Previously, several individuals with X-linked SCID (SCID-X1) were treated by gene therapy to restore the missing IL-2 receptor γ (IL2RG) gene to CD34 + BM precursor cells using gammaretroviral vectors. While 9 of 10 patients were successfully treated, 4 of the 9 developed T cell leukemia 31-68 months after gene therapy. In 2 of these cases, blast cells contained activating vector insertions near the LIM domain-only 2 (LMO2) protooncogene. Here, we report data on the 2 most recent adverse events, which occurred in patients 7 and 10. In patient 10, blast cells contained an integrated vector near LMO2 and a second integrated vector near the proto-oncogene BMI1. In patient 7, blast cells contained an integrated vector near a third proto-oncogene, CCND2. Additional genetic abnormalities in the patients' blast cells included chromosomal translocations, gain-of-function mutations activating NOTCH1, and copy number changes, including deletion of tumor suppressor gene CDKN2A, 6q interstitial losses, and SIL-TAL1 rearrangement. These findings functionally specify a genetic network that controls growth in T cell progenitors. Chemotherapy led to sustained remission in 3 of the 4 cases of T cell leukemia, but failed in the fourth. Successful chemotherapy was associated with restoration of polyclonal transduced T cell populations. As a result, the treated patients continued to benefit from therapeutic gene transfer.

We recently reported (April 18 issue) 1 the sustained correction of X-linked severe combined immunodeficiency disease by ex vivo, retrovirally mediated transfer of the g c gene into CD34+ cells in four of five patients with the disease. These results have since been confirmed in four additional patients with typical X-linked severe combined immunodeficiency. Of the first four successfully treated patients, three continue to do well up to 3.6 years after gene therapy, whereas a serious adverse event occurred in the fourth patient. At a routine checkup 30 months after gene therapy, lymphocytosis consisting of a monoclonal population of V g 9/V d 1, g / d T cells of mature phenotype was detected. One proviral integration site was found, located on the short arm of chromosome 11 within the LMO-2 locus, as determined with the use of linearamplification mediated polymerase-chain-reaction analysis. 2 This proviral integration within the LMO-2 locus was associated with aberrant expression of the LMO-2 transcript in the monoclonal T-cell population. Aberrant expression of LMO-2 has been reported in acute lymphoblastic leukemia arising from T cells with a / b receptors, usually with the chromosomal translocation t(11;14). 3 Tests for replicationcompetent retrovirus were repeatedly negative in our patient's lymphocytes. Between 30 and 34 months after gene therapy, the patient's lymphocyte count rose to 300,000 per cubic millimeter, and hepatosplenomegaly developed. Further investigations showed the presence of a t(6;13) translocation, which had not been detected 30 months after the therapy. Treatment with a chemotherapy regimen based on a high-risk protocol for acute lymphocytic leukemia (a protocol of the Dutch Childhood Leukemia Study Group) was initiated and has resulted, to date, in a dramatic reduction in the abnormal cells.

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A CBFA2T3-GLIS2 fusion gene was identified in 31% of non–Down syndrome AMKL.

PAX5 is the main target of somatic mutations in acute B lymphoblastic leukemia (B-ALL). We analyzed 153 adult and child B-ALL harboring karyotypic abnormalities at chromosome 9p, to determine the frequency and the nature of PAX5 alterations. We found PAX5 internal rearrangements in 21% of the cases. To isolate fusion partners, we used classic and innovative techniques (rolling circle amplification-rapid amplification of cDNA ends) and single nucleotide polymorphism-comparative genomic hybridization arrays. Recurrent and novel fusion partners were identified, including NCoR1, DACH2, GOLGA6, and TAOK1 genes showing the high variability of the partners. We noted that half the fusion genes can give rise to truncated PAX5 proteins. Furthermore, malignant cells carrying PAX5 fusion genes displayed a simple karyotype. These data strongly suggest that PAX5 fusion genes are early players in leukemogenesis.