Efficient Engraftment Research Articles

Donor bone marrow–derived macrophage engraftment into the central nervous system of patients following allogeneic transplantation

AbstractHematopoietic stem cell transplantation is a well-known treatment for hematologic malignancies, wherein nascent stem cells provide regenerating marrow and immunotherapy against the tumor. The progeny of hematopoietic stem cells also populate a wide spectrum of tissues, including the brain, as bone marrow–derived macrophages similar to microglial cells. We developed a sensitive and novel combined immunohistochemistry (IHC) and XY fluorescence in situ hybridization assay to detect, quantify, and characterize donor cells in the cerebral cortices of 19 female patients who underwent allogeneic stem cell transplantation. We showed that the number of male donor cells ranged from 0.14% to 3.0% of the total cells or from 1.2% to 25% of microglial cells. Using tyramide-based fluorescent IHC, we found that at least 80% of the donor cells expressed the microglial marker ionized calcium-binding adapter molecule-1, consistent with bone marrow–derived macrophages. The percentage of donor cells was related to pretransplantation conditioning; donor cells from radiation-based myeloablative cases averaged 8.1% of microglial cells, whereas those from nonmyeloablative cases averaged only 1.3%. The number of donor cells in patients conditioned with busulfan- or treosulfan-based myeloablation was similar to that in total body irradiation-based conditioning; donor cells averaged 6.8% of the microglial cells. Notably, patients who received multiple transplantations and those with the longest posttransplantation survival had the highest level of donor engraftment, with donor cells averaging 16.3% of the microglial cells. Our work represents the largest study characterizing bone marrow–derived macrophages in patients after transplantation. The efficiency of engraftment observed in our study warrants future research on microglial replacement as a therapeutic option for disorders of the central nervous system.

TNF-α/IL-1β-licensed hADSCs alleviate cholestatic liver injury and fibrosis in mice via COX-2/PGE2 pathway

BackgroundAdipose tissue-derived stem cell (ADSC) transplantation has been shown to be effective for the management of severe liver disorders. Preactivation of ADSCs enhanced their therapeutic efficacy. However, these effects have not yet been examined in relation to cholestatic liver injury.MethodsIn the present study, a cholestatic liver injury model was established by bile duct ligation (BDL) in male C57BL/6 mice. Human ADSCs (hADSCs) with or without tumor necrosis factor-alpha (TNF-α) and interleukin-1beta (IL-1β) pretreatment were administrated into the mice via tail vein injections. The efficacy of hADSCs on BDL-induced liver injury was assessed by histological staining, real-time quantitative PCR (RT-qPCR), Western blot, and enzyme-linked immune sorbent assay (ELISA). In vitro, the effects of hADSC conditioned medium on the activation of hepatic stellate cells (HSCs) were investigated. Small interfering RNA (siRNA) was used to knock down cyclooxygenase-2 (COX-2) in hADSCs.ResultsTNF-α/IL-1β preconditioning could downregulate immunogenic gene expression and enhance the engraftment efficiency of hADSCs. Compared to control hADSCs (C-hADSCs), TNF-α/IL-1β-pretreated hADSCs (P-hADSCs) significantly alleviated BDL-induced liver injury, as demonstrated by reduced hepatic cell death, attenuated infiltration of Ly6G + neutrophils, and decreased expression of pro-inflammatory cytokines TNF-α, IL-1β, C-X-C motif chemokine ligand 1 (CXCL1), and C-X-C motif chemokine ligand 2 (CXCL2). Moreover, P-hADSCs significantly delayed the development of BDL-induced liver fibrosis. In vitro, conditioned medium from P-hADSCs significantly inhibited HSC activation compared to that from C-hADSCs. Mechanistically, TNF-α/IL-1β upregulated COX-2 expression and increased prostaglandin E2 (PGE2) secretion. The blockage of COX-2 by siRNA transfection reversed the benefits of P-hADSCs for PGE2 production, HSC activation, and liver fibrosis progression.ConclusionIn conclusion, our results suggest that TNF-α/IL-1β pretreatment enhances the efficacy of hADSCs in mice with cholestatic liver injury, partially through the COX-2/PGE2 pathway.

