IL-12 Gene Therapy of Tumors

The present invention relates generally to the field of treatment of tumors, and relates in particular to the direct delivery into skin cells of a genetic construct containing the IL-12 gene.

Interleukin (IL) 12, formerly termed natural killer cell-stimulatory factor or cytotoxic lymphocyte maturation factor, is a disulfide-linked heterodimeric cytokine composed of 35-and 40-kDa subunits; the subunits are commonly designated "p35" and "p40". The complimentary DNAs encoding the p35 and p40 subunits from both the mouse and humans have been sequenced and cloned, and both human and mouse IL-12 have been shown to act as growth factors for natural killer ("NK") cell and T-cell, in vitro and in vivo. Furthermore, IL-12 has also proven to be effective in regression and complete disappearance of murine tumors. Tahara et al., Cancer Research 54 (1): 182-9, 1994; Brunda et al., J. EXP. MED. 178 (4): 123-30, 1993.

However, because IL-12 has a short half life in vivo, frequent injections of the cytokine are needed to achieve therapeutic effects. Moreover, relatively large quantities of IL-12 (in the range of 1-10 .mu.g/day) are typically required. Therefore, administration of recombinant IL-12 often resulted in toxicity.

IL-12 gene therapy using retroviral vectors is underway in several laboratories, and its anti-tumor effect has been demonstrated. Lotze, M. T., et al., J. Cell. Biochem., p.184, 1993.; Robbins, et al., Cancer Gene Therapy 1(2):147, 1994. In the Lotze, et al. study, the genes for IL-12 p35 and p40 subunits were inserted into NIH 3T3 fibroblasts. The fibroblasts were used to deliver IL-12 at the site of tumors, delaying growth of a variety of murine tumors. In the Robbins, et al. study, the direct delivery of IL-12 to several different mouse tumor lines by retroviral-mediated transduction prior to inoculation or to fibroblasts that were then coadministered with tumor cells resulted in inhibition of tumor growth as well as in the induction of antitumor immunity.

However, to date, it was not possible to cause reliable regression of established tumors and their spontaneous metastases using direct IL-12 gene therapy.

The present invention is summarized in that an anti-tumor response can be effected after transfer to a mammalian animal of a DNA molecule that encodes the cytokine IL-12.

In one aspect the invention is a method to treat tumors in an animal, preferably a mammal and most preferably a human, by genetic therapy. In the method, copies of a foreign genetic construction are prepared. The genetic construction includes a promoter operative in cells of the animal and protein coding regions encoding both the p35 and p40 subunits of the cytokine IL-12. The foreign genetic construction is then physically delivered into the epidermis of the tumor-bearing animal in need of such genetic therapy.

In another aspect, the invention provides a genetic construct for treating tumors. The construct is provided by operatively joining DNA sequences encoding the p35 and p40 subunits of the cytokine IL-12 to a promoter effective in the animal's cells. The construct is suitable for transduction into cells of an animal by, for example, a particle-mediated transfection process.

It is an object of the present invention to enable the treatment of tumors through the use of an IL-12 genetic construct.

It is a feature of the present invention in that it is adapted to either epidermal or mucosal delivery of the genetic construct.

It is an advantage of the genetic treatment of the present invention that it is inherently safe, not painful to administer, and should not result in adverse consequences to treated individuals.

It is a further advantage of the genetic treatment of the present invention that the genetic treatment is effective even when delivered to a site distant from the tumor, and immunological memory is retained after genetic treatment ceases.

Other objects, advantages and features of the present invention will become apparent from the following specification.

FIG. 1 is a plasmid map of the IL-12 plasmid pWRG3169.

FIG. 2 is a plasmid map of the IL-12 plasmid pWRG3196.

FIG. 3 is a graph presenting tumor growth patterns in IL-12 gene-treated and control mice.

FIGS. 4A-4F are graphs presenting change in diameter of various induced solid tumors after treatment using IL-12 genes.

The present specification describes a method to treat tumors by delivering a genetic construct encoding the p35 and p40 subunits of IL-12 protein into the epidermis of a patient at the tumor site. The tumors can be solid tumors or metastatic or disseminated tumors, and can be microscopic or visible with the naked eye. Once the construct is delivered, the heterodimeric IL-12 cytokine is expressed, resulting in the creation of an anti-tumor response in treated individuals, even when the tumor is far removed from the delivery site.

