Adenovirus serotype 5 infects human dendritic cells via a coxsackievirus-adenovirus receptor-independent receptor pathway mediated by lactoferrin and DC-SIGN

The coxsackievirus-adenovirus receptor (CAR) is the described primary receptor for adenovirus serotype 5 (Ad5), a common human pathogen that has been exploited as a viral vector for gene therapy and vaccination. This study showed that monocytes and dendritic cells (DCs), such as freshly isolated human blood myeloid DCs, plasmacytoid DCs and monocyte-derived DCs, are susceptible to recombinant Ad5 (rAd5) infection despite their lack of CAR expression. Langerhans cells and dermal DCs from skin expressed CAR, but blocking CAR only partly decreased rAd5 infection, together suggesting that other receptor pathways mediate viral entry of these cells. Lactoferrin (Lf), an abundant protein in many bodily fluids known for its antiviral and antibacterial properties, promoted rAd5 infection in all cell populations except plasmacytoid DCs using a CAR-independent process. Lf caused phenotypic differentiation of the DCs, but cell activation played only a minor role in the increase in infection frequencies. The C-type lectin receptor DC-SIGN facilitated viral entry of rAd5-Lf complexes and this was dependent on high-mannose-type N-linked glycans on Lf. These results suggest that Lf present at high levels at mucosal sites can facilitate rAd5 attachment and enhance infection of DCs. A better understanding of the tropism and receptor mechanisms of Ad5 may help explain Ad5 pathogenesis and guide the engineering of improved rAd vectors.

Fiber-chimeric adenoviruses expressing fibers from serotype 16 and 50 improve gene transfer to human pancreatic adenocarcinoma

Survival of patients with pancreatic cancer is poor. Adenoviral (Ad) gene therapy employing the commonly used serotype 5 reveals limited transduction efficiency due to the low amount of coxsackie-adenovirus receptor on pancreatic cancer cells. To identify fiber-chimeric adenoviruses with improved gene transfer, a library of Ad vectors based on Ad5 and carrying fiber molecules consisting of 16 other serotypes were transduced to human pancreatic carcinoma cell lines. Adenoviruses containing fibers from serotype 16 and 50 showed increased gene transfer and were further analyzed. In a gene-directed prodrug activation system using cytosine deaminase, these adenoviruses proved to be effective in eradicating primary pancreatic tumor cells. Fiber-chimeric Ad5 containing fiber 16 and wild-type Ad5 were also transduced ex vivo to slices of normal human pancreatic tissue and pancreatic carcinoma tissue obtained during surgery. It was shown that fiber-chimeric Ad5 with fiber 16 revealed an improved gene delivery to primary pancreatic tumor tissue compared to Ad5. In conclusion, fiber-chimeric adenoviruses carrying fiber 16 and 50 reveal a significantly enhanced gene transfer and an increased specificity to human pancreatic adenocarcinoma compared to Ad5, whereas transduction to normal pancreatic tissue was decreased. These findings expand the therapeutic window of Ad gene therapy for pancreatic cancer.

Trafficking of antigen-specific CD8+ T lymphocytes to mucosal surfaces following intramuscular vaccination

A critical goal of vaccine development for a wide variety of pathogens is the induction of potent and durable mucosal immunity. However, it has been assumed that this goal would be difficult to achieve by systemic vaccination due to the anatomic and functional distinctness of the systemic and mucosal immune systems and the resultant compartmentalization of immune responses. In this study, we show that Ag-specific CD8(+) T lymphocytes traffic efficiently to mucosal surfaces following systemic vaccination. Intramuscular immunization with recombinant adenovirus (rAd) vector-based vaccines expressing SIV Gag resulted in potent, durable, and functional CD8(+) T lymphocyte responses at multiple mucosal effector sites in both mice and rhesus monkeys. In adoptive transfer studies in mice, vaccine-elicited systemic CD8(+) T lymphocytes exhibited phenotypic plasticity, up-regulated mucosal homing integrins and chemokine receptors, and trafficked rapidly to mucosal surfaces. Moreover, the migration of systemic CD8(+) T lymphocytes to mucosal compartments accounted for the vast majority of Ag-specific mucosal CD8(+) T lymphocytes induced by systemic vaccination. Thus, i.m. vaccination can overcome immune compartmentalization and generate robust mucosal CD8(+) T lymphocyte memory. These data demonstrate that the systemic and mucosal immune systems are highly coordinated following vaccination.