Optimizing of the isolation of hematopoietic stem cell in bone marrow transplantation in children

Most of collected hematopoietic stem cell (HSCs) products need processing in order to isolate stem cells, squeeze out of plasma and erythrocytes. There are two main aims for bone marrow (BM) enrichment: reduction of immunogenicity of AB0 incompatible transplants and/or preventing toxicity of hemolysis during cryopreservation. In our center we have implemented two methods for BM enrichment: manual technic using 10 % HAES (hydroxyethyl starch) and automatic cell separator. In order to optimize the process, we examined retrospectively the parameters which could have a great impact on final efficiency of engraftment, such as reduction of hematocrit, CD34 + , WBC recovery and cell viability. This study was a retrospective analysis of 46 pediatric patients (pts) who underwent autologous or allogeneic HSCT. There were performed 27 procedures using cell separator and 19 with HAES technique. This study showed that cell separator processing is significantly less damaging for stem cells than widely longer, manual HAES technique. Comparing RBC depletion and WBC recovery both used techniques are same efficient and good enough but we found out a significant difference in the efficiency of CD34 + recovery which was much higher in a technique of cell separator. We examined also the effect of addition of packed red blood cells (PRBCs) to the BM on purifying and efficiency of HSCs isolation. Doing so it decreased only the WBC recovery during sell separator processing. To sum up after series of analyzes we found out that cell separator is more convenient than HAES technique in most of considered aspects. Furthermore, cell separator use is cheaper and needs less time for processing.

Development and characterization of ferret ex vivo tracheal injury and cell engraftment model.

The field of airway biology research relies primarily on in vitro and in vivo models of disease and injury. The use of ex vivo models to study airway injury and cell-based therapies remains largely unexplored although such models have the potential to overcome certain limitations of working with live animals and may more closely replicate in vivo processes than in vitro models can. Here, we characterized a ferret ex vivo tracheal injury and cell engraftment model. We describe a protocol for whole-mount staining of cleared tracheal explants, and showed that it provides a more comprehensive structural overview of the surface airway epithelium (SAE) and submucosal glands (SMGs) than 2D sections, revealing previously underappreciated structural anatomy of tracheal innervation and vascularization. Using an ex vivo model of tracheal injury, we evaluated the injury responses in the SAE and SMGs that turned out to be consistent with published in vivo work. We used this model to assess factors that influence engraftment of transgenic cells, providing a system for optimizing cell-based therapies. Finally, we developed a novel 3D-printed reusable culture chamber that enables live imaging of tracheal explants and differentiation of engrafted cells at an air-liquid interface. These approaches promise to be useful for modeling pulmonary diseases and testing therapies. Graphical abstract1,2. We describe here a method for differential mechanical injury of ferret tracheal explants that can be used to evaluate airway injury responses ex vivo. 3. Injured explants can be cultured at ALI (using the novel tissue-transwell device on the right) and submerged long-term to evaluate tissue-autonomous regeneration responses. 4. Tracheal explants can also be used for low throughput screens of compounds to improve cell engraftment efficiency or can be seeded with particular cells to model a disease phenotype. 5. Lastly, we demonstrate that ex vivo-cultured tracheal explants can be evaluated by various molecular assays and by immunofluorescent imaging that can be performed live using our custom-designed tissue-transwell.

Abstract 2918: In vivo delivery of CD3-directed CD19-CAR lentivectors leads to the generation of CAR T and NK-like (CAR-TaNK) cells capable of complete ablation of B cells in the blood, bone marrow, and tissue of NSG-SGM3 CD34+ humanized mice

