POLYMERIC IMMUNOGLOBULIN RECEPTOR (PIGR)-BINDING DOMAINS AND METHODS OF USE THEREFOR

Abstract: The present invention identifies a domain located in the C alpha 3 domain of IgA that is reponsible for targeting of the polymeric immunoglobulin receptor (pIgR) and transport of the antibody to the mucosal epithelium. This pIgR-binding domain may be used to target a wide variety of compositions, including proteins, nucleic acids, drugs and diagnositic agents, to the mucosal surface. Other more specific targeting agents may be used in conjunction with the pIgR-binding domain to define further the ultimate localization of the complexes in the body. Treatment of a large number of disease conditions such as viral, fungal and bacterial infections, as well as cancer, may be improved through the use of a pIgR-binding domain.

Description: DESCRIPTION POLYMERIC IMMUNOGLOBULIN RECEPTOR (PIGRVBINDING DOMAINS AND METHODS OF USE THEREFOR BACKGROUND OF THE INVENTION This application claims priority to United States provisional patent application 60/119,932, filed on February 12, 1999, which is specifically incorporated by reference in its entirety herein without disclaimer. The United States government owns rights in the present invention pursuant to grant number AI44206-01A1 from the National Institutes of Health. 1. Field of the Invention The present invention relates generally to the fields of diagnostic, preventative, and therapeutic treatment compositions and methods. More particularly, it concerns a system for delivering agents to mucosal epithelia using a binding domain that recognizes and binds a polymeric immunoglobulin receptor. 2. Description of Related Art The largest area of the body that is exposed to external pathogens is the mucosal surfaces, which constitutes 400 square meters of surface area, as compared to 1.8 square meters of skin coverage (Childers et al, 1989). Not surprisingly, infections frequently involve the mucosal surfaces. IgA is the antibody class primarily found in mucosal secretions; thus, IgA antibodies serve as a first line of immune defense. To be released in mucosal secretions, IgA, which is produced by plasma cells, requires translocation across mucosal epithelium from the basal membrane side of the cells to the apical membrane side. Endocytosis and transcytosis of IgA is mediated through the polymeric immunoglobulin receptor (plgR), which is located at the basal membrane of mucosal epithelium (Mostov, 1994; Mostov et al, 1982). IgA in mucosal secretions is then able to mediate an active or passive immune response. Two different mechanisms have been described to account for IgA's antipathogenic activities: active immunity involves generating a molecular and cellular immune response against the pathogen through Fc receptor binding or complement activation; passive immunity does not involve stimulation of the immune system and instead occurs, for example, through IgA's ability to block viral attachment to host cells or to inhibit bacterial motility. A number of studies have demonstrated the association between strong mucosal IgA responses and protection against viral infection with rotavirus (Underdown and Schiff, 1986, Feng et al, 1994), influenza virus (Taylor and Dimmock, 1985, Liew et al, 1984), poliovirus (Ogra and Karzon, 1970), respiratory syncytial virus (Kaul et al, 1981), cytomegalovirus (Tamura et al, 1980) and Epstein-Barr virus (Yao et al, 1991). Secretory IgA is therefore, successful in preventing these viruses from gaining access to the body by blocking infection at the site of entry, namely the mucosal surface. Passive immunotherapy with intranasal IgG Fabs was protective against respiratory syncytial virus (Crowe et al, 1994), showing that the mere presence of neutralizing anti-viral antibodies, without any effector function, at the mucosal surface can prevent viral infection. Furthermore, HIV-specific IgA, which is transported to mucosal secretions, may be used as a vaccine to elicit protective antibody-mediated immunity (U.S. Serial No. 08/779,597, hereby incorporated by reference). Despite this information, there remain a number of questions regarding how IgA functions and, in particular, how IgA is transported. It would be of great benefit to know the nature and identity of the structures, including IgA structures, that are responsible for targeting and transport of IgA to mucosal epithelium via plgR. SUMMARY OF THE INVENTION Therefore, it is a goal of the present invention to provide structures that confers targeting and transport to the mucosal epithelium. It also is a goal of the present invention to provide a variety of compositions and uses for this structure. In accomplishing these and other goals, there is provided an isolated plgR- binding domain. A "plgR-binding domain" refers to an amino acid motif or structure that is capable of binding a polymeric immunoglobin receptor (plgR). This domain confers, upon molecules to which it is attached, the ability to be targeted to mucosal epithelium. In particular embodiments, the invention relates to an isolated peptide of between 10 and about 50 residues comprising a plgR-binding domain. Additional embodiments recite a peptide containing a plgR-binding domain that is 10 residues in length, about 15 residues in length, about 20 residues in length, about 25 residues in length, about 30 residues in length, about 35 residues in length, about 40 residues in length, about 45 residues in length, or about 50 residues in length. The invention further comprises a peptide that comprises the sequence SEQ ID NO:l, as well as a peptide that comprises a sequence selected from the group consisting of SEQ ID NOS:2-33. Moreover, in other embodiments, the plgR-binding domain comprises the Cα3 domain of IgA and fragments thereof. Amino acids flanking a plgR-binding domain that includes the Cα3 domain of IgA may also be included in compositions of the present invention. Flanking regions could include 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 50, or more amino acids on one or both sides of a plgR-binding domain. It is contemplated that the limitations and embodiments related to a peptide that contains one plgR-binding domain could also be employed with respect to a peptide containing more than one plgR-binding domain. Such a multimeric peptide could contain 2, 3, 4, 5, 6, 7, 8, 9, 10, or more plgR-binding domains. Other embodiments of the present invention include a peptide containing a plgR-binding domain, where the peptide is attached to a linking moiety such as SMTP, SPDP, LC-SPDP, Sulpho-LC-SDPD, SMCC, Sulfo-SMCC, MBS, Sulfo- MBS, SIAB, Sulfo-SIAB, SMPB, Sulfo-SMPB, EDC/Sulfo-NHS, and ABF Generally, the term "linking moiety" refers to a structure having the chemical or pharmacological property of linking or being able to link other compounds. In a multimeric peptide containing more than one plgR-binding domain, a linking moiety may connect two or more plgR-binding domains with each other. The peptide can also be attached via the linking moiety to a selected agent, which in some embodiments is a therapeutic or preventative compound. The selected agent can be, for example, a peptide, a polypeptide, an oligonucleotide, a polynucleotide, a detectable label, or a drug. Moreover, the present invention further comprises a polypeptide that is an enzyme, antibody region, region involved in protein-protein interactions or ligand-receptor interactions, cytokine, growth factor, hormone, toxin, tumor suppressor, transcription factor, or inducer of apoptosis. In additional embodiments, the selected agent is a polynucleotide that encodes a polypeptide, a single chain antibody, an antisense construct, or a ribozyme. Other examples of the invention disclose a detectable label that is rhodamine or fluorescein, or is a radiolabel. In still further embodiments, the peptide containing the plgR- binding domain is linked to a drug, such as an antibiotic, a DNA damaging agent, an enzyme inhibitor, or a metabolite. The present invention also describes in some embodiments a plgR-binding domain within a peptide that is linked to a non-pIgR targeting agent. A "non-pIgR targeting agent" or "non-pIgR moiety" refers to a structure that allows the targeting of a molecule that is not plgR. In some cases, the non-pIgR targeting agent is an antigen binding domain of an antibody, while in other cases it is a receptor ligand or a ligand binding domain. Thus, in these examples, the targeted molecule is either an antigen, a receptor, or a ligand, respectively. In yet further embodiments, the invention covers a fusion protein containing a plgR-binding domain covalently linked to a non-antibody peptide or polypeptide. Some examples of the present invention involve a plgR-binding domain that comprises a Cα3 domain of IgA. The non-antibody peptide or polypeptide can be selected from the group consisting of an enzyme, region that mediates protein-protein or ligand-receptor interaction, cytokine, growth factor, hormone, toxin, tumor suppressor, transcription factor, and inducer of apoptosis. The present invention additionally encompasses a polynucleotide that encodes a fusion protein containing a plgR-binding domain covalently linked to a non- antibody peptide or polypeptide sequence. In some embodiments, the non-antibody peptide or polypeptide is selected from the group consisting of an enzyme, region that mediates protein-protein or ligand-receptor interaction, cytokine, growth factor, hormone, toxin, tumor suppressor, transcription factor, and inducer of apoptosis. The invention also includes a method for targeting a selected agent to mucosal epithelium by at least providing a complex containing the selected agent and an isolated peptide of between 10 and about 50 residues that comprises a plgR-binding domain; and administering the targeting complex to a mammal, such that the complex binds to cells expressing plgR, is taken up by those cells, and is transported to the mucosal epithelium. Embodiments further describe this method, which is administered via oral, inhalation, ocular, nasal, vaginal, rectal, intravenous, subcutaneous, intramuscular, or intraarterial routes. In some examples, this method also includes a second, non-pIgR targeting moiety. Another method of the present invention for targeting a non-antibody peptide or polypeptide to mucosal epithelium includes: providing a fusion protein containing a plgR-binding domain covalently linked to a non-antibody peptide or polypeptide; and administering said targeting complex to a mammal, whereby the targeting complex binds to cells expressing plgR, is taken up by said cells, and is transported to the mucosal epithelium. In yet further embodiments, this method can be administered via oral, ocular, nasal, vaginal, rectal, intravenous, or intraarterial routes. More embodiments disclose a method where the fusion protein also includes a second targeting moiety such as a non-pIgR targeting agent. The invention described herein also encompasses a method of delivering a selected agent to a cell comprising: providing a complex containing the selected agent and an isolated peptide of between 10 and about 50 residues comprising a plgR- binding domain; and contacting the targeting complex with a cell expressing plgR. Additional examples include transforming the cell with an expression construct encoding plgR under the control of a promoter operable in said cell before providing the complex. Still further embodiments disclose a complex that also contains a second targeting moiety such as a non-pIgR targeting agent. Another method of delivering a non-antibody peptide or polypeptide to a cell comprises: providing a fusion protein comprising a plgR-binding domain covalently linked to a non-antibody peptide or polypeptide; and contacting that fusion protein with a cell expressing plgR. This method also embraces the step of first transforming the cell with an expression construct encoding plgR under the control of a promoter operable in the cell before providing the fusion protein. Other embodiments of this method include a fusion protein that also contains a second targeting moiety such as a non-pIgR targeting agent. The use of the word "a" or "an" when used in conjunction with the term "comprising" in the claims and/or the specification may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one." Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. BRIEF DESCRIPTION OF THE DRAWINGS The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein. FIG. 1A-D. Binding of monomeric and dimeric IgA/IgG domain swap mutant antibodies to plgR expressed on MDCK cells. FIG. 1A. Staining of MDCK cells with sheep anti-pIgR (heavy line) antiserum or normal sheep serum (broken line) followed by anti-sheep IgG FITC conjugate. FIG. IB. Binding of wild-type IgA monomer (thin line) or dimer (heavy line) to plgR on MDCK cells. FIG. 1C. Binding of VGAA mutant expressed as monomer (thin line) or dimer (heavy line) to plgR on MDCK cells. FIG. ID. Binding of VGGA mutant expressed as monomer (thin line) or dimer (heavy line) to plgR on MDCK cells. Bound IgA or IgA G chimeric antibodies were detected by rabbit anti-human kappa chain-FITC conjugate. Negative controls are shown as broken lines. FIG. 2. Alignment of deduced peptide sequences from selection of phage display peptide library against plgR receptor-expressing cells with the human Cα3 domain amino acid sequence (SEQ ID NOS:2-33). Peptides designated A or M are from the acid-eluted and cell-associated fractions respectively. Numbering of IgA 1 is according to reference (Putnam et al, 1979). FIG. 3A-C. Comparison of IgGl and IgAl CH3 sequences and IgGl structure in the area homologous to several phage-derived peptides. FIG. 3A. The A12 peptide alignment with both human IgAl and IgGl. IgGSTR indicates structural features of IgGl where < denotes a β-strand running in a descending orientation (i.e. hinge to CH3 direction), > denotes a β-strand running in an ascending direction (i.e. CH3 to hinge direction) and - denotes a loop or open structure (Deisenhofer et al, 1981). FIG. 3B. Comparison of several mammalian IgA sequences with the four human IgG subclasses showing the additional IgA-specific amino acids present in the loop at positions 402-410 in the IgA sequence. hu=human, gr=gorilla, mur=murine, rab=rabbit. FIG. 3C. IgAl Cα3 mutants LI, L2 and L3 aligned with the Cα3 and Cγ3 wild-type sequences and Cγ3 structure (IgGSTR). = denotes sequence identity in the mutants, - denotes a space introduced in the IgG sequence to maximize homology and IgGSTR is labeled according to FIG 3a above. Numbering of IgAl and IgGl is according to Putnam et al, 1979 and Deisenhofer et al, 1981, respectively. FIG. 4. Binding of IgA mutants LI, L2 and L3 to purified human plgR by ELISA. The extracellular domain of human plgR was purified following expression in baculovirus and coated onto ELISA plates at 10 μg/ml. Chimeric IgAl and IgAl C 3 mutants LI, L2 and L3 were expressed as both monomeric (m) and dimeric (d) forms along with chimeric IgGl, purified and incubated on the plgR-coated plates to compare their abilities to bind to plgR. Bound antibodies were detected with anti human-κ light chain alkaline phosphatase conjugate. FIG. 5. Alignment of phage peptides selected by transcytosis with human IgA using the program LALIGN. FIG. 6A-C. Basolateral to apical transport of phage peptides measured in the MDCK transcytosis system. 5 x 10 10 phage were added to the basolateral medium of wells containing 1.0 μm pore inserts confluent with either polarized MDCK or plgR- transfected MDCK cells. Transcytosis was allowed to occur for 4 hours. The apical supernatant fluids were collected and phage titers determined. A. SAM, IPS, and RSR peptides were evaluated. Note the very low phage titer level with the SAM peptide in the absence of plgR (bar graph is slightly above y-axis-0). B. MFV, NDD, and QRΝ peptides were evaluated. C. LNL and WQA peptides were evaluated. FIG. 7. Procedure and kinetics determination of blood phage peptides transported into hepatic bile. FIG. 8. Transcytosis of thioredoxin fusion proteins through non-transfected and plgR-transfected MDCK cells. DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS The present invention is directed to compositions and methods employing sequences, including IgA sequences, that target plgR for the delivery of therapeutic compounds to the mucosal surfaces. The identification of a plgR binding motif of IgA or of plgR-binding peptide sequences reduces the complexity of using a whole IgA monomer or polymer to provide a targeted delivery system to the mucosal epithelium. Delivery of therapeutic compounds to this area would bestow preventative and therapeutic benefits through the body's enhanced ability to prevent, inhibit, or reduce the incidence of infections, diseases, or conditions. The present invention encompasses both general targeting of compounds to the mucosal epithelium using the plgR-binding domain, and additional specific targeting of compounds to particular sites of action within the mucosal epithelium. Specific targeting is accomplished through the use of other targeting mechanisms that utilize sequences involved in specific protein-protein interactions, such as antigen-antibody interactions or ligand-receptor associations. I. Treatment Uses Mucosal surfaces of the body serve as a boundary with the environment. They constitute the largest exposed area of the body to external pathogens (Childers et al, 1989), and consequently, infections commonly involve these surfaces. The principal mucosal antibody is IgA, which is considered to form a first line of immune defense, particularly against microbes, toxins, and other antigens. A. IgA Antibodies The present invention encompasses sequences from IgA antibodies that mediate IgA's binding to the plgR, such as sequences within the Cα3 domain of IgA; in further embodiments of the present invention, other sequences from IgA antibodies are used such as those involved required for eliciting an immune response, which can include sequences that mediate antigen specificity. These IgA sequences can be utilized in additional embodiments in conjunction with a preventative or therapeutic compound, which gets directed to mucosal epithelia via the plgR-binding domain of IgA. IgA antibodies generally are produced in the greatest quantities, and they are manufactured locally by plasma cells within mucosal membranes before they are released in mucosal secretions. They are located in respiratory, nasopharyngeal, ocular, gastrointestinal, urinary, and genital tracts, as well as being present in saliva, serum, tears, and colostrum. IgA, like IgG, contains three constant domains (Cαl, Cα2, Cα3) with a hinge region joining the Cαl and Coc2 domains. Unlike IgG, however, IgA isotypes have an 18 residue "tailpiece" that is located at the C-terminal end of CH3, which allows IgA polymers to form (Putnam et al, 1979). Additionally, a small glycoprotein called the "J chain" forms disulfide bonds with two tailpiece cysteine residues, while the tailpieces each form a direct disulfide bond with each other (Garcia-Pardo et al, 1981; Bastian, et al, 1992). The J chain mediates serum IgA dimer formation (Zikan et al, 1986) by making polymerization more efficient, but it is not absolutely required (Hendrickson, et al, 1995). IgA is secreted from plasma cells that underlie the mucosal epithelial primarily as dimers joined by an intersubunit J chain, with each IgA composed of two identical light chains and two identical heavy chains that confer its specificity. The IgA dimers bind to the polymeric immunoglobulin receptor (plgR) on the basolateral surface of mucosal epithelia. Through its external IgA-binding domain, a plgR-IgA complex is formed through high-affinity non-covalent binding of plgR domain I (Frutiger et al, 1986; Bakos et al, 1991), and this complex is subsequently endocytosed. The plgR cytoplasmic domains contains sorting signals that cause the complex the be transcytosed via vesicles to the apical surface, where proteolytic cleavage separates the external domain of plgR (referred as "secretory component") from its membrane spanning domain (Lindh et al, 1974; Fallgrenn-Gebauer et al, 1993; Underdown et al, 1977). Consequently, the dimeric IgA-secretory component complex (termed "secretory IgA" or slgA) is released into the mucosal secretions (Underdown et al, 1977). The polymeric immunoglobulin receptor (plgR) is a type I transmembrane protein with five immunoglobulin superfamily homology domains (I-V) constituting the extracellular region (Mostov et al, 1984). Polymeric immunoglobulins, IgA and IgM, are bound by plgR at the basolateral surface of mucosal epithelial cells, transported through these cells, and then secreted at the mucosae (Mostov et al, 1982). While much is known about the macromolecular interaction and activity of IgA and plgR, relatively little is understood about the requirements of that interaction on a molecular scale. According to the present invention, a region of IgA that mediates plgR binding has been identified. The major binding motif of IgA to plgR has been localized to the Cα3 domain, particularly to amino acids 402-410, which form a portion of a predicted exposed loop of the Cα3 domain. A plgR-binding domain may comprise any portion of amino acids 402-410 by itself or in combination with other plgR-binding sequences, including IgA sequences, and can be utilized as a targeting peptide to recruit compounds to the mucosal epithelium; moreover, sequences that mediate plgR binding that are not derived from IgA are also considered to be a plgR binding domain, and thus, part of the present invention. Thus, complexes comprising a plgR-binding domain and a selected agent are contemplated by the present invention. The plgR-binding domain and the therapeutic/preventative compound will bind either as a monomer or as a polymer (including concatemers) to a plgR located at the basal membrane of mucosal epithelium and be collectively endocytosed. This complex will then be transcytosed until it reaches the apical membrane where the secretory component of plgR is cleaved with the targeting peptide and the therapeutic/preventative compound. Once secreted, the therapeutic compound can be utilized for various functions as will be discussed below, including prevention of diseases or conditions caused by pathogens; reduction or amelioration of disease states, conditions, or disorders, including cancer; and, mucosal immunity via vaccinations. The mucosal surfaces of the body offer an important advantage over serum as a site of immunological prevention or inhibition of disease, in that rather than responding to an infection that has already occurred, an immunological response at the mucosal surface prevents the infective agent from entering the body. Such a preventative method, as provided by the present disclosure, would be of dramatic benefit, not only in the prevention of sexually transmitted infections and maternal transmission of those diseases during birth, but also in the prevention of other infections that enter the body through mucosal surfaces such as the genitourinary tract, mouth, nasal passages, lungs, eyes, etc., in man and in domestic or non-domestic animals. Furthermore, access to the mucosal epithelia provides a method of treating many diseases, conditions, or disorders that are proximal to the mucosal epithelia by providing a passageway for preventative or therapeutic compounds to reach sites where they are needed. This targeting is accomplished through the use of targeting sequences of IgA that are involved in mediating its interaction with the polymeric immunoglobulin receptor (plgR). The plgR serves to shuttle IgA from the basal mucosal epithelium for its release in mucosal secretions. The present invention seeks to exploit the inventors' identification of a domain within IgA that is responsible for this targeting function. Therefore, IgA targeting sequences can be utilized to shuttle preventative and therapeutic compounds to mucosal epithelia for the treatment of diseases, conditions, or disorders. Additionally, it is contemplated that the present invention includes the use of peptide sequences that mimic the binding activity of IgA to plgR such that these sequences can be used as the previously described delivery shuttle system. As will be understood by those of skill in the art, small modification and changes may be made in the structure of a domain that binds plgR, including those changes that confer greating binding affinity for plgR than a sequence from IgA. Furthermore, certain amino acids may be substituted for other amino acids in a protein structure without appreciable loss of interactive binding capacity with the plgR. Since it is the interactive capacity and nature of a protein that defines that protein's biological functional activity, certain amino acid sequence substitutions can be made in a protein sequence (or, of course, its underlying DNA coding sequence) and nevertheless obtain a protein with like (agonistic) properties. It is thus contemplated by the inventors that various changes may be made in the plgR binding sequence of IgA or therapeutic or preventative compound polypeptides or peptides (or underlying DNA) without appreciable loss of their biological utility or activity. In the present invention, residues shown to be necessary for a plgR binding generally should be substituted with conservative amino acids or not changed at all, such as the group of residues located in the region constituting a loop between two flanking β-strand sequences of IgA. Introduction of alanine substitutions into the LI and L3 regions of the exposed loop abrogated plgR binding, as they comprise a major binding domain of IgA. Amino acid substitutions are generally based on the relative similarity of the amino acid side-chain substituents, for example, their hydrophobicity, hydrophilicity, charge, size, and the like. An analysis of the size, shape, and type of the amino acid side-chain substituents reveals that arginine, lysine, and histidine are all positively charged residues; that alanine, glycine, and serine are all a similar size; and that phenylalanine, tryptophan, and tyrosine all have a generally similar shape. Therefore, based upon these considerations, the following subsets are defined herein as biologically functional equivalents: arginine, lysine, and histidine; alanine, glycine, and serine; and phenylalanine, tryptophan, and tyrosine. To effect more quantitative changes, the hydropathic index of amino acids may be considered. Each amino acid has been assigned a hydropathic index on the basis of their hydrophobicity and charge characteristics, these are: isoleucine (+4.5) valine (+4.2); leucine (+3.8); phenylalanine (+2.8); cysteine/cystine (+2.5) methionine (+1.9); alanine (+1.8); glycine (-0.4); threonine (-0.7); serine (-0.8) tryptophan (-0.9); tyrosine (-1.3); proline (-1.6); histidine (-3.2); glutamate (-3.5) glutamine (-3.5); aspartate (-3.5); asparagine (-3.5); lysine (-3.9); and arginine (-4.5). The importance of the hydropathic amino acid index in conferring interactive biological function on a protein is generally understood in the art (Kyte & Doolittle, 1982, incorporated herein by reference). It is known that certain amino acids may be substituted for other amino acids having a similar hydropathic index or score and still retain a similar biological activity. In making changes based upon the hydropathic index, the substitution of amino acids whose hydropathic indices are within ±2 is preferred, those which are within ±1 are particularly preferred, and those within ±0.5 are even more particularly preferred. It also is understood in the art that the substitution of like amino acids can be made effectively on the basis of hydrophilicity, particularly where the biological functional equivalent protein or peptide thereby created is intended for use in immunological embodiments, as in the present case. U.S. Patent 4,554,101, incorporated herein by reference, states that the greatest local average hydrophilicity of a protein, as governed by the hydrophilicity of its adjacent amino acids, correlates with its immunogenicity and antigenicity, i.e. with a biological property of the protein. As detailed in U.S. Patent 4,554,101, the following hydrophilicity values have been assigned to amino acid residues: arginine (+3.0); lysine (+3.0); aspartate (+3.0 ± 1); glutamate (+3.0 ± 1); serine (+0.3); asparagine (+0.2); glutamine (+0.2); glycine (0); threonine (-0.4); proline (-0.5 ± 1); alanine (-0.5); histidine (-0.5); cysteine (-1.0); methionine (-1.3); valine (-1.5); leucine (-1.8); isoleucine (-1.8); tyrosine (-2.3); phenylalanine (-2.5); tryptophan (-3.4). In making changes based upon similar hydrophilicity values, the substitution of amino acids whose hydrophilicity values are within ±2 is preferred, those which are within ±1 are particularly preferred, and those within ±0.5 are even more particularly preferred. It also is conceivable that non-peptide structures such as "peptide mimetics" may be used to duplicate the structure and contact points within the plgR-binding domain structure, thereby also duplicating its ability to bind to, and hence target, the plgR. B. Treatment Uses The present invention can be used to prevent or combat any diseases, ailments, or conditions that involve mucosal epithelium, which includes any disease, ailment or condition that is accessible to mucosal epithelia. The effects described herein can be achieved within mucosal epithelia cells as well as in mucosal secretions or in the lumen after compounds of the present invention cross the mucosal epithelia. The present invention encompasses treatment of mucosal epithelia, which includes, but is not limited to, epithelia within respiratory, nasopharyngeal, ocular, gastrointestinal, urinary, and genital tracts. Within the respiratory tract, the present invention includes, but is not limited to, treatment of the following: asthma; bronchitis; emphysema; cystic fibrosis; bronchiectasis; bronchiolitis; pulmonary edema; viral tracheobronchitis; sleep apnea syndrome; infectious diseases such as bacterial pneumonia, Mycoplasma pneumonia, influenza, tuberculosis, endemic fungal pneumonias, and invasive aspergillosis; neoplastic conditions such as lung cancer, carcinomas and lymphomas; noninfectious, nonneoplastic diseases such as Loffler's syndrome, tropical pulmonary eosinophilia, sarcoidosis, pulomonary fibrosis, Caplan's sy drome, Wagner's granulomatosis, bronchogenic cysts; disorders of the chest wall such as kyphoscoliosis, neuromuscular syndrome, diffuse parenchymal lung disease; as well as other chronic diffuse infiltrative lung diseases. The present invention is directed also to treatment of nasopharyngeal and gastrointestinal disorders including, but not limited to, the following: dysphagia; peptic ulcers; diarrheal diseases; inflammatory bowel diseases such as ulcerative colitis and Chrohn's disease; acute pancreatitisgallstones and biliary tract disease; acute hepatits; chronic hepatitis; cirrhosis; gastrointestinal bleeding caused by ulcers, mucosal erosive diseases, malignancies, colonic diverticulosis, colitis, and hemorrhoids among other causes; malabsorption and maldigestion diseases; gastrointestinal motility disorders; and diverticulosis, diverticulitis, and appendicitis. In further embodiments, the present invention also covers the treatment of urogenital tract disorders and conditions including renal disorders of water and sodium imbalance; disorders of acid-base and potassium balance; glomerular diseases; systemic vasculitis; tubulointerstitial diseases; polycistic kidney disease; Alport's syndrome; medullary cystic disease; nephrolithiasis; hyperproliferative diseases such as neoplasias and malignancies; sexually transmitted diseases such as AIDS, hepatitis, genital warts, herpes, gonorrhea, syphillis, and chlamydia. Also contemplated by the present invention is the treatment of diseases and disorders involving cell hyperprohferation including the treatment or prevention of malignancies, premalignant conditions (hyperplasia, metaplasia, dysplasia), benign tumors, hyperproliferative disorders, and benign dysproliferative disorders, for example. The present invention further encompasses the treatment of cancer or precancer cells and tumors derived from bladder, blood, bone, bone marrow, brain, breast, colon, esophagus, gastrointestine, head, kidney, liver, lung, nasopharynx, neck, ovary, prostate, skin, stomach, and uterus. C. Pathogenic Protection Another embodiment of the invention is the use of the target agent to deliver a therapeutic/preventative compound to mucosal epithelia to prevent or inhibit pathogenic infection. The present invention contemplates the generation of passive and active immunity, in addition to therapeutic compounds and methods. One mode of operation includes a dlgA specific to a particular pathogen to prevent or inhibit infection against that particular pathogen. The compositions of the invention are administered to a subject, such as an animal or a human and are subsequently, after a latent period of up to 24 hours, transported across a mucosal barrier. After active or passive transportation into the mucosa, the antibodies of the invention are available to inhibit an infection at that site. Because this is a method of passive immunity, it is understood based on the serum half lives of antibodies, that the protection may last for a period of several weeks and that the compositions may then be re-administered if the need persists. The invention provides, therefore, a method of inhibiting an infection prior to entry into the body, offering a first line of defense prior to exposure to the particular pathogen. Pathogens that may be inhibited from infecting a subject include, but are not limited to, viruses, bacteria, and macroscopic parasites such as protozoans. The present invention would have applications therefore in the prevention and treatment of viral diseases that may enter or exit the body through the mucosal surfaces such as the following pathogenic viruses which are mentioned by way of example, influenza A, B and C, parainfluenza, paramyxoviruses, Newcastle disease virus, respiratory syncytial virus, measles, mumps, adenoviruses, adenoassociated viruses, parvoviruses, Epstein-Barr virus, rhinoviruses, coxsackieviruses, echoviruses, reoviruses, rhabdoviruses, lymphocytic choriomeningitis, coronavirus, polioviruses, herpes simplex, human immunodeficiency viruses, cytomegaloviruses, papillomaviruses, virus B, varicella-zoster, poxviruses, rubella, rabies, picomaviruses, rotavirus and Kaposi associated herpes virus. In addition to the viral diseases mentioned above, the present invention is also useful in the prevention, inhibition, or treatment of bacterial infections, including, but not limited to, the 83 or more distinct serotypes of pneumococci, streptococci such as S. pyogenes, S. agalactiae, S. equi, S. canis, S. bovis, S. equinus, S. anginosus, S. sanguis, S. salivarius, S. mitis, S. mutans, other viridans streptococci, peptostreptococci, other related species of streptococci, enterococci such as Enter ococcus faecalis, Enter ococcus faecium, Staphylococci, such as Staphylococcus epidermidis, Staphylococcus aureus, particularly in the nasopharynx, Hemophilus influenzae, pseudomonas species such as Pseudomonas aeruginosa, Pseudomonas pseudomallei, Pseudomonas mallei, brucellas such as Brucella melitensis, Brucella suis, Brucella abortus, Bordetella pertussis, Neisseria meningitidis, Neisseria gonorrhoeae, Moraxella catarrhalis, Corynebacterium diphtheriae, Corynebacterium ulcerans, Corynebacterium pseudotuberculosis, Corynebacterium pseudodiphtheriticum, Corynebacterium urealyticum, Corynebacterium hemolyticum, Corynebacterium equi, etc. Listeria monocytogenes, Nocordia asteroides, Bacteroides species, Actinomycetes species, Treponema pallidum, Leptospirosa species and related organisms. The invention may also be useful against gram negative bacteria such as Klebsiella pneumoniae, Escherichia coli, Proteus, Serratia species, Acinetobacter, Yersinia pestis, Francisella tularensis, Enterobacter species, Bacteriodes and Legionella species and the like. In addition, the invention may prove useful in controlling protozoan or macroscopic infections by organisms such as Cryptosporidium, Isospora belli, Toxoplasma gondii, Trichomonas vaginalis, Cyclospora species, for example, and for Chlamydia trachomatis and other Chlamydia infections such as Chlamydia psittaci, or Chlamydia pneumoniae, for example. Of course it is understood that the invention may be used on any pathogen against which an effective antibody can be made. In light of the present disclosure, one of skill in the art would be able to produce a composition of dimeric IgA antibodies immunoreactive with any such pathogen and would further be able to administer such a composition to a subject. Several groups have reported the use of the IgA isotype as protective antibodies against a wide range of human pathogens. These include: viruses, such as HIV (Burnett et al., 1994), influenza A (Liew et al, 1984), Sendai (Manzanec et al, 1987), and respiratory syncytial virus (Weltzin et al, 1994); bacteria, such as Salmonella typhimurium (Michetti, 1992), Vibrio cholerae (Apter et al, 1993, Winner et al, 1991), Chlamydia trachomatis (Cotter et al, 1995); bacterial toxins, and macroscopic parasites (Grzych et al, 1993). Moreover, a recombinant dimeric IgA with antigen specificity directed against transmissible gastroenteritis coronavirus (TGEV) reduced TGEV production significantly when transfected into a cell line (Castilla et α/., 1997). D. Therapeutic Compounds The targeting agent of the present invention may be operatively linked or attached to a selective agent or compound. Different and varied therapeutic compounds are illustrated. These include enzymes, drugs (e.g., antibacterial, antifungal, anti-viral), antibody regions, regions that mediate protein-protein or ligand-receptor interactions, cytokines, growth factors, hormones, toxins, polynucleotides coding for proteins, antisense sequences, radiotherapeutics, chemotherapeutics, ribozymes, tumor suppressors, transcription factors, inducers of apoptosis, or liposomes containing any of the foregoing. In addition to encompassing the delivery of purified compounds, the present invention further contemplates the delivery of nucleic acids that encode cognate compounds such as polypeptides. Therefore, according to the present invention, both purified compounds and nucleic acid sequences encoding that compound, e.g., a cytokine, may be delivered in conjunction with the plgR-binding domain. 1. Enzymes Various enzymes are of interest according to the present invention. Enzymes that could be attached to the plgR-binding domain include cytosine deaminase, adenosine deaminase, hypoxanthine-guanine phosphoribosyltransferase, galactose-1- phosphate uridyltransferase, phenylalanine hydroxylase, glucose-6-phosphate dehydrogenase, HSV thymidine kinase, and human thymidine kinase and extracellular proteins such as collagenase and matrix metalloprotease, lysosomal glucosidase (Pompe's disease), muscle phosphorylase (McArdle's syndrome), glucocerebosidase (Gaucher's disease), α-L-iduronidase (Hurler syndrome), L-iduronate sulfatase (Hunter syndrome), sphingomyelinase (Niemann-Pick disease) and hexosaminidase (Tay-Sachs disease). 2. Drugs According to the present invention, a drug may be operatively linked to a plgR-binding domain to deliver the drug to the mucosal epithelia. It is contemplated that drugs such as antimetabolites (e.g., purine analogs, pyrimidine analogs, folinic acid analogs), enzyme inhibitors, metabolites, or antibiotics (e.g., mitomycin) are useful in the present invention. 3. Antibody Regions Regions from the various members of the immunoglobulin family are also encompassed by the present invention. Both variable regions from specific antibodies are covered within the present invention, including complementarity determining regions (CDRs), as are antibody neutralizing regions, including those that bind effector molecules such as Fc regions. Antigen specific-encoding regions from antibodies, such as variable regions from IgGs, IgMs, or IgAs, can be employed with the plgR-binding domain in combination with an antibody neutralization region or with one of the therapeutic compounds described above. In yet another embodiment, one gene may comprise a single-chain antibody. Methods for the production of single-chain antibodies are well known to those of skill in the art. The skilled artisan is referred to U.S. Patent No. 5,359,046, (incorporated herein by reference) for such methods. A single chain antibody is created by fusing together the variable domains of the heavy and light chains using a short peptide linker, thereby reconstituting an antigen binding site on a single molecule. Single-chain antibody variable fragments (scFvs) in which the C-terminus of one variable domain is tethered to the N-terminus of the other via a 15 to 25 amino acid peptide or linker, have been developed without significantly disrupting antigen binding or specificity of the binding (Bedzyk et al, 1990; Chaudhary et al, 1990). These Fvs lack the constant regions (Fc) present in the heavy and light chains of the native antibody. Antibodies to a wide variety of molecules are contemplated, such as oncogenes, cytokines, growth factors, hormones, enzymes, transcription factors or receptors. Also contemplated are secreted antibodies targeted against serum, angiogenic factors (VEGF/VPF; βFGF; αFGF; and others), coagulation factors, and endothelial antigens necessary for angiogenesis (i.e., V3 integrin). Specifically contemplated are growth factors such as transforming growth factor, fibroblast growth factor, and platelet derived growth factor (PDGF) and PDGF family members. The present invention further embodies composition targeting specific pathogens through the use of antigen-specific sequences or targeting specific cell types, such as those expressing cell surface markers to identify the cell. Examples of such cell surface markers would include tumor-associated antigens or cell-type specific markers such as CD4 or CD8. 4. Regions Mediating Protein-Protein or Ligand-Receptor Interaction The use of a region of a protein that mediates protein-protein interactions, including ligand-receptor interactions, also is contemplated by the present invention. This region could be used as an inhibitor or competitor of a protein-protein interaction or as a specific targeting motif. Consequently, the invention covers using the plgR- binding domain to recruit a protein region that mediates a protein-protein interaction to mucosal epithelium. Once the compositions of the present invention reach the mucosal epithelia, more specific targeting of the composition is contemplated through the use of a region that mediates protein-protein interactions including ligand-receptor interactions. Protein-protein interactions include interactions between and among proteins such as receptors and ligands; receptors and receptors; polymeric complexes; transcription factors; kinases and downstream targets; enzymes and substrates; etc. For example, a ligand binding domain mediates the protei protein interaction between a ligand and its cognate receptor. Consequently, this domain could be used either to inhibit or compete with endogenous ligand binding or to target more specifically cell types that express a receptor that recognizes the ligand binding domain operatively attached to the plgR-binding domain. Examples of ligand binding domains include ligands such as VEGF/NPF; βFGF; αFGF; coagulation factors, and endothelial antigens necessary for angiogenesis (i.e., V3 integrin); growth factors such as transforming growth factor, fibroblast growth factor, colony stimulating factor, Kit ligand (KL), flk-2/flt-3, and platelet derived growth factor (PDGF) and PDGF family members; ligands that bind to cell surface receptors such as MHC molecules, among other. The most extensively characterized ligands are asialoorosomucoid (ASOR) (Wu and Wu, 1987) and transferrin (Wagner et al, 1990). Recently, a synthetic neoglycoprotein, which recognizes the same receptor as ASOR, has been used as a gene delivery vehicle (Ferkol et al, 1993; Perales et al, 1994) and epidermal growth factor (EGF) has also been used to deliver genes to squamous carcinoma cells (Myers, EPO 0273085). In other embodiments, Νicolau et al. (1987) employed lactosyl-ceramide, a galactose-terminal asialganglioside, incorporated into liposomes and observed an increase in the uptake of the insulin gene by hepatocytes. Also, the human prostate- specific antigen (Watt et al, 1986) may be used as the receptor for mediated delivery to prostate tissue. 5. Cytokines Another class of compounds that is contemplated to be operatively linked to the plgR-binding domain of the present invention includes interleukins and cytokines, such as interleukin 1 (IL-1), IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-8, IL-9, IL-10, IL- 11, IL-12, IL-13, IL-14, IL-15, β-interferon, α-interferon, γ-interferon, angiostatin, thrombospondin, endostatin, METH-1, METH-2, Flk2/Flt3 ligand, GM-CSF, G-CSF, M-CSF, and tumor necrosis factor (TNF). 6. Growth Factors In other embodiments of the present invention, growth factors or ligands will be encompassed by the therapeutic agent. Examples include VEGF/VPF, FGF, TGFβ, ligands that bind to a TIE, tumor-associated fibronectin isoforms, scatter factor, hepatocyte growth factor, fibroblast growth factor, platelet factor (PF4), PDGF, KIT ligand (KL), colony stimulating factors (CSFs), LIF, and TIMP. 7. Hormones Additional embodiments embrace the use of a hormone as a selective agent. For example, the following hormones or steroids can be implemented in the present invention: prednisone, progesterone, estrogen, androgen, gonadotropin, ACTH, CGH, or gastrointestinal hormones such as secretin. 8. Toxins In certain embodiments of the present invention, therapeutic agents will include generally a plant-, fungus-, or bacteria-derived toxin such as ricin A-chain (Burbage, 1997), a ribosome inactivating protein, α-sarcin, aspergillin, restrictocin, a ribonuclease, diphtheria toxin A (Masuda et al, 1997; Lidor, 1997), pertussis toxin A subunit, E. coli enterotoxin toxin A subunit, cholera toxin A subunit, and pseudomonas toxin c-terminal. Recently, it was demonstrated that transfection of a plasmid containing a fusion protein regulatable diphtheria toxin A chain gene was cytotoxic for cancer cells. Thus, gene transfer of regulated toxin genes might also be applied to the treatment of diseases (Masuda et al, 1997). 9. Antisense Constructs Antisense methodology takes advantage of the fact that nucleic acids tend to pair with "complementary" sequences. By complementary, it is meant that polynucleotides are those which are capable of base-pairing according to the standard Watson-Crick complementarity rules. That is, the larger purines will base pair with the smaller pyrimidines to form combinations of guanine paired with cytosine (G:C) and adenine paired with either thymine (A:T) in the case of DNA, or adenine paired with uracil (A:U) in the case of RNA. Inclusion of less common bases such as inosine, 5-methylcytosine, 6-methyladenine, hypoxanthine and others in hybridizing sequences does not interfere with pairing. Targeting double-stranded (ds) DNA with polynucleotides leads to triple-helix formation; targeting RNA will lead to double-helix formation. Antisense polynucleotides, when introduced into a target cell, specifically bind to their target polynucleotide and interfere with transcription, RNA processing, transport, translation and/or stability. Antisense RNA constructs, or DNA encoding such antisense RNA's, may be employed to inhibit gene transcription or translation or both within a host cell, either in vitro or in vivo, such as within a host animal, including a human subject. Antisense constructs may be designed to bind to the promoter and other control regions, exons, introns or even exon-intron boundaries of a gene. It is contemplated that the most effective antisense constructs will include regions complementary to intron/exon splice junctions. Thus, it is proposed that a preferred embodiment includes an antisense construct with complementarity to regions within 50-200 bases of an intron-exon splice junction. It has been observed that some exon sequences can be included in the construct without seriously affecting the target selectivity thereof. The amount of exonic material included will vary depending on the particular exon and intron sequences used. One can readily test whether too much exon DNA is included simply by testing the constructs in vitro to determine whether normal cellular function is affected or whether the expression of related genes having complementary sequences is altered. As stated above, "complementary" or "antisense" means polynucleotide sequences that are substantially complementary over their entire length and have very few base mismatches. For example, sequences of fifteen bases in length may be termed complementary when they have complementary nucleotides at thirteen or fourteen positions. Naturally, sequences which are completely complementary will be sequences which are entirely complementary throughout their entire length and have no base mismatches. Other sequences with lower degrees of homology also are contemplated. For example, an antisense construct that has limited regions of high homology, but also contains a non-homologous region (e.g., ribozyme; see below) could be designed. These molecules, though having less than 50% homology, would bind to target sequences under appropriate conditions. It may be advantageous to combine portions of genomic DNA with cDNA or synthetic sequences to generate specific constructs. For example, where an intron is desired in the ultimate construct, a genomic clone will need to be used. The cDNA or a synthesized polynucleotide may provide more convenient restriction sites for the remaining portion of the construct and, therefore, would be used for the rest of the sequence. Particular oncogenes that are targets for antisense constructs are ras, myc, neu, raf, erb, src, fms, jun, trk, ret, hst, gsp, bcl-2, and abl. Also contemplated to be useful are anti-apoptotic genes and angiogenesis promoters. Other antisense constructs can be directed at genes encoding viral or microbial genes to reduce or eliminate pathogenicity. Specific constructs target genes such as viral env, pol, gag, rev, tat or coat or capsid genes, or microbial endotoxin, recombination, replication, or transcription genes. 10. Ribozymes Although proteins traditionally have been used for catalysis of nucleic acids, another class of macromolecules has emerged as useful in this endeavor. Ribozymes are RNA-protein complexes that cleave nucleic acids in a site-specific fashion. Ribozymes have specific catalytic domains that possess endonuclease activity (Kim and Cook, 1987; Gerlach et al, 1987; Forster and Symons, 1987). For example, a large number of ribozymes accelerate phosphoester transfer reactions with a high degree of specificity, often cleaving only one of several phosphoesters in an oligonucleotide substrate (Michel and Westhof, 1990; Reinhold-Hurek and Shub, 1992). This specificity has been attributed to the requirement that the substrate bind via specific base-pairing interactions to the internal guide sequence ("IGS") of the ribozyme prior to chemical reaction. Ribozyme catalysis has primarily been observed as part of sequence-specific cleavage/ligation reactions involving nucleic acids (Joyce, 1989; Cook et al, 1981). For example, U.S. Patent No. 5,354,855 reports that certain ribozymes can act as endonucleases with a sequence specificity greater than that of known ribonucleases and approaching that of the DNA restriction enzymes. Thus, sequence-specific ribozyme-mediated inhibition of gene expression may be particularly suited to therapeutic applications (Scanlon et al, 1991; Sarver et al, 1990). Recently, it was reported that ribozymes elicited genetic changes in some cells lines to which they were applied; the altered genes included the oncogenes H-ras, c-fos and genes of HIV. Most of this work involved the modification of a target mRNA, based on a specific mutant codon that is cleaved by a specific ribozyme. Targets for this embodiment will include angiogenic genes such as VEGFs and angiopoeiteins as well as the oncogenes (e.g., ras, myc, neu, raf, erb, src, fms, jun, trk, ret, hst, gsp, bcl-2, EGFR, grb2 and abl). Other constructs will include overexpression of anti-apoptotic genes such as bcl-2, as well as microbial genes directed to viral or bacterial genes. 11. Chemo- and Radiotherapeutics According to the invention, chemotherapeutic and radiotherapeutic compounds can be operatively attached to a plgR targeting motif. Chemotherapeutic agents contemplated to be of use include, e.g., adriamycin, bleomycin, 5-fluorouracil(5FU), etoposide (VP- 16), camptothecin, actinomycin-D, mitomycin C, cisplatin (CDDP), podophyllotoxin, verapamil, and even hydrogen peroxide. 12. Transcription Factors and Regulators Another class of genes that can be applied in an advantageous combination are transcription factors, both negative and positive regulators. Examples include C/EBPα, IκB, NFKB, AP-1, YY-1, Spl, CREB, VP16, and Par-4. 