In order to achieve the genetic treatment sought of the present invention, an IL-12 genetic construction is created in which the IL-12-encoding genes are placed under the control of a promoter operative in the cells of a target mammalian animal. When transfected into cells of a treated animal, a suitable construct causes expression of the IL-12 protein.

IL-12 protein is actually a heterodimer that includes a 35 kDa (p35) and a 40 kDa (p40) subunit. Each subunit is encoded by a distinct gene. The IL-12 p35- and p40-encoding DNA sequences can be obtained or derived from a mammalian animal source, preferably from a human source. A full-length DNA sequence encoding human IL-12 subunits has been published by Gubler, et al., Proc. Natl. Acad. Sci. USA 88: 4143-4147, 1991. The published human nucleic acid and amino acid sequences of a p35 subunit are available at GenBank Accession number M65271. Similarly, the nucleic acid and amino acid sequences of a human p40 subunit are also available at GenBank Accession number M65272.

Alternatively, the IL-12 subunit-encoding sequences can be obtained from any other non-human animal that produces IL-12. The IL-12 subunit-encoding sequences may be obtained or derived from other species which demonstrate sufficient sequence identity to be functionally equivalent to human IL-12. For example, IL-12 is known to be produced by mice. Mice sequences were used in the example constructs reported herein. A p35-encoding DNA is reported at GenBank Accession number M86672. The p40-encoding DNA is also available from GenBank.

Also, in vitro-synthesized coding sequences encoding IL-12 p35 and p40 subunits can readily be prepared in quantities sufficient for molecular cloning using standard recombinant molecular biological techniques, including PCR amplification and hybridization, using the published DNA sequence as a guiding template.

It may also be possible to further modify the subunit-encoding DNA molecules and protein subunits disclosed herein, while still maintaining the antitumor activity of the present invention. The present invention is intended to include truncated natural IL-12 DNA having the nucleic acid sequences described herein, as well as all altered, varied and modified forms of the DNA. These can include, but are not limited to substantially homologous DNA fragments having additions, deletions, and point mutations, relative to the disclosed nucleic acid sequences including truncation at the 5' and/or 3' end. A substantially homologous DNA fragment is one wherein the fragment encodes a polypeptide that exhibits significant antitumor activity and/or regression after delivery, even if such DNA differs in nucleic sequence or encodes a protein that differs in amino acid sequence from the DNA fragments or proteins disclosed herein. Anti-tumor activity of such truncated DNA molecules can be monitored as described below.

One skilled in the art will recognize that certain silent changes to the nucleic acid sequence have no effect on the amino acid encoded by a particular triplet. Even certain amino acid changes that do not affect, or only somewhat affect, the IL-12 activity of the encoded protein may be used within the scope of the invention. Any nucleic acid or amino acid sequence that results in anti-tumor activity that is at least 75% of the activity obtained using the murine IL-12 (mIL-12) genes tested as described in the following Examples may be used in the present invention.

Of course, if the gene encoding an IL-12 protein is engineered into a genetic construct for delivery into a host of a species other than that from which the gene derives, an immune response may occur after gene transfer. However, one skilled in the art will understand that by modifying the nucleic acid sequence of the mature IL-12 portion of the delivery gene, it is possible to eliminate such effect.

To properly express the IL-12 subunit genetic sequences in transfected cells, a promoter sequence operable in the target cells is needed. Several such promoters are known for mammalian systems which may be joined 5', or upstream, of the coding sequence for the protein to be expressed. A preferred promoter is the CMV promoter, the sequence of which is well known and which has been published at Cell, 41:521-530 (1995). A downstream transcriptional terminator, or polyadenylation sequence, may also be added 3' to the protein coding sequence. A preferred polyadenylation sequence is the bovine growth hormone poly A region, the sequence of which is known. Splice donor and splice acceptor (SD/SA) sites, such as the SV40 SD/SA, may also be positioned in the construct if desired, as may an internal ribosome entry site (IRES), such as the IRES cloned from encephalomyocarditis virus.

