Patent 6,867,353

The present invention relates to a method for producing recombinant rotavirus structural proteins by culturing a transformed plant cell, and to a vaccine composition comprising the same as an effective component. More specifically, the method comprises the steps of preparing the expression vector comprising cDNA fragments encoding rotavirus structural proteins; transforming a plant cell with the expression vector; and recovering the vaccine composition, including rotavirus antigens, from the cell culture. The method for producing the recombinant rotavirus structural proteins is advantageous in that higher yields of more than 0.3 mg/L are obtained, as well as a lower cost and a lower contamination hazard than those of eukaryotic expression systems such as baculovirus and animal cell. Furthermore, the method can be used to produce a edible vaccine. The invention also proves that the rotavirus structural protein can be produced with a high aspect rotary vessel reactor.

Description of the Invention

FIELD OF THE INVENTION

The present invention relates to a method for producing the structural proteins of the recombinant rotavirus by culturing a transformed plant cell, and the vaccine composition comprising such proteins as an effective component. More particularly, the method comprises the steps of producing the recombinant expression plasmid including the gene encoding the human rotavirus structural protein, transforming the plant cell with the expression plasmid, cultivating the plant cell, and obtaining the vaccine composition including rotavirus antigen recovered from the culture solution.

BACKGROUND OF THE INVENTION

In 1973, Bishop discovered the Rotavirus in Australia firstly. The rotavirus is a double stranded RNA virus and belongs to the Reoviridae family. The rotavirus causes acute gastroenteritis in infant and is infected via fecal-oral route after an incubation period of about 1 to 3 weeks. The disease is severe in 6 to 24 week infants, but is mild or asymptomatic in neonate or most of adults. Thus, the acute infectious diarrhea by the rotavirus is a main cause of the death in the world. Moreover, it is estimated that about a million of patients are died of the infectious diarrhea by the rotavirus in the developing countries [see reference: Blacklow, N. R. & Greenburg, H. B., (1991) Viral gastroentertitis N. Engl. J. Med., 325:152-164, 1991]. Therefore, world health organization (WHO) considered more efficient suppression and prevention for the infection by the rotavirus the first research subject [see reference: Glass, R. I et al., (1994) Rotavirus vaccines: success by reassortment Science 265-1389-1391].

The rotavirus is usually globular shape and is named after the outer and inner shells or double-shelled capsid structure of the same. The outer capsid is about 70 nm, and inner capsid is about 55 nm in diameter, respectively. The double-shelled capsid of the rotavirus surrounds the core including the inner protein shell and genome. The genome of the rotavirus consists of double stranded RNA segments encoding at least 11 rotavirus proteins. The inner capsid includes VP6 and VP2 proteins. VP4 and VP7 lie in outer side of the double-shelled capsid and constitute the outer capsid. Depending upon the antigenicity of VP6 which is a group-specific antigen, the rotavirus is divided into seven groups, A to G. VP2 protein is related to the synthesis of RNA. Group A rotavirus is further divided into the G-type (glycoprotein type) on the basis of the glycoprotein VP7, and P-type (protease-cleaved protein) on the basis of the VP4 which are associated with an important immunogenicity of the virus by forming a neutralizing antibody [see references: Estes M. K., et al., (1987) Synthesis and immunogenicity of the rotavirus major capsid antigen using a baculovirus expression system, J. Virol. 61:1488-1494; Estes M. K. & Cohen J., (1989) Rotavirus gene structure and function. Microbiol. Rev. 53:410--419; Desselberger U & McCrae M. A., (1994) The rotavirus genome. Curr. Microbiol. Immuno. 185:31-66].

