Universal protection against influenza infection by a multidomain antibody to influenza hemagglutinin.

Broadly neutralizing antibodies against highly variable pathogens have stimulated the design of vaccines and therapeutics. We report the use of diverse camelid single-domain antibodies to influenza virus hemagglutinin to generate multidomain antibodies with impressive breadth and potency. Multidomain antibody MD3606 protects mice against influenza A and B infection when administered intravenously or expressed locally from a recombinant adeno-associated virus vector. Crystal and single-particle electron microscopy structures of these antibodies with hemagglutinins from influenza A and B viruses reveal binding to highly conserved epitopes. Collectively, our findings demonstrate that multidomain antibodies targeting multiple epitopes exhibit enhanced virus cross-reactivity and potency. In combination with adeno-associated virus-mediated gene delivery, they may provide an effective strategy to prevent infection with influenza virus and other highly variable pathogens.

High-level expression from two independent expression cassettes in replication-incompetent adenovirus type 35 vector.

Replication-incompetent adenovirus type 35 (rAd35) represents a potent vaccine carrier that elicits strong, antigen-specific T- and B-cell responses in diverse preclinical models. Moreover, Ad35 is rare in human populations, resulting in the absence of neutralizing antibodies against this carrier, in contrast to the commonly used rAd5. Therefore, rAd35 is being investigated as a vaccine carrier for a number of diseases for which an effective vaccine is needed, including malaria, AIDS and tuberculosis. However, it can be perceived that effective immunization will require insertion of multiple antigens into adenoviral vectors. We therefore wanted to create rAd35 vectors carrying double expression cassettes, to expand within one vector the number of insertion sites for foreign DNA encoding antigenic proteins. We show that it is possible to generate rAd35 vectors carrying two cytomegalovirus promoter-driven expression cassettes, provided that the polyadenylation signals in each expression cassette are not identical. We demonstrate excellent rAd35 vector stability and show that expression of a transgene is not influenced by the presence of a second expression cassette. Moreover, by using two model vaccine antigens, i.e. the human immunodeficiency virus-derived Env-gp120 protein and the Plasmodium falciparum-derived circumsporozoite protein, we demonstrate that potent T- and B-cell responses are induced to both antigens expressed from a single vector. Such rAd35 vectors thus expand the utility of rAd35 vaccine carriers for the development of vaccines against, for example, malaria, AIDS and tuberculosis.

Protective immune responses to a recombinant adenovirus type 35 tuberculosis vaccine in two mouse strains: CD4 and CD8 T-cell epitope mapping and role of gamma interferon.

There is an urgent need for an efficacious vaccine against tuberculosis (TB). Cellular immune responses are key to an effective protective response against TB. Recombinant adenovirus (rAd) vectors are especially suited to the induction of strong T-cell immunity and thus represent promising vaccine vehicles for the prevention of TB. We have previously reported on rAd vector serotype 35, the serotype of choice due to low preexisting immunity worldwide, which expresses a unique fusion protein of Mycobacterium tuberculosis antigens Ag85A, Ag85B, and TB10.4 (Ad35-TBS). Here, we demonstrate that Ad35-TBS confers protection against M. tuberculosis when administered to mice through either an intranasal or an intramuscular route. Histological evaluation of lung tissue corroborated the protection and, in addition, demonstrated differences between two mouse strains, with diffuse inflammation in BALB/c mice and distinct granuloma formation in C57BL/6 mice. Epitope mapping analysis in these mouse strains showed that the major T-cell epitopes are conserved in the artificial fusion protein, while three novel CD8 peptides were discovered. Using a defined set of T-cell epitopes, we reveal differences between the two mouse strains in the type of protective immune response, demonstrating that different antigen-specific gamma interferon (IFN-gamma)-producing T cells can provide protection against M. tuberculosis challenge. While in BALB/c (H-2(d)) mice, a dominant CD8 T-cell response was detected, in C57BL/6 (H-2(b)) mice, more balanced CD4/CD8 T-cell responses were observed, with a more pronounced CD4 response in the lungs. These results unify conflicting reports on the relative importance of CD4 versus CD8 T-cell responses in protection and emphasize the key role of IFN-gamma.

