ALBERT

Description: Dendritic cells (DCs) play a central role in innate immunity and adaptive immunity. DCs are antigen presenting cells capable of inducing primary T cell responses or facilitating self-tolerance. Myeloid DCs (mDC) express CD11c. They are further divided into Type 1 myeloid DCs (mDC1) which are CD1c+CD141+ and Type 2 mDCs (mDC2) which are CD1c-CD141+, and plasmacytoid DC which are CD11c- and express CD303. Plasmacytoid DCs are the main source of type 1 interferon upon infection. CD34+ cells are a heterogeneous population of cells which contain both hematopoietic progenitors and stem cells. The microarray signature of CD34+CXCR4 (CD184)+ cells in both human and non-human primates suggest that this cell population plays a role in innate immunity. The signaling pathway for the Triggering Receptor Expressed on Myeloid Cells 1 (TREM1) is the most up-regulated pathway in both human and non-human primate sorted CD34+CD184+ cells. The TREM family is involved in the amplification and regulation of inflammatory responses. Upon sorting both human and rhesus CD34+ cells into CD34+CD184+ and CD34+CD184-, we observe that CD34+CD184+ cells are both adherent and non-adherent in nature (Figure 1) and while maintained in Flt3-L, IL-3, and SCF form progeny which appear dendritic in nature (Figure 2). In addition, we have found the CD34+CD184+ subpopulation to be resistant to lentiviral vector transduction. Upon culturing in defined, serum free media supplemented with cytokines, the progeny of the CD34+CD184+ population using both flow cytometry and confocal microscopy are CD11c+ and contain both CD1c+ and CD1c- subpopulations (Figure 3) with a predominately CD80(B7-1)+, CD123(IL-3R)+, CD197 (CCR7)+ , and HLA-Dr+ immunophenotype, having variability in CD86(B7-2) +/-, CD141(BDCA-3/Thrombomodulin)+/- , and CD144 (VE-cadherin)+/- expression, and being negative for CD303(BDCA-2)and CD309(VEGFR). Of special interest is that the CD34+CD184+ progeny contain both CD1c-CD16+ and CD1c+CD16- subpopulations of mDC. CD1c-CD16+ mDC have been shown to have strong pro-inflammatory activity, whereas CD1c+CD16- mDC are mainly inducers of chemotaxis. The progeny of the CD34+CD184+ cells can be stimulated by LPS and IFNγ to produce IL-12 based on an enzyme-linked immunosorbent assay. These results demonstrate the importance of the CD34+CXCR4+ progenitor in mDC development and allow one to speculate on how this mDC progenitor might prove of therapeutic benefit in vaccine development and cancer therapy.Figure 1Human CD34+CD184+ Sorted PopulationFigure 1. Human CD34+CD184+ Sorted PopulationFigure 2Cultured Progeny CD34+CD184+Figure 2. Cultured Progeny CD34+CD184+Figure 3Non-Human Primate CD34+CD184+ Confocal MicroscopyFigure 3. Non-Human Primate CD34+CD184+ Confocal Microscopy Disclosures: No relevant conflicts of interest to declare.

Description: Elevated fetal hemoglobin (HbF, α2γ2) levels are clinically beneficial for patients with β-hemoglobinopathies. Editing of the erythroid-specific BCL11A enhancer induces HbF, inhibiting sickling and restoring globin chain balance in erythroid cells derived from hematopoietic stem and progenitor cells (HSPCs) from SCD and β-thalassemia patients respectively, without detectable genotoxicity or adverse effects on hematopoietic stem cell (HSC) function (Wu Y, Nat Med, 2019). Here, we sought to evaluate engraftment and HbF induction potential of erythroid-specific BCL11A enhancer edited CD34+ HSPCs in a non-human primate transplantation model in which hemoglobin switching is conserved. We targeted the erythroid-specific +58 DNAse I hypersensitive site of BCL11A, which has identical human and rhesus sequences at the spacer and protospacer adjacent motif (PAM) of the potent #1617 sgRNA. Ribonucleoprotein complex (RNP) composed of 3x-NLS SpCas9 protein and either BCL11A enhancer targeting (#1617) or AAVS1 targeting sgRNA was electroporated into rhesus CD34+ HSPCs (n=3). Following erythroid differentiation, substantial γ-globin expression (54-77%, p