The methods to treat the acute diarrhea disease caused by the rotavirus were restricted to administer non-specific physical strength supplements such as water and electrolyte. Thus, the vaccine as an effective therapeutic agent has been required for completely preventing the human from the all serum-type of human rotavirus. As an attempt, a live vaccine of attenuated human rotavirus, animal rotavirus such as cow, or reassortants comprised of RNA segments derived from different serotypes human and animal rotavirus have been used. As a result of such study, Wyeth Laboratories, a manufacturing company of vaccines, reported first rotavirus vaccine, RotaShield (trademark). The vaccine was produced by reassorting rotavirus of Rhesus monkey and human rotavirus of 3 serum types and was firstly approved by Food and Drug Administration (FDA) in the world in 1998. However, the FDA's approval to the vaccine was tentatively canceled in 1999, because of the side effects such as intussusception [MMWR Morb. Mortal Wkly. Rep., (1999) 5;48(43):1007].

Apart from the above, a study that the part of rotavirus is produced on a large scale through genetic recombinant technology and is used as a subunit vaccine is proceeding. In this point, many researchers have studied the expression of the rotavirus capsid proteins in E. coli expression system, baculrovirus expression system or mammalian expression system [Smith R. E. et al., (1989) Cloning and expression of the major inner capsid protein of SA-11 simian rotavirus in E. coli. Gene 79:239-248; Tosser G. et al., (1992) Expression of the major capsid protein VP6 of group C rotavirus and synthesis of chimeric single-shelled particles by using recombinant baculoviruses. J. Virol. 66:5825-5831; Ito H. et al., (1997) Expression of the major inner capsid protein, VP6, of avian rotavirus in mammalian cells. Vet. Microbiol. 49:257-265].

However, it is difficult to produce the rotavirus on a large scale by cell culture, because the rotavirus is infected through the mucus cell. That is, because it is difficult to produce the virus protein particles similar to natural virus in prokaryotic expression systems such as E. coli expression system, the particle does not elicit antigenecity. In view of contamination hazard during culture process, purification problem, high cost and low yield, the mammalian expression system is not satisfactory.

Also, most of disease caused by rotavirus is commonly occurred in developing countries which are deficient in sanitary facilities and vaccine supplement. Even if technical success of the method for producing the virus structural proteins in other cells and the vaccine composition comprising the proteins is possible, long time and many studies are required for commercializing the method in view of high production cost and sale price. On the other hand, if the rotavirus structural protein can be produced by using plant, especially edible plant and can be used for producing the vaccine, it is very economical in view of low production cost, no purification process, and efficiency in transport and storage.

Therefore, the present inventors found that rotavirus structural proteins capable of inducing the mucus and systemic immune response can be produced in the plant cell which is transformed with plant expression vector including rotavirus capsid gene, and then the plant cell is cultured under the suitable condition. Also, the vaccine composition comprising the rotavirus structural proteins can be obtained.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides the structural proteins of the recombinant human rotavirus obtained by culturing transformed plant cells, and the vaccine composition comprising such proteins as an effective component.

The method for producing antigenic recombinant human rotavirus structural protein in plant cell comprising the steps of:

1) preparing the recombinant expression plasmid by inserting cDNA fragment encoding human rotavirus structural protein into the expression plasmid for transforming plant, which comprises the promoter regulating plant-specific expression and selection marker;

2) introducing the recombinant expression plasmid of step 1 into plant cell;

3) inducing formation of callus from the plant cell which is introduced with the recombinant expression plasmid of step 2;

4) regenerating the callus of step 3 to the whole plants; and

5) recovering the recombinant human rotavirus structural protein in the plants of step 4.

The wide range of sources (e.g., human rotavirus and animal rotavirus such as cow) are available for the gene encoding rotavirus structural protein of step 1, as long as the gene encodes the rotavirus capsid protein. And, it is preferable to use the gene encoding inner capsid protein VP6, the gene encoding inner capsid protein VP2, the gene encoding outer capsid protein VP4, and the gene encoding outer capsid protein VP7. The rotavirus gene of the interest can be obtained by amplifying the gene from the feces of the subject hating rotavirus-related disease with the known polymerase chain reaction (PCR). In a desired embodiment of the present invention, VP6 gene fragment can be available by excising the gene from the plasmid pGEM-VP6 (KCTC 8984P). In another embodiment of the invention, cDNA fragment encoding VP2, VP4, and VP7 serotype G1, VP7 serotype G2, VP7 serotype G3 and VP7 serotype G4 can be used by isolating and amplifying the cDNA fragment from the faces of the subject having rotavirus-related disease.