Serum-free transient protein production system based on adenoviral vector and PER.C6 technology: high yield and preserved bioactivity

Stable E1 transformed cells, like PER.C6, are able to grow at scale and to high cell densities. E1-deleted adenoviruses replicate to high titer in PER.C6 cells whereas subsequent deletion of E2A from the vector results in absence of replication in PER.C6 cells and drastically lowers the expression of adenovirus proteins in such cells. We therefore considered the use of an DeltaE1/DeltaE2 type 5 vector (Ad5) to deliver genes to PER.C6 cells growing in suspension with the aim to achieve high protein yield. To evaluate the utility of this system we constructed DeltaE1/DeltaE2 vector carrying different classes of protein, that is, the gene coding for spike protein derived from the Coronavirus causing severe acute respiratory syndrome (SARS-CoV), a gene coding for the SARS-CoV receptor or the genes coding for an antibody shown to bind and neutralize SARS-CoV (SARS-AB). The DeltaE1/DeltaE2A-vector backbones were rescued on a PER.C6 cell line engineered to constitutively over express the Ad5 E2A protein. Exposure of PER.C6 cells to low amounts (30 vp/cell) of DeltaE1/DeltaE2 vectors resulted in highly efficient (>80%) transduction of PER.C6 cells growing in suspension. The efficient cell transduction resulted in high protein yield (up to 60 picogram/cell/day) in a 4 day batch production protocol. FACS and ELISA assays demonstrated the biological activity of the transiently produced proteins. We therefore conclude that DeltaE1/DeltaE2 vectors in combination with the PER.C6 technology may provide a viable answer to the increasing demand for high quality, high yield recombinant protein.

Adenovirus serotype 5 hexon mediates liver gene transfer

Adenoviruses are used extensively as gene transfer agents, both experimentally and clinically. However, targeting of liver cells by adenoviruses compromises their potential efficacy. In cell culture, the adenovirus serotype 5 fiber protein engages the coxsackievirus and adenovirus receptor (CAR) to bind cells. Paradoxically, following intravascular delivery, CAR is not used for liver transduction, implicating alternate pathways. Recently, we demonstrated that coagulation factor (F)X directly binds adenovirus leading to liver infection. Here, we show that FX binds to the Ad5 hexon, not fiber, via an interaction between the FX Gla domain and hypervariable regions of the hexon surface. Binding occurs in multiple human adenovirus serotypes. Liver infection by the FX-Ad5 complex is mediated through a heparin-binding exosite in the FX serine protease domain. This study reveals an unanticipated function for hexon in mediating liver gene transfer in vivo.

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.

Species B adenovirus serotypes 3, 7, 11 and 35 share similar binding sites on the membrane cofactor protein CD46 receptor

We recently characterized the domains of the human cofactor protein CD46 involved in binding species B2 adenovirus (Ad) serotype 35. Here, the CD46 binding determinants are mapped for the species B1 Ad serotypes 3 and 7 and for the species B2 Ad11. Ad3, 7 and 11 bound and transduced CD46-positive rodent BHK cells at levels similar to Ad35. By using antibody-blocking experiments, hybrid CD46–CD4 receptor constructs and CD46 single point mutants, it is shown that Ad3, 7 and 11 share many of the Ad35-binding features on CD46. Both CD46 short consensus repeat domains SCR I and SCR II were necessary and sufficient for optimal binding and transgene expression, provided that they were positioned at an appropriate distance from the cell membrane. Similar to Ad35, most of the putative binding residues of Ad3, 7 and 11 were located on the same glycan-free, solvent-exposed face of the SCR I or SCR II domains, largely overlapping with the binding surface of the recently solved fiber knob Ad11–SCR I–II three-dimensional structure. Differences between species B1 and B2 Ads were documented with competition experiments based on anti-CD46 antibodies directed against epitopes flanking the putative Ad-binding sites, and with competition experiments based on soluble CD46 protein. It is concluded that the B1 and B2 species of Ad engage CD46 through similar binding surfaces.

