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 3

SNP array analysis shows LOH.

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Gene expression levels and retroviral insertion site. (A) Microarray ana...
A genome-wide SNP array was used to examine gross deletions or rearrangements within the patient’s chromosomes. Signal from the array showing homozygosity (AA/BB) and heterozygosity (AB) of alleles on each chromosome are shown by blue or red dots, respectively. Strikingly, analysis of chromosome 9 revealed a LOH of a large region of the short arm in leukemia cells (top panel) when compared with DNA from pre–gene therapy cells (middle panel). LOH as identified by a hidden Markov model (HMM) is represented graphically in purple to show the area altered between constitutive and leukemic DNA. The tumor suppressor gene CDKN2A, which encodes p14(ARF1) and p16(INK4a), is located at 9p21, shown in the lower panel by an arrow. Alterations within this genomic locus are probably the cause for downregulation of CDKN2A expression (as described in Figure 2A).