Expression of exogenous polynucleotide sequences in a vertebrate

Abstract: A method for delivering an isolated polynucleotide to the interior of a cell in a vertebrate, comprising the interstitial introduction of an isolated polynucleotide into a tissue of the vertebrate where the polynucleotide is taken up by the cells of the tissue and exerts a therapeutic effect on the vertebrate. The method can be used to deliver a therapeutic polypeptide to the cells of the vertebrate, to provide an immune response upon in vivo translation of the polynucleotide, to deliver antisense polynucleotides, to deliver receptors to the cells of the vertebrate, or to provide transitory gene therapy.

Description: BACKGROUND OF THE INVENTION The present invention relates to introduction of DNA and RNA sequences into a mammal to achieve controlled expression of an immunogenic peptide. Current research in gene therapy has focused on "permanent" cures, in which DNA is integrated into the genome of the patient. Viral vectors are presently the most frequently used means for transforming the patient's cells and introducing DNA into the genome. In an indirect method, viral vectors, carrying new genetic information, are used to infect target cells removed from the body, and these cells are then re-implanted. Direct in vivo gene transfer into postnatal animals has been reported for formulations of DNA encapsulated in liposomes and DNA entrapped in proteoliposomes containing viral envelope receptor proteins (Nicolau et al., Proc. Natl. Acad Sci USA 80:1068-1072 (1983); Kaneda et al., Science 243:375-378 (1989); Mannino et al., Biotechniques 6:682-690 (1988). Positive results have also been described with calcium phosphate co-precipitated DNA (Benvenisty and Reshef Proc. Natl. Acad Sci USA 83:9551-9555 (1986)). The clinical application of gene therapy, as well as the utilization of recombinant retrovirus vectors, has been delayed because of safety considerations. Integration of exogenous DNA into the genome of a cell can cause DNA damage and possible genetic changes in the recipient cell that could predispose to malignancy. A method which avoids these potential problems would be of significant benefit in making gene therapy safe and effective. Vaccination with immunogenic proteins has eliminated or reduced the incidence of many diseases; however there are major difficulties in using proteins associated with other pathogens and disease states as immunogens. Many protein antigens are not intrinsically immunogenic. More often, they are not effective as vaccines because of the manner in which the immune system operates. The immune system of vertebrates consists of several interacting components. The best characterized and most important parts are the humoral and cellular (cytolytic) branches. Humoral immunity involves antibodies, proteins which are secreted into the body fluids and which directly recognize an antigen. The cellular system, in contrast, relies on special cells which recognize and kill other cells which are producing foreign antigens. This basic functional division reflects two different strategies of immune defense. Humoral immunity is mainly directed at antigens which are exogenous to the animal whereas the cellular system responds to antigens which are actively synthesized within the animal. Antibody molecules, the effectors of humoral immunity, are secreted by special B lymphoid cells, B cells, in response to antigen. Antibodies can bind to and inactivate antigen directly (neutralizing antibodies) or activate other cells of the immune system to destroy the antigen. Cellular immune recognition is mediated by a special class of lymphoid cells, the cytotoxic T cells. These cells do not recognize whole antigens but instead they respond to degraded peptide fragments thereof which appear on the surface of the target cell bound to proteins called class I major histocompatibility complex (MHC) molecules. Essentially all nucleated cells have class I molecules. It is believed that proteins produced within the cell are continually degraded to peptides as part of normal cellular metabolism. These fragments are bound to the MHC molecules and are transported to the cell surface. Thus the cellular immune system is constantly monitoring the spectra of proteins produced in all cells in the body and is poised to eliminate any cells producing foreign antigens. Vaccination is the process of preparing an animal to respond to an antigen. Vaccination is more complex than immune recognition and involves not only B cells and cytotoxic T cells but other types of lymphoid cells as well. During vaccination, cells which recognize the antigen (B cells or cytotoxic T cells) are clonally expanded. In addition, the population of ancillary cells (helper T cells) specific for the antigen also increase. Vaccination also involves specialized antigen presenting cells which can process the antigen and display it in a form which can stimulate one of the two pathways. Vaccination has changed little since the time of Louis Pasteur. A foreign antigen is introduced into an animal where it activates specific B cells by binding to surface immunoglobulins. It is also taken up by antigen processing cells, wherein it is degraded, and appears in fragments on the surface of these cells bound to Class II MHC molecules. Peptides bound to class II molecules are capable of stimulating the helper class of T cells. Both helper T cells and activated B cells are required to produce active humoral immunization. Cellular immunity is thought to be stimulated by a similar but poorly understood mechanism. Thus two different and distinct pathways of antigen processing produce exogenous antigens bound to class II MHC molecules where they can stimulate T helper cells, as well as endogenous proteins degraded and bound to class I MHC molecules and recognized by the cytotoxic class of T cells. There is little or no difference in the distribution of MHC molecules. Essentially all nucleated cells express class I molecules whereas class II MHC proteins are restricted to some few types of lymphoid cells. Normal vaccination schemes will always produce a humoral immune response. They may also provide cytotoxic immunity. The humoral system protects a vaccinated individual from subsequent challenge from a pathogen and can prevent the spread of an intracellular infection if the pathogen goes through an extracellular phase during its life cycle; however, it can do relatively little to eliminate intracellular pathogens. Cytotoxic immunity complements the humoral system by eliminating the infected cells. Thus effective vaccination should activate both types of immunity. A cytotoxic T cell response is necessary to remove intracellular pathogens such as viruses as well as malignant cells. It has proven difficult to present an exogenously administered antigen in adequate concentrations in conjunction with Class I molecules to assure an adequate response. This has severely hindered the development of vaccines against tumor-specific antigens (e.g., on breast or colon cancer cells), and against weakly immunogenic viral proteins (e.g., HIV, Herpes, non-A, non-B hepatitis, CMV and EBV). It would be desirable to provide a cellular immune response alone in immunizing against agents such as viruses for which antibodies have been shown to enhance infectivity. It would also be useful to provide such a response against both chronic and latent viral infections and against malignant cells. The use of synthetic peptide vaccines does not solve these problems because either the peptides do not readily associate with histocompatibility molecules, have a short serum half-life, are rapidly proteolyzed, or do not specifically localize to antigen-presenting monocytes and macrophages. At best, all exogenously administered antigens must compete with the universe of self-proteins for binding to antigen-presenting macrophages. Major efforts have been mounted to elicit immune responses to poorly immunogenic viral proteins from the herpes viruses, non-A, non-B hepatitis, HIV, and the like. These pathogens are difficult and hazardous to propagate in vitro. As mentioned above, synthetic peptide vaccines corresponding to viral-encoded proteins have been made, but have severe pitfalls. Attempts have also been made to use vaccinia virus vectors to express proteins from other viruses. However, the results have been disappointing, since (a) recombinant vaccinia viruses may be rapidly eliminated from the circulation in already immune individuals, and (b) the administration of complex viral antigens may induce a phenomenon known as "antigenic competition," in which weakly immunogenic portions of the virus fail to elicit an immune response because they are out-competed by other more potent regions of the administered antigen. Another major problem with protein or peptide vaccines is anaphylactic reaction which can occur when injections of antigen are repeated in efforts to produce a potent immune response. In this phenomenon, IgE antibodies formed in response to the antigen cause severe and sometimes fatal allergic