Myeloid and plasmacytoid dendritic cells are susceptible to recombinant adenovirus vectors and stimulate polyfunctional memory T cell responses

Although replication-incompetent recombinant adenovirus (rAd) type 5 is a potent vaccine vector for stimulating T and B cell responses, high seroprevalence of adenovirus type 5 (Ad5) within human populations may limit its clinical utility. Therefore, alternative adenovirus serotypes have been studied as vaccine vectors. In this study, we characterized the ability of rAd5 and rAd35 to infect and induce maturation of human CD11c(+) myeloid dendritic cells (MDCs) and CD123(+) plasmacytoid dendritic cells (PDCs), and their ability to stimulate Ag-specific T cells. Both MDCs and PDCs were found to express the primary receptor for Ad35 (CD46) but not Ad5 (coxsackie-adenovirus receptor; CAR). Both dendritic cell (DC) subsets were also more susceptible to rAd35 than to rAd5. MDCs were more susceptible to both rAd35 and rAd5 than were PDCs. Whereas rAd35 used CD46 for entry into DCs, entry of rAd5 may be through a CAR-independent pathway. Exposure to rAd35 but not rAd5 induced high levels of IFN-alpha in PDCs and phenotypic differentiation in both DC subsets. MDCs and PDCs exposed to either rAd5 or rAd35 encoding for CMV pp65 were able to present pp65 and activate CMV-specific memory CD8(+) and CD4(+) T cells in a dose-dependent manner, but MDCs stimulated the highest frequencies of pp65-specific T cells. Responding T cells expressed multiple functions including degranulation (CD107a surface mobilization) and production of IFN-gamma, IL-2, TNF-alpha, and MIP-1beta. Thus, the ability of rAd35 to naturally target important DC subsets, induce their maturation, and appropriately present Ag to T cells may herald greater in vivo immunogenicity than has been observed with rAd5.

Increased immunogenicity of recombinant Ad35-based malaria vaccine through formulation with aluminium phosphate adjuvant

Previously, we have shown the potency of recombinant Adenovirus serotype 35 viral vaccines (rAd35) to induce strong immune response against the circumsporozoite protein (CS) of the plasmodium parasite. To further optimize immunogenicity of Ad35-based malaria vaccines we formulated rAd35.CS vaccine with aluminium phosphate adjuvant (AlPO(4)). In contrast to the conventional protein based vaccines no absorption to aluminium adjuvant was observed and rAd35 viral in vitro infectivity in mammalian cells was preserved. Immunization with Ad35.CS formulated with AlPO(4) resulted in significantly higher CS specific T and B cell responses in mice upon either single or prime-boost vaccination regimens as compared to rAd35.CS alone. With these results we report for the first time the feasibility of using an AlPO(4) adjuvant to increase the potency of a live adenovirus serotype 35-based vaccine.

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.

Influence of coagulation factor zymogens on the infectivity of adenoviruses pseudotyped with fibers from subgroup D

Recent evidence supports a role for vitamin K-dependent coagulation zymogens in adenovirus serotype 5 (Ad5, subgroup C) infection of hepatocytes. Here, we assessed the effect of virus-zymogen interaction on cellular transduction using a panel of fiber (f)-pseudotyped viruses derived from subgroup D (f47, f33, f24, f45, f17, f30). Each virus directly bound factor X (FX) as determined by surface plasmon resonance, resulting in enhanced cell surface binding. Infection of HepG2 cells was promoted by FX but not by FVII or FIX, while transduction of CHO cells was blocked in heparan sulfate proteoglycan-deficient cells. This suggests a broad role for FX in adenovirus infectivity.

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.

Expression and immunogenicity of the Plasmodium falciparum circumsporozoite protein: the role of GPI signal sequence

Previous studies have shown that the immunogenicity of rodent malaria parasite-derived circumsporozoite protein (CS) can be improved by deleting the glycosyl-phosphatidyl-inositol (GPI) signal sequence. To study whether GPI signal sequence deletion would also improve immunogenicity of CS derived from the major plasmodium species causing mortality in humans (P. falciparum), we tested different variants of the P. falciparum CS protein in the context of a live vector-based vaccine carrier (rAd35). We demonstrate that deletion of the GPI signal sequence from CS did not result in altered expression or secretion. In contrast, cellular localization was clearly altered, which perhaps helps to explain the significant improvement of anti-CS antibody and T-cell responses observed in mice using deletion variants in the context of the rAd35 carrier. Our results show that rational design of antigens is warranted for further development of malaria vaccines.