Comparative seroprevalence and immunogenicity of six rare serotype recombinant adenovirus vaccine vectors from subgroups B and D.

Recombinant adenovirus serotype 5 (rAd5) vector-based vaccines are currently being developed for both human immunodeficiency virus type 1 and other pathogens. The potential limitations associated with rAd5 vectors, however, have led to the construction of novel rAd vectors derived from rare Ad serotypes. Several rare serotype rAd vectors have already been described, but a detailed comparison of multiple rAd vectors from subgroups B and D has not previously been reported. Such a comparison is critical for selecting optimal rAd vectors for advancement into clinical trials. Here we describe the construction of three novel rAd vector systems from Ad26, Ad48, and Ad50. We report comparative seroprevalence and immunogenicity studies involving rAd11, rAd35, and rAd50 vectors from subgroup B; rAd26, rAd48, and rAd49 vectors from subgroup D; and rAd5 vectors from subgroup C. All six rAd vectors from subgroups B and D exhibited low seroprevalence in a cohort of 200 individuals from sub-Saharan Africa, and they elicited Gag-specific cellular immune responses in mice both with and without preexisting anti-Ad5 immunity. The rAd vectors from subgroup D were also evaluated using rhesus monkeys and were shown to be immunogenic after a single injection. The rAd26 vectors proved the most immunogenic among the rare serotype rAd vectors studied, although all rare serotype rAd vectors were still less potent than rAd5 vectors in the absence of anti-Ad5 immunity. These studies substantially expand the portfolio of rare serotype rAd vectors that may prove useful as vaccine vectors for the developing world.

Age dependence of adenovirus-specific neutralizing antibody titers in individuals from sub-Saharan Africa.

We assessed neutralizing antibody titers to adenovirus serotype 5 (Ad5) and six rare adenovirus serotypes, serotypes 11, 35, 50, 26, 48, and 49, in pediatric populations in sub-Saharan Africa. We observed a clear age dependence of Ad5-specific neutralizing antibody titers. These data will help to guide the development of Ad vector-based vaccines for human immunodeficiency virus type 1 and other pathogens.

Generation of a novel replication-incompetent adenoviral vector derived from human adenovirus type 49: manufacture on PER.C6 cells, tropism and immunogenicity.

Recombinant adenoviral vectors based on type 5 (rAd5) show great promise as a vaccine carrier. However, neutralizing activity against Ad5 is prevalent and high-titred among human populations, and significantly dampens Ad5-based vaccine modalities. The generation of alternative adenoviral vectors with low seroprevalence thus receives much research attention. Here, it is shown that a member from human adenovirus subgroup D, i.e. Ad49, does not cross-react with Ad5 neutralizing activity, making it a candidate serotype for vector development. Therefore, a plasmid system that allows formation of replication-incompetent adenovirus serotype 49 vaccine vectors (rAd49) was constructed and it was demonstrated that rAd49 can be successfully propagated to high titres on existing Ad5.E1-complementing cell lines such as PER.C6. Using an rAd49 vector carrying the luciferase marker gene, detailed seroprevalence studies were performed, demonstrating that rAd49 has low seroprevalence and neutralizing antibody titres worldwide. Also, we have initiated rAd49 vector receptor usage suggesting that rAd49 utilizes hCD46 as a cellular receptor. Finally, the immunogenicity of the rAd49 vector was assessed and it was shown that an rAd49.SIVGag vaccine induces strong anti-SIVGag CD8+ T-lymphocytes in naïve mice, albeit less than an rAd5.SIVGag vaccine. However, in mice with high anti-Ad5 immunity the rAd5.SIVGag vaccine was severely blunted, whereas the anti-SIVGag response was not significantly suppressed using the rAd49.SIVGag vaccine. These data demonstrate the potential of a replication deficient human group D adenoviral vector for vaccination purposes.

Immunogenicity of heterologous prime-boost regimens involving recombinant adenovirus serotype 11 (Ad11) and Ad35 vaccine vectors in the presence of anti-ad5 immunity.

