From Marrow to Bone and Fat: Exploring the Multifaceted Roles of Leptin Receptor Positive Bone Marrow Mesenchymal Stromal Cells.

The bone marrow (BM) stromal cell microenvironment contains non-hematopoietic stromal cells called mesenchymal stromal cells (MSCs). MSCs are plastic adherent, form CFU-Fs, and give rise to osteogenic, adipogenic, chondrogenic progenitors, and most importantly provide HSC niche factor chemokine C-X-C motif ligand 12 (CXCL12) and stem cell factor (SCF). Different authors have defined different markers for mouse MSC identification like PDGFR+Sca-1+ subsets, Nestin+, or LepR+ cells. Of these, the LepR+ cells are the major source of SCF and CXCL12 in the BM microenvironment and play a major role in HSC maintenance and hematopoiesis. LepR+ cells give rise to most of the bones and BM adipocytes, further regulating the microenvironment. In adult BM, LepR+ cells are quiescent but after fracture or irradiation, they proliferate and differentiate into mesenchymal lineage osteogenic, adipogenic and/or chondrogenic cells. They also play a crucial role in the steady-state hematopoiesis process, as well as hematopoietic regeneration and the homing of hematopoietic stem cells (HSCs) after myeloablative injury and/or HSC transplantation. They line the sinusoidal cavities, maintain the trabeculae formation, and provide the space for HSC homing and retention. However, the LepR+ cell subset is heterogeneous; some subsets have higher adipogenic potential, while others express osteollineage-biased genes. Different transcription factors like Early B cell factor 3 (EBF3) or RunX2 help maintain this balance between the self-renewing and committed states, whether osteogenic or adipogenic. The study of LepR+ MSCs holds immense promise for advancing our understanding of HSC biology, tissue regeneration, metabolic disorders, and immune responses. In this review, we will discuss the origin of the BM resident LepR+ cells, different subtypes, and the role of LepR+ cells in maintaining hematopoiesis, osteogenesis, and BM adipogenesis following their multifaceted impact.

Third-party virus-specific T cells for the treatment of double-stranded DNA viral reactivation and posttransplant lymphoproliferative disease after solid organ transplant.

Reactivation or primary infection with double-stranded DNA viruses is common in recipients of solid organ transplants (SOTs) and is associated with significant morbidity and mortality. Treatment with conventional antiviral medications is limited by toxicities, resistance, and a lack of effective options for adenovirus (ADV) and BK polyomavirus (BKPyV). Virus-specific T cells (VSTs) have been shown to be an effective treatment for infections with ADV, BKPyV, cytomegalovirus (CMV), and Epstein-Barr virus (EBV). Most of these studies have been conducted in stem cell recipients, and no large studies have been published in the SOT population to date. In this study, we report on the outcome of quadrivalent third-party VST infusions in 98 recipients of SOTs in the context of an open-label phase 2 trial. The 98 patients received a total of 181 infusions, with a median of 2 infusions per patient. The overall response rate was 45% for BKPyV, 65% for cytomegalovirus, 68% for ADV, and 61% for Epstein-Barr virus. Twenty percent of patients with posttransplant lymphoproliferative disorder had a complete response and 40% of patients had a partial response. All the VST infusions were well tolerated. We conclude that VSTs are safe and effective in the treatment of viral infections in SOT recipients.

Slow cycling and durable Flt3+ progenitors contribute to hematopoiesis under native conditions.

The dynamics of the hematopoietic flux responsible for blood cell production in native conditions remains a matter of debate. Using CITE-seq analyses, we uncovered a distinct progenitor population that displays a cell cycle gene signature similar to the one found in quiescent hematopoietic stem cells. We further determined that the CD62L marker can be used to phenotypically enrich this population in the Flt3+ multipotent progenitor (MPP4) compartment. Functional in vitro and in vivo analyses validated the heterogeneity of the MPP4 compartment and established the quiescent/slow-cycling properties of the CD62L- MPP4 cells. Furthermore, studies under native conditions revealed a novel hierarchical organization of the MPP compartments in which quiescent/slow-cycling MPP4 cells sustain a prolonged hematopoietic activity at steady-state while giving rise to other lineage-biased MPP populations. Altogether, our data characterize a durable and productive quiescent/slow-cycling hematopoietic intermediary within the MPP4 compartment and highlight early paths of progenitor differentiation during unperturbed hematopoiesis.