Immunogenicity of heterologous recombinant adenovirus prime-boost vaccine regimens is enhanced by circumventing vector cross-reactivity

The high prevalence of preexisting immunity to adenovirus serotype 5 (Ad5) in human populations has led to the development of recombinant adenovirus (rAd) vectors derived from rare Ad serotypes as vaccine candidates for human immunodeficiency virus type 1 and other pathogens. Vaccine vectors have been constructed from Ad subgroup B, including rAd11 and rAd35, as well as from Ad subgroup D, including rAd49. However, the optimal combination of vectors for heterologous rAd prime-boost vaccine regimens and the extent of cross-reactive vector-specific neutralizing antibodies (NAbs) remain poorly defined. We have shown previously that the closely related vectors rAd11 and rAd35 elicited low levels of cross-reactive NAbs. Here we show that these cross-reactive NAbs correlated with substantial sequence homology in the hexon hypervariable regions (HVRs) and suppressed the immunogenicity of heterologous rAd prime-boost regimens. In contrast, vectors with lower hexon HVR homology, such as rAd35 and rAd49, did not elicit detectable cross-reactive vector-specific NAbs. Consistent with these findings, rAd35-rAd49 vaccine regimens proved more immunogenic than both rAd35-rAd5 and rAd35-rAd11 regimens in mice with anti-Ad5 immunity. These data suggest that optimal heterologous rAd prime-boost regimens should include two vectors that are both rare in human populations to circumvent preexisting antivector immunity as well as sufficiently immunologically distinct to avoid cross-reactive antivector immunity.

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.

Intradermal Delivery of Adenoviral Type-35 Vectors Leads to High Efficiency Transduction of Mature, CD8+T Cell-Stimulating Skin-Emigrated Dendritic Cells

Recombinant adenovirus (Ad) type 35 (rAd35) shows great promise as vaccine carrier with the advantage of low pre-existing immunity in human populations, in contrast to the more commonly used rAd5 vector. The rAd35 vector uses CD46 as a high-affinity receptor, which, unlike the rAd5 receptor, is expressed on human dendritic cells (DC), the most powerful APCs identified to date. In this study, we show that in contrast to rAd5, rAd35 infects migrated and mature CD83+ cutaneous DC with high efficiency (up to 80%), when delivered intradermally in an established human skin explant model. The high transduction efficiency is in line with high expression levels of CD46 detected on migratory cutaneous DC, which proved to be further increased upon intradermal administration of GM-CSF and IL-4. As compared with Ad5, these Ad35 infection characteristics translate into higher absolute numbers of skin-emigrated DC per explant that both express the transgene and are phenotypically mature. Finally, we demonstrate that upon intracutaneous delivery of a rAd35 vaccine encoding the circumsporozoite (CS) protein of Plasmodium falciparum, emigrated DC functionally express and process CS-derived epitopes and are capable of activating specific CD8+ effector T cells, as evidenced by activation of an HLA-A2-restricted CS-specific CD8+ T cell clone. Collectively, these data demonstrate the utility of rAd35 vectors for efficient in vivo human DC transduction.

Viral vectors for malaria vaccine development

A workshop on viral vectors for malaria vaccine development, organized by the PATH Malaria Vaccine Initiative, was held in Bethesda, MD on October 20, 2005. Recent advancements in viral-vectored malaria vaccine development and emerging vector technologies were presented and discussed. Classic viral vectors such as poxvirus, adenovirus and alphavirus vectors have been successfully used to deliver malaria antigens. Some of the vaccine candidates have demonstrated their potential in inducing malaria-specific immunity in animal models and human trials. In addition, emerging viral-vector technologies, such as measles virus (MV), vesicular stomatitis virus (VSV) and yellow fever (YF) virus, may also be useful for malaria vaccine development. Studies in animal models suggest that each viral vector is unique in its ability to induce humoral and/or cellular immune responses. Those studies have also revealed that optimization of Plasmodium genes for mammalian expression is an important aspect of vaccine design. Codon-optimization, surface-trafficking, de-glycosylation and removal of toxic domains can lead to improved immunogenicity. Understanding the vector's ability to induce an immune response and the expression of malaria antigens in mammalian cells will be critical in designing the next generation of viral-vectored malaria vaccines.