Description: Plerixafor (AMD3100) and granulocyte colony-stimulating factor (G-CSF) mobilize peripheral blood stem cells by different mechanisms. A rhesus macaque model was used to compare plerixafor and G-CSF–mobilized CD34+ cells. Three peripheral blood stem cell concentrates were collected from 3 macaques treated with G-CSF, plerixafor, or plerixafor plus G-CSF. CD34+ cells were isolated by immunoselection and were analyzed by global gene and microRNA (miR) expression microarrays. Unsupervised hierarchical clustering of the gene expression data separated the CD34+ cells into 3 groups based on mobilization regimen. Plerixafor-mobilized cells were enriched for B cells, T cells, and mast cell genes, and G-CSF–mobilized cells were enriched for neutrophils and mononuclear phagocyte genes. Genes up-regulated in plerixafor plus G-CSF–mobilized CD34+ cells included many that were not up-regulated by either agent alone. Two hematopoietic progenitor cell miR, miR-10 and miR-126, and a dendritic cell miR, miR-155, were up-regulated in G-CSF–mobilized CD34+ cells. A pre-B-cell acute lymphocytic leukemia miR, miR-143-3p, and a T-cell miR, miR-143-5p, were up-regulated in plerixafor plus G-CSF–mobilized cells. The composition of CD34+ cells is dependent on the mobilization protocol. Plerixafor-mobilized CD34+ cells include more B-, T-, and mast cell precursors, whereas G-CSF–mobilized cells have more neutrophil and mononuclear phagocyte precursors.

Description: In this study, we used the rhesus macaque model to determine the impact that AMD3100 has on lymphocyte mobilization, both alone and in combination with G-CSF. Our results indicate that, unlike G-CSF, AMD3100 substantially mobilizes both B and T lymphocytes into the peripheral blood. This led to significant increases in the peripheral blood content of both effector and regulatory T-cell populations, which translated into greater accumulation of these cells in the resulting leukapheresis products. Notably, CD4+/CD25high/CD127low/FoxP3+ Tregs were efficiently mobilized with AMD3100-containing regimens, with as much as a 4.0-fold enrichment in the leukapheresis product compared with G-CSF alone. CD8+ T cells were mobilized to a greater extent than CD4+ T cells, with accumulation of 3.7 ± 0.4-fold more total CD8+ T cells and 6.2 ± 0.4-fold more CD8+ effector memory T cells in the leukapheresis product compared with G-CSF alone. Given that effector memory T-cell subpopulations may mediate less GVHD compared with other effector T-cell populations and that Tregs are protective against GVHD, our results indicate that AMD3100 may mobilize a GVHD-protective T-cell repertoire, which would be of benefit in allogeneic hematopoietic stem cell transplantation.

Description: Abstract 692 HIV1-based vectors transduce rhesus hematopoietic stem cells poorly due to a species specific block by restriction factors, such as TRIM5αa which target HIV1 capsid proteins. The use of simian immunodeficiency virus (SIV)-based vectors can circumvent this restriction, yet use of this system precludes the ability to directly evaluate HIV1-based lentiviral vectors prior to their use in human clinical trials. To address this issue, we previously developed a chimeric HIV1 vector (χHIV vector) system wherein the HIV1-based lentiviral vector genome is packaged in the context of SIV capsid sequences. We found that this allowed χHIV vector particles to escape the intracellular defense mechanisms operative in rhesus hematopoietic cells as judged by the efficient transduction of both rhesus and human CD34+ cells. Following transplantation of rhesus animals with autologous cell transduced with the χHIV vector, high levels of marking were observed in peripheral blood cells (J Virol. 2009 Jul. in press). To evaluate whether χHIV vectors could transduce rhesus blood cells as efficiently as SIV vectors, we performed a competitive repopulation assay in two rhesus macaques for which half of the CD34+ cells were transduced with the standard SIV vector and the other half with the χHIV vector both at a MOI=50 and under identical transduction conditions. The transduction efficiency for rhesus CD34+ cells before transplantation with the χHIV vector showed lower transduction rates in vitro compared to those of the SIV vector (first rhesus: 41.9±0.83% vs. 71.2±0.46%, p