reactions. Accordingly, there is a need for a method for invoking a safe and effective immune response to this type of protein or polypeptide. Moreover, there is a great need for a method that will associate these antigens with Class I histocompatibility antigens on the cell surface to elicit a cytotoxic T cell response, avoid anaphylaxis and proteolysis of the material in the serum, and facilitate localization of the material to monocytes and macrophages. A large number of disease states can benefit from the administration of therapeutic peptides. Such peptides include lymphokines, such as interleukin-2, tumor necrosis factor, and the interferons; growth factors, such as nerve growth factor, epidermal growth factor, and human growth hormone; tissue plasminogen activator; factor VIII:C; granulocyte-macrophage colony-stimulating factor; erythropoietin; insulin; calcitonin; thymidine kinase; and the like. Moreover, selective delivery of toxic peptides (such as ricin, diphtheria toxin, or cobra venom factor) to diseased or neoplastic cells can have major therapeutic benefits. Current peptide delivery systems suffer from significant problems, including the inability to effectively incorporate functional cell surface receptors onto cell membranes, and the necessity of systemically administering large quantities of the peptide (with resultant undesirable systemic side effects) in order to deliver a therapeutic amount of the peptide into or onto the target cell. These above-described problems associated with gene therapy, immunization, and delivery of therapeutic peptides to cells are addressed by the present invention. The present invention relates to immunizing a vertebrate. In one aspect, the present invention provides use of a positively charged liposome and an expressible polynucleotide coding for an immunogenic peptide in the manufacture of a medicament for administration to a mammal wherein said medicament is incorporated into a cell where an immunogenic translation product of the polynucleotide is formed, and the product is processed and presented by the cell in the context of the major histocompatibility complex, thereby eliciting an immune response against the immunogenic peptide. In another aspect, the present invention provides a composition comprising positively charged liposomes mixed with an expressible polynucleotide coding for an immunogenic peptide, for administration to a mammal wherein said composition is incorporated into a cell where an immunogenic translation product of the polynucleotide is formed, and the product is processed and presented by the cell in the context of the major histocompatibility complex, thereby eliciting an immune response against the immunogenic peptide. The polynucleotide may be a mRNA. The polynucleotide may be a DNA comprising a promoter. The medicament or composition may be for administration by injection into muscle. The medicament or composition may be for administration by injection into skin. The medicament or composition may be for administration by introduction into a body cavity. The mammal may be a human. The liposome may comprise N-(2,3-di-(9-(Z)octadecenyloxy))-prop-1-yl-N,N,N-trimethylammonium chloride (DOTMA) or 1,2-bis(oleoyloxy)-3-(trimethylammonio)propane (DOTAP). DETAILED DESCRIPTION OF THE INVENTION The practice of the present invention requires obtaining polynucleotide operatively coding for a polypeptide for incorporation into vertebrate cells. A polynucleotide operatively codes for a polypeptide when it has all the genetic information necessary for expression by a target cell, such as promoters and the like. These polynucleotides can be administered to the vertebrate by any method that delivers injectable materials to cells of the vertebrate, such as by injection into the interstitial space of tissues such as muscles or skin, introduction into the circulation or into body cavities or by inhalation or insufflation. A polynucleotide is injected or otherwise delivered to the animal with a pharmaceutically acceptable liquid carrier. For all applications, the liquid carrier is aqueous or partly aqueous, comprising sterile, pyrogen-free water. The pH of the preparation is suitably adjusted and buffered. The embodiments of the invention require use of liposomes and the polynucleotide is to be associated with a liposome, so the invention requires a material for forming positively charged liposomes, and requires that liposomal preparations be made from these materials. With the liposomal material in hand, the polynucleotide may advantageously be used to transfect cells in vitro for use as immunizing agents, or to administer polynucleotides into bodily sites where liposomes may be taken up by phagocytic cells. Polynucleotide Materials The DNA sequences used in these methods can be those sequences which do not integrate into the genome of the host cell. These may be non-replicating DNA sequences, or specific replicating sequences genetically engineered to lack the genome-integration ability. Therapeutic polynucleotides provided by the invention can also code for immunity-conferring polypeptides, which can act as endogenous immunogens to provoke a humoral or cellular response, or both. Polynucleotide sequences of the invention preferably code for immunogenic polypeptides, and these sequences may be used in association with other polynucleotide sequences coding for regulatory proteins that control the expression of these polypeptides. The regulatory protein can act by binding to genomic DNA so as to regulate its transcription; alternatively, it can act by binding to messenger RNA to increase or decrease its stability or translation efficiency. The polynucleotide material delivered to the cells in vivo can take any number of forms, and the present invention is not limited to any particular polynucleotide coding for any particular polypeptide or group of polypeptides. It may contain only a fragment of a gene, or may code for multiple polypeptide sequences, and may additionally contain recognition and promoter sequences. Plasmids containing genes coding for a large number of physiologically active peptides and antigens or immunogens have been reported in the literature and can be readily obtained by those of skill in the art. Where the polynucleotide is to be DNA, promoters suitable for use in various vertebrate systems are well known. For example, for use in murine systems, suitable strong promoters include RSV LTR, MPSV LTR, SV40 IEP, and metallothionein promoter. In humans, on the other hand, promoters such as CMV IEP may advantageously be used. All forms of DNA, whether replicating or non-replicating, which do not become integrated into the genome, and which are expressible, are within the methods contemplated by the invention. With the availability of automated nucleic acid synthesis equipment, both DNA and RNA can be synthesized directly when the nucleotide sequence is known or by a combination of PCR cloning and fermentation. Moreover, when the sequence of the desired polypeptide is known, a suitable coding sequence for the polynucleotide can be inferred. When the polynucleotide is mRNA, it can be readily prepared from the corresponding DNA in vitro. For example, conventional techniques utilize phage RNA polymerases SP6, T3, or T7 to prepare mRNA from DNA templates in the presence of the individual ribonucleoside triphosphates. An appropriate phage promoter, such as a T7 origin of replication site is placed in the template DNA immediately upstream of the gene to be transcribed. Systems utilizing T7 in this manner are well known, and are described in the literature, e.g., in Current Protocols in Molecular Biology , §3.8 (Vol.1 1988). One particularly preferred method for obtaining the mRNA used in the present invention is set forth in Examples 2-5. In general, however, it should be apparent that the pXGB plasmid or any similar plasmid that can be readily constructed by those of ordinary skill in the art can be used with a virtually unlimited number of cDNAs in practicing the present invention. Such plasmids may advantageously comprise a promoter for a desired RNA polymerase, followed by a 5' untranslated region, a 3' untranslated region, and a template for a poly A tract. There should be a unique restriction site between these 5' and 3' regions to facilitate the insertion of any desired cDNA into the plasmid. Then, after cloning the plasmid containing the desired gene, the plasmid is linearized by cutting in the polyadenylation region and is transcribed in vitro to form mRNA transcripts. These transcripts are preferably provided with a 5' cap, as demonstrated in Example 5. Alternatively, a 5' untranslated sequence such as EMC can be used which does not require a 5' cap. While the foregoing represents a preferred method for preparing the mRNA, it will be apparent to those of skill in the art that many alternative methods also exist. For example, the mRNA can be prepared in commercially-available nucleotide synthesis apparatus. Alternatively, mRNA in circular form can be prepared. Exonuclease-resistant RNAs such as circular mRNA, chemically blocked mRNA, and