13. Cell Cycle Regulators Cell cycle regulators provide possible advantages, when combined with other genes. Such cell cycle regulators include p27, pi 6, p21, p57, pi 8, p73, pi 9, pi 5, E2F-1, E2F-2, E2F-3, pl07, pl30, and E2F-4. Other cell cycle regulators include anti-angiogenic proteins, such as soluble Flkl (dominant negative soluble VEGF receptor), soluble Wnt receptors, soluble Tie2/Tek receptor, soluble hemopexin domain of matrix metalloprotease 2, and soluble receptors of other angiogenic cytokines (e.g., VEGFRl, VEGFR2/KDR, VEGFR3/Flt4, and neutropilin-1 and -2 coreceptors). 14. Chemokines Chemokines also may be used in the present invention. Chemokines generally act as chemoattractants to recruit immune effector cells to the site of chemokine expression. It may be advantageous to express a particular chemokine gene in combination with, for example, a cytokine gene, to enhance the recruitment of other immune system components to the site of treatment. Such chemokines include RANTES, MCAF, MlPl-alpha, MlPl-beta, and IP-10. The skilled artisan will recognize that certain cytokines are also known to have chemoattractant effects and could also be classified under the term chemokines. 15. Tumor Suppressors A number of proteins have been characterized as tumor suppressors, which define a class of proteins that are involved with regulated cell proliferation. The loss of wild-type tumor suppressor activity is associated with neoplastic or unregulated cell growth. It has been shown by several groups that the neoplastic growth of cells lacking a wild-type copy of a particular tumor suppressor can be halted by the addition of a wild-type version of that tumor suppressor. This has been observed, for example, with p53 (Diller et al, 1990). The present invention contemplates the use of a plgR-binding domain to target mucosal epithelia for the delivery of a tumor suppressor, such as p53. Other tumor suppressors that may be employed according to the present invention include p21, pl5, BRCAl, BRCA2, IRF-1, PTEN (MMAC1), Rb, APC, DCC, NF-1, NF-2, WT-1, MEN-I, MEN-II, zacl, p73, VHL, FCC, and MCC. 16. Inducer s of Apoptosis Inducers of apoptosis, such as Bax, Bak, Bcl-X s , Bad, Bim, Bik, Bid, Harakiri, Ad E1B, and ICE-CED3 proteases, similarly could be of use according to the present invention. 17. Liposomes as Carriers of Selected Agents In another embodiment of the invention, the selected agent may be entrapped in a liposome. Liposomes are vesicular structures characterized by a phospholipid bilayer membrane and an inner aqueous medium. Multilamellar liposomes have multiple lipid layers separated by aqueous medium. They form spontaneously when phospholipids are suspended in an excess of aqueous solution. The lipid components undergo self-rearrangement before the formation of closed structures and entrap water and dissolved solutes between the lipid bilayers (Ghosh and Bachhawat, 1991). Also contemplated are cationic lipid-nucleic acid complexes, such as lipofectamine-nucleic acid complexes. "Liposome" is a generic term encompassing a variety of single and multilamellar lipid vehicles formed by the generation of enclosed lipid bilayers. Phospholipids are used for preparing the liposomes according to the present invention and can carry a net positive charge, a net negative charge or are neutral. Dicetyl phosphate can be employed to confer a negative charge on the liposomes, and stearylaminecan be used to confer a positive charge on the liposomes. Lipids suitable for use according to the present invention can be obtained from commercial sources. For example, dimyristyl phosphatidylcholine ("DMPC") can be obtained from Sigma Chemical Co., dicetyl phosphate ("DCP") is obtained from K & K Laboratories (Plainview, NY); cholesterol ("Choi") is obtained from Calbiochem-Behring; dimyristyl phosphatidylglycerol ("DMPG") and other lipids may be obtained from Avanti Polar Lipids, Inc. (Birmingham, Ala.). Stock solutions of lipids in chloroform, chloroform/methanol or t-butanol can be stored at about -20°C. Preferably, chloroform is used as the only solvent since it is more readily evaporated than methanol. Phospholipids from natural sources, such as egg or soybean phosphatidylcholine, brain phosphatidic acid, brain or plant phosphatidylinositol, heart cardiolipin and plant or bacterial phosphatidylethanolamineare preferably not used as the primary phosphatide, i.e., constituting 50% or more of the total phosphatide composition, because of the instability and leakiness of the resulting liposomes. Liposomes used according to the present invention can be made by different methods. The size of the liposomes varies depending on the method of synthesis. A liposome suspended in an aqueous solution is generally in the shape of a spherical vesicle, having one or more concentric layers of lipid bilayer molecules. Each layer consists of a parallel array of molecules represented by the formula XY, wherein X is a hydrophilic moiety and Y is a hydrophobic moiety. In aqueous suspension, the concentric layers are arranged such that the hydrophilic moieties tend to remain in contact with an aqueous phase and the hydrophobic regions tend to self-associate. For example, when aqueous phases are present both within and without the liposome, the lipid molecules will form a bilayer, known as a lamella, of the arrangement XY-YX. Liposomes within the scope of the present invention can be prepared in accordance with known laboratory techniques. In one preferred embodiment, liposomes are prepared by mixing liposomal lipids, in a solvent in a container, e.g., a glass, pear-shaped flask. The container should have a volume ten-times greater than the volume of the expected suspension of liposomes. Using a rotary evaporator, the solvent is removed at approximately 40°C under negative pressure. The solvent normally is removed within about 5 min to 2 hours, depending on the desired volume of the liposomes. The composition can be dried further in a desiccator under vacuum. The dried lipids generally are discarded after about 1 week because of a tendency to deteriorate with time. Dried lipids can be hydrated at approximately 25-50 mM phospholipid in sterile, pyrogen-free water by shaking until all the lipid film is resuspended. The aqueous liposomes can be then separated into aliquots, each placed in a vial, lyophilized and sealed under vacuum. In the alternative, liposomes can be prepared in accordance with other known laboratory procedures: the method of Bangham et αl. (1965), the contents of which are incorporated herein by reference; the method of Gregoriadis, as described in DRUG CARRIERS IN BIOLOGY AND MEDICINE, G. Gregoriadis ed. (1979) pp. 287-341, the contents of which are incorporated herein by reference; the method of Deamer and Uster (1983), the contents of which are incorporated by reference; and the reverse-phase evaporation method as described by Szoka and Papahadjopoulos (1978). The aforementioned methods differ in their respective abilities to entrap aqueous material and their respective aqueous space-to-lipid ratios. The dried lipids or lyophilized liposomes prepared as described above may be reconstituted in a solution of nucleic acid and diluted to an appropriate concentration with an suitable solvent, e.g. , DPBS. The mixture is then vigorously shaken in a vortex mixer. Unencapsulated nucleic acid is removed by centrifugation at 29,000 x g and the liposomal pellets washed. The washed liposomes are resuspended at an appropriate total phospholipid concentration, e.g., about 50-200 mM. The amount of nucleic acid encapsulated can be determined in accordance with standard methods. After determination of the amount of nucleic acid encapsulated in the liposome preparation, the liposomes may be diluted to appropriate concentration and stored at 4°C until use. In another embodiment, the lipid dioleoylphosphatidylchoine is employed. Nuclease-resistant oligonucleotides were mixed with lipids in the presence of excess t-butanol. The mixture was vortexed before being frozen in an acetone/dry ice bath. The frozen mixture was lyophilized and hydrated with Hepes-buffered saline (1 mM Hepes, 10 mM NaCl, pH 7.5) overnight, and then the liposomes were sonicated in a bath type sonicator for 10 to 15 min. The size of the liposomal-oligonucleotides typically ranged between 200-300 nm in diameter as determined by the submicron particle sizer autodilute model 370 (Nicomp, Santa Barbara, CA). E. Diagnostic Compounds Certain examples of protein conjugates are those conjugates in which a protein sequence such as a peptide containing a plgR-binding domain is linked to a detectable label. "Detectable labels" are compounds or elements that can be detected due to their specific functional properties, or chemical characteristics, the use of which allows the peptide or protein to which they are attached to be detected, and further quantified if desired. Many appropriate imaging agents are known in the art, as are methods for their attachment to proteins (see, e.g. , U.S. patents 5,021,236 and 4,472,509, both incorporated herein by reference). Certain attachment methods involve the use of a metal chelate complex employing, for example, an organic chelating agent such a DTPA attached to the antibody (U.S. Patent 4,472,509). Protein sequences may also be reacted with an enzyme in the presence of a coupling agent such as glutaraldehyde or periodate. Conjugates with fluorescein markers are prepared in the presence of these coupling agents or by reaction with an isothiocyanate. Rhodamine markers can also be prepared. In the case of paramagnetic ions, one might mention by way of example ions such as chromium (III), manganese (II), iron (III), iron (II), cobalt (II), nickel (II), copper (II), neodymium (III), samarium (III), ytterbium (III), gadolinium (III), vanadium (II), terbium (III), dysprosium (III), holmium (III) and erbium (III), with gadolinium being particularly preferred. Ions useful in other contexts, such as X-ray imaging, include but are not limited to lanthanum (III), gold (III), lead (II), and especially bismuth (III). In the case of radioactive isotopes for therapeutic and/or diagnostic application, one might mention astatine 211 , 14 carbon, 51 chromium, 36 chlorine, 57 cobalt, 58 cobalt, copper 67 , 152 Eu, gallium 67 , 3 hydrogen, iodine 123 , iodine 125 , iodine 131 , indium 111 , 59 iron, 32 phosphorus, rhenium 186 , rhenium 188 , 75 selenium, 35 sulphur, technicium 09 " 1 and yttrium 90 . 125 Iodine is often being preferred for use in certain embodiments, and technicium 991 " and indium 111 are also often preferred due to their low energy and suitability for long range detection. F. Combined therapy with immunotherapy, traditional chemotherapy, radiotherapy or other anti-cancer agents In many therapies, it will be advantageous to provide more than one functional therapeutic. Such "combined" therapies may have particular import in treating aspects of multidrug resistant (MDR) cancers and in antibiotic resistant bacterial infections. Thus, one aspect of the present invention utilizes a plgR-binding domain to deliver therapeutic compounds to mucosal epithelia for treatment of diseases, while a second therapy, either targeted or non-targeted, also is provided. The non-targeted treatment may precede or follow the targeted agent treatment by intervals ranging from minutes to weeks. In embodiments where the other agent and expression construct are applied separately to the cell, one would generally ensure that a significant period of time did not expire between the time of each delivery, such that the agent and expression construct would still be able to exert an advantageously combined effect on the cell. In such instances, it is contemplated that one would contact the cell with both modalities within about 12-24 hours of each other and, more preferably, within about 6-12 hours of each other, with a delay time of only about 12 hours being most preferred. In some situations, it may be desirable to extend the time period for treatment significantly, however, where several days (2, 3, 4, 5, 6 or 7) to several weeks (1 , 2, 3, 4, 5, 6, 7 or 8) lapse between the respective administrations. It also is conceivable that more than one administration of either agent will be desired. Various combinations may be employed, where the targeted agent is "A" and the non-targeted agent is "B", as exemplified below: A/B/A B/A/B B/B/A A A/B B/A/A A/B/B B/B/B/A B/B/A B A/A/B/B A/B/A/B A/B/B/A B/B/A/A B/A/B/A B/A/A/B B/B/B/A A/A/A/B B/A/A/A A/B/A/A A/A/B/A A/B/B/B B/A/B/B B/B/A/B Other combinations are contemplated. For example, in the context of the present invention, it is contemplated that mucosal-epithelia-targeted therapy of the present invention could be used in conjunction with non-targeted anti-cancer agents, including chemo- or radiotherapeutic intervention. To kill cells, inhibit cell growth, inhibit metastasis, inhibit angiogenesis or otherwise reverse or reduce the malignant phenotype of tumor cells, using the methods and compositions of the present invention, one would generally contact a "target" cell with a targeting agent/therapeutic agent and at least one other agent; these compositions would be provided in a combined amount effective achieve these goals. This process may involve contacting the cells with the expression construct and the agent(s) or factor(s) at the same time. This may be achieved by contacting the cell with a single composition or pharmacological formulation that includes both agents, or by contacting the cell with two distinct compositions or formulations, at the same time, wherein one composition includes the expression construct and the other includes the agent. Alternatively, a gene therapy treatment involving a tumor suppressor gene, an antisense oncogene or oncogene-specific ribozyme may be used. Agents or factors suitable for use in a combined cancer therapy are any chemical compound or treatment method with anticancer activity; therefore, the term "anticancer agent" that is used throughout this application refers to an agent with anticancer activity. These compounds or methods include alkylating agents, topisomerase I inhibitors, topoisomerase II inhibitors, RNA DNA antimetabolites, DNA antimetabolites, antimitotic agents, as well as DNA damaging agents, which induce DNA damage when applied to a cell. Examples of alkylating agents include, inter alia, chloroambucil, cis-platinum, cyclodisone, flurodopan, methyl CCNU, piperazinedione, teroxirone. Topisomerase I inhibitors encompass compounds such as camptothecin and camptothecin derivatives, as well as morpholinodoxorubicin. Doxorubicin, pyrazoloacridine, mitoxantrone, and rubidazone are illustrations of topoisomerase II inhibitors. RNA DNA antimetabolites include L-alanosine, 5-fluoraouracil, aminopterin derivatives, methotrexate, and pyrazofurin; while the DNA antimetabolite group encompasses, for example, ara-C, guanozole, hydroxyurea, thiopurine. Typical antimitotic agents are colchicine, rhizoxin, taxol, and vinblastine sulfate. Other agents and factors include radiation and waves that induce DNA damage such as, γ-irradiation, X-rays, UV-irradiation, microwaves, electronic emissions, and the like. A variety of anti-cancer agents, also described as "chemotherapeutic agents," function to induce DNA damage, all of which are intended to be of use in the combined treatment methods disclosed herein. Chemotherapeutic agents contemplated to be of use, include, e.g., adriamycin, bleomycin, 5-fluorouracil (5FU), etoposide (VP-16), camptothecin, actinomycin-D, mitomycin C, cisplatin (CDDP), podophyllotoxin, verapamil, and even hydrogen peroxide. The invention also encompasses the use of a combination of one or more DNA damaging agents, whether radiation-based or actual compounds, such as the use of X-rays with cisplatin or the use of cisplatin with etoposide. The skilled artisan is directed to "Remington's Pharmaceutical Sciences" 15th Edition, chapter 33, in particular pages 624-652. Some variation in dosage will necessarily occur depending on the condition of the subject being treated. The person responsible for administration will, in any event, determine the appropriate dose for the individual subject. Moreover, for human administration, preparations should meet sterility, pyrogenicity, general safety and purity standards as required by FDA Office of Biologies standards. The inventors propose that local, regional delivery of a therapeutic/preventative agent targeted to the mucosal epithelium in patients with cancers, precancers, or hyperproliferative conditions that can be reached via mucosal epithelia will be a very efficient method for delivering a therapeutically effective compound to counteract the clinical disease. Similarly, the chemo- or radiotherapy may be directed to a particular, affected region of the subjects body. Alternatively, systemic delivery of compounds and/or the agents may be appropriate in certain circumstances, for example, where extensive metastasis has occurred. In addition to combining mucosal epithelia-targeted therapies with chemo- and radiotherapies, it also is contemplated that combination with gene therapies will be advantageous. For example, targeting of mucosal epithelia using a combination of p53, pi 6, p21, Rb, APC, DCC, NF-1, NF-2, BCRA2, pi 6, FHIT, WT-1, MEN-I, MEN-II, BRCAl , VHL, FCC, or MCC, or antisense versions of the oncogenes ras, myc, neu, raf, erb, src, fms, jun, trk, ret, gsp, hst, bcl or abl are included within the scope of the invention. Another example of combined therapies is in the treatment of bacterial infections. Likely combinations would be (a) two drugs or (b) a drug and an antibody. Various antibiotics include the fluoroquinolones (pefloxacin, norfloxacin, ciprofloxacin, ofloxacin, levofloxacin, enoxacin, fleroxacin, lomefloxacin, temofloxacin, amifloxacin, tosufloxacin, flumequine, rufloxacin, clinafloxacin), the penicillins (penicilln G or V, methicillin, oxacillin, nafcilling, cloxacillin, dicloxacillin, ampicillin, amoxicillin, carbenicillin, ticarcillin, azlocillin, mexlocillin, piperacillin), the sulfonamides (silfanilamide, sulfamethoxazole, sulfadiazine, sulfisoxazole, sulfacetamide), the cephalosporins (cephalothin, cephapirin, cefazolin, cephalexin, cephradine, cefadroxil, cefamanadole, cefoxitin, cefaclor, cefuroxime, cefonicid, cefotetan, ceforanide, cefotaxime, ceftizoxime, ceftriaxone, cefoperazone, ceftazidime), the aminoglycosides (gentamicin, tobramycin, netilmicin, amikacin, kanamycin, neomycin), tetracyclines, erythromycin, lycomycin, clindamycin, spectinomycin, vancomycin, and streptomycin. Anti-fungal agents (amphotericin B, flycytosine, ketoconazole, fluconazole, griseofulvin, clotrimazole, econazole, miconazole, ciclopirox olamine, halprogein, tolnaftate, naftifine, natamycin and nystatin) and anti-virals (AZT, acyclovir, ganciclovir, vidarabine, idoxuridine, trifluiridine, foscarnet, alpha interferon, amatidine, ribavirin, and rimantidine) also will be useful in therapy of these diseases. It should be reiterated that any of the agents listed here also can be used individually to treat the related condition in conjunction with targeting to the mucosal epithelium by plgR (see above). II. Preparation Methods The compounds of the present invention include a targeting agent and in some embodiments, a therapeutic agent or diagnostic agent. The targeting agent of the invention may be linked, or operatively attached, to the therapeutic or diagnostic agent by either chemical conjugation (e.g., crosslinking) or through recombinant DNA techniques to produce the compound. A. Protein Purification To prepare a composition comprising the plgR-binding domain and a selective agent, it may be desirable to purify the components or variants thereof. According to one embodiment of the present invention, purification of a peptide comprising the plgR-binding domain can be utilized ultimately to operatively link this domain with a selective agent. Protein purification techniques are well known to those of skill in the art. These techniques involve, at one level, the crude fractionation of the cellular milieu to polypeptide and non-polypeptide fractions. Having separated the polypeptide from other proteins, the polypeptide of interest may be further purified using chromatographic and electrophoretic techniques to achieve partial or complete purification (or purification to homogeneity). Analytical methods particularly suited to the preparation of a pure peptide are ion-exchange chromatography, exclusion chromatography; polyacrylamide gel electrophoresis; isoelectric focusing. A particularly efficient method of purifying peptides is fast protein liquid chromatography or even HPLC. Certain aspects of the present invention concern the purification, and in particular embodiments, the substantial purification, of an encoded protein or peptide, such as IgA or plgR-binding domain. The term "purified protein or peptide" as used herein, is intended to refer to a composition, isolatable from other components, wherein the protein or peptide is purified to any degree relative to its naturally- obtainable state. A purified protein or peptide therefore also refers to a protein or peptide, free from the environment in which it may naturally occur. Generally, "purified" will refer to a protein or peptide composition, such as the plgR-binding domain, that has been subjected to fractionation to remove various other components, and which composition substantially retains its expressed biological activity. Where the term "substantially purified" is used, this designation will refer to a composition in which the protein or peptide forms the major component of the composition, such as constituting about 50%, about 60%, about 70%, about 80%, about 90%, about 95% or more of the proteins in the composition. Various methods for quantifying the degree of purification of the protein or peptide will be known to those of skill in the art in light of the present disclosure. These include, for example, determining the specific activity of an active fraction, or assessing the amount of polypeptides within a fraction by SDS/PAGE analysis. A preferred method for assessing the purity of a fraction is to calculate the specific activity of the fraction, to compare it to the specific activity of the initial extract, and to thus calculate the degree of purity, herein assessed by a "-fold purification number." The actual units used to represent the amount of activity will, of course, be dependent upon the particular assay technique chosen to follow the purification and whether or not the expressed protein or peptide exhibits a detectable activity. Various techniques suitable for use in protein purification will be well known to those of skill in the art. These include, for example, precipitation with ammonium sulphate, PEG, antibodies and the like or by heat denaturation, followed by centrifugation; chromatography steps such as ion exchange, gel filtration, reverse phase, hydroxylapatite and affinity chromatography; isoelectric focusing; gel electrophoresis; and combinations of such and other techniques. As is generally known in the art, it is believed that the order of conducting the various purification steps may be changed, or that certain steps may be omitted, and still result in a suitable method for the preparation of a substantially purified protein or peptide. There is no general requirement that the protein or peptide always be provided in their most purified state. Indeed, it is contemplated that less substantially purified products will have utility in certain embodiments. Partial purification may be accomplished by using fewer purification steps in combination, or by utilizing different forms of the same general purification scheme. For example, it is appreciated that a cation-exchange column chromatography performed utilizing an HPLC apparatus will generally result in a greater "-fold" purification than the same technique utilizing a low pressure chromatography system. Methods exhibiting a lower degree of relative purification may have advantages in total recovery of protein product, or in maintaining the activity of an expressed protein. It is known that the migration of a polypeptide can vary, sometimes significantly, with different conditions of SDS/PAGE (Capaldi et al, 1977). It will therefore be appreciated that under differing electrophoresis conditions, the apparent molecular weights of purified or partially purified expression products may vary. High Performance Liquid Chromatography (HPLC) is characterized by a very rapid separation with extraordinary resolution of peaks. This is achieved by the use of very fine particles and high pressure to maintain an adequate flow rate. Separation can be accomplished in a matter of minutes, or at most an hour. Moreover, only a very small volume of the sample is needed because the particles are so small and close-packed that the void volume is a very small fraction of the bed volume. Also, the concentration of the sample need not be very great because the bands are so narrow that there is very little dilution of the sample. Gel chromatography, or molecular sieve chromatography, is a special type of partition chromatography that is based on molecular size. The theory behind gel chromatography is that the column, which is prepared with tiny particles of an inert substance that contain small pores, separates larger molecules from smaller molecules as they pass through or around the pores, depending on their size. As long as the material of which the particles are made does not adsorb the molecules, the sole factor determining rate of flow is the size. Hence, molecules are eluted from the column in decreasing size, so long as the shape is relatively constant. Gel chromatography is unsurpassed for separating molecules of different size because separation is independent of all other factors such as pH, ionic strength, temperature, etc. There also is virtually no adsorption, less zone spreading and the elution volume is related in a simple matter to molecular weight. Affinity Chromatography is a chromatographic procedure that relies on the specific affinity between a substance to be isolated and a molecule that it can specifically bind to. This is a receptor-ligand type interaction. The column material is synthesized by covalently coupling one of the binding partners to an insoluble matrix. The column material is then able to specifically adsorb the substance from the solution. Elution occurs by changing the conditions to those in which binding will not occur (e.g., alter pH, ionic strength, and temperature.). A particular type of affinity chromatography useful in the purification of carbohydrate containing compounds is lectin affinity chromatography. Lectins are a class of substances that bind to a variety of polysaccharides and glycoproteins. Lectins are usually coupled to agarose by cyanogen bromide. Conconavalin A coupled to Sepharose was the first material of this sort to be used and has been widely used in the isolation of polysaccharides and glycoproteins other lectins that have been include lentil lectin, wheat germ agglutinin which has been useful in the purification of N-acetyl glucosaminyl residues and Helix pomatia lectin. Lectins themselves are purified using affinity chromatography with carbohydrate ligands. Lactose has been used to purify lectins from castor bean and peanuts; maltose has been useful in extracting lectins from lentils and jack bean; N-acetyl-D galactosamine is used for purifying lectins from soybean; N-acetyl glucosaminyl binds to lectins from wheat germ; D-galactosamine has been used in obtaining lectins from clams and L-fucose will bind to lectins from lotus. The matrix should be a substance that itself does not adsorb molecules to any significant extent and that has a broad range of chemical, physical and thermal stability. The ligand should be coupled in such a way as to not affect its binding properties. The ligand also should provide relatively tight binding. And it should be possible to elute the substance without destroying the sample or the ligand. One of the most common forms of affinity chromatography is immunoaffmity chromatography. The generation of antibodies that would be suitable for use in accord with the present invention is discussed below. 