As the inventors describe in more detail in the Examples, below, it has been determined that expression of the two protein-encoding sequences from separate transcription units on a single plasmid results in significantly higher protein levels than are observed when bicistronic expression of the genes is driven from a single promoter. Thus, for purposes of this invention, it is preferred that each coding region be provided with a separate promoter.

In the present invention, a suitable genetic construct encoding IL-12 protein subunits is transferred into the susceptible individual. A genetic treatment can be delivered in a non-invasive manner to a variety of susceptible tissue types in order to achieve the desired immunological response in the individual.

It is herein disclosed that when treating tumors with the IL-12 genetic construct, the preferred target cells are epidermal cells rather than cells of deeper skin layers such as the dermis. Epidermal cells are preferred recipients of the IL-12 genetic construct because they are the most accessible cells of the body. Patients in need of such genetic therapy may advantageously, therefore, be treated non-invasively. Moreover, quite unexpectedly, and contrary to what some might think, epidermal delivery of the IL-12 gene successfully treats tumors far removed from the delivery site, and furthermore, generates systemic anti-tumor immunity, immunological memory, and cytotoxic responses. Therefore, epidermal delivery is well particularly suited for non-invasive delivery of the IL-12 genes.

Inasmuch as IL-12 genetic construct treatment has proven successful in eliciting successful anti-tumor responses following gene gun-based IL-12 genetic construct delivery to the skin, it is also probable that non-invasive delivery of the IL-12 genetic construct to mucosal surfaces will result in successful treatment responses as well.

It is also specifically envisioned that aqueous droplets containing naked IL-12 DNA can be delivered directly into the tissues of the individual sought to be treated. At some frequency, such "naked" DNA will be taken up in the treated tissues.

The preferred transfer means for non-invasive delivery is an accelerated particle gene transfer device, although any means that can reliably transfer the construct into the suitable target sites (epidermis or mucosal tissue) is acceptable. The technique of accelerated-particle gene delivery is based on the coating of genetic constructions to be delivered into cells onto extremely small carrier particles, preferably gold particles, which are designed to be small in relation to the cells sought to be transformed by the process. The gold particles may be beads or spheres or amorphous gold. All are suitable for use in the present invention. Reference herein to particles is intended to include all such forms. Amorphous gold, such as Englehard microcrystalline gold, has been demonstrated in other biological target systems to achieve higher delivery into target cells than other types of gold.

Without regard to the type of particle acceleration apparatus or suitable particles used, the coated carrier particles are then physically accelerated toward the cells to be transformed such that the carrier particles lodge in the interior of the target cells. This technique can be used either with cells in vitro or in vivo. At some frequency, the DNA which has been previously coated onto the carrier particles is expressed in the target cells. This gene expression technique has been demonstrated to work in procaryotes and eukaryotes, from bacteria and yeasts to higher plants and animals. Thus, the accelerated particle method provides a convenient methodology for delivering genes into the cells of a wide variety of tissue types, and offers the capability of delivering those genes to cells in situ and in vivo without any adverse impact or effect on the treated individual. The accelerated particle method is also preferred in that it allows a genetic treatment construction to be directed both to a particular tissue, and to a particular cell layer in a tissue, by varying the delivery site and the force with which the particles are accelerated, respectively.

The general approach of accelerated particle gene transfection technology is described in U.S. Pat. No. 4,945,050 to Sanford, incorporated herein by reference. An instrument based on an improved variant of that approach is available commercially from BioRad Laboratories. An alternative approach to an accelerated particle transfection apparatus is disclosed in U.S. Pat. No. 5,015,580, herein incorporated by reference, which, while directed to the transfection of soybean plants, describes an apparatus which is equally adaptable for use with mammalian cells and intact whole mammals. U.S. Pat. No. 5,149,655, incorporated herein by reference, describes a convenient hand-held version of an accelerated particle gene delivery device. Other such devices can be based on other propulsive sources using, for example, compressed gas as a motive force.

Gene gun delivery allows for precise control over the level and form of IL-12 production in a given epidermal site because intracellular DNA delivery can be controlled by systematically varying the number of particles delivered and the number of plasmid copies per particle. This precise control over the level and form of cytokine production may allow for control over the nature of the resultant response.

