Engraftment In Brain Research Articles

Brain-Engrafted Monocyte-derived Macrophages from Blood and Skull-Bone Marrow Exhibit Distinct Identities from Microglia.

Microglia are thought to originate exclusively from primitive macrophage progenitors in the yolk sac (YS) and to persist throughout life without much contribution from definitive hematopoiesis. Here, using lineage tracing, pharmacological manipulation, and RNA-sequencing, we elucidated the presence and characteristics of monocyte-derived macrophages (MDMs) in the brain parenchyma at baseline and during microglia repopulation, and defined the core transcriptional signatures of brain-engrafted MDMs. Lineage tracing mouse models revealed that MDMs transiently express CD206 during brain engraftment as CD206 + microglia precursors in the YS. We found that brain-engrafted MDMs exhibit transcriptional and epigenetic characteristics akin to meningeal macrophages, likely due to environmental imprinting within the meningeal space. Utilizing parabiosis and skull transplantation, we demonstrated that monocytes from both peripheral blood and skull bone marrow can repopulate microglia-depleted brains. Our results reveal the heterogeneous origins and cellular dynamics of brain parenchymal macrophages at baseline and in models of microglia depletion.

Scientific and ethical challenges of brain chimeras converge on an ‘enriched’ approach

Transplantation of human brain organoids into nonhuman animals has the potential to advance our molecular understanding of human cognition. Yet hybridized nervous systems raise novel scientific and ethical questions that appear to be oriented toward opposing ends – as models become more sophisticated, ethical concerns become more salient. I posit that scientific and ethical challenges arising from interspecies human brain engraftment may be akin to ‘birds of a feather’ that are more entangled, rather than in tension. The scientific value of engrafted organoids depends on the extent to which they provide insights into human neurobiology, while ethical concerns tend to focus on the wellbeing of engrafted animals. Based on a synthesis of empirical and theoretical evidence from neuroscience and philosophical bioethics, respectively, I argue that scientific and ethical challenges converge on a shared interest in achieving the fullest possible maturation of the host animal. The conditions which are favorable to the wellbeing of animals are also consistent with factors that contribute to the elaboration of neuronal features during development and later behavioral traits. Treating engrafted animals as if they already possess higher moral status may, in fact, be necessary for them to develop the neuronal, cognitive, and behavioral traits that are most relevant to our understanding of the human brain. Studies have shown that enriched environments provide the conditions for neurons to mature, more fully, into neural circuits that contribute to complex behaviors, while supporting the wellbeing and individuation of animals. I conceptualize an ‘enriched’ approach toward research using interspecies brain engraftment and offer a case study examining how enriched environments can be used to study the neurobiology of human speech circuits in grafted animals. The uncertainties posed by interspecies brain engraftment illustrates how joint consideration of scientific and ethical perspectives can reveal convergent pathways for advancing human brain research.

Engraftment potential of maternal adipose-derived stem cells for fetal transplantation

Advances in prenatal molecular testing have made it possible to diagnose most genetic disorders early in gestation. In utero mesenchymal stem cell (MSC) therapy can be a powerful tool to cure the incurable. With this in mind, this method could ameliorate potential physical and functional damage. However, the presence of maternal T cells trafficking in the fetus during pregnancy is thought to be the major barrier to achieving the engraftment into the fetus. We investigated the possibility of using maternal adipose-derived stem cells (ADSCs) for in utero transplantation to improve engraftment, thus lowering the risk of graft rejection. Herein, fetal brain engraftment using congenic and maternal ADSC grafts was examined via in utero stem cell transplantation in a mouse model. ADSCs were purified using the mesenchymal stem cell markers, PDGFRα, and Sca-1 via fluorescence-activated cell sorting. The PDGFRα+Sca-1+ ADSCs were transplanted into the fetal intracerebroventricular (ICV) at E14.5. The transplanted grafts grew for at least 28 days after in utero transplantation with PDGFRα+Sca-1+ ADSC, and mature neuronal markers were also detected in the grafts. Furthermore, using the maternal sorted ADSCs suppressed the innate immune response, preventing the infiltration of CD8 T cells into the graft. Thus, in utero transplantation into the fetal ICV with the maternal PDGFRα+Sca-1+ ADSCs may be beneficial for the treatment of congenital neurological diseases because of the ability to reduce the responses after in utero stem cell transplantation and differentiate into neuronal lineages.