1. Synthetic Peptides The present invention also describes a plgR-binding domain, including an IgA Cα3 peptide, for use in various embodiments of the present invention. Encompassed within the invention is a peptide that demonstrates greater binding affinity for plgR than even the corresponding region of IgA. The peptides of the invention can be synthesized in solution or on a solid support in accordance with conventional techniques. Various automatic synthesizers are commercially available and can be used in accordance with known protocols. See, for example, Stewart and Young, (1984); Tam et al, (1983); Merrifield, (1986); and Barany and Merrifield (1979), each incorporated herein by reference. Short peptide sequences, or libraries of overlapping peptides, usually from about 6 up to about 35 to 50 amino acids, which correspond to the selected regions described herein, can be readily synthesized and then screened in screening assays designed to identify reactive peptides. Peptides with at least about 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or up to about 100 amino acid residues are contemplated by the present invention. The compositions of the invention may include a peptide comprising a plgR- binding domain that has been modified to enhance its plgR-binding capability or to render it biologically protected. Biologically protected peptides have certain advantages over unprotected peptides when administered to human subjects and, as disclosed in U.S. patent 5,028,592, incorporated herein by reference, protected peptides often exhibit increased pharmacological activity. Compositions for use in the present invention may also comprise peptides that include all L-amino acids, all D-amino acids, or a mixture thereof. The use of D- amino acids may confer additional resistance to proteases naturally found within the human body and are less immunogenic and can therefore be expected to have longer biological half lives. 2. Linkers/Coupling Agents If desired, dimers or multimers of the plgR-binding domain, such as dimeric IgA polypeptides, and the therapeutic or preventative compound may be joined via a biologically-releasable bond, such as a selectively-cleavable linker or amino acid sequence. For example, peptide linkers that include a cleavage site for an enzyme preferentially located or active within a tumor environment are contemplated. Exemplary forms of such peptide linkers are those that are cleaved by urokinase, plasmin, thrombin, Factor IXa, Factor Xa, or a metallaproteinase, such as collagenase, gelatinase, or stromelysin. It is also contemplated that a peptide containing multimers of plgR-binding domains may be comprised of heteromeric sequences, in which the plgR-binding sequences are not identical to each other, or homomeric sequences, in which a plgR- binding domain sequence is repeated at least once. Amino acids such as selectively- cleavable linkers, synthetic linkers, or other amino acid sequences may be used to separate a plgR-binding domain from another plgR-binding domain. Alternatively, linker sequences may be employed both between at least once set of plgR-binding domains, as well as between a plgR-binding domain and a selective agent or compound. Additionally, while numerous types of disulfide-bond containing linkers are known which can successfully be employed to conjugate the toxin moiety with the targeting agent, certain linkers will generally be preferred over other linkers, based on differing pharmacologic characteristics and capabilities. For example, linkers that contain a disulfide bond that is sterically "hindered" are to be preferred, due to their greater stability in vivo, thus preventing release of the toxin moiety prior to binding at the site of action. Furthermore, while certain advantages in accordance with the invention will be realized through the use of any of a number of toxin moieties, the inventors have found that the use of ricin A chain, and even more preferably deglycosylated A chain, will provide particular benefits. a. Biochemical cross-linkers The joining of any of the above components, to targeting peptide will generally employ the same technology as developed for the preparation of immunotoxins. It can be considered as a general guideline that any biochemical cross-linker that is appropriate for use in an immunotoxin will also be of use in the present context, and additional linkers may also be considered. Cross-linking reagents are used to form molecular bridges that tie together functional groups of two different molecules, e.g., a stablizing and coagulating agent. To link two different proteins in a step-wise manner, hetero-bifunctional cross-linkers can be used that eliminate unwanted homopolymer formation. TABLE 1 HETERO-BIFUNCTIONAL CROSS-LINKERS An exemplary hetero-bifunctional cross-linker contains two reactive groups: one reacting with primary amine group (e.g., N-hydroxy succinimide) and the other reacting with a thiol group (e.g., pyridyl disulfide, maleimides, halogens, etc.). Through the primary amine reactive group, the cross-linker may react with the lysine residue(s) of one protein (e.g., the selected antibody or fragment) and through the thiol reactive group, the cross-linker, already tied up to the first protein, reacts with the cysteine residue (free sulfhydryl group) of the other protein (e.g., the selective agent). It can therefore be seen that a targeted peptide composition will generally have, or be derivatized to have, a functional group available for cross-linking purposes. This requirement is not considered to be limiting in that a wide variety of groups can be used in this manner. For example, primary or secondary amine groups, hydrazide or hydrazine groups, carboxyl alcohol, phosphate, or alkylating groups may be used for binding or cross-linking. For a general overview of linking technology, one may wish to refer to Ghose & Blair (1987). The spacer arm between the two reactive groups of a cross-linkers may have various length and chemical compositions. A longer spacer arm allows a better flexibility of the conjugate components while some particular components in the bridge (e.g., benzene group) may lend extra stability to the reactive group or an increased resistance of the chemical link to the action of various aspects (e.g., disulfide bond resistant to reducing agents). The use of peptide spacers, such as L-Leu-L-Ala-L-Leu-L-Ala, is also contemplated. It is preferred that a cross-linker having reasonable stability in blood will be employed. Numerous types of disulfide-bond containing linkers are known that can be successfully employed to conjugate targeting and therapeutic/preventative agents. Linkers that contain a disulfide bond that is sterically hindered may prove to give greater stability in vivo, preventing release of the targeting peptide prior to reaching the site of action. These linkers are thus one group of linking agents. Another cross-linking reagents for use in immunotoxins is SMPT, which is a bifunctional cross-linker containing a disulfide bond that is "sterically hindered" by an adjacent benzene ring and methyl groups. It is believed that stearic hindrance of the disulfide bond serves a function of protecting the bond from attack by thiolate anions such as glutathione which can be present in tissues and blood, and thereby help in preventing decoupling of the conjugate prior to the delivery of the attached agent to the tumor site. It is contemplated that the SMPT agent may also be used in connection with the bispecific coagulating ligands of this invention. The SMPT cross-linking reagent, as with many other known cross-linking reagents, lends the ability to cross-link functional groups such as the SH of cysteine or primary amines (e.g., the epsilon amino group of lysine). Another possible type of cross-linker includes the hetero-bifunctional photoreactive phenylazides containing a cleavable disulfide bond such as sulfosuccinimidyl-2-(p-azido salicylamido) ethyl- l,3'-dithiopropionate. The N-hydroxy-succinimidyl group reacts with primary amino groups and the phenylazide (upon photolysis) reacts non-selectively with any amino acid residue. In addition to hindered cross-linkers, non-hindered linkers also can be employed in accordance herewith. Other useful cross-linkers, not considered to contain or generate a protected disulfide, include SATA, SPDP and 2-iminothiolane (Wawrzynczak & Thorpe, 1987). The use of such cross-linkers is well understood in the art. Once conjugated, the targeting peptide generally will be purified to separate the conjugate from unconjugated targeting agents or coagulants and from other contaminants. A large a number of purification techniques are available for use in providing conjugates of a sufficient degree of purity to render them clinically useful. Purification methods based upon size separation, such as gel filtration, gel permeation or high performance liquid chromatography, will generally be of most use. Other chromatographic techniques, such as Blue-Sepharose separation, may also be used. In addition to chemical conjugation, a purified IgA protein or peptide may be modified at the protein level. Included within the scope of the invention are IgA protein fragments or other derivatives or analogs that are differentially modified during or after translation, for example by glycosylation, acetylation, phosphorylation, amidation, derivatization by known protecting/blocking groups, and proteolytic cleavage. Any number of chemical modifications may be carried out by known techniques, including but not limited to specific chemical cleavage by cyanogen bromide, trypsin, chymotrypsin, papain, V8 protease, NaBH 4 ; acetylation, formylation, famesylation, oxidation, reduction; metabolic synthesis in the presence of tunicamycin. B. Assays Other aspects of the present invention involve the generation of an complex that comprises a plgR-binding domain and a selected agent, with the intent to target the complex to mucosal epithelium. Such compounds may be tested both in vitro, for plgR binding, and in vivo, for targeting. The various assays for use in determining such changes in function are routine and easily practiced by those of ordinary skill in the art. In vitro assays involve the use of isolated plgR or cells bearing plgR. A convenient way to monitor binding is by use of a detetable label, and assess the binding of the label to the receptor which, for example, may be fixed to a support (column, plate, well, dipstick). Alternatively, a functional read out may be preferred, for example, the ability to affect (kill, promote growth of) a target cells. In vivo assays, such as an MDCK transcytosis system assay, also can be easily conducted (Mostov et al, 1986). In these systems, it again is generally preferred to label the test candidate IgA constructs with a detectable marker and to follow the presence of the marker after administration to the animal, preferably via the route intended in the ultimate therapeutic treatment strategy. As part of this process, one would take samples of body fluids, particularly mucosal epithelial samples, and one would analyze the samples for the presence of the marker associated with the IgA construct. C. Recombinant DNA Techniques Alternatively, recombinant DNA technology may be employed as a way of providing a polypeptide or peptide wherein a nucleotide sequence that encodes a polypeptide or peptide of the invention is inserted into an expression vector, transformed or transfected into an appropriate host cell and cultivated under conditions suitable for expression. While discussion has focused on functionally equivalent polypeptides arising from amino acid changes, it will be appreciated that these changes may be effected by alteration of the encoding DNA, taking into consideration also that the genetic code is degenerate and that two or more codons may encode the same amino acid. A table of amino acids and their codons is presented hereinabove for use in such embodiments, as well as for other uses, such as in the design of probes and primers and the like. As with the synthetic peptides previously discussed, it is contemplated that multimers of plgR-binding domains may be comprised within a peptide, such that the peptide contains more than plgR-binding domain. It is further contemplated that the plgR-binding domains of a peptide may be identical (i.e., homomeric) or not identical (i.e., "heteromeric") to one another. Thus, the multimeric peptides of the present invention can be encoded by nucleic acid sequences. Linkers composed of amino acids may be employed to separate plgR-binding domains from each other or from a selective compound or agent. Such linkers and/or selective agents, if composed of amino acids, may be provided to a cell or organism by providing a nucleic acid sequence encoding them such that the cell can express the encoded amino acid sequences. 1. IgA or Preventative/Therapeutic Compound Polypeptides and Fragments Thereof Aspects of the present invention concern the use of isolated DNA segments and recombinant vectors encoding wild-type, polymorphic, or mutant IgA polypeptides or preventative/therapeutic compound polypeptides, and fragments thereof, and the use of recombinant host cells through the application of DNA technology that express those wild-type, polymorphic or mutant polypeptides. Alternatively, non-IgA peptides or polypeptides may be used in the present invention as a plgR-binding domain. A mutant IgA polypeptide can be a sequence that is not identical to the wild-type sequence, but still retains plgR binding activity. Embodiments of the claimed methods include the use of amino acids from the Cα3 region of IgA, possibly including residues from the region encompassing amino acids 402-410 of IgA. Moreover, the present invention encompasses the use of DNA segments and recombinant vectors encoding residues that mediate plgR binding and that are not derived from IgA. The present invention encompasses recombinant DNA techniques to produce a plgR-binding domain by itself or in combination with other IgA regions, or other antibodies, or with other selective agents. A number of these techniques are well known to those of skill in the art. a. Amplification and PCR The plgR-binding domain or other regions may be produced using recombinant DNA techniques such as nucleic acid amplification methods. Nucleic acid used as a template for amplification of IgA sequences is isolated from cells contained in the biological sample, according to standard methodologies (Sambrook et al, 1989). The nucleic acid may be genomic DNA or fractionated or whole cell RNA. Where RNA is used, it may be desired to convert the RNA to a complementary DNA. In one embodiment, the RNA is whole cell RNA and is used directly as the template for amplification. A number of template dependent processes are available to amplify the marker sequences present in a given template sample. One of the best known amplification methods is the polymerase chain reaction (referred to as PCR) which is described in detail in U.S. Patent Nos. 4,683,195, 4,683,202 and 4,800,159, and each incorporated herein by reference in entirety. A reverse transcriptase PCR amplification procedure may be performed in order to quantify the amount of mRNA amplified. Methods of reverse transcribing RNA into cDNA are well known and described in Sambrook et al, 1989. Alternative methods for reverse transcription utilize thermostable, RNA-dependent DNA polymerases. These methods are described in WO 90/07641, filed December 21, 1990, incorporated herein by reference. Polymerase chain reaction methodologies are well known in the art. Another method for amplification is the ligase chain reaction ("LCR"), disclosed in EPA No. 320 308, incorporated herein by reference in its entirety. U.S. Patent 4,883,750 describes a method similar to LCR for binding probe pairs to a target sequence. An isothermal amplification method, in which restriction endonucleases and ligases are used to achieve the amplification of target molecules that contain nucleotide 5'-[alpha-thio]-triphosphates in one strand of a restriction site may also be useful in the amplification of nucleic acids in the present invention. Strand Displacement Amplification (SDA) is another method of carrying out isothermal amplification of nucleic acids which involves multiple rounds of strand displacement and synthesis, i.e., nick translation. A similar method, called Repair Chain Reaction (RCR), involves annealing several probes throughout a region targeted for amplification, followed by a repair reaction in which only two of the four bases are present. The other two bases can be added as biotinylated derivatives for easy detection. A similar approach is used in SDA. Target specific sequences can also be detected using a cyclic probe reaction (CPR). In CPR, a probe having 3' and 5' sequences of non-specific DNA and a middle sequence of specific RNA is hybridized to DNA that is present in a sample. Upon hybridization, the reaction is treated with RNase H, and the products of the probe identified as distinctive products that are released after digestion. The original template is annealed to another cycling probe and the reaction is repeated. Other nucleic acid amplification procedures include transcription-based amplification systems (TAS), including nucleic acid sequence based amplification (NASBA) and 3SR Gingeras et al, PCT Application WO 88/10315, incorporated herein by reference. Davey et al, EPA No. 329 822 (incorporated herein by reference in its entirety) disclose a nucleic acid amplification process involving cyclically synthesizing single-stranded RNA ("ssRNA"), ssDNA, and double-stranded DNA (dsDNA), which may be used in accordance with the present invention. Miller et al, PCT Application WO 89/06700 (incorporated herein by reference in its entirety) disclose a nucleic acid sequence amplification scheme based on the hybridization of a promoter/primer sequence to a target single-stranded DNA ("ssDNA") followed by transcription of many RNA copies of the sequence. This scheme is not cyclic, i.e., new templates are not produced from the resultant RNA transcripts. Other amplification methods include "RACE" and "one-sided PCR" (Frohman, M.A., In: PCR PROTOCOLS: A GUIDE TO METHODS AND APPLICATIONS, Academic Press, N.Y., 1990 incorporated by reference). b. Recombinant DNA cloning The present invention also concerns DNA segments, isolatable from mammalian and human cells, that are free from total genomic DNA and that are capable of expressing a protein or polypeptide that binds to plgR, including one that is derived from IgA, particularly the Cα3 domain. As used herein, the term "DNA segment" refers to a DNA molecule that has been isolated free of total genomic DNA of a particular species. Therefore, a DNA segment encoding an IgA polypeptide refers to a DNA segment that contains wild-type, polymorphic, or mutant IgA polypeptide coding sequences yet is isolated away from, or purified free from, total mammalian or human genomic DNA. Included within the term "DNA segment," are DNA segments and smaller fragments of such segments, and also recombinant vectors, including, for example, plasmids, cosmids, phage, viruses, and the like. Similarly, a DNA segment comprising an isolated or purified wild-type, polymorphic, or mutant IgA polypeptide gene or plgR-binding domain refers to a DNA segment including wild-type, polymorphic, or mutant IgA polypeptide or plgR- binding domain coding sequences and, in certain aspects, regulatory sequences, isolated substantially away from other naturally occurring genes or protein encoding sequences. In this respect, the term "gene" is used for simplicity to refer to a functional protein, polypeptide, or peptide-encoding unit. As will be understood by those in the art, this functional term includes genomic sequences, cDNA sequences, and smaller engineered gene segments that express, or may be adapted to express, proteins, polypeptides, domains, peptides, fusion proteins, and mutants. "Isolated substantially away from other coding sequences" means that the gene of interest, in this case the wild-type, polymorphic, or mutant IgA polypeptide gene, forms the significant part of the coding region of the DNA segment, and that the DNA segment does not contain large portions of naturally-occurring coding DNA, such as large chromosomal fragments or other functional genes or cDNA coding regions. Of course, this refers to the DNA segment as originally isolated, and does not exclude genes or coding regions later added to the segment by human manipulation. In particular embodiments, the invention concerns isolated DNA segments and recombinant vectors incorporating DNA sequences that encode a wild-type, polymorphic, or mutant IgA polypeptide or peptide that includes within its amino acid sequence a contiguous amino acid sequence in accordance with, or essentially corresponding to wild-type, polymorphic, or mutant IgA polypeptides. In other embodiments, the invention concerns isolated DNA segments and recombinant vectors incorporating DNA sequences that encode a IgA polypeptide or peptide that includes within its amino acid sequence a contiguous amino acid sequence in accordance with, or essentially corresponding to IgA's plgR-binding domain. The term "biologically functional equivalent" is well understood in the art and is further defined in detail herein. Accordingly, sequences that have between about 70% and about 80%; or more preferably, between about 81% and about 90%; or even more preferably, between about 91% and about 99%; of amino acids that are identical or functionally equivalent to the amino acids of IgA polypeptide sequences provided the targeting activity of the protein is maintained. The term "functionally equivalent codon" is used herein to refer to codons that encode the same amino acid, such as the six codons for arginine or serine, and also refers to codons that encode biologically equivalent amino acids (see Table 2, below). TABLE 2 CODON TABLE Amino Acids Codons Alanine Ala A GCA GCC GCG GCU Cysteine Cys C UGC UGU Aspartic acid Asp D GAC GAU Glutamic acid Glu E GAA GAG Phenylalanine Phe F UUC uuu Glycine Gly G GGA GGC GGG GGU Histidine His H CAC CAU Isoleucine He I AUA AUC AUU Lysine Lys K AAA AAG Leucine Leu L UUA UUG CUA CUC CUG CUU Methionine Met M AUG Asparagine Asn N AAC AAU Proline Pro P CCA CCC CCG CCU Glutamine Gin Q CAA CAG Arginine Arg R AGA AGG CGA CGC CGG CGU Serine Ser S AGC AGU UCA UCC UCG UCU Threonine Thr T ACA ACC ACG ACU Valine Val V GUA GUC GUG GUU Tryptophan Trp w UGG Tyrosine Tyr Y UAC UAU It will also be understood that amino acid and nucleic acid sequences may include additional residues, such as additional N- or C-terminal amino acids or 5' or 3' sequences, and yet still be essentially as set forth in one of the sequences disclosed herein, so long as the sequence meets the criteria set forth above, including the maintenance of biological protein activity where protein expression is concerned. The addition of terminal sequences particularly applies to nucleic acid sequences that may, for example, include various non-coding sequences flanking either of the 5' or 3' portions of the coding region or may include various internal sequences, i.e., introns, which are known to occur within genes. The nucleic acid segments used in the present invention, regardless of the length of the coding sequence itself, may be combined with other DNA sequences, such as promoters, polyadenylation signals, additional restriction enzyme sites, multiple cloning sites, other coding segments, and the like, such that their overall length may vary considerably. It is therefore contemplated that a nucleic acid fragment of almost any length may be employed, with the total length preferably being limited by the ease of preparation and use in the intended recombinant DNA protocol. The DNA segments used in the present invention encompass biologically functional equivalent IgA proteins and peptides. Such sequences may arise as a consequence of codon redundancy and functional equivalency that are known to occur naturally within nucleic acid sequences and the proteins thus encoded. Alternatively, functionally equivalent proteins or peptides may be created via the application of recombinant DNA technology, in which changes in the protein structure may be engineered, based on considerations of the properties of the amino acids being exchanged. Changes designed by man may be introduced through the application of site-directed mutagenesis techniques, e.g., to introduce improvements to the antigenicity of the protein or to test mutants in order to examine DNA binding activity at the molecular level. Encompassed by the invention are DNA segments encoding relatively small peptides, such as, for example, peptides of from about 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or up to about 100 amino acids in length; and also larger polypeptides up to and including proteins corresponding to the full-length sequences of the IgA polypeptide. 