Abstract Introduction: Direct in vivo delivery of lentiviral vectors (LV) to generate CD19 CAR+ cells without the need for ex vivo preparation represents a promising approach to transform autologous CAR therapy into an off-the-shelf treatment. In these studies, direct administration of a new LV encoding a CD19 CAR into humanized NOD SCID gamma (NSG) mice expressing human IL-3, GM-CSF, and SCF (NSG-SGM3) resulted in a dose-dependent elimination of B cells in the peripheral blood, peritoneal fluid, bone marrow, and tissue of treated mice. Methods: CD3-directed LV encoding a CD19 CAR with a novel synthetic driver element was manufactured utilizing a 25L clinical scale suspension-based process. NSG-SGM3 mice transplanted with human CD34+ cells from cord blood were injected with LV doses (1E6 IU, 1E7 IU, or 5E7 IU) intraperitoneally (IP) or 1E7 IU intravenously (IV). Quantification of CD19 CAR+ cells and CD20+ B cells in peripheral blood, peritoneal fluid, and bone marrow was assessed by flow cytometry. Additionally, immunohistochemical analysis was performed to evaluate the tissue-resident human B cells and for any other histopathological observations following test article administration. Results: All CD34+ humanized NSG-SGM3 mice were confirmed to exhibit efficient human hematopoietic engraftment by flow cytometry prior to test article administration (peripheral blood hCD45: 68.9% ± 4.93%; hCD19+ B cells: 53.7% ± 5.11%). Direct LV administration at the 1E7 IU and 5E7 IU doses demonstrated a dose-dependent reduction in circulating human B cells compared to the control and 1E6 IU dose (p < 0.05). The synthetic driver elements co-expressed with the CAR led to the formation of unique CD3+ CD8+ CD56+ T and NK-like (TaNK) CD19 CAR+ cells in circulation. The 1E7 IU IP dose demonstrated ablation of B cells (total cells/uL) in peripheral blood (control: 9.67 ± 3.72 vs. LV treated: 0.157 ± 0.117), intraperitoneal fluid (control: 0.322 ± 0.244 vs. LV treated: 0.038 ± 0.029), bone marrow (control: 9.16± 1.83 vs. LV treated: 0.734 ± 0.864), and splenic tissue. Both IP and IV routes of administration showed significant B cell depletion at the 1E7 IU dose. However, complete B cell elimination in splenic tissue was only observed at the 5E7 IU dose. Non-treated CD34+ humanized NSG-SGM3 mice exhibited hepatic portal inflammation and moderate graft-versus-host disease (GVHD) in the colon. Interestingly, mice treated with LV encoding CD19 CAR exhibited decreased inflammatory pathology, suggesting potential B cell involvement in the inflammatory response in this model. Conclusion: In this study, direct in vivo delivery of LV encoding CD19 CAR resulted in the generation of functionally active CD19 CAR TaNK cells capable of eliminating target B cells in peripheral blood, peritoneal fluid, bone marrow, and tissue. Citation Format: Frederic Vigant, Ani Kundu, Ramya Yarlagadda, Cody Gowan, Michael Betts, Jonathan Kato, Renata Soares, Alan Ponce, Lintao Liu, Junyi Zhang, Ewa Jaruga-Killeen, Michelle Andraza, Suraj Kachgal, Gregory Schreiber, Wei Zhang, Gregory Wade, Gregory I. Frost, Sid P. Kerkar. In vivo delivery of CD3-directed CD19-CAR lentivectors leads to the generation of CAR T and NK-like (CAR-TaNK) cells capable of complete ablation of B cells in the blood, bone marrow, and tissue of NSG-SGM3 CD34+ humanized mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2918.

Abstract 333: Interleukin 23 receptor is a critical regulator of the mitotic spindle and necessary for AML viability

Abstract Classically, the interleukin-23 receptor (IL-23R) is expressed on the surface of T cells where activation by its ligand, interleukin-23 (IL-23) leads to T cell activation through the JAK/STAT pathway. Here, we identify a novel localization and function for IL-23R in which intracellular IL-23R is necessary for AML viability by regulating mitotic spindle and centrosome formation. IL-23R was identified as a potential target through InterLinked Therapeutics’ ITX machine learning platform. IL-23R was identified through this unbiased in silico screen as a top hit and a potential regulator of the G2/M checkpoint and mitotic spindle. We confirmed that IL-23R protein was overexpressed >2-fold in 6 of 8 primary AML patient samples compared to mean IL-23R expression in normal hematopoietic cells. Consistent with prior studies, we confirmed cell surface localization of IL-23R in double negative T cells by flow cytometry and confocal microscopy. In contrast, only small amounts of IL-23R were detected on the surface of AML cells and primary AML patient samples. Rather, IL-23R was located intracellularly as demonstrated by flow cytometry, confocal microscopy, and immunoblotting of subcellular fractions. We confirmed intracellular localization of IL-23R in AML cells using 4 different antibodies targeted against 4 different epitopes of the receptor. We used BioID mass spectrometry to identify novel protein interactors with intracellular IL-23R and identified 61 interacting proteins. 36 of those 61 were nuclear or cytoplasmic in localization and the largest subset was associated with mitotic spindle regulation. By Proximity Ligation Assay, we confirmed the interactions between endogenous IL-23R with known mitotic spindle proteins NUMA, TMEM201, BAG6, and TACC1 in OCI-AML2 cells and primary AML samples. By confocal microscopy, we discovered that IL-23R co-localized with the mitotic spindle and centrosomes in AML cells. Genetic knockout of IL-23R increased spindle defects with multipolarity, lagging chromosomes, and spindle orientation errors. Interestingly, heterodimeric partner of IL-23R, IL12Rβ1 was also detected to be co-localized with mitotic spindles but the cytokine, IL-23, could not be detected. Knockdown of IL-23R also reduced cell growth in OCI-AML2, TEX, K562, NB4, and U937 cells. IL-23R knockdown also reduced the clonogenic growth and engraftment efficiency of TEX leukemia cells into murine bone marrow. In summary, intracellular IL-23R is a critical regulator of mitosis in AML and is necessary for AML viability. This study highlights a novel function and localization of IL-23R in AML and identifies a potential therapeutic target. Citation Format: Nathan Duong, Dilshad H. Khan, Geethu E. Thomas, Rose Hurren, Jong Bok Lee, Jonathan St-Germain, Lily Drimmer, Yongran Yan, Neil MacLean, Marcela Gronda, Brandon D. Brown, Brian Raught, Andrea Arruda, Hong Chang, Mark D. Minden, Li Zhang, Steven M. Kornblau, Vito Spadavecchio, Aaron D. Schimmer. Interleukin 23 receptor is a critical regulator of the mitotic spindle and necessary for AML viability [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 333.

