Characterization of human T lymphocytes engineered to express interleukin-15 and herpes simplex virus-thymidine kinase

Introduction-Preclinical studies have demonstrated that tumor reactive T cells expressing the IL-15 transgene had enhanced activity.Gene therapy strategies utilizing IL-15 should include a safety mechanism in anticipation of possible adverse effects because IL-15 overexpression has been implicated in autoimmune disorders and may be involved in the pathogenesis of some leukemias.We developed a retroviral vector carrying both IL-15 and the HSV-TK suicide gene and characterized its application in the transduction of human T lymphocytes.Methods-A retroviral vector carrying IL-15 and HSV-TK genes was optimized for the transduction of human T lymphocytes.IL-15 production was measured by ELISA.Thymidine incorporation and cell viability assays were utilized to assess the efficacy of the HSV-TK suicide gene.Genetically modified tumor infiltrating lymphocytes (TILs) were assayed for survival after withdrawal from exogenous IL-2.The activity and specificity of retrovirally transduced TILs was assessed utilizing tumor coculture assays.Results-Human T cells transduced with the IL-15/HSV-TK vector exhibited thymidine uptake in the absence of exogenous cytokine support and survived in culture for up to 80 days without IL-2.IL-15/HSV-TK transduced T cells were efficiently killed by ganciclovir at concentrations as low as 0.1 uM.TILs transduced with the IL-15/HSV-TK vector retained specific recognition of HLA-A2+, MART1+ melanomas, even after withdrawal of IL-2. Conclusions-HumanT lymphocytes genetically modified with the IL-15/HSV-TK retroviral vector retained the ability to recognize tumor antigen while gaining the ability to secrete IL-15 and prolong their own survival.IL-15/HSV-TK transduced T cells expressed HSV-TK and could be efficiently eliminated by ganciclovir.