SLAM-enriched hematopoietic stem cells maintain long-term repopulating capacity after lentiviral transduction using an abbreviated protocol

Advances in HIV Gene Therapy

Early gene therapy studies held great promise for the cure of heritable diseases, but the occurrence of various genotoxic events led to a pause in clinical trials and a more guarded approach to progress. Recent advances in genetic engineering technologies have reignited interest, leading to the approval of the first gene therapy product targeting genetic mutations in 2017. Gene therapy (GT) can be delivered either in vivo or ex vivo. An ex vivo approach to gene therapy is advantageous, as it allows for the characterization of the gene-modified cells and the selection of desired properties before patient administration. Autologous cells can also be used during this process which eliminates the possibility of immune rejection. This review highlights the various stages of ex vivo gene therapy, current research developments that have increased the efficiency and safety of this process, and a comprehensive summary of Human Immunodeficiency Virus (HIV) gene therapy studies, the majority of which have employed the ex vivo approach.

Combination of ruxolitinib with ABT-737 exhibits synergistic effects in cells carrying concurrent JAK2V617F and ASXL1 mutations

The V617F mutation in Janus kinase 2 is considered one of the driver mutations leading to Philadelphia-negative myeloproliferative neoplasms (MPNs). Concurrent JAK2V617F and ASXL1 mutations accelerate the progression of myelofibrosis in patients with MPNs. Few therapies are currently available for patients with these two mutations. In our study, the combination of ruxolitinib with ABT-737 was evaluated in cells carrying JAK2V617F and ASXL1 double mutations. RNA sequencing indicated overactivated oxidative phosphorylation in JAK2V617F;Asxl1+/- cKit+ cells. The cell line model with JAK2V617F and ASXL1 double mutations (HEL-AKO cells) also exhibited dysregulated mitochondrial function with an increase in the reactive oxygen species levels and a decrease in the ATP levels. The colony growth inhibition rates of cells with JAK2V617F and ASXL1 double mutations were significantly lower than those of cells with only the JAK2V617F mutation. Combined treatment with ruxolitinib and ABT-737 promoted apoptosis and inhibited the proliferation of HEL-AKO cells. Cotreatment with the two drugs also inhibited the growth of bone marrow mononuclear cells isolated from patients with concurrent JAK2V617F and ASXL1 mutations. In conclusion, we provide preclinical evidence showing that the combination of ruxolitinib and ABT-737 is a promising therapeutic strategy for MPN patients with concurrent JAK2V617F and ASXL1 mutations.

IFN-γ-mediated hematopoietic cell destruction in murine models of immune-mediated bone marrow failure

Interferon gamma (IFN-γ) has been reported to have both negative and positive activity on hematopoietic cells, adding complexity to the interpretation of its pleiotropic functions. We examined the effects of IFN-γ on murine hematopoietic stem cells (HSCs) and progenitors in vitro and in vivo by using mouse models. IFN-γ treatment expanded bone marrow (BM) c-Kit(+)Sca1(+)Lin(-) (KSL) cell number but reduced BM KLCD150(+) and KLCD150(+)CD48(-) cells. IFN-γ-expanded KSL cells engrafted poorly when tested by competitive repopulation in vivo. KSL, KLCD150(+), and KLCD150(+)CD48(-) cells from IFN-γ-treated animals all showed significant upregulation in Fas expression. When cocultured with activated T cells in vitro, KSL and KLCD150(+) cells from IFN-γ-treated donors showed increased apoptosis relative to those from untreated animals, and infusion of activated CD8 T cells into IFN-γ-injected animals in vivo led to partial elimination of KSL cells. Exposure of BM cells or KSL cells to IFN-γ increased expression of Fas, caspases, and related proapoptotic genes and decreased expression of Ets-1 and other hematopoietic genes. In mouse models of BM failure, mice genetically deficient in IFN-γ receptor expression showed attenuation of immune-mediated marrow destruction, whereas effector lymphocytes from IFN-γ-deficient donors were much less potent in initiating BM damage. We conclude that the activity of IFN-γ on murine hematopoiesis is context dependent. IFN-γ-augmented apoptotic gene expression facilitates destruction of HSCs and progenitors in the presence of activated cytotoxic T cells, as occurs in human BM failure.

Use of manipulated stem cells for prenatal therapy

Prenatal stem cell therapy has broad potential for therapeutic application. "Stem cells" of interest include multipotent adult-derived stem cells, cord blood, amniotic fluid, or fetal stem cells, and embryonic or induced pluripotent stem cells. Potential manipulations of stem cells prior to their administration may include harvest, processing, enrichment, expansion, and genetic transduction. A complete description of the methodology related to all of the above is well beyond the scope of this chapter. In the interest of practical application and proven efficacy, we limit our description to adult-derived hematopoietic stem cells (HSCs) and their application to in utero transplantation with or without HSC-targeted gene transfer.

Entry kinetics and cell-cell transmission of surface-bound retroviral vector particles

BACKGROUND

Transduction with recombinant HIV-1 derived lentivirus vectors is a multi-step process initiated by surface attachment and subsequent receptor-directed uptake into the target cell. We previously reported the retention of vesicular stomatitis virus G protein pseudotyped particles on murine progenitor cells and their delayed cell-cell transfer.

METHODS

To examine the underlying mechanism in more detail, we used a combination of approaches focused on investigating the role of receptor-independent factors in modulating attachment.

RESULTS

The investigation of synchronized transduction reveals cell-type specific rates of vector particle clearance with substantial delays during particle entry into murine hematopoietic progenitor cells. The observed uptake kinetics from the surface of the 1 degrees cell correlate inversely with the magnitude of transfer to 2 degrees targets, corresponding with our initial observation of preferential cell-cell transfer in the context of brief vector exposures. We further demonstrate that vector particle entry into cells is associated with the cell-type specific abundance of extracellular matrix fibronectin. Residual particle-extracellular fibronectin matrix binding and 2 degrees transfer can be competitively disrupted by heparin exposure without affecting murine progenitor homing and repopulation.

CONCLUSIONS

Although cellular attachment factors, including fibronectin, aid gene transfer by colocalizing particles to cells and disfavoring early dissociation from targets, they also appear to stabilize particles on the cell surface. The present study highlights the inadvertent consequences for cell entry and cell-cell transfer.