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Murine leukemia following irradiation conditioning for transplantation of lentivirally‐modified hematopoietic stem cells
Author(s) -
Siapati Elena K.,
Bigger Brian W.,
Kashofer Karl,
Themis Mike,
Thrasher Adrian J.,
Bonnet Dominique
Publication year - 2007
Publication title -
european journal of haematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.904
H-Index - 84
eISSN - 1600-0609
pISSN - 0902-4441
DOI - 10.1111/j.1600-0609.2006.00813.x
Subject(s) - insertional mutagenesis , biology , leukemia , haematopoiesis , viral vector , genetic enhancement , vector (molecular biology) , transplantation , cancer research , retrovirus , stem cell , virology , immunology , gene , medicine , genetics , recombinant dna , virus , genome
Abstract Emerging reports are conclusively demonstrating the mutagenic risks involved in using retroviral vectors for gene therapy. Animal studies, as well as cases from a human clinical trial, have proven the potential of insertional leukemogenesis caused by a retroviral vector. Here, we report the observation of six T‐lymphoblastic leukemia cases arising during the course of a gene therapy study for hemophilia B after transplantation of ex vivo transduced hematopoietic stem cells (HSCs) by a lentivirus vector. Three of these animals comprised secondary recipients of the same donor and LAM‐PCR was performed to identify the vector integration loci. We located integrations in repeat elements of known genes, including a candidate brain‐tumor locus, but none of these clones could be tracked in the leukemic blasts. Although transduced clones with an intact proviral cassette were detected in the spleen of the leukemic animals, they comprised a very small proportion, not correlating to the levels of leukemic blasts. After propagation of the latter in NOD/SCID mice, we could no longer detect the proviral cassette suggesting that the leukemic blasts were untransduced. We did, however, detect increased levels of reverse transcriptase activity in the leukemic blasts which may suggest activation of endogenous retroviruses. This study demonstrates that tumors arising in these type of gene therapy protocols are not necessarily due to vector insertional mutagenesis and highlights the importance of careful functional studies to delineate the nature of tumorigenesis.