2. Recombinant Fusion Proteins The plgR targeted compositions of the invention may also be fusion proteins prepared by molecular biological techniques, whereby a plgR-binding domain, such as Cα3 domain from IgA including the plgR targeting motif, is fused with a preventative or therapeutic compound. Alternatively, it is contemplated that a plgR- binding domain can be expressed in the context of a non-IgA antibody, such as IgG or IgGM, to target that antibody to the mucosal epithelia. Furthermore, it is contemplated that multiple plgR-binding domains may be contained on a single molecule, such as dimers and trimers of plgR-binding domains. The use of recombinant DNA techniques to achieve such ends is now standard practice to those of skill in the art. These methods include, for example, in vitro recombinant DNA techniques, synthetic techniques and in vivo recombination/genetic recombination. DNA and RNA synthesis may, additionally, be performed using an automated synthesizers (see, for example, the techniques described in Sambrook et al, 1989; and Ausubel et al, 1989). The preparation of such a fusion protein generally entails the preparation of a first and second DNA coding region and the functional ligation or joining of said regions, in frame, to prepare a single coding region that encodes the desired fusion protein. In the present context, the plgR-binding domain DNA sequence will generally be joined in frame with a DNA sequence encoding a preventative or therapeutic compund and/or inert protein carrier, immunoglobulin, Fc region, or such like. The invention encompasses constructs where either the IgA portion of the fusion protein or the non-IgA portion is prepared as the N-terminal region or as the C- terminal region. Once the coding region desired has been produced, an expression vector is created. Expression vectors contain one or more promoters upstream of the inserted DNA regions that act to promote transcription of the DNA and to thus promote expression of the encoded recombinant protein. This is the meaning of "recombinant expression" and has been discussed elsewhere in the specification. In addition to the many known vectors that are commercially available, other useful vectors include pIN vectors (Inouye et al, 1985); and pGEX vectors, for use in generating glutathione S-transferase (GST) soluble fusion proteins for later purification and separation or cleavage. Other suitable fusion proteins are those with β-galactosidase, ubiquitin, hexahistidine, or the like. 3. Vectors for Cloning, Gene Transfer, and Expression Within certain embodiments, expression vectors are employed to express the plgR-binding domain polypeptide product, which can then be purified and, for example, be used to vaccinate animals to generate antisera or monoclonal antibody with which further studies may be conducted. In other embodiments, the expression vectors are used to express a protein of interest in mucosal epithelia. In either case, expression requires that appropriate signals be provided in the vectors, and which include various regulatory elements, such as enhancers/promoters from both viral and mammalian sources that drive expression of the genes of interest in host cells. Elements designed to optimize messenger RNA stability and translatability in host cells also are defined. The conditions for the use of a number of dominant drug selection markers for establishing permanent, stable cell clones expressing the products also are provided, as is an element that links expression of the drug selection markers to expression of the polypeptide. The construction and use of expression vectors and plasmids is well known to those of skill in the art. Virtually any mammalian cell expression vector may thus be used connection with the humanized genes disclosed herein. Preferred vectors and plasmids will be constructed with at least one multiple cloning site. In certain embodiments, the expression vector will comprise a multiple cloning site that is operatively positioned between a promoter and sequences from IgA. Such vectors may be used, in addition to their uses in other embodiments, to create N-terminal fusion proteins by cloning a second protein-encoding DNA segment into the multiple cloning site so that it is contiguous and in-frame with the plgR-binding domain sequence, including the plgR-binding domain sequence from IgA. In other embodiments, expression vectors may comprise a multiple cloning site that is operatively positioned downstream from expressible IgA nucleic acid sequences. These vectors are useful, in addition to their uses, in creating C-terminal fusion proteins by cloning a second protein-encoding DNA segment into the multiple cloning site so that it is contiguous and in-frame with the IgA sequence. Vectors and plasmids in which a second protein- or RNA-encoding nucleic acid segment is also present are, of course, also encompassed by the invention, irrespective of the nature of the nucleic acid segment itself. A second reporter gene may be included within an expression vector of the present invention. The second reporter gene may be comprised within a second transcriptional unit. Suitable second reporter genes include those that confer resistance to agents such as neomycin, hygromycin, puromycin, zeocin, mycophenolic acid, histidinol and methotrexate. Expression vectors may also contain other nucleic acid sequences, such as IRES elements, polyadenylation signals, splice donor/splice acceptor signals, and the like. a. Viral vectors The methods and compositions described herein include multigene adenoviral constructs; the methods and compositions described may be applicable to the construction of multigene constructs using other viral vectors including but not limited to retroviruses, herpes viruses, adeno-associated viruses, vaccinia viruses. The discussion below provides details regarding the characteristics of each of these viruses in relation to their application in therapeutic compositions. i) Adenovirus One of the preferred methods for in vivo delivery involves the use of an adenovirus expression vector. "Adenovirus expression vector" is meant to include those constructs containing adenovirus sequences sufficient to (a) support packaging of the construct and (b) to express an antisense polynucleotide, a protein, a polynucleotide (e.g., ribozyme, or an mRNA) that has been cloned therein. In this context, expression does not require that the gene product be synthesized. The expression vector comprises a genetically engineered form of adenovirus. Knowledge of the genetic organization of adenovirus, a 36 kb, linear, double-stranded DNA virus, allows substitution of large pieces of adenoviral DNA with foreign sequences up to 7 kb (Grunhaus and Horwitz, 1992). In contrast to retroviruses, the adenoviral infection of host cells does not result in chromosomal integration because adenoviral DNA can replicate in an episomal manner without potential genotoxicity. As used herein, the term "genotoxicity" refers to permanent inheritable host cell genetic alteration. Also, adenoviruses are structurally stable, and no genome rearrangement has been detected after extensive amplification of normal derivatives. Adenovirus can infect virtually all epithelial cells regardless of their cell cycle stage. Adenovirus is particularly suitable for use as a gene transfer vector because of its mid-sized genome, ease of manipulation, high titer, wide target cell range and high infectivity. Both ends of the viral genome contain 100-200 base pair inverted repeats (ITRs), which are cis elements necessary for viral DNA replication and packaging. The early (E) and late (L) regions of the genome contain different transcription units that are divided by the onset of viral DNA replication. The El region (El A and EIB) encodes proteins responsible for the regulation of transcription of the viral genome and a few cellular genes. The expression of the E2 region (E2A and E2B) results in the synthesis of the proteins for viral DNA replication. These proteins are involved in DNA replication, late gene expression and host cell shut-off (Renan, 1990). The products of the late genes, including the majority of the viral capsid proteins, are expressed only after significant processing of a single primary transcript issued by the major late promoter (MLP). The MLP, (located at 16.8 m.u.) is particularly efficient during the late phase of infection, and all the mRNA's issued from this promoter possess a 5'-tripartite leader (TPL) sequence which makes them preferred mRNA's for translation. The E3 region encodes proteins that appears to be necessary for efficient lysis of Ad infected cells as well as preventing TNF -mediated cytolysis and CTL mediated lysis of infected cells. In general, the E4 region encodes is believed to encode seven proteins, some of which activate the E2 promoter. It has been shown to block host mRNA transport and enhance transport of viral RNA to cytoplasm. Further the E4 product is in part responsible for the decrease in early gene expression seen late in infection. E4 also inhibits El A and E4 (but not EIB) expression during lytic growth. Some E4 proteins are necessary for efficient DNA replication however the mechanism for this involvement is unknown. E4 is also involved in post-transcriptional events in viral late gene expression; i.e., alternative splicing of the tripartite leader in lytic growth. Nevertheless, E4 functions are not absolutely required for DNA replication but their lack will delay replication. Other functions include negative regulation of viral DNA synthesis, induction of sub-nuclear reorganization normally seen during adenovirus infection, and other functions that are necessary for viral replication, late viral mRNA accumulation, and host cell transcriptional shut off. In a current system, recombinant adenovirus is generated from homologous recombination between shuttle vector and provirus vector. Possible recombination between the proviral vector and Ad sequences in 293 cells, or in the case of pJM17 plasmid spontaneous deletion of the inserted pBR322 sequences, may generate full length wild-type Ad5 adenovirus. Therefore, it is critical to isolate a single clone of virus from an individual plaque and examine its genomic structure. Generation and propagation of the current adenovirus vectors, which are replication deficient, depend on a unique helper cell line, designated 293, which was transformed from human embryonic kidney cells by Ad5 DNA fragments and constitutively expresses El proteins (Graham et al, 1977). Since the E3 region is dispensable from the adenovirus genome (Jones and Shenk, 1978), the current adenovirus vectors, with the help of 293 cells, carry foreign DNA in either the El, the E3 or both regions (Graham and Prevec, 1991). In nature, adenovirus can package approximately 105% of the wild-type genome (Ghosh-Choudhury et al, 1987), providing capacity for about 2 extra kb of DNA. Combined with the approximately 5.5 kb of DNA that is replaceable in the El and E3 regions, the maximum capacity of the current adenovirus vector is under 7.5 kb, or about 15% of the total length of the vector. Helper cell lines may be derived from human cells such as human embryonic kidney cells, muscle cells, hematopoietic cells or other human embryonic mesenchymal or epithelial cells. Alternatively, the helper cells may be derived from the cells of other mammalian species that are permissive for human adenovirus. Such cells include, e.g., Vero cells or other monkey embryonic mesenchymal or epithelial cells. As stated above, the preferred helper cell line is 293. Recently, Racher et al. (1995) disclosed improved methods for culturing 293 cells and propagating adenovirus. In one format, natural cell aggregates are grown by inoculating individual cells into 1 liter siliconized spinner flasks (Techne, Cambridge, UK) containing 100-200 ml of medium. Following stirring at 40 rpm, the cell viability is estimated with trypan blue. In another format, Fibra-Cel microcarriers (Bibby Sterlin, Stone, UK) (5 g/1) is employed as follows. A cell inoculum, resuspended in 5 ml of medium, is added to the carrier (50 ml) in a 250 ml Erlenmeyer flask and left stationary, with occasional agitation, for 1 to 4 h. The medium is then replaced with 50 ml of fresh medium and shaking is initiated. For virus production, cells are allowed to grow to about 80% confluence, after which time the medium is replaced (to 25% of the final volume) and adenovirus added at an MOI of 0.05. Cultures are left stationary overnight, following which the volume is increased to 100% and shaking commenced for another 72 h. Other than the requirement that the adenovirus vector be replication defective, or at least conditionally defective, the nature of the adenovirus vector is not believed to be crucial to the successful practice of the invention. The adenovirus may be of any of the 42 different known serotypes or subgroups A-F. Adenovirus type 5 of subgroup C is the preferred starting material in order to obtain the conditional replication-defective adenovirus vector for use in the present invention. This is because Adenovirus type 5 is a human adenovirus about which a great deal of biochemical, medical and genetic information is known, and it has historically been used for most constructions employing adenovirus as a vector. As stated above, the typical vector according to the present invention is replication defective and will not have an adenovirus El region. Thus, it will be most convenient to introduce the polynucleotide encoding the gene of interest at the position from which the El -coding sequences have been removed. However, the position of insertion of the construct within the adenovirus sequences is not critical to the invention. The polynucleotide encoding the gene of interest may also be inserted in lieu of the deleted E3 region in E3 replacement vectors as described by Karlsson et al. (1986), or in the E4 region where a helper cell line or helper virus complements the E4 defect. Adenovirus is easy to grow and manipulate and exhibits broad host range in vitro and in vivo. This group of viruses can be obtained in high titers, e.g., 10 9 -10" plaque-forming units per ml, and they are highly infective. The life cycle of adenovirus does not require integration into the host cell genome. The foreign genes delivered by adenovirus vectors are episomal and, therefore, have low genotoxicity to host cells. No side effects have been reported in studies of vaccination with wild-type adenovirus (Couch et al, 1963; Top et al, 1971), demonstrating their safety and therapeutic potential as in vivo gene transfer vectors. Adenovirus vectors have been used in eukaryotic gene expression investigations (Levrero et al, 1991 ; Gomez-Foix et al, 1992) and vaccine development (Grunhaus and Horwitz, 1992; Graham and Prevec, 1992). Recently, animal studies suggested that recombinant adenovirus could be used for gene therapy (Stratford-Perricaudet and Perricaudet, 1991; Stratford-Perricaudet et al, 1990; Rich et al, 1993). Studies in administering recombinant adenovirus to different tissues include trachea instillation (Rosenfeld et al, 1991; Rosenfeld et al, 1992), muscle injection (Ragot et al, 1993), peripheral intravenous injections (Herz and Gerard, 1993), intranasal inoculation (Ginsberg et al, 1991), aerosol administration to lung (Bellon, 1996) intra-peritoneal administration (Song et al, 1997), Intra-pleural injection (Elshami et al, 1996) administration to the bladder using intra- vesicular administration (Werthman, et al, 1996), Subcutaneous injection including intraperitoneal, intrapleural, intramuscular or subcutaneously) (Ogawa, 1989) ventricular injection into myocardium (heart, French et al, 1994), liver perfusion (hepatic artery or portal vein, Shiraishi et al, 1997) and stereotactic inoculation into the brain (Le Gal La Salle et al, 1993). ii) Retrovirus The retroviruses are a group of single-stranded RNA viruses characterized by an ability to convert their RNA to double-stranded DNA in infected cells by a process of reverse-transcription (Coffin, 1990). The resulting DNA then stably integrates into cellular chromosomes as a provirus and directs synthesis of viral proteins. The integration results in the retention of the viral gene sequences in the recipient cell and its descendants. The retroviral genome contains three genes, gag, pol, and env that code for capsid proteins, polymerase enzyme, and envelope components, respectively. A sequence found upstream from the gag gene contains a signal for packaging of the genome into virions. Two long terminal repeat (LTR) sequences are present at the 5' and 3' ends of the viral genome. These contain strong promoter and enhancer sequences and are also required for integration in the host cell genome (Coffin, 1990). In order to construct a retroviral vector, a nucleic acid encoding a gene of interest is inserted into the viral genome in the place of certain viral sequences to produce a virus that is replication-defective. In order to produce virions, a packaging cell line containing the gag, pol, and env genes but without the LTR and packaging components is constructed (Mann et al, 1983). When a recombinant plasmid containing a cDNA, together with the retroviral LTR and packaging sequences is introduced into this cell line (by calcium phosphate precipitation for example), the packaging sequence allows the RNA transcript of the recombinant plasmid to be packaged into viral particles, which are then secreted into the culture media (Nicolas and Rubenstein, 1988; Temin, 1986; Mann et al, 1983). The media containing the recombinant retroviruses is then collected, optionally concentrated, and used for gene transfer. Retroviral vectors are able to infect a broad variety of cell types. However, integration and stable expression require the division of host cells (Paskind et al, 1975). A novel approach designed to allow specific targeting of retrovirus vectors was recently developed based on the chemical modification of a retrovirus by the chemical addition of lactose residues to the viral envelope. This modification could permit the specific infection of hepatocytes via sialoglycoprotein receptors. A different approach to targeting of recombinant retroviruses was designed in which biotinylated antibodies against a retroviral envelope protein and against a specific cell receptor were used. The antibodies were coupled via the biotin components by using streptavidin (Roux et al, 1989). Using antibodies against major histocompatibility complex class I and class II antigens, they demonstrated the infection of a variety of human cells that bore those surface antigens with an ecotropic virus in vitro (Roux et al, 1989). There are certain limitations to the use of retrovirus vectors in all aspects of the present invention. For example, retrovirus vectors usually integrate into random sites in the cell genome. This can lead to insertional mutagenesis through the interruption of host genes or through the insertion of viral regulatory sequences that can interfere with the function of flanking genes (Varmus et al, 1981). Another concern with the use of defective retrovirus vectors is the potential appearance of wild-type replication-competent virus in the packaging cells. This can result from recombination events in which the intact- sequence from the recombinant virus inserts upstream from the gag, pol, env sequence integrated in the host cell genome. However, new packaging cell lines are now available that should greatly decrease the likelihood of recombination (Markowitz et al, 1988; Hersdorffer et al, 1990). iii) Herpesvirus Because herpes simplex virus (HSV) is neurotropic, it has generated considerable interest in treating nervous system disorders. Moreover, the ability of HSV to establish latent infections in non-dividing neuronal cells without integrating in to the host cell chromosome or otherwise altering the host cell's metabolism, along with the existence of a promoter that is active during latency makes HSV an attractive vector. And though much attention has focused on the neurotropic applications of HSV, this vector also can be exploited for other tissues given its wide host range. Another factor that makes HSV an attractive vector is the size and organization of the genome. Because HSV is large, incorporation of multiple genes or expression cassettes is less problematic than in other smaller viral systems. In addition, the availability of different viral control sequences with varying performance (temporal, strength, etc.) makes it possible to control expression to a greater extent than in other systems. It also is an advantage that the virus has relatively few spliced messages, further easing genetic manipulations. HSV also is relatively easy to manipulate and can be grown to high titers. Thus, delivery is less of a problem, both in terms of volumes needed to attain sufficient MOI and in a lessened need for repeat dosings. For a review of HSV as a gene therapy vector, see Glorioso et al. (1995). HSV, designated with subtypes 1 and 2, are enveloped viruses that are among the most common infectious agents encountered by humans, infecting millions of human subjects worldwide. The large, complex, double-stranded DNA genome encodes for dozens of different gene products, some of which derive from spliced transcripts. In addition to virion and envelope structural components, the virus encodes numerous Other proteins including a protease, a ribonucleotides reductase, a DNA polymerase, a ssDNA binding protein, a helicase/primase, a DNA dependent ATPase, a dUTPase and others. HSV genes form several groups whose expression is coordinately regulated and sequentially ordered in a cascade fashion (Honess and Roizman, 1974; Honess and Roizman 1975; Roizman and Sears, 1995). The expression of genes, the first set of genes to be expressed after infection, is enhanced by the virion protein number 16, or α-transinducing factor (Post et al, 1981 ; Batterson and Roizman, 1983; Campbell, et al, 1983). The expression of β genes requires functional α gene products, most notably ICP4, which is encoded by the α4 gene (DeLuca et al, 1985). γ genes, a heterogeneous group of genes encoding largely virion structural proteins, require the onset of viral DNA synthesis for optimal expression (Holland et al, 1980). In line with the complexity of the genome, the life cycle of HSV is quite involved. In addition to the lytic cycle, which results in synthesis of virus particles and, eventually, cell death, the virus has the capability to enter a latent state in which the genome is maintained in neural ganglia until some as of yet undefined signal triggers a recurrence of the lytic cycle. Avirulent variants of HSV have been developed and are readily available for use in gene therapy contexts (U.S. Patent No. 5,672,344). iv) Adeno-Associated Virus Recently, adeno-associated virus (AAV) has emerged as a potential alternative to the more commonly used retroviral and adenoviral vectors. While studies with retroviral and adenoviral mediated gene transfer raise concerns over potential oncogenic properties of the former, and immunogenic problems associated with the latter, AAV has not been associated with any such pathological indications. In addition, AAV possesses several unique features that make it more desirable than the other vectors. Unlike retroviruses, AAV can infect non-dividing cells; wild-type AAV has been characterized by integration, in a site-specific manner, into chromosome 19 of human cells (Kotin and Berns, 1989; Kotin et al, 1990; Kotin et al, 1991; Samulski et al, 1991); and AAV also possesses anti-oncogenic properties (Ostrove et al, 1981; Berns and Giraud, 1996). Recombinant AAV genomes are constructed by molecularly cloning DNA sequences of interest between the AAV ITRs, eliminating the entire coding sequences of the wild-type AAV genome. The AAV vectors thus produced lack any of the coding sequences of wild-type AAV, yet retain the property of stable chromosomal integration and expression of the recombinant genes upon transduction both in vitro and in vivo (Berns, 1990; Berns and Bohensky, 1987; Bertran et al, 1996; Kearns et al, 1996; Ponnazhagan et al, 1997a). Until recently, AAV was believed to infect almost all cell types, and even cross species barriers. However, it now has been determined that AAV infection is receptor-mediated (Ponnazhagan et al, 1996; Mizukami et al, 1996). AAV utilizes a linear, single-stranded DNA of about 4700 base pairs. Inverted terminal repeats flank the genome. Two genes are present within the genome, giving rise to a number of distinct gene products. The first, the cap gene, produces three different virion proteins (VP), designated VP-1, VP-2 and VP-3. The second, the rep gene, encodes four non-structural proteins (NS). One or more of these rep gene products is responsible for transactivating AAV transcription. The sequence of AAV is provided by Srivastava et al, (1983) and in U.S. Patent 5,252,479 (entire text of which is specifically incorporated herein by reference). The three promoters in AAV are designated by their location, in map units, in the genome. These are, from left to right, p5, pi 9 and p40. Transcription gives rise to six transcripts, two initiated at each of three promoters, with one of each pair being spliced. The splice site, derived from map units 42-46, is the same for each transcript. The four non-structural proteins apparently are derived from the longer of the transcripts, and three virion proteins all arise from the smallest transcript. AAV is not associated with any pathologic state in humans. Interestingly, for efficient replication, AAV requires "helping" functions from viruses such as herpes simplex virus I and II, cytomegalovirus, pseudorabies virus and, of course, adenovirus. The best characterized of the helpers is adenovirus, and many "early" functions for this virus have been shown to assist with AAV replication. Low level expression of AAV rep proteins is believed to hold AAV structural expression in check, and helper virus infection is thought to remove this block. v) Vaccinia Virus Vaccinia virus vectors have been used extensively because of the ease of their construction, relatively high levels of expression obtained, wide host range and large capacity for carrying DNA. Vaccinia contains a linear, double-stranded DNA genome of about 186 kb that exhibits a marked "A-T" preference. Inverted terminal repeats of about 10.5 kb flank the genome. The majority of essential genes appear to map within the central region, which is most highly conserved among poxviruses. Estimated open reading frames in vaccinia virus number from 150 to 200. Although both strands are coding, extensive overlap of reading frames is not common. At least 25 kb can be inserted into the vaccinia virus genome (Smith and Moss, 1983). Prototypical vaccinia vectors contain transgenes inserted into the viral thymidine kinase gene via homologous recombination. Vectors are selected on the basis of a tk-phenotype. Inclusion of the untranslated leader sequence of encephalomyocarditis virus, the level of expression is higher than that of conventional vectors, with the transgenes accumulating at 10% or more of the infected cell's protein in 24 h (Elroy-Stein et al, 1989). b. Non-viral