Preparation and identification of monoclonal antibodies against the adenovirus vector

Objective： To prepare and identity monoclonal antibodies （McAbs） against the capsid proteins of adenovirus vector. Methods： BALB/c mice were immunized with a mixture of the purified adenovirus vector （Adv） and AI（OH）3. McAbs were produced using cell fusion technique in a conventional way. The sensitivity and specificity of monoclonal antibodies was identified by indirect enzyme linked immunosorbent assay （ELISA）, immunocytochemical staining and Western blotting. Results： Six strains of hybridoma cells （A4H11, A8C7, F1H5, G1D2, G4E3 and H2G8） that can stably secrete the IgG1 McAb against Adv were obtained. After 3 months subculture and low concentration of serum adapting culture, six strains retained their stability to secrete McAb. The ascites titers were between 1：10^6 and 1：10^8. Western blot analysis demonstrated that all the McAbs reacted with one protein （about 114 kDa） which is present in wild type 3 adenovirus （wtAd3）, wild type 5 adenovirus （wtAd5）, wild type 7 adenovirus （wtAd7） and adenovirus vector. Conclusion： Successfully prepared six strains of hybridoma cell secreted monoclonal antibodies against the hexon proteins of adenovirus vector, and provided the substantial foundation of preclinical research of adenovirus vectors.

Adenoviral gene therapy in gastric cancer: A review

Gastric cancer is one of the most common malignancies worldwide. With current therapeutic approaches the prognosis of gastric cancer is very poor, as gastric cancer accounts for the second most common cause of death in cancer related deaths. Gastric cancer like almost all other cancers has a molecular genetic basis which relies on disruption in normal cellular regulatory mechanisms regarding cell growth, apoptosis and cell division. Thus novel therapeutic approaches such as gene therapy promise to become the alternative choice of treatment in gastric cancer. In gene therapy, suicide genes, tumor suppressor genes and anti-angiogenesis genes among many others are introduced to cancer cells via vectors. Some of the vectors widely used in gene therapy are Adenoviral vectors. This review provides an update of the new developments in adenoviral cancer gene therapy including strategies for inducing apoptosis, inhibiting metastasis and targeting the cancer cells.

Therapy of cancer by cytokines mediated by gene therapy approach

Gene therapy offers a new approach for treatment of cancer. Transfer of genes encoding immunostimulatory cytokines has been used with remarkable success to eliminate cancer in animals. However, clinical trials in patients with this strategy had limited efficacy. Therefore, improvement ofgene transfer vector system is necessary. A hybrid viral vector, consisting of SFV replicon with either murine IL-12 or reporter LacZ gene, was constructed. This hybrid vector showed specificity and high level of expression in HCC both in vitro and in vivo. In a rat orthotropic liver tumor model, treatment of established tumors by the hybrid vector with raiL- 12 gene resulted in a strong anti-tumor activity without accompanying toxicity. Subsequently, a helper-dependent adenovirus vectors containing a mifepristone （RU486） inducible system was constructed for controlled and liver-specific expression of human interleukin 12 （hIL- 12） （HD-Ad/RUhIL- 12） and mouse IL-12 （mIL-12） （HD-Ad/RUmIL-12）. Data showed that high and sustained serum levels of hlL-12 could be attained by continuing administration of RU486 every 12 or 24 h. Repetitive induction ofhlL-12 could be obtained over, at least, a period of 48 weeks after a single injection of HD-Ad/RUhlL-12. Treatment of liver metastases with of HD-Ad/RUmIL- 12 plus RU846 resulted in complete tumor regression in all animals. Then, different cytokine genes were inserted into conditional replicative adenoviruses vectors （also called oncolytic adenovirus）. Replication ofadenovirus in tumor cells would kill tumor cells and release viruses, which infect surrounding tumor cells. The combination of cytopathic effect by oncolytic adenovirus and biological effect of transgene would exert strong antitumor activity. These new types of vectors may provide a potent and safe tool for cancer gene therapy.

