Induction of the glucocorticoid-induced leucine zipper gene limits the efficacy of dendritic cell vaccines.

Dendritic cell (DC) vaccines have shown great promise in generating antitumor immune responses but have generally fallen short of producing durable cures. Determining mechanisms by which these vaccines fail will provide one strategy toward improving their success. Several manipulations of DCs have improved their migration and longevity, but the immune inhibitory environment surrounding tumors provides a powerful suppressive influence. To determine the mechanisms by which DCs at the site of the tumor convert to a suppressive phenotype, we evaluated pathways in DCs that become expressed at the tumor site. Our results revealed that tumors lead to induction of the glucocorticoid-induced leucine zipper (GILZ) gene in DCs, and that this gene is critical for the development of tumor-induced tolerance of both DCs and T cells. Previous data suggested that GILZ is a pivotal gene in the balance between activation and tolerance of DCs. Our new data show that GILZ is highly upregulated in DCs in the tumor microenvironment in vivo and that blockade of this gene in DC vaccines significantly improves long-term survival. These results suggest that GILZ may be an ideal candidate gene to target for novel immune-based tumor therapies.

Behavioral and pathological outcomes in MOG 35-55 experimental autoimmune encephalomyelitis.

We measured inflammatory and neural markers of disease from 7 days to one year after induction of experimental autoimmune encephalomyelitis (EAE) by immunization with myelin oligodendrocyte glycoprotein (MOG) peptide. Axon loss began before behavioral signs when T cell infiltration and microglial activation were very subtle. Remyelination was only detectable ultrastructurally. Axon numbers in the dorsal column plateau around day 30 p.i. while behavioral measures (EAE scores, rotarod, grip strength) partially recover. These results provide a starting point for testing potential neuroprotective treatments for multiple sclerosis (MS).

Transgenic mice expressing Tel-FLT3, a constitutively activated form of FLT3, develop myeloproliferative disease.

Evidence is continuing to accumulate that the FMS-like tyrosine kinase 3 (FLT3) receptor plays an important role in acute leukemias. Acute myeloid leukemia patients often express constitutive active mutant forms of the receptor in their leukemic cells. A t(12;13)(p13;q12) translocation between Tel and the FLT3 receptor was recently described in a patient with myeloproliferative disease (MPD). Here a Tel-FLT3 construct mimicking this fusion protein was used to generate transgenic mice. The fusion protein was previously found to constitutively activate FLT3 signaling and transform Ba/F3 cells. Expression of the fusion protein in the transgenic mice was found in all tissues assayed including spleen, bone marrow (BM), thymus and liver. These mice developed splenomegaly and had a high incidence of MPD with extramedullary hematopoiesis in the liver and lymph nodes. Spleens also had increased dendritic and natural killer cell populations. In vitro analysis of the hematopoietic progenitor cells derived from Tel-FLT3 transgenic mice showed a significant increase in the number of CFU-GM in the BM, and CFU-GM, BFU-E and CFU-GEMM in the spleen. BM also showed significant increases of in vivo CFU-S colonies. Thus, transgenic mice expressing constitutively activated Tel-FLT3 develop MPD with a long latency and also result in the expansion of the hematopoietic stem/progenitor cells.

An open-label trial of combination therapy with interferon beta-1a and oral methotrexate in MS.

An open-label study was performed to evaluate the safety and efficacy of combination therapy with weekly oral methotrexate (20 mg) and interferon beta-1a (IFN beta-1a) in 15 patients with MS who had experienced exacerbations while receiving IFN beta monotherapy. Nausea was the only major side effect. A 44% reduction in the number of gadolinium-enhanced lesions seen on MRI scan was observed during combination therapy (p = 0.02). There was a trend toward fewer exacerbations. This combination therapy appears to be safe and well tolerated, and should be studied in a controlled trial.

Recombinant interferon alpha2a synergistically enhances ganciclovir-mediated tumor cell killing in the herpes simplex virus thymidine kinase system.