Transplantation-based screen identifies inducers of muscle progenitor cell engraftment across vertebrate species

Stem cell transplantation presents a potentially curative strategy for genetic disorders of skeletal muscle, but this approach is limited by the deleterious effects of cell expansion invitro and consequent poor engraftment efficiency. In an effort to overcome this limitation, we sought to identify molecular signals that enhance the myogenic activity of cultured muscle progenitors. Here, we report the development and application of a cross-species small-molecule screening platform employing zebrafish and mice, which enables rapid, direct evaluation of the effects of chemical compounds on the engraftment of transplanted muscle precursor cells.Using this system, we screened a library of bioactive lipids to discriminate those that could increase myogenic engraftment invivo in zebrafish and mice. This effort identified two lipids, lysophosphatidic acidand niflumic acid, both linked to the activation of intracellular calcium-ion flux, which showed conserved,dose-dependent, and synergistic effects in promoting muscle engraftment across these vertebrate species.

Construction, Characterization, and Regenerative Application of Self-Assembled Human Mesenchymal Stem Cell Aggregates.

Mesenchymal stem cells (MSCs), characterized by their self-renewal ability and multilineage differentiation potential, can be derived from various sources and are emerging as promising candidates for regenerative medicine, especially for regeneration of the tooth, bone, cartilage, and skin. The self-assembled approach of MSC aggregation, which notably constructs cell clusters mimicking the developing mesenchymal condensation, allows high-density stem cell delivery along with preserved cell-cell interactions and extracellular matrix (ECM) as the microenvironment niche. This method has been shown to enable efficient cell engraftment and survival, thus promoting the optimized application of exogenous MSCs in tissue engineering and safeguarding clinical organ regeneration. This paper provides a detailed protocol for the construction and characterization of self-assembled aggregates based on umbilical cord mesenchymal stem cells (UCMSCs), as well as an example of the cranial bone regenerative application. The implementation of this procedure will help guide the establishment of an efficient MSC transplantation strategy for tissue engineering and regenerative medicine.

Extracellular vesicles from adipose-derived stem cells relieve extremity lymphedema in mouse models.

Transplantation of adipose-derived mesenchymal stem cells (ADSCs) has been reported to improve the severity of chronic lymphedema. Extracellular vesicles (EVs) derived from mesenchymal stem cells have been reported to exert effects such as the promotion of angiogenesis, suppression of inflammation, and regeneration of damaged organs. In this study, we showed that lymphangiogenesis was induced by EVs derived from ADSCs and revealed the therapeutic potential of these EVs for the treatment of lymphedema. We examined in vitro effects of ADSC-EVs to lymphatic endothelial cells (LECs). Next, we conducted in vivo analysis of ADSC-EVs to mouse lymphedema models. Furthermore, Bioinformatics analysis was also performed to evaluate the implications of the altered miRNA expression. We showed that ADSC-EVs promoted the proliferation, migration, and tube formation of LECs, and the gene expression of lymphatic markers was elevated in the ADSC-EV-treated group. Notably, a mouse lymphedema model revealed that legs treated with ADSC-EVs had markedly improved edema with increased numbers of capillary vessels and lymphatic channels. Bioinformatics analysis revealed that ADSC-EV-associated microRNAs, such as miR-199a-3p, miR-145-5p, miR-143-3p, miR-377-3p, miR-100-3p, miR-29a-3p, miR-495-3p, and miR-29c-3p, targeted MDM2, which contributed to the stability of HIF1 and resulted in angiogenesis and lymphangiogenesis in LECs. The present study showed lymphangiogenic effects of ADSC-EVs, which will lead to new treatment options for chronic lymphedema. Cell-free therapy with EVs has fewer potential risks, such as poor engraftment efficiency and potential tumor formation, than stem cell transplantation and could be a promising tool for patients suffering from lymphedema.