In vitro suppression of vascular smooth muscle cell proliferation using adenovirus-mediated transfer of the cd gene

Objective : To develop a treatment strategy for restenosis with a replication-deficient recombinant adenovirus (AdCMVCD) containing the cd gent whose gene product phosphorylates the prodrug 5-flurocytosine to form a nucleoside analog that inhibits DNA synthesis. Methods: Cultured primary rabbit smooth muscle cell (SMC) infected with AdCMVCD was incubated in 5- flurocytosine-containing medium and assayed with a Coulter Counter on day 2, 6, 10, and 14 for the establish- ment of proliferation curves. In addition, to observe an inhibitory effect on neighboring SMC, only a portion of the SMC population received the cd transgene. Results : The antiproliferative effect of AdCMVCD was dependent on both concentation of virus and concentration of 5-flurocytosine . Transformed cells demonstrated a bystander effect wherein SMC expressing cd gene exerted an antiproliferative effect on neighboring cells that did not express cd gene . Conclusion:Theresult demonstrates the potential utility of adenovirus-mediated cd gene transfer for the treatment of restenosis after balloon injury.

Exogenous p16 gene therapy combined with X-ray irradiation suppresses the growth of human glioma cells

In this study, we infected human glioma U251 cells with a replication-defective recombinant adenovirus carrying the p16 gene. This adenovirus constructed was able to transfect exogenous p16 into the human glioma cells efficiently, and direct a high level of p16 protein expression. Tumor-inhibition experiments demonstrated that treatment with the adenovirus-p16 significantly inhibited the growth of glioma cells in vitro as well as the in vivo development of tumors in nude mice bearing a brain glioma. The combination of adenovirus-p16 gene treatment and X-ray irradiation resulted in a greater inhibition of tumor growth. Adenovirus-mediated p16 gene therapy conferred a significant antitumor effect against human glioma cells both in vitro and in vivo, and that there was a synergistic effect when X-ray irradiation was also used.

Gene therapy for pathological scar with hepatocyte growth factor mediated by recombinant adenovirus vector

A complementary DNA (cDNA) encoding human hepatocyte growth factor was intro-duced into a replication-defective type 5 adenovirus (lacking E1, E3 domains) vector by homolo-gous recombination of intracellular plasmid DNA, thus a recombinant vector containing HGF (Ad-HGF) was obtained. Ad-HGF and Ad-GFP (adenovirus vector carrying green fluorescence protein gene) were expanded in 293 cells and purified by cesium chloride gradient centrifugation for large-scale preparation, then were infected to the primarily cultured scar fibroblast of rabbit ear to observe the transfer efficiency and expression level of HGF in vitro. To evaluate the effect of Ad-HGF on established scar Ad-HGF solution was injected into excessively formed scar, which bears some clinical and histologic similarities to human hypertrophic scars. The results showed that: (i) the transfer efficiency was 36.8%±14.1% on day 3 in primarily cultured scar fibroblasts treated with Ad-GFP and lasted more than 20 d; (ii) high-level expression of HGF protein was de-tected by means of ELISA in supernatant of scar fibroblasts treated with Ad-HGF, the amount of expression was 76 ng/4.0×105 cells on day 3; (iii) on day 32 after a single intradermal injection of Ad-HGF at different doses (8.6×109 pfu, 8.6×108 pfu, 8.6×107 pfu, 8.6×106 pfu) per scar, most of the scars in the former two dose groups were dramatically flattened, some were even similar to that of the normal skin. The value of HI (hypertrophic index) showed that there was a therapeutic effect of Ad-HGF on scars at the dose of 109 pfu and 108 pfu. Whereas no therapeutic effects were seen at lower dose (107 pfu and 106 pfu of Ad-HGF) groups. In addition, clusters of hair were ob-served to different extent on healed wound treated with Ad-HGF. Histopathologic examination re-vealed that in most healed wounds of Ad-HGF treated group, the dermal layer was thinner, the amount of fibrous tissue was much fewer, and hair follicles growth and sebaceous glands were observed. In Sirius red-stained sections the amount of type I collagen in the Ad-HGF-treated scars was diminished markedly, compared to that in Ad-GFP group, in which a huge amount of type I collagen was still observed; (iv) immune response against HGF was absent. Antibody against HGF was not detectable by ELISA in serum from rabbit treated with Ad-HGF; (v) no local or systemic side-effects and toxicity associated with the gene transfer were found. These results demonstrated the potential use of treating pathologic scar by Ad-HGF, an alterative strategy of gene therapy for scar in clinical practice.