Also, recombinant plasmid expressing the cDNA fragment encoding the human rotavirus structural protein of the interest of step 1 can be constructed from the known plant expression vector as a basic vector. The binary vector, cointegration vector, or a general vector which is designed not to include T-DNA region but to be capable of being expressed in plant can be also available.

In the present invention, the examples of the desired binary vector include final binary vectors, for example, pILTAB357-VP6, pILTAB357-VP2, pILTAB357-VP4, pILTAB357-VP7, which are prepared by inserting the cDNA fragment encoding each human rotavirus structural proteins, VP6, VP2, VP4 or VP7 into binary vectors comprising left border of T-DNA relating lo infection of a foreign gene and right border of T-DNA for transforming a plant cell, cassava vein mosaic virus promoter between the left border and the right border, nopalin synthase promoter, transcription termination region of nopalin synthase, and selection marker for selecting transformants.

As the promoter regulating the plant-specific expression, all the known expression vectors maximally expressing the recombinant proteins in plant cell can be used, and the promoter includes ubiquitin promoter, actin promoter, PG promoter or endosperm-specific promoter other than the cassava vein mosaic virus promoter.

In the transformation of the plant cell in step 2, when the binary vector or the cointegration vector is used, the plant cell transformation method mediated by agrobacterium will be employed. In such case, Agrobacterium tumefaciens or Agrobacterium rhizogenes can be used.

In the desired embodiment of the present invention, the final binary vector can be introduced into Agrobacterium tumefaciens via the known triparental mating. The tirparental mating is a method of introducing the plasmid having the gene of interest to the agrobacterium by coculturing E. coli including helper plasmid for conjugation. E. coli including the recombinant plasmid having the gene of interest and Agrobacterium for transforming the plant cell all together. More specifically, the parent E. coli used for triparent mating can be E. coli having the pILTAB357-VP6, and tomato seedling cotyledon can be transformed with the agrobacterium transformed by the tirparental mating.

In case of transforming the monocotyledon plant with the vector which does not include T-DNA region, polyethylene glycol-mediated uptake, electroporation, or microparticle bombardment can be used and transformation using single DNA and simultaneous transformation using multiple DNA also can be used.

The transformed cell can be redifferentiated by using the standard technologies known to those skilled in the art. The plant cell which may be transformed by the above method includes dicotyledon plant such as lettuce, Chinese cabbage, radish, potato, and tomato, etc. and monocotyledon plant such as rice, barley, and banana, etc. Especially, in case of producing the human rotavirus structural protein and the particle similar to the same by transforming edible plant, uptake of the transformed plant itself can induce directly the immune response, so it can be effectively used as a edible vaccine.

The selection marker to select the transformed plant cell is usually antibiotic resistant gene, but is not limited to the same. For examples, herbicide resistant gene, metabolism-related gene, luminous gene, green fluorescence protein (GFP), .beta.-glucuronidase (GUS) gene, .beta.-galactosidase (GAL) gene can be used as selection marker. Specifically, neomycin phosphotransferase II (NPTII) gene, hygromycin phosphotransferase gene, phosphynotricin acetyltransferase gene, or dihydrofolate reductase gene can be used.

Meanwhile, the transformed plant cell of the present invention can be cultured by employing microgravity culture in High Aspect Rotating-Wall Vessel as well as the suspension culture. When the High Aspect Rotating-Wall Vessel is used, the cell growth rate is very slow compared to the general suspension culture method, because the lag phase is longer in order to fit the circumstance of the mimic microgravity. However, it is found that rotavirus protein yield per cell weight in the rotary reactor is similar to that in the suspension culture.

Also, the present invention provides rotavirus-like particle which can be made by folding the human rotavirus structural proteins of the invention, VP2, VP6, VP4 and VP7. Herein, `rotavirus-like particle` is intended to mean the antigenic particle obtained from an assembly of at least a capsid protein, or self-assembly of the same.

