WO2005037218A2

WO2005037218A2 - Lentiviral vector delivery of il-21 for treatment of cancer

Info

Publication number: WO2005037218A2
Application number: PCT/US2004/034096
Authority: WO
Inventors: Paul Toman
Original assignee: Actis Biologics, Inc.
Priority date: 2003-10-17
Filing date: 2004-10-18
Publication date: 2005-04-28
Also published as: WO2005037218A3

Abstract

Lentiviral vectors are advantageously used to obtain IL-21 expression.

Description

LENTIVIRAL VECTOR DELIVERY OF B -21 FOR TREATMENT OF CANCER FIELD OF THE INVENTION

[0001] The invention relates to compositions and methods for treating cancer or malignancies by administering a lentiviral vector containing the interleukin-21 (IL- 21) gene to patients in a manner in which the gene will be expressed to produce secreted bioactive IL-21 protein in a target tissue.

BACKGROUND OF INVENTION

[0002] Cytokines are small soluble molecules that operate in all tissues and play a key role in immune and inflammatory processes. They affect several physiological processes, including cellular division and proliferation, differentiation, and activation of subsets of mature hematopoietic and immune cells. Although their structures are different, the cytokines can be classified into several groups. For example, IL-2, LL-4 and EL- 15 show homology with each other, and members within the interferon-alpha (EFN-α) and IFN-β families show similar structural motifs.

[0003] Cytokines act as soluble mediators that transmit their effect through ligand- specific receptors. These receptors are either class I or class II receptors. The class I receptor family includes the receptors for IL-2 to -7, IL-9, IL-11 to -13, EL-15, and leptin and growth factor. The class II receptor family includes receptors for EL- 10, and EFN-α, IFN-β and IFN-γ.

[0004] A description of several of the interleukins are summarized in Principles and Practice of the Biologic Therapy of Cancer (S. Rosenberg, Ed.) Lippincott Williams & Wilkins, 2000. To date, only one interleukin has been approved for human therapeutic use. IL-2 was originally discovered as a growth factor for T- cells and is currently approved for treatment of malignant melanoma and renal cell carcinoma (Proleukin, Chiron, Emeryville, CA). IL-2 is produced by activated T- cells. However, IL-2 has multiple life-threatening side effects in patients including capillary leak syndrome, flu-like symptoms, and other toxicities including low blood pressure, decreased kidney and lung function, respiratory distress, cardiac abnormalities and changes in mental status and edema. As a result, IL-2 often is administered to patients in the intensive care unit of a hospital for the duration of the treatment.

[0005] IL-21 gene sequence and biological activity has been described by Parrish- Novak et al. (2000) Nature 408, 57-63, Kasaian et al. (2002) Immunity 16, 559-69, Parrish-Novak et al. (2002) J. Leukocyte Biol. 72, 856-63, and the polypeptide has been produced using recombinant methodology by Parrish-Novak et al (2000) and Asano et al. (2002) FEBS Lett. 528, 70-6. The receptor for IL-21 was first discovered by Parrish-Novak et al. (2000) ibid, and from that work the human and mouse IL-21 polypeptide was first described in the literature. The IL-21 receptor also has been described by Ozaki et al. (2000) Proc. Natl. Acad. Sci. 97, 11439-44. The structures of the genes for IL-2, IL-15 and IL-21 show similarities, suggesting that they arose from a common ancestral gene.

[0006] IL-21 is not detectable in normal tissues by Northern blot analysis but the CD4⁺ subset of T-cells can be stimulated to produce IL-21 using anti-CD3 and anti-CD28 antibodies. IL-21 has no effect on resting B-cells, but enhances B-cell proliferation when stimulated by anti-CD40 antibodies. It is postulated that IL-21 plays a key regulatory role in the immune response by expanding CD4⁺ helper T- cells and enhances B-cell activation after its interaction with T-cells.

[0007] Natural killer (NK) cells, also known as null cells, play multiple roles in the innate immune response in humans and mammals. However, their main role is to help control infections due to microbial pathogens and viruses (Biron et al. (1999) Ann. Rev. Immunol. 17, 189-220). During acute microbial or viral infections, infected cells secrete cytokine mediators that stimulate NK activation. NK cells respond to these mediators by proliferation and maturation, and by increased cytokine production e.g. EFN-γ production, and increased cytotoxicity response. NK cells also play a role in the immune response to malignant cells and may help control cancer. Whiteside et al. (1998) Curr. Top. Microbiol. Immunol. 230, 221- 44 discusses the role of NK cells in the control of tumors.

