HSV-tk Gene Research Articles

Strategy of gene therapy for liver cirrohosis and hepatocellular carcinoma.

Liver cirrhosis and hepatocellular carcinoma (HCC) are major causes of morbidity and mortality worldwide, without effective therapies. Our aim was to establish a novel approach for the diseases utilizing in-vivo gene therapy. To achieve effective gene expression in vivo, we employed a well-established transfection method, hemagglutinating virus of Japan (HVJ)-liposome. Liver cirrhosis, characterized by parenchymal collapse, was induced by dimethylnitrosamine (DMN) in rats, leading to accumulation of fibrous tissue. Muscle-directed gene transfer of hepatocyte growth factor (HGF) was performed in this model. As an approach for HCC therapy, suicide gene therapy using ganciclovir (GCV) with transfer of the herpes thymidine kinase (HSVtk) gene was tested. Alpha-fetoprotein (AFP) is highly expressed in many cases of HCC. To achieve specific gene expression of HSVtk in AFP-producing tumors, we employed the HSVtk gene driven by the AFP promoter (AFP-TK1), encapsulated in the HVJ-liposome. APF-producing HUH7 tumors in vivo were established in the livers of severe combined immunodeficiency (SCID) mice, by the injection of HUH7 cells into the portal vein. All cirrhotic rats died of liver dysfunction by 7 weeks after the initial injection of DMN. After repeated transfection with the HGF gene, increased concentrations of HGF in plasma and tyrosine phosphorylation of the c-Met/HGF receptor in the liver were detected, and the established massive hepatic fibrosis had almost totally disappeared and all cirrhotic rats survived. Repeated in-vivo transfection with AFP-TK1, using the HVJ-liposome, followed by GCV treatment, achieved abrogation of tumors in the liver, and improved survival. Our data indicate that the gene therapy may hold promise for the treatment of patients with liver cirrhosis and HCC.

Treatment of human papillomavirus (HPV) type 16-infected cells using herpes simplex virus type 1 thymidine kinase-mediated gene therapy transcriptionally regulated by the HPV E2 protein.

Human papillomavirus type 16 (HPV-16) is associated with development of anogenital squamous cell cancers (SCCs) and their precursor, intraepithelial neoplasia (IN). Few approaches to the treatment of IN to prevent SCC are targeted specifically to HPV. We have designed an HPV-specific therapy using the herpes simplex virus type 1 thymidine kinase (HSV-1 TK) gene driven by an HPV-specific promoter in the HPV-16 long control region (LCR) (nucleotide 7450-nucleotide 104), which is regulated by the HPV E2 protein. Expression of the HSV-1 TK gene is designed to render HPV-infected cells sensitive to the prodrugs ganciclovir (GCV) and acyclovir (ACV). To assess the E2 specificity of gene expression driven by the HPV-16 LCR, we measured luciferase expression in HPV-positive and HPV-negative cell lines. Significant induction of luciferase activity was observed in HPV-positive cells when compared with four different HPV-negative epithelial cell lines. Cotransfection of an HPV-negative cell line, MDCK, with an HPV-16 E2-expressing plasmid resulted in 15- to 20-fold induction of luciferase activity, suggesting specific activation by E2 protein. A plasmid expressing the HSV-1 TK gene driven by the LCR was transfected into CaSki and SiHa cells. Treatment of transfected cells with either GCV or ACV (20-30 microg/ml) for 6-10 days resulted in 80-95% cell death. Cell death was progressive, dose dependent, and mediated by apoptosis. These results suggest that direct gene transfer of the HSV-1 TK gene into HPV-16-infected cells expressing E2 protein, accompanied by treatment with either GCV or ACV, may be a clinically feasible therapeutic strategy.

Dexamethasone inhibits the anti-tumor effect of interleukin 4 on rat experimental gliomas.