transfer Several non-viral methods for the transfer of expression constructs into cultured mammalian cells also are contemplated by the present invention. These include calcium phosphate precipitation (Graham and Van Der Eb. 1973; Chen and Okayama, 1987; Rippe et al, 1990) DEAE-dextran (Gopal, 1985), electroporation (Tur-Kaspa et al, 1986; Potter et al, 1984), direct microinjection (Harland and Weintraub, 1985), DNA-loaded liposomes (Nicolau and Sene, 1982; Fraley et al, 1979), cell sonication (Fechheimer et al, 1987), gene bombardment using high velocity microprojectiles (Yang et al, 1990), and receptor-mediated transfection (Wu and Wu, 1987; Wu and Wu, 1988). For therapeutic endeavors, once the construct has been delivered into the cell, the gene may be positioned and expressed at different sites. In certain embodiments, the nucleic acid encoding the therapeutic gene may be stably integrated into the genome of the cell. This integration may be in the cognate location and orientation via homologous recombination (gene replacement) or it may be integrated in a random, non-specific location (gene augmentation). In yet further embodiments, the nucleic acid may be stably maintained in the cell as a separate, episomal segment of DNA. Such nucleic acid segments or "episomes" encode sequences sufficient to permit maintenance and replication independent of or in synchronization with the host cell cycle. How the expression construct is delivered to a cell and where in the cell the nucleic acid remains is dependent on the type of expression construct employed. In a particular embodiment of the invention, the expression construct may be entrapped in a liposome. Liposomes are vesicular structures characterized by a phospholipid bilayer membrane and an inner aqueous medium. Multilamellar liposomes have multiple lipid layers separated by aqueous medium. They form spontaneously when phospholipids are suspended in an excess of aqueous solution. The lipid components undergo self-rearrangement before the formation of closed structures and entrap water and dissolved solutes between the lipid bilayers (Ghosh and Bachhawat, 1991). The addition of DNA to cationic liposomes causes a topological transition from liposomes to optically birefringent liquid-crystalline condensed globules (Radler et al, 1997). These DNA-lipid complexes are potential non- viral vectors for use in gene therapy. Liposome-mediated nucleic acid delivery and expression of foreign DNA in vitro has been very successful. Using the β-lactamase gene, Wong et al. (1980) demonstrated the feasibility of liposome-mediated delivery and expression of foreign DNA in cultured chick embryo, HeLa, and hepatoma cells. Nicolau et al. (1987) accomplished successful liposome-mediated gene transfer in rats after intravenous injection. Also included are various commercial approaches involving "lipofection" technology. In certain embodiments of the invention, the liposome may be complexed with a hemagglutinating virus (HVJ). This has been shown to facilitate fusion with the cell membrane and promote cell entry of liposome-encapsulated DNA (Kaneda et al, 1989). In other embodiments, the liposome may be complexed or employed in conjunction with nuclear nonhistone chromosomal proteins (HMG-1) (Kato et al, 1991). In yet further embodiments, the liposome may be complexed or employed in conjunction with both HVJ and HMG-1. In that such expression constructs have been successfully employed in transfer and expression of nucleic acid in vitro and in vivo, then they are applicable for the present invention. Other vector delivery systems that can be employed to deliver a nucleic acid encoding a therapeutic gene into cells are receptor-mediated delivery vehicles. These take advantage of the selective uptake of macromolecules by receptor-mediated endocytosis in almost all eukaryotic cells. Because of the cell type-specific distribution of various receptors, the delivery can be highly specific (Wu and Wu, 1993). In another embodiment of the invention, the expression construct may simply consist of naked recombinant DNA or plasmids. Transfer of the construct may be performed by any of the methods mentioned above which physically or chemically permeabilize the cell membrane. This is applicable particularly for transfer in vitro, however, it may be applied for in vivo use as well. Dubensky et al. (1984) successfully injected polyomavirus DNA in the form of CaPO 4 precipitates into liver and spleen of adult and newborn mice demonstrating active viral replication and acute infection. Benvenisty and Neshif (1986) also demonstrated that direct intraperitoneal injection of CaPO 4 precipitated plasmids results in expression of the transfected genes. 4. Regulatory Elements The recombinant DNA techniques encompassed by the present invention to prepare and produce plgR-targeted compositions including compositions comprising IgA sequences may utilize recombinant vectors or expression constructs containing regulatory elements. These regulatory elements can include promoters (tissue- specific, non-tissue-specific, and inducible) and enhancers, polyadenylation sequences, and internal ribosomal entry sites (IRES). a. Promoters Throughout this application, the term "expression construct" is meant to include any type of genetic construct containing a nucleic acid coding for gene products in which part or all of the nucleic acid encoding sequence is capable of being transcribed. The transcript may be translated into a protein, but it need not be. In certain embodiments, expression includes both transcription of a gene and translation of mRNA into a gene product. In other embodiments, expression only includes transcription of the nucleic acid encoding genes of interest. The nucleic acid encoding a gene product is under transcriptional control of a promoter. A "promoter" refers to a DNA sequence recognized by the synthetic machinery of the cell, or introduced synthetic machinery, required to initiate the specific transcription of a gene. The phrase "under transcriptional control" means that the promoter is in the correct location and orientation in relation to the nucleic acid to control RNA polymerase initiation and expression of the gene. The term promoter will be used here to refer to a group of transcriptional control modules that are clustered around the initiation site for RNA polymerase II. Much of the thinking about how promoters are organized derives from analyses of several viral promoters, including those for the HSV thymidine kinase (tk) and SV40 early transcription units. These studies, augmented by more recent work, have shown that promoters are composed of discrete functional modules, each consisting of approximately 7-20 bp of DNA, and containing one or more recognition sites for transcriptional activator or repressor proteins. At least one module in each promoter functions to position the start site for RNA synthesis. The best known example of this is the TATA box, but in some promoters lacking a TATA box, such as the promoter for the mammalian terminal deoxynucleotidyl transferase gene and the promoter for the SV40 late genes, a discrete element overlying the start site itself helps to fix the place of initiation. Additional promoter elements regulate the frequency of transcriptional initiation. Typically, these are located in the region 30-110 bp upstream of the start site, although a number of promoters have recently been shown to contain functional elements downstream of the start site as well. The spacing between promoter elements frequently is flexible, so that promoter function is preserved when elements are inverted or moved relative to one another. In the tk promoter, the spacing between promoter elements can be increased to 50 bp apart before activity begins to decline. Depending on the promoter, it appears that individual elements can function either cooperatively or independently to activate transcription. The particular promoter employed to control the expression of a nucleic acid sequence of interest is not believed to be important, so long as it is capable of directing the expression of the nucleic acid in the targeted cell. Thus, where a human cell is targeted, it is preferable to position the nucleic acid coding region adjacent to and under the control of a promoter that is capable of being expressed in a human cell. Generally speaking, such a promoter might include either a human or viral promoter. In various embodiments, the human cytomegalovirus (CMV) immediate early gene promoter, the SV40 early promoter, the Rous sarcoma virus long terminal repeat, β-actin, rat insulin promoter and glyceraldehyde-3 -phosphate dehydrogenase can be used to obtain high-level expression of the coding sequence of interest. The use of other viral or mammalian cellular or bacterial phage promoters which are well-known in the art to achieve expression of a coding sequence of interest is contemplated as well, provided that the levels of expression are sufficient for a given purpose. By employing a promoter with well-known properties, the level and pattern of expression of the protein of interest following transfection or transformation can be optimized. Selection of a promoter that is regulated in response to specific physiologic or synthetic signals can permit inducible expression of the gene product. For example in the case where expression of a transgene, or transgenes when a multicistronic vector is utilized, is toxic to the cells in which the vector is produced in, it may be desirable to prohibit or reduce expression of one or more of the transgenes. Examples of transgenes that may be toxic to the producer cell line are pro-apoptotic and cytokine genes. Several inducible promoter systems are available for production of viral vectors where the transgene product may be toxic. The ecdysone system (Invitrogen, Carlsbad, CA) is one such system. This system is designed to allow regulated expression of a gene of interest in mammalian cells. It consists of a tightly regulated expression mechanism that allows virtually no basal level expression of the transgene, but over 200-fold inducibility. The system is based on the heterodimeric ecdysone receptor of Drosophila, and when ecdysone or an analog such as muristerone A binds to the receptor, the receptor activates a promoter to turn on expression of the downstream transgene high levels of mRNA transcripts are attained. In this system, both monomers of the heterodimeric receptor are constitutively expressed from one vector, whereas the ecdysone-responsive promoter that drives expression of the gene of interest is on another plasmid. Engineering of this type of system into the gene transfer vector of interest would therefore be useful. Cotransfection of plasmids containing the gene of interest and the receptor monomers in the producer cell line would then allow for the production of the gene transfer vector without expression of a potentially toxic transgene. At the appropriate time, expression of the transgene could be activated with ecdysone or muristeron A. Another inducible system that would be useful is the Tet-Off™ or Tet-On™ system (Clontech, Palo Alto, CA) originally developed by Gossen and Bujard (Gossen and Bujard, 1992; Gossen et al, 1995). This system also allows high levels of gene expression to be regulated in response to tetracycline or tetracycline derivatives such as doxycycline. In the Tet-On™ system, gene expression is turned on in the presence of doxycycline, whereas in the Tet-Off™ system, gene expression is turned on in the absence of doxycycline. These systems are based on two regulatory elements derived from the tetracycline resistance operon of E. coli. The tetracycline operator sequence to which the tetracycline repressor binds, and the tetracycline repressor protein. The gene of interest is cloned into a plasmid behind a promoter that has tetracycline- responsive elements present in it. A second plasmid contains a regulatory element called the tetracycline-controlled transactivator, which is composed, in the Tet-Off™ system, of the VP16 domain from the herpes simplex virus and the wild-type tertracycline repressor. Thus in the absence of doxycycline, transcription is constituitively on. In the Tet-On™ system, the tetracycline repressor is not wild type and in the presence of doxycycline activates transcription. For gene therapy vector production, the Tet-Off™ system would be preferable so that the producer cells could be grown in the presence of tetracycline or doxycycline and prevent expression of a potentially toxic transgene, but when the vector is introduced to the patient, the gene expression would be constituitively on. In some circumstances, it may be desirable to regulate expression of a transgene in a gene therapy vector. For example, different viral promoters with varying strengths of activity may be utilized depending on the level of expression desired. In mammalian cells, the CMV immediate early promoter if often used to provide strong transcriptional activation. Modified versions of the CMV promoter that are less potent have also been used when reduced levels of expression of the transgene are desired. When expression of a transgene in hematopoetic cells is desired, retroviral promoters such as the LTRs from MLV or MMTV are often used. Other viral promoters that may be used depending on the desired effect include SV40, RSV LTR, HIV-1 and HIV-2 LTR, adenovirus promoters such as from the Ε1A, Ε2A, or MLP region, AAV LTR, cauliflower mosaic virus, HSV-TK, and avian sarcoma virus. Similarly tissue specific promoters may be used to effect transcription in specific tissues or cells so as to reduce potential toxicity or undesirable effects to non- targeted tissues. In the present invention, embodiments cover promoters that direct expression in epithelium cells, particularly mucosal epithelium. Endothelial-specific promoters direct the regulation of genes such as E-selectin, von Willebrand factor, TIE (Korhonen et al, 1995) and KDR/flk-1. In certain indications, it may be desirable to activate transcription at specific times after administration of the gene therapy vector. This may be done with such promoters as those that are hormone or cytokine regulatable. For example in gene therapy applications where the indication is a gonadal tissue where specific steroids are produced or routed to, use of androgen or estrogen regulated promoters may be advantageous. Such promoters that are hormone regulatable include MMTV, MT-1, ecdysone and RuBisco. Other hormone regulated promoters such as those responsive to thyroid, pituitary and adrenal hormones are expected to be useful in the present invention. Cytokine and inflammatory protein responsive promoters that could be used include K and T Kininogen (Kageyama et al, 1987), c-fos, TNF-alpha, C- reactive protein (Arcone et al, 1988), haptoglobin (Oliviero et al, 1987), serum amyloid A2, C/EBP alpha, IL-1, IL-6 (Poli and Cortese, 1989), Complement C3 (Wilson et al, 1990), IL-8, alpha- 1 acid glycoprotein (Prowse and Baumann, 1988), alpha-1 antitypsin, lipoprotein lipase (Zechner et al, 1988), angiotensinogen (Ron et al, 1991), fibrinogen, c-jun (inducible by phorbol esters, TNF-alpha, UV radiation, retinoic acid, and hydrogen peroxide), collagenase (induced by phorbol esters and retinoic acid), metallothionein (heavy metal and glucocorticoid inducible), Stromelysin (inducible by phorbol ester, interleukin-1 and EGF), alpha-2 macroglobulin and alpha-1 antichymotrypsin. It is envisioned that cell cycle regulatable promoters may be useful in the present invention. For example, in a bi-cistronic gene therapy vector, use of a strong CMV promoter to drive expression of a first gene such as pi 6 that arrests cells in the GI phase could be followed by expression of a second gene such as p53 under the control of a promoter that is active in the GI phase of the cell cycle, thus providing a "second hit" that would push the cell into apoptosis. Other promoters such as those of various cyclins, PCNA, galectin-3, E2F1, p53 and BRCAl could be used. Tumor specific promoters such as osteocalcin, hypoxia-responsive element (HRE), MAGE-4, CEA, alpha-fetoprotein, GRP78/BiP and tyrosinase may also be used to regulate gene expression in tumor cells. Other promoters that could be used according to the present invention include Lac -regulatable, chemotherapy inducible (e.g. MDR), and heat (hyperthermia) inducible promoters, radiation-inducible (e.g., EGR (Joki et al, 1995)), Alpha-inhibin, RNA pol III tRNA met and other amino acid promoters, UI snRNA (Bartlett et al, 1996), MC-1, PGK, β-actin and α-globin. Many other promoters that may be useful are listed in Walther and Stein (1996). It is envisioned that any of the above promoters alone or in combination with another may be useful according to the present invention depending on the action desired. In addition, this list of promoters is should not be construed to be exhaustive or limiting, those of skill in the art will know of other promoters that may be used in conjunction with the promoters and methods disclosed herein. b. Enhancers Enhancers are genetic elements that increase transcription from a promoter located at a distant position on the same molecule of DNA. Enhancers are organized much like promoters. That is, they are composed of many individual elements, each of which binds to one or more transcriptional proteins. The basic distinction between enhancers and promoters is operational. An enhancer region as a whole must be able to stimulate transcription at a distance; this need not be true of a promoter region or its component elements. On the other hand, a promoter must have one or more elements that direct initiation of RNA synthesis at a particular site and in a particular orientation, whereas enhancers lack these specificities. Promoters and enhancers are often overlapping and contiguous, often seeming to have a very similar modular organization. In some embodiments of the invention, the expression construct comprises a virus or engineered construct derived from a viral genome. The ability of certain viruses to enter cells via receptor-mediated endocytosis and to integrate into host cell genome and express viral genes stably and efficiently have made them attractive candidates for the transfer of foreign genes into mammalian cells (Ridgeway, 1988; Nicolas and Rubenstein, 1988; Baichwal and Sugden, 1986; Temin, 1986). The first viruses used as gene vectors were DNA viruses including the papovaviruses (simian virus 40, bovine papilloma virus, and polyoma) (Ridgeway, 1988; Baichwal and Sugden, 1986) and adenoviruses (Ridgeway, 1988; Baichwal and Sugden, 1986). These have a relatively low capacity for foreign DNA sequences and have a restricted host spectrum. Furthermore, their oncogenic potential and cytopathic effects in permissive cells raise safety concerns. They can accommodate only up to 8 kB of foreign genetic material but can be readily introduced in a variety of cell lines and laboratory animals (Nicolas and Rubenstein, 1988; Temin, 1986). c. Polyadenylation signals Where a cDNA insert is employed, one will typically desire to include a polyadenylation signal to effect proper polyadenylation of the gene transcript. The nature of the polyadenylation signal is not believed to be crucial to the successful practice of the invention, and any such sequence may be employed such as human or bovine growth hormone and SV40 polyadenylation signals. Also contemplated as an element of the expression cassette is a terminator. These elements can serve to enhance message levels and to minimize read through from the cassette into other sequences. d. IRES In certain embodiments of the invention, the use of internal ribosome entry site (IRES) elements is contemplated to create multigene, or polycistronic, messages. IRES elements are able to bypass the ribosome scanning model of 5' methylated Cap dependent translation and begin translation at internal sites (Pelletier and Sonenberg, 1988). IRES elements from two members of the picornavirus family (poliovirus and encephalomyocarditis) have been described (Pelletier and Sonenberg, 1988), as well an IRES from a mammalian message (Macejak and Sarnow, 1991). IRES elements can be linked to heterologous open reading frames. Multiple open reading frames can be transcribed together, each separated by an IRES, creating polycistronic messages. By virtue of the IRES element, each open reading frame is accessible to ribosomes for efficient translation. Multiple genes can be efficiently expressed using a single promoter/enhancer to transcribe a single message. Any heterologous open reading frame can be linked to IRES elements. This includes genes for secreted proteins, multi-subunit proteins, encoded by independent genes, intracellular or membrane-bound proteins and selectable markers. In this way, expression of several proteins can be simultaneously engineered into a cell with a single construct and a single selectable marker. 5. In vitro protein production Following transduction with an expression construct or vector according to some embodiments of the present invention, primary mammalian cell cultures may be prepared in various ways. In order for the cells to be kept viable while in vitro and in contact with the expression construct, it is necessary to ensure that the cells maintain contact with the correct ratio of oxygen and carbon dioxide and nutrients but are protected from microbial contamination. Cell culture techniques are well documented and are disclosed herein by reference (Freshner, 1992). One embodiment of the foregoing involves the use of gene transfer to immortalize cells for the production and/or presentation of proteins. The gene for the protein of interest may be transferred as described above into appropriate host cells followed by culture of cells under the appropriate conditions. The gene for virtually any polypeptide may be employed in this manner. The generation of recombinant expression vectors, and the elements included therein, are discussed above. Alternatively, the protein to be produced may be an endogenous protein normally synthesized by the cell in question. Another embodiment of the present invention uses cell lines, which are transfected with an expression construct or vector that expresses IgA protein. Examples of mammalian host cell lines include Vero and HeLa cells, other B- and T- cell lines, such as CEM, 721.221, H9, Jurkat, Raji, etc., as well as cell lines of Chinese hamster ovary, W138, BHK, COS-7, 293, HepG2, 3T3, RIN and MDCK cells. In addition, a host cell strain may be chosen that modulates the expression of the inserted sequences, or that modifies and processes the gene product in the manner desired. Such modifications (e.g., glycosylation) and processing (e.g., cleavage) of protein products may be important for the function of the protein. Different host cells have characteristic and specific mechanisms for the post-translational processing and modification of proteins. Appropriate cell lines or host systems can be chosen to insure the correct modification and processing of the foreign protein expressed. A number of selection systems may be used including, but not limited to, HSV thymidine kinase, hypoxanthine-guanine phosphoribosyltransferase and adenine phosphoribosyltransferase genes, in tk-, hgprt- or aprt- cells, respectively. Also, anti- metabolite resistance can be used as the basis of selection: for dhfr, which confers resistance to; gpt, which confers resistance to mycophenolic acid; neo, which confers resistance to the aminoglycoside G418; and hygro, which confers resistance to hygromycin. Animal cells can be propagated in vitro in two modes: as non-anchorage- dependent cells growing in suspension throughout the bulk of the culture or as anchorage-dependent cells requiring attachment to a solid substrate for their propagation (i.e., a monolayer type of cell growth). Non-anchorage dependent or suspension cultures from continuous established cell lines are the most widely used means of large-scale production of cells and cell products. However, suspension cultured cells have limitations, such as tumorigenic potential and lower protein production than adherent cells. III. Therapeutic Formulations and Routes of Administration The present invention discloses the compositions and methods involving a plgR-binding domain that provides a targeting system for delivering selective agents to the mucosal epithelia. While systemic administration of formulations can provide a treatment method, frequently this delivery method fails to reach a location where it can confer a therapeutic benefit or it does so with reduced efficacy. The present invention, however, provides in some embodiments the ease of systemic formulation while providing a targeting method that allows the delivery of formulations specifically to the mucosal epithelia. Where clinical applications are contemplated, it will be necessary to prepare the compositions of the present invention as pharmaceutical compositions, i.e., in a form appropriate for in vivo applications. Generally, this will entail preparing compositions that are essentially free of pyrogens, as well as other impurities that could be harmful to humans or animals. A. Formulations One will generally desire to employ appropriate salts and buffers to render delivery vectors stable and allow for uptake by target cells. Buffers also will be employed when recombinant cells are introduced into a patient. Aqueous compositions of the present invention comprise an effective amount of the vector to cells, dissolved or dispersed in a pharmaceutically acceptable carrier or aqueous medium. Such compositions also are referred to as inocula. The phrase "pharmaceutically or pharmacologically acceptable" refer to molecular entities and compositions that do not produce adverse, allergic, or other untoward reactions when administered to an animal or a human. As used herein, "pharmaceutically acceptable carrier" includes any and all solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absoφtion delaying agents and the like. The use of such media and agents for pharmaceutically active substances is well know in the art. Except insofar as any conventional media or agent is incompatible with the vectors or cells of the present invention, its use in therapeutic compositions is contemplated. Supplementary active ingredients also can be incorporated into the compositions. The active compositions of the present invention include classic pharmaceutical preparations. Administration of these compositions according to the present invention will be via any common route so long as the target tissue is available via that route. This includes oral, nasal, buccal, rectal, vaginal or topical. Alternatively, administration may be by orthotopic, intradermal, subcutaneous, intramuscular, intraperitoneal or intravenous injection. Such compositions would normally be administered as pharmaceutically acceptable compositions, described supra. The active compounds may be administered via any suitable route, including parenterally or by injection or inhalation. Solutions of the active compounds as free base or pharmacologically acceptable salts can be prepared in water suitably mixed with a surfactant, such as hydroxypropylcellulose. Dispersions also can be prepared in glycerol, liquid polyethylene glycols, and mixtures thereof and in oils. Under ordinary conditions of storage and use, these preparations contain a preservative to prevent the growth of microorganisms. The pharmaceutical forms suitable for injectable use include sterile aqueous solutions or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersions. In all cases the form must be sterile and must be fluid to the extent that easy syringability exists. It must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms, such as bacteria and fungi. The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, polyol (for example, glycerol, propylene glycol, and liquid polyethylene glycol, and the like), suitable mixtures thereof, and vegetable oils. The proper fluidity can be maintained, for example, by the use of a coating, such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants. The prevention of the action of microorganisms can be brought about by various antibacterial an antifungal agents, for example, parabens, chlorobutanol, phenol, sorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars or sodium chloride. Prolonged absoφtion of the injectable compositions can be brought about by the use in the compositions of agents delaying absoφtion, for example, aluminum monostearate and gelatin. Sterile injectable solutions are prepared by incoφorating the active compounds in the required amount in the appropriate solvent with various of the other ingredients enumerated above, as required, followed by filtered sterilization. Generally, dispersions are prepared by incoφorating the various sterilized active ingredients into a sterile vehicle which contains the basic dispersion medium and the required other ingredients from those enumerated above. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum-drying and freeze-drying techniques which yield a powder of the active ingredient plus any additional desired ingredient from a previously sterile- filtered solution thereof. As used herein, "pharmaceutically acceptable carrier" includes any and all solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absoφtion delaying agents and the like. The use of such media and agents for pharmaceutical active substances is well known in the art. Except insofar as any conventional media or agent is incompatible with the active ingredient, its use in the therapeutic compositions is contemplated. Supplementary active ingredients also can be incoφorated into the compositions. For oral administration the polypeptides and expression constructs of the present invention may be incoφorated with excipients and used in the form of non- ingestible mouthwashes and dentifrices. A mouthwash may be prepared incoφorating the active ingredient in the required amount in an appropriate solvent, such as a sodium borate solution (Dobell's Solution). Alternatively, the active ingredient may be incoφorated into an antiseptic wash containing sodium borate, glycerin and potassium bicarbonate. The active ingredient may also be dispersed in dentifrices, including: gels, pastes, powders and slurries. The active ingredient may be added in a therapeutically effective amount to a paste dentifrice that may include water, binders, abrasives, flavoring agents, foaming agents, and humectants. The compositions of the present invention may be formulated in a neutral or salt form. Pharmaceutically-acceptable salts include the acid addition salts (formed with the free amino groups of the protein) and which are formed with inorganic acids such as, for example, hydrochloric or phosphoric acids, or such organic acids as acetic, oxalic, tartaric, mandelic, and the like. Salts formed with the free carboxyl groups also can be derived from inorganic bases such as, for example, sodium, potassium, ammonium, calcium, or ferric hydroxides, and such organic bases as isopropylamine, trimethylamine, histidine, procaine and the like. Upon formulation, solutions will be administered in a manner compatible with the dosage formulation and in such amount as is therapeutically effective. The formulations are easily administered in a variety of dosage forms such as injectable solutions, drug release capsules and the like. For parenteral administration in an aqueous solution, for example, the solution should be suitably buffered if necessary and the liquid diluent first rendered isotonic with sufficient saline or glucose. These particular aqueous solutions are especially suitable for intravenous, intramuscular, subcutaneous and intraperitoneal administration. Compositions may be conventionally administered parenterally, by injection, for example, either subcutaneously or intramuscularly. Additional formulations which are suitable for other modes of administration include suppositories and, in some cases, oral formulations. For suppositories, traditional binders and carriers may include, for example, polyalkalene glycols or triglycerides: such suppositories may be formed from mixtures containing the active ingredient in the range of about 0.5% to about 10%, preferably about 1 to about 2%. Oral formulations include such normally employed excipients as, for example, pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, sodium saccharine, cellulose, magnesium carbonate and the like. These compositions take the form of solutions, suspensions, tablets, pills, capsules, sustained release formulations or powders and contain about 10 to about 95% of active ingredient, preferably about 25 to about 70%. 1. Liposomes Liposomes are formed from phospholipids that are dispersed in an aqueous medium and spontaneously form multilamellar concentric bilayer vesicles. Liposomes bear many resemblances to cellular membranes and are contemplated for use in connection with the present invention as drug delivery agents. The formation and use of liposomes is generally known to those of skill in the art. For example, several U.S. Patents concern the preparation and use of liposomes that encapsulate biologically active materials, e.g., U.S. Patent 4,485,054; 4,089,801; 4,234,871; and 4,016,100; each incoφorated herein by reference. Mostly, it is contemplated that intravenous injection of liposomal preparations would be used, but pessaries are also possible. 2. Nasal Administration One may also use nasal solutions or sprays, aerosols or inhalants in the present invention. Nasal solutions are usually aqueous solutions designed to be administered to the nasal passages in drops or sprays. Nasal solutions are prepared so that they are similar in many respects to nasal secretions, so that normal ciliary action is maintained. Thus, the aqueous nasal solutions usually are isotonic and slightly buffered to maintain a pH of 5.5 to 6.5. In addition, antimicrobial preservatives, similar to those used in ophthalmic preparations, and appropriate drug stabilizers, if required, may be included in the formulation. Various commercial nasal preparations are known and include, for example, antibiotics and antihistaminesand are used for asthma prophylaxis. 3. Oral Administration In certain embodiments, active compounds may be administered orally. This is contemplated to be useful as many substances contained in tablets designed for oral use are absorbed by mucosal epithelia along the gastrointestinal tract. Also, if desired, the peptides, antibodies and other agents may be rendered resistant, or partially resistant, to proteolysis by digestive enzymes. Such compounds are contemplated to include chemically designed or modified agents; dextrorotatory peptides; and peptide and liposomal formulations in time release capsules to avoid peptidase and lipase degradation. For oral administration, the active compounds may be administered, for example, with an inert diluent or with an assimilable edible carrier, or they may be enclosed in hard or soft shell gelatin capsule, or compressed into tablets, or incoφorated directly with the food of the diet. For oral therapeutic administration, the active compounds may be incoφorated with excipients and used in the form of ingestible tablets, buccal tables, troches, capsules, elixirs, suspensions, syrups, wafers, and the like. The oral compositions and preparations should contain at least 0.1 % of active compound. The percentage of the compositions and preparations may, of course, be varied and may conveniently be between about 2 to about 60% of the weight of the unit. The amount of active compounds in such therapeutically useful compositions is such that a suitable dosage will be obtained. The tablets, troches, pills, capsules and the like may also contain the following: a binder, as gum tragacanth, acacia, cornstarch, or gelatin; excipients, such as dicalcium phosphate; a disintegrating agent, such as corn starch, potato starch, alginic acid and the like; a lubricant, such as magnesium stearate; and a sweetening agent, such as sucrose, lactose or saccharin may be added or a flavoring agent, such as peppermint, oil of wintergreen, or cherry flavoring. When the dosage unit form is a capsule, it may contain, in addition to materials of the above type, a liquid carrier. Various other materials may be present as coatings or to otherwise modify the physical form of the dosage unit. For instance, tablets, pills, or capsules may be coated with shellac, sugar or both. A syrup of elixir may contain the active compounds sucrose as a sweetening agent methyl and propylparabens as preservatives, a dye and flavoring, such as cherry or orange flavor. Of course, any material used in preparing any dosage unit form should be pharmaceutically pure and substantially non-toxic in the amounts employed. In addition, the active compounds may be incoφorated into sustained- release preparation and formulations. Upon formulation, the compounds will be administered in a manner compatible with the dosage formulation and in such amount as is therapeutically effective. The formulations are easily administered in a variety of dosage forms, as described herein. 4. Pessaries Additional formulations which are suitable for other modes of administration include vaginal suppositories and pessaries. A rectal pessary or suppository may also be used. Suppositories are solid dosage forms of various weights and shapes, usually medicated, for insertion into the rectum, vagina or the urethra. After insertion, suppositories soften, melt or dissolve in the cavity fluids. In general, for suppositories, traditional binders and carriers may include, for example, polyalkylene glycols or triglycerides; such suppositories may be formed from mixtures containing the active ingredient in the range of 0.5% to 10%, preferably l%-2%. Vaginal suppositories or pessaries are usually globular or oviform and weighing about 5 g each. Vaginal medications are available in a variety of physical forms, e.g., creams, gels or liquids, which depart from the classical concept of suppositories. Vaginal tablets, however, do meet the definition, and represent convenience both of administration and manufacture. B. Vaccines The present invention contemplates vaccines for use in both active and passive immunization embodiments. Immunogenic compositions, proposed to be suitable for use as a vaccine, may be prepared most readily directly from immunogenic calcium binding peptides prepared in a manner disclosed herein. Preferably the antigenic material is extensively dialyzed to remove undesired small molecular weight molecules and/or lyophilized for more ready formulation into a desired vehicle. The preparation of vaccines that contain IgR-binding domain sequences as active ingredients is generally well understood in the art, as exemplified by U.S. Patents 4,608,251; 4,601,903; 4,599,231; and 4,599,230, all incoφorated herein by reference. Typically, such vaccines are prepared as injectables. Either as liquid solutions or suspensions: solid forms suitable for solution in, or suspension in, liquid prior to injection may also be prepared. The preparation may also be emulsified. The active immunogenic ingredient is often mixed with excipients which are pharmaceutically acceptable and compatible with the active ingredient. Suitable excipients are, for example, water, saline, dextrose, glycerol, ethanol, or the like and combinations thereof. In addition, if desired, the vaccine may contain minor amounts of auxiliary substances such as wetting or emulsifying agents, pH buffering agents, or adjuvants which enhance the effectiveness of the vaccines. Additionally, iscom, a supramolecular spherical structure, may be used for parenteral and mucosal vaccination (Morein et al. , 1998). Vaccines may be conventionally administered parenterally, by injection, for example, either subcutaneously or intramuscularly. Additional formulations which are suitable for other modes of administration include suppositories and, in some cases, oral formulations. For suppositories, traditional binders and carriers may include, for example, polyalkalene glycols or triglycerides: such suppositories may be formed from mixtures containing the active ingredient in the range of about 0.5% to about 10%, preferably about 1 to about 2%. Oral formulations include such normally employed excipients as, for example, pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, sodium saccharine, cellulose, magnesium carbonate and the like. These compositions take the form of solutions, suspensions, tablets, pills, capsules, sustained release formulations or powders and contain about 10 to about 95% of active ingredient, preferably about 25 to about 70%. The calcium binding protein-derived peptides of the present invention may be formulated into the vaccine as neutral or salt forms. Pharmaceutically-acceptablesalts, include the acid addition salts (formed with the free amino groups of the peptide) and those which are formed with inorganic acids such as, for example, hydrochloric or phosphoric acids, or such organic acids as acetic, oxalic, tartaric, mandelic, and the like. Salts formed with the free carboxyl groups may also be derived from inorganic bases such as, for example, sodium, potassium, ammonium, calcium, or ferric hydroxides, and such organic bases as isopropylamine, trimethylamine, 2-ethylamino ethanol, histidine, procaine, and the like. The vaccines are administered in a manner compatible with the dosage formulation, and in such amount as will be therapeutically effective and immunogenic. The quantity to be administered depends on the subject to be treated, including, e.g. , the capacity of the individual's immune system to synthesize antibodies, and the degree of protection desired. Precise amounts of active ingredient required to be administered depend on the judgment of the practitioner. However, suitable dosage ranges are of the order of several hundred micrograms active ingredient per vaccination. Suitable regimes for initial administration and booster shots are also variable, but are typified by an initial administration followed by subsequent inoculations or other administrations. The manner of application may be varied widely. Any of the conventional methods for administration of a vaccine are applicable. These are believed to include oral application on a solid physiologically acceptable base or in a physiologically acceptable dispersion, parenterally, by injection or the like. The dosage of the vaccine will depend on the route of administration and will vary according to the size of the host. Various methods of achieving adjuvant effect for the vaccine includes use of agents such as aluminum hydroxide or phosphate (alum), commonly used as about 0.05 to about 0.1%) solution in phosphate buffered saline, admixture with synthetic polymers of sugars (Carbopol®) used as an about 0.25% solution, aggregation of the protein in the vaccine by heat treatment with temperatures ranging between about 70° to about 101 °C for a 30-second to 2-minute period, respectively. Aggregation by reactivating with pepsin treated (Fab) antibodies to albumin, mixture with bacterial cells such as C. parvum or endotoxins or lipopolysaccharide components of Gram-negative bacteria, emulsion in physiologically acceptable oil vehicles such as mannide mono-oleate (Aracel A) or emulsion with a 20% solution of a perfluorocarbon (Fluosol-DA®) used as a block substitute may also be employed. In many instances, it will be desirable to have multiple administrations of the vaccine, usually not exceeding six vaccinations, more usually not exceeding four vaccinations and preferably one or more, usually at least about three vaccinations. The vaccinations will normally be at from two to twelve week intervals, more usually from three to five week intervals. Periodic boosters at intervals of 1 -5 years, usually three years, will be desirable to maintain protective levels of the antibodies. The course of the immunization may be followed by assays for antibodies for the supernatant antigens. The assays may be performed by labeling with conventional labels, such as radionuclides, enzymes, fluorescents, and the like. These techniques are well known and may be found in a wide variety of patents, such as U.S. Patent Nos. 3,791,932; 4, 174,384 and 3,949,064, as illustrative of these types of assays. "Unit dose" is defined as a discrete amount of a therapeutic composition dispersed in a suitable carrier. For example, in accordance with the present methods, viral doses include a particular number of virus particles or plaque forming units (pfu). For embodiments involving adenovirus, particular unit doses include 10 3 , 10 4 , 10 5 , 10 6 , 10 7 , 10 8 , 10 9 , 10 10 , 10", 10 12 , 10 13 or 10' 4 pfu. Particle doses may be somewhat higher (10 to 100-fold) due to the presence of infection defective particles. In this connection, sterile aqueous media which can be employed will be known to those of skill in the art in light of the present disclosure. For example, a unit dose could be dissolved in 1 ml of isotonic NaCl solution and either added to 1000 ml of hypodermoclysis fluid or injected at the proposed site of infusion, (see for example, "Remington's Pharmaceutical Sciences" 15th Edition, pages 1035-1038 and 1570- 1580). Some variation in dosage will necessarily occur depending on the condition of the subject being treated. The person responsible for administration will, in any event, determine the appropriate dose for the individual subject. Moreover, for human administration, preparations should meet sterility, pyrogenicity, general safety and purity standards as required by FDA Office of Biologies standards. In a preferred embodiment, the present invention is directed at the treatment of human malignancies. A variety of different routes of administration are contemplated. For example, a classic and typical therapy will involve direct, intratumoral injection of a discrete tumor mass. The injections may be single or multiple; where multiple, injections are made at about 1 cm spacings across the accessible surface of the tumor. Alternatively, targeting the tumor vasculature by direct, local or regional intra-arterial injection are contemplated. The lymphatic systems, including regional lymph nodes, present another likely target given the potential for metastasis along this route. Further, systemic injection may be preferred when specifically targeting secondary (i.e., metastatic) tumors. In another embodiment, the viral gene therapy may precede or following resection of the tumor. Where prior, the gene therapy may, in fact, permit tumor resection where not possible before. Alternatively, a particularly advantageous embodiment involves the prior resection of a tumor (with or without prior viral gene therapy), followed by treatment of the resected tumor bed. This subsequent treatment is effective at eliminating microscopic residual disease which, if left untreated, could result in regrowth of the tumor. This may be accomplished, quite simply, by bathing the tumor bed with a viral preparation containing a unit dose of viral vector. Another preferred method for achieving the subsequent treatment is via catheterization of the resected tumor bed, thereby permitting continuous perfusion of the bed with virus over extended post-operative periods. C. Kits All the essential materials and reagents required for delivering agents to the mucosal epithelia using a plgR-binding domain may be assembled together in a kit. This generally will comprise selected expression constructs. Also included may be various media for replication of the expression constructs and host cells for such replication. Such kits will comprise distinct containers for each individual reagent. When the components of the kit are provided in one or more liquid solutions, the liquid solution preferably is an aqueous solution, with a sterile aqueous solution being particularly preferred. For in vivo use, the expression construct may be formulated into a pharmaceutically acceptable syringeable composition. In this case, the container means may itself be an inhalent, syringe, pipette, eye dropper, or other such like apparatus, from which the formulation may be applied to an infected area of the body, such as the lungs, injected into an animal, or even applied to and mixed with the other components of the kit. The components of the kit may also be provided in dried or lyophilized forms. When reagents or components are provided as a dried form, reconstitution generally is by the addition of a suitable solvent. It is envisioned that the solvent also may be provided in another container means. The kits of the present invention also will typically include a means for containing the vials in close confinement for commercial sale such as, e.g. , injection or blow-molded plastic containers into which the desired vials are retained. Irrespective of the number or type of containers, the kits of the invention also may comprise, or be packaged with, an instrument for assisting with the injection/administration or placement of the ultimate complex composition within the body of an animal. Such an instrument may be an inhalant, syringe, pipette, forceps, measured spoon, eye dropper or any such medically approved delivery vehicle. The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. EXAMPLE 1: Materials and Methods A. Baculovirus Expression Arsonate hapten-specific chimeric IgAl and IgAl /IgGl domain swap mutants were expressed as described (Carayannopoulos et al, 1994; O'Reilly et al, 1992). Dimeric IgA was generated by coexpression of IgA with J chain. Affinity purification was carried out on arsonate-sepharose. Antibodies were eluted with 200 mM arsanillic acid (Sigma, St. Louis, MO), 200 mM Tris-HCl pH8.0, which was removed by extensive dialysis against PBS. Monomeric and dimeric IgA was confirmed by 4% non-reducing SDS-PAGE analysis. The hexahistidine tagged human plgR extracellular domain was expressed in a similar manner and purified on aNi-NTA Agarose (Qiagen, Chatsworth, CA) column (Rindisbacher et al, 1995). B. Construction of Mutant IgA Antibodies for Baculovirus Expression The Cα3 loop mutants LI, L2 and L3 were constructed by PCR SOEing (Splicing by Overlap Extension, Horton et al, 1990) using the following complementary pairs of sense (S) and antisense (AS) primers: L1S 5'-GAGC CCAGCGCGGGCGCCGCCGCCTTCGCTGTG-3', LIAS 5 ' -CTCGGGTCGCGCCCGCGGCGGCGGAAGCGACAC-3 ' ; L2S 5 ' TACCTGACTGCGGCAGCCGCGCAGGAGCCC- 3 ' , L2AS 5 ' -ATGGACTGACGCCGTCGGCGCGT CCTCGGG-3'; L3S 5 ' -CGGCAGGAGGCCGCCGCGGCCACCACCACC-3 ' , L3AS 5'-GCCGTCCTCCGGCGG CGCCGGTGGTGGTGG-3 ' . The outer primers Bl-2 (5'-CCTATAACCATGGGATGGAGCTTCATC- 3 ' ), specific for the 5' leader of the VH region of this chimeric IgA heavy chain, and C 3-3' (s • - CCCTCTAGATTAGTAGCAGGTGCCGTCCAC-3 ' ) , specific for the 3' tailpiece-encoding sequence of the IgAl gene, were used with the above primer pairs L1-L3 to generate pairs of 5' and 3' fragments with complementary overlaps. These fragments were gel purified then spliced in a further PCR reaction using the outer primers Bl-2 and Cα3- 3'. Modified IgAl genes were cloned into the baculovirus transfer vector using Xba I and Neo I digestion and the insert sequences verified. Recombinant baculovirus were produced using the BacPAK system (Clontech, Palo Alto, CA). C. FACS Analysis MDCK cells were placed in serum-free MEM plus Earle's salts (MediaTech, Inc., Herndon, VA) 16 hr before the experiment. Cells were harvested in 10 mM EDTA in PBS and washed in PBS 0.1% BSA. plgR binding of human IgAl antibodies and mutants was assessed by incubation of 100 μl antibody in PBS/BSA with approximately 10 6 cells for 1 hr. Cells were washed three times in PBS/BSA and bound antibody was detected with 100 μl of an anti-human kappa FITC conjugate (Sigma, St. Louis, MO) diluted 1/100. Cells were washed as above and resuspended in 1 ml PBS/BSA. FACS analysis was carried out on a Becton Dickinson FACSCAN instrument. Data collection and analysis were performed with the LYSYSII (Becton Dickinson, San Jose, CA) and WinMIDI (http//facs.scripps.edu) or with the CELLQUEST programs (Becton Dickinson, San Jose, CA). D. Phage Display Peptide Library Selection The random 40mer peptide library was constructed in the pCANTAB5e vector and has an actual total diversity of 1.55x10 10 (Ravera et al, 1998). The random 40mer is flanked by two peptide tag sequences, preceded by a leader peptide and fused to the membrane-proximal domain of the Ml 3 phage coat protein III. l-2xl0 6 MDCK cells were harvested in 5 ml PBS + 10 mM EDTA at 37°C, washed twice in 15 ml PBS and resuspended in 1.8 ml PBS at 4 °C. 100 μl phagemid library stock (4.5x10 12 cfu) was added and incubated for one hour at 37°C or 4°C. The cells were then washed five times with 15 ml PBS at 4 °C. Bound phage were eluted with 2 ml of 0.1 M HCl/glycine pH 2.2 containing 0.1% BSA for 10 min and neutralized immediately with 400 μl of 2 M Tris base. Phage rescue and amplification were carried out in E. coli strain TGI (Pharmacia, Piscataway, NJ) according to standard procedures (Hexham, 1998). E. DNA Sequencing and Analysis DNA sequencing was carried out on double-stranded plasmid or phagemid DNA using an ABI 377 Prism automated sequencer. Alignments of deduced peptide sequences and immunoglobulin constant regions were carried out using the MAP (Huang, 1994) and PIMA (Smith et al, 1992) software. EXAMPLE 2: Domain Mapping of dIG A Chimeric human IgAl (Caryannopoulos et al, 1994) and a