Description: Abstract 3587 Poster Board III-524 The mechanism whereby neutrophils traffic from the circulation in response to G-CSF has remained unclear despite the observation of ourselves and others that there is a dramatic, yet transient, loss of circulating neutrophils shortly following the administration of G-CSF in humans, non-human primates, and mice (Gordon BC, et al. Exp Hematol. 35:872-8, 2007). To determine the role of the CD18 leukocyte integrin on neutrophils in the egress of neutrophils from the circulation, we used dogs with canine leukocyte adhesion deficiency (CLAD), a genetic disease in which a mutation in CD18 prevents CD18 surface expression. We selected CLAD dogs who had 5-10% CD18+ neutrophils following either matched littermate allogeneic transplant or autologous gene therapy for CLAD. Three CLAD dogs meeting these criteria were evaluated. Three carrier dogs served as controls. G-CSF was administered at 10μg/kg SQ to all six animals. Peripheral blood samples (EDTA) were taken immediately prior to G-CSF administration, and at 15, 30, 60, 120, 240 minutes, and 24 hours following G-CSF administration. Total white blood cell counts, neutrophil counts, and the number and percentage of CD18+ peripheral blood leukocytes were assessed. As anticipated, the control dogs had a 60% decrease in circulating neutrophils 30 minutes following G-CSF administration: the mean +/− standard of deviation (SD) absolute neutrophil baseline count decreased from 6806+/−1072/μL to 2727+/−767/μL. In five control animals the neutrophil nadir occurred at 30 minutes post-G-CSF, and in one control dogs it occurred 15 minutes following G-CSF administration. Experimental CLAD dogs had only a 35% decline in neutrophil numbers at 30 minutes, from a mean baseline of 6777+/− 672/μL to 4433+/−265/μL. In these dogs the neutrophil count returned to pre-G-CSF levels by 60 minutes post-G-CSF. By 24 hours after G-CSF, the neutrophil level was increased 3-fold from baseline. Immunophenotyping using an anti-CD18 and a canine specific anti-neutrophil PE conjugated antibody indicated that only the CD18+ neutrophils disappeared from the circulation following G-CSF administration. At baseline the transplanted CLAD dogs had a mean of 15.2+/−3.9% CD18+ peripheral blood leukocytes, of these 50.7+/−7.1% were CD18+ neutrophils. Thirty minutes following G-CSF administration the mean+/−SD percentage of CD18+ leukocytes declined to 13.7+/−3.7% with 33.4+/−5.8% being neutrophils. There was also a slight decline in CD14+CD18+ monocytes from 6.2 +/− 1.5% to 4.0 +/− 1.2%, which was not observed in the controls. There was no change in CD18- leukocyte numbers. The percentage of CD18+ neutrophils returned to baseline by 60 minutes and remained there at subsequent time points. These results demonstrate that the CD18 leukocyte integrin on circulating neutrophils mediates the transient neutropenia associated with G-CSF administration. Disclosures: No relevant conflicts of interest to declare.

Description: Abstract 2523 Poster Board II-500 Prostaglandin E2 (PGE2), a member of the eicosanoid family, is a local signaling molecule released from mammalian blood vessel walls and other hematopoietic niches. PGE2 produces tissue specific effects by interacting with G protein receptors in cell membranes. It has been found to be an important regulator of hematopoietic stem cell (HSC) number during embryogenesis and is required for the development of HSCs (North et al., Nature 447:1007–1011, 2007). Additionally, PGE2 enhances HSC engraftment in competitive transplantation assays (North et al., Nature 447:1007–1011, 2007) through alterations in the survival, proliferation and homing of transplanted cells (Hoggatt et al., Blood 113:5444–5455, 2009). Immunoselected CD34+ cells were isolated from the leukapheresis products of both human and non-human primates following cytokine mobilization with G-CSF. CD34+ cells were incubated in X-Vivo 10™ with either 50μM or no PGE2 for one hour at 37°C on RetroNectin™ coated plates. After one hour incubation, media was replaced with X-Vivo 10™ supplemented with 10ng/mL SCF and IL-6 and cells were kept at 37°C and collected either prior to or at 2, 6, 12 and 24 hours following PGE2 exposure. Total RNA was isolated from cells and amplified to cRNA. Control cRNA was labeled with Cy3 dye and experimental cRNA was labeled with Cy5 dye. Control and experimental labeled cRNA was co-hybridized to a custom-made 17.5K cDNA (UniGene cluster) microarray. The relationship between the cells was analyzed using an unsupervised Eisen's hierarchical clustering method and gene regulation was analyzed at each time point using an Array scatter plot comparison. Statistical analysis was done using Array Class Comparison analysis and pathway analysis was carried out using Ingenuity Pathway Analysis. Many of the significantly up regulated genes were associated with pathways activated by PGE2, including genes involved in the inflammatory response, signal transduction, and G proteins. Interestingly the human CD34+ cells showed at 2 hours a 21.8-fold increase of 3′,5′-cyclic AMP phosphodiesterase mRNA consistent with prior observations in zebrafish and murine cells (Goessling et al. Cell 136: 1136–1148). Pathways that increased at 2 hours include molecular mechanisms of cancer, and those that were down regulated include CCR5, CTLA4, and leukocyte extravasation signaling. At 6 hours the molecular mechanisms of cancer pathway predominated even more (diminishing by 12 hours) while oxidative phosphorylation was down regulated. Genes involved in cAMP and WNT signaling are observed to be up regulated at earlier time points but diminish with time. These results correlate with protein expression observations that have been made in the zebrafish and murine models following PGE2 treatment (Goessling et al. Cell 136: 1136–1148) and are consistent with the observation that PGE2 may influence the self renewal of HSCs. Disclosures: Goessling: Fate Therapeutics: Consultancy, Patents & Royalties.