Transplantation of adipose tissue-derived microvascular fragments promotes therapy of critical limb ischemia

BackgroundAdipose tissue-derived microvascular fragments are functional vessel segments derived from arterioles, capillaries, and veins. Microvascular fragments can be used as vascularization units in regenerative medicine and tissue engineering containing microvascular networks. However, the in vivo therapeutic and vascularization properties of human microvascular fragments have not been investigated.MethodsIn this study, we isolated microvascular fragments, stromal vascular fractions, and mesenchymal stem cells from human lipoaspirate and studied their therapeutic efficacy and in vivo vasculogenic activity in a murine model of hindlimb ischemia. In addition, in vivo angiogenic activity and engraftment of microvascular fragments into blood vessels were measured using Matrigel plug assay.ResultsBoth microvascular fragments and stromal vascular fractions contain not only mesenchymal stem cells but also endothelial progenitor cells. In a Matrigel plug assay, microvascular fragments increased the number of blood vessels containing red blood cells more than mesenchymal stem cells and stromal vascular fractions did. The engraftment of the microvascular fragments transplanted in blood vessels within the Matrigel plug significantly increased compared to the engraftment of mesenchymal stem cells and stromal vascular fractions. Moreover, intramuscular injection of microvascular fragments markedly increased blood flow in the ischemic hindlimbs and alleviated tissue necrosis compared to that of mesenchymal stem cells or stromal vascular fractions. Furthermore, transplanted microvascular fragments formed new blood vessels in ischemic limbs.ConclusionsThese results suggest that microvascular fragments show improved engraftment efficiency and vasculogenic activity in vivo and are highly useful for treating ischemic diseases and in tissue engineering.Graphical Adipose tissue-derived microvascular fragments are vascularization units in regenerative medicine and tissue engineering containing microvascular networks. Intramuscular injection of microvascular fragments markedly increased blood flow in the ischemic hindlimbs and alleviated tissue necrosis. The present study suggests that microvascular fragments show improved engraftment efficiency and vasculogenic activity in vivo and are highly useful for treating ischemic diseases and in tissue engineering.

374 - High Throughput Drug Screening in Zebrafish for Identifying Novel Compounds That Influence Engraftment Efficiency

374 - High Throughput Drug Screening in Zebrafish for Identifying Novel Compounds That Influence Engraftment Efficiency

Characterization and Safety Profile of a New Combined Advanced Therapeutic Medical Product Platelet Lysate-Based Fibrin Hydrogel for Mesenchymal Stromal Cell Local Delivery in Regenerative Medicine.

Adipose-derived mesenchymal stromal cells (ASC) transplant to recover the optimal tissue structure/function relationship is a promising strategy to regenerate tissue lesions. Because filling local tissue defects by injection alone is often challenging, designing adequate cell carriers with suitable characteristics is critical for in situ ASC delivery. The aim of this study was to optimize the generation phase of a platelet-lysate-based fibrin hydrogel (PLFH) as a proper carrier for in situ ASC implantation and (1) to investigate in vitro PLFH biomechanical properties, cell viability, proliferation and migration sustainability, and (2) to comprehensively assess the local in vivo PLFH/ASC safety profile (local tolerance, ASC fate, biodistribution and toxicity). We first defined the experimental conditions to enhance physicochemical properties and microscopic features of PLFH as an adequate ASC vehicle. When ASC were mixed with PLFH, in vitro assays exhibited hydrogel supporting cell migration, viability and proliferation. In vivo local subcutaneous and subgingival PLFH/ASC administration in nude mice allowed us to generate biosafety data, including biodegradability, tolerance, ASC fate and engraftment, and the absence of biodistribution and toxicity to non-target tissues. Our data strongly suggest that this novel combined ATMP for in situ administration is safe with an efficient local ASC engraftment, supporting the further development for human clinical cell therapy.

Pancreatic islets implanted in an irreversible electroporation generated extracellular matrix in the liver.

Pancreatic islet transplantation via infusion through the portal vein, has become an established clinical treatment for patients with type 1 diabetes. Because the engraftment efficiency is low, new approaches for pancreatic islets implantation are sought. The goal of this study is to explore the possibility that a non-thermal irreversible electroporation (NTIRE) decellularized matrix in the liver could be used as an engraftment site for pancreatic islets. Pancreatic islets or saline controls were injected at sites pre-treated with NTIRE in the livers of 7 rats, 16 hours after NTIRE treatment. Seven days after the NTIRE treatment, islet graft function was assessed by detecting insulin and glucagon in the liver with immunohistochemistry. Pancreatic islets implanted into a NTIRE-treated volume of liver became incorporated into the liver parenchyma and produced insulin and glucagon in 2 of the 7 rat livers. Potential reasons for the failure to observe pancreatic islets in the remaining 5/7 rats may include local inflammatory reaction, graft rejection, low numbers of starting islets, timing of implantation. This study shows that pancreatic islets can become incorporated and function in an NTIRE-generated extracellular matrix niche, albeit the success rate is low. Advances in the field could be achieved by developing a better understanding of the mechanisms of failure and ways to combat these mechanisms.

Poor Mobilizers in Lymphoma but Not Myeloma Patients Had Significantly Poorer Progression-Free Survival after Autologous Stem Cell Transplantation: Results of a Large Retrospective, Single-Center Observational Study.

