Efficient retrovirus-mediated PIG-A gene transfer and stable restoration of GPI-anchored protein expression in cells with the PNH phenotype.

Paroxysmal nocturnal hemoglobinuria (PNH) is a clonal hematopoietic stem cell disorder characterized by complement-mediated hemolysis due to deficiencies of glycosylphosphatidylinositol-anchored proteins (GPI-APs) in subpopulations of blood cells. Acquired mutations in the X-linked phosphatidylinositol glycan-class A (PIG-A) gene appear to be the characteristic and pathogenetic cause of PNH. To develop a gene therapy approach for PNH, a retroviral vector construct, termed MPIN, was made containing the PIG-A complementary DNA along with an internal ribosome entry site and the nerve growth factor receptor (NGFR) as a selectable marker. MPIN transduction led to efficient and stable PIG-A and NGFR gene expression in a PIG-A-deficient B-cell line (JY5), a PIG-A-deficient K562 cell line, an Epstein-Barr virus-transformed B-cell line (TK-14(-)) established from a patient with PNH, as well as peripheral blood (PB) mononuclear cells from a patient with PNH. PIG-A expression in these cell lines stably restored GPI-AP expression. MPIN was transduced into bone marrow mononuclear cells from a patient with PNH, and myeloid/erythroid colonies and erythroid cells were derived. These transduced erythroid cells restored surface expression of GPI-APs and resistance to hemolysis. These results indicate that MPIN is capable of efficient and stable functional restoration of GPI-APs in a variety of PIG-A-deficient hematopoietic cell types. Furthermore, MPIN also transduced into PB CD34(+) cells from a normal donor, indicating that MPIN can transduce primitive human progenitors. These findings set the stage for determining whether MPIN can restore PIG-A function in multipotential stem cells, thereby providing a potential new therapeutic option in PNH.

Multiparameter-fluorescence activated cell sorting analysis of retroviral vector gene transfer into primitive umbilical cord blood cells.

Retroviral vector gene transfer strategies are currently being developed to treat a variety of hematopoietic disorders. To date, genetic modification of human pluripotent hematopoietic stem cells has been inefficient. In the present study we developed reagents and procedures for rapidly screening retroviral vector gene transfer conditions using a multiparameter fluorescence-activated cell sorting (FACS) assay. To identify transduced cells using FACS analysis, we developed a retroviral vector, termed MN, which stably expressed high levels of a truncated version of the low-affinity nerve growth factor receptor (LNGFR). In addition, procedures were developed for enriching CD34+ cells from cryopreserved umbilical cord blood. These cells were transduced with MN and evaluated using multiparameter FACS analysis for expression of CD34, CD38, and LNGFR. Stem cell maintenance was determined by measuring the CD34hi and CD34hiCD38lo/- cells remaining after ex vivo gene transfer. Gene transfer into these cells was measured by evaluating cells expressing high levels of LNGFR. Initial studies with this assay and with in vitro functional assays indicated that retroviral gene transfer following pre-incubation with a variety of cytokines in serum containing conditions resulted in 1) poor maintenance of hematopoietic stem cells and 2) gene transfer predominantly in relatively mature cells. When gene transfer in serum-free conditions was performed, some improvement was observed in the maintenance of cells retaining primitive immunophenotypes with no reduction in the gene transfer efficiency. The MN vector and multiparameter FACS analysis will be useful in efficiently screening ongoing efforts designed to improve stem cell gene transfer.