UM171 Enhances Lentiviral Gene Transfer and Recovery of Primitive Human Hematopoietic Cells.

Enhanced gene transfer efficiencies and higher yields of transplantable transduced human hematopoietic stem cells are continuing goals for improving clinical protocols that use stemcell-based gene therapies. Here, we examined the effect of the HSC agonist UM171 on these endpoints in both in vitro and in vivo systems. Using a 22-hr transduction protocol, we found that UM171 significantly enhances both the lentivirus-mediated transduction and yield of CD34+ and CD34+CD45RA- hematopoietic cells from human cord blood to give a 6-fold overall higher recovery of transduced hematopoietic stem cells, including cells with long-term lympho-myeloid repopulating activity in immunodeficient mice. The ability of UM171 to enhance gene transfer to primitive cord blood hematopoietic cells extended to multiple lentiviral pseudotypes, gamma retroviruses, and non-integrating lentiviruses and to adult bone marrow cells. UM171, thus, provides an interesting reagent for improving the ex vivo production of gene-modified cells and for reducing requirements of virus for a broad range of applications.

Aldehyde dehydrogenases are regulators of hematopoietic stem cell numbers and B-cell development.

High levels of the aldehyde dehydrogenase isoform ALDH1A1 are expressed in hematopoietic stem cells (HSCs); however, its importance in these cells remains unclear. Consistent with an earlier report, we find that loss of ALDH1A1 does not affect HSCs. Intriguingly, however, we find that ALDH1A1 deficiency is associated with increased expression of the ALDH3A1 isoform, suggesting its potential to compensate for ALDH1A1. Mice deficient in ALDH3A1 have a block in B-cell development as well as abnormalities in cell cycling, intracellular signaling, and gene expression. Early B cells from these mice exhibit excess reactive oxygen species and reduced metabolism of reactive aldehydes. Mice deficient in both ALDH3A1 and ALDH1A1 have reduced numbers of HSCs as well as aberrant cell cycle distribution, increased reactive oxygen species levels, p38 mitogen-activated protein kinase activity and sensitivity to DNA damage. These findings demonstrate that ALDH3A1 can compensate for ALDH1A1 in bone marrow and is important in B-cell development, both ALDH1A1 and 3A1 are important in HSC biology; and these effects may be due, in part, to changes in metabolism of reactive oxygen species and reactive aldehydes.