The term transfected is used herein to refer to cells which have incorporated the delivered foreign IL-12 genetic construction, whichever delivery technique is used. The term transfected is used in preference to the term transformation, to avoid the ambiguity inherent in the latter term, which is also used to refer to cellular changes in the process of oncogenesis.

The present invention will be more fully understood by reference to the following examples, which are intended to be merely exemplary of the invention. In the examples, mice have been used as a model recipient for the IL-12 expression construct. Mice are the standard animal model for extrapolation to human tumors, and general FDA policy requires researchers to demonstrate efficacy of a proposed cancer treatment in mouse models before undertaking clinical trials.

Two murine IL-12 constructs have been used, each of which encodes both the p35 and the p40 subunits of mIL-12. These subunits were cloned from a mouse spleen cDNA library. All plasmids were made with the express purpose of increasing cytokine gene expression of IL-12, and with the immediate intended use in a cancer gene therapy program.

Plasmid pWRG3169 is a tandem plasmid encoding both mIL-12 subunit genes. A map of plasmid pWRG3169 is provided in FIG. 1 and the complete nucleotide sequence of the plasmid is presented in SEQ ID NO:1. The p35 and p40 products of the plasmid are reported as SEQ ID NO:2 and SEQ ID NO:3, respectively. Each subunit-encoding gene is under the transcriptional control of a separate cytomegalovirus (CMV) promoter. An SV40 splicing donor/splicing acceptor (sa/sd) is provided between each subunit-encoding segment and its CMV promoter. Just downstream (3') to each subunit-encoding segment is a bovine growth hormone polyadenylation signal (bGH pA). Each unit (promoter--sa/sd--coding region--poly A signal unit) is transcribed in series (i.e., in the same direction) from the plasmid. The pUC19 plasmid backbone is derived from a Bluescript.RTM. SK(+) vector with an ampicillin resistance gene which is available commercially from Stratagene Cloning Systems, La Jolla, Calif.

Plasmid pWRG3196 is a bicistronic plasmid encoding both subunits of mIL-12. A map of plasmid pWRG3196 is provided in FIG. 2 and the complete sequence is shown in SEQ ID NO:4. The p35 and p40 products of the plasmid are reported as SEQ ID NO:5 and SEQ ID NO:6, respectively. The pUC19 plasmid backbone was derived from a Bluescript SK(+) vector with an ampicillin resistance gene. This vector contains a single cytomegalovirus (CMV) promoter, SV40 splicing donor/splicing acceptor, and bovine growth hormone polyadenylation signal. Both the p35 and p40 genes are provided downstream from the sd/sa site and upstream from the SV40 poly A site. The p35 gene is upstream from (i.e., closer to the promoter than) the p40 gene. Between the p35 and p40 genes is an internal ribosome entry site element (IRES) cloned from encephalomyocarditis virus. The IRES element is a non-coding region which functions as an internal entry point for initiation or continued translation by eukaryotic ribosomes.

Both pWRG3169 and pWRG3196 direct expression of mIL-12. From a molecular standpoint, however, the bicistronic IRES vector (pWRG3196) produces a single mRNA, whereas the tandem vector (pWRG3169) produces separate mRNA for p35 and p40. In gene expression studies, the present inventors discovered that pWRG3169 induced at least twice the expression of the bicistronic pWRG3196, both in vivo and in vitro. For example, when the pWRG3169 and pWRG3196 vectors were transfected separately into B16 tumor cells in vitro, or into murine skin in vivo, 3-8 fold higher mIL-12 protein expression levels were observed when the pWRG3169 vector was transfected. Still lower expression levels were observed when two separate vectors, each encoding one of mIL-12 subunit proteins, were transfected.

Importantly, biologically active IL-12 cytokine was detected locally after transfer to B16 murine melanoma cells and after skin bombardment using a particle acceleration instrument. When 1.25 .mu.g of pWRG3169 DNA was delivered by particle acceleration into 1.times.10.sup.6 B16 cells, 49.8.+-.10.2 ng/ml were detected after 24 hours. Twenty-four hours after skin was bombarded four times with a total of 5 .mu.g of pWRG3169 DNA, 266.+-.27.8 pg of IL-12 were detected per 0.172.+-.0.026 gm of tissue in a standard 1.5.times.1.5 cm.sup.2 full thickness skin biopsy which contained four treated sites. The level of IL-12 was determined using a cell proliferation assay using murine Con-A-activated splenocytes as described by Schoenhaut, et al., J. Immunol. 148:3433 (1992).

