Insertional mutagenesis combined with acquired somatic mutations causes leukemogenesis following gene therapy of SCID-X1 patients
Steven J. Howe, … , H. Bobby Gaspar, Adrian J. Thrasher
Steven J. Howe, … , H. Bobby Gaspar, Adrian J. Thrasher
Published August 7, 2008
Citation Information: J Clin Invest. 2008;118(9):3143-3150. https://doi.org/10.1172/JCI35798.
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Research Article

Insertional mutagenesis combined with acquired somatic mutations causes leukemogenesis following gene therapy of SCID-X1 patients

Abstract

X-linked SCID (SCID-X1) is amenable to correction by gene therapy using conventional gammaretroviral vectors. Here, we describe the occurrence of clonal T cell acute lymphoblastic leukemia (T-ALL) promoted by insertional mutagenesis in a completed gene therapy trial of 10 SCID-X1 patients. Integration of the vector in an antisense orientation 35 kb upstream of the protooncogene LIM domain only 2 (LMO2) caused overexpression of LMO2 in the leukemic clone. However, leukemogenesis was likely precipitated by the acquisition of other genetic abnormalities unrelated to vector insertion, including a gain-of-function mutation in NOTCH1, deletion of the tumor suppressor gene locus cyclin-dependent kinase 2A (CDKN2A), and translocation of the TCR-β region to the STIL-TAL1 locus. These findings highlight a general toxicity of endogenous gammaretroviral enhancer elements and also identify a combinatorial process during leukemic evolution that will be important for risk stratification and for future protocol design.

Authors

Steven J. Howe, Marc R. Mansour, Kerstin Schwarzwaelder, Cynthia Bartholomae, Michael Hubank, Helena Kempski, Martijn H. Brugman, Karin Pike-Overzet, Stephen J. Chatters, Dick de Ridder, Kimberly C. Gilmour, Stuart Adams, Susannah I. Thornhill, Kathryn L. Parsley, Frank J.T. Staal, Rosemary E. Gale, David C. Linch, Jinhua Bayford, Lucie Brown, Michelle Quaye, Christine Kinnon, Philip Ancliff, David K. Webb, Manfred Schmidt, Christof von Kalle, H. Bobby Gaspar, Adrian J. Thrasher

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Figure 1

Normal γc surface expression and a lack of constitutive signaling through the IL receptor complex.

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Normal γc surface expression and a lack of constitutive signaling throug...
(A) Representation of T cell recovery following gene therapy in 10 patients with SCID-X1. The immunological reconstitution of patient 8 (P8) to normal levels is indicated in red up to 3 weeks prior to diagnosis of leukemia. (B) Expression of γc on the surface of leukemic blasts measured by flow cytometry was within the normal range of control peripheral blood T cells. (C) Phosphorylation of the tyrosine residue of STAT5 is indicative of signaling through the JAK-STAT pathway when relevant ILs bind to cell-surface receptor complexes containing γc. Insert shows the presence of phosphorylated STAT5 by flow cytometry in response to IL-7 and IL-15 from the patient and PBMCs from a control. The response to different cytokines and different concentrations of IL-7 is shown in the main panel. Constitutive phosphorylation of STAT5 is not detectable and is also not induced by IL-2 or IL-15. Unstim, unstimulated. (D) Spectratype analysis revealed a dominant TCR Vβ6b clone in both CD4+ and CD8+ cells (d717, at time of leukemia diagnosis), which disappeared following chemotherapy (d735), allowing the emergence of a normal distribution of clones (see also Supplemental Figure 1).