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.

A Lentiviral Fluorescent Genetic Barcoding System for Flow Cytometry-Based Multiplex Tracking.

Retroviral integration site analysis and barcoding have been instrumental for multiplex clonal fate mapping, although their use imposes an inherent delay between sample acquisition and data analysis. Monitoring of multiple cell populations in real time would be advantageous, but multiplex assays compatible with flow cytometric tracking of competitive growth behavior are currently limited. We here describe the development and initial validation of three generations of lentiviral fluorescent genetic barcoding (FGB) systems that allow the creation of 26, 14, or 6 unique labels. Color-coded populations could be tracked in multiplex in vitro assays for up to 28 days by flow cytometry using all three vector systems. Those involving lower levels of multiplexing eased color-code generation and the reliability of vector expression and enabled functional in vitro and in vivo studies. In proof-of-principle experiments, FGB vectors facilitated in vitro multiplex screening of microRNA (miRNA)-induced growth advantages, as well as the in vivo recovery of color-coded progeny of murine and human hematopoietic stem cells. This novel series of FGB vectors provides new tools for assessing comparative growth properties in in vitro and in vivo multiplexing experiments, while simultaneously allowing for a reduction in sample numbers by up to 26-fold.

UV-inactivated HSV-1 potently activates NK cell killing of leukemic cells.

Herein we demonstrate that oncolytic herpes simplex virus-1 (HSV-1) potently activates human peripheral blood mononuclear cells (PBMCs) to lyse leukemic cell lines and primary acute myeloid leukemia samples, but not healthy allogeneic lymphocytes. Intriguingly, we found that UV light-inactivated HSV-1 (UV-HSV-1) is equally effective in promoting PBMC cytolysis of leukemic cells and is 1000- to 10 000-fold more potent at stimulating innate antileukemic responses than UV-inactivated cytomegalovirus, vesicular stomatitis virus, reovirus, or adenovirus. Mechanistically, UV-HSV-1 stimulates PBMC cytolysis of leukemic cells, partly via Toll-like receptor-2/protein kinase C/nuclear factor-κB signaling, and potently stimulates expression of CD69, degranulation, migration, and cytokine production in natural killer (NK) cells, suggesting that surface components of UV-HSV-1 directly activate NK cells. Importantly, UV-HSV-1 synergizes with interleukin-15 (IL-15) and IL-2 in inducing activation and cytolytic activity of NK cells. Additionally, UV-HSV-1 stimulates glycolysis and fatty acid oxidation-dependent oxygen consumption in NK cells, but only glycolysis is required for their enhanced antileukemic activity. Last, we demonstrate that T cell-depleted human PBMCs exposed to UV-HSV-1 provide a survival benefit in a murine xenograft model of human acute myeloid leukemia (AML). Taken together, our results support the preclinical development of UV-HSV-1 as an adjuvant, alone or in combination with IL-15, for allogeneic donor mononuclear cell infusions to treat AML.

Cord blood expansion. Pyrimidoindole derivatives are agonists of human hematopoietic stem cell self-renewal.

The small number of hematopoietic stem and progenitor cells in cord blood units limits their widespread use in human transplant protocols. We identified a family of chemically related small molecules that stimulates the expansion ex vivo of human cord blood cells capable of reconstituting human hematopoiesis for at least 6 months in immunocompromised mice. The potent activity of these newly identified compounds, UM171 being the prototype, is independent of suppression of the aryl hydrocarbon receptor, which targets cells with more-limited regenerative potential. The properties of UM171 make it a potential candidate for hematopoietic stem cell transplantation and gene therapy.