Amplification and propagation of interleukin-1ß signaling by murine brain endothelial and glial cells.

BACKGROUND: During acute infections and chronic illnesses, the pro-inflammatory cytokine interleukin-1ß (IL-1ß) acts within the brain to elicit metabolic derangements and sickness behaviors. It is unknown which cells in the brain are the proximal targets for IL-1ß with respect to the generation of these illness responses. We performed a series of in vitro experiments to (1) investigate which brain cell populations exhibit inflammatory responses to IL-1ß and (2) examine the interactions between different IL-1ß-responsive cell types in various co-culture combinations. METHODS: We treated primary cultures of murine brain microvessel endothelial cells (BMEC), astrocytes, and microglia with PBS or IL-1ß, and then performed qPCR to measure inflammatory gene expression or immunocytochemistry to evaluate nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation. To evaluate whether astrocytes and/or BMEC propagate inflammatory signals to microglia, we exposed microglia to astrocyte-conditioned media and co-cultured endothelial cells and glia in transwells. Treatment groups were compared by Student's t tests or by ANOVA followed by Bonferroni-corrected t tests. RESULTS: IL-1ß increased inflammatory gene expression and NF-κB activation in primary murine-mixed glia, enriched astrocyte, and BMEC cultures. Although IL-1ß elicited minimal changes in inflammatory gene expression and did not induce the nuclear translocation of NF-κB in isolated microglia, these cells were more robustly activated by IL-1ß when co-cultured with astrocytes and/or BMEC. We observed a polarized endothelial response to IL-1ß, because the application of IL-1ß to the abluminal endothelial surface produced a more complex microglial inflammatory response than that which occurred following luminal IL-1ß exposure. CONCLUSIONS: Inflammatory signals are detected, amplified, and propagated through the CNS via a sequential and reverberating signaling cascade involving communication between brain endothelial cells and glia. We propose that the brain's innate immune response differs depending upon which side of the blood-brain barrier the inflammatory stimulus arises, thus allowing the brain to respond differently to central vs. peripheral inflammatory insults.

Anchored Lentiviral Vector Episomes for Stem Cell Gene Therapy in Fanconi Anemia.

Fanconi anemia (FA) is an autosomal recessive, multisystem DNA repair disorder with prominent defects in the hematopoietic stem cell maintenance that result in the progressive attrition and failure in the early school age. Allogeneic stem cell transplantation has proved curative for patients with suitable donors. This, along with the characteristic survival advantage of phenotypically normal over non-corrected FA stem cells underscores the compelling rationale for stem cell gene therapy in the FA. While integrating lentiviral vectors (LV) have become the preferred platform for genetic correction in several hematologic and immunodeficiency disorders, the residual oncogenic potential by these vectors raises concerns in the FA stem cells about insertional mutagenic genetic lesions. On this backdrop, investigators are developing a new generation of non-integrating viral vectors capable of nuclear persistence through serial mitotic cycles and stable under selection to offset the comparatively lower transduction rates. Here, we review the competing approaches to develop such non-integrating lentiviral (NILV) episome vectors that faithfully replicate in the stem cells.

Mesenchymal Stromal Cell-derived Extracellular Vesicles Promote Myeloid-biased Multipotent Hematopoietic Progenitor Expansion via Toll-Like Receptor Engagement.

Mesenchymal stromal cells (MSCs) present in the bone marrow microenvironment secrete cytokines and angiogenic factors that support the maintenance and regenerative expansion of hematopoietic stem and progenitor cells (HSPCs). Here, we tested the hypothesis that extracellular vesicles (EVs) released by MSCs contribute to the paracrine crosstalk that shapes hematopoietic function. We systematically characterized EV release by murine stromal cells and demonstrate that MSC-derived EVs prompt a loss of HSPC quiescence with concomitant expansion of murine myeloid progenitors. Our studies reveal that HSPC expansion by MSC EVs is mediated via the MyD88 adapter protein and is partially blocked by treatment with a TLR4 inhibitor. Imaging of fluorescence protein-tagged MSC EVs corroborated their cellular co-localization with TLR4 and endosomal Rab5 compartments in HSPCs. The dissection of downstream responses to TLR4 activation reveals that the mechanism by which MSC EVs impact HSPCs involves canonical NF-κB signaling and downstream activation of Hif-1α and CCL2 target genes. Our aggregate data identify a previously unknown role for MSC-derived EVs in the regulation of hematopoiesis through innate immune mechanisms and illustrate the expansive cell-cell crosstalk in the bone marrow microenvironment.

S/MAR sequence confers long-term mitotic stability on non-integrating lentiviral vector episomes without selection.

Insertional oncogene activation and aberrant splicing have proved to be major setbacks for retroviral stem cell gene therapy. Integrase-deficient human immunodeficiency virus-1-derived vectors provide a potentially safer approach, but their circular genomes are rapidly lost during cell division. Here we describe a novel lentiviral vector (LV) that incorporates human ß-interferon scaffold/matrix-associated region sequences to provide an origin of replication for long-term mitotic maintenance of the episomal LTR circles. The resulting 'anchoring' non-integrating lentiviral vector (aniLV) achieved initial transduction rates comparable with integrating vector followed by progressive establishment of long-term episomal expression in a subset of cells. Analysis of aniLV-transduced single cell-derived clones maintained without selective pressure for >100 rounds of cell division showed sustained transgene expression from episomes and provided molecular evidence for long-term episome maintenance. To evaluate aniLV performance in primary cells, we transduced lineage-depleted murine hematopoietic progenitor cells, observing GFP expression in clonogenic progenitor colonies and peripheral blood leukocyte chimerism following transplantation into conditioned hosts. In aggregate, our studies suggest that scaffold/matrix-associated region elements can serve as molecular anchors for non-integrating lentivector episomes, providing sustained gene expression through successive rounds of cell division and progenitor differentiation in vitro and in vivo.