Karin Jooss

Immune responses to vector-corrected cells have limited the application of gene therapy for treatment of chronic disorders such as inherited deficiency states. We have found that recombinant adeno-associated virus (AAV) efficiently transduces muscle fibers in vivo without activation of cellular and humoral immunity to neoantigenic transgene products such as beta-galactosidase, which differs from the experience with recombinant adenovirus, where vibrant T-cell responses to the transgene product destroy the targeted muscle fibers. T cells activated following intramuscular administration of adenovirus expressing lacZ (AdlacZ) can destroy AAVlacZ-transduced muscle fibers, indicating a prior state of immunologic nonresponsiveness in the context of AAV gene therapy. Adoptive transfer of dendritic cells infected with AdlacZ leads to immune mediated elimination of AAVlacZ-transduced muscle fibers. AAVlacZ-transduced antigen-presenting cells fail to demonstrate beta-galactosidase activity and are unable to elicit transgene immunity in adoptive transfer experiments. These studies indicate that vector-mediated transduction of dendritic cells is necessary for cellular immune responses to muscle gene therapy, a step which AAV avoids, providing a useful biological niche for its use in gene therapy.

Lymphangiogenic growth factors vascular endothelial growth factor (VEGF)-C and VEGF-D have been shown to promote lymphatic metastasis by inducing tumor-associated lymphangiogenesis. In this study, we have investigated how tumor cells gain access into lymphatic vessels and at what stage tumor cells initiate metastasis. We show that VEGF-C produced by tumor cells induced extensive lymphatic sprouting towards the tumor cells as well as dilation of the draining lymphatic vessels, suggesting an active role of lymphatic endothelial cells in lymphatic metastasis. A significant increase in lymphatic vessel growth occurred between 2 and 3 weeks after tumor xenotransplantation, and lymph node metastasis occurred at the same stage. These processes were blocked dose-dependently by inhibition of VEGF receptor 3 (VEGFR-3) signaling by systemic delivery of a soluble VEGFR-3-immunoglobulin (Ig) fusion protein via adenoviral or adeno-associated viral vectors. However, VEGFR-3-Ig did not suppress lymph node metastasis when the treatment was started at a later stage after the tumor cells had already spread out, suggesting that tumor cell entry into lymphatic vessels is a key step during tumor dissemination via the lymphatics. Whereas lymphangiogenesis and lymph node metastasis were significantly inhibited by VEGFR-3-Ig, some tumor cells were still detected in the lymph nodes in some of the treated mice. This indicates that complete blockade of lymphatic metastasis may require the targeting of both tumor lymphangiogenesis and tumor cell invasion.

Human adenoviruses have been developed as an attractive vehicle for in vivo liver-directed gene therapy. Problems with the application of first generation recombinant adenoviruses to liver-directed gene therapy have been transient expression of the recombinant gene and development of hepatitis. Previous studies in mouse models of gene transfer to liver and lung suggested that MHC class I-restricted cytotoxic T lymphocytes (CTLs) to viral antigens may be effectors in the elimination of transgene expression. The goal of this study was to evaluate the importance of viral antigens versus transgene product in inducing CTL mediated hepatocyte destruction in vivo. Immunization of C57BL/6 mice with a lacZ-expressing adenovirus elicited CTL responses to both viral antigens and the transgene product, beta-galactosidase (beta-gal). Adoptive transfer experiments, as well as studies involving lacZ-transgenic mice (ROSA-26) revealed that CTLs to viral antigens are sufficient to destroy virus-infected hepatocytes, indicating that CTLs to beta-gal can not solely account for the observed hepatocyte destruction that has characterized the use of first generation viruses. In addition, we confirmed that B cell-mediated events do not participate in destruction of hepatocytes in vivo, despite the production of virus- and beta-gal-specific antibodies. These data confirm the hypothesis that viral gene expression elicits host responses that contribute to the problem of transgene instability. Recombinant adenoviruses must be redesigned to diminish viral gene expression if they are to be used in the treatment of chronic diseases.