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

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Abstract
Hematopoietic stem cells (HSCs) represent an important target for the treatment of various blood disorders. As the source of critical cells within the immune system, genetic modification of HSCs can also be used to modulate immune responses. The effectiveness of HSC-mediated gene therapy largely depends on efficient gene delivery into long-term repopulating progenitors and targeted transgene expression in an appropriate progeny of the transduced pluripotent HSCs. Self-inactivating (SIN) lentiviral vectors have been demonstrated to be capable of transducing mitotically inactive cells, including HSCs, and accommodating a nonviral promoter to control the transgene expression in transduced cells. In this study, we constructed 2 SIN lentiviral vectors, EF.GFP and DR.GFP, to express the green fluorescent protein (GFP) gene controlled solely by the promoter of either a housekeeping gene EF-1α or the human HLA-DRα gene, which is selectively expressed in antigen-presenting cells (APCs). We demonstrated that both vectors efficiently transduced human pluripotent CD34+cells capable of engrafting nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. When the EF.GFP vector was used, constitutive high-level GFP expression was obtained in all the human HSC progeny detectable in NOD/SCID mice and in subsequent in vitro differentiation assays, indicating that engrafting human HSCs have been transduced. In contrast, the DR.GFP vector mediated transgene expression specifically in human HLA-DR+ cells and highly in differentiated dendritic cells (DCs), which are critical in regulating immunity. Furthermore, human DCs derived from transduced and engrafted human cells potently stimulated allogeneic T-cell proliferation. This study demonstrated successful targeting of transgene expression to APCs/DCs after stable gene transduction of pluripotent HSCs.