Malignant transformation of mature T cells after gammaretrovirus mediated transfer of nucleophosminanaplastic lymphoma kinase oncogene.

Background: Gene therapy has been in use to cure hereditary and acquired diseases by incorporating the desired gene into the cells with the help of gammaretroviral vectors. Despite the success of this therapy in X-linked severe combined immunodefi ciency syndrome, few patients developed leukemia as a major adverse event due to retroviral insertional mutagenesis within stem cells. In experimental animals also, retroviral-mediated gene transfer technique resulted in the development of leukemia. On the other hand, evidence suggests that mature T cells (TC) are relatively resistant to transformation even after retroviral-mediated transfer of potent oncogenes Tcl1, ΔTrkA and LMO2 with no reported side effects yet. Aims: To further address the safety issue for TC use in gene therapy, this study investigated susceptibility of mature polyclonal TC to malignant transformation by the retroviral-mediated transfer of nucleophosminanaplastic lymphoma kinase (NPM-ALK) oncogene. Materials and Methods: Wild-type mature TC, isolated from C57BL/6 donor mice (genetic background Ly5.1) were transduced with gamma-retroviral vectors encoding the potent TC oncogene NPM-ALK or the control vector enhanced green fl uorescent protein eGFP. The cells were then transplanted into RAG-1 defi cient recipient mice (genetic background Ly5.2). Results: Two out of fi ve mice from NPM-ALK oncogene group developed leukemia/lymphoma after latency periods (153 and 250 days, respectively). None of the mice from the control group developed any malignancy throughout the observational period. Conclusion: Mature polyclonal TC are relatively susceptible to malignant transformation after gamma-retroviral mediated transfer of NPM-ALK oncogene; hence safety of TC use in gene therapy should be further investigated to avoid the possible side-effect of development of leukemia/lymphoma.