mRNA with a 5' cap are preferred, because of their greater half-life in vivo . In particular, one preferred mRNA is a self-circularizing mRNA having the gene of interest preceded by the 5' untranslated region of polio virus. It has been demonstrated that circular mRNA has an extremely long half-life (Harland & Misher, Development 102: 837-852 (1988)) and that the polio virus 5' untranslated region can promote translation of mRNA without the usual 5' cap (Pelletier & Sonnenberg, Nature 334 :320-325 (1988), hereby incorporated by reference). This material may be prepared from a DNA template that is self-splicing and generates circular "lariat" mRNAs, using the method of Been & Cech, Cell 47 :206-216 (1986) (hereby incorporated by reference). We modify that template by including the 5' untranslated region of the polio virus immediately upstream of the gene of interest, following the procedure of Maniatis, T. et al. MOLECULAR CLONING: A LABORATORY MANUAL , Cold Spring Harbor, New York (1982). In addition, the present invention includes the use of mRNA that is chemically blocked at the 5' and/or 3' end to prevent access by RNAse. (This enzyme is an exonuclease and therefore does not cleave RNA in the middle of the chain.) Such chemical blockage can substantially lengthen the half life of the RNA in vivo . Two agents which may be used to modify RNA are available from Clonetech Laboratories, Inc., Palo Alto, California: C2 AminoModifier (Catalog # 5204-1) and Amino-7-dUTP (Catalog # K1022-1). These materials add reactive groups to the RNA. After introduction of either of these agents onto an RNA molecule of interest, an appropriate reactive substituent can be linked to the RNA according to the manufacturer's instructions. By adding a group with sufficient bulk, access to the chemically modified RNA by RNAse can be prevented. Transient Gene Therapy Unlike gene therapies proposed in the past, one major advantage of the present invention is the transitory nature of the polynucleotide synthesis in the cells. (We refer to this as reversible gene therapy, or TGT.) With mRNA introduced according to the present invention, the effect will generally last about one day. Also, in marked contrast to gene therapies proposed in the past, mRNA does not have to penetrate the nucleus to direct protein synthesis; therefore, it should have no genetic liability. In some situations, however, a more prolonged effect may be desired without incorporation of the exogenous polynucleic acid into the genome of the host organism. In order to provide such an effect, a preferred embodiment of the invention provides introducing a DNA sequence coding for a specific polypeptide into the cell. We have found, according to the methods of the invention, that non-replicating DNA sequences can be introduced into cells to provide production of the desired polypeptide for periods of about up to six months, and we have observed no evidence of integration of the DNA sequences into the genome of the cells. Alternatively, an even more prolonged effect can be achieved by introducing the DNA sequence into the cell by means of a vector plasmid having the DNA sequence inserted therein. Preferably, the plasmid further comprises a replicator. Such plasmids are well known to those skilled in the art, for example, plasmid pBR322, with replicator pMB1, or plasmid pMK16, with replicator ColE1 (Ausubel, Current Protocols in Molecular Biology , John Wiley and Sons, New York (1988) §II:1.5.2. Results of studies of the time course of expression of DNA and mRNA introduced into muscle cells as described in Examples 1 and 13 indicate that mRNA expression is more rapid, although shorter in duration than DNA expression. An immediate and long lived gene expression can be achieved by administering to the cell a liposomal preparation comprising both DNA and an RNA polymerase, such as the phage polymerases T7, T3, and SP6. The liposome also includes an initial source of the appropriate RNA polymerase, by either including the actual enzyme itself, or alternatively, an mRNA coding for that enzyme. When the liposome is introduced into the organism, it delivers the DNA and the initial source of RNA polymerase to the cell. The RNA polymerase, recognizing the promoters on the introduced DNA, transcribes both genes, resulting in translation products comprising more RNA polymerase and the desired polypeptide. production of these materials continues until the introduced DNA (which is usually in the form of a plasmid) is degraded. In this manner, production of the desired polypeptide in vivo can be achieved in a few hours and be extended for one month or more. The polynucleotides may be delivered to the interstitial space of tissues of the animal body, including those of muscle, skin, brain, lung, liver, spleen, bone marrow, thymus, heart, lymph, blood, bone, cartilage, pancreas, kidney, gall bladder, stomach, intestine, testis, ovary, uterus, rectum, nervous system, eye, gland, and connective tissue. Interstitial space of the tissues comprises the intercellular, fluid, mucopolysaccharide matrix among the reticular fibers of organ tissues, elastic fibers in the walls of vessels or chambers, collagen fibers of fibrous tissues, or that same matrix within connective tissue ensheathing muscle cells or in the lacunae of bone. It is similarly the space occupied by the plasma of the circulation and the lymph fluid of the lymphatic channels. Delivery to the interstitial space of muscle tissue is preferred for the reasons discussed below. They may be conveniently delivered by injection into the tissues comprising these cells. They are preferably delivered to and expressed in persistent, non-dividing cells which are differentiated, although delivery and expression may be achieved in non-differentiated or less completely differentiated cells, such as, for example, stem cells of blood or skin fibroblasts. We have discovered that in vivo muscle cells are particularly competent in their ability to take up and express polynucleotides. This ability may be due to the singular tissue architecture of muscle, comprising multinucleated cells, sarcoplasmic reticulum, and transverse tubular system. Polynucleotides may enter the muscle through the transverse tubular system, which contains extracellular fluid and extends deep into the muscle cell. It is also possible that the polynucleotides enter damaged muscle cells which then recover. Muscle is also advantageously used as a site for the delivery and expression of polynucleotides in a number of therapeutic applications because animals have a proportionately large muscle mass which is conveniently accessed by direct injection through the skin; for this reason, a comparatively large dose of polynucleotides can be deposited in muscle by multiple injections, and repetitive injections, to extend therapy over long periods of time, are easily performed and can be carried out safely and without special skill or devices. Muscle tissue can be used as a site for injection and expression of polynucleotides. In immunization strategies, muscle cells may be injected with polynucleotides coding for immunogenic peptides, and these peptides will be presented by muscle cells in the context of antigens of the major histocompatibility complex to provoke a selected immune response against the immunogen. DNA and mRNA Vaccines According to the invention, both expressible DNA and mRNA can be delivered to cells to form therein a polypeptide translation product. If the nucleic acids contain the proper control sequences, they will direct the synthesis of relatively large amounts of the encoded protein. When the DNA and mRNA delivered to the cells codes for an immunizing peptide, the methods can be applied to achieve improved and more effective immunity against infectious agents, including intracellular viruses, and also against tumor cells. Since the immune systems of all vertebrates operate similarly, the applications described can be implemented in all vertebrate systems, comprising mammalian and avian species, as well as fish. The methods of the invention may be applied by direct injection of the polynucleotide into cells of the animal in vivo . The polynucleotides may be delivered to various cells of the animal body, including muscle, skin, brain, lung, liver, spleen, or to the cells of the blood. Delivery of the polynucleotides directly in vivo is preferably to the cells of muscle or skin. The polynucleotides may be injected into muscle or skin using an injection syringe. They may also be delivered into muscle or skin using a vaccine gun. It has recently been shown that cationic lipids can be used to facilitate the transfection of cells in certain applications, particularly in vitro transfection. Cationic lipid based transfection technology is preferred over other methods; it is more efficient and convenient than calcium phosphate, DEAE dextran or electroporation methods, and retrovirus mediated transfection, as discussed previously, can lead to integration events in the host cell genome that result in oncogene activation or other undesirable consequences. The knowledge