The lymphatic vasculature transports extravasated tissue fluid, macromolecules and cells back into the blood circulation. Recent reports have focused on the molecular mechanisms regulating the lymphatic vessels. Vascular endothelial growth factor (VEGF)-C and VEGF-D have been shown to stimulate lymphangiogenesis and their receptor, VEGFR-3, has been linked to human hereditary lymphedema. Here we show that a soluble form of VEGFR-3 is a potent inhibitor of VEGF-C/VEGF-D signaling, and when expressed in the skin of transgenic mice, it inhibits fetal lymphangiogenesis and induces a regression of already formed lymphatic vessels, though the blood vasculature remains normal. Transgenic mice develop a lymphedema-like phenotype characterized by swelling of feet, edema and dermal fibrosis. They survive the neonatal period in spite of a virtually complete lack of lymphatic vessels in several tissues, and later show regeneration of the lymphatic vasculature, indicating that induction of lymphatic regeneration may also be possible in humans.

Glioblastoma is an aggressive brain tumor with a dismal prognosis. Gene therapy may offer a new option for the treatment of these patients. Several gene therapy approaches have shown anti-tumor efficiency in experimental studies, and the first clinical trials for the treatment of malignant glioma were conducted in the 1990s. HSV-tk gene therapy has been the pioneering and most commonly used approach, but oncolytic conditionally replicating adenoviruses and herpes simplex virus mutant vectors, p53, interleukins, interferons, and antisense oligonucleotides have also been used. During the past few years, adenoviruses have become the most popular gene transfer vectors, and some recent randomized, controlled trials have shown significant anti-tumor efficacy in clinical use. However, efficient gene delivery into the brain still presents a major problem, and there is a lack of definitive phase III trials, which would avoid potential problems associated with a small number of patients, inadvertent patient selection, and overinterpretation of results based on a few long-time survivors. For clinical efficacy, median survival is one of the most rigorous endpoints. It is used here to evaluate the usefulness of various treatment approaches and current clinical status of gene therapy for malignant glioma.

We have treated Caki -2 human renal cell carcinoma in vivo using herpes simplex virus thymidine kinase ( HSV -tk ) gene therapy. Both stably transduced Caki -2 tumors, generated using retrovirus -mediated ex vivo HSV -tk gene transfer and direct intratumoral adenovirus -mediated HSV -tk gene transfer of wild type tumors, were tested. Similar treatments with LacZ containing retro -and adenoviruses were used as controls. The outcome was evaluated by imaging the tumors before and after the treatment with magnetic resonance imaging, and using histology, immunocytochemistry, and survival analysis. When implanted orthotopically into nude mouse kidneys, Caki -2 cells formed reproducible cystic papillary kidney carcinomas. In vivo magnetic resonance imaging provided an important tool for the evaluation of tumor growth. Transduction efficiency of wild -type tumors in vivo with adeno -LacZ was 22 14%. Significant tumor regression was achieved with direct intratumoral adeno -HSV -tk transduction followed by intraperitoneal ganciclovir ( GCV ) ( P < .001 ). Also, the treatment of stably transduced Caki -2 tumors with intraperitoneal GCV resulted in a significant treatment response in the HSV -tk group as compared to the LacZ group ( P < .009 ). Increased apoptosis and macrophage infiltrations, reduced proliferation, and degenerative changes were observed in the tumors treated with HSV -tk and GCV. Also, significant prolongation in survival was achieved with adeno -HSV -tk ± and GCV -treated mice as compared to the controls. It is concluded that adeno -HSV -tk gene therapy may be useful for the treatment of renal cell carcinoma in vivo. Cancer Gene Therapy ( 2001 ) 8, 529 ± 536

Background and methods: Gene therapy may offer a new tool for the treatment of renal cell carcinoma ( RCC ). We have tested a combination of cytotoxic and antiangiogenic gene therapy for wild -type orthotopic human RCC xenografts in nude mice using intratumoral adenovirus -mediated herpes simplex virus thymidine kinase ( HSV -tk ) and endostatin ( ES ) gene therapy. In vivo magnetic resonance imaging, morphometry, immunocytochemistry, and survival were used to evaluate the treatment effect. Adenovirus -mediated marker gene transfers ( GFP ) were used as controls. Results: In vivo transduction efficiency, measured using GFP gene transfer, was 27 ± 7%. The combination gene therapy with HSV -tk and ES adenoviruses resulted in a significant antitumor effect ( P < .01 ) compared to single HSV -tk ( n.s. ) or ES ( n.s. ). In the survival study, all tumors with single gene therapy using HSV -tk, ES, and marker gene adenoviruses showed progression in magnetic resonance imaging. In contrast, the majority of the tumors in the combination treatment group remained dormant or were eradicated ( 57% ). Survival of these mice equaled healthy nude mice, and was significantly prolonged ( P < .0001 ) compared to HSV -tk ( P < .028 ) and ES ( n.s. ) groups. Conclusions: It is concluded that the inhibition of angiogenesis using ES gene transfer together with the cytotoxic HSV -tk gene therapy results in a significantly improved treatment effect in RCC compared to the single gene treatments.