The high prevalence of preexisting immunity to adenovirus serotype 5 (Ad5) in human populations will likely limit the immunogenicity and clinical utility of recombinant Ad5 (rAd5) vector-based vaccines for human immunodeficiency virus type 1 and other pathogens. A potential solution to this problem is to utilize rAd vaccine vectors derived from rare Ad serotypes such as Ad35 and Ad11. We have previously reported that rAd35 vectors were immunogenic in the presence of anti-Ad5 immunity, but the immunogenicity of heterologous rAd prime-boost regimens and the extent that cross-reactive anti-vector immunity may limit this approach have not been fully explored. Here we assess the immunogenicity of heterologous vaccine regimens involving rAd5, rAd35, and novel rAd11 vectors expressing simian immunodeficiency virus Gag in mice both with and without anti-Ad5 immunity. Heterologous rAd prime-boost regimens proved significantly more immunogenic than homologous regimens, as expected. Importantly, all regimens that included rAd5 were markedly suppressed by anti-Ad5 immunity. In contrast, rAd35-rAd11 and rAd11-rAd35 regimens elicited high-frequency immune responses both in the presence and in the absence of anti-Ad5 immunity, although we also detected clear cross-reactive Ad35/Ad11-specific humoral and cellular immune responses. Nevertheless, these data suggest the potential utility of heterologous rAd prime-boost vaccine regimens using vectors derived from rare human Ad serotypes.

Neutralizing antibodies to adenovirus serotype 5 vaccine vectors are directed primarily against the adenovirus hexon protein.

The utility of recombinant adenovirus serotype 5 (rAd5) vector-based vaccines for HIV-1 and other pathogens will likely be limited by the high prevalence of pre-existing Ad5-specific neutralizing Abs (NAbs) in human populations. However, the immunodominant targets of Ad5-specific NAbs in humans remain poorly characterized. In this study, we assess the titers and primary determinants of Ad5-specific NAbs in individuals from both the United States and the developing world. Importantly, median Ad5-specific NAb titers were >10-fold higher in sub-Saharan Africa compared with the United States. Moreover, hexon-specific NAb titers were 4- to 10-fold higher than fiber-specific NAb titers in these cohorts by virus neutralization assays using capsid chimeric viruses. We next performed adoptive transfer studies in mice to evaluate the functional capacity of hexon- and fiber-specific NAbs to suppress the immunogenicity of a prototype rAd5-Env vaccine. Hexon-specific NAbs were remarkably efficient at suppressing Env-specific immune responses elicited by the rAd5 vaccine. In contrast, fiber-specific NAbs exerted only minimal suppressive effects on rAd5 vaccine immunogenicity. These data demonstrate that functionally significant Ad5-specific NAbs are directed primarily against the Ad5 hexon protein in both humans and mice. These studies suggest a potential strategy for engineering novel Ad5 vectors to evade dominant Ad5-specific NAbs.

Novel replication-incompetent vector derived from adenovirus type 11 (Ad11) for vaccination and gene therapy: low seroprevalence and non-cross-reactivity with Ad5.

A novel plasmid-based adenovirus vector system that enables manufacturing of replication-incompetent (DeltaE1) adenovirus type 11 (Ad11)-based vectors is described. Ad11 vectors are produced on PER.C6/55K cells yielding high-titer vector batches after purification. Ad11 seroprevalence proves to be significantly lower than that of Ad5, and neutralizing antibody titers against Ad11 are low. Ad11 seroprevalence among human immunodeficiency virus-positive (HIV(+)) individuals is as low as that among HIV(-) individuals, independent of the level of immune suppression. The low level of coinciding seroprevalence between Ad11 and Ad35 in addition to a lack of correlation between high neutralizing antibody titers towards either adenovirus strongly suggest that the limited humoral cross-reactive immunity between these two highly related B viruses appears not to preclude the use of both vectors in the same individual. Ad11 transduces primary cells including smooth muscle cells, synoviocytes, and dendritic cells and cardiovascular tissues with higher efficiency than Ad5. Ad11 and Ad35 appear to have a similar tropism as judged by green fluorescent protein expression levels determined by using a panel of cancer cell lines. In addition, Ad5 preimmunization did not significantly affect Ad11-mediated transduction in C57BL/6 mice. We therefore conclude that the Ad11-based vector represents a novel and useful candidate gene transfer vehicle for vaccination and gene therapy.

Adenovirus types 5 and 35 seroprevalence in AIDS risk groups supports type 35 as a vaccine vector.

The seroprevalence of adenovirus types 5 (Ad5) and 35 (Ad35) was investigated in patients at risk of AIDS. The seroprevalence of Ad5 was higher than Ad35 in HIV-infected patients from The Netherlands (60% versus 7%) and sub-Saharan Africa (90% versus 20%). The seroprevalence was similar among HIV-infected and uninfected individuals, and remained constant during progression to AIDS. Ad35 is less prone to neutralization than Ad5, encouraging the further development of Ad35 for vaccination against HIV.

Common structure of rare replication-deficient E1-positive particles in adenoviral vector batches.

The use of the PER.C6 adenovirus packaging cell line in combination with a designated vector plasmid system, whereby the cell line and vector with E1 deleted have no sequence overlap, eliminates the generation of replication-competent adenovirus during vector production. However, we have found cytopathic effect (CPE)-inducing particles in 2 out of more than 40 large-scale manufacturing lots produced in PER.C6 cells. The CPE inducer was detected at a frequency of 1 event in 7.5 x 10(12) vector particles. Despite amplification, it was not readily purified, indicating that the agent itself is replication deficient and requires the parental recombinant adenovirus serotype 5 (rAd5) vector for replication and packaging. Therefore, we designated the agent as a helper-dependent E1-positive region containing viral particle (HDEP). Here, we report the molecular structure of the HDEP genome, revealing an Ad comprised of E1 sequences derived from PER.C6 cells flanked by inverted terminal repeat, packaging signal, and transgene sequences. These sequences form a palindromic structure devoid of E2, E3, E4, and late genes. Since only 5 bp were shared between E1 sequences in the PER.C6 genome and viral vector sequences, the data strongly suggested that insertion of genomic DNA into an adenoviral genome had occurred essentially via nonhomologous recombination. HDEPs have been found in unrelated virus batches and appear to share a common structure that may explain their mechanism of generation. This finding allowed development of an HDEP assay to screen batches of rAd5 produced on the PER.C6 cell line and resulted in detection of seven HDEP agents from four different transgene-virus vector constructs in separate batches of Ad.

The tumor-selective viral protein apoptin effectively kills human biliary tract cancer cells.

Biliary tract cancer, or cholangiocarcinoma, has a poor prognosis. Resection is the only curative treatment, but only a minority of patients are eligible. Chemotherapy and gamma-irradiation are merely palliative, as they are unable to remove the malignancy completely. The chicken anemia virus-derived protein apoptin induces apoptosis in a wide range of human tumor cells and is not hindered by mutations inactivating p53 or by overexpression of Bcl-2, changes known to frustrate chemotherapy and radiation therapy. We examined whether apoptin kills human biliary tract cancer cells. Expression of apoptin by means of plasmids caused extensive cell death in three independent cholangiocarcinoma cell lines, CC-LP, CC-SW, and Mz-ChA-1, regardless of their oncogenic mutations, which included inactivated p16 and p53 and the disruption of the transforming growth factor beta signaling pathway. In vitro delivery of apoptin by an adenoviral vector completely eradicated cholangiocarcinoma cells. Moreover, coexpression of the broad-spectrum caspase inhibitor p35 with apoptin only delayed the induced cell death. Changes in nuclear morphology still occurred early after transfection, and nuclei eventually disintegrated, suggesting that apoptin-induced cell death in these cells is not blocked by mutations in either the initiation or execution phase of apoptosis. The efficient induction of cell death by apoptin in cholangiocarcinoma cell lines makes apoptin an attractive candidate for molecular therapy of biliary tract cancer.

Quantifying adenovirus-neutralizing antibodies by luciferase transgene detection: addressing preexisting immunity to vaccine and gene therapy vectors.