that cationic lipid technology works with messenger RNA is a further advantage to this approach because RNA is turned over rapidly by intracellular nucleases and is not integrated into the host genome. A transfection system that results in high levels of reversible expression is preferred to alternative methodology requiring selection and expansion of stably transformed clones because many of the desired primary target cells do not rapidly divide in culture. The ability to transfect cells at high efficiency with cationic liposomes provides an alternative method for immunization. The gene for an antigen is introduced in to cells which have been removed from an animal. The transfected cells, now expressing the antigen, are reinjected into the animal where the immune system can respond to the (now) endogenous antigen. The process can possibly be enhanced by coinjection of either an adjuvant or lymphokines to further stimulate the lymphoid cells. Vaccination with nucleic acids containing a gene for an antigen may also provide a way to specifically target the cellular immune response. Cells expressing proteins which are secreted will enter the normal antigen processing pathways and produce both a humoral and cytotoxic response. The response to proteins which are not secreted is more selective. Non-secreted proteins synthesized in cells expressing only class I MHC molecules are expected to produce only a cytotoxic vaccination. Expression of the same antigen in cells bearing both class I and class II molecules may produce a more vigorous response by stimulating both cytotoxic and helper T cells. Enhancement of the immune response may also be possible by injecting the gene for the antigen along with a peptide fragment of the antigen. The antigen is presented via class I MHC molecules to the cellular immune system while the peptide is presented via class II MHC molecules to stimulate helper T cells. In any case, this method provides a way to stimulate and modulate the immune response in a way which has not previously been possible. A major disadvantage of subunit vaccines is that glycoprotein antigens are seldom modified correctly in the recombinant expression systems used to make the antigens. Introducing the gene for a glycoprotein antigen will insure that the protein product is synthesized, modified and processed in the same species and cells that the pathogen protein would be. Thus, the expression of a gene for a human viral glycoprotein will contain the correct complement of sugar residues. This is important because it has been demonstrated that a substantial component of the neutralizing antibodies in some viral systems are directed at carbohydrate epitopes. Any appropriate antigen which is a candidate for an immune response, whether humoral or cellular, can be used in its nucleic acid form. The source of the cells could be fibroblasts taken from an individual which provide a convenient source of cells expressing only class I MHC molecules. Alternatively, peripheral blood cells can be rapidly isolated from whole blood to provide a source of cells containing both class I and class II MHC proteins. They could be further fractionated into B cells, helper T cells, cytotoxic T cells or macrophage/monocyte cells if desired. Bone marrow cells can provide a source of less differentiated lymphoid cells. In all cases the cell will be transfected either with DNA containing a gene for the antigen or by the appropriate capped and polyadenylated mRNA transcribed from that gene or a circular RNA, chemically modified RNA, or an RNA which does not require 5' capping. The choice of the transfecting nucleotide may depend on the duration of expression desired. For vaccination purposes, a reversible expression of the immunogenic peptide, as occurs on mRNA transfection, is preferred. Transfected cells are injected into the animal and the expressed proteins will be processed and presented to the immune system by the normal cellular pathways. Such an approach has been used to produce cytotoxic immunity in model systems in mice. cell lines, malignant continuously growing cells, can be stably transformed with DNA. When cells are injected into animals, they induce cellular immunity to the expressed antigen. The cationic lipid delivery system will allow this approach to be extended to normal, non-malignant cells taken from a patient. There are several applications to this approach of targeting cellular immunity. The first is vaccination against viruses in which antibodies are known to be required or to enhanced viral infection. There are two strategies that can be applied here. One can specifically target the cellular pathway during immunization thus eliminating the enhancing antibodies. Alternatively one can vaccinate with the gene for a truncated antigen which eliminate the humoral epitomes which enhance infectivity. The use of DNA or mRNA vaccine therapy could similarly provide a means to provoke an effective cytotoxic T-cell response to weakly antigenic tumors. We propose, for example, that if a tumor-specific antigen were expressed by mRNA inside a cell in an already processed form, and incorporated directly into the Class I molecules on the cell surface, a cytotoxic T cell response would be elicited. A second application is that this approach provides a method to treat latent viral infections. Several viruses (for example, Hepatitis B, HIV and members of the Herpes virus group) can establish latent infections in which the virus is maintained intracellularly in an inactive or partially active form. There are few ways of treating such an infections. However, by inducing a cytolytic immunity against a latent viral protein, the latently infected cells will be targeted and eliminated. A related application of this approach is to the treatment of chronic pathogen infections. There are numerous examples of pathogens which replicate slowly and spread directly from cell to cell. These infections are chronic, in some cases lasting years or decades. Examples of these are the slow viruses (e.g. Visna), the Scrapie agent and HIV. One can eliminate the infected cells by inducing an cellular response to proteins of the pathogen. Finally, this approach may also be applicable to the treatment of malignant disease. Vaccination to mount a cellular immune response to a protein specific to the malignant state, be it an activated oncogene, a fetal antigen or an activation marker, will result in the elimination of these cells. The use of DNA/mRNA vaccines could in this way greatly enhance the immunogenicity of certain viral proteins, and cancer-specific antigens, that normally elicit a poor immune response. The mRNA vaccine technique should be applicable to the induction of cytotoxic T cell immunity against poorly immunogenic viral proteins from the Herpes viruses, non-A, non-B hepatitis, and HIV, and it would avoid the hazards and difficulties associated with in vitro propagation of these viruses. For cell surface antigens, such as viral coat proteins (e.g., HIV gp120), the antigen would be expressed on the surface of the target cell in the context of the major histocompatibility complex (MHC), which would be expected to result in a more appropriate, vigorous and realistic immune response. It is this factor that results in the more efficacious immune responses frequently observed with attenuated virus vaccines. Delivery of a single antigen gene by TGT would be much safer than attenuated viruses, which can result in a low frequency of disease due to inadequate attenuation. There is an additional advantage of TGT which can be exploited during the vaccine development phase. One of the difficulties with vaccine development is the requirement to screen different structural variants of the antigen, for the optimal immune response. If the variant is derived from a recombinant source, the protein usually must be expressed and purified before it can be tested for antigenicity. This is a laborious and time consuming process. With in vitro mutagenesis, it is possible to obtain and sequence numerous clones of a given antigen. If these antigen can be screened for antigenicity at the DNA or RNA level by TGT, the vaccine development program could be made to proceed much faster. Finally, in the case of the DNA/mRNA vaccines, the protein antigen is never exposed directly to serum antibody, but is always produced by the transfected cells themselves following translation of the mRNA. Hence, anaphylaxis should not be a problem. Thus, the present invention permits the patient to be immunized repeatedly without the fear of allergic reactions. The use of the DNA/mRNA vaccines of the present invention makes such immunization possible. One can easily conceive of ways in which this technology can be modified to enhance still further the immunogenicity of antigens. T cell immunization can be augmented by increasing the density of Class I and Class II histocompatibility antigens on the macrophage or other cell surface and/or by inducing the transfected cell to release cytokines that promote lymphocyte proliferation. To this end, one may incorporate in the same