In our single-center study, 357 myeloma and lymphoma patients between 2009 and 2019 were mobilized with granulocyte colony-stimulating factor (G-CSF 7.5 µg/kg bid for four days) plus a fixed dose of 24 mg Plerixafor when indicated (Plerixafor Group, n = 187) or G-CSF alone (G-CSF Group, n = 170). The target CD34 cell yields were ≥2.0 × 106 CD34+ cells/kg in lymphoma and ≥4.0 × 106 CD34+ cells/kg in myeloma patients to enable putative second transplants in the latter. There were no significant differences in engraftment kinetics or transfusion requirements between the Plerixafor Group and the control group in the myeloma cohort, with lymphoma patients not requiring Plerixafor showing significantly faster neutrophil recovery, a trend to faster platelet recovery, and a significantly lower need for platelet transfusions, probably due to the significantly lower number of CD34-positive cells re-transfused. While in myeloma patients the outcome (overall survival, progression-free survival) following autologous stem cell transplantation (ASCT) was similar between the Plerixafor Group and the control group, hard to mobilize lymphoma patients had significantly poorer progression-free survival (47% vs. 74% at 36 months after ASCT, p = 0.003) with a trend also to poorer overall survival (71% vs. 84%). In conclusion, while there seem to be no differences in stemness capacity and long-term engraftment efficiency between the Plerixafor and the G-CSF Group in lymphoma as well as myeloma patients, poor mobilizing lymphoma patients per se constitute a high-risk population with a poorer outcome after ASCT. Whether disease characteristics and/or a more intense or stem cell-toxic pre-mobilization chemo-/radiotherapy burden in this cohort are responsible for this observation remains to be shown in future studies.

State of the Art and Future of Stem Cell Therapy in Ischemic Stroke: Why Don't We Focus on Their Administration?

Stroke is one of the leading causes of death and disability worldwide, so there is an urgent need to find a therapy for the tragic outcomes of this cerebrovascular disease. Stem cells appeared to be a good solution for many conditions, so different experiments were made to establish stem cells as a feasible therapy for stroke. The aim of this review is to analyze the state of the art of stem cell therapy for stroke and if the route of administration could represent a valid adjusting point for ameliorating the therapy's outcome. To obtain this, we searched the scientific literature of the last 10 years for relevant in vitro and in vivo evidence regarding stem cells' potential in stroke therapy. In vitro evidence points to hypoxia, among the preconditioning strategies, as the most used and probably efficient method to enhance cells qualities, while in vivo results raise the question if it is the type of cells or how they are administrated which can make the difference in terms of efficiency. Unfortunately, despite the number of clinical trials, only a few were successfully concluded, demonstrating how urgent the necessity is to translate pre-clinical results into clinics. Since any type of stem cell seems suitable for therapy, the chosen route of administration corresponds to different engraftment rates, distribution and efficiency in terms of the beneficial effects of stem cells. Intravenous administration was widely used for delivering stem cells into the human body, but recently intranasal administration has given promising results in vivo. It allows stem cells to efficiently reach the brain that was precluded to intravenous administration, so it is worth further investigation.

Lkb1 loss in regulatory T cells leads to dysregulation of hematopoietic stem cell expansion and differentiation in bone marrow.

The tumor suppressor Lkb1 is known to regulate the expression of forkhead box P3 (Foxp3), thereby maintaining the levels of Foxp3+ regulatory T cells (Treg) that play a crucial role in self-tolerance. However, the effect of Lkb1 in Treg on hematopoietic stem cells (HSCs) in the bone marrow (BM) remains obscure. Here, we demonstrated that conditional deletion of Lkb1 in Treg causes loss of Treg in the BM, which leads to failure of HSC homeostasis and the abnormal expansion. Moreover, the loss of BM Treg results in dysregulation of other developing progenitors/stem cell populations, leading to the defective differentiation of T cells and B cells. In addition, HSC from the BM with Treg loss exhibited poor engraftment efficiency, indicating that loss of Treg leads to irreversible impairment of HSC. Collectively, these results demonstrated the essential role of Lkb1 in Treg for maintaining HSC homeostasis and differentiation in mice. These findings provide insight into the mechanisms of HSC regulation and guidance for a strategy to improve the outcomes and reduce complications of HSC transplantation.

Cellular modifications and biomaterial design to improve mesenchymal stem cell transplantation.