Retroviral-mediated gene transfer of the IL-4 gene into experimental gliomas can cause tumor rejection, supporting the clinical use of this form of gene therapy for glioblastomas (GBM). In a clinical setting, the administration of dexamethasone (dex) is a standard procedure for GBM patients. This led us to examine the effects of dex on IL-4 gene therapy. We injected intracranially Fischer 344 rats with phosphate-buffered saline, 9L gliosarcoma cells mixed with E86.L4SN(200) cells (retroviral producer cells, RPC, transducing IL-4 cDNA) and 9L cells mixed with PA317.STK.SBA cells (control RPC expressing the HSV-tk gene). The rats from each group were treated with 0, 50, 100 or 250 microg dex/kg/day released by osmotic pumps implanted subcutaneously. While 80-100% of rats receiving 9L cells mixed with IL-4 RPC and not treated by dex survived for at least 2 months following tumor injection, only 50% and 17% of rats receiving 50 or 100 microg/kg/day of dex, respectively, reached this time point. These results indicate that dex significantly diminished the anti-tumor effect of IL-4. Thus, in a clinical setting, IL-4 gene transfer should be performed when low levels of dex are administered or in the absence of dex.

Adenovirus-mediated suicide gene therapy using the human telomerase catalytic subunit (hTERT) gene promoter induced apoptosis of ovarian cancer cell line.

Telomerase is a ribonucleoprotein complex the function of which is to add telomeric repeats (TTAGGG)(n) to chromosomal ends, and it is known to play an important role in cellular immortalization. Telomerase is highly active in most tumor cells, yet not in normal cells. As such, it may have possible applications in cancer gene therapy. Telomerase consists of two essential components, telomerase RNA template (hTR) and catalytic subunit (hTERT). hTERT is expressed only in cells and tissues positive for telomerase activity, i.e., tumor and fetal cells. We here tested the possibility of the utilization of the hTERT promoter in targeted cancer gene therapy. We cloned the hTERT promoter in the replace of the CMV promoter and sub-cloned HSV-TK gene to be controlled by hTERT gene promoter in adenovirus shuttle plasmid. Then we constructed recombinant adenovirus Ad-hT-TK, and infected them into normal and human gynecological cancer cell lines. Through these experiments, we identified the selective tumor specific cell death by Ad-hT-TK. Furthermore, FACS analysis and TUNEL assay suggests that the reduced viability is mediated through the induction of apoptosis, indicating that this approach may be a useful method for suppressing cancer growth in targeted cancer gene therapy. These results show that Ad-hT-TK could be used for gynecological cancer gene therapy.

CL1-SR39: A Noninvasive Molecular Imaging Model of Prostate Cancer Suicide Gene Therapy Using Positron Emission Tomography

We developed a prostate cancer tumor model capable of being noninvasively imaged using positron emission tomography (PET) based on expression of the herpes simplex virus thymidine kinase (HSV1-tk) reporter gene. The androgen independent, metastatic prostate cancer cell lines CL1 and CL1-GFP were stably transfected with the mutant HSV1-tk gene pcDNA3.1/pCMV-sr39tk, which has increased ability to phosphorylate penciclovir. The presence of the sr39tk gene product was analyzed by Western blot analysis and relative thymidine kinase enzyme activity was assessed by a functional thymidine kinase enzyme activity assay. Subcutaneous and orthotopic CL1 and CL1-SR39 tumor xenografts were established in SCID mice. The ability to image CL1-SR39 was assessed using fluorodeoxyglucose and F-penciclovir ( F-FHBG) micro-PET (a rodent PET scanner). To investigate the systemic distribution of intratumoral sr39tk injections established CL1 tumors were transiently injected with first generation adenoviral vectors carrying the sr39tk gene under control of the strong cytomegalovirus promoter Ad-CMV-HSV1-sr39tk and imaged using micro-PET. Transfection of sr39tk into CL1 cells was successful. CL1-SR39 thymidine kinase enzyme activity was greater than twice the activity of the glioma cell line C6-SR39 control and above the threshold necessary for micro-PET detection. Fluorodeoxyglucose micro-PET in SCID mice was positive for CL1 and CL1-SR39 tumors. Selective micro-PET of subcutaneous CL1-SR39 tumors was done using F-FHBG. Micro-PET imaging after systemic and intratumoral injection of Ad-CMV-HSV1-sr39tk revealed significant systemic transgene leakage with significant hepatic expression of sr39TK protein. Molecular based imaging of sr39tk transfected prostate cancer tumors and adenoviral delivered HSV1-tk suicide gene therapy based on the selective conversion and intracellular trapping of F-FHBG by sr39tk is feasible. Potential applications include noninvasive monitoring of the location, duration and intensity of gene constructs, which may contribute to the safety of clinical gene therapy protocols, and noninvasive imaging of the prostate cancer xenograft response to experimental therapy.

