Hematopoietic stem cell gene therapy: towards clinically significant gene transfer efficiency

Abstract

Early clinical gene therapy and gene marking trials using retroviral vectors to transduce hematopoietic stem cells (HSC) revealed two major shortcomings of this new treatment modality. One was insufficient expression or even silencing of the integrated vector sequences, and the second was the low gene transfer efficiency achieved to in vivo repopulating cells. It became clear that neither rodent models nor human in vitro surrogate assays for stem cells were predictive of in vivo transgene levels in human target cells. Using the rhesus monkey model we have focused on improving gene transfer efficiency into HSC. Immune rejection of trans duced cells has been shown to occur in mature peripheral target cells such as lymphocytes or myocytes. Our studies and those from other investiga tors suggest that transgenes introduced via HSC induces immunologic tolerance towards the foreign product. In vivo priming of target cells, i.e. mobilization of HSC into the circulation with granulocyte colony stimulating factor and stem cell factor, as well as optimization of the in vitro transduction conditions, now allow a stable in vivo gene transfer efficiency of up to 10-15% in both lymphoid and myeloid circulating cells in non-human primates, levels that would be adequate for many clinical applications.

A novel murine model of Cooley anemia and its rescue by lentiviral-mediated human β-globin gene transfer

“…At present, the efficacy of lentiviral vectors in transducing human HSCs appears to be at least as good as that of oncoretroviral vectors. This matter is still under investigation, [34][35][36][37][38][39][40][41][42] including, importantly, marking studies in nonhuman primates. [43][44][45] The transduction efficiency of lentiviral vectors would have to prove to be vastly superior to that of oncoretroviral vectors to justify their clinical investigation for this reason alone.…”

Manipulation of Mouse Hematopoietic Progenitors by Specific Retroviral Infection

“…In vivo gene transfer into hematopoietic cells is extremely enticing, but in practice this has proven to be difficult (31). Previous observations based on purification of bone marrow cells expressing the lacZ transgene driven by the scl promoter/ enhancer (16) strongly suggest that it should be possible to target hematopoietic stem cells using the scl-tva mouse.…”

Targeting transgene expression to antigen-presenting cells derived from lentivirus-transduced engrafting human hematopoietic stem/progenitor cells

“…[1][2][3][4][5][6][7][8][9][10] However, RV transduction requires division of the target cells while most of primitive HSPCs are mitotically quiescent. Although significant progress has been made in improving conditions for ex vivo HSPC culture and transduction, RV design and production, and RV-mediated transgene expression, [11][12][13][14][15][16] RVs still possess intrinsic limitations.…”

“…Therefore, stable gene transfer to these stem cells has great potential to achieve both long-term and short-term therapeutic effects for the treatment of inherited and acquired hematopoietic disorders. [1][2][3][4][5][6] Currently, retroviral (including oncoretroviral and lentiviral) vectors remain the only choice to stably transduce hematopoietic stem/progenitor cells (HSPCs) efficiently, resulting in permanent integration of the transgene into the host genome. [7][8][9] However, transgene expression in all progenies of the transduced HSPCs is often unnecessary and may even be detrimental in many circumstances.…”