liposomes that contain mRNA for the antigen, other mRNA species that encode interferons or interleukin-1. These cytokines are known to enhance macrophage activation. Their systemic use has been hampered because of side effects. However, when encapsulated in mRNA, along with mRNA for antigen, they should be expressed only by those cells that co-express antigen. In this situation, the induction of T cell immunity can be enhanced greatly. Therapeutic Formulations Polynucleotide salts: Administration of pharmaceutically acceptable salts of the polynucleotides described herein is included within the scope of the invention. Such salts may be prepared from pharmaceutically acceptable non-toxic bases including organic bases and inorganic bases. Salts derived from inorganic bases include sodium, potassium, lithium, ammonium, calcium, magnesium, and the like. Salts derived from pharmaceutically acceptable organic non-toxic bases include salts of primary, secondary, and tertiary amines, basic amino acids, and the like. For a helpful discussion of pharmaceutical salts, see S. M. Berge et al., Journal of Pharmaceutical Sciences 66:1-19 (1977) the disclosure of which is hereby incorporated by reference. Polynucleotides for injection, a preferred route of delivery, may be prepared in unit dosage form in ampules, or in multidose containers. The polynucleotides may be present in such forms as suspensions, solutions, or emulsions in oily or preferably aqueous vehicles. Alternatively, the polynucleotide salt may be in lyophilized form for reconstitution, at the time of delivery, with a suitable vehicle, such as sterile pyrogen-free water. Both liquid as well as lyophilized forms that are to be reconstituted will comprise agents, preferably buffers, in amounts necessary to suitably adjust the pH of the injected solution. For any parenteral use, particularly if the formulation is to be administered intravenously, the total concentration of solutes should be controlled to make the preparation isotonic, hypotonic, or weakly hypertonic. Nonionic materials, such as sugars, are preferred for adjusting tonicity, and sucrose is particularly preferred. Any of these forms may further comprise suitable formulatory agents, such as starch or sugar, glycerol or saline. The compositions per unit dosage, whether liquid or solid, may contain from 0.1% to 99% of polynucleotide material. The units dosage ampules or multidose containers, in which the polynucleotides are packaged prior to use, may comprise an hermetically sealed container enclosing an amount of polynucleotide or solution containing a polynucleotide suitable for a pharmaceutically effective dose thereof, or multiples of an effective dose. The polynucleotide is packaged as a sterile formulation, and the hermetically sealed container is designed to preserve sterility of the formulation until use. The container in which the polynucleotide is packaged is labeled, and the label bears a notice in the form prescribed by a governmental agency, for example the Food and Drug Administration, which notice is reflective of approval by the agency under Federal law, of the manufacture, use, or sale of the polynucleotide material therein for human administration. Federal law requires that the use of pharmaceutical agents in the therapy of humans be approved by an agency of the Federal government. Responsibility for enforcement is the responsibility of the Food and Drug Administration, which issues appropriate regulations for securing such approval, detailed in 21 U.S.C. 301-392. Regulation for biologic material, comprising products made from the tissues of animals is provided under 42 U.S.C 262. Similar approval is required by most foreign countries. Regulations vary from country to country, but the indivdual procedures are well known to those in the art. Dosage and Route of Administration The dosage to be administered depends to a large extent on the condition and size of the subject being treated as well as the frequency of treatment and the route of administration. Regimens for continuing therapy, including dose and frequency may be guided by the initial response and clinical judgment. The parenteral route of injection into the interstitial space of tissues is preferred, although other parenteral routes, such as inhalation of an aerosol formulation, may be required in specific administration, as for example to the mucous membranes of the nose, throat, bronchial tisues or lungs. Regulation of TGT Just as DNA based gene transfer protocols require appropriate signals for transcribing (promoters, enhancers) and processing (splicing signals, polyadenylation signals) the mRNA transcript, mRNA based TGT requires the appropriate structural and sequence elements for efficient and correct translation, together with those elements which will enhance the stability of the transfected mRNA. In general, translational efficiency has been found to be regulated by specific sequence elements in the 5' non-coding or untranslated region (5'UTR) of the RNA. Positive sequence motifs include the translational initiation consensus sequence (GCC) A CC ATG G (Kozak, Nucleic Acids Res.15: 8125 (1987)) and the 5 G 7 methyl GpppG cap structure (Drummond et al., Nucleic Acids Res. 13 :7375 (1985)). Negative elements include stable intramolecular 5' UTR stem-loop structures (Muesing et al., cell 48 :691(1987)) and AUG sequences or short open reading frames preceded by an appropriate AUG in the 5' UTR (Kozak, Supra, Rao et al., Mol. and Cell. Biol. 8: 284(1988)). In addition, certain sequence motifs such as the beta globin 5' UTR may act to enhance translation (when placed adjacent to a heterologous 5' UTR) by an unknown mechanism. There are also examples of specific 5' UTR sequences which regulate eukaryotic translational efficiency in response to environmental signals. These include the human ferritin 5' UTR (Hentze et al., Proc. Natl. Acad. Sci. USA 84: 6730 (1987)) and the drosophila hsp 7 05' UTR (Klemenz et al., EMBO Journal 4 :2053 (1985)). Finally, there are viral 5' UTR sequences which are able to bypass normal cap dependant translation and translational controls and mediate ann efficient translation of viral or chimeric mRNAs (Dolph et al., J. of Virol. 62 :2059 (1988)), Pelletier and Sonnenberg, Nature 334 , 320 (1988)). MRNA based TGT protocols must therefore include appropriate 5' UTR translational elements flanking the coding sequence for the protein of interest. In addition to translational concerns, mRNA stability must be considered during the development of mRNA based TGT protocols. As a general statement, capping and 3' polyadenylation are the major positive determinants of eukaryotic mRNA stability (Drummond, supra ; Ross, Mol. Biol. Med. 5 :1(1988)) and function to protect the 5' and 3' ends of the mRNA from degradation. However, regulatory elements which affect the stability of eukaryotic mRNAs have also been defined, and therefore must be considered in the development of mRNA TGT protocols. The most notable and clearly defined of these are the uridine rich 3' untranslated region (3' UTR) destabilizer sequences found in many short half-life mRNAs (Shaw and Kamen Cell 46 :659 (1986)), although there is evidence that these are not the only sequence motifs which result in mRNA destabilization (Kabnick and Housman, Mol. and Cell. Biol. 8 :3244 (1988)). In addition, specific regulatory sequences which modulate cellular mRNA half life in response to environmental stimuli have also been demonstrated. These include the estrogen mediated modulation of Vitellogenin mRNA stability (Brock and Shapiro, Cell 34 :207 (1983)), the iron dependant regulation of transferrin receptor mRNA stability (Mullner and Kuhn, Cell 53 :815 (1988)) which is due to a specific 3' UTR motif, the prolactin mediated control of Casein mRNA stability (Guyette et al., Cell 17 :1013 (1989)), the regulation of Fibronectin mRNA stability in response to a number of stimuli (Dean et al., J. Cell. Biol. 106 :2159 (1988)), and the control of Histone mRNA stability (Graves et al., Cell 48: 615 (1987)). Finally, just as viral RNA sequences have evolved which bypass normal eukaryotic mRNA translational controls, likewise some viral RNA sequences seem to be able to confer stability in the absence of 3' polyadenylation (McGrae and Woodland, Eur. J. of Biochem. 