Third-Party and Patient-Specific Donor-Derived Virus-Specific T Cells Demonstrate Similar Efficacy and Safety for Management of Viral Infections after Hematopoietic Stem Cell Transplantation in Children and Young Adults.

Infections with double-stranded DNA viruses are a common complication after hematopoietic stem cell transplantation (HSCT) and cause significant morbidity and mortality in the post-transplantation period. Both donor-derived (DD) and third-party (TP) virus-specific T cells (VSTs) have shown efficacy and safety in viral management following HSCT in children and young adults. Owing to a greater degree of HLA matching between the recipient and stem cell donor, DD VSTs potentially persist longer in circulation compared to TP VSTs, because they are collected from a well-matched donor. However, TP VSTs are more easily accessible, particularly for smaller transplantation centers that do not have VST manufacturing capabilities, and more economical than creating a customized product for each transplant recipient. We conducted the present study to compare clinical efficacy and safety outcomes for DD VSTs and TP VSTs in a large cohort of pediatric and young adult HSCT recipients and to determine whether DD VSTs are associated with improved outcomes owing to potentially longer persistence in the recipient's circulation. This retrospective cohort study included 145 patients who received VSTs at Cincinnati Children's Hospital Medical Center (CCHMC) between 2017 and 2021 for the treatment of adenovirus, BK virus, cytomegalovirus, and/or Epstein-Barr virus. Viruses were detected using quantitative polymerase chain reaction. Patients received VSTs on a DD (NCT02048332) or TP (NCT02532452) protocol, and VST products for both protocols were manufactured in an identical fashion. The primary study outcome was clinical response to VSTs, evaluated 4 weeks after VST administration, defined as decrease in viral load to under the inclusion thresholds, or resolution of symptoms of invasive viral infection, without the need for additional conventional antiviral medication following VST administration. Secondary outcomes included graft-versus-host-disease, transplant-associated thrombotic microangiopathy, renal function, hospital length of stay, and overall survival at 30 days and 100 days after VST administration and 1 year after HSCT. Statistical analysis was performed using the Fisher exact test or chi-square test. An unpaired t test was used to compare continuous variables. The study group comprised 77 patients in the DD cohort and 68 patients in the TP cohort. Eighteen patients in the TP cohort underwent HSCT at CCHMC, and the other 50 underwent HSCT at other institutions and presented to CCHMC solely for VST administration. There was no statistically significant difference in clinical response rates between DD and TP cohorts (65.6% versus 62.7%; odds ratio [OR], 1.162; 95% confidence interval [CI], .619 to 2.164; P = .747). There were no significant differences in secondary outcomes between the 2 cohorts. The percentage of patients requiring multiple infusions for a clinical response did not differ significantly between the DD and TP cohorts (38.2% versus 32.5%; OR, .780; 95% CI, .345 to 1.805; P = .666). We found no significant difference in clinical response rate between DD VSTs and TP VSTs and a similar safety profile. Our data suggest that TP VSTs may be sufficient to control viral infection until immune reconstitution occurs despite the potential for more rapid VST clearance compared to DD VSTs. The lack of significant differences between DD VSTs and TP VSTs is an important finding, indicating that it is not necessary for every transplant center to manufacture customized DD VSTs, and that TP VSTs are a satisfactory substitute.

Retinoid X receptor promotes hematopoietic stem cell fitness and quiescence and preserves hematopoietic homeostasis.