MGTA-456, a First-in-Class Cell Therapy Produced from a Single Cord Blood Unit, Enables a Reduced Intensity Conditioning Regimen and Enhances Speed and Level of Human Microglia Engraftment in the Brains of NSG Mice

Background. Allogeneic bone marrow transplant (BMT) is a promising, curative approach for patients with inherited metabolic disorders (IMDs), a class of pediatric diseases characterized by a single enzyme deficiency. The goal of transplant is to provide cells that produce functional enzymes otherwise deficient in these patients, and thereby prevent or ameliorate neurological complications associated with selected IMDs. Donor-derived microglial cells are protective, limiting neurological disease progression. For IMD patients who do not have an HLA matched, non-carrier related donor, cord blood (CB) is the preferred HSPC source given its rapid availability and superior clinical outcomes compared to other graft sources. CB, however, is associated with delayed hematopoietic recovery and relatively poor engraftment due to the limited numbers of hematopoietic stem cells (HSCs) in a CB unit, delaying enzyme/protein reconstitution and cross-correction of non-hematopoietic cells.An aryl hydrocarbon receptor antagonist (AHRa)-based culture has been shown to expand CB CD34+ and CD34+CD90+ cells 330-fold and 100-fold, respectively, leading to rapid hematopoietic recovery after infusion of the clinical product, MGTA-456 (Wagner et al., Cell Stem Cell 2016 and Orchard et al., ASH 2018). As microglia are thought to be derived from HSCs, we hypothesized that MGTA-456 might lead to faster and greater microglial engraftment and potentially enable reduced intensity conditioning. Here, we assessed human hematopoietic and brain engraftment in NSG mice after transplant with MGTA-456 and showed that microglia engrafted faster with MGTA-456, less conditioning was needed, and that, mechanistically, these cells are derived from the CD34+CD90+ cell fraction.Methods. CB CD34+ cells were expanded in growth factor-supplemented media with or without an AHRa for 10 days. NSG mice were transplanted with unmanipulated CB CD34+ cells or the expanded product after 200 cGy total body irradiation or busulfan (BU) dosed at 20 or 40 mg/kg ip. Microglial engraftment was measured by flow cytometry of homogenized brains, quantitating the number of CD45+CD11b+Iba1+ cells, and by immunohistochemistry of brain sections.Results. Relative to naïve, unmanipulated CB CD34+ cells, transplant of MGTA-456 into sublethally irradiated mice led to an 8-fold increase in hematopoietic engraftment and a 10-fold increase in microglial engraftment in the brain (p<0.0001, n=15 mice), with histology consistent with engrafting microglia. As high dose BU enables enhanced microglia engraftment relative to irradiation by crossing the blood brain barrier and clearing host microglia (Capotondo et al., PNAS 2013), we evaluated the effectiveness of MGTA-456 after BU conditioning at 20 or 40 mg/kg. Transplant of MGTA-456 led to a 37-fold increase in engraftment relative to mice transplanted with unmanipulated CB CD34+ cells (p<0.001, n=8). Notably, transplant of MGTA-456 into mice conditioned with low-dose BU (20 mg/kg) led to a 15-fold increase in engraftment relative to high-dose BU (40 mg/kg)-conditioned animals transplanted with unmanipulated CB CD34+ cells (p<0.001, n=8). To evaluate speed of microglial engraftment, we evaluated brains weekly to 16 weeks after transplant. A 28-fold increase in microglial engraftment was demonstrated as early as 2 weeks post-transplant with MGTA-456 (p<0.0001, n=8). Number of engrafting hematopoietic cells in the periphery correlated with number of engrafting microglia in the brain (p<0.0001). Lastly, subpopulations of MGTA-456 were evaluated to determine the source of microglial engraftment. Only CD34+CD90+ cells, but not CD34+CD90- or CD34- cells, led to brain engraftment, consistent with the subpopulation of cells that result in hematopoietic engraftment following transplant of unexpanded cells (Radtke et al., Sci Trans Med 2017 and Goncalves et al., Blood 2017 130:659).Conclusions. These studies demonstrate that microglial engraftment is faster and greater in recipients of MGTA-456 even after lower dose BU conditioning, that microglial engraftment correlates with peripheral blood recovery, and that microglia cells are derived from CD34+CD90+ cells. These results suggest that lower dose BU may improve safety without jeopardizing efficacy in IMD recipients of MGTA-456. A Phase 2 clinical trial is ongoing to evaluate transplant of MGTA-456 in patients with select IMDs. [Display omitted] DisclosuresGoncalves:Magenta Therapeutics: Employment, Equity Ownership, Patents & Royalties. Li:Magenta Therapeutics: Employment, Equity Ownership. Brooks:Magenta Therapeutics: Employment, Equity Ownership. Hyzy:Magenta Therapeutics: Employment, Equity Ownership. Boitano:Magenta Therapeutics: Employment, Equity Ownership, Patents & Royalties. Cooke:Magenta Therapeutics: Employment, Equity Ownership, Patents & Royalties.