116 : 467 (1981)). Some 5', such as EMC, according to Example 21, are known to function without a cap. This cacophony of stability modulating elements must also be carefully considered in developing mRNA based TGT protocols, and can be used to modulate the effect of an mRNA treatment. Liposome-forming materials The science of forming liposomes is now well developed. Liposomes are unilamellar or multilamellar vesicles, having a membrane portion formed of lipophilic material and an interior aqueous portion. The aqueous portion is used in the present invention to contain the polynucleotide material to be delivered to the target cell. It is preferred that the liposome forming materials used herein have a cationic group, such as a quaternary ammonium group, and one or more lipophilic groups, such as saturated or unsaturated alkyl groups having from about 6 to about 30 carbon atoms. One group of suitable materials is described in European Patent Publication No. 0187702. These materials have the formula: wherein R 1 and R 2 are the same or different and are alkyl or alkenyl of 6 to 22 carbon atoms, R 3 , R 4 , and R 5 are the same or different and are hydrogen, alkyl of 1 to 8 carbons, aryl, aralkyl of 7 to 11 carbons, or when two or three of R 3 , R 4 , and R 5 are taken together they form quinuclidino, piperidino, pyrrolidino, or morpholino; n is 1 to 8, and X is a pharmaceutically acceptable anion, such as a halogen. These compounds may be prepared as detailed in the above-identified patent application; alternatively, at least one of these compounds, N-(2,3-di-(9-(Z)-octadecenyloxy))-prop-1-yl-N,N,N-trimethylammonium chloride (DOTMA), is commercially available from Bethesda Research Laboratories (BRL), Gaithersburg, Maryland 20877, USA. These quaternary ammonium diether compounds, however, do have some drawbacks. Because of the ether linkages, they are not readily metabolized in vivo. When long-term therapy is contemplated, there is some possibility that these materials could accumulate in tissue, ultimately resulting in lipid storage disease and toxic side effects. Accordingly, a preferred class of compositions for use in the present invention has the formula: wherein R 1 and R 2 are the same or different and are alkyl or alkenyl of 5 to 21 carbon atoms, R 3 , R 4 , and R 5 are the same or different and are hydrogen, alkyl of 1 to 8 carbons, aryl, aralkyl of 7 to 11 carbons, or when two or three of R 3 , R 4 , and R 5 are taken together they form quinuclidino, piperidino, pyrrolidino, or morpholino; n is 1 to 8, and X is a pharmaceutically acceptable anion, such as a halogen. These compounds may be prepared using conventional techniques, such as nucleophilic substitution involving a carboxylic acid and an alkyl halide, by transesterification, or by condensation of an alcohol with an acid or an acid halide. Moreover, many suitable liposome-forming cationic lipid compounds are described in the literature. See, e.g., L. Stamatatos, et al., Biochemistry 27 :3917-3925 (1988); H. Eibl, et al., Biophysical Chemistry 10 :261-271 (1979). Liposome Preparation Suitable liposomes for use in the present invention are commercially available. DOTMA liposomes, for example, are available under the trademark Lipofectin from Bethesda Research Labs, Gaithersburg, Maryland. Alternatively, liposomes can be prepared from readily-available or freshly synthesized starting materials of the type previously described. The preparation of DOTAP liposomes is detailed in Example 6. Preparation of DOTMA liposomes is explained in the literature, see, e.g., P. Felgner, et al., Proc. Nat'l Acad. Sci. USA 84 :7413-7417. Similar methods can be used to prepare liposomes from other cationic lipid materials. Moreover, conventional liposome forming materials can be used to prepare liposomes having negative charge or neutral charge. Such materials include phosphatidyl choline, cholesterol, phosphatidyl-ethanolamine, and the like. These materials can also advantageously be mixed with the DOTAP or DOTMA starting materials in ratios from 0% to about 75%. Conventional methods can be used to prepare other, noncationic liposomes. These liposomes do not fuse with cell walls as readily as cationic liposomes. However, they are taken up by macrophages in vivo, and are thus particularly effective for delivery of polynucleotide to these cells. For example, commercially dioleoyl-phosphatidyl choline (DOPC), dioleoylphosphatidyl glycerol (DOPG), and dioleoylphosphatidyl ethanolamine (DOPE) can be used in various combinations to make conventional liposomes, with or without the addition of cholesterol. Thus, for example, DOPG/DOPC vesicles can be prepared by drying 50 mg each of DOPG and DOPC under a stream of nitrogen gas into a sonication vial. The sample is placed under a vacuum pump overnight and is hydrated the following day with deionized water. The sample is then sonicated for 2 hours in a capped vial, using a Heat Systems model 350 sonicator equipped with an inverted cup (bath type) probe at the maximum setting while the bath is circulated at 15°C. Alternatively, negatively charged vesicles can be prepared without sonication to produce multilamellar vesicles or by extrusion through nucleopore membranes to produce unilamellar vesicles of discrete size. Other methods are known and available to those of skill in the art. The present invention is described below in detail using the 23 examples given below; however, the methods described are broadly applicable as described herein and are not intended to be limited by the Examples. EXAMPLE 1: PREPARATION OF LIPOSOME-FORMING DOTAP The cationic liposome-forming material 1,2-bis (oleoyloxy) -3-(trimethylammonio)propane (DOTAP) is prepared as reported by L. Stamatatos, et al. (supra) or H. Eibl, et al. (supra). Briefly, Stamatatos, et al. report that 1 mmol of 3-bromo-1,2-propanediol (Aldrich) was acylated for 48 hours at 20°C with 3 mmol of oleyl chloride (freshly prepared from oleic acid and oxaloyl chloride) in dry, alcohol-free diethyl ether (20 ml) containing 5 mmol of dry pyridine. The precipitate of pyridinium hydrochloride was filtered off, and the filtrate was concentrated under nitrogen and redissolved in 10 ml of hexane. The hexane solution was washed 3 times with an equal volume of 1:1 methanol/0.1 N aqueous NCOONa, pH 3.0, 3 times with 1:1 methanol/0.1 N aqueous NaOH, an d1 time with 1% aqueous NaCl. The crude 3-bromo-1,2-bis-(oleolyloxy)propane was then stirred for 72 hours in a sealed tube with a solution of 15% trimethylamine in dry dimethyl sulfoxide (30 ml) at 25°C. The products of this reaction were dissolved in chloroform (200 ml), which was repeatedly washed with 1:1 methanol/100 mM aqueous HCOONa, pH 3.0, and then evaporated in vacuo to yield a light yellow oil. This material was purified on a column of silicic acid (Bio-Sil A, Bio-Rad Laboratories), eluting with a 0-15% gradient of methanol in chloroform to give the desired product in pure form at 9-10% methanol. The purified product was a colorless, viscous oil that migrates with an R f of 0.4 on thin layer chromatography plates (silica gel G) that were developed with 50:15:5:5:2 CHCl 3 /acetone/CH 3 OH/CH 3 COOH/H 2 O. EXAMPLE 2: PREPARATION OF PLASMIDS FOR MAKING DNA TEMPLATES FOR ANY GENE OF INTEREST Suitable template DNA for production of mRNA coding for a desired polypeptide may be prepared in accordance with standard recombinant DNA methodology. As has been previously reported (P. Kreig, et al., Nucleic Acids Res. 12: 7057-7070 (1984)), a 5' cap facilitates translation of the mRNA. Moreover, the 3' flanking regions and the poly A tail are believed to increase the half life of the mRNA in vivo . The readily-available SP6 cloning vector pSP64T provides 5' and 3' flanking regions from β-globin, an efficiently translated mRNA. The construction of this plasmid is detailed by Kreig, et al. (supra), and is hereby incorporated by this reference. Any cDNA containing an initiation codon can be introduced into this plasmid, and mRNA can be prepared from the resulting template DNA. This particular plasmid can be cut with BglII to insert any desired cDNA coding for a polypeptide of interest. Although good results can be obtained with pSP64T when linearized and then transcribed in vivo with SP6 RNA polymerase, we prefer to use the xenopus β-globin flanking sequences of pSP64T with phage T7 RNA polymerase. These flanking sequences are purified from pSP64T as the small (approx. 150 bp) HindIII to EcoRI fragment. These sequences are then inserted into a purified linear HindIII/EcoRI fragment (approx. 