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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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 4

FISH analysis reveals a chromosomal rearrangement.

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SNP array analysis shows LOH. A genome-wide SNP array was used to examin...
Metaphase cells showing a rearrangement of the TCR-β locus by FISH. (A) Normal copy of chromosome 7 with intact TCR-β (colocalization of a red-green probe) (s). Rearrangement partner chromosome 1 (blue) showing the translocated portion of the probe containing the remainder of the 732-kb region upstream of the TCR-β breakpoint cluster (t). Derivative chromosome 7 with intact portion of the probe (red signal) covering 320 kb downstream of the TCR-β breakpoint cluster region with a residual signal from the probe (green signal) covering the proximal region 732 kb upstream from the TCR-β breakpoint cluster region (u). The insertion was located in the STIL-TAL1 region (1p32–1p36). Additional probes show (B) the red/green signal of the normal TCR-β region probe with the inserted fragment (v, green only), (C) the position of chromosome 1 using the 1p36 (false-colored orange) and 1q25 probe sets (false-colored blue), and (D) an overlay of the 2 previous pictures, locating the insertion proximal to 1p36. (E) Red/green signals of the normal (w) and abnormal (x) TCR-β region probes and normal-sized STIL-TAL1 (y) and large STIL-TAL probe signal apparently encompassing the inserted green TCR-β region probe signal (z). Original magnification, ×100.