mapped to 10 discrete regions, which made up three major immunodominant domains within residues 51 to 120, 193 to 230, and 311 to 408, respectively. One of these domains (residues 311 to 408) overlapped the highly conserved, integrin-binding RGD (Arg-Gly-Asp) motif. The contribution of antibodies directed to RGD and other epitopes in Ad neutralization activity was determined indirectly by using a phage-mediated depletion assay. Our results suggested that circulating RGD antibodies were not prevalent and were poorly neutralizing and that other peptide motifs within residues 51 to 60, 216 to 226, and 311 to 408 in Pb sequence represented major target sites for neutralizing antibodies.

Shortening adenovirus type 5 fiber shaft decreases the efficiency of postbinding steps in CAR-expressing and nonexpressing cells

The coxsackie B virus and adenovirus receptor (CAR) functions as an attachment receptor for multiple adenovirus serotypes. It has been shown that apart from virus-cellular receptor interactions, the fiber shaft length also influences viral tropism. We therefore generated Ad5FbDelta639 virus with 8beta-repeats in the shaft, instead of the 22beta-repeats present in the wild-type. Here, we show that the extent of attachment of the virus with shortened fiber to CAR-expressing cells was three- to fivefold lower than that of the wild-type. Transduction studies, however, clearly showed that infection of CAR-expressing cells with Ad5FbDelta639 was strongly impaired by comparison with the wild-type virus. Since this impairment was not linked to a proportional reduction in binding to cells, it appeared to be linked to subsequent/later events in infection. A similar decrease in efficacy of postbinding steps was also evidenced in cells that did not express CAR.