[0008] IL-21 stimulates both cytotoxicity and EFN-γ production in activated NK cells. IL-21 works in conjunction with IL-15 to expand the population of NK cells. Combination treatment of IL-21 with either IL-2 or IL-15 enhances the lytic function of NK cells and increases the production of IFN-γ over treatment of IL-2 or IL-15 alone (Parrish-Novak et al. (2002).

[0009] As a result of IL-21 ' s involvement with both the innate arm of the immune response through its action on NK cells, and influence on the adaptive immune response through activated B- and T-cells, it has been postulated by Kasaian et al. that IL-21 may play a key role in the transition between these two arms of the immune response.

[00010] One issue with the use of IL-21 protein, as for other proteins, for cancer therapy is the fluctuation of IL-21 concentration at the tumor site. IL-21 protein delivered as a bolus to the tumor site or systemically through IN injection will result in a protein concentration spike followed by removal and degradation, resulting in potential sub-therapeutic levels at the tumor site. As examples, Intron- A^® (interferon-alpha, Schering, Kenilworth, ΝJ) and Proleukin (interleukin-2, Chiron, Emeryville, CA) have elimination half-lives of approximately 2 and 1.5 hours, respectively (see package insert for each product). Pegylation of proteins often extends therapeutic protein half-lives (Harris and Chess (2003) Nat. Rev. Drug Discov. 2, 214-21), but patients still require re-treatment to elevate protein concentrations to therapeutic levels. For long-term patient treatment, multiple deliveries of IL-21 protein will be required to inhibit tumor growth. For therapeutic proteins with short half-lives, such as IL-2 and IFN-α, patient treatment can be as frequent as one-to-three times a day. A substantial need is to deliver a constant therapeutic dose to patients over the long periods of time required to ameliorate tumors or malignancies. [00011 ] An alternative approach to deliver therapeutic levels of IL-21 include delivering the IL-21 gene operatively linked to a promoter into cells which then will synthesize and secrete bioactive IL-21 protein. Naked DNA and liposome- coated DNA are two established non-viral methods of delivering genes into cells. However, these methods also result in transient expression of the therapeutic proteins (Romano et al. (2000) Stem Cells 18, 19-39) and are not suitable for long- term delivery of consistent levels required for maximal therapeutic treatment. An additional shortcoming of non- viral delivery systems is that large amounts of naked DNA are required for therapeutic effects as a result of cellular defense systems (Crystal (1995) Nat. Med. 1, 15-7).

[00012] Viral gene delivery systems are described in Romano et al. and Mah et al. (2002) Clin. Pharmcokin. 41, 901-11. Common viral systems include Adenovirus, Adeno-associated virus (AAV), and retroviruses. These systems have been used to deliver a variety of genes to ameliorate genetic deficiencies in cells. They also have been used to correct genetic deficiencies in animals and humans, with either direct administration into patients or ex vivo treatment of cells with subsequent re- introduction of these cells into animals or patients. However, Adenoviral and AAV vectors do not integrate into the host cells and express proteins transiently, also requiring re-administration to patients for long-term therapeutic treatment. Retroviral sequences integrate into the host cell but often are inactivated after a few weeks by methylation of their promoter region by the host cell (Duch et al. (1994) J. Virol. 68, 5596-601; Chang and He (2001) Curr. Opin. Mol. Therap. 3, 468-75).

[00013] The lentiviral vector has several advantages over other gene delivery systems; it is highly efficient for transduction of foreign genes into mammalian cells, it can transduce non-dividing cells, it can direct the long-term expression of therapeutic proteins, and it can be delivered efficiently both in vitro and in vivo (Naldini (1998) Curr. Opin. Biotechnol. 8, 457-63). [00014] Lentiviral vectors have been developed and are targeted for treatment of a variety of genetic and acquired diseases (Galimi and Verma (2001) Curr. Topics Micro. Immunol. 261, 245-54; Klimatcheva et al. (1999) Front. Biosci. 4, D481- 96). A major focus of lentiviral vectors for human disease treatments are for gene transfer into neurons for CNS disease treatment e.g. for treatment of lysosomal storage diseases, Huntington's and Parkinson's diseases, into hematopoietic progenitor cells for treatment of lympho-hematological disorders e.g. sickle cell and β-thalassemia as well as for hemophilias, and for applications to HIV infections (Yee and Zaia (2001) Som. Cell Mol. Genet. 26, 159-74; Deglon and Aebischer (2001) Curr. Topics Micro. Immunol. 261, 191-210; Salmon and Trono, Curr. Topics Micro. Immunol. 261, 211-28; Amado and Chen, Curr. Topics Micro. Immunol. 261, 229-44).