Acyclic nucleoside analogues as novel inhibitors of human mitochondrial thymidine kinase.

A series of acyclic nucleoside analogues of 5'-O-tritylthymidine have been synthesized and evaluated as potential human mitochondrial thymidine kinase (TK-2) inhibitors. In this series, the sugar moiety of the parent 5'-O-tritylthymidine has been replaced by aliphatic chains including (E)- and (Z)-butenol, butynol, or butanol. Among them the (Z)-butenyl derivative (10) showed an IC(50) against TK-2 of 1.5 microM, being 1 order of magnitude more potent than the parent 5'-O-tritylthymidine. This lead compound has been further modified by replacing the thymine base by other pyrimidine bases such as 5-iodouracil, 5-ethyluracil, 5-methylcytosine, 3-N-methylthymine, or 5,6-dihydrothymine, as well as by the purine base guanine. The trityl group has also been replaced by different aliphatic and aromatic acyl moieties including tert-butylacetyl, hexanoyl, decanoyl, and diphenylacetyl moieties. The evaluation of the compounds against TK-2 and the phylogenetically close HSV-1 TK has shown that the base moiety plays a crucial role in their interaction against these pyrimidine nucleoside kinases. Also, the presence of a lipophilic substituent, preferentially an aromatic moiety such as diphenylmethyl or triphenylmethyl, is required for efficient TK-2 inhibition. Whereas some compounds showed marked specificity for either TK-2 (i.e, the 5,6-dihydrothymine derivative, 26) or HSV-1 TK (i.e., the butynyl derivative, 11), some others, including the (Z)-and (E)-butenyl derivatives 10 and 12, showed significant inhibition against both enzymes. They also proved to be inhibitory against HSV-1 TK in intact human osteosarcoma cells that were transduced with the HSV-1 TK gene.

Noninvasive, repetitive, quantitative measurement of gene expression from a bicistronic message by positron emission tomography, following gene transfer with adenovirus.

Gene therapy protocols are hampered by the inability to monitor the location, magnitude, and duration of ectopic gene expression following DNA delivery. Consequently, it is difficult to establish quantitative correlations and/or causal relationships between therapeutic gene expression and phenotypic responses in treated individuals. One approach to monitor "therapeutic gene" expression indirectly is to incorporate reporter genes that can be imaged in vivo into bicistronic transcription units, along with the therapeutic genes. Expression of the dopamine D2 receptor (D2R) and herpes simplex virus thymidine kinase (HSV1-TK) can both be monitored, in vivo, by positron-emission tomography (PET). We created ad.DTm, an adenovirus containing a cytomegalovirus (CMV) early promoter-driven transcription unit, in which the D2R gene is placed proximal to an encephalomyocarditis virus internal ribosomal entry site (IRES) and a modified HSV1-tk gene is placed distal to the IRES. Following intravenous ad.DTm injection into mice, correlated hepatic D2R and HSV1-sr39tk PET reporter gene expression was demonstrated. Repeated microPET scanning quantitated both D2R-dependent sequestration of a positron-emitting ligand and HSV1-TK-dependent sequestration of a positron-emitting product. It is possible, in living mice, to investigate noninvasively and to measure quantitatively and repeatedly correlated expression of two coding regions from a bicistronic transcription unit over a 3-month period following adenovirus delivery.

Suicide gene transduction sensitizes murine embryonic and human mesenchymal stem cells to ablation on demand-- a fail-safe protection against cellular misbehavior.