It is envisioned that similar expression-competent vector constructs can be created which will include human p35 and human p40, the sequence of which are provided herein) for use in cancer gene therapy clinical studies. In addition, future vectors will include Intron A and possibly an episomal element such as EBNA-1 from Epstein-Barr virus.

Renal cell adenocarcinoma (Renca) and methylcholanthrene-induced fibrosarcoma (MethA) tumor cell lines, are syngeneic in Balb/c mice. L5178Y lymphoma and P815 mastocytoma are syngeneic in DBA/2 mice. SA-1 sarcoma and B16 melanoma are syngeneic in A/Sn and C57Bl/6, respectively. Tumor cell lines were maintained in vitro under established conditions.

To induce tumor formation, suitable recipient mice were shaved in their abdominal area and were injected with 1.times.10.sup.6 tumor cells in 50 .mu.l of PBS intradermally (except 10.sup.5 B16 cells were delivered). Tumor growth was monitored 2-3 times a week by measuring two perpendicular tumor diameters using calipers.

The experiments utilized a helium-pulse particle acceleration device of the type described in published PCT application number PCT/US95/00780 (Publication number WO 95/19799), which is incorporated herein by reference. Plasmid DNA was precipitated onto 2 micron gold particles using PEG/CaCl.sub.2 or spermidine/CaCl.sub.2. Particles were suspended in a solution of 0.1 mg/ml polyvinylpyrrolidone in absolute ethanol. This DNA/gold particle preparation was coated onto the inner surface of Tefzel tubing as described in the incorporated published application. The tubing was then cut into cartridges of 0.5 inch length, to achieve delivery of 0.5 mg gold and 1.25 .mu.g plasmid DNA per bombardment with a single cartridge.

The deposited DNA-coated particles were lifted from the cartridges and were delivered into mouse epidermis under the force of a 300 psi helium pulse. Histologic examination and standard immunohistochemical analyses using a monoclonal anti-IL-12 antibody demonstrated that under this force, the gold particles primarily penetrated to the epidermal cell layers of the mouse skin tissue, but did not penetrate into the underlying tumor cells, and, likewise, that transgenic mIL-12 was expressed only in epidermal cell layers.

At each transfection timepoint, individual mice received four bombardments with the mIL-12 DNA genetic construct or with control DNA (pCMVLuc; Cheng, et al., 90 Proc. Natl. Acad. Sci. USA 4455 (1993)). One bombardment was directly over the tumor, and three additional bombardments were evenly spaced around the circumference of the tumor in a triangle pattern.

Balb/c mice were inoculated as described above with 1.times.10.sup.6 Renca or MethA tumor line cells. At the indicated time after inoculation, the tumor injection sites were bombarded once per day for 3-5 days with pWRG3196, with pWRG3169 or with control plasmid pCMVLuc, starting on day 7 of tumor growth (in the first experiment, bombardment started on days 1, 4, or 7 of tumor growth).

The results of four preliminary experiments are presented in Table 1. In the first experiment, 3 of 7 (42%), 3 of 6 (50%), and 5 of 7 (71%) mice treated on days 1-5, 4-8, and 7-11, respectively, completely rejected their tumors, whereas all control (untreated) mice were sacrificed by day 18 due to progressive tumor growth. The tumor growth pattern in IL-12 gene-treated and control mice is presented in FIG. 3.

It can be seen that regression started several days after terminating the treatment, suggesting that the anti-tumor effect is immunologically-mediated. Moreover, it is important to note that in this and other experiments, in situ bombardment with the mIL-12 encoding plasmid caused regression of established (5-10 mm in diameter) solid murine tumors.

In the second experiment, mIL-12 treatment caused rapid regression in the tumors in all mice. Due to the heavy skin bombardment, however, 28% of mice transfected with the control gene also rejected their tumors. In order to eliminate this nonspecific and anti-tumor effect, the duration of the treatment was reduced to three bombardments every other day.