Hematopoietic stem cells (HSCs) balance self-renewal and differentiation to maintain hematopoietic fitness throughout life. In steady-state conditions, HSC exhaustion is prevented by the maintenance of most HSCs in a quiescent state, with cells entering the cell cycle only occasionally. HSC quiescence is regulated by retinoid and fatty-acid ligands of transcriptional factors of the nuclear retinoid X receptor (RXR) family. Herein, we show that dual deficiency for hematopoietic RXRα and RXRß induces HSC exhaustion, myeloid cell/megakaryocyte differentiation, and myeloproliferative-like disease. RXRα and RXRß maintain HSC quiescence, survival, and chromatin compaction; moreover, transcriptome changes in RXRα;RXRß-deficient HSCs include premature acquisition of an aging-like HSC signature, MYC pathway upregulation, and RNA intron retention. Fitness loss and associated RNA transcriptome and splicing alterations in RXRα;RXRß-deficient HSCs are prevented by Myc haploinsufficiency. Our study reveals the critical importance of RXRs for the maintenance of HSC fitness and their protection from premature aging.

Mesenchymal stromal cells, metabolism, and mitochondrial transfer in bone marrow normal and malignant hematopoiesis.

Hematopoietic stem cell (HSC) transplantation-based treatments are in different phases of clinical development, ranging from current therapies to a promise in the repair and regeneration of diseased tissues and organs. Mesenchymal stromal/stem cells (MSCs), which are fibroblast-like heterogeneous progenitors with multilineage differentiation (osteogenic, chondrogenic, and adipogenic) and self-renewal potential, and exist in the bone marrow (BM), adipose, and synovium, among other tissues, represent one of the most widely used sources of stem cells in regenerative medicine. MSCs derived from bone marrow (BM-MSCs) exhibit a variety of traits, including the potential to drive HSC fate and anti-inflammatory and immunosuppressive capabilities via paracrine activities and interactions with the innate and adaptive immune systems. The role of BM-MSC-derived adipocytes is more controversial and may act as positive or negative regulators of benign or malignant hematopoiesis based on their anatomical location and functional crosstalk with surrounding cells in the BM microenvironment. This review highlights the most recent clinical and pre-clinical findings on how BM-MSCs interact with the surrounding HSCs, progenitors, and immune cells, and address some recent insights on the mechanisms that mediate MSCs and adipocyte metabolic control through a metabolic crosstalk between BM microenvironment cells and intercellular mitochondrial transfer in normal and malignant hematopoiesis.

Novel blood derived hemostatic agents for bleeding therapy and prophylaxis.

PURPOSE OF REVIEW: Hemorrhage is a major cause of preventable death in trauma and cancer. Trauma induced coagulopathy and cancer-associated endotheliopathy remain major therapeutic challenges. Early, aggressive administration of blood-derived products with hypothesized increased clotting potency has been proposed. A series of early- and late-phase clinical trials testing the safety and/or efficacy of lyophilized plasma and new forms of platelet products in humans have provided light on the future of alternative blood component therapies. This review intends to contextualize and provide a critical review of the information provided by these trials. RECENT FINDINGS: The beneficial effect of existing freeze-dried plasma products may not be as high as initially anticipated when tested in randomized, multicenter clinical trials. A next-generation freeze dried plasma product has shown safety in an early phase clinical trial and other freeze-dried plasma and spray-dried plasma with promising preclinical profiles are embarking in first-in-human trials. New platelet additive solutions and forms of cryopreservation or lyophilization of platelets with long-term shelf-life have demonstrated feasibility and logistical advantages. SUMMARY: Recent trials have confirmed logistical advantages of modified plasma and platelet products in the treatment or prophylaxis of bleeding. However, their postulated increased potency profile remains unconfirmed.

A Limited Role for AMD3100 Induced Stem Cell Mobilization for Modulation of Thoracic Trauma Outcome.