Stem cells and their progeny constitute a potential resource for replacing damaged tissues or supplying missing functions, but also pose a threat of aberrant behavior, including neoplastic growth or immunopathology. Suicide genes introduced into these cells before transplantation might provide a means of addressing this threat by permitting the ablation of the cells if they subsequently misbehave. Retroviral transduction of the E. coli gpt and herpes thymidine kinase (HSVtk) suicide genes was used to determine the degree to which stem cells could be sensitized to the prodrugs 6-thioxanthine (6TX) and ganciclovir (GCV) respectively, and whether this sensitivity could persist over many cell generations. The ES-E14TG2a murine embryonic stem cell line was rendered sensitive to quantitative ablation at prodrug concentrations well tolerated by untransduced cells (50 microM 6TX, 1 microg/ml GCV). The HSVtk gene also conferred GCV sensitivity on human mesenchymal stem cells and hematopoietic precursors derived from the murine cells, although ablation was not complete. Because ES-E14TG2a cells are deficient in the cellular enzyme HPRT, they are sensitive to hypoxanthine/aminopterin/thymidine (HAT). This property enhanced the persistence of chemosensitivity in gpt-transduced cells by permitting cells that lost 6TX sensitivity to be ablated with HAT.

Adenoviral herpes simplex virus thymidine kinase gene therapy in an orthotopic lung cancer model

Background. Although adenovirus-mediated herpes simplex virus thymidine kinase (HSV tk) gene therapy is a potential candidate for a novel effective therapy for lung cancer, previous studies have been performed only in a subcutaneous tumor model employing nude mice. We studied therapeutic potentials in correlation with accurate adenoviral gene transduction efficiency in a more clinically relevant orthotopic lung cancer model employing imunocompetent mice. Methods. To analyze the cytotoxicity of adenoviral HSV tk gene transduction and ganciclovir, a cell proliferation assay was performed in vitro. A survival study was carried out in immunocompetent mice with orthotopic lung cancer, which was generated by intrapulmonary inoculation with syngeneic murine lung cancer cells that had been infected beforehand with each adenoviral vector at the predetermined gene transduction efficiencies. Results. Tumor cells were efficiently killed by infection with adenovirus carrying the HSV tk gene with the addition of ganciclovir in vitro. In the in vivo experiment all control mice died of rapid growth of the primary lung cancer and of metastases to mediastinal lymph nodes within 26 days after tumor inoculation. In contrast 50% and 100% of mice survived more than 40 days after inoculation with adenovirally HSV tk-transfected tumor cells that moderately and highly expressed HSV tk, respectively, when followed by ganciclovir administration. Gene transduction efficiencies were 67%. Conclusions. Adenovirus-mediated HSV tk gene therapy may be therapeutic for lung cancer when gene transduction efficiencies and sufficient expression levels of HSV tk can be achieved. Moreover, the present findings underscore the importance of the mouse orthotopic lung cancer model for studies of gene therapy.

553. Retroviral Packaging Cell-Mediated Approach to the Malignant Glioma, Using the HSVtk Gene, Endostatin and IL-2 in Combination

553. Retroviral Packaging Cell-Mediated Approach to the Malignant Glioma, Using the HSVtk Gene, Endostatin and IL-2 in Combination

Adenovirus-mediated suicide-gene therapy in an orthotopic murine bladder tumor model.

Patients with high-grade transitional-cell carcinoma (TCC) of the bladder frequently experience recurrence and progress and have a low response rate to chemotherapy in metastatic TCC. In this study, we evaluated the feasibility and long-term efficacy of suicide-gene therapy using adenovirus (Ad)-mediated herpes simplex virus thymidine kinase gene (HSV-TK) and prodrug ganciclovir (GCV) as a potential therapeutic approach in murine-orthotopic models of TCC. A replication defective adenoviral vectors containing toxic HSV-TK gene under the transcriptional control of RSV (Rous sarcoma virus) promoter (Ad-RSV-TK) was used. Orthotopic bladder TCC was established with 1 x 106 murine (MBT-2) TCC cells in syngenic C3H/He female mice. Intratumoral injection of Ad-RSV-TK in combination with GCV (20 mg/kg body weight/day i.p. b.i.d. x 7 days) was administered in vivo for the determination of treatment efficacy and long-term host survival in separate controlled experiments. In vivo experiments demonstrated greater than three-fold reductions in MBT-2 tumor growth for the animals treated with Ad-RSV-TK (5 x 108 plaque forming units (pfu)/GCV therapy (P < 0.01)). Central tumor necrosis and apoptosis were revealed by histomorphology and immunohistochemistry compared with other control animals (non-treated, GCV alone, Ad-RSV-TK alone). Direct intratumoral injection with Ad-RSV-TK/GCV also resulted in significantly improved survival over the control groups in separated experiment (log-rank test, P < 0.05). Suicide-gene therapy using Ad-RSV-TK/GCV provides an effective therapy in an experimental murine orthotopic bladder cancer by significantly inhibiting tumor growth and improving long-term host survival.