Expression of aberrantly glycosylated tumor mucin-1 on human DC after transduction with a fiber-modified adenoviral vector

BACKGROUND

DC-presenting tumor Ag are currently being developed to be used as a vaccine in human cancer immunotherapy. To increase chances for successful therapy it is important to deliver full-length tumor Ag instead of loading single peptides.

METHODS

In this study we used a fiber-modified adenoviral vector (rAd5F35) containing full-length tumor Ag cDNA to transduce human monocyte (Mo)-derived DC in vitro. Cells were efficiently transduced and survived for at least 3 days after adenoviral transduction. Phenotype and function after maturation of Mo-DC were not impaired by infection with adenovirus particles. Expression of the tumor-associated Ag mucin-1 (MUC1) was detected using MAb defining different MUC1 glycoforms.

RESULTS

Non-transduced mature Mo-DC express endogenous MUC1 with normal glycosylation. After transduction with the rAd5F35-MUC1 adenoviral vector, Mo-DC also expressed MUC1 with tumor-associated glycosylation (Tn and T glycoforms), although no changes in mRNA levels of relevant glycosyltransferases could be demonstrated.

DISCUSSION

The presence of aberrantly glycosylated MUC1 may influence Ag presentation of the tumor glycoforms of MUC1 to immune cells, affecting tumor cell killing. These findings could be highly relevant to developing strategies for cancer immunotherapy based on DC vaccines using MUC1 as tumor Ag.

Hexon-chimaeric adenovirus serotype 5 vectors circumvent pre-existing anti-vector immunity

A common viral immune evasion strategy involves mutating viral surface proteins in order to evade host neutralizing antibodies. Such immune evasion tactics have not previously been intentionally applied to the development of novel viral gene delivery vectors that overcome the critical problem of anti-vector immunity. Recombinant, replication-incompetent adenovirus serotype 5 (rAd5) vector-based vaccines for human immunodeficiency virus type 1 and other pathogens have proved highly immunogenic in preclinical studies but will probably be limited by the high prevalence of pre-existing anti-Ad5 immunity in human populations, particularly in the developing world. Here we show that rAd5 vectors can be engineered to circumvent anti-Ad5 immunity. We constructed novel chimaeric rAd5 vectors in which the seven short hypervariable regions (HVRs) on the surface of the Ad5 hexon protein were replaced with the corresponding HVRs from the rare adenovirus serotype Ad48. These HVR-chimaeric rAd5 vectors were produced at high titres and were stable through serial passages in vitro. HVR-chimaeric rAd5 vectors expressing simian immunodeficiency virus Gag proved comparably immunogenic to parental rAd5 vectors in naive mice and rhesus monkeys. In the presence of high levels of pre-existing anti-Ad5 immunity, the immunogenicity of HVR-chimaeric rAd5 vectors was not detectably suppressed, whereas the immunogenicity of parental rAd5 vectors was abrogated. These data demonstrate that functionally relevant Ad5-specific neutralizing antibodies are focused on epitopes located within the hexon HVRs. Moreover, these studies show that recombinant viral vectors can be engineered to circumvent pre-existing anti-vector immunity by removing key neutralizing epitopes on the surface of viral capsid proteins. Such chimaeric viral vectors may have important practical implications for vaccination and gene therapy.

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.

