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At least 811 records · Page 45Linked to original sources
PubMed2001

Antitumor activity of recombinant adenoviral vectors expressing murine IFN-alpha in mice injected with metastatic IFN-resistant tumor cells.

Recent studies have shown that gene therapy with type I interferon (IFN) in an adenovirus vector is a powerful tool to suppress the growth of human tumors transplanted in immune-deficient mice. However, in these studies the host immune-mediated effects, which may be important in mediating the long-term control of tumor growth by these cytokines, was not studied. In this paper, we evaluate the antitumor efficacy of different adenoviral vectors containing mouse IFN-alpha genes (i.e., a first-generation replication-defective vector containing IFN-alpha1 and two different second-generation vectors containing IFN-alpha2) in immunocompetent DBA/2 mice transplanted with highly metastatic Friend leukemic cells resistant in vitro to type I IFN. We found that injection of all the different adenovirus vectors containing mouse IFN-alpha( genes resulted in a marked antitumor response in mice transplanted either subcutaneously or intravenously with IFN-resistant Friend leukemic cells compared to tumor-bearing animals inoculated with a control vector. Tumor growth inhibition after injection of IFN-adenovirus vectors was associated with a prolonged presence of high IFN levels in the sera of the injected mice. Suppression of metastatic tumor growth was also observed after a single injection of the IFN--adenovirus recombinant vectors, whereas a comparable antitumor response generally required several injections of high doses of IFN. Altogether, these results demonstrate that IFN--adenoviral vectors can efficiently inhibit metastatic tumor growth by host-mediated mechanisms and suggest that adenovirus-mediated IFN-alpha gene therapy may represent an attractive alternative to the conventional clinical use of this cytokine, which generally requires multiple injections of high IFN doses for a prolonged period of time.

Adenoviridae↗
PubMed2003

Comparison of HSV-1 thymidine kinase-dependent and -independent inhibition of replication-competent adenoviral vectors by a panel of drugs.

Replication-competent adenoviral vectors hold the promise to be more efficient gene delivery vehicles than their replication-deficient counterparts, but they are also associated with a higher risk for adverse effects, especially in light of the fact that there is no established effective therapy for serious, disseminated adenovirus infection. To assess whether the therapeutic options to inhibit adenoviral replication can be enhanced by expressing a suicide gene, we examined the antiadenoviral effects of 15 drugs against wild-type adenovirus type 5 (Ad5) and an Ad5-based replication-competent vector expressing herpes simplex virus-1 thymidine kinase (HSV-tk) (Ad.OW34) using a real-time polymerase chain reaction -based assay and flow cytometry. Ad5 and Ad.OW34 were highly susceptible to the fluorinated pyrimidine analogs 5-fluoro-2'-deoxyuridine (FUdR), 5-fluorouridine (FUR), and trifluorothymidine (TFT), with a mean 50% inhibitory concentration (IC(50)) ranging from 0.12 to 0.32 microM. The mean IC(50) of ribavirin and cidofovir (CDV) for Ad5, the most frequently used drugs to treat adenovirus disease, was 6.87 and 3.19 microM, respectively. In contrast to Ad5, the Ad.OW34 vector was susceptible to (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVdU, IC(50) 0.09 microM), ganciclovir (GCV, IC(50) 0.19 microM), and acyclovir (ACV, IC(50) 32.04 microM). Additionally, we demonstrated in an animal model that Ad.OW34 vector replication can be inhibited significantly by GCV, CDV, and TFT by 35.2, 7.7, and 3.7-fold, respectively, compared to untreated animals. The observed antiadenoviral effects were primarily not through cell killing, since the in vitro 50% cytotoxic concentrations (CC(50)) were more than 1000 times higher than the antiadenoviral IC(50) of the drugs examined, even in cells stably expressing HSV-tk. Since for HSV-tk-dependent inhibition of adenoviral vectors, stability of HSV-tk expression is crucial, we examined Ad.OW34 vector stability, by passaging the vector 10 times serially in the presence of 10 microM GCV. The HSV-tk/GCV system neither changed the susceptibility of Ad.OW34 to GCV significantly nor detectable vector rearrangements occurred, suggesting that the system might be suitable as a fail-safe mechanism to stop adenoviral vector replication.

Adenoviridae↗
PubMed1997

A simple procedure to determine the biological titer of recombinant retroviral vectors.

Retroviral vectors are widely used to deliver genetic material to live cells both in experimental and clinical settings. The ability of these vectors to transduce target cells is an important aspect of their clinical applicability and one of the factors determining their transduction efficiency is vector functional titer. Current methods for titrating retroviral vectors involve measuring the number of target cells in culture transduced by a given volume of vector solution. In this report, we describe a new procedure which allows one to estimate the actual number of infectious particles capable of transducing a permissive cell type. Vector biological titer is calculated from the fractional decline in transduction efficiency observed when a given volume of vector solution is sequentially added to multiple dishes containing permissive cells. Values determined this way are greater than those obtained from a single transduction experiment, with the difference being inversely proportional to the degree of cell permissiveness for vector entry. The present procedure is simple, reliable and expeditious. It will be useful to standardize vector biological titers determined in different laboratories, and help implement strategies for efficient gene delivery protocols.

Animals↗
PubMed1997

Optimized conditions for the production of recombinant amphotropic retroviral vector preparations.

The production and stability of recombinant retroviral vectors was examined at various temperatures. The two studied recombinant retroviral vectors, based on different packaging cell lines, exhibited a four-fold increased half-life at 32 degrees C as compared to 37 degrees C. Surprisingly, this increased stability at 32 degrees C was only observed within a very narrow temperature window. At 30 degrees C and 34 degrees C, retroviral vector half-lives were quite similar to that at 37 degrees C. Regardless of the vector half-life, retroviral vectors accumulated in the culture medium for a period of 48 h before an equilibrium was reached between retroviral vector production and decay. Maximal accumulated recombinant retroviral titers were five- to ten-fold increased after a medium incubation at 32 degrees C as compared to 37 degrees C. Furthermore, multiple cycles of freezing and thawing of retroviral vector supernatants hardly affected the recombinant retroviral vector titer, independent of the presence of serum. This knowledge on characteristics of recombinant retroviral vectors has practical implications for the manufacturing of these viruses for clinical gene therapy protocols.

Cell Line↗
PubMed1997

Novel retroviral packaging cell lines: complementary tropisms and improved vector production for efficient gene transfer.

We report increased transduction of human hematopoietic progenitor cells through a combination of novel retroviral vector packaging cell lines, and improved vector supernatant production. The new ProPak packaging cell lines produce either murine leukemia virus (MLV) xenotropic (ProPak-X cells) or amphotropic particles (ProPak-A cells), and ProPak-based producer cells were demonstrated to be free of replication-competent retrovirus (RCR) by stringent testing. Vector supernatants from ProPak or existing packaging cell lines producing different pseudotyped particles (amphotropic MLV, xenotropic MLV or gibbon ape leukemia virus) were compared for the ability to transduce clinically relevant human hematopoietic cells. All vector types transduced primary human CD34-positive or CD4-positive cells, regardless of tropism. However, consistently higher transduction of target cells was achieved with ProPak-derived amphotropic vector than with PA317-packaged amphotropic vector. The highest transduction of human hematopoietic progenitor cells was achieved with vector supernatant generated from a coculture of the ProPak-X and ProPak-A cell lines. This ping-pong amplification yielded supernatant containing vector targeted to two distinct receptors present on human cells, and did not result in detectable RCR formation. In addition, we describe conditions for improved vector supernatant production in a packed-bed bioreactor.

3T3 Cells↗
PubMed1998

Intratumoral coinjection of adenoviral vectors expressing IL-2 and IL-12 results in enhanced frequency of regression of injected and untreated distal tumors.

We have studied the ability of adenoviral (Ad) vectors expressing the cytokines IL-2 or IL-12 to mediate regression of established tumors in a mouse model of mammary adenocarcinoma. Previous results indicated that intratumoral injection of vectors expressing IL-2 (AdCAIL-2), or IL-12 (AdmIL-12.1) induced complete tumor regression in approximately 30-40% of treated animals. In the current studies, we investigated the mechanism of tumor killing in responding animals and the efficacy of AdIL-2 and AdIL-12 vector administration in combination compared with the use of either vector alone. Animals bearing subcutaneous mammary tumors were injected intratumorally with Ad vectors expressing IL-2 or IL-12 or were coinjected with both vectors. Animals receiving the combination treatment responded substantially better than animals which had received either vector alone, with 65% of animals treated with both vectors undergoing complete tumor regression. In all three treatment regimens, tumor regression was associated with the presence of specific antitumor antigen cytotoxic T-lymphocytes (CTLs), which secreted elevated levels of IFN-gamma. Consistent with circulating CTLs being involved in regression, when animals bearing bilateral tumors were inoculated in a single tumor with IL-2 or IL-12 expressing vectors, both tumors regressed in many cases. Again, treatment with both AdCAIL-2 and AdmIL-12.1 was most effective, with 63% of animals undergoing complete regression of both treated and untreated tumors, compared to 18 or 22% of animals injected with either AdCAIL-2 or AdmIL-12.1 alone. These data indicate that the combination of IL-2 and IL-12 is a more effective inducer of antitumor immune responses than either one alone, and that the resulting antitumor responses are effective in mediating the regression of distal untreated tumors, a property which may aid in the treatment of metastatic disease.

Adenocarcinoma↗
PubMed1999

Efficient CFTR expression from AAV vectors packaged with promoters--the second generation.

Gene therapy studies of cystic fibrosis (CF) have shown that AAV-based vector was efficient in transferring but not in expressing the CFTR cDNA in the target cells. The levels of CFTR gene expression were limited by the small packaging capacity of AAV because it had been difficult to package the CFTR cDNA with an efficient promoter. In the present study we have developed a new generation of AAV/CFTR vectors which contain efficient short promoters to express the CFTR gene in target cells. To do so, we reduced the size of the CFTR cDNA by determining the minimal untranslated regions required for expression of CFTR cDNA. We also identified short and efficient promoters that could be packaged with the down-sized CFTR cDNA into a novel AAV vector that had a maximal packaging capacity. Functional analyses showed that the new vectors were packaged efficiently and expressed higher levels of CFTR than a vector in which the CFTR gene was driven by the ITR sequence of AAV. Transduction of airway epithelial cells containing [symbol: see text] 508 mutation with the new vectors demonstrated efficient expression of the wild-type CFTR and correction of the CF phenotype. In contrast, no significant CFTR expression was detected in cells infected with the vector that express the CFTR gene from the ITR. These findings support the notion that the AAV can be developed into an efficient vector to transduce the CFTR gene and vectors expressing higher levels of CFTR from an efficient promoter should provide better efficacy for gene therapy of cystic fibrosis.

Cystic Fibrosis↗
PubMed2001

A highly efficient and consistent method for harvesting large volumes of high-titre lentiviral vectors.

Lentiviral vectors pseudotyped with vesicular stomatitis virus glycoprotein (VSV-G) are emerging as the vectors of choice for in vitro and in vivo gene therapy studies. However, the current method for harvesting lentivectors relies upon ultracentrifugation at 50,000 g for 2 h. At this ultra-high speed, rotors currently in use generally have small volume capacity. Therefore, preparations of large volumes of high-titre vectors are time-consuming and laborious to perform. In the present study, viral vector supernatant harvests from vector-producing cells (VPCs) were pre-treated with various amounts of poly-L-lysine (PLL) and concentrated by low speed centrifugation. Optimal conditions were established when 0.005% of PLL (w/v) was added to vector supernatant harvests, followed by incubation for 30 min and centrifugation at 10,000 g for 2 h at 4 degrees C. Direct comparison with ultracentrifugation demonstrated that the new method consistently produced larger volumes (6 ml) of high-titre viral vector at 1 x 10(8) transduction unit (TU)/ml (from about 3,000 ml of supernatant) in one round of concentration. Electron microscopic analysis showed that PLL/viral vector formed complexes, which probably facilitated easy precipitation at low-speed concentration (10,000 g), a speed which does not usually precipitate viral particles efficiently. Transfection of several cell lines in vitro and transduction in vivo in the liver with the lentivector/PLL complexes demonstrated efficient gene transfer without any significant signs of toxicity. These results suggest that the new method provides a convenient means for harvesting large volumes of high-titre lentivectors, facilitate gene therapy experiments in large animal or human gene therapy trials, in which large amounts of lentiviral vectors are a prerequisite.

Animals↗
PubMed2002

Inhibition of HIV-1 replication by novel lentiviral vectors expressing transdominant Rev and HIV-1 env antisense.

Retroviral vectors expressing transdominant negative mutants of Rev (TdRev) inhibit HIV-1 replication by preventing the nuclear export of unspliced viral transcripts, thus inhibiting the synthesis of Gag-Pol, Env and reducing the levels of genomic RNA available for packaging. Due to these effective mechanisms of inhibition, production of HIV-1-based lentiviral vectors expressing TdRev has been difficult. Here we describe HIV-based vectors in which expression of TdRev is negatively regulated by Rev expression. In these vectors, we maintained the wild-type HIV-1 Tat/Rev exons and intron configuration and its mode of splicing regulation. The second Rev exon was mutated to encode TdRev. Inhibition of TdRev expression by Rev during vector production yields high titer vector preparations. A second vector containing an additional anti-HIV gene (env-antisense) was constructed by flipping a 1.2-kb env fragment contained within the Tat/TdRev intron. SupT1 cells and primary CD4+ lymphocytes transduced with these vectors inhibit HIV-1 replication and show a preferential advantage for survival. Although these vectors are poorly mobilized to secondary target cells by wild-type HIV-1, they reduce the infectivity of the wild-type virions escaping inhibition.

CD4-Positive T-Lymphocytes↗
PubMed2004

Unexpected pulmonary uptake of adenovirus vectors in animals with chronic liver disease.

When adenovirus vectors are injected intravenously, most of the virions are quickly taken up by the reticuloendothelial system, primarily by the liver macrophages known as Kupffer cells. However, little is known about the behavior of adenovirus vectors when there is pre-existing liver disease. To study this, we examined the biodistribution of intravenously injected vector in a rat model of cirrhosis induced by bile duct ligation. Using quantitative PCR and fluorescently tagged adenovirus vectors, we observed a significant reduction in vector uptake by the cirrhotic liver and increased accumulation in the lungs. Immunocytochemistry and electron microscopy demonstrated that this was due to changes in the reticuloendothelial system, with the vector being taken up by large numbers of pulmonary intravascular macrophages in the lungs of cirrhotic rats. Interestingly, expression of vector-encoded luciferase was significantly reduced in the livers of cirrhotic rats, but was not increased in the lungs. These data demonstrate that the biodistribution of adenovirus vectors in rats is altered by cirrhosis, which suggests the possibility that these vectors might behave unexpectedly in patients with pre-existing liver conditions, particularly since pulmonary reticuloendothelial changes are known to occur in human disease.

Adenoviridae↗
PubMed2004

Comparative analysis of genomic HSV vectors for gene delivery to motor neurons following peripheral inoculation in vivo.

The use of viral vectors for gene delivery to motor neurons in vivo has been hampered by the need to perform invasive surgery to inject directly the vector into the anterior horn of the spinal cord. Here, we have characterized the features of herpes simplex virus-1 (HSV)-derived vectors, in terms of gene mutations and promoter constructs, that are required to allow efficient transduction of motor neurons following a relatively noninvasive peripheral administration via sciatic nerve or footpad injection. Owing to the wide variety of animal models used to study neurodegenerative diseases of motor neurons, we analysed the effectiveness of these vectors in adult mice and adult and neonatal rats. We tested viruses with differing degrees of disablement based on the 1764 backbone (deleted for ICP34.5 and an insertional inactivation in VP16) rendered completely replication incompetent by the deletion of the essential immediate-early genes ICP27 and/or ICP4. In the adult mouse, prolonged gene expression in motor neurons was obtained after sciatic nerve inoculation with a vector defective in ICP4 and ICP27. In the adult rat, both the vector defective in ICP4 and the vector defective in ICP4 and ICP27 were capable of transducing motor neurons for extended periods of time during viral latency. This study demonstrates the feasibility of using HSV vectors for persistent transgene expression in motor neurons in a safe and nontoxic manner following peripheral administration. These vectors are potentially useful tools to investigate the functions of genes involved in motor neuronal survival and regeneration in models of motor neuron diseases in vivo.

Animals↗
PubMed2005

Complement regulatory proteins are incorporated into lentiviral vectors and protect particles against complement inactivation.

Lentiviral vectors pseudotyped with G glycoprotein from vesicular stomatitis virus (VSV-G) and baculovirus gp64 are inactivated by human complement. The extent of vector inactivation in serum from individual donors was examined and results showed wide donor-dependent variation in complement sensitivity for VSV-G-pseudotyped lentivectors. Amphotropic envelope (Ampho)-pseudotyped vectors were generally resistant to serum from all donors, while gp64-pseudotyped vectors were inactivated but showed less donor-to-donor variation than VSV-G. In animal sera, the vectors were mostly resistant to inactivation by rodent complement, whereas canine complement caused a moderate reduction in titer. In a novel advance for the lentiviral vector system, human complement-resistant-pseudotyped lentivector particles were produced through incorporation of complement regulatory proteins (CRPs). Decay accelerating factor (DAF)/CD55 provided the most effective protection using this method, while membrane cofactor protein (MCP)/CD46 showed donor-dependent protection and CD59 provided little or no protection against complement inactivation. Unlike previous approaches using CRPs to produce complement-resistant viral vectors, CRP-containing lentivectors particles were generated for this study without engineering the CRP molecules. Thus, through overexpression of native DAF/CD55 in the viral producer cell, an easy method was developed for generation of lentiviral vectors that are almost completely resistant to inactivation by human complement. Production of complement-resistant lentiviral particles is a critical step toward use of these vectors for in vivo gene therapy applications.

