57. Targeted Gene Delivery of Alpha-Interferon by Genetically Modified Hematopoietic Cells Inhibits Glioma Vascularization and Growth without Systemic Toxicity
Authors: Michele DePalma, Rossella Galli, Mary Anna Venneri, Letterio S. Politi, Ferdinando Pucci, Lucia Sergi Sergi, Elena Binda, Ehud Hauben, Luigi Naldini
Journal: Molecular Therapy (2006)

We recently described a lineage of proangiogenic monocytes implicated in tumor angiogenesis. These cells, identified by expression of the angiopoietin receptor (Tie2-Expressing Monocytes, TEMs), are selectively recruited to tumors and promote angiogenesis in a paracrine manner by interacting with locally derived endothelial cells (De Palma et al., Cancer Cell, 2005). Because Tie2 is specifically expressed by TEMs among the progeny of hematopoietic stem cells (HSCs), transplanting HSCs transduced by lentiviral vectors (LVs) containing the Tie2 promoter provides for selective gene expression in TEMs. Here we explored the feasibility of targeted delivery of cancer gene therapy using TEMs as selective cellular vehicles. We transduced HSCs with LVs expressing the potent anti- angiogenic factor alpha-interferon (IFN) or GFP under the control of either the Tie2 or the ubiquitously active PGK promoter, and transplanted the transduced cells into nude mice. All PGK-IFN mice died of graft failure, indicating that ubiquitous expression of IFN in the HSC progeny was severely myelotoxic. In contrast, Tie2-GFP and Tie2-IFN mice were fully reconstituted by transduced HSCs. To compare TEM-mediated delivery with systemic expression of IFN, a group of Tie2-GFP mice received an intravascular injection of PGK-IFN LV, which led to sustained IFN expression in the plasma. Eight weeks post-transplant, we injected human glioma cells intracranially and monitored tumor growth by magnetic resonance imaging. Remarkably, while all other mice displayed large brain tumors, Tie2-IFN mice were tumor free 9 days after challenge. Ten days later, tumors became detectable also in Tie2-IFN mice, although they were markedly necrotic and smaller than in Tie2-GFP mice. Serial brain sections showed that tumors of Tie2-GFP mice were viable and highly vascularized, with GFP+ TEMs surrounding typical angiogenic vessels. By contrast, tumors grown in Tie2-IFN mice had reduced vascular area and exhibited normalized/regressing blood vessels. In these tumors, we observed overexpression of IFN in a subset of tumor-infiltrating myeloid cells, likely corresponding to TEMs, suggesting that targeted expression of IFN in close proximity to neoangiogenic vessels effectively inhibited endothelial cell proliferation. Surprisingly, systemic expression of IFN not only failed to inhibit tumor angiogenesis, but also induced body wasting and severe myelotoxicity. In conclusion, targeted delivery of IFN by TEMs achieved substantial anti-tumor activity in the absence of systemic toxicity, whereas ubiquitous expression in BM-derived cells or systemic delivery were not efficacious and were highly toxic. These results provide proof of principle of a new gene therapy paradigm in which ex vivo transduction of HSCs can be used to safely deliver potent anti-cancer molecules in a tumor-targeted fashion.