Immunogenicity and protection of a recombinant human adenovirus serotype 35-based malaria vaccine against Plasmodium yoelii in mice

Given the promise of recombinant adenovirus type 5 (rAd5) as a malaria vaccine carrier in preclinical models, we evaluated the potency of rAd35 coding for Plasmodium yoelii circumsporozoite protein (rAd35PyCS). We chose rAd35 since a survey with serum samples from African subjects demonstrated that human Ad35 has a much lower seroprevalence of 20% and a much lower geometric mean neutralizing antibody titer (GMT) of 48 compared to Ad5 (seroprevalence, 85%; GMT, 1,261) in countries with a high malaria incidence. We also demonstrated that immunization with rAd35PyCS induced a dose-dependent and potent, CS-specific CD8(+) cellular and humoral immune response and conferred significant inhibition (92 to 94%) of liver infection upon high-dose sporozoite challenge. Furthermore, we showed that in mice carrying neutralizing antibody activity against Ad5, mimicking a human situation, CS-specific T- and B-cell responses were significantly dampened after rAd5PyCS vaccination, resulting in loss of inhibition of liver infection upon sporozoite challenge. In contrast, rAd35 vaccine was as potent in naive mice as in Ad5-preimmunized mice. Finally, we showed that heterologous rAd35-rAd5 prime-boost regimens were more potent than rAd35-rAd35 because of induction of anti-Ad35 antibodies after rAd35 priming. The latter data provide a further rationale for developing rAd prime-boost regimens but indicate that priming and boosting Ad vectors must be immunologically distinct and also should be distinct from Ad5. Collectively, the data presented warrant further development of rAd35-based vaccines against human malaria.

Immunogenicity of recombinant fiber-chimeric adenovirus serotype 35 vector-based vaccines in mice and rhesus monkeys

Preexisting immunity to adenovirus serotype 5 (Ad5) has been shown to suppress the immunogenicity of recombinant Ad5 (rAd5) vector-based vaccines for human immunodeficiency virus type 1 (HIV-1) in both preclinical studies and clinical trials. A potential solution to this problem is to utilize rAd vectors derived from rare Ad serotypes, such as Ad35. However, rAd35 vectors have appeared less immunogenic than rAd5 vectors in preclinical studies to date. In this study, we explore the hypothesis that the differences in immunogenicity between rAd5 and rAd35 vectors may be due in part to differences between the fiber proteins of these viruses. We constructed capsid chimeric rAd35 vectors containing the Ad5 fiber knob (rAd35k5) and compared the immunogenicities of rAd5, rAd35k5, and rAd35 vectors expressing simian immunodeficiency virus Gag and HIV-1 Env in mice and rhesus monkeys. In vitro studies demonstrated that rAd35k5 vectors utilized the Ad5 receptor CAR rather than the Ad35 receptor CD46. In vivo studies showed that rAd35k5 vectors were more immunogenic than rAd35 vectors in both mice and rhesus monkeys. These data suggest that the Ad5 fiber knob contributes substantially to the immunogenicity of rAd vectors. Moreover, these studies demonstrate that capsid chimeric rAd vectors can be constructed to combine beneficial immunologic and serologic properties of different Ad serotypes.

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.

The dendritic cell-derived protein DC-STAMP is highly conserved and localizes to the endoplasmic reticulum

Recently, we described the molecular identification of dendritic cell-specific TrAnsMembrane protein (DC-STAMP), a multimembrane-spanning protein preferentially expressed by human DC (hDC). In this report, we describe the identification and expression profile of the murine homologue of DC-STAMP (mDC-STAMP) as well as the characterization of the DC-STAMP protein. The results demonstrate that mDC-STAMP is over 90% homologous to hDC-STAMP and is also preferentially expressed by DC in vitro and ex vivo. mDC-STAMP expression is enhanced by interleukin-4 and down-regulated upon DC maturation. Analysis of differently tagged DC-STAMP proteins further demonstrates that hDC-STAMP and mDC-STAMP are glycosylated and primarily localize to an intracellular compartment. Applying confocal microscopy and electron microscopy, we demonstrate that hDC-STAMP localizes to the endoplasmic reticulum (ER) in human embryonic kidney 293 cells as well as hDC transduced with an adenovirus encoding hDC-STAMP-green fluorescent protein fusion protein. These data imply that DC-STAMP may exert its effect in the ER.