[00015] There are several reports of the use of lentiviral vectors for potential use in oncology. Lentiviral vectors have been used ex vivo to deliver immunogenic proteins to inactivated cancer cells for production of anti-cancer vaccines (Nawrocki et al. (2001) Expert Opin. Biol. Ther. 1, 193-204; Koya et al. (2002) Leukemia 1 , 1645-54), ex vivo to deliver immunomodulatory proteins to dendritic cells to stimulate an anti-tumor response (Stripecke et al. (2003) Blood Cells Mol. Dis. 31, 28-37), and to delivery toxins e.g. diphtheria toxin (Yu et al (2001) Cancer Gene Ther. 8, 628-35), suicide genes e.g. HSV thymidine kinase (Kong et al. (2003) In Vivo 17, 153-6; Del Palma et al. (2003) Nat. Med. 9, 789- 95) or transporter proteins (Dingli et al. (2003) Gene Ther. 102, 489-96) in attempts to directly kill cancer cells. With the exception of lentiviral delivery of INF-α to mice previously injected with ovarian cancer cells (Indraccolo et al. (2002) Cancer Res. 62, 6099-107), no other use of a lentivirus vector has been used to deliver an immunomodulating protein in vivo.

[00016] There is one report by Ugai et al. (2003) Cancer Gene Ther. 10, 187-92, in which mouse IL-21 is delivered to colon carcinoma cells and subsequently injected into mice to show anti-tumor activity. However, this work utilizes a retroviral delivery system, and the cells are transduced and selected for high IL-21 expression ex vivo before implantation into mice.

[00017] Our instant invention is based on in vivo delivery of the IL-21 gene via a lentiviral delivery system. Production and secretion of IL-21 protein into the tumor microenvironment can be accomplished by either tumor cells or normal cells surrounding the tumor.

[00018] Although a focus on cancer therapy has been a high priority in the medical community, new treatments are required to address the progression of this set of diseases. Most cancer treatments have a high toxicity profile and are not tolerated by patients. New therapeutic molecules targeted to the tumor site without systemic delivery promises to provide improved efficacy of the drugs while minimizing side effects.

[00019] IL-21 shows significant promise for the treatment of melanoma, renal cell carcinoma, leukemia, colon carcinoma and potentially other types of cancer. As with most therapies, dosage levels will be key for maximum efficacy of this protein. Ideally, the delivery of IL-21 protein at a constant dose over long periods of time i.e. greater than 6 months, would be the most primary treatment for the mitigation of melanoma and renal cell carcinomas or malignancies.

SUMMARY OF THE INVENTION

[00020] This invention is directed to a method for the production of therapeutic levels of bioactive IL-21 at a tumor or malignancy site. The lentiviral vector containing the IL-21 gene operatively linked to a promoter active in the targeted tissue is delivered at or near the tumor site. The lentiviral vector delivers the IL-21 gene operatively linked to a promoter into a cell where it stably integrates into the cell's DNA. The promoter directs the synthesis of bioactive IL-21 protein that is secreted from the cell and provides therapeutic levels of IL-21 to the tumor microenvironment. Through IL-21 's biological activity on NK (also known as natural killer cell or null cell), T- or B-cells located at or near the tumor site, the host's immune response will target the cancer cells within the tumor for recognition and eradication by the host's immune system.

[00021] The human IL-21 gene sequence is described in GenBank Accession No. AF254069 and NM_021803, the bovine IL-21 gene sequence is described in AB073021, and the mouse sequence is described in AF254070. Either the entire gene or cDNA, or fragments thereof, that code for a protein that is capable of activating NK, T- or B-cells to direct the host's immune response to target and eradicate cancer cells within a tumor can be used in this instant invention.