1289. Development and Application of Quantitative Real Time PCR and RT-PCR Assays That Discriminate between the Full-Length and Truncated HSV-TK Gene

1289. Development and Application of Quantitative Real Time PCR and RT-PCR Assays That Discriminate between the Full-Length and Truncated HSV-TK Gene

Evaluation of 2'-Deoxy-2'-Flouro-5-Methyl-1-β-D-Arabinofuranosyluracil as a Potential Gene Imaging Agent for &lt;I&gt;HSV-tk&lt;/I&gt; Expression In Vivo

2'-Deoxy-2'-flouro-5-methyl-1-beta-D-arabinofuranosyluracil (FMAU) has been evaluated in HT-29 cells as a potential positron emission tomography (PET) radiotracer for imaging HSV-tk gene expression in vivo. In vitro experiments demonstrate that the accumulation of [14C]-FMAU in HSV-tk-expressing cells is 2.4-fold (p < .02), 4.0-fold (p < .001), and 5.3-fold (p < .001) higher than the wild-type cells at 1, 3, and 5 hr, respectively. In vivo studies revealed that the tumor uptake in HSV-tk-expressing cells was 2.3-fold (p < .001), 3.0-fold (p < .001), and 5.5-fold (p < .001) higher than the control cells at 1, 2, and 5 hr, respectively. FMAU was found to be more sensitive compared to our earlier studies using 9-[(3-18F-fluoro-1-hydroxy-2-propoxy)methyl]-guanine ([18F]-FHPG) and 9-(4-[18F]-fluoro-3-hydroxy-methylbutyl)guanine ([18F]-FHBG) in the same cell lines, although, the specificity was less than FHBG. These results suggest that while FMAU labeled with PET isotopes may be useful for imaging HSV-tk-expressing tumors in vivo, multitracer studies across additional tumor models are necessary in order to identify an optimal PET radiotracer.

Evaluation of 2'-deoxy-2'-flouro-5-methyl-1-beta-D-arabinofuranosyluracil as a potential gene imaging agent for HSV-tk expression in vivo.

2'-Deoxy-2'-flouro-5-methyl-1-beta-D-arabinofuranosyluracil (FMAU) has been evaluated in HT-29 cells as a potential positron emission tomography (PET) radiotracer for imaging HSV-tk gene expression in vivo. In vitro experiments demonstrate that the accumulation of [14C]-FMAU in HSV-tk-expressing cells is 2.4-fold (p < .02), 4.0-fold (p < .001), and 5.3-fold (p < .001) higher than the wild-type cells at 1, 3, and 5 hr, respectively. In vivo studies revealed that the tumor uptake in HSV-tk-expressing cells was 2.3-fold (p < .001), 3.0-fold (p < .001), and 5.5-fold (p < .001) higher than the control cells at 1, 2, and 5 hr, respectively. FMAU was found to be more sensitive compared to our earlier studies using 9-[(3-18F-fluoro-1-hydroxy-2-propoxy)methyl]-guanine ([18F]-FHPG) and 9-(4-[18F]-fluoro-3-hydroxy-methylbutyl)guanine ([18F]-FHBG) in the same cell lines, although, the specificity was less than FHBG. These results suggest that while FMAU labeled with PET isotopes may be useful for imaging HSV-tk-expressing tumors in vivo, multitracer studies across additional tumor models are necessary in order to identify an optimal PET radiotracer.