2.9k bp) from pIBI 31 (commercially available from International Biotechnologies, Inc., Newhaven, Connecticut 06535) with T4 DNA ligase. Resulting plasmids, designated pXBG, are screened for orientation and transformed into E. coli . These plasmids are adapted to receive any gene of interest at a unique BglII restriction site, which is situated between the two xenopus β-globin sequences. EXAMPLE 3: PREPARATION OF PLASMID CODING FOR CHLORAMPHENICOL ACETYLTRANSFERASE A convenient marker gene for demonstrating in vivo expression of exogenous polynucleotides is chloramphenicol acetyltransferase, CAT. A plasmid pSP-CAT containing the CAT gene flanked by the xenopus β-globin 5' and 3' sequences was produced by adding the CAT gene into the BgIII site of pSP64T. We used CAT gene in the form of the small BamHI/HindIII fragment from pSV2-CAT (available from the American Type Culture Collection, Rockville, Maryland, Accession No. 37155). However, the CAT gene is commonly used in molecular biology and is available from numerous sources. Both the CAT BamHI/HindIII fragment and the BgIII-cleaved pSP64T were incubated with the Klenow fragment to generate blunt ends, and were then ligated with T4 DNA ligase to form pSP-CAT. The small PstI/HindIII fragment was then generated and purified, which comprises the CAT gene between the 5' and 3' β-globin flanking sequences of pSP64T. pIBI31 (International Biotechnologies, Inc.) was cleaved with PstI and HindIII, and the long linear sequence was purified. This fragment was then combined with the CAT-gene containing sequence and the fragments were ligated with T4 DNA ligase to form a plasmid designated pT7CAT An. Clones are selected on the basis of β-galactosidase activity with Xgal and ampicillin resistance. EXAMPLE 4: PREPARATION OF PURIFIED DNA TEMPLATE The plasmid DNA from Example 3 is grown up and prepared as per Maniatis (supra), except without RNAse, using 2 CsCl spins to remove bacterial RNA. Specifically, E. coli containing pT7CAT An from Example 3 was grown up in ampicillin-containing LB medium. The cells were then pelleted by spinning at 5000 rpm for 10 min. in a Sorvall RC-5 centrifuge (E.I. DuPont, Burbank, California 91510), resuspended in cold TE, pH 8.0, centrifuged again for 10 min. at 5000 rpm., resuspended in a solution of 50 mM glucose, 25 mM Tris-Cl pH 8.0, 10 mM EDTA, and 40 mg/ml lysozyme. After incubation for 5 to 10 minutes with occasional inversion, 0.2 N NaOH containing 1% SDS was added, followed after 10 minutes at 0° C with 3 M potassium acetate and 2 M acetic acid. After 10 more minutes, the material was again centrifuged at 6000 rpm, and the supernatant was removed with a pipet. The pellet was then mixed into 0.6 vol. isopropanol (-20° C), mixed, and stored at -20° C for 15 minutes. The material was then centrifuged again at 10,000 rpm for 20 min., this time in an HB4 swinging bucket rotor apparatus (DuPont, supra) after which the supernatant was removed and the pellet was washed in 70% EtOH and dried at room temperature. Next, the pellet was resuspended in 3.5 ml TE, followed by addition of 3.4 g CsCl and 350 µl of 5 mg/ml EtBr. The resulting material was placed in a quick seal tube, filled to the top with mineral oil. The tube was spun for 3.5 hours at 80,000 rpm in a VTi80 centrifuge (Beckman Instruments, Pasadena, California, 91051). The band was removed, and the material was centrifuged again, making up the volume with 0.95 g CsCl/ml and 0.1 ml or 5 mg/ml EtBr/ml in TE. The EtBr was then extracted with an equal volume of TE saturated N-Butanol after adding 3 volumes of TE to the band, discarding the upper phase until the upper phase is clear. Next, 2.5 vol. EtOH was added, and the material was precipitated at -20 C for 2 hours. The resultant DNA precipitate is used as a DNA template for preparation of mRNA in vitro. EXAMPLE 5: PREPARATION OF mRNA FOR TRANSFECTION The DNA from Example 4 was linearized downstream of the poly A tail with a 5-fold excess of PstI. The linearized DNA was then purified with two phenol/chloroform extractions, followed by two chloroform extractions. DNA was then precipitated with NaOAc (0.3 M) and 2 volumes of EtOH. The pellet was resuspended at about 1 mg/ml in DEP-treated deionized water. Next, a transcription buffer was prepared, comprising 400 mM Tris HCl (pH 8.0), 80 mM MgCl 2 , 50 mM DTT, and 40 mM spermidine. Then, the following materials were added in order to one volume of DEP-treated water at room temperature: 1 volume T7 transcription buffer, prepared above; rATP, rCTP, and rUTP to 1 mM concentration; rGTP to 0.5 mM concentration; 7meG(5')ppp(5')G cap analog (New England Biolabs, Beverly, Massachusetts, 01951) to 0.5 mM concentration; the linearized DNA template prepared above to 0.5 mg/ml concentration; RNAsin (Promega, Madison, Wisconsin) to 2000 U/ml concentration; and T7 RNA polymerase (N.E. Biolabs) to 4000 U/ml concentration. This mixture was incubated for I hour at 37 C. The successful transcription reaction was indicated by increasing cloudiness of the reaction mixture. Following generation of the mRNA, 2 U RQ1 DNAse (Promega) per microgram of DNA template used was added and was permitted to digest the template for 15 minutes. Then, the RNA was extracted twice with chloroform/phenol and twice with chloroform. The supernatant was precipitated with 0.3 M NaOAc in 2 volumes of EtOH, and the pellet was resuspended in 100 µl DEP-treated deionized water per 500 µl transcription product. This solution was passed over an RNAse-free Sephadex G50 column (Boehringer Mannheim #100 411). The resultant mRNA was sufficiently pure to be used in transfection of vertebrates in vivo. EXAMPLE 6: PREPARATION OF LIPOSOMES A number of liposome preparation methods can be used to advantage in the practice of the present invention. One particularly preferred liposome is made from DOTAP as follows: A solution of 10 mg dioleoyl phosphatidylethanolamine (PE) and 10 mg DOTAP (from Example 1) in 1 ml chloroform is evaporated to dryness under a stream of nitrogen, and residual solvent is removed under vacuum overnight. Liposomes are prepared by resuspending the lipids in deionized water (2 ml) and sonicating to clarity in a closed vial. These preparations are stable for at least 6 months. Polynucleotide complexes were prepared by mixing 0.5 ml polynucleotide solution (e.g., from Example 5) at 0.4 mg/ml by slow addition through a syringe with constant gentle vortexing to a 0.5 ml solution of sonicated DOTMA/PE or DOTAP/PE liposomes at 20 mg/ml, at room temperature. This procedure results in positively charged complexes which will spontaneously deliver the polynucleotide into cells in vivo . Different ratios of positively charged liposome to polynucleotide can be used to suit the particular need in any particular situation. Alternatively, as reported by Felgner, et al. (supra), it may be advantageous to dilute the polynucleotide (DNA or RNA) with Hepes buffered saline (150 mM NaCl; 20 mM Hepes, pH 7.4) prior to combining the materials to spontaneously form liposome/polynucleotide complexes. In many instances, however, the use of solutions having low ionic strength (such as sucrose) instead of saline solution is believed to be preferable; in particular, it is believed that such solutions facilitate delivery of polynucleotide to the cell by minimizing precipitation of polynucleotide/lipid complex. EXAMPLE 7: IN VIVO EXPRESSION OF LIPOSOMALLY AND NON-LIPOSOMALLY INTRODUCED mRNA IN THE RAT The ability of mRNA coding for chloramphenicol acetyl transferase (CAT) to transfect cells in vivo and the subsequent expression of the CAT protein was demonstrated by directly injecting 0.200 µl of each of the formulations below, prepared as indicated, into the abdominal muscle of rats, forming a bleb. Six replicates of each formulation were tested. After 12 to 14 h, the segment of the abdominal muscle into which the injection was made, weighing approximately 0.1 to 0.2 grams, was excised, minced, and placed in a 1.5 ml disposable mortar (Kontes, Morton Grove, Illinois) together with 200 ml of the an aqueous formulation having the following components: 20 mM Tris, pH 7.6; 2 mM MgCl 2 ; and 0.1% Triton X-100 surfactant. The contents of the mortar were then ground for 1 minute with a disposable pestle. The mortar was then covered (with Parafilm) and placed in a 1 liter Parr cell disrupter bomb (Parr Instrument Company, Moline, Illinois) and pressurized to 6 atmospheres with nitrogen at 4°C. After 30 minutes, the pressure was quickly released to disrupt the tissue and produce a crude lysate. The lysate was then centrifuged in a microcentrifuge at 13,000 rpm, 4°C, for 10 minutes. The supernatant was then decanted and stored at -20°C until analyzed. The lysates were then assayed for the presence of the CAT protein by thin-layer chromatography. First, 75 µl of each sample (the supernatant prepared above) was incubated for two hours at 37°C with 5 µl C 14 chloramphenicol (Amersham); 20 µl 4 mM Acetyl CoA; and 50 µl 1 M Tris, pH 7.8. Thereafter, 20 µl of 4 mM Acetyl CoA was added, and the mixture was again incubated for 2 hours at 37°C. The resulting solution was extracted- with 1 ml EtOAc, and the organic phase was removed and lyophilized in a vacuum centrifuge (SpeedVac, Savant Co.). The pellet was resuspended in 20 µl EtOAc, and was spotted onto a silica gel thin layer chromatography plate. The plate was developed for 45 minutes in 95% chloroform/5% methanol, was dried, and was sprayed with a radioluminescent indicator (Enhance Spray for Surface Radiography, New England Nuclear Corp.). The plate was then sandwiched with Kodak XAR5 film with overnight exposure at -70°C, and the film was developed per manufacturer's instructions. The following results were obtained: FORMULATION mRNA Expression (No. positive/total) 1. 1 ml Optimem;37.5 µg DOTMA 0/6 2. 1 ml Optimem; 15 µg CAT.RNA 3/6 3. Formulation 1 plus 15 µg CAT RNA 4/6 4. 10% Sucrose; 37.5 µg DOTMA; 15 µg CAT RNA 3/6 5. 