Resistance of mature T cells to oncogene transformation

Abstract

Leukemia caused by retroviral insertional mutagenesis after stem cell gene transfer has been reported in several experimental animals and in patients treated for X-linked severe combined immunodeficiency. Here, we analyzed whether gene transfer into mature T cells bears the same genotoxic risk. To address this issue in an experimental "worst case scenario," we transduced mature T cells and hematopoietic progenitor cells from C57BL/6 (Ly5.1) donor mice with high copy numbers of gamma retroviral vectors encoding the potent T-cell oncogenes LMO2, TCL1, or ⌬TrkA, a constitutively active mutant of TrkA. After transplantation into RAG-1-deficient recipients (Ly5.2), animals that received stem cell transplants developed T-cell lymphoma/leukemia for all investigated oncogenes with a characteristic phenotype and after characteristic latency periods. Ligation-mediated polymerase chain reaction analysis revealed monoclonality or oligoclonality of the malignancies. In striking contrast, none of the mice that received IntroductionGamma retroviral vectors integrate into the target cell genome, thus supporting long-term transgene expression. They are among the best-established therapeutic vector systems and have successfully been used for gene transfer to hematopoietic stem cells (HSCs) in the treatment of X-linked and adenosine deaminase-deficient severe combined immunodeficiency (SCID). A limitation of retroviral gene transfer to HSC has been the risk of insertional mutagenesis, which was reported to lead to the preferential expansion of individual hematopoietic cell clones (clonal dominance) or even overt leukemia/lymphoma. 1 At the date of submission, 4 human cases of leukemia resulting from retroviral insertional mutagenesis had been described, all after initially successful treatment of X-linked SCID. 2-4 Three of these cases were associated with the activation of the T-cell oncogene LMO2 near the retroviral integration site, and all cases manifested as T-cell lineage leukemias. 5 It has been long known that leukemias can be linked to specific chromosomal translocations that juxtapose a strong promoter/ enhancer element to a cellular oncogene, such as LMO2 or TCL1, 6,7 thus up-regulating the expression of the oncogene. For several of these oncogenes, transgenic mouse models have confirmed their transforming activity. 8,9 LMO2-transgenic mice develop T-cell leukemia of an immature phenotype, whereas TCL1 is found to induce mature T-cell malignancies. A deletion mutant of the receptor tyrosine kinase TrkA (⌬TrkA) for nerve growth factor was described that is constitutively active. ⌬TrkA was found to generate acute myeloid leukemia as well as immature T-cell leukemia after retroviral gene transfer and a very short latency period. 10 Activation of potential oncogenes by retroviral insertion alone is not thought to be sufficient for transformation. 11,12 One factor that may determine the penetrance of overt leukemia after oncogene activation is thought to be the level of cell lineage differentiation. In general, stem cells a...

Lineage- and stage-restricted lentiviral vectors for the gene therapy of chronic granulomatous disease

“…25 Whereas gamma-retroviral vectors have caused T-cell leukemias following transduction of HSC, it has been shown that mature T cells are relatively resistant to transformation by oncogenes. 26 Different strategies can be deployed to achieve this feat, several of which were combined in this study. We first chose the context of a selfinactivating lentiviral vector, the provirus of which is devoid of transcriptional ability per se.…”

Retroviral Insertional Mutagenesis Can Contribute to Immortalization of Mature T Lymphocytes

“…In a previous study, we addressed this issue by the gammaretroviral transduction of potent (proto)oncogenes into hematopoietic stem cells (HSCs) and mature T lymphocytes. For that experimental setting, we clearly demonstrated that mature T-cell populations are less susceptible to transformation than HSCs (16).…”

“…This is unexpected as T lymphocytes present unique characteristics associated with susceptibility to malignant transformation (16,29). They have an impressive replicative capacity allowing them to respond to antigen challenges with dramatic proliferation bursts and they are capable of long-term self-renewal.…”

“…MP91-EGFP and MP91-LMO2-EGFP were described previously (16). The cDNA of the murine IL2RA was generated via reverse transcription (SuperScript II Reverse Transcriptase, Invitrogen, Carlsbad, CA, USA).…”

Contributions of Gene Marking to Cell and Gene Therapies

“…The lack of malignant transformation was also demonstrated in a murine study in which T cells and HSCs were genetically modified with gammaretrovirus vectors that expressed T-cell oncogenes. While the enforced expression of LMO2, TCL1, or TrkA into HSCs resulted in T-cell leukemia/lymphoma in the transplanted animals, the infusion of similar genetically modified T cells was well tolerated (Newrzela et al, 2008).…”