Research has advanced considerably since the first clinical trial of human mesenchymal stem cells (MSCs) in the early 1990s. During this period, our understanding of MSC biology and our ability to expand and manipulate these cells have provided hope for the repair of damaged tissues due to illness or injury. MSCs have conventionally been injected systemically or locally into target tissue; however, inconsistent cell homing and engraftment efficiencies represent a major bottleneck that has led to mixed results in clinical studies. To overcome these issues, MSCs have been pre-conditioned with biomolecules, genetically altered, or surface engineered to enhance their homing and engraftment capabilities. In parallel, a variety of cell-encapsulating materials have been designed to improve cell delivery and post-transplantation survival and function. In this review, we discuss the current strategies that have been employed on cultured MSCs to improve targeted cell delivery and retention for tissue repair. We also discuss the advances in injectable and implantable biomaterial technologies that drive the success of MSC-based therapies in regenerative medicine. Multi-faceted approaches combining cellular modification and cell-instructive material design can pave the way for efficient and robust stem cell transplantation for superior therapeutic outcomes.

Transient regulation of RNA methylation in human hematopoietic stem cells promotes their homing and engraftment

Enhancing the efficiency of hematopoietic stem cell (HSC) homing and engraftment is critical for cord blood (CB) hematopoietic cell transplantation (HCT). Recent studies indicate that N6-methyladenosine (m6A) modulates the expression of mRNAs that are critical for stem cell function by influencing their stability. Here, we demonstrate that inhibition of RNA decay by regulation of RNA methylation, enhances the expression of the homing receptor chemokine C-X-C receptor-4 (CXCR4) in HSCs. We show that YTH N6-methyladenosine RNA binding protein 2 (YTHDF2), a m6A reader and FTO α-ketoglutarate dependent dioxygenase (FTO), a m6A eraser play an opposite role in this process. Through screening, we identified several FDA-approved compounds that regulate the expression of YTHDF2 and FTO in CB CD34+ cells. We show that transient downregulation of YTHDF2 or activation of FTO by using these compounds inhibits CXCR4 decay in CB HSCs and promotes their homing and engraftment. Our results demonstrate a novel regulation strategy to enhance the function of CB HSCs and provide a translational approach to enhance the clinical efficacy of HCT.

M2 Macrophages Drive Resistance to Phagocytosis and Improve Mitochondrial Metabolism in Acute Myeloid Leukemia Facilitating Leukemic Transformation and In Vivo Engraftment

Acute myeloid leukemia (AML) is a heterogeneous disease, which also extends to its tumor microenvironment (TME). Using single cell RNA-seq data (GSE116256), we performed differential gene expression analysis on macrophages from AML patients (AML-derived macrophages, AdMs) compared to healthy bone marrow macrophages. Thus, 306 upregulated genes in AdMs were identified as involved in different biological pathways such as proliferation, inflammation and cellular metabolism. Down-regulated genes (232) were mainly associated with the regulation of apoptosis. Single cell gene set enrichment analysis associated AdMs with an M2-like phenotype and an immunosuppression transcriptional program. We then investigated the macrophage landscape in a large cohort of AML patients by flow cytometry (n = 61) and immunohistochemistry, which revealed a large heterogeneity whereby AML patients with a predominant M2-like TME showed poor prognosis. Next, we evaluated the immune function of AdMs compared to healthy donor-derived macrophages. Thus, we showed that AdMs displayed decreased phagocytic capacity towards AML cells compared to healthy macrophages. Since AdMs might directly descend from the mutated leukemic clones we evaluated whether these mutations could affect the immune function of macrophages. Cord blood-derived CD34+ cells were lentivirally transduced with FLT3-ITD, differentiated towards macrophages, and these FLT3-ITD+ macrophages displayed decreased phagocytic activity. We questioned whether endogenous murine macrophages that are still present in immunodeficient mouse strains that are often used for human studies might form a barrier that needs to be taken to achieve efficient engraftment of human cells. Macrophages were isolated from NSG mice and were used in phagocytosis assays. The percentage of phagocytosed primary AML blasts by murine macrophages ranged between 3.2-51.4%, similar to phagocytosis levels observed when using human macrophages for the same AML samples. While performing these phagocytosis assays, we noted that the cells that remained and were not phagocytosed had an altered appearance and were very viable, as if these cells had gained fitness. We tested this further by exposing leukemic blasts to M2 macrophages for 48 h, after which the remaining cells were analyzed functionally. We observed that the 48 h "training" of primary leukemic blasts significantly enhanced their mitochondrial metabolism (in part mediated via mitochondrial transfer from macrophages to leukemic blasts), enhanced their in vitro and in vivo homing capacity and that they became resistant to phagocytosis. As a most striking example we used primary APL cells that are notoriously difficult to engraft in NSG mice, which we hypothesized could be in line with their high intrinsic susceptibility to macrophage-mediated phagocytosis. APL cells were exposed to M2 macrophages for 48h resulting in two cellular fates: 91.7% of cells were phagocytosed, but the remaining 8.3% APL blasts were able to induce fatal leukemia when transplanted into NSGS mice in all evaluated cases (n = 6), while prior to training these cells did not engraft long-term and were not able to confer disease. We also tested the tumor supportive capacity on M2 macrophages by performing intrafemoral injection in NSGS mice after which non-trained APL blasts were injected intravenously. Again, efficient engraftment and fatal leukemia development were observed, but only in mice co-injected with M2 macrophages. Strategies to target the supportive AdM subpopulation would be of interest. In our scRNA-seq analysis, we identified the metabolic enzyme Nicotinamide phosphoribosyltransferase (NAMPT) to be upregulated in AdMs. Ex vivo studies revealed that while conventional chemotherapeutics, AraC/venetoclax, efficiently target the AML blasts (CD34+/CD117+) with minimum effects on the AdMs, NAMPT inhibition with KPT-9274 was able to efficiently target both the AML blasts and the AdM fractions. Functionally, treatment of M2 macrophages with KPT-9274 shifted their polarization towards an M1 phenotype, with reduced support to AML cells in co-culture assays. In conclusion, we uncover the heterogeneity in the macrophage landscape in AML patients, show the functional relevance of M2-polarized macrophages for leukemic transformation, and provide alternative approaches for targeting aimed at the tumor-supportive microenvironment.