Furthermore, the present invention provides a vaccine composition useful for treatment and prevention from rotavirus-related disease comprising the human rotavirus structural protein of the present invention as an effective component. More specifically, the vaccine composition comprises at least one selected form the group consisting of VP4, G1 serotype VP7, G2 serotype VP7, G3 serotype VP7, and G4 serotype VP7, or preferably comprises VP2 and VP6.

To prepare for the vaccine composition, the human rotavirus structural proteins produced by the transformed plant cell can be isolated and purified from the cell culture by using the known purification method, but in case of transforming by using edible plant cell, it is more preferable to prepare the rotavirus structural proteins using plant cell itself, the part of redifferentiated transformed plant or the extract of plant without purification process in view of the production cost and process management.

The vaccine useful for treatment and prevention for rotavirus-related disease can be administered orally or parenterally, and can be used in the usual form of drug.

Namely, the human rotavirus vaccine composition can be prepared by containing optionally a pharmaceutically acceptable diluent or excipient such as filler, extender, binding agent, wetting agent, integrant, and surfactant. The solid preparation for oral administration includes tablet, pill, powder, grannule, capsule, and can be prepared by mixing at least one of the excipient such as starch, calcium carbonate, sucrose, lactose, and gelatin with rotavirus vaccine composition. Also, lubricant such as magnesium stearate, talc as well as simple excipients can be used. The liquid preparation for oral administration can contain suspension, liquid drug, emulsion, and syrup, and include many excipient (e.g., wetting agent, sweetening agent, fragrant, preserving agent) other than commonly used simple diluents such as water, liquid and paraffin. The preparation for parenteral administration contains sterilized solution, non-aqueous solvent, suspension solvent, is emulsifier, freeze-drying agent or suppository. The non-aqueous solvent or suspension solvent can include propylene glycol, polyethylene glycol, vegetable oil such as olive oil, injectable ester such as ethyloleate. The basic material of suppository includes witepsol, macrogol, tween 61, cacao paper, laurin paper, glycerogelatin.

However, because most of rotavirus vaccine are administered to infant, especially 2 to 24 month-old infant, it is preferable to be administered as soon as possible before firstly exposed to the rotavirus, and the dosage form of the vaccine is more preferably oral preparation in liquid, injectable preparation, or suppository in order to easily administer to the infant.

As described below, the present invention will be more specifically illustrated by examples of the expression system that cDNA encoding the recombinant human rotavirus structural protein is expressed in the transformed tomato cell in culture systems, and the expression system that the High Aspect Rotating-Wall Vessel designed by NASA is employed for optimally culturing the recombinant human rotavirus structural proteins. However, modification or change of the method can be used, and thus the method does not limited to the following definite working examples.

Preparation of Vector Including cDNA Fragment Encoding Rotavirus Structural Protein

The gene cloning technology used herein can be easily performed by employing the method known to those skilled in the art. Such methods are well described in the following references such as Sambrook et al., 1989, Molecular Cloning A Laboratory Manual, Cold Spring Harbor Laboratory, N.Y.; and Ausubel et al., 1989, Current Protocols in Molecular Biology, Greene Publishing Associate and Wiley Interscience, N.Y.

A kind of binary vector used for transforming dicotyledon plant, especially tomato, is very various, and most of binary vectors can be available in international depository authority, for example, Center for the Application of Molecular Biology to International Agriculture (CAMBIA, GPO Box 3200, Canberra ACT2601, Australia). Basic binary vector which is variously modified to include selection marker, promoter, transcription terminator region in left border and right border region of transferred gene is used.

