Glycoprotein Ibα Promoter Drives Megakaryocytic Lineage-Restricted Expression After Hematopoietic Stem Cell Transduction Using a Self-Inactivating Lentiviral Vector

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Abstract
Megakaryocytic (MK) lineage is an attractive target for cell/gene therapy approaches, aiming at correcting platelet protein deficiencies. However, MK cells are short-lived cells, and their permanent modification requires modification of hematopoietic stem cells with an integrative vector such as a lentiviral vector. Glycoprotein (Gp) IIb promoter, the most studied among the MK regulatory sequences, is also active in stem cells. To strictly limit transgene expression to the MK lineage after transduction of human CD34+ hematopoietic cells with a lentiviral vector, we looked for a promoter activated later during MK differentiation. Human cord blood, bone marrow, and peripheral-blood mobilized CD34+ cells were transduced with a human immunodeficiency virus-derived self-inactivating lentiviral vector encoding the green fluorescent protein (GFP) under the transcriptional control of GpIbα, GpIIb, or EF1α gene regulatory sequences. Both GpIbα and GpIIb promoters restricted GFP expression (analyzed by flow cytometry and immunoelectron microscopy) in MK cells among the maturing progeny of transduced cells. However, only the GpIbα promoter was strictly MK-specific, whereas GpIIb promoter was leaky in immature progenitor cells not yet engaged in MK cell lineage differentiation. We thus demonstrate the pertinence of using a 328-base-pair fragment of the human GpIbα gene regulatory sequence, in the context of a lentiviral vector, to tightly restrict transgene expression to the MK lineage after transduction of human CD34+ hematopoietic cells. Disclosure of potential conflicts of interest is found at the end of this article.

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