Developing a Humanized Murine Model for Co-Transplantation of Acute Myeloid Leukemia

Humanized mouse models and primary disease xenografts have produced significant translational insight into the biology of the bone marrow (BM) niche and aided drug discovery in acute myeloid leukemia (AML). To enable the study of cell-cell interactions between hematopoietic stem and progenitor cells (HSPCs) and AML as an emerging source of drug resistance, we describe two complementary approaches to humanized AML xenotransplantation models. One strategy utilizes the sequential transplantation of humanized hCD34+ cells followed by human AML cells. Recipient NBSGW mice (NOD.Cg-Kit W-41J Tyr + Prkdcscid Il2rgtm1Wjl/ThomJ), known for high rates of medullary engraftment, were conditioned with 15mg/kg busulfan followed by injection with either granulocyte colony-stimulating (G-CSF)-mobilized or BM-derived human CD34+ HSPCs. Flow cytometric analysis of the BM following injection of hCD34+ cells revealed efficient BM engraftment by both G-CSF- and BM- derived hCD34+ cells, demonstrated by BM human chimerism (hCD45%) of 63.7±10.0% by 8-weeks post-injection. Further BM hCD45 subtype analyses revealed B-cell (hCD45+ hCD19+) dominant repopulation (78.3±4.48%), followed by myeloid cell (hCD45+ hCD33+) repopulation (18.12±4.19%). T-cell repopulation was predictably minimal (0.008±0.01%). At 9- and 15- weeks post hCD34+ cells injection, GFP-expressing MOLM-14 AML cells (MOLM-14-GFP; 1E5, 1E6, or 2E6 cells) were injected. Flow cytometric analyses of MOLM-14-GFP BM chimerism up to 21 days post-injection showed complete absence of MOLM-14-GFP cells in the BM with no significant changes in overall hCD45 chimerism and hCD45 subtype composition compared to a PBS-injected control. These observations are consistent with a potential role for residual healthy hematopoietic cells in suppressing AML engraftment in the BM, previously shown in congenic studies. To test this hypothesis, we developed a second humanized AML model designed to investigate immunotherapeutic approaches for AML, where AML blasts are engrafted first, then followed by a human immune cell challenge. FA-AML1 or Kasumi-1 AML cells were injected into NSG mice (NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ) at 8 weeks of age. Injected mice were monitored for AML engraftment by HLA-DR expression in peripheral blood (PB). Engraftment occurred 6-12 weeks post-injection. After AML engraftment, we reconstituted a human immune system in the mice with a one-time injection of peripheral blood mononuclear cells (PBMCs), confirmed by flow cytometry for CD3+ T-cells (14.7±9.2%), CD33+ myeloid cells, and CD19+ B-cells. AML burden in the PB decreased 5-10% upon PBMC engraftment. In this model, a PB burden of <10% AML engraftment confers durable leukemic remission, whereas at >60% AML engraftment, leukemic cells persist in the periphery for over 100 days. Flow cytometric analysis demonstrated immune cell numbers peak in week 1 post-injection (30%), then decrease by week 4 to less than 1% in both the BM and PB, but persist at this low level for over 100 days. Altogether, these models confirm the ability of human hematopoietic cells to actively suppress leukemic engraftment in the BM microenvironment. More broadly, we demonstrate the development of two complementary humanized AML co-transplantation models that can attain dynamic ranges of human immune cell and AML cell engraftment to facilitate preclinical therapeutic development studies.