[00022] The promoter operatively linked to the IL-21 gene within the lentiviral vector can be constitutive or inducible, and may be tissue-specific. A number of tissue- specific promoters are known. Suitable target cells for expressing the IL-21 gene of interest include muscle cells, colon cells, ovarian cells, liver cells, renal cells and immune cells, for example. The cells can be epithelial cells, endothelial cells or fibroblasts. The leader sequence of the IL-21 can be homologous or heterologous. The IL-21 gene may be a full-length gene that contains introns, a cDNA, a fragment of the gene or cDNA, or a combination thereof. The lentiviral vector may be derived from human, simian, feline, equine, bovine or lentiviruses that infect other mammalian species. The lentiviral vector may contain another therapeutic or suicide or toxic gene e.g. HSV thymidine kinase, operatively linked to an inducible promoter separate from the promoter operatively linked to the IL- 21 gene, or through an IRES (internal ribosome entry site) (de Felipe (2002) Curr. Gene Ther. 2, 355-78). In addition, the lentivirus pharmaceutical formulation can be delivered in conjunction with other therapeutic modalities for the treatment of cancer or malignancies.

[00023] The IL-21 gene, delivered by a lentiviral vector, will result in long-term, stable expression of IL-21 protein. The expression of exogenous IL-21 directed by the lentiviral vector will stimulate NK cell cytokine release, enhance NK cell cytotoxicity activity, reduce tumor cell growth rate, stimulate T-cell proliferation, or stimulate B-cell proliferation. As a result of IL-21's action on NK, T- or B-cells, the patient's tumor burden at or near the site of IL-21 lentiviral vector delivery will stabilize or decrease. Such immune system cells are suitable hosts for expressing the IL-21 of interest.

[00024] We describe a method for the treatment of melanoma, renal cell carcinoma, leukemia, colon carcinoma and potentially other cancer types in patients by delivering a lentiviral vector containing the IL-21 gene that will express a local therapeutic level of bioactive IL-21 protein at the tumor site. The method involves administering the lentiviral vector into or near the tumor site using direct injection. The lentiviral vector can transduce either the cancer cells or the nearby normal cells, or both cell populations, and contribute to the therapeutic effect within the microenvironment of the tumor. The lentiviral vector containing the IL-21 gene can be delivered in conjunction with other cancer treatments, such as surgical intervention, radiation therapy, hormonal therapy, immunotherapy, chemotherapy or cryotherapy. DETAILED DESCRIPTION OF THE INVENTION

[00025] The present invention relates to methods of treating a cancer or malignancy in a patient by administering a lentiviral vector with the gene for IL-21 operatively linked to a promoter to deliver an effective therapeutic amount of IL-21 at the tumor site. Such cancer or malignancy include melanoma, renal cell carcinoma, leukemia, colon carcinoma, and potentially other cancer types in which the cancer cells do not elicit a strong host immune response.

[00026] The genetic material for use of the method of the invention coding for the desired IL-21 is available. The gene sequence for human IL-21 is described in GenBank Accession No. AF254069 and NM_021803, the bovine IL-21 gene sequence is described in AB073021, and the mouse sequence is described in AF254070.

[00027] "Gene", as used herein, refers to mammalian IL-21 , preferably human IL-21 , gene, cDNA, DNA, nucleic acid, oligonucleotide, polynucleotide, or fragments or portions thereof that encode all or part of IL-21. This gene may contain introns. The IL-21 gene encompasses naturally occurring polymorphisms described in the general population that change the nucleotide sequence and may change the amino acid sequence. By way of a non-limiting example, fragments or portions include nucleic acid fragments at least 70-100 nucleotides or greater. The gene can be made by chemical, enzymatic or recombinant methods.

[00028] "Variant", as used herein, refers to an IL-21 gene that has nucleotide changes, as not to change the translated amino acid sequence, or nucleotide changes that result in the translated amino acid sequence generated from the IL-21 gene with an alteration of one or more amino acids in a bioactive IL-21 molecule. The term "variant" includes gene sequences coding for amino acid deletions or insertions, or both, within the IL-21 gene. The term "variant" also includes gene sequences coding for the addition or removal of amino acid residues that participate or direct glycosylation or other post-translational modifications within the IL-21 protein, and may include the presence of a leader sequence or additional amino acids at the N-terminus of the IL-21 polypeptide. A variant of IL-21 also may include gene sequences coding a fusion protein e.g. Glutathione-S-Transferase, linked to the IL- 21 gene.

[00029] An IL-21 polypeptide that is "bioactive", as used herein, refers to polypeptides exhibiting activities similar, but not necessarily identical, to an activity of an IL-21 polypeptide. The bioactive IL-21 polypeptide will stimulate IFN-γ production or cytotoxicity activity in NK cells, or stimulate T-cell or B-cell proliferation. The dose dependency may not be identical to IL-21 polypeptide. The polypeptide can be made in a variety of cells including prokaryotic and eukaryotic cells, including bacteria, insect cells and mammalian cells, such as rat, mouse and human, for example.