The herpes simplex virus thymidine kinase (HSV-TK) gene is being developed in the treatment of many different types of tumors. The HSV-TK gene sensitizes tumor cells to the antiviral drug ganciclovir (GCV) and mediates the bystander effect in which unmodified tumor cells are killed as well. Although this approach has shown a significant antitumor effect, the need to potentiate this therapy exists. The results of this study indicate that recombinant interferon alpha2a (1FNalpha2a) acts synergistically with GCV to kill HSV-TK-expressing PA1 human ovarian tumor cells. Furthermore, it enhances the bystander killing of nearby unmodified tumor cells that do not express the HSV-TK gene. Previous studies have suggested that in vitro and in vivo bystander effects may be mediated by different mechanisms. However, IFNalpha2a enhanced bystander killing in both systems, with the survival of mice bearing preexisting tumors being significantly prolonged when they were treated with IFNalpha2a and HSV-TK/GCV compared with either treatment alone. Mechanism studies have shown that treatment with IFNalpha2a and GCV caused an increase in cells in S phase 24 hours after therapy in the HSV-TK-expressing cells, but the mechanism of action of IFNalpha2a does not seem to be related to an increase in DNA damage, because GCV incorporation was not increased after treatment with IFNalpha2a. These findings suggest that IFNalpha2a may be a useful adjunctive therapy for the HSV-TK/GCV system.

Predictive sensitivity of human cancer cells in vivo using semipermeable polysulfone fibers.

An in vivo experimental model was developed to predict efficiently and accurately chemosensitivity of human tumors. Human cancer cells either from cultured cell lines or from patients' tumors were injected directly into semipermeable polysulfone fibers subsequently implanted into immunocompetent rats. Results suggest utility of this novel model system for predicting tumor sensitivity to a wide range of anticancer agents and for potentially guiding the treatment of cancer patients in the clinical setting.

In situ use of suicide genes for cancer therapy.

Gene therapy has now become a standard experimental approach for treating cancers that have failed conventional therapies. As the understanding of the molecular nature of carcinogenesis develops, new approaches are being taken to directly target tumor cells, thus bypassing the difficulties of killing cells that are resistant to chemotherapy and radiation. One emerging gene therapy approach has been through the genetic modification of tumor cells with a suicide gene such as the herpes simplex virus thymidine kinase gene (HSV-TK) and ganciclovir (GCV) therapy. Death of tumor cells modified with the HSV-TK gene leads to killing of unmodified in situ tumor cells in a phenomenon termed the "bystander effect." The basis both for this effect and other gene therapy trials underway for the treatment of cancer will be discussed.

Gene-modified cells for the treatment of cancer.

Gene therapy involves the insertion of a gene into an organism to treat a disease. Since its early development in the 1970s, gene therapy has expanded rapidly both in terms of the methods available and the number of candidate diseases for treatment. This report reviews gene therapy for cancer, including methodology, pre-clinical studies and experimental clinical trials.

The "bystander effect": tumor regression when a fraction of the tumor mass is genetically modified.

Tumor cells expressing the herpes simplex virus thymidine kinase (HSV-TK) gene are sensitive to the drug ganciclovir (GCV). We demonstrate here that HSV-TK-positive cells exposed to GCV were lethal to HSV-TK-negative cells as a result of a "bystander effect." HSV-TK-negative cells were killed in vitro when the population of cultured cells contained only 10% HSV-TK-positive cells. The mechanism of this "bystander effect" on HSV-TK-negative cells appeared to be related to the process of apoptotic cell death when HSV-TK-positive cells were exposed to GCV. Flow cytometric and electron microscopic analyses suggested that apoptotic vesicles generated from the dying gene-modified cells were phagocytized by nearby, unmodified tumor cells. Prevention of apoptotic vesicle transfer prevented the bystander effect. The toxic effect of HSV-TK-positive cells on HSV-TK-negative cells was reproduced in an in vivo model. A mixed population of tumor cells consisting of HSV-TK-positive and HSV-TK-negative cells was inoculated s.c. into mice. Regression of the tumor mass occurred when the inoculum consisted of as few as 10% HSV-TK-expressing tumor cells. The bystander effect was also demonstrated in i.p. tumor studies. Initial experiments demonstrated that prolonged survival (> 70 days) occurred when a mixture containing 50% HSV-TK-positive and 50% HSV-TK-negative cells was injected i.p. followed by GCV treatment. Further, survival was prolonged for mice with a preexisting HSV-TK-negative i.p. tumor burden by injecting HSV-TK-positive cells and GCV. These results suggest that genetic modification of tumor cells may be useful for developing cancer therapies.

Oncogene elements within an endogenous retrovirus.

The human genome contains a large number of endogenous retroviral-related sequences. While the function of these sequences is unknown, they may contribute to disease processes through their regions of homology with infectious retroviruses. We have been further characterizing a recently reported HTLV-1 related endogenous retroviral sequence cloned from T lymphocytes isolated from a patient with essential cryoglobulinemia. We here report further detailed transcriptional analysis of the sequence for tissue and cell-cycle specificity and a novel finding of an association between the endogenous retrovirus and a ras-related gene.