ADENOVIRUS-MEDIATED WILD-TYPE P53 EXPRESSION SUPPRESSES GROWTH OF LUNG ADENOCARCINOMA CELLS

Objective: To study the growth suppression of lung adenocarcinoma cell by the introduction of wild type P53 gene and explore a gene therapy approach for lung adenocarcinoma. Methods: A replication deficient adeno virus vector encoding a wild type P53 was constructed and transfected into the cultured human lung adeno carcinoma cell line GLC 82. The efficiency of gene transfection and expression was detected by immuno chemical staining and polymerase chain reaction. The cell growth rate and cell cycle were analysed by cell counting and flow cytometry. Results: Wild type P53 gene could be quickly and effectively transfected into the cells by adenovirus vector. Wild type P53 expression could inhibit GLC 82 cell proliferation and induce apoptosis. Conclusion: The results indicated that recombinant adenovirus expressing wild type P53 might be useful vector for gene therapy of human lung adenocarcinoma.

Gene Therapy of HSV-TK Transferred by the EBV based Expression Vector on Experimental Hepatocellular Carcinoma

To study the therapeutic effects of herpes simplex virus thymidine kinase gene transferred by the EBV based expression vector on experimental hepatocellular carcinoma, pDR2 TK gene was delivered into human hepatocellular carcinoma cell line SMMC 7721 by using liposome mediated transfection technique,and then gene expression was detected by RT PCR, and the killing effects were examined through MTT method. In the nude mice hepatoma model,the antitumor effects of pDR2 TK /GCV system was evaluated in terms of tumor growth. MTT results showed that the pDR2 TK /GCV had cytotoxic effect and about 70 % SMMC 7721 cells were killed when GCV was at 1000 μmol/L. In vivo experiment showed that the tumor size in nude mice with transferred pDR2 TK gene was significantly smaller than that in control group . On the 10th day the tumor in 3 mice (60 %) disappeared completely after GCV treatment. It is concluded that the pDR2 TK/GCV system has marked killing effects on the experimental hepatocellular carcinoma.

Adenovirus-mediated gene delivery:Potential applications for gene and cell-based therapies in the new era of personalized medicine

With rapid advances in understanding molecular pathogenesis of human diseases in the era of genome sciences and systems biology,it is anticipated that increasing numbers of therapeutic genes or targets will become available for targeted therapies.Despite numerous setbacks,efficacious gene and/or cell-based therapies still hold the great promise to revolutionize the clinical management of human diseases.It is wildly recognized that poor gene delivery is the limiting factor for most in vivo gene therapies.There has been a long-lasting interest in using viral vectors,especially adenoviral vectors,to deliver therapeutic genes for the past two decades.Among all currently available viral vectors,adenovirus is the most efficient gene delivery system in a broad range of cell and tissue types.The applications of adenoviral vectors in gene delivery have greatly increased in number and efficiency since their initial development.In fact,among over 2000 gene therapy clinical trials approved worldwide since 1989,a significant portion of the trials have utilized adenoviral vectors.This review aims to provide a comprehensive overview on the characteristics of adenoviral vectors,including adenoviral biology,approaches to engineering adenoviral vectors,and their applications in clinical and preclinical studies with an emphasis in the areas of cancer treatment,vaccination and regenerative medicine.Current challenges and future directions regarding the use of adenoviral vectors are also discussed.It is expected that the continued improvements in adenoviral vectors should provide great opportunities for cell and gene therapies to live up to its enormous potential in personalized medicine.

Effect of adenoviral vector-mediated rat antisense AT1B gene transfer on neointima proliferation after rat carotid injury

Objective: Angiotensin Ⅱ is a growth-promoting factor for vascular smooth muscle cells in culture andin the intact animal. The biological effects of angiotensin Ⅱ are manifested only by binding to specific receptors oncell membranes. In the study, we observed that the effect of rat antisense AT1B gene transfer mediated by adenoviral vector-on neointimal proliferation following rat carotid injury. Methods: Antisense AT1B gene was transductedinto the carotid by adenoviral vector after carotid bal1oon injury and the restenosis model was established in SD rat.We measured neointima/media area ratio in local artery at day 21 after gene transfer. Results: Rat antisense AT1Bgene was successfully transducted into local carotid after the carotid balloon injury. Neointima/media area ratiowas significantly reduced (47 %, P<0. 01) at day 21 after gene transfer compared with the control group. Conclusion: The results suggest it is possible that antisense AT1B gene transfer as a potential therapeutic approach prevent neointimal hyperplasia.