ABSTRACT: Thoracic trauma is a major cause of mortality due to the associated inflammatory acute respiratory distress syndrome and morbidity due to impaired tissue regeneration. Trauma-induced lung inflammation is characterized by the early recruitment of cells with pro- or anti-inflammatory activity to the lung. Therapeutic interventions reducing the level of tissue inflammation may result in decreased tissue damage and improved healing and recovery. Stem cells might be able to improve trauma outcome via immunomodulation or by enhancing tissue regeneration.Here, we describe the migratory dynamics of murine mesenchymal, hematopoietic and endothelial stem and progenitor cells (SPCs) as well as mature inflammatory cells (monocytes, neutrophils, lymphocytes) to peripheral blood (PB) and lung tissue between 0.2 and 48 h post-blunt chest trauma (TXT). We demonstrate that the kinetics of immune cell and SPC distribution upon trauma are both cell-type and tissue-dependent. We identified a transient, early increase in the number of inflammatory cells in PB and lung at 2 h post-TXT and a second wave of infiltrating SPCs in lungs by 48 h after TXT induction, suggesting a role for SPCs in tissue remodeling after the initial inflammatory phase. Cxcl12/Cxcr4 blockade by AMD3100 within the first 6 h after TXT, while inducing a strong and coordinated mobilization of SPCs and leukocytes to PB and lung tissue, did not significantly affect TXT associated inflammation or tissue damage as determined by inflammatory cytokine levels, plasma markers for organ function, lung cell proliferation and survival, and myofibroblast/fibroblast ratio in the lung. Further understanding the dynamics of the distribution of endogenous SPCs and inflammatory cells will therefore be indispensable for stem cell-based or immunomodulation therapies in trauma.

P2RY14 cAMP signaling regulates Schwann cell precursor self-renewal, proliferation, and nerve tumor initiation in a mouse model of neurofibromatosis.

Neurofibromatosis type 1 (NF1) is characterized by nerve tumors called neurofibromas, in which Schwann cells (SCs) show deregulated RAS signaling. NF1 is also implicated in regulation of cAMP. We identified the G-protein-coupled receptor (GPCR) P2ry14 in human neurofibromas, neurofibroma-derived SC precursors (SCPs), mature SCs, and mouse SCPs. Mouse Nf1-/- SCP self-renewal was reduced by genetic or pharmacological inhibition of P2ry14. In a mouse model of NF1, genetic deletion of P2ry14 rescued low cAMP signaling, increased mouse survival, delayed neurofibroma initiation, and improved SC Remak bundles. P2ry14 signals via Gi to increase intracellular cAMP, implicating P2ry14 as a key upstream regulator of cAMP. We found that elevation of cAMP by either blocking the degradation of cAMP or by using a P2ry14 inhibitor diminished NF1-/- SCP self-renewal in vitro and neurofibroma SC proliferation in in vivo. These studies identify P2ry14 as a critical regulator of SCP self-renewal, SC proliferation, and neurofibroma initiation.

Scheduled administration of virus-specific T cells for viral prophylaxis after pediatric allogeneic stem cell transplant.

Infections with double-stranded DNA viruses are a significant cause of morbidity and mortality in pediatric patients following allogeneic hematopoietic stem cell transplantation (HSCT). Virus-specific T-cell therapies (VSTs) have been shown to be an effective treatment for infections with adenovirus, BK virus, cytomegalovirus (CMV), and Epstein-Barr virus (EBV). To date, prophylactic regimens to prevent or mitigate these infections using conventional antiviral medications provide suboptimal response rates. Here we report on a clinical trial (NCT03883906) performed to assess the feasibility of rapid manufacturing and early infusion of quadrivalent VSTs generated from stem cell donors ("donor-derived VSTs") into allogeneic HSCT recipients with minimal or absent viremia. Patients were eligible to receive scheduled VSTs as early as 21 days after stem cell infusion. Twenty-three patients received scheduled VSTs. Twenty of 23 patients had no viremia at the time of infusion, while 3 patients had very low-level BK viremia. Two developed clinically significant graft-versus-host disease (GVHD), although this incidence was not outside of expected incidence early after HSCT, and both were successfully treated with systemic corticosteroids (n = 2). Five patients were deemed treatment failures. Three developed subsequent significant viremia/viral disease (n = 3). Eighteen patients did not fail treatment, 7 of whom did not develop any viremia, while 11 developed low-level, self-limited viremia that resolved without further intervention. No infusion reactions occurred. In conclusion, scheduled VSTs appear to be safe and potentially effective at limiting serious complications from viral infections after allogeneic transplantation. A randomized study comparing this scheduled approach to the use of VSTs to treat active viremia is ongoing.

M-CSF supