T-cells as carriers of telomerase transcriptionally targeted retroviral vectors or oncolytic vesicular stomatitis virus for enhanced delivery of cancer gene therapy

1366 The utility of systemic administration of viral gene therapy vectors in clinical trials is limited. Strategies to improve efficacy are therefore vital.
 Viral ‘hitchhiking’ tackles this problem by exploiting the non-specific adherence of various viral vectors to the surface of T-cell carriers and their subsequent localized release at the tumor site. Here we investigate T-cells as carriers of transcriptionally-targeted, replication-defective, retroviral vectors or oncolytic vesicular stomatitis virus (VSV) in two contrasting systems.
 We have previously shown that hitchhiking of replication-defective viral vectors on T-cells improves the systemic delivery of gene therapy and can result in tumor control in murine models (1). To further investigate T-cells as carriers of transcriptionally targeted replication-defective vectors in epithelial tumors, we have developed a variety of self-inactivating (SIN) retroviral vectors. Internal tumor-selective telomerase promoters (human telomerase reverse transcriptase promoter-hTERTp, and human telomerase RNA promoter- hTRp) drive expression of an enhanced Green Fluorescent Protein (eGFP) marker transgene. We have successfully demonstrated the ability of these SIN vectors to transduce epithelial tumour cell lines. This results in telomerase-dependent eGFP expression, maintained (at lower levels) when the human Jurkat T cell line is used to carry the vectors in vitro, as assessed by FACS analysis.
 We also present a comparison of the cytotoxicity of directly transduced versus hitchhiked SIN vectors containing Herpes Simplex Virus Thymidine Kinase (HSV-tk) and Nitroreductase (NTR) suicide transgenes.
 An alternative approach is to harness oncolytic viral vectors which hold the potential to improve the efficacy of virus-mediated cancer gene therapy. We have used T-cells as carriers of oncolytic VSV in a haematological context. We demonstrate tumour-selective oncolytic ability of VSV variants VSV-delta 51 and VSV-GFP when directly transducing malignant haematological cell lines, but, importantly, not primary T cells, in vitro. Over 80% cell kill was observed in haematological malignant human cell lines, at multiplicity of infection (MOI) as low as 0.1. In contrast, primary T-cells from healthy human donors are relatively resistant to the virus, with 85-90% survival, at MOI as high as 100. Our in vitro model of a potential clinical scenario uses adoptively transferred, autologous T cells as carriers of oncolytic VSV to haematological tumours. We therefore investigated the ability of VSV-GFP to hitchhike on primary T-cells and have demonstrated transgene expression in Molt-4 cells. In vivo assessment of the efficacy of viral hitchhiking on T cells is on going.
 (1) Cole et al. Nat. Med. 2005; 11: 1073-1081.