Stage Ⅰ Clinical Trial of Gene Therapy for Hemophilia B

This paper describes the first human gene therapy trial for hemophilia B. Retroviruses were used to introduce human factor Ⅸ into autologous, primary human skin fibroblasts from the patients. Recombinant retroviral vector containing human FIX cDNA driven by viral LTR promoter (XL-Ⅸ) and double-copy retroviral vector driven by human cytomegalovirus enhancer-promoter (N2CMV-Ⅸ)were constructed. After the safety assessment, including soft-agar test, cell morphology observation, analysis of endotoxin, chromosome karyotype, allergic reaction test, nude mice test, routine pathological test, electromicroscopic analysis, and virus detection by PCR, etc., the engineered cells were pooled and embedded in collagen mixture, autologously injected into the patients respectively. The concentration of human FIX protein of Patient 1 increased from 71 ng/ml to 220 ng/ml, witha maximum level of 245 ng/ml. The expression of FIX has lasted for 6 months at the time of writing. The clotting activity also increased from 2.9% to 6.3%, his clinical symptoms have been alleviated obviously. The secretion rate of FIX for Patient 2 increased from 130 to 250 ng/ml, maintained at the level of 220 ng/ml for 5.5 months at the time of writing, but the clotting activity has not been increased steadily. There is no deleterious effect to be found in the two patients since the ex-vivo cells were implanted. The two patients are now under follow-up investigation. We suggested that retrovirus-mediated transfer of genes into skin fibroblasts, to be embedded in collagen and subcutaneously injected into patients, is a simple and effective approach for the gene therapy for hemophilia B.

Selective gene therapy for human lung adenocarcinoma by tumor-specific expression of herpes simplex virus thymidine kinase gene

According to the fact that CEA gene expressed only in lung adenocarcinoma but not in normal lung cells, a retroviral expression vector (pCEATK) of the herpes simplex virus thymidine kinase (HSV-TK) gene regulated by CEA promoter was constructed and introduced into CEA-producing human lung adenocarcinoma cells GL and non-CEA-producing HeLa cells. The expression of pCEATK and Ganciclovir (GCV) sensitivity of the transfected cells were tested in vitro and in vivo . pCEATK expressed only in CEA-producing GL cells but not in non-CEA-producing HeLa cells. The sensitivity to GCV of pCEATK-transfected GL was 992 times higher compared with that of the parental cell line and there was obvious 'bystander effect' in vitro. HeLa cells transfected wtih pCEATK were still resistant to GCV. Injection of GCV resulted in significant regression of pCEATK-transfected GL tumors in nude mice. In addition, all mice with any fraction of GL cells expressing HSV-TK exhibited a significant reduction in tumor growth, including mice with only 10% of GL cells expressing HSV-TK. These results show the possibility of HSV-TK gene-drug therapy using the tumor-specific promoter of CEA gene against CEA-producing lung cancers which was usually refractory to conventional chemotherapy.

Construction of retroviral vectors to induce a strong expression of human interferon-β gene in human hepatoma cells

Establishing the hepatoma cell-specific expression of human interferon gene mediated by retroviral vectors. Methods: Human interferon-β complementary DNA (IFN-β cDNA) was inserted into polylinker site of pMNSM retroviral vector to construct recombinant retroviral vector pMNSIFNB, where the transcription of IFN-β gene was driven by SV40 early region promoter, and MNAIFNB, where the transcription of IFN-β gene was driven by SV40 early region promoter regulated by α-fetoprotein enhancer. The retroviral constructs were respectively introduced into PA317 amphotropic packaging cells by means of lipofectamine mediated gene transfer procedure. The plasmids transfection efficiency was among (4-25)ｘ103 colonies/μg DNA/106 PA317 cells. The retrovirus infection efficiency was among (4. 5-500)ｘ104 Colony Forming Units (CFU)/ml. The recombinant retroviruses were used to infect human hepatoma cells, renal cell carcinoma cells and melanoma cell lines in the presence of 4 μg/ml polybrene. Results: Dot hybridization of total RNA from the neomycin resistant colonies and interferon expression assay indicated that human α-fetoprotein enhancer induced efficient and specific transcription and expression of IFN-β gene driven by the promoter of different origin in human hepatoma cells by which α-fetoprotein was highly produced. Conclusion: Cis-active element of α-fetoprotein gene can drive IFN-β gene specifically expressed in human hepatoma cells, which presents some valuable materials for the hepatoma-specific immune gene therapy.