Animals↗
PubMed2005

Quantitative comparison of polyethylenimine formulations and adenoviral vectors in terms of intracellular gene delivery processes.

An objective of designing molecular vehicles exhibiting virus-like transgene delivery capabilities but with low toxicity and immunogenicity continues to drive synthetic vector development. As no single step within the gene delivery pathway represents the critical limiting barrier for all vector types under all circumstances, improvements in synthetic vehicle design may be aided by quantitative analysis of the contributions of each step to the overall delivery process. To our knowledge, however, synthetic and viral gene delivery methods have not yet been explicitly compared in terms of these delivery pathway steps in a quantitative manner. As a first address of this challenge, we compare here quantitative parameters characterizing intracellular gene delivery steps for an E1/E3-deleted adenoviral vector and three polyethylenimine (PEI)-based vector formulations, as well as the liposomal transfection reagent Lipofectamine and naked DNA; the cargo is a plasmid encoding the beta-galactosidase gene under a CMV promoter, and the cell host is the C3A human hepatocellular carcinoma line. The parameters were determined by applying a previously validated mathematical model to transient time-course measurements of plasmid uptake and trafficking (from whole-cell and isolated nuclei lysates, by real-time quantitative PCR), and gene expression levels, enabling discovery of those for which the adenoviral vector manifested superiority. Parameter-sensitivity analysis permitted identification of processes most critically rate-limiting for each vector. We find that the adenoviral vector advantage in delivery appears to reside partially in its import to the nuclear compartment, but that its vast superiority in transgene expression arises predominantly in our situation from postdelivery events: on the basis of per-nuclear plasmid, expression efficiency from adenovirus is superior by orders of magnitude over the PEI vectors. We find that a chemical modification of a PEI-based vector, which substantially improves its performance, appears to do so by enhancing certain trafficking rate parameters, such as binding and uptake, endosomal escape, and binding to nuclear import machinery, but leaves endosomal escape as a barrier over which transgene delivery could be most sensitively increased further for this polymer.

Adenoviridae↗
PubMed2005

Intracellular trafficking of nonviral vectors.

Nonviral vectors continue to be attractive alternatives to viruses due to their low toxicity and immunogenicity, lack of pathogenicity, and ease of pharmacologic production. However, nonviral vectors also continue to suffer from relatively low levels of gene transfer compared to viruses, thus the drive to improve these vectors continues. Many studies on vector-cell interactions have reported that nonviral vectors bind and enter cells efficiently, but yield low gene expression, thus directing our attention to the intracellular trafficking of these vectors to understand where the obstacles occur. Here, we will review nonviral vector trafficking pathways, which will be considered here as the steps from cell binding to nuclear delivery. Studies on the intracellular trafficking of nonviral vectors has given us valuable insights into the barriers these vectors must overcome to mediate efficient gene transfer. Importantly, we will highlight the different approaches used by researchers to overcome certain trafficking barriers to gene transfer, many of which incorporate components from biological systems that have naturally evolved the capacity to overcome such obstacles. The tools used to study trafficking pathways will also be discussed.

Animals↗
PubMed2006

Characterization of capsid-modified adenovirus vectors containing heterologous peptides in the fiber knob, protein IX, or hexon.

Adenovirus (Ad) vectors are widely used in gene therapy and in vitro/in vivo gene transfer because of their high transduction efficiency. However, Ad vector application in the gene therapy field is limited by poor transduction into cells not expressing the primary receptor, coxsackievirus and adenovirus receptor. To overcome this problem, several types of capsid-modified Ad vectors have been developed. The HI loop or C-terminus of the fiber knob, the C-terminus of the protein IX (pIX) and the hypervariable region 5 of the hexon are promising candidate locations for displaying foreign peptide sequences. In the present study, we constructed Ad vectors in which each of the above region was modified by a simple in vitro ligation-based method, and examined the characterization of each Ad vector containing the FLAG tag (DYKDDDDK) or RGD (CDCRGDCFC) peptide. Enzyme-linked immunosorbent assay examining the surface expression of foreign peptides on the virus suggested that foreign peptides are exposed on virion surfaces in all types vectors and that the hexon was the most efficiently reacted, reflecting the copy number of the modification. However, in the case of the transduction efficiency of Ad vectors containing the RGD peptides, the modification of pIX and the hexon showed no effect. The modification of the HI loop of the fiber knob was the most efficient, followed by the modification of the C-terminus region of the fiber knob. These comparative analyses, together with a simple construction method for each modified Ad vector, could provide basic information for the generation of capsid-modified Ad vectors.