Polyethylenimine-Mediated Suicide Gene Transfer Induces a Therapeutic Effect for Hepatocellular Carcinoma in Vivo by Using an Epstein–Barr Virus-Based Plasmid Vector

The present study aimed to establish a novel efficient nonviral strategy for suicide gene transfer in hepatocellular carcinoma (HCC) in vivo. We employed branched polyethylenimine (PEI) and combined it with Epstein–Barr virus (EBV)-based plasmid vectors. The HCC cells transfected with an EBV-based plasmid carrying the herpes simplex virus-1 thymidine kinase (HSV-1 Tk) gene (pSES.Tk) showed up to 30-fold higher susceptibilities to ganciclovir (GCV) than those transfected with a conventional plasmid vector carrying the HSV-1 Tk gene (pS.Tk). The therapeutic effect in vivo was tested by intratumoral injection of the plasmids into HuH-7 hepatomas transplanted into C.B-17 scid/scid mutant (SCID) mice and subsequent GCV administrations. Treatment with pSES.Tk, but not pS.Tk, markedly suppressed growth of hepatomas in vivo, resulting in a significantly prolonged survival period of the mice. These findings suggest that PEI-mediated gene transfer system can confer efficient expression of the suicide gene in HCC cells in vivo by using EBV-based plasmid vectors.

Tumor-specific transcriptional targeting of suicide gene therapy.

Transcriptional targeting of gene expression has been plagued by the weakness of tissue-specific promoters. Thus, to increase promoter strength while maintaining tissue specificity, we constructed a recombinant adenovirus containing a binary promoter system with a tumor-specific promoter (CEA; carcinoembryonic antigen) driving a transcription transactivator, which then activates a minimal promoter to express a suicide gene (HSV-tk; herpes simplex virus thymidine kinase). This ADV/binary-tk induced equal or greater cell killing in a CEA-specific manner in vitro compared with the CEA-independent killing of a vector with a constitutive viral promoter driving HSV-tk (ADV/RSV-tk). To monitor adenovirus-mediated HSV-tk gene expression in vivo, we employed noninvasive nuclear imaging using a radioiodinated nucleoside analog ([((1)31)I]-FIAU) serving as a substrate for HSV-tk. [((1)31)I]-FIAU-derived radioactivity accumulated after intratumoral injection of ADV/binary-tk only in the area of CEA-positive tumors with significantly less spread to the adjacent liver tissue than after administration of the universally expressed ADV/RSV-tk. Both viruses exhibited similar antitumor efficacy upon injection of liver metastases. Importantly, in vivo dose escalation studies demonstrated significantly reduced toxicity after intravenous administration of ADV/binary-tk versus ADV/RSV-tk. In summary, the increased therapeutic index of this novel, amplified CEA-driven suicide gene therapy vector is a proof of principle for the powerful enhancement of a weak tissue-specific promoter for effective tumor restricted gene expression.

Targeted Gene Therapy of Ovarian Cancer Using an Ovarian-Specific Promoter

Objectives. The “suicide” gene therapy of cancer using promoters such as cytomegalovirus could cause severe toxicity to normal tissues due to a lack of specificity of prodrug activation. Therefore, we investigated gene therapy of ovarian cancer using ovarian-specific promoter (OSP1) to limit the synthesis of the prodrug activating enzyme HSVtk to ovarian cancer cells.Methods. The HSVtk expressing plasmid pOSP1–HSVtk was created and transfected into an ovarian cancer cell line OVCAR3. The ganciclovir (GCV) sensitivity of the stable transfectants was evaluated with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method. Tissue specificity of this promoter was evaluated by comparing the sensitivity to GCV between ovarian and nonovarian cancer cell lines after they were transfected with pOSP1–HSVtk. One transfectant sensitive to GCV was implanted intraperitoneally to immunocompromised mice which were treated subsequently with GCV. Furthermore, this ovarian cancer survival model was used to evaluate the in vivo efficacy of cationic lipid mediated pOSP1–HSVtk gene delivery followed by GCV treatment.Results. Stable transfectants of OVCAR3 cells bearing OSP1–HSVtk became more sensitive to GCV treatment compared to the parental cell line and vector transfected OVCAR3 cell line. OSP1–HSVtk could specifically sensitize the OVCAR3 ovarian cancer cell line to GCV. SCID mice transplanted with the OVCAR3 transfectant and treated with GCV survived longer than the mice without GCV treatment (P = 0.032). In vivo gene delivery mediated by a cationic lipid (GL67) followed by GCV treatment yielded a longer survival in the OVCAR3 survival model (P = 0.016).Conclusions. The OSP1 promoter can selectively direct suicide gene therapy of ovarian cancer and the in vivo efficacy is improved by using a cationic lipid GL67 as delivery vehicle as opposed to the direct injection of plasmid.