Busulfan Conditioning Enhances Engraftment of Hematopoietic Donor-derived Cells in the Brain Compared With Irradiation

Hematopoietic stem cell gene therapy for neurological disorders relies on transmigration of donor-derived monocytes to the brain, where they can engraft as microglia and deliver therapeutic proteins. Many mouse studies use whole-body irradiation to investigate brain transmigration pathways, but chemotherapy is generally used clinically. The current evidence for transmigration to the brain after chemotherapy is conflicting. We compared hematopoietic donor cell brain engraftment after bone marrow (BM) transplants in busulfan- or irradiation-conditioned mice. Significantly more donor-derived microglial cells engrafted posttransplant in busulfan-conditioned brain compared with the irradiated, in both the short and long term. Although total Iba-1(+) microglial content was increased in irradiated brain in the short term, it was similar between groups over long-term engraftment. MCP-1, a key regulator of monocyte transmigration, showed long-term elevation in busulfan-conditioned brain, whereas irradiated brains showed long-term elevation of the proinflammatory chemokine interleukin 1α (IL-1α), with increased in situ proliferation of resident microglia, and significant increases in the relative number of amoeboid activated microglia in the brain. This has implications for the choice of conditioning regimen to promote hematopoietic cell brain engraftment and the relevance of irradiation in mouse models of transplantation.

Human mesenchymal stem cells home specifically to radiation-injured tissues in a non-obese diabetes/severe combined immunodeficiency mouse model

The therapeutic potential of bone marrow-derived human mesenchymal stem cells (hMSC) has recently been brought into the spotlights of many fields of research. One possible application of the approach is the repair of tissue injuries related to side effects of radiotherapy. The first challenge in cell therapy is to assess the quality of the cell and the ability to retain their differentiation potential during the expansion process. Efficient delivery to the sites of intended action is also necessary. We addressed both challenges using hMSC cultured and then infused to non-obese diabetes/severe combined immunodeficiency (NOD/SCID) mice submitted to total body irradiation. Furthermore, we tested the impact of additional abdominal irradiation superimposed to total body irradiation (TBI), as a model of local therapeutic irradiation. Our results showed that the hMSC used for transplant have been expanded without significant loss in their differentiation capacities. After transplantation into adult unconditioned mice, hMSC not only migrate in bone marrow but also into other tissues. Total body irradiation increased hMSC implantation in bone marrow and muscle and further led to engraftment in brain, heart and liver. Local irradiation in addition to TBI, increased homing of injected cells to the injured tissues and to other tissues outside the local irradiation field. Morphological recovery of irradiated tissues after MSC transplantation and/or differentiation of MSC into specific organ cell types needs to be investigated. This study suggests that using the potential of hMSC to home to various organs in response to tissue injuries might be a strategy to repair the radiation-induced damages.