Adenoviridae↗
PubMed2007

Construction and characterization of efficient, stable and safe replication-deficient foamy virus vectors.

As serious side effects affected recent virus-mediated gene transfer studies, novel vectors with improved safety profiles are urgently needed. In the present study, replication-deficient retroviral vectors based on feline foamy virus (FFV) were constructed and analyzed. The novel FFV vectors are devoid of almost the complete env gene plus the internal promoter - accessory bel gene cassette including the gene for the viral transcriptional transactivator Bel1/Tas. In these Bel1/Tas-independent vectors, expression of the lacZ (beta-galactosidase) marker gene is directed by the heterologous, constitutively active human ubiquitin C promoter (ubi). Env-transcomplemented vectors have un-concentrated titers of more than 10(5) transducing units/ml. The vectors allow efficient transduction of a broad array of diverse target cells, which can be increased by repeated vector exposure. However, the number of lacZ marker gene expressing cells decreased slightly upon serial passages of the transduced cells. Vectors carrying a self-inactivating (SIN) deletion of the TATA box and most parts of the viral promoter were not rescued by wt FFV whereas those with the intact or a partially deleted promoter were readily reactivated. This finding indicates that the viral promoters are in fact non-functional, pointing to a highly advantageous safety profile of these new FFV-ubi-lacZ-SIN vectors.

Animals↗
PubMed2002

Development of gene therapy for hematopoietic stem cells using lentiviral vectors.

Lentiviral vectors are promising tools for the development of gene therapy since they can transduce both quiescent and dividing target cells. Lentiviral vectors may be particularly promising gene delivery tools for hematopoietic stem cells since these target cells tend to be quiescent and are therefore difficult target cells for vectors that require dividing targets. Human hematopoietic stem cells that can repopulate NOD/SCID mice have been efficiently transduced using HIV-1-based lentiviral vectors and similar vectors can also transduce murine hematopoietic stem cells. HIV-1 vectors that contain strong general promoters can generate high levels of transgene expression and very high expression levels can be generated in erythroid cells in vivo using beta-globin regulatory sequences to control the expression of the transgene. Current lentiviral vectors have a similar level of biosafety as oncoretroviral vectors and can therefore theoretically be used in clinical gene therapy protocols. Future challenges include the generation of lentiviral vectors that can express more than one transgene at high levels and the generation of safe permanent packaging cells for practical use in clinical gene therapy trials.

Animals↗
PubMed2007

Baculovirus-based vaccination vectors allow for efficient induction of immune responses against plasmodium falciparum circumsporozoite protein.

Baculovirus vectors are able to transduce a large variety of mammalian cell types and express transgenes placed under the control of heterologous promoters. In this study, we evaluated the potential of baculovirus vectors for malaria vaccination. To induce efficient CD4(+) and CD8(+) T-cell responses, we produced a series of vectors that display the Plasmodium falciparum circumsporozoite (CS) protein in the virion envelope and/or allow for CS expression upon transduction of mammalian cells. We found that baculovirus vectors can transduce professional antigen-presenting cells and trigger their maturation, which is a prerequisite for efficient antigen presentation. Upon intramuscular injection into mice, the vector that both displayed and expressed CS induced higher anti-CS antibody titers (of the immunoglobulin (IgG)1 and IgG2a type) and a higher frequency of interferon-gamma-producing T cells specific to CS, than the vectors which either only displayed or only expressed CS. The baculovirus CS display/expression vector was also superior in inducing CS-specific CD4(+) and CD8(+) T-cell responses in vitro using human peripheral blood mononuclear cells from naive donors. This, together with the absence of pre-existing immunity to baculoviruses in humans, the absence of viral gene expression in mammalian cells, and the relative low immunogenicity of baculovirus virions, makes these vectors promising tools for vaccination. Furthermore, the ability to produce large amounts in serum-free medium at a low cost adds a further advantage to this vector system.

Animals↗