Indeed in the third experiment, all tumors bombarded with the control gene grew progressively, whereas 62% of mice bombarded with the mIL-12 genetic construct rejected their tumors.

In experiment 4, MethA sarcoma was used instead of Renca tumor and showed similar high sensitivity to IL-12 gene treatment.

Additional demonstrations of tumor regression

The present inventors also used the IL-12 treatment method of the present invention with other murine tumors, as described below. In all cases, reduction of tumor growth was observed following mIL-12 gene transfection.

It is known that certain murine immunogenic tumors can induce a T cell-mediated immune response which is best detected on days 7-9 of tumor growth in defined tumor models (17). Therefore mIL-12 cDNA treatments were begun at 7 days post-implantation of tumor cells, to enhance the already activated endogenous antitumor immune response. Using this experimental strategy, the in vivo delivery of the chimeric IL-12 genes into skin tissues overlying established 7-day tumors resulted in complete tumor regression or suppression of tumor growth in 4 tumor models. In suitable mice bearing Renca, L5178Y, MethA or Sa-1 tumors, complete tumor regression was achieved in 87.5% (7/8), 87.5% (7/8), 57% (4/7) and 37.5 (3/8) of test mice, respectively. Nearly identical results were achieved with Renca tumors after a single IL-12 cDNA treatment on day 7. The effect of mIL-12 gene therapy on tumor growth in these 4 tumor models are shown in FIG. 4.

Furthermore, in mice bearing P815 mastocytoma or B16 melanoma, a significant suppression of tumor growth was achieved (FIG. 4). For example, on day 13 post P815 tumor cell implantation, the mean tumor diameter in mice treated with pWRG3169 was 8.89.+-.0.27, as opposed to 12.28.+-.0.46 mm for the pCMVLuc control gene in the same expression plasmid (p<0.001). Likewise, on day 15 post B16 tumor cell implantation, tumor diameter in mice treated with pWRG3169 was 6.30.+-.0.045 as opposed to 11.8.+-.0.31 mm for the pCMVLuc control gene plasmid (p<0.001). For these two weakly immunogenic tumor systems, it is unclear whether modified gene transfer regimes or schedules can improve the therapy and result in tumor regression, and this apparently warrants systematic evaluations in future studies.

The mIL-12 gene therapy experiments were repeated 5 times with the Renca tumor system, 4 times with MethA and P815 tumors, 3 times with the B16 tumor, and once with L5178Y tumor model, and similar results were obtained. At each treatment, mice received four transfections with IL-12 DNA (circles) or pCMVLuc DNA (squares). The arrows in FIGS. 4A-4F indicate the days post tumor implantation on which treatment was carried out. Each group contained 7-8 mice, except the B16 tumor model which contained 12 mice per group.

It is important to note that for all tested mouse tumor models, the tumors were already well-established at the beginning of the therapy, and had reached 5-8 mm in diameter. To our knowledge, this is the first evidence that IL-12 gene therapy can cause a complete regression of large, established tumors. Previous studies have shown that IL-12 gene therapy using retroviral vectors resulted in prevention of tumor development, or regression of small, 3-day-old MCA207 sarcomas in 33% of treated mice. It is also noteworthy that only 1-4 days of therapy (using 4 bombardments per tumor site on each day of therapy) resulted in tumor regression or growth suppression in virtually all of our experiments.

In previous studies using recombinant protein therapy, tumor regression required daily injections of IL-12 at doses from 0.1 to 10 .mu.g for 1 weeks, or 5 days a week for 4 weeks. In conjunction with our previous findings using other cytokine genes, the results presented in FIGS. 1, 2 suggest that transgenic IL-12 production by normal epidermal cells in the vicinity of the tumor can be responsible for the antitumor effect of IL-12 gene therapy.