panel of IgAl/IgGl constant region domain swap mutants (Caryannopoulos et al, 1996) with murine-encoded arsonate-specificity were expressed in baculovirus as both monomer and dimer, affinity purified, and then used to define the plgR binding site. Dimeric IgA (dlgA) was operationally defined as an IgA preparation generated by co- expression of IgA with J chain. MDCK cells, transfected with rabbit plgR (Mostov et al, 1986), were used to measure binding of recombinant IgAl mutants to the receptor by FACS analysis (FIG. 1A). Specific binding was observed with dlgA and not with monomeric IgA (FIG. IB), a medium control (FIG. lb) or IgG. Mutant VGAA, in which the Cαl domain was substituted with the Cγl domain, bound to the plgR in a similar manner to wild-type IgAl (FIG. 1C). The dimeric molecule (heavy line) bound to the receptor, while the monomer (light line) did not. Similarly, the VGGA mutant, in which both Cαl and Cα2 including the hinge of IgA were replaced with the analogous domains from IgG, bound as a dimer but not as a monomer (FIG. ID). Thus, the Cαl and Cα2 domains of dlgA are not necessary for plgR binding suggesting that the presence of the Cα3 domain is required. EXAMPLE 3: IgA Minimum Peptide Binding Unit dlgA contains four Cα3 domains and the covalently bound J chain which, together with the IgA tailpiece, are responsible for IgA polymerization. To reduce the complexity of this problem, a library of random 40mer peptides, expressed as a phage display library (Ravera et al, 1998), was selected against plgR-expressing MDCK cells. The goal was to identify putative plgR binding sites within IgA by reducing them to a minimum peptide binding unit, a proven approach for several receptor- ligand interactions (Cwirla et al, 1990; Parmley et al, 1988; Devlin et al, 1990). Selection was carried out on live plgR-expressing MDCK cells in suspension with negative selection on non-receptor expressing cells. Bound phage were eluted with acid or by cell lysis. Recovery of both acid-eluted and cell-associated phage increased gradually from approximately 6xl0 4 to 5xl0 7 c.f.u. over 4-6 successive rounds, indicating enrichment for specific binding clones. Individual clones were randomly selected from the final panning from the acid-eluted and membrane- associated fractions and sequenced. Binding of the enriched phage populations to recombinant human plgR, as measured by ELISA, increased with successive rounds of panning and was inhibited by polymeric IgM. Sequencing of phagemid DNA showed that 20 out of 32 acid-eluted clones and 12 out of 32 cell-associated clones had open reading frames (FIG. 2). There is little clonality among these two groups of sequences, although the A22 peptide was recovered three times. These peptides were aligned for maximum homology with the human IgAl Cα3 region amino acid sequence (FIG. 2) using the PIMA program (Smith et al, 1992). Many of the peptides, particularly A12 (9/30 identical amino acids) (FIG. 3 A), show homology with human IgAl Cα3 domain, prompting a further examination of the amino acid sequence and structure in this area. EXAMPLE 4: Mutational Analysis The human Cα3 domain is 40% identical and 62% homologous to the corresponding region of human IgGl at the amino acid level. In addition, all the sequence hallmarks of the immunoglobulin superfamily fold are conserved. Accordingly, the human IgGl crystal structure (Deisenhofer et al, 1981) was used to predict the likely positions of the major structural motifs (β-strands and loops) within the IgAl sequence, an approach used previously to map the FcαR (CD89) binding site on IgAl (Caryannopoulos et al, 1996). FIG. 3 A shows the alignment of the peptide A12 with the IgAl sequence and the corresponding IgGl sequence with its secondary structural features. The A12 peptide is homologous to a region that in the IgG structure forms an exposed 6 amino acid loop between two β-strands. However, in IgAl, this area contains a 3 amino acid insertion to expand the loop to 9 amino acids. The flanking β-strand sequences and part of the loop are conserved between IgA and IgG, which suggests that gross structural features are also conserved. FIG. 3B shows alignment of this region in the CH3 domain of five mammalian IgA molecules aligned with the four human IgG subclasses. Despite sequence differences in the loop, all IgA sequences have the additional 3 amino acids whereas the IgG sequences do not. Similar to IgA, the sequence of IgM contains a two amino acid insertion at this site. On the basis of these observations, three mutant IgAl molecules were constructed and expressed in baculovirus to examine the effect of amino acid changes in this area on plgR binding (FIG. 3C). Mutations were made in the loop itself (LI and L3) and in the β-strand N-terminal to the loop (L2) as a negative control. Binding was then measured to the physiologically relevant human receptor by ELISA using the purified recombinant extracellular domain of human plgR expressed in baculovirus as described (Rindisbacher et al, 1995). FIG. 4 shows the binding of IgAl monomer and dimer compared to the monomeric and dimeric forms of the LI, L2 and L3 mutants to purified human plgR. Only dimeric wild-type IgAl and dimeric L2 mutant, in which the mutations are in the β-strand N-terminal to the loop, show binding. Mutations within the loop itself, namely LI and L3, abrogate the binding of the dimeric IgAl mutant molecules to the plgR. Similar binding patterns were obtained with the loop mutants and rabbit plgR-expressing cells as measured by FACS. These results indicate that this Cα3 loop is the major binding motif for the plgR on dlgA, and based on this observation and on the selection of random peptides and comparison between them and the IgA sequence, amino acids 402-410 of IgA (SEQ ID NO:l) constitute a binding site to plgR. IgA is, in functional terms, closely related to IgM, sharing its ability to polymerize and be secreted. However, the overall IgA domain organization resembles that of IgG. The presence of amino acid sequence insertions in all the polymeric immunoglobulins that are ligands for this receptor and the absence of insertions from non-pIgR-binding immunoglobulins (FIG. 3b) supports its role in immunoglobulin secretion. The variation in the insertion size and the actual IgA and IgM sequences may reflect differences in fine structure of these polymeric antibodies or in their affinity for plgR binding. The fact that monomeric IgA is not secreted suggests that either a conformational change induced by polymerization is required for dlgA binding to the receptor or that the binding requires a polyvalent interaction of these Cα3 sites with the receptor. The presence of J chain is required for optimal IgA (or IgM) polymerization but its precise role in Ig secretion remains to be elucidated. The increase in binding observed with dimeric L3 when compared to monomeric L3 (and to a lesser extent with the LI mutants) suggests that J chain and/or polymerization may play a role in binding (FIG. 4). Although amino acids 402-410 in the Cα3 domain of dlgA define a major plgR-binding site, other dlgA structures may be involved. J chain deficient mice express lower levels of polymeric IgA, have impaired hepatic transport of IgA (which humans lack) but normal levels of IgA at mucosal epithelial sites, compared to wild type mice (Hendrickson et al, 1995; Hendrickson et al, 1996). J chain may thus not be necessary for secretion of IgA but required for stable binding to the secretory component in the mucosal environment, however alternative secretory mechanisms may also be involved. EXAMPLE 5: Protective Immunity Protective immunity against various pathogenic microorganisms will be delivered with the plgR-binding domain linked to single-chain Fv (scFv) antibodies with anti-microbial specificity. The prevention of HIV infection may be accomplished in the SHIV/baboon model for heterosexual AIDS transmission using anti-gpl20 scFv linked to the plgR-binding domain. Single-chain Fv fragments linked to the plgR-binding domain will be generated from a human anti-gpl20 IgG antibody employing oligonucleotide primers in a series of polymerase chain reactions (PCR) using "splice by overlap extension" (SOE). The resulting fragment will consist of the VH gene, a linker sequence, the VL gene segment, and the plgR-binding domain. The 5' primer will contain a restriction site, Xho I, and the 3 ' primer will contain a second site, Spe I, for cloning into the phage display vector, pCOMB3 (Barbas, 1991). The resulting product will be cloned into the Xho I and Spe I sites contained within the pCOMB3 vector. Consequently, this vector will contain the bacterial periplasmic signal peptide, pelB, cloned in-frame and upstream from a single-chain Fv and the carboxy-terminus of the filamentous phage coat protein III. Phage particles will be generated using helper phage, VCSM13, as described previously (Barbas, 1991). The resulting phage will be used in a panning technique to select for antigen-specificity. The techniques for panning with HIV antigens to select to high affinity antibodies are straightforward and have been published (Hexham, 1996). Briefly, gpl20 antigen will be coated onto the wells of ELISA plates. Varying amounts of specific- and non-specific phage will be added to the wells and allowed to bind to the antigens. Unbound phage will be removed by washing and stored. Bound phage will be eluted from the wells using low pH, followed by re-infection of fresh bacterial cultures, and further rounds of selection. DNA from selected phage will then be modified by restriction digestion with Spe I and Nhe I to facilitate excision of the gene III fragment. The vector will be re- ligated (Spe I and Nhe I have compatible ends) to form a vector that will allow for production of soluble scFv. The fragment is under the control of the lacZ promoter, inducible with IPTG, for maximal protein production. In this system, a hexahistidine sequence has been inserted into the vector between the Nhe I site and the stop codons, resulting in a protein with a hexahistidine tag. This permits the purification of any protein using Ni ++ affinity chromatography. To determine if the recombinant scFv antibody binds comparably to the native molecule, the affinities of both will be compared using BIAcore and ELISA determinations. After purification of the scFV-pIgR-binding domain, the ability of this molecule to prevent HIV infection in a baboon SHIV model for heterosexual AIDS transmission will be assessed. Using the same approach, other anti-pathogen scFV-pIgR binding-domain combinations can be utilized to mediate immunity against influenza, respiratory syncytial virus, and gonorrhoeae. EXAMPLE 6: Identify Other Peptide Motifs with High Binding Affinity for plgR Phage display technology was used to identify peptide motifs that would bind to the plgR with high affinity. More specifically, a modification of the MDCK (Madin-Darby canine kidney) cell transcytosis system was employed for screening random 40-mer and 20-mer peptide phage libraries. Three separate rounds of experiments were conducted: the first two involved the 40-mer peptide library while the third involved the 20-mer peptide library. The MDCK cell line, transfected with the plgR, is used as an in vitro transcytosis assay (Mostov et al, 1995). MDCK is a polarized cell line, capable of forming monolayers with tight junctions, which, when grown on a semipermeable support, will transport dlgA from the lower (basolateral) to the upper (apical) chamber of a tissue culture well. MDCK cells expressing plgR and non-transfected MDCK cells were seeded on tissue culture inserts with 1.0 μm pore size polycarbonate membranes to allow pore sizes to which the phage may traverse. The phage library is introduced into the lower or basolateral chamber of the wells and incubated for 3-4 hours at 37°C. Phage that display peptides capable of transcytosis are then collected by harvesting the apical supernatant fluid. The collected phage are then amplified and subjected to further rounds of selection by transcytosis. After successive rounds of panning (assessed by phage titer but typically about 6), random phage clones were chosen and sequenced. Twenty clones from the first round of experiments (40-mer library) and 18 clones from the second (40-mer library) and third rounds (20-mer library) of experiments were chosen at random and sequenced. Table 3 shows the eight phage peptides selected from the three experiments and the frequency of selection as indicated by sequences obtained (in parentheses): TABLE 3 EXP 1 SAM FVPFDIAVGVRDGOQGLGGSRRKGARLREAISSYAE 9/20 IPS VTRMTVGGTLRKEFQDWLGVIFG V VINRCSFL 3/20 LVL RGNQVFAFCRSDN RQQAPAGCCYVGFSLFVTRGGYE 1/20 ΞXP 2 QA YPVQYLFWATGYGGKVI HLRGKVRRESADQVPGYF 4/18 MFV CVDAKQCL GAAGGLR IFA 3/18 VDD LTLQSRSPPSQLNSQHLL SQLCGYWMFRVRSRSCCG 1/18 RSR MFVLGVLEVDSG NCLC VGVSVDGRKSSCR TAY 1/18 EXP 3 QRN PR R IRRHPTLRIPPI 11/18 There were no apparent sequence motifs among the peptides as assessed by peptide alignment computer programs. However, when these selected phage peptides were aligned to the sequence of IgA, three peptides (VDD, SAM, and IPS) show significant identity in and around the 402-410 region that has previously been shown by the inventors to be important for plgR binding (Hexham et al, 1999) (FIG. 5). Phage peptides are referred to by the first three amino acids of their sequence. The eight phage peptides shown above were selected by successive rounds of transcytosis through plgR-transfected cells, a positive selection method. Therefore, the ability of the individual phage-displayed peptides to be transcytosed specifically by the plgR in the MDCK transcytosis system was assessed using both plgR- transfected and non-transfected MDCK cells as a negative control (FIG. 6). These results clearly indicate that the SAM, IPS, RSR, MFV, VDD, and QRN peptides displayed on the surface of the phage allow the phage to be specifically transported by the plgR through MDCK cells (FIGs. 6A & 6B). In contrast, the LVL and WQA phage peptides direct apical transport of phage by an alternate transcytosis pathway (FIG. 6C). Further peptides are being selected using different phage display libraries, i.e., constrained libraries. The molecules that result from these and other experiments described in the original submission will be tested in the rat model. Furthermore, mutagenic libraries will be derived from the peptides and derivatives selected by transcytosis. These libraries will produce more candidate transport molecules that will ultimately be tested in both the in vitro MDCK transcytosis system and the rat in vivo model described below. EXAMPLE 7: in vivo Transcytosis Model The ability of the phage peptides to transport in an in vivo model of transcytosis was then evaluated. In the rat, polymeric immunoglobulins are selectively transported from the blood to the bile by plgR expressed by the liver. The rat hepatic bile transcytosis system was therefore chosen as a means to assess the transport of the phage peptides in vivo. For this experiment, a rat was fasted overnight before bile duct cannulation. The rat was anesthetized with ketamine hydrocloride (44 mg/kg body weight), an intravenous (i.v.) saline line was established, and then the bile duct was cannulated with the outlet of the cannula resting approximately 10 cm below the rat. Bile collection began after i.v. injection of test phage and negative control phage particles (in 0.2 ml sterile saline) and was continued for 30 minute time points in separate tubes. Duplicate serum samples may also be obtained to assess peripheral clearance of the phage particles. After bile and serum collection was complete, the animal was sacrificed. FIG. 7 shows the procedure used and results from one rat injected with the IPS test phage. One hundred percent of the phage recovered from all time points displayed the IPS peptide. No nonspecific phage was recovered in this experiment. In addition to hepatic bile transport, the rat model also allows sampling of various other mucosal sites for the presence of a targeting molecule. Mutagenesis studies can be employed to further optimize the binding and transcytosis of the selected phage peptides as well as the native region from dlgA. These reagents will first be tested for transcytosis in the in vitro MDCK transcytosis system and then will need to be assessed in an in vivo model of secretion. EXAMPLE 8: Multimeric Peptides Other experiments were aimed at localizing the smallest possible peptide(s) required for the plgR- dlgA interaction. To this end, the native region from IgA (amino acids 402-410) that is involved in plgR-binding was synthesized in both monomeric and dimeric form (with a small linker) as thioredoxin or Green Fluorescent Protein (GFP) fusion proteins. Flanking amino acids (five residues) on each side of the plgR-binding domain were included. With both the monomer and dimer, a GP(G) 6 PG non-cleavable linker moiety was placed between a plgR-binding domain and the selected agent (SA), either thioredoxin or GFP. An additional GP(G) 6 PG linker was placed between the plgR-binding domains as well. MONOMERIC PEPTIDE: TWASRQEPSQGTTTFAVTSGP fG ) f PG- [SA] 402-410 linker DIMERIC PEPTIDE: TWASRQEPSQGTTTFAVTSGF ( G ) g PGTWASRQEPSOGTTTFAVTSGP ( G ) 6 PG - [SA] 402-410 linker 402-410 linker The peptides were constructed by standard PCR (for the monomeric peptide) and PCR SOEing reactions (for the dimeric peptide) (Horton et al, 1990) using human IgA cDNA and primers which added the GP(G) 6 PG linker as well as convenient restriction sites to the ends of the PCR products. The monomeric and dimeric peptide constructs were then cloned into thioredoxin and GFP fusion protein vectors, expressed in E. coli, and purified by affinity chromatography methods. The ability of thioredoxin alone (negative control) and the thioredoxin fusion proteins to be specifically transported by the plgR in the MDCK transcytosis system has been assessed (FIG. 8). Data indicate that a peptide derived from the native region from the CH3 region of dlgA can indeed direct transport of a fusion protein through plgR-transfected MDCK cells. There appears to be a significant amount of polymerization or aggregation in the preparations of thioredoxin fusion proteins. Clearance/transport analyses will be performed using intact dimeric IgA, Fc fragments of dlgA, recombinant peptides with and without a selected agent, synthetic peptides, and monomeric IgA and IgG as controls. In these experiments, rats will be injected intravenously with the various proteins, the clearance of the molecules measured from serum samples, and the mucosal transport of the molecules assessed from bile samples. In addition, other mucosal sites may be sampled to provide information concerning the quantitative limits of detection of these molecules in this system. All of the compositions and methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain agents that are both chemically and physiologically related may be substituted for the agents described herein while the same or similar results would be achieved. 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Claims: CLAIMS: 1. An isolated peptide of between 10 and about 50 residues comprising a plgR- binding domain. 2. The peptide of claim 1, wherein said peptide is 10 residues in length. 3. The peptide of claim 1, wherein said peptide is about 15 residues in length. 4. The peptide of claim 1, wherein said peptide is about 20 residues in length. 5. The peptide of claim 1, wherein said peptide is about 25 residues in length. 6. The peptide of claim 1, wherein said peptide is about 30 residues in length. 7. The peptide of claim 1, wherein said peptide is about 35 residues in length. 8. The peptide of claim 1, wherein said peptide is about 40 residues in length. 9. The peptide of claim 1, wherein said peptide is about 45 residues in length. 10. The peptide of claim 1 , wherein said peptide is about 50 residues in length. 11. The peptide of claim 1 , wherein said peptide comprises the sequence SEQ ID NO:l. 12. The peptide of claim 1 , wherein said peptide comprises a sequence selected from the group consisting of SEQ ID NOS:2-33. 13. The peptide of claim 1, wherein said peptide comprises a sequence selected from the group consisting of SEQ ID NO:34-41. 14. The peptide of claim 1, further comprising a linking moiety attached to said peptide. 15. The peptide of claim 14, wherein said linking moiety is selected from the group consisting of SMTP, SPDP, LC-SPDP, Sulpho-LC-SDPD, SMCC, Sulfo- SMCC, MBS, Sulfo-MBS, SIAB, Sulfo-SIAB, SMPB, Sulfo-SMPB, EDC/Sulfo- NHS, and ABH. 16. The peptide of claim 14, wherein said linking moiety further is attached to a selected agent. 17. The peptide of claim 16, wherein said selected agent is a peptide, a polypeptide, an oligonucleotide, a polynucleotide, a detectable label, or a drug. 18. The peptide of claim 17, wherein said polypeptide is an enzyme, antibody region, region mediating protein-protein interaction, cytokine, growth factor, hormone, toxin, tumor suppressor, transcription factor, or inducer of apoptosis. 19. The peptide of claim 17, wherein said polynucleotide encodes a polypeptide, a single chain antibody, an antisense construct, or a ribozyme. 20. The peptide of claim 17, wherein said detectable label is rhodamine, fluorescein, or GFP. 21. The peptide of claim 17, wherein said detectable label is a radiolabel. 22. The peptide of claim 17, wherein said drug is an antibiotic, a DNA damaging agent, an enzyme inhibitor, or a metabolite. 23. The peptide of claim 1 , further comprising a non-pIgR targeting agent linked to said peptide. 24. The peptide of claim 23, wherein said non-pIgR targeting agent is an antigen binding domain of an antibody. 25. The peptide of claim 23, wherein said non-pIgR targeting agent is a receptor ligand or a ligand binding domain. 26. The peptide of claim 1 , wherein said peptide comprises two plgR-binding domains. 27. The peptide of claim 26, wherein said peptide further comprises a linking moiety. 28. The peptide of claim 27, wherein said linking moiety further is attached to a selected agent. 29. The peptide of claim 28, wherein said selected agent is a peptide, a polypeptide, an oligonucleotide, a polynucleotide, a detectable label, or a drug. 30. The peptide of claim 29, wherein said polypeptide is an enzyme, antibody region, region mediating protein-protein interaction, cytokine, growth factor, hormone, toxin, tumor suppressor, transcription factor, or inducer of apoptosis. 31. The peptide of claim 30, wherein said polynucleotide encodes a polypeptide, a single chain antibody, an antisense construct, or a ribozyme. 32. A fusion protein comprising a plgR-binding domain covalently linked to a non-antibody peptide or polypeptide. 33. The fusion protein of claim 32, wherein said domain is Cα3 domain. 34. The fusion protein of claim 32, wherein said non-antibody peptide or polypeptide is selected from the group consisting of an enzyme, region mediating proteimprotein interaction, cytokine, growth factor, hormone, toxin, tumor suppressor, transcription factor, and inducer of apoptosis. 35. A polynucleotide encoding a fusion protein comprising a plgR-binding domain covalently linked to a non-antibody peptide or polypeptide sequence. 36. The polynucleotide of claim 35, wherein said non-antibody peptide or polypeptide is selected from the group consisting of an enzyme, region mediating protein-protein interaction, cytokine, growth factor, hormone, toxin, tumor suppressor, transcription factor, and inducer of apoptosis. 37. A method for targeting a selected agent to mucosal epithelium comprising: (i) providing a complex comprising said selected agent and an isolated peptide of between 10 and about 50 residues comprising a plgR- binding domain; and (ii) administering said targeting complex to a mammal, wherein said complex binds to cells expressing plgR, is taken up by said cells, and is transported to said mucosal epithelium. 38. The method of claim 37, wherein administering is via oral, inhalation, ocular, nasal, vaginal, rectal, intravenous, subcutaneous, intramuscular, or intraarterial routes. 39. The method of claim 37, wherein said complex further comprises a non-pIgR targeting agent. 40. A method for targeting a non-antibody peptide or polypeptide to mucosal epithelium comprising: (i) providing a fusion protein comprising a plgR-binding domain covalently linked to said non-antibody peptide or polypeptide; and (ii) administering said targeting complex to a mammal, wherein said targeting complex binds to cells expressing plgR, is taken up by said cells, and is transported to said mucosal epithelium. 41. The method of claim 40, wherein administering is via oral, ocular, nasal, vaginal, rectal, intravenous or intraarterial routes. 42. The method of claim 40, wherein said fusion protein comprises two plgR- binding domains. 43. A method of delivering a selected agent to a cell comprising: (i) providing a complex comprising said selected agent and an isolated peptide of between 10 and about 50 residues comprising a plgR-binding domain; and (ii) contacting said targeting complex with a cell expressing plgR. 44. The method of claim 43, further comprising a step before step (i) of transforming said cell with an expression construct encoding plgR under the control of a promoter operable in said cell. 45. The method of claim 43, wherein said complex further comprises a non-pIgR targeting agent. 46. The method of claim 43, wherein said complex comprises two plgR-binding domains. 47. A method of delivering a non-antibody peptide or polypeptide to a cell comprising: (i) providing a fusion protein comprising a plgR-binding domain covalently linked to said non-antibody peptide or polypeptide; and (ii) contacting said fusion protein with a cell expressing plgR. 48. The method of claim 47, further comprising a step before step (i) of transforming said cell with an expression construct encoding plgR under the control of a promoter operable in said cell. 49. The method of claim 47, wherein said complex further comprises a nonpIgR targeting agent. 50. The method of claim 47, wherein said fusion protein comprises two plgR- binding domains.

Inventors: CAPRA J DONALD, HEXHAM J MARK, MANDECKI WLODECK, WHITE KENDRA, CAPRA, J., DONALD, HEXHAM, J., MARK, MANDECKI, WLODECK, WHITE, KENDRA
Applicants: CAPRA J DONALD, DGI BIOTECHNOLOGIES, HEXHAM J MARK, MANDECKI WLODECK, OKLAHOMA MED RES FOUND, UNIV TEXAS, WHITE KENDRA, BOARD OF REGENTS, THE UNIVERSITY OF TEXAS SYSTEM, CAPRA, J., DONALD, HEXHAM, J., MARK, MANDECKI, WLODECK, OKLAHOMA MEDICAL RESEARCH FOUNDATION, WHITE, KENDRA
Application year: 2000
Main classification: C07K14
IPC codes: A61K38, A61K45, A61K47, A61P1, A61P11, A61P13, A61P29, A61P31, A61P33, A61P35, C07K14, C07K19, C12N15, C40B40