The main objective of research in Dr. Lieber’s laboratory is to modify adenoviruses for gene therapy. The work is currently focused on three main areas. 1) Oncolytic adenoviruses for the treatment of metastatic tumors. We have developed an adenovirus-based system that achieves tumor-specific transgene expression in hepatic metastases after systemic application in mouse tumor models. These vectors specifically replicate in and spread throughout tumors. We have also generated adenovirus vectors with specific tropism to liver metastases derived from human cervical or breast cancer cells. We are currently testing vectors expressing anti-tumor genes in pre-clinical models. Future studies are aimed toward the combination of oncolytic and immuno-stimulatory strategies. 2) Integrating hybrid vectors for sickle cell gene therapy. To produce Ad vectors devoid of all viral genes (ΔAd.IR), we have recently employed a new technique based on recombination between inverted homology regions. ΔAd.IR vectors can accommodate transgene cassettes of up to 15kb. To mediate transgene integration, we have developed a specific modification of ΔAd.IR vectors containing AAV ITRs (ΔAd.AAV). We have produced ΔAd.AAV vectors with chimeric capsid containing adenovirus type 35 or type 11 fibers, which conferred efficient and stable transduction of human hematopoietic stem cells. Ongoing studies focus on the improvement of integration frequency of ΔAd.AAV vectors and on the stimulation of site-specific integration by incorporating the AAV Rep function into hybrid vectors. We are developing helper-dependent (“gutless”) adenovirus vectors with heterologous capsids derived from adenovirus type 11. Future plans include the application of capsid-modified ΔAd.AAV vectors in a large animal model. 3) Gene transfer into bone marrow stem cells with subsequent trans-differentiation into hepatocytes. The rational for using bone marrow derived stem cells as targets for liver gene therapy is based on the recently reported ability of bone marrow stem cells to engraft in livers and differentiate into hepatocytes in mice. We have demonstrated in cross-sex transplantation studies in mice that trans-differentiation of murine bone marrow or human CD34+ cells can be stimulated by mobilization of bone marrow cells with G-CSF and by liver damage. We are currently testing the ability of bone marrow cells, transduced ex vivo with capsid-modified ΔAd.AAV vectors, to repopulate mouse livers.