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Hematopoietic stem cell gene therapy holds the promise of being able to treat a variety of inherited and acquired diseases of the hematopoietic stem cell. However, to date, genetic modification of the human hematopoietic stem cell has been relatively inefficient. Here, we report the results of using a bioreactor system to expand hematopoietic cells after a brief retrovirus infection using a high titer, replication defective virus encoding for murine CD18. The retrovirus transduced culture continued to produce genetically modified hematopoietic progenitors for up to 6 weeks, the duration of the culture period. Up to one-third of the long-term culture initiating cell (LTC-IC) are genetically modified by the culture conditions. Murine CD18 can be expressed on the cell surface of up to 20% of the mature cells generated by the culture system, suggesting that clinically significant levels of gene transfer may be occurring. These results demonstrate the feasibility of using continuous perfusion bioreactors as a method of efficiently modifying human hematopoietic stem cells.

Recurring interstitial loss of all or part of the long arm of chromosome 5, del(5q), is associated with myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Although the affected genes have not been identified, two critical deleted regions (CDR) on 5q have been established, a proximal CDR located in 5q31, and another distal CDR in 5q32–33. We investigated the expression of 28 genes located in the 5q31 CDR, in enriched populations of normal hematopoietic stem cells (HSCs) and leukemic initiating cells (L-ICs) by the reverse transcription polymerase chain reaction (RT-PCR). Of the 28 5q CDR genes investigated, 12 (42%) were expressed in HSCs (CD34+Thy-1+CD38-Lin-), including HNRPA0(Hs.77492), LOC51306(Hs.82035), SMAP(Hs.5464), CDC23(Hs.153546), LOC51307(Hs.102469), LOC51780(Hs.24125), EGRI(Hs.326035), ETF1(Hs.77324), HSBPA9B(Hs.3069), CTNNA1(Hs.178452), MATR3(Hs.223745) and UBE2D2(Hs.108332). We also isolated L-ICs (CD34+CD123+CD38-Lin-) from 11 cases of MDS/AML with 5q-, and investigated their expression levels of these 12 HSC genes. Expression of CTNNA1was not detected in the L-ICs of 8 of the 11 cases of del(5q) MDS/AML using standard RT-PCR, while the other 11 genes were expressed in each patient at levels comparable to those of HSCs. Quantitative analysis of CTNNA1expression in L-ICs by real-time RT-PCR confirmed expression levels <30% of HSC levels in 4 of the 6 cases tested with del(5q) MDS/AML. Analysis of protein expression by immunofluorescence also verified a lack of detectable CTNNA1 in L-ICs for the two del(5q) cases tested. CTNNA1expression levels were normal in each of the 11 non-del(5q) MDS/AML cases tested. Methylation of the CTNNA1promoter region correlated with the downregulation of CTNNA1transcript in the del(5q) HL-60 cell line, in which CTNNA1expression was partially restored following treatment with 5-aza-2-deoxycytidine. Our results suggest that epigenetic suppression of the expression of the intact CTNNA1allele may contribute to the pathogenesis of MDS/AML with del(5q). We are currently using mouse and zebrafish models to study the role of CTNNA1 loss-of-function in del(5q) MDS/AML leukemogenesis.