Efecto antitumoral del gen suicida hsv-tk y ganciclovir en un modelo experimental de carcinoma epidermoide de cabeza y cuello

IntroductionWe studied the transfection by adenoviral vectors and the antitumoral effect of HSV-tk gene associated with ganciclovir (AdCMVtk/GCV) in KB human oral cavity squamous cell carcinoma, in vitro and in vivo. Materials and methodsTransfection was assessed by the X-gal stain. It was used in cell cultures and tumoral sections previously exposed to adenoviral vector AdCMVlacZ. In vitro, in order to study the antitumoral effect of AdCMVtk/GCV, survival of cell cultures exposed to AdCMVtk/GCV and to AdCMVlacZ/ GCV was compared. In vivo, necrotic volume as a percentage of total tumoral volume, was compared between AdCMVtk/GCV treated group and AdCMVlacZ/GCV exposed group. Hepatic and renal toxicities were assessed. ResultsIn vitro, survival of cell cultures treated with AdCMVtk/GCV was less than AdCMVlacZ/GCV exposed cells. In vivo, necrotic volume was larger in AdCMVtk/GCV treated group than in AdCMVlacZ/GCV exposed group. No toxicity was found (hepatic, renal). ConclusionsKB cells are transfected by adenoviral vectors and are killed by AdCMVtk/GCV, both in vitro and in vivo (no toxicity was found in the animal model).

Adenovirus-mediated herpes simplex thymidine kinase gene therapy for brain tumors.

Adenovirus-mediated HSVtk gene therapy has been shown to be eefective for the treatment of malignant glioma when the gene transfer efficiency is high. Adenoviruses are currently the most promising vectors for gene therapy of malignant glioma especially because of their high efficiency of gene transfer. Experiences from preclinical in vitro and in vivo studies are promising and in the near future the first reports of clinical phase I and II studies should be available. These results will significantly advance our understanding about the efficacy of adenovirus-mediated gene transfers in the treament of malignant glioma in man.

The use of graft engineering in allogeneic transplantation for myeloid malignancies

Although methods for engineering of allogeneic stem cell grafts are available for decades, the use of manipulated vs. unmanipulated grafts is still mainly dependent on the policy of individual centers. In transplantation regimens using engineered grafts not only the manipulation of the graft itself, but also the additional use of other transplant components and the impact of modifications of the conditioning regimen must be taken into consideration. The most frequently used technique for graft engineering remains T-cell depletion for GvHD prophylaxis, now mostly performed by positive selection of CD34+ cells. With the currently available techniques, e.g. with the Clinimacs device (Miltenyi) a highly effective reduction of T-cells with high recovery rates of CD34+ cells can reproducibly be achieved. For compensation of the reduced graft versus leukemia effect different strategies are used. Donor lymphocyte infusions are given after T-cell depleted transplants either prophylactically, based on the monitoring of hematopoietic chimerism or of minimal residual disease. With incremental doses of T-cells infused, the risk of inducing severe GvHD can be reduced and the strategy has been shown to be effective especially in CML. Several groups have started to use HSV-tk gene transduced lymphocytes for better control of severe GvHD by the potential to induce suicide of the T-cells with gancyclovir. This approach is highly attractive in concepts using manipulated stem cell grafts although recent findings have caused a debate on its efficacy and safety. The use of manipulated grafts can further be influenced by the choice of the conditioning regimen. The application of radiolabeled antibodies in addition to the conventional conditioning increases the antileukemic activity and may allow to utilize the advantage of better GvHD control with T-cell depleted transplants in diseases where the GvL effect is less active than in CML, e.g. in high risk AML.