10% Sucrose; 187 µg DOTMA; 75 µg CAT RNA 0/6 Optimem: Serum-free media (Gibco Laboratories, Life Technologies, Inc, Grand Island, N.Y. 14072) DOTMA: (Lipofectin brand; Bethesda Research Labs, Gaithersburg, MD) CAT RNA: From Example 5 All formulations made up in DEPC-treated RNAse-free water (International Biotechnologies, Inc., New Haven, CT 06535). EXAMPLE 8: mRNA VACCINATION OF MICE TO PRODUCE THE gp120PROTEIN OF HIV VIRUS A liposomal formulation containing mRNA coding for the gp120 protein of the HIV virus is prepared according to Examples 1 through 5, except that the gene for gp120 (pIIIenv3-1 from the Aids Research and Reagent Program, National Institute of Allergy and Infectious Disease, Rockville, MD 20852) is inserted into the plasmid pXBG in the procedure of Example 4. A volume of 200 µl of a formulation, prepared according to Example 6, and containing 200 µg/ml of gp120 mRNA and 500 µg/ml 1:1 DOTAP/PE in 10% sucrose is injected into the tail vein of mice 3 times in one day. At about 12 to 14 h after the last injection, a segment of muscle is removed from the injection site, and prepared as a cell lysate according to Example 7. The HIV specific protein gp120 is identified in the lysate also according to the procedures of Example 7. The ability of gp120 antibody present in serum of the mRNA vaccinated mice to protect against HIV infection is determined by a HT4-6C plaque reduction assay, as follows: HT4-6C cells (CD4+ HeLa cells) are obtained from Dr. Bruce Chesebro, (Rocky Mountain National Lab, Montana) and grown in culture in RPMI media (BRL, Gaithersburg, MD). The group of cells is then divided into batches. Some of the batches are infected with HIV by adding approximately 10 5 to 10 6 infectious units of HIV to approximately 10 7 HT4-6C cells. Other batches are tested for the protective effect of gp120 immune serum against HIV infection by adding both the HIV and approximately 50 µl of serum from a mouse vaccinated with gp120 mRNA. After 3 days of incubation, the cells of all batches are washed, fixed and stained with crystal violet, and the number of plaques counted. The protective effect of gp120 immune serum is determined as the reduction in the number of plaques in the batches of cells treated with both gp120 mRNA-vaccinated mouse serum and HIV compared to the number in batches treated with HIV alone. EXAMPLE 9: mRNA VACCINATION OF HUMAN STEM CELL-BEARING SCID MICE WITH NEF mRNA FOLLOWED BY HIV CHALLENGE Severe combined immunodeficient mice (SCID mice (Molecular Biology Institute, (MBI), La Jolla, CA 92037)) were reconstituted with adult human peripheral blood lymphocytes by injection into the peritoneal cavity according to the method of Mosier (Mosier et al., Nature 335 :256 (1988)). Intraperitoneal injection of 400 to 4000 infectious units of HIV-1 was then performed. The mice were maintained in a P3 level animal containment facility in sealed glove boxes. MRNA coding for the nef protein if HIV was prepared by obtaining the nef gene in the form of a plasmid (pGM92, from the NIAID, Rockville, MD 20852); removing the nef gene from the plasmid; inserting the nef gene in the pXBG plasmid for transcription; and purifying the transcription product nef mRNA as described in Examples 2 through 5. The nef mRNA was then incorporated into a formulation according to Example 6. 200 microliter tail vein injections of a 10% sucrose solution containing 200 ug/ml NEF RNA and 500 ug/ml 1:1 DOTAP:DOPE (in RNA/liposome complex form) were performed daily on experimental animals, while control animals were likewise injected with RNA/liposome complexes containing 200 ug/ml yeast tRNA and 500 ug/ml 1:1 DOTAP/DOPE liposomes. At 2, 4 and 8 weeks post injection, biopsy specimens were obtained from injected lymphoid organs and prepared for immunohistochemistry. At the same time points, blood samples were obtained and assayed for p24 levels by means of an ELISA kit (Abbott Labs, Chicago, IL) and virus titer by the plaque assay of Example 8. Immunostaining for HIV-1 was performed as described (Namikawa et al., science 242:1684 (1988)) using polyclonal serum from a HIV infected patient. Positive cells were counted and the number of infected cells per high power field (400x) were determined. Using these assays, at least a 2 fold reduction in the number of positive staining cells was observed at 8 weeks, and titer and p24 expression was reduced by at least 50%. Together, these results indicate a moderate anti-viral effect of the ( in vivo ) treatment. A volume of 200 µl of the formulation, containing 200 µg/ml of nef mRNA, and 500 µg/ml 1:1 DOTAP:DOPE in 10% sucrose is injected into the tail vein of the human stem cell-containing SCID mice 3 times in one day. Following immunization, the mice are challenged by infection with an effective dose of HIV virus. Samples of blood are periodically withdrawn from the tail vein and monitored for production of the characteristic HIV protein p24 by an ELISA kit assay (Abbott Labs, Chicago, IL). EXAMPLE 10: A METHOD OF PROVIDING ADENOSINE DEAMINASE TO MICE BY IN VIVO mRNA TRANSPECTION The full-length sequence for the cDNA of the human adenosine deaminase (ADA) gene is obtained from the 1,300 bp EcoR1-AccI fragment of clone ADA 211 (Adrian, G. et al. Mol. Cell Biol. 4 :1712 (1984). It is blunt-ended, ligated to BgIII linkers and then digested with BgIII. The modified fragment is inserted into the BgIII site of pXBG. ADA mRNA is transcribed and purified according to Examples 2 through 5, and purified ADA mRNA is incorporated into a formulation according to Example 6. Balb 3T3 mice are injected directly in the tail vein with 200 µl of this formulation, containing 200 µg/ml of ADA mRNA, and 500 µg/ml DOTAP in 10% sucrose. The presence of human ADA in the tissues of the liver, skin, and muscle of the mice is confirmed by an isoelectric focusing (IEF) procedure. Tissue extracts were electrofocused between pH 4 and 5 on a non-denaturing gel. The gel was then stained for in situ ADA activity as reported by Valerio, D. et al. Gene 31:137-143 (1984). A preliminary separation of human and non-human ADA is carried out by fast protein liquid chromatography (FPLC). The proteins are fractionated on a Pharmacia (Piscataway, NJ) MonoQ column (HR5/5) with a linear gradient from 0.05 to 0.5 M KCl, 20 mM Tris (pH 7.5). Activity for ADA within the fractions is measured by reacting the fractions with 14 C-adenosine (Amersham, Chicago, IL) which is converted to inosine. Thin layer chromatography (0.1 M NaPi pH 6.8 saturated ammonium sulfate:n-propylalcohol/100:60:2) is used to separate the radioactive inosine from the substrate adenosine.

Claims: Use of a positively charged liposome and an expressible polynucleotide coding for an immunogenic peptide in the manufacture of a medicament for administration to a mammal wherein said medicament is incorporated into a cell where an immunogenic translation product of the polynucleotide is formed, and the product is processed and presented by the cell in the context of the major histocompatibility complex, thereby eliciting an immune response against the immunogenic peptide. Use according to claim 1 wherein said polynucleotide is a mRNA. Use according to claim 1 wherein said polynucleotide is a DNA comprising a promoter. Use according to any one of claims 1 to 3 wherein the medicament is for administration by injection into muscle. Use according to any one of claims 1 to 3 wherein the medicament is for administration by injection into skin. Use according to any one of claims 1 to 3 wherein said medicament is for administration by introduction into a body cavity. Use according to any one of claims 1 to 6 wherein said mammal is a human. Use according to any one of claims 1 to 7 wherein said liposome comprises N-(2,3-di-(9-(Z)octadecenyloxy))-prop-1-yl-N,N,N-trimethylammonium chloride (DOTMA) or 1,2-bis(oleoyloxy)-3-(trimethylammonio)propane (DOTAP). A composition comprising positively charged liposomes mixed with an expressible polynucleotide coding for an immunogenic peptide, for administration to a mammal wherein said composition is incorporated into a cell where an immunogenic translation product of the polynucleotide is formed, and the product is processed and presented by the cell in the context of the major histocompatibility complex, thereby eliciting an immune response against the immunogenic peptide. A composition according to claim 9 wherein said polynucleotide is a mRNA. A composition according to claim 9 wherein said polynucleotide is a DNA comprising a promoter. A composition according to any one of claims 9 to 11, for administration by injection into muscle. A composition according to any one of claims 9 to 11, for administration by injection into skin. A composition according to any one of claims 9 to 11 for administration by introduction into a body cavity. A composition according to any one of claims 9 to 14 wherein said mammal is a human. A composition according to any one of claims 9 to 15 wherein said liposome comprises N-(2,3-di-(9-(Z)-octadecenyloxy))-prop-1-yl-N,N,N-trimethylammonium chloride (DOTMA) or 1,2-bis(oleoyloxy)-3-(trimethylammonio)propane (DOTAP).

Inventors: CARSON DENNIS A, FELGNER PHILIP L, MALONE ROBERT WALLACE, RHODES GARY H, WOLFF JON ASHER, CARSON, DENNIS A., FELGNER, PHILIP L., MALONE, ROBERT WALLACE, RHODES, GARY H., WOLFF, JON ASHER
Applicants: VICAL INC, WISCONSIN ALUMNI RES FOUND, VICAL, INC., WISCONSIN ALUMNI RESEARCH FOUNDATION
Application year: 1990
Main classification: C12N15
IPC codes: A61P31, A61K38, C12N15, A61P35, A61K48, A61K39, C07H21, C07K14, A61K47, A61K35, A61K31, A61P37, C12N9, A61P43, A61K9