Cytokine-independent growth and clonal expansion of a primary human CD8+ T-cell clone following retroviral transduction with the IL-15 gene

Abstract

Malignancies arising from retrovirally transduced hematopoietic stem cells have been reported in animal models and human gene therapy trials. Whether mature lymphocytes are susceptible to insertional mutagenesis is unknown. We have characterized a primary human CD8 ؉ Tcell clone, which exhibited logarithmic ex vivo growth in the absence of exogenous cytokine support for more than 1 year after transduction with a murine leukemia virus-based vector encoding the T-cell growth factor IL-15. Phenotypically, the clone was CD28 ؊ , CD45RA ؊ , CD45RO ؉ , and CD62L ؊ , a profile consistent with effector memory T lymphocytes. After gene transfer with tumor-antigenspecific T-cell receptors, the clone secreted IFN-␥ upon encountering tumor targets, providing further evidence that they derived from mature lymphocytes. IntroductionHuman gene therapy strategies using replication-incompetent retroviral vectors were implemented cautiously because of many concerns, including the potential for adverse events resulting from vector insertions in the human genome. 1 Theoretical concerns about insertional mutagenesis became reality with the report that 3 of 11 patients with severe combined immunodeficiency-X1 (SCID-X1) developed T-cell leukemia after treatment with hematopoietic stem cells (HSCs) engineered with the common ␥-chain cytokine receptor gene. These leukemias resulted from integration events which activated the LMO2 proto-oncogene. 2 Nevertheless, after more than 17 years of clinical gene therapy trials this remains the only report of overt cancer development resulting from genemodified cell therapy. Our understanding of the pathogenesis of human malignancy resulting from insertional mutagenesis remains limited to this specific clinical scenario.Several observations from the SCID-X1 gene therapy trial fall in line with general principles established through animal models and other human clinical trials investigating retroviral gene transfer. The well-characterized murine leukemia virus (MLV)-based gene transfer vectors integrate preferentially in the vicinity of cellular promoters, 3,4 potentially increasing the probability of activating or inactivating vector insertions which may dysregulate gene expression. 5,6 The target cells most at risk of insertional mutagenesis are believed to be primitive progenitor cells. 7 Potentially, therapeutic transgenes may have leukemogenic properties in the appropriate setting. 6 The interactions between retroviral gene transfer vectors and hematopoietic cells are being investigated intensely.In this report, we have characterized a primary human T-cell clone, which exhibited continuous growth after transduction with an MLV-based retroviral vector encoding the T-cell growth factor, IL-15. This was an unexpected and intriguing finding for several reasons. First, human cells are inherently difficult to immortalize, and the process of transformation in human cells is believed to be considerably more complex than that of experimental animals. Second, the cells that were transduced consisted of...

Network model of survival signaling in large granular lymphocyte leukemia

“…It is worth noting that IL-15 has been shown to be important for CTL activation and generation of long-lived CD8ϩ memory cells (24,25). Both the CD8ϩ cells in the IL15 transgenic mice (26) and the IL15 transduced primary human CD8ϩ cells (27) indeed showed similar phenotypes as leukemic T-LGL. However, IL-15 alone cannot fully inhibit the onset of apoptosis in our model (Fig.…”

Extending the lifespan and efficacies of immune cells used in adoptive transfer for cancer immunotherapies–A review

“…Induces Apoptosis 107,108 Telomerase activation 122 Unconfirmed Unconfirmed IL- 15 Decrease apoptosis 136 Decrease apoptosis 130,131 Unconfirmed Telomerase activation [123][124][125] Decrease apoptosis 132 engineering of cells described here, that can be regulated by transfection with suicide genes such as those for herpes simplex virus thymidine kinase (TK) 140 or CD20 141 or the use of transfected extracellular FK506 binding domains with Caspase-9 signaling motifs to cause cell death upon treatment with FK506. 142 …”

“…122 Considering CD8 C T cells, IL-15 has been shown to increase CD8 C memory T cell longevity by inducing telomerase activity through JAK3 and PI3K signaling pathways. 123,124 A further study, looking at both IL-7 and IL-15 showed an upregulation of na€ ıve CD8 C T cells when incubated with these cytokines, with a higher response seen with IL-15. 125 Stimulation of telomerase activity in immune cells makes these cytokines potentially harmful to administer in cancers such as leukemia, where there is already uncontrolled telomerase activity occurring in T cells.…”

Chimeric antigen receptor modified T cell therapy for B cell malignancies

“…Addition of transgenes encoding IL-2, IL-7, IL-15 or IL-21 has been studied in an effort to improve the effector function, persistence or in vivo efficacy of CAR-modified T cells [43]; however, the finding of persistent autonomous proliferation of a CD8 ? T cell clone transduced to express IL-15 suggests that caution is warranted in translation of this approach [44]. A similar approach, which involves introduction of a transgene encoding IL-12 with the CAR construct, has been investigated as a strategy to overcome the suppressive effects of regulatory CD4 ?…”