In the examples of the present invention, pGEM-VP6 (KCTC 0944BP) including cDNA encoding human rotavirus VP6 protein was used in order to constitute the binary vector. Also, the plasmids including cDNA fragment encoding human rotavirus VP2 of SEQ ID NO:1, cDNA fragment encoding human rotavirus VP4 of SEQ ID NO:2, cDNA fragment encoding human rotavirus VP6 of SEQ ID NO:3, and cDNA fragment encoding human rotavirus VP7 of SEQ ID NO:4 to SEQ ID NO:7 having different serotype, respectively, were used. However, the vector suitable for the present invention is not limited to the above plasmids, and all range of the vectors which efficiently express the genes can be used. In the examples of the present invention, the plasmid transforming plant cell was constructed by inserting cDNA fragment to the cloning site of known plasmid, pILTAB357 (Scripps Research Institute, U.S.A.; Verdaguer et al, Isolation and expression in transgenic tobacco and nice plants, of the cassava vein mosaic virus promoter, Plant Molecular Biology 31: 1129-1139, 1996), using CsVMV promoter in T-DNA region of pILTAB357 and inserting neomycin phosphotransferase II (NPTII) gene as a selection marker (see FIGS. 1a-1d).

Transformation Procedure

Transformation can be performed according to the method known to those skilled in the art which the present invention pertains to. The plant can be transformed via agrobacterium-mediated transformation which is illustrated in Paszkowsky et al., EMBO J 3:2717-2722 (1984). For example, agrobacterium-mediated transformation for the tomato is described in An et al., EMBO J 4-227-288 (1985). The transformation of monocotyledon plant can be achieved by directly implanting the gene into plasma via PEG or electroporation, or by introducing the gene into the callus tissue via particle bombardment. The transformed cell can be redifferentiated to the whole plant via the standard method known to those skilled in the art. The host cell for transformation can be usually Agrobacterium tumefaciens, and Agrobacterium tumefaciens strain LBA4404 which is well-known in the art was used in the desired embodiment of the present invention.

The binary vector of the, present invention was introduced to Agrobacterium tumefaciens via triparental mating. In such case, for example, E. coli MM294 including pILTAB357-VP6 which has the inserted cDNA fragment encoding human rotavirus VP6 protein was used as parent strain. Then, cotyledon excised from tomato (Lycopersicon esclentum Mill) seedling was transformed with recombinant Agrobacterium tumefaciens LBA 4404.

Transformant Culture Procedure

To culture the transformed tomato cells, suspension culture and High Aspect Rotating-Wall Vessel were used. To do this, sterilized tomato (Lycopersicon esclentum Mill) seed was inoculated on MS (Murashige and Skoog) medium, and was germinated, and then co-cultured with suspension culture solution containing Agrobacterium tumefaciens LBA 4404 including recombinant expression plasmid, and cultured successively. Also, to determine the culture system that can optimally produce recombinant rotavirus structural proteins, VP6, VP2, VP4 and VP7, the transformed tomato cell was cultured in a microgravity model system with High Aspect Rotating-Wall vessel designed by NASA.

The Expression of the Recombinant Rotavirus Structural Proteins

The transformed tomato cell was established from the selected kanamycin-resistant callus, and was maintained in liquid medium added by kanamycin 200 mg/L for 3 months. The degree of gene expression was analyzed using the transformed tomato cell on two weeks after culture and normal tomato cell. Recombinant rotavirus structural proteins, VP6, VP2, VP4 and VP7 could be detected in the transformed tomato cell by western blotting.

For example, recombinant rotavirus protein VP6 is largely in intracellular fraction, and has molecular weight of about 44 kDa. VP2 has molecular weight of 94 kDa, and VP4 has a molecular weight of 87 kDa and VP7 has a molecular weight of 34 kDa. Such measured molecular weight of the proteins is almost consistent with those derived from the nucleotide sequencing. Recombinant rotavirus proteins, VP6, VP2, VP4 and VP7 were not detected in the non-transformed cell or fraction. The fact means that VP6, VP2, VP4 and VP7 were expressed from pILTAB357-VP6, pILTAB357-VP2, pILTAB357-VP4 and pILTAB357-VP7 transformed in the tomato cell.

Claim 1 of 1 Claim

1. A transformed tomato comprising cDNA fragment encoding human rotavirus structural protein having the sequence represented by SEQ ID NO:3 encoding VP6 derived from human rotavirus.

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