Immunogenicity of recombinant adenovirus serotype 35 vaccine in the presence of pre-existing anti-Ad5 immunity

The high prevalence of pre-existing immunity to adenovirus serotype 5 (Ad5) in human populations may substantially limit the immunogenicity and clinical utility of recombinant Ad5 vector-based vaccines for HIV-1 and other pathogens. A potential solution to this problem is to use vaccine vectors derived from adenovirus (Ad) serotypes that are rare in humans, such as Ad35. However, cross-reactive immune responses between heterologous Ad serotypes have been described and could prove a major limitation of this strategy. In particular, the extent of immunologic cross-reactivity between Ad5 and Ad35 has not previously been determined. In this study we investigate the impact of pre-existing anti-Ad5 immunity on the immunogenicity of candidate rAd5 and rAd35 vaccines expressing SIV Gag in mice. Anti-Ad5 immunity at levels typically found in humans dramatically blunted the immunogenicity of rAd5-Gag. In contrast, even high levels of anti-Ad5 immunity did not substantially suppress Gag-specific cellular immune responses elicited by rAd35-Gag. Low levels of cross-reactive Ad5/Ad35-specific CD4(+) T lymphocyte responses were observed, but were insufficient to suppress vaccine immunogenicity. These data demonstrate the potential utility of Ad35 as a candidate vaccine vector that is minimally suppressed by anti-Ad5 immunity. Moreover, these studies suggest that using Ad vectors derived from immunologically distinct serotypes may be an effective and general strategy to overcome the suppressive effects of pre-existing anti-Ad immunity.

An adenoviral type 5 vector carrying a type 35 fiber as a vaccine vehicle: DC targeting, cross neutralization, and immunogenicity

Substituting the coat proteins of adenoviral vector serotype 5 (Ad5) can alter vector tropism and circumvent vector neutralization. Here we report that an Ad5 vector carrying a part of the fiber molecule of human subgroup B adenovirus serotype 35 (Ad5.Fib35) transduces cultured human dendritic cells (DC) and circulating myeloid derived DC with approximately 10-fold greater efficiency than Ad5 in vitro. The improved DC transduction results in increased T-cell activation ex vivo. In vivo however, immunogenicity of the vectors in mice and non-human primates did not correlate with in vitro DC tropism. Ad5.Fib35 was less immunogenic in monkeys than Ad5, despite the improved primate DC tropism of Ad5.Fib35. In mice with high Ad5 vector-specific immunity, Ad5.Fib35 showed no significant difference in anti-insert immunity over Ad5 indicating that fiber exchange alone does not evade pre-existing Ad5 immunity. We thus conclude that, for ex vivo vaccination, Ad5.Fib35 shows promise as vector for loading of DC but is unable to circumvent anti-Ad5 immunity limiting its in vivo utility.

Neutralizing antibodies and CD8+ T lymphocytes both contribute to immunity to adenovirus serotype 5 vaccine vectors

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 vector-based vaccines for human immunodeficiency virus type 1 and other pathogens. Ad5-specific neutralizing antibodies (NAbs) are thought to contribute substantially to anti-Ad5 immunity, but the potential importance of Ad5-specific T lymphocytes in this setting has not been fully characterized. Here we assess the relative contributions of Ad5-specific humoral and cellular immune responses in blunting the immunogenicity of a rAd5-Env vaccine in mice. Adoptive transfer of Ad5-specific NAbs resulted in a dramatic abrogation of Env-specific immune responses following immunization with rAd5-Env. Interestingly, adoptive transfer of Ad5-specific CD8(+) T lymphocytes also resulted in a significant and durable suppression of rAd5-Env immunogenicity. These data demonstrate that NAbs and CD8(+) T lymphocytes both contribute to immunity to Ad5. Novel adenovirus vectors that are currently being developed to circumvent the problem of preexisting anti-Ad5 immunity should therefore be designed to evade both humoral and cellular Ad5-specific immune responses.

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.

Induction of CAMEL/NY-ESO-ORF2-specific CD8+ T cells upon stimulation with dendritic cells infected with a modified Ad5 vector expressing a chimeric Ad5/35 fiber

Delivery of the full-length tumor antigen might be more successful in immunotherapy than single peptides and has the advantage that patients no longer need to be selected for their HLA type. In this study, we tested the in vitro induction of CAMEL/NY-ESO-ORF2-specific T cells by dendritic cells infected with an adenovirus (Ad) type 5 vector containing the fiber shaft and knob of human serotype Ad35 (Ad5F35 vector). Our data show induction of CD8(+) T cells specific for the known HLA-A(*)0201-binding CAMEL/NY-ESO-ORF2(1-11) epitope by DC infected with Ad5F35-CAMEL, but not by DC pulsed with the recombinant CAMEL protein. In one healthy donor, even CD8(+) T cells specific for a new HLA-B7-binding CAMEL/NY-ESO-ORF2(46-54) epitope were raised. In conclusion, the in vitro induction of CAMEL/NY-ESO-ORF2-specific CD8(+) T cells in healthy donors by DC infected with Ad5F35-CAMEL strongly supports further investigation of the Ad5F35 vector as a vehicle for gene transfer into DC for the generation of tumor antigen-specific CD8(+) T cell responses in vivo.