IL-12 induced Tumor regression involves CD8.sup.+ cells

The observed tumor regression depended upon the presence of CD8.sup.+ cells. In vivo depletion of CD8.sup.+ T cells, but not the depletion of CD4.sup.+ T cells, abrogated the effect of mIL-12 gene therapy. To demonstrate this, Balb/c mice were injected intradermally with 1.times.10.sup.6 Renca cells. Skin was transfected with IL-12 or pCMVLuc cDNA expression vectors on days 7, 9 and 11 post tumor implantation. Anti-CD4 mAb (clone GK1.5) or anti-CD8 mAb (clone 2.43), both obtained from Trudeau Institute, Saranac Lake, N.Y., were administered intraperitoneally on days 8 (300 .mu.g/mouse) and 12 (150 .mu.g/mouse) after tumor implantation. Control groups included mice that were treated with the IL-12 gene and received rat IgG (Sigma) at the same doses and schedule as the anti CD8-and CD4 mAb, or mice treated with the pCMVLuc gene instead of the IL-12 gene. The anti-CD4 and Anti-CD8 mAb used in this study caused depletion of more than 90% of relevant T cell subsets in mice for 4-days following a single injection. Tumor mass for 8 mice per group continued to enlarge when CD8.sup.+ T cells were eliminated, but tumor regression or elimination was observed when CD4.sup.+ T cells were removed, or when rat IgG was injected. These data are in agreement with the findings of Brunda et al., J. Exp. Med. 178(4):123-30 (1993) that tumor regression caused by recombinant IL-12 is mediated by CD8.sup.+ T cells, but not CD4.sup.+ T cells. In fact, depletion of CD4.sup.+ T cells with anti-CD4 monoclonal antibody (mAb) appeared to result in slightly accelerated tumor regression, implying that CD4.sup.+ T cells may suppress the anti-tumor effect of IL-12 in this tumor model. Indeed, it has been shown that established tumors induce Th2-like CD4.sup.+ T suppressor cells, which can inhibit CD8.sup.+ T cell-mediated immune responses. The beneficial effect of anti-CD4 mAb treatment for tumor immunotherapy with recombinant IL-2 protein or IL-12 gene has been previously reported. Supporting data show that IL-12 protein can activate tumor-specific CD8.sup.+ T cells in vitro, and mediate an anti-suppressive effect on Th2 CD4.sup.+ T cells in vivo.

Gene Gun Delivery of the IL-12 Gene into the Tumor Site Causes Systemic Anti-Tumor Effect Resulting in Reduction of Growth of a Distant Tumor

The observation that tumor regression caused by local IL-12 gene therapy requires CD8.sup.+ T cells suggest that local IL-12 gene delivery might result in a systemic antitumor effect. This hypothesis was tested using the P815 tumor system, in which tumor cells metastasize into the visceral organs several days after the intradermal implantation, thereby causing the death of the mice even when the primary tumor has been surgically removed.

DBA/2 mice were injected intradermally with 1.times.10.sup.6 P815 cells. Skin tissues overlying and surrounding the target tumor were treated with pWRG3169 delivered by particle acceleration (8 mice/group), or pCMVLuc (5 mice/group) on days 12 and 14 after tumor cell implantation. Surgical excision of the tumor was performed on day 15, when tumor size reached about 13 mm in diameter. Additional transfections of control and test constructs into skin on both sides of the abdomen were performed on days 16, 18 and 20 post implantation.

All mice treated with pCMVLuc died in 28.0.+-.0.6 days after tumor cell implantation. Macroscopic examination revealed that death was caused by spontaneous metastases of tumor cells into the internal organs, primarily the liver. mIL-12 gene therapy effectively prolonged the survival of mice (survival time 41.4.+-.4.9 days, p<0.05), and 1 of 8 mice was "cured."

This experiment was repeated without additional transfections post tumor excision, and showed that all of the Luc cDNA treated mice (n=11) died in 43.9.+-.7.1 days, whereas 5 or 12 (41.6%) IL-12 gene therapy-treated mice survived for at least 180 days and thus were considered "cured." These results suggest that local delivery of IL-12 gene into the skin tissues overlying and surrounding the primary tumor can augment systemic antitumor immune response and lead to eradication of established spontaneous metastases.