Tracking of systemically administered mononuclear cells in the ischemic brain by high-field magnetic resonance imaging

This study was designed to track systemically administered mononuclear cells (MNCs) in the ischemic mouse brain using 7 T magnetic resonance imaging (MRI). Splenectomized wild-type mice were subjected to brain ischemia by 30 or 60 min filamentous occlusion of the middle cerebral artery (MCAo) and reperfusion. Spleen-derived MNCs were labeled with very small superparamagnetic iron-oxide particles (VSOP) and transfused into recipient mice 30 min, 8 h, or 24 h after MCAo via the tail vein. High-resolution MRI sequences were designed to monitor the dynamics of brain ischemia and to observe the migration and engraftment of transfused cells into the ischemic brain. T2*-weighted (gradient-echo) hypointense signal changes became apparent at 24–48 h after transfusion, were typically associated with the ischemic lesion border, and could be followed up to 5 weeks after the insult. Such presumed MNC-associated signal changes in MRI were confirmed by histochemical detection of iron (Prussian blue staining) and detection of constitutively expressed green fluorescent protein (GFP) in a subset of animals transfused with MNCs derived from GFP transgenic mice. Taken together, our results demonstrate that brain engraftment of systemically administered mononuclear cells can be visualized non-invasively over time and space using high-resolution MRI.

Brain engraftment and therapeutic potential of stem/progenitor cells derived from mouse skin

Skin stem/progenitor cells (SKPs) derive from the dermis and in culture can generate mesodermal and neural progenies. To investigate their potential for the treatment of brain diseases, we first injected SKPs into the brain of syngeneic mice. Brain histology indicated that most SKPs remained undifferentiated and clustered at the injection site, while, in vitro, 17% of SKPs expressed neural markers, as assessed by flow cytometry. After labeling with magnetodendrimers, murine and human SKPs were detected by magnetic resonance imaging even 5 months after brain injection. To evaluate their therapeutic potential on malignant gliomas, IL-4 SKPs (i.e. SKPs transduced by a lentiviral vector carrying the cDNA of the anti-glioma cytokine interleukin-4) were injected into GL261 experimental gliomas. IL-4-SKPs prolonged significantly the survival of tumor-bearing mice: furthermore, GL261 gliomas attracted SKPs originally injected into the contralateral hemisphere. Thus, prolonged survival, capacity for transgene expression, and lack of uncontrolled proliferation suggest that SKPs warrant further consideration as therapeutic tools for brain tumors and, possibly, other neurological disorders.

Human Mesenchymal Stem Cells (MSC) Home at Injured Sites after Local Irradiation and Contribute To Reduce Radiation-Induced Intestinal Lesion.

Some patients who undergo radiotherapy may develop side effects that can be life threatening. Tissue complications can result in functional alterations of organs caused by radiation-induced stem cell depletion. Stem cell therapy is a promising approach to improve radiotherapy-enhanced tissue complications. The multipotential of Mesenchymal Stem Cells (MSC), their easy isolation and high ex vivo expansive capacity make these cells good candidates for replenishment of the depleted stem cell compartment during radiotherapy. In this study, we make the assumption that radiation-induced normal tissue injuries might play a role in the recruitment of MSC for tissue repair. We isolated MSC from the human bone marrow (hMSC) and transplanted them via the systemic route into immunotolerent NOD/SCID mice. Using two models of radiation-induced lesion (total body irradiation: TBI, total abdominal irradiation: TAI), we have studied the link between tissue damage and hMSC implantation. Tissue alterations were studied by histological analysis. hMSC in tissues of transplant was quantified by real-time PCR assay 14 days after their injection. In unirradiated NOD/SCID mice, hMSC homed significantly in lung (0.06% of total lung cells), muscle (0.07%) and bone marrow (0.14%). Following TBI of NOD/SCID mice at a sublethal dose (3.2 Gy), we observed an increase of engraftment in brain (0.07%), heart (0.05%), liver (0.11%), muscle (0.12%) and bone marrow (0.37%) compared to unirradiated mice. TAI (8 Gy) induced a significant increase of hMSC engraftment levels in kidney (0.10%), stomach (0.12%), liver (0.44%), spleen (0.94%), and small intestine (0.17%) compared to TBI mice. Histological study show that MSC reduce radiation-induced intestinal lesion: following AI, MSC accelerate the renewal of small intestine in participating to their regenerative process. From 3 days after radiation exposure, when hMSC are injected, the integrity of small intestine is already regained. The villus length is significantly increased (1.7 fold compared with control). We also observe many proliferating zone). 15 days after irradiation, the villus length remains elevated and is significantly increased in comparison with uninjected or unirradiated group. We then demonstrated that hMSC could accelerate and favour small intestinal regeneration after radiation-induced their damages. We conclude that mainly MSC implantation takes place in radiation-injured organs of exposed areas. We demonstrate the capacity of hMSC to improve the spontaneous renewal of NOD/SCID mice small intestine. The characterization of the capacity of MSC in intestinal functional recover is under progress in our laboratory.