The presence of various levels of anti-adenovirus serotype 5 (Ad5)-neutralizing antibodies in humans is thought to contribute to the inconsistent clinical results obtained so far in diverse gene transfer and vaccination studies and might preclude universal dosing with recombinant Ad5. Prescreening of individuals eligible for Ad5 or alternative serotype treatment and subsequently tailoring the vector dose might aid in ensuring the consistency of clinical parameters. For this purpose, a qualified Ad neutralization assay is required. Here we have tested the different protocols used to date to determine anti-Ad neutralizing activity. Based on simplicity, speed, high throughput, sensitivity, and robustness, we propose a qualified assay in which Ad neutralization is monitored by luciferase reporter gene expression.

Replication-deficient human adenovirus type 35 vectors for gene transfer and vaccination: efficient human cell infection and bypass of preexisting adenovirus immunity.

Replication-deficient human adenovirus type 5 (Ad5) can be produced to high titers in complementing cell lines, such as PER.C6, and is widely used as a vaccine and gene therapy vector. However, preexisting immunity against Ad5 hampers consistency of gene transfer, immunological responses, and vector-mediated toxicities. We report the identification of human Ad35 as a virus with low global prevalence and the generation of an Ad35 vector plasmid system for easy insertion of heterologous genes. In addition, we have identified the minimal sequence of the Ad35-E1B region (molecular weight, 55,000 [55K]), pivotal for complementation of fully E1-lacking Ad35 vector on PER.C6 cells. After stable insertion of the 55K sequence into PER.C6 cells a cell line was obtained (PER.C6/55K) that efficiently transcomplements both Ad5 and Ad35 vectors. We further demonstrate that transduction with Ad35 is not hampered by preexisting Ad5 immunity and that Ad35 efficiently infects dendritic cells, smooth muscle cells, and synoviocytes, in contrast to Ad5.

The organotypic multicellular spheroid is a relevant three-dimensional model to study adenovirus replication and penetration in human tumors in vitro.

The use of adenoviruses for gene transfer and as oncolytic agents is currently receiving widespread attention. As specific constraints to adenovirus distribution and spread cannot be studied in cell cultures, there is a need for an in vitro three-dimensional (3D) model mimicking the in vivo biology of tumors. We studied the interactions between tumor and adenoviruses using multicellular spheroids grown from primary brain tumor material. Using beta-galactosidase and luciferase reporter genes expressed by replication-defective adenoviruses, we showed that infection was restricted to the first layer of cells. Using a replication-competent adenovirus expressing the luciferase gene, we showed that transgene expression in the spheroid was considerably enhanced and that viral spreading deep into the 3D structure took place. In addition, a tetrazolium salt-based metabolic assay could be used to compare the oncolytic activity of different concentrations of replication-competent adenoviruses. We can conclude that organotypic spheroids offer a versatile in vitro system for studying distribution, spread, and oncolysis by adenoviruses in a clinically relevant model.

Imaging expression of adenoviral HSV1-tk suicide gene transfer using the nucleoside analogue FIRU.