Effect of NHE1 antisense gene transfection on the biological behavior of SGC-7901 human gastric carcinoma cells

AIM: To study the effect of type 1 Na+/H+ exchanger (NHE1 ) antisense human gene transfection on the biological behavior of gastric carcinoma cell line SGC-7901. METHODS: Antisense NHE1 eukaryotic expression on vector pcDNA3.1 was constructed by recombinant DNA technique and transfected into gastric carcinoma cell line SGC-7901 with DOTAP liposome transfection method. Morphological changes of cells were observed with optic and electron microscopes. Changes in cell proliferative capacity, apoptosis, intracellular pH (pHi), cell cycle, clone formation in two-layer soft agar, and tumorigenicity in nude mice were examined. RESULTS: Antisense eukaryotic expressing vectors were successfully constructed and transfected into SGC-7901. The transfectant obtained named 7901 -antisense (7901-AS) stablely produced antisense NHE1. There was a significant difference between the pHi of 7901-AS cells (6.77 ± 0.05) and that of 7901-zeo cells and SGC-7901 cells (7.24 ± 0.03 and 7.26 ± 0.03, P < 0.01). Compared with SGC-7901 and 7901-zeo cells, 7901-AS cells mostly showed cell proliferation inhibition, G1/G0 phase arrest, increased cell apoptotic rate, recovery of contact inhibition, and density contact. The tumorigenicity in nude mice and cloning efficiency in the two-layer soft agar were clearly inhibited. CONCLUSION: NHE1 antisense gene significantly restrains the malignant behavior of human gastric carcinoma cells, suppresses cell growth and induces cell apoptosis, and partially reverses the malignant phenotypes of SGC-7901 . These results suggest a potential role for human tumor gene therapy.

CONSTRUCTION AND EXPRESSION OF THE REPLICATION-DEFI-CIENT ADENONIRUS VECTOR OF HUMAN GM-CSF

The full-length cDNA encoding human Granulocyte macrophage colony stimulating factor (GM CSF) was cloned by RT PCR, placed under the control of CMV promoter, and inserted into adenovirus vector of E1 substitution type, pAx1cw. Subsequently, the cassette cosmid was cotransfected into 293 cells together with EcoT22I digested Ad5 TPC, and the replication deficient recombinant adenoviruses(Ad) of human GM CSF were generated efficiently by homologous recombination, with the titers of 1.51×10 9pfu/ml. 48 hours after infection with prepared human GM CSF recombinant adenoviruses in vitro, HeLa cells and primary human skin fibroblasts expressed high levels of human GM CSF (80～400ng/ 10 6cells/24hr). These suggest that the recombinant Ad of human GM CSF prepared by COS/TPC method is effective in mediating GM CSF gene transfer and might be used in cancer gene therapy.

Killing effect of adenoviral mediated cytosine deaminase gene on human pancreatic cancer cell line PaTu8988

Objective:To evaluatethein vitro killingeffectsof cytosinedeaminasegene mediatedby adenovirusvector on humanpancreaticcarcinoma.Methods:CytosineDeaminase(CD)genewas clonedintopAdTrack-CMV-CD,pAd-Track-CMV-CDandpAdEasy-1wererecombinedinbacteria,andtheproductscontaininggreenfluorescentprotein(GFP)werepropagatedin293cellsandpurifiedby cesiumchloridegradientcentrifugation.Humanpancreaticcarcinomacellline8988wereinfectedwiththisvirus,then5-FCwasadded;XTTassaywasusedto estimatetherelativenumbersof viable cells.Results:Thepositivecloneswereconfirmedby usingendonucleasedigestion,andthetiterof theviruscontaining CD genewas2×10 11 pfu/ml.Itwasfoundthat5-FCpossessedsignificantcytotoxicactivitiesforCD genetransfected8988cellline,buthadlittleeffectson non-transfectedpancreaticcarcinomacells.Conclusion:CD genemediatedby adenovirus hasa highinfectivityandis efficientforkillingculturedpancreaticcarcinomacells,indicatingsuicidegenemaybe effec-tiveforpancreaticcancerinfuture.