Balb/c mice were injected intradermally with 10.sup.6 Renca cells, both in the left and right sides of the abdomen. The tumors on the right side were bombarded with either pWRG3169 or pCMVLuc on days 5, 7, and 9 of tumor growth. IL-12 gene therapy resulted in significant growth reduction in the untreated (left) tumor as compared with the growth of untreated tumors in control mice (tumor diameter on day 22: 9.58.+-.1.82 and 13.18.+-.2.03, respectively; n=8 mice/set, p<0.005). A similar experiment was performed in which the L5178Y tumors on the right side of the abdomen were bombarded with either pWRG3169 or pCMVLuc on days 3 and 6 of tumor growth. In this experimental setting, IL-12 gene therapy resulted in complete tumor regression of the treated (right) as well as untreated (left) tumors in all mice (n=8). An additional experiment has shown that IL-12 gene bombardment of the skin, away from the tumor vicinity, does not affect tumor growth. These results suggest that local activation of immune cells at the tumor site during IL-12 gene therapy generates systemic anti-tumor immunity.

Mice that Rejected the Tumors Following IL-12 Gene Therapy Develop Tumor-Specific Immunological Memory

A. Rejection of secondary tumor challenge followed IL-12 gene therapy. Balb/c mice that rejected Renca or MethA tumors following IL-12 gene therapy were injected one month later with 1.times.10.sup.6 of both Renca cells and MethA cells on the right and the left side of abdomen, respectively. As a control, the tumor cells were injected into age-matched naive Balb/c mice (5-8 mice per group).

Mice that rejected intradermal Renca (Group A) or MethA tumors (Group B) following IL-12 gene therapy, or control naive mice, were injected into the right side of the abdomen with Renca cells, and into the left side of the abdomen with MethA cells. Whereas all control mice developed both tumors, mice of Group A developed MethA tumors but not Renca tumors, and vice versa, that is, mice of Group B developed Renca tumors but not MethA tumors.

B. Induction of CTL activity in mice that rejected tumors following IL-12 gene therapy. Tumor-specific CTL were generated in vitro as described by Rakhmilevich et al., Int. J. Cancer, 55:338 (1993). Spleen cells (5.times.10.sup.6), derived from Balb/c mice that had rejected Renca tumors due to IL-12 gene therapy and had remained tumor-free for two months, or from age-matched naive mice, were co-cultured with 5.times.10.sup.4 mytomicin-C-treated Renca cells in 24-well culture plates in complete RPMI-1640 media. After culturing for 5 days in vitro, graded numbers of viable effector cells and .sup.51 Cr-labeled Renca cells (10.sup.4) were placed into the wells of round-bottomed 96-well plates. After incubating for 4 hr at 37.degree. C., radioactivity in supernatants was determined. Mean.+-.SEM of 4 mice per group. Spleen cells from IL-12 gene-treated mice generated 3-4-fold higher levels of CTL activity than spleen cells from naive mice (p<0.005). These results indicate that IL-12 gene therapy generates systemic anti-tumor immunity.

In a similar study, using spleen cells from mice that had previously rejected L5178Y tumors, CTL generated were able to lyse L5178Y cells but not syngeneic P815 cells.

All in all, the results indicate that IL-12 gene therapy with a particle-mediated gene transfer instrument is effective against various murine tumors and may be applied as a treatment of immunogenic human tumors. In addition, the findings indicate that IL-12 DNA is delivered into skin, but not into the tumor tissue following in vivo bombardment. Therefore, particle-mediated IL-12 gene therapy can be routinely applied to subcutaneous tumors or metastatic nodules without any surgical manipulations.

Furthermore, the inventors found about 250 pg of IL-12 at the tumor bombardment site which is about 1/400 to 1/40,000 of the "therapeutic dose" of recombinant IL-12 (0.1-10 .mu.g). Moreover, the therapeutic dose of IL-12 is also known to cause unacceptable toxicity levels. Therefore, in comparison with treatment with recombinant IL-12, treatment with the IL-12 gene therapy of the present invention is much less (if at all) toxic, and much less expensive.

Thus it is demonstrated that circulating levels of cytokine IL-12 can be created in vivo by delivering into a patient in need of treatment for a tumor not quantities of IL-12 itself, but rather by delivering into the patient gene sequences causing expression of IL-12 in cells in the treated individual. The gene therapy method of the present invention enables the creation of an anti-tumor response in a treated individual without delivering IL-12 protein into the individual.