Substrates for monitoring HSV1-tk gene expression include uracil and acycloguanosine derivatives. The most commonly used uracil derivative to monitor HSV1-tk gene transfer is 1-(2-fluoro-2-deoxy--D-arabinofuranosyl)-5-[*I]iodouracil (fialuridine; I*-FIAU), where the asterisk denotes any of the radioactive iodine isotopes that can be used. We have previously studied other nucleosides with imaging properties as good as or better than FIAU, including 1-(2-fluoro-2-deoxy--D-ribofuranosyl)-5-[*I]iodouracil (FIRU). The first aim of this study was to extend the biodistribution data of 123I-labelled FIRU. Secondly, we assessed the feasibility of detecting differences in HSV1-tk gene expression levels following adenoviral gene transfer in vivo with 123I-FIRU. 9L rat gliosarcoma cells were stably transfected with the HSV1-tk gene (9L-tk+). 123I-FIRU was prepared by radioiodination of 1-(2-fluoro-2-deoxy--D-ribofuranosyl)-5-tributylstannyl uracil (FTMRSU; precursor compound) and purified using an activated Sep-Pak column. Incubation of 9L-tk+ cells and the parental 9L cells with 123I-FIRU resulted in a 100-fold higher accumulation of radioactivity in the 9L-tk+ cells after an optimum incubation time of 4 h. NIH-bg-nu-xid mice were then inoculated subcutaneously with HSV1-tk (-) 9L cells or HSV1-tk (+) 9L-tk+ cells into both flanks. Biodistribution studies and gamma camera imaging were performed at 15 min and 1, 2, 4 and 24 h p.i. At 15 min, the tumour/muscle, tumour/blood and tumour/brain ratios were 5.2, 1.0 and 30.3 respectively. Rapid renal clearance of the tracer from the body resulted in increasing tumour/muscle, tumour/blood and tumour/brain ratios, reaching values of 32.2, 12.5 and 171.6 at 4 h p.i. A maximum specific activity of 22%ID/g tissue was reached in the 9L-tk+ tumours 4 h after 123I-FIRU injection. Two Ad5-based adenoviral vectors containing the HSV1-tk gene were constructed: a replication-incompetent vector with the transgene in the former E1 region, driven by a modified CMV promoter, and a novel replication-competent vector with the HSV1-tk gene in E3 driven by the natural E3 promoter. The human glioma cell lines U87MG and T98G were infected with a multiplicity of infection (m.o.i.) of 10. Forty-eight hours later the cells were incubated with 123I-FIRU and radioactivity was measured in a gamma counter. We found significantly higher levels of radioactivity in both cell lines following infection with the replication-competent vector (P<0.001). NIH-bg-nu-xid mice were then inoculated subcutaneously with U87MG cells. Tumours (approximately 1,000 mm3) were injected with 108 and 109 Infectious Units (I.U.) of either vector. After 48 h, the tracer was injected, followed by gamma camera imaging and direct measurement of radioactivity in the tumours at 4 h p.i. Images and direct measurements indicated increased uptake of tracer with higher I.U. and also demonstrated increased accumulation of tracer in the tumours treated with the replication-competent adenoviral vector (P=0.03). These results demonstrate that 123I-FIRU in combination with HSV1-tk is a valuable tracer for in vivo monitoring of adenoviral gene transfer.

A single short stretch of homology between adenoviral vector and packaging cell line can give rise to cytopathic effect-inducing, helper-dependent E1-positive particles.

An undesirable byproduct from recombinant adenoviral vectors is the emergence of replication competent adenovirus (RCA) that result from rare homologous recombination events between the viral E1-containing (permissive) mammalian host cell genome and the virus itself, restoring the E1 gene to the viral genome. To reduce or eliminate the problem of RCA, we evaluated production of a first generation Ad5 vector (Ad5FGF4) in the cell line PER.C6. This E1-transformed human cell line contains only Ad5 nucleotides 459-3510, which precludes double crossover-type homologous recombination because the Ad5FGF-4 only contains 5' Ad5 sequence up to nucleotide 453. The Ad5FGF4 vector does, however, retain 177 nucleotides of the 3' end of the E1B-55K gene that are also present in PER.C6. With only this single region of homology between vector and cell line, we were surprised to detect virus-specific cytopathic effects (CPE) in our cell-based assay for RCA. This CPE-inducing agent was amplified in nonpermissive A549 cells but also supported amplification of the parental Ad5FGF-4. Because we were unable to isolate the CPE-inducing agent in pure form we first identified it as atypical RCA. Polymerase chain reaction (PCR) and Southern blot experiments identified viral DNA segments in which recombination had occurred between the 177 nucleotides of E1B present in both Ad5FGF-4 and PER.C6. The atypical RCA genomes contain a copy of the original (PGK promoter-E1 gene carrying) plasmid used in the construction of the PER.C6 cell line and they retained the parental FGF-4 transgene. However, significant deletions occurred within the recombined genomes in compensation for the large insertion from PER.C6 sequences and resulted in the loss of essential viral genes. This deletion renders these recombinant viruses replication defective, requiring helper functions from remaining parental Ad5FGF-4 for amplification. These atypical RCA entities may be more properly designated as helper-dependent E1-positive particles (HDEPs). This finding shows the importance of avoiding the use of "nonmatched" vectors where any overlap exists between the recombinant vector and E1 sequences in the packaging cell line. The cloning of the FGF-4 transgene into an adenoviral vector specifically "matched" for PER.C6 (lacking the 177 nucleotide region of homology) has allowed extensive virus propagation (Ad5.1FGF-4) with no CPE- or HDEP-like events yet detected.