Human skin-derived stem cells migrate throughout forebrain and differentiate into astrocytes after injection into adult mouse brain.

Recent evidence indicates that neural stem cell properties can be found among a mammalian skin-derived multipotent population. A major barrier in the further characterization of the human skin-derived neural progenitors is the inability to isolate this population based on expression of cell surface markers. Our work has been devoted to purified human skin-derived stem cells that are capable of neural differentiation, based on the presence or absence of the AC133 cell surface marker. The enriched skin-derived AC133(+) cells express the CD34 and Thy-1 antigens. These cells cultured in a growth medium containing epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) proliferate, forming spheres, and differentiate in vitro into neurons, astrocytes, and rarely into oligodendrocytes. Single cells from sphere cultures initiated from human purified AC133(+) cells were replated as single cells and were able to generate new spheres, demonstrating the self-renewing ability of these stem cell populations. Brain engraftment of cells obtained from human purified AC133(+)-derived spheres generated different neural phenotypes: immature neurons and a most abundant population of well differentiated astrocytes. The AC133-derived astrocytes assumed perivascular locations in the frontal cortex. No donor-derived oligodendrocytes were found in the transplanted mouse brains. Several donor small, rounded cells that expressed endothelial markers were found close to the host vessel and near the subventricular zone. Thus, mammalian skin AC133-derived cells behave as a multipotent population with the capacity to differentiate into neural lineages in vitro and, prevalently, endothelium and astrocytes in vivo, demonstrating the great plasticity of these cells and suggesting potential clinical application.

Alternative Sources of Neurons and Glia from Somatic Stem Cells

Stem cell populations have been shown to be extremely versatile: they can generate differentiated cells specific to the tissue in which they reside and descendents that are of different germ layer origin. This raises the possibility of obtaining neuronal cells from new biological source of the same adult human subjects. In this study, we found that epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) cooperated to induce the proliferation, self-renewal, and expansion of neural stem cell-like population isolated from several newborn and adult mouse tissues: muscle and hematopoietic tissues. This population, in both primary culture and secondary expanded clones, formed spheres of undifferentiated cells that were induced to differentiate into neurons, astrocytes, and oligodendrocytes. Brain engraftment of the somatic-derived neural stem cells generated neuronal phenotypes, demonstrating the great plasticity of these cells with potential clinical application.

Brain engraftment of autologous macrophages transduced with a lentiviral flap vector: an approach to complement brain dysfunctions.

Transplantation of ex vivo gene-corrected autologous cells represents an attractive therapeutic approach for brain diseases. Among the cells of the central nervous system, brain macrophages are promising candidates due to their role in tissue homeostasis and their implication in several neurological diseases. Up to now, gene transfer into macrophages has proven difficult by most currently available gene delivery methods. We describe herein, an efficient transduction of rat bone marrow-derived and brain macrophages with an HIV-1-derived vector containing a central DNA flap and encoding the GFP reporter gene (TRIP-DeltaU3-GFP). In primary cultures of macrophages our results show that more than 90% of the cells were transduced by the TRIP vector and that GFP expression remained stable for 1 month without cytopathic effect. In vivo, transplants of transduced macrophages into the striatum of adult rats exhibited long-term expression of GFP up to 3 months. Transduced macrophages were observed around the brain injection site and exhibited the brain macrophage/microglia phenotype. There was no significant sign of astrogliosis around the graft. These results confirm the potential of lentiviral vectors for efficient and stable ex vivo transduction of macrophages. Moreover, transduced autologous macrophages appear as a valuable vehicle for long-term and localized gene expression into the brain.