CD4+ Th2 cell recognition of HLA-DR-restricted epitopes derived from CAMEL: a tumor antigen translated in an alternative open reading frame

Tumor Ag NY-ESO-1 is an attractive target for immunotherapy of cancer, since both CD8(+) CTL and CD4(+) Th cells against NY-ESO-1 have been described. Moreover, NY-ESO-1 as well as the highly homologous tumor Ag LAGE-1 are broadly expressed in various tumor types. Interestingly, the NY-ESO-1 and LAGE-1 genes also encode for proteins translated in an alternative open reading frame. These alternatively translated NY-ESO-ORF2 and CAMEL proteins, derived from the NY-ESO-1 and LAGE-1 genes, respectively, have been demonstrated to be immunogenic, since CTL specific for these proteins have been isolated from melanoma patients. In this study a panel of advanced melanoma patients was screened for the presence of Th cells specific for the alternatively translated tumor Ags NY-ESO-ORF2 and CAMEL. PBMC of melanoma patients were stimulated for 4 days with mixes of overlapping peptides covering the entire NY-ESO-ORF2 and CAMEL protein sequences and were tested for the release of type 1 (IFN-gamma) and type 2 (IL-13) cytokines in ELISPOT assays. In three of 15 patients, T cells specific for two CAMEL peptides (CAMEL(71-92) and CAMEL(81-102)) could be detected. From one of these patients, CD4(+) T cell clones specific for CAMEL(81-102) could be generated. These clones recognized a naturally processed epitope presented in both HLA-DR11 and HLA-DR12 and produced high levels of IL-4, IL-5, and IL-13. In conclusion, this study shows the presence of Th cells specific for the alternatively translated tumor Ag CAMEL in melanoma patients and is the first report that describes the isolation of tumor Ag-specific CD4(+) Th 2 clones.

Exploiting the natural diversity in adenovirus tropism for therapy and prevention of disease

Since targeting of recombinant adenovirus vectors to defined cell types in vivo is a major challenge in gene therapy and vaccinology, we explored the natural diversity in human adenovirus tissue tropism. Hereto, we constructed a library of Ad5 vectors carrying fibers from other human serotypes. From this library, we identified vectors that efficiently infect human cells that are important for diverse gene therapy approaches and for induction of immunity. For several medical applications (prenatal diagnosis, artificial bone, vaccination, and cardiovascular disease), we demonstrate the applicability of these novel vectors. In addition, screening cell types derived from different species revealed that cellular receptors for human subgroup B adenoviruses are not conserved between rodents and primates. These results provide a rationale for utilizing elements of human adenovirus serotypes to generate chimeric vectors that improve our knowledge concerning adenovirus biology and widen the therapeutic window for vaccination and many different gene transfer applications.

Odocoileus hemionus deer adenovirus is related to the members of Atadenovirus genus

The Odocoileus hemionus deer adenovirus (OdAdV-1) causes systemic and local vasculitis and proves extremely lethal for mule deer. To characterize the virus, part of the genome flanking the fiber gene was cloned and sequenced. The sequence revealed two open-reading frames that mapped to pVIII hexon-associated protein precursor and fiber protein of several other adenoviruses. The highest amino acid homology for pVIII and fiber was found with the members of the proposed Atadenovirus genus: ovine adenovirus isolate 287 (OAdV-287), bovine adenovirus 4 (BAdV-4) and duck adenovirus 1 (DAdV-1). The homology with bovine adenovirus type 3 (BAdV-3) proved low. The E3 region was not found between the gene for pVIII and fiber. These data suggest that OdAdV-1 is a member of the Atadenovirus genus.