Description: Ameliorating hemoglobin disorders such as sickle cell disease (SCD) using hematopoietic stem cell (HSC) gene therapy is under development. Unlike in other diseases, therapeutic globin vectors have demanding requirements including high-level β-globin expression, tissue specificity among erythroid cells, long-term persistence, and high-level modification at the HSC level. These demanding requirements necessitate the inclusion of complex genetic elements including the locus control region (LCR), β-globin promoter, β-globin gene, and the 3' untranslated region (3'UTR), all now feasible using lentiviral vectors. The additional requirement of intron 2 for high-level β-globin expression dictates a reverse-oriented globin-expression cassette to prevent loss by RNA splicing during viral preparation. This reverse-orientation is in contrast to all other therapeutic vectors under clinical development. Current reverse-oriented globin vectors can drive phenotypic correction in mouse models for both b-thalassemia and SCD, while they are limited by lower viral titers and lower transduction efficiency in primary human HSCs, limiting their prospects, especially in SCD. We hypothesized that the reverse-orientation impedes both viral preparation and vector transduction, as despite deletion of cryptic polyadenylation (polyA) signals to optimize a conventional reverse-oriented globin vector, titers were still 10-fold lower than a standard GFP-vector. We thus designed a forward-oriented globin-expressing vector, which was further optimized by minimizing the size of the LCR, inclusion of a large segment of the β-globin promoter and an enhancer region of the 3'UTR lacking the polyA signal. Viral titers of the forward-oriented vectors (1.0±0.2x10e9 IU/mL) were 6-fold higher than the optimized vector in the reverse orientation (1.6±0.2x10e8 IU/mL, p

Description: Although the successful application of gene transfer to hematopoietic stem cells using HIV based vectors for the hemoglobinopathies and thalassemias has recently been achieved in rodents, concerns regarding possible side effects, including insertional mutagenesis, mandate large animal preclinical testing. HIV vectors transduce rhesus blood cells poorly due to a species specific block by TRIM5a and APOBEC3G which target HIV capsid proteins (CAs) and viral infectivity factor (Vif), respectively. We developed a lentiviral vector capable of transducing both human and rhesus blood cells by combining components of both HIV and SIV by including SIV CA and SIV Vif. Titers of HIV vectors prepared with SIV Vif (8.4±0.69x106 IU/ml, p=0.73) or SIV CA (delta-HIV 8.1±1.1x106 IU/ml, p=0.73) were comparable to that of a normal HIV vector (9.2±0.46x106 IU/ml), while titers of chimeric HIV vectors that included SIV gag-pol or rev-tat were dramatically decreased (0.18-4.5x105 IU/ml, p

Description: Key Points Single-photon emission computed tomography imaging can be used to image immune recovery in lymphoid tissues following transplant. There is discordance between lymphoid tissues and the peripheral blood in numbers of CD4+ cells following various doses of irradiation.