Tyrosine hydroxylase gene transfections to different sites of striatum in the rat model of Parkinson’s disease

The use of gene therapy has been intensively studied as a potential method to treat Parkinson’s disease (PD) and other degenerative brain diseases. However, the effects of experimental measures and approaches on the outcome of gene delivery or on the physiological state of target tissues have not been analyzed as much and systematically. Therefore, we have infused adenovirus vectors expressing either a therapeutic tyrosine hydroxylase (TH) gene or a lacZ reporter gene into striatum in a rat model of PD. The experimental procedures were tested using the Ad lacZ vector in order to optimize concentrations, volumes, infusion speeds and transfection times. The expression of Ad lacZ vector was lower and declined earlier in the lesioned than unlesioned striatum suggesting that the lesion affects on the transfection efficiency and outcome of gene transfection. The effect of three different approaches of Ad TH vector transfection was compared: 1) the delivery of Ad TH gene vector alone into one single site of striatum, 2) the delivery of Ad TH gene vector alone into multiple sites of striatum, and 3) the delivery of Ad TH gene vector into one site of striatum followed by a continuous infusion of tetrahydrobiopterin (BH4) cofactor with a mini pump. There was a small and transient unsignificant decrease in the turning behavior when the Ad TH vector was delivered into one site of the striatum. Simultaneous infusion into several sites or together with BH4 cofactor did not improve more the effect of gene delivery. Thus, although the effects were unsignificant, the Ad TH transfection seemed to decrease the turning behavior in the rat model of PD and the optimal effect was seen at some specific doses and time points. Furthermore, the outcome of gene therapy could depend in addition to the amount and efficacy of gene vectors also on the physiological state and experimental strategies.

Intramammary expression and therapeutic effect of a human lysozyme-expressing vector for treating bovine mastitis

To develop a gene therapy strategy for treating bovine mastitis, a new mammary-specific vector containing human lysozyme (hLYZ) cDNA and kanamycin resistance gene was constructed for intramammary expression and clinical studies. After one time acupuncture or intracisternal infusion of healthy cows with 400 μg of the p215C3LYZ vector, over 2.0 μg/ml of rhLYZ could be detected by enzymatic assay for about 3 weeks in the milk samples. Western blotting showed that rhLYZ secreted into milk samples from the vector-injected cows had molecular weight similar to that of the natural hLYZ in human colostrums. Twenty days after the primary injection, the quarters were re-injected with the same vector by quarter acupuncture and even higher concentrations of rhLYZ could be detected. Indirect competitive ELISA of milk samples showed that the vector injection did not induce detectable humoral immune response against hLYZ. Clinical studies showed that twice acupuncture of quarters with the p215C3LYZ vector had overt therapeutic effect on clinical and subclinical mastitis previously treated with antibiotics, including disappearance of clinical symptoms and relatively high microbiological cure rates. These data provide a solid rationale for using the vector to develop gene therapy for treating bovine mastitis.

Gene-viral vectors: a promising way to target tumor cells and express anticancer genes simultaneously

OBJECTIVE: To develop a new kind of vector system called gene-viral vector, which combines the advantages of gene and virus therapies. METHODS: Using recombinant technology, an anti-tumor gene was inserted into the genome of replicative virus specific for tumor cells. The cell killing effect, reporter gene expression of the green fluorescence protein, anti-tumor gene expression of mouse interleukin-12 (mIL-12) and replication of virus were observed by the methods of cell pathology, fluorescence microscopy, ELISA and electron microscopy, respectively. RESULTS: A new kind of gene-viral vector system of adenovirus, in which the E1b-55 kD gene was deleted but the E1a gene was preserved, was constructed. The vector system, like the replicative virus ONYX-015, replicated and proliferated in tumor cells but not in normal ones. Our vector had an advantage over ONYX-015 in that it carried different kinds of anti-tumor genes to enhance its therapeutic effect. The reporter gene expression of the green fluorescence protein in tumor cells was much better than the adenovirus vector employed in conventional gene the rapy, and the expression in our vector system was as low as or even less than that in the conventional adenovirus gene therapy system. Similar results were observed in experiments with this vector system carrying the anti-tumor gene mIL-12. Replication and proliferation of the virus carrying the mIL-12 gene in tumor cells were confirmed by electron microscopy. CONCLUSIONS: Gene-viral vectors are new vectors with an anti-tumor gene inserted into the genome of replicative virus specific for tumor cells. Because of the specific replication and proliferation of the virus in tumor cells, expression of the anti-tumor gene is increased hundreds to thousands of times. This approach takes full advantages of gene therapy and virus therapy to enhance the effect on the tumor. It overcomes the disadvantages of conventional gene therapy, such as low transfer rate, low gene expression, lack of target tropism, and low anti-tumor activity. We believe that this is a promising means for future tumor treatment.