[00030] A "lentiviral vector", as used herein, includes vectors based on HTV-1 or HIV-2, or Simian, Feline, Equine, or Bovine Immunodeficiency Virus, or lentiviruses that can infect other mammalian species. The vector of interest is replication defective. A well-developed system for use in the invention method utilizes the HIV- 1 -based lentiviral vector. This system is summarized in Ailles and Naldini, (2002) Curr. Topics Micro. Immunol. 261, 31-52. The lentiviral vector has been extensively modified to increase its safety profile for use in humans. Only approximately 10% of the original viral sequences remain in the transfer vector. The packaging cell required to produce the lentiviral vector is transfected with up to four separate plasmids to minimize recombination.

[00031] "Pharmaceutical compositions", as used herein, include a lentiviral vector that includes the IL-21 gene in association with one or more pharmaceutically acceptable carriers, diluents, or excipients, and may include other active ingredients. Formulations of pharmaceutical compositions may be isotonic aqueous or non-aqueous sterile solutions or suspensions. A preferred formulation is phosphate-buffered saline (PBS). Other carriers, such as lactose, sucrose, mannitol, sorbitol, histidine, glycine, gelatin, collagen, polyvinyl pyrrolidone can be present in the PBS solution. The list of carriers is not exhaustive. The pharmaceutical preparation can be stored at 4° C, -20° C, or -80° C and brought to room temperature, or reconstituted from a powder or dry formulation, prior to administration to a patient.

[00032] The lentiviral vector that includes the IL-21 gene may be administered to a patient by a variety of routes, including injection or topical application. The lentiviral vector pharmaceutical formulation can be injected into a tissue site using a syringe. The site of injection can be intratumoral, intravascular, subcutaneous, intramuscular, or intraperitoneal. The pharmaceutical formulation can be topically applied to a surgical site e.g. after excision of a primary tumor. Additionally, the formulation can be aerosolized for inhalation administration.

[00033] The lentiviral vector can be delivered in a pharmaceutical formulation with other cancer treatments. For example, topoisomerase inhibitor (e.g. campthothecin), tubulin-binding agent (e.g. paclitaxel), alkylating agent (e.g. chlorambucil), antimetabolites (e.g. L-asparaginase), or immune suppressant (e.g. dexamethasone) formulations can be admixed or re-formulated with the lentiviral vector formulation and either injected or topically applied to a patient.

[00034] A patient, as used herein, is a human that has been diagnosed with a cancer or malignancy by a physician. The cancer can originate or be located in a variety of tissues or organs, including but not limited to skin, kidney colon, or hematopoietic or lymphatic systems. This patient may have an early-stage cancer or a later-stage cancer. Other cancer treatments may be applied prior to, concurrently, or after treatment with a lentiviral pharmaceutical formulation containing the IL-21 gene.

[00035] A therapeutic dose refers to the amount of lentiviral vector containing the IL- 21 gene that ameliorates, reduces, or eliminates the cancer or malignancy. The amount of lentiviral vector containing the IL-21 gene will vary depending on the route of administration, the tissue to which it is applied, and the status of the patient, including age, weight, and gender and severity of the cancer or malignancy, all of which will be determined by the physician or practitioner. Therapeutic efficacy and toxicity can be determined by standard procedures using cell culture and animal models to determine a range of therapeutic doses and the toxic dose. Measurements of the lentiviral vector dose can be determined by infection of cells in culture and limiting dilution, or it can be based on ELISA to measure p24 capsid protein (Perkin-Elmer, Boston, MA). The preferred dose is one that has a high efficacy index and a low toxicity index. The range of lentiviral vector as measured by transducing units (TU) for therapeutic treatment of cancer in patients ranges from 10⁵ to 10¹⁰ TU/dose.

[00036] The following non-limiting examples describe the reduction to practice of this invention for the therapeutic treatment of melanoma. However, the invention is not limited to melanoma but can be used for treatment of other cancers such as renal cell carcinoma, lymphoma and colon cancer.

[00037] Example 1. Construct of a lentiviral vector containing the human or mouse IL-21 gene and demonstration that it is capable of directing the synthesis of IL-21 in transduced mammalian cells.

[00038] CD3⁺ cells are isolated from human or mouse peripheral blood mononuclear cells using a Dynabeads CD3 kit (Dynal Biotech, Oslo, Norway). Isolated CD3⁺ cells are treated with 10 ng/ml PMA and 0.5 ug/ml ionomycin (Calbiochem, San Diego, CA) for 13h. mRNA is isolated from these cells using Oligotex Direct mRNA kit (Qiagen, Valencia, CA). Double-stranded cDNA is synthesized using the Superscript™ One-Step RT-PCR System (Invitrogen, Carlsbad, CA) using two primers e.g. forward primer of 5'-ccaaggtctagctctactgttggtac-3' and reverse primer of 5'-gtaacatagtgtccaactgcaagttag-3' for synthesis of the human IL-21 gene, or forward primer of 5 ' -tcatcagctcctggagactcagttc-3 ' and reverse primer of 5 ' - gaatcttctcggatcctcaggaatctt-3' for synthesis of the mouse IL-21 gene, under conditions of 45° C annealing, 72° C extension and 94° C denaturation in a Perkin- Elmer Model 480 Thermal Cycler (Shelton, CT). The resulting PCR products for the human and mouse IL-21 genes are cloned into pBluescript II (Stratagene, La Jolla, CA).

[00039] Lentiviral vectors are described in Zufferey et al. (1998) J. Virol. 72, 9873- 80; Yam et al. (2002) Mol. Ther. 5, 479-84; and Logan et al. (2002) Curr. Opin. Biotechnol. 13, 429-36, and can be obtained from commercial sources e.g. ViraPower™ Lentiviral Expression System (Invitrogen) and LentiPak™ (Genetix Pharmaceuticals, Cambridge, MA). These vectors have convenient restriction sites for insertion of cDNA and contain the CMV promoter. The human or mouse IL-21 gene is introduced in combination with its homologous signal sequence and poly(A) sites. The vector plasmid constructs are co-transfected with 2 core packaging plasmids and the VSV-G envelope plasmid by Calcium Phosphate precipitation. 20 ug (450 ul) of plasmid mix is added to a 100 mm dish containing 5 x 10⁶ 293 cells (CRL-1573, ATCC, Manassas, VA) grown in Iscove modified Dulbecco culture medium (JRH Biosciences, Lenexa, KS) with 10% FBS. Fresh media is added at 16 h post-transfection, and conditioned media is harvested at 24 h after fresh media addition. The media is cleared by low-speed centrifugation, filtered through a 0.2 um cellulose acetate filter, and stored at -80° C. Titer of the viral preparation (in Transducing Units, TU) is determined by quantitative PCR using limited dilution on 293 cells as well as measurement of total viral particles using a p24 capsid protein ELISA assay (Perkin-Elmer).

[00040] Lentiviral vector preparation (10⁷ TU/ml) is added to HeLa cells seeded at 2 x 10⁵ cells. Media is harvested at 48 h and the amount of human or mouse IL-21 protein is quantified by an ELISA specific for either human or mouse IL-21, respectively.

[00041] Example 2. Measurement of IL-21 specific activity.

[00042] Five 100 mm plates of 293 cells are transfected with the lentiviral vector containing either the human or mouse IL-21 as described in Example 1. Conditioned media is harvested at 24 and 48 h post-transfection, pooled and processed as described in Example 1. This media is characterized for p24 capsid protein and TU. The conditioned media is added into HeLa cells and conditioned media containing IL-21 from these cultures is harvested after 24 and 48 h as described in Example 1. IL-21 protein production is quantified by ELISA as described in Example 1 and concentrated to approx. 100 ng/ml.

[00043] Human NK cells are isolated using the NK Isolation Kit II (Miltenyi Biotec, Auburn, CA) according to the manufacturer's instructions. Mouse NK cells are isolated using the NK Isolation Kit (Miltenyi Biotec) according to the manufacturer's instructions. NK cells are activated with and without IL-21 for 16 h and the NK cytotoxicity assay is performed as described in the next paragraph.

[00044] Five effector cell dilutions are prepared to give a starting effector/target (E/T) ratio of 6.6: 1. K562 target cells (CCL-243, ATCC), an NK sensitive cell line, are labeled with ⁵¹Cr. Effector and target cells are added in triplicate to a 96-well plate. Six wells with target cells plus media and six wells with target cells plus 3% Triton X-100 are prepared to measure spontaneous and total release respectively. The assay is run in triplicate. Plates are incubated in a humidified 37° C, 5% C0₂ incubator for 4 hours. Supernatant from each well is harvested and radioactivity of the samples is measured using a gamma counter. Percent lysis of each effector cell dilution is calculated.

[00045] Example 3. Transduction efficiency in melanoma, renal cell carcinoma, leukemia, and colon carcinoma cells in vitro.

[00046] The following cell lines (obtained from ATCC) are transduced with lentiviral vector containing either the human or mouse IL-21 gene, respectively, at a MOI of 1 - 5.

Cancer Type Human Cell Mouse Cell Melanoma A375 (CRL-1619) B16-F10 (CRL-6475) Renal Carcinoma Caki-1 (HT-46) Renca Leukemia MOLT-4 (CRL-1582) L1210 (CCL-219) Colon Carcinoma SW480 (CCL-228) CT26.WT (CRL-2638)

[00047] After 48 h, one-half of the cells are harvested and the percentages of cells that are transduced are measured by quantitative PCR using primers specific to the lentivirus vector. Also at 48 h, the 2nd half of the cells are harvested and processed for analysis in the NK cytotoxicity assay as described in Example 2. Media is harvested and quantified for IL-21 protein production by ELISA as described in Example 1.

[00048] Example 4. Determine the efficacy of IL-21 delivered via gene delivery by treating mice previously inoculated with mouse melanoma cancer cells for the mitigation of tumor growth, and compare efficacy by IL-21 -gene delivery vs. delivery of an IL-21 protein depot.

[00049] Four BALB/c mouse cohorts of 5 animals per cohort are tested: 1) no treatment control, 2) treatment with lentiviral vector containing the mouse IL-21 gene, 3) treatment with mouse IL-21 protein, and 4) control vector. 3 x 10⁶ Bl/6- F10 tumor cells are injected subcutaneously into each mouse. After 7-10 days post- tumor injection, 1 of 3 concentrations (as defined in Example 3) of lentiviral vector containing the mouse IL-21 gene are injected into each tumor site of one cohort of mice using a syringe. As positive control, mouse IL-21 protein is injected into the tumor site of a separate cohort of animals. As negative controls, a 3rd cohort of mice is injected with saline, and a 4th cohort is injected with a lentiviral vector without the IL-21 gene. Caliper measurements are performed every 2nd day to measure the size of the developing tumors. When the tumor size reaches 20 mm in any dimension (approximately 5-7 weeks), the mice are sacrificed and the primary tumors, draining lymph nodes, and lungs are examined by gross visualization, histopathology, and immunohistochemistry. RT-PCR and PCR measure the presence of mouse IL-21 protein expression, mouse IL-21 RNA transcripts, and the presence of lentiviral vector DNA. [00050] All references cited herein are herein incorporated by reference in entirety.

[00051 ] The invention hereinabove being described, it will be evident that various modifications can be made thereto without departing from the scope and spirit of the invention.

Claims

WE CLAIM:

1. A method for the expression of a polypeptide comprising stably introducing into a target mammalian cell a DNA construct comprising a nucleotide sequence encoding an IL-21 polypeptide or a functional variant thereof, wherein said DNA construct is contained in a lentiviral gene delivery vehicle.

2. The method of claim 1 , wherein said DNA construct is introduced into said target mammalian cell in vivo by injection of said lentiviral gene delivery vehicle into a target tissue or organ containing said target mammalian cell.

3. The method of claim 1 , wherein said DNA construct is introduced into said target mammalian cell in vitro by transduction of said lentiviral gene delivery vehicle.

4. The method of claim 1, 2, or 3, wherein said target mammalian cell is a muscle cell.

5. The method of claim 1 , 2, or 3, wherein said target mammalian cell is a colon epithelial cell.

6. The method of claim 1, 2, or 3, wherein said target mammalian cell is an ovarian epithelial cell.

7. The method of claim 1, 2, or 3, wherein said target mammalian cell is a renal epithelial cell.

8. The method of claim 1, 2, or 3, wherein said target mammalian cell s a fibroblast.

9. The method of claim 1, 2, or 3, wherein said target mammalian cell is a hepatocyte.

10. The method of claim 1, 2, or 3, wherein said target mammalian cell is a B cell.

11. The method of claim 1 , 2, or 3 , wherein said target mammalian cell is a T cell.

12. The method of claim 1, 2, or 3, wherein said target mammalian cell is a null cell.

13. The method of claim 1 , 2, or 3, wherein said DNA construct further comprises a promoter operably linked to said nucleotide sequence encoding IL-21 polypeptide or a functional variant thereof and is operable in said target mammalian cell in vivo or in vitro.

14. The method of claim 13, wherein said promoter is a muscle cell- specific promoter.

15. The method of claim 13, wherein said promoter is a colon cell- specific promoter.

16. The method of claim 13, wherein said promoter is an ovarian cell- specific promoter.

17. The method of claim 13, wherein said promoter is a renal cell- specific promoter.

18. The method of claim 13 , wherein said promoter is a fibroblast- specific promoter.

19. The method of claim 13 , wherein said promoter is a hepatocyte- specific promoter.

20. The method of claim 13, wherein said promoter is a B cell-specific promoter.

21. The method of claim 13 , wherein said promoter is a T cell-specific promoter.

22. The method of claim 13, wherein said promoter is a null cell- specific promoter.

23. The method of claim 13, wherein said promoter is a constitutive promoter.

24. The method of claim 13, wherein said promoter is an inducible promoter.

25. The method of claim 13, wherein said DNA construct further comprises a suicide gene.

26. A method of inhibiting the growth of a tumor in a mammal, the method comprising directly administering to cells in a target tissue or organ containing said tumor, a lentiviral vector comprising a nucleic acid sequence encoding a IL-21 polypeptide operably linked to a promoter, wherein expression of said nucleic acid sequence results in a modulation of tumor growth.

27. The method of claim 26, wherein said vector is administered to said target tissue or organ by injection so said vector is at or near said tumor.

28. The method of claim 26, wherein said modulation of tumor growth is enhancing natural killer cell activity.

29. The method of claim 26, wherein said modulation of tumor growth is reduction in tumor cell growth rate.

30. The method of claim 26, wherein said modulation is destruction of said tumor.

31. The method of claim 16, further comprising additional treatment selected from surgical intervention, radiation therapy, hormonal therapy, immunotherapy, chemotherapy, and cryotherapy.

32. A target mammalian cell having stably incorporated a lentiviral DNA construct comprising a nucleotide sequence encoding an IL-21 polypeptide or a functional variant thereof, operably linked to a promoter active in said target mammalian cell.

33. The transformed target mammalian cell of claim 32, wherein said promoter is muscle cell-specific.

34. The transformed target mammalian cell of claim 32, wherein said promoter is colon cell-specific.

35. The transformed target mammalian cell of claim 32, wherein said promoter is ovarian cell-specific.

36. The transformed target mammalian cell of claim 32, wherein said promoter is renal cell-specific.

37. The transformed target mammalian cell of claim 32, wherein said promoter is fibroblast-specific.

38. The transformed target mammalian cell of claim 32, wherein said promoter is hepatocyte-specific.

39. The transformed target mammalian cell of claim 32, wherein said promoter is B cell-specific.

40. The transformed target mammalian cell of claim 32, wherein said promoter is T cell-specific.

41. The transformed target mammalian cell of claim 32, wherein said promoter is null cell-specific.

42. The transformed target mammalian cell of claim 32, wherein said promoter is constitutive.

43. The transformed target mammalian cell of claim 32, wherein said promoter is inducible.

44. The transformed target mammalian cell of claim 32, wherein said cell is from a mouse.

45. The transformed target mammalian cell of claim 32, wherein said cell is from a rat.

46. The transformed target mammalian cell of claim 32, wherein said cell is from a human.

47. An epithelial cell that expresses a normal IL-21 gene introduced therein through lentiviral transduction.

48. A recombinant lentiviral vector comprising a normal IL-21 gene or a functional variant thereof, operatively linked to a promoter that is operable in a target cell in vivo or in vitro.

49. The recombinant vector of claim 48, which is replication-defective.

50. The recombinant vector of claim 48, wherein said target cell is a muscle cell.

51. The recombinant vector of claim 48, wherein said target cell is a colon cell.

52. The recombinant vector of claim 48, wherein said target cell is a ovarian cell.

53. The recombinant vector of claim 48, wherein said target cell is a renal cell.

54. The recombinant vector of claim 48, wherein said target cell is a fibroblast.

55. The recombinant vector of claim 48, wherein said target cell is a hepatocyte.

56. The recombinant vector of claim 48, wherein said target cell is a B cell.

57. The recombinant vector of claim 48, wherein said target cell is a T cell.

58. The recombinant vector of claim 48, wherein said target cell is a null cell.

59. A pharmaceutical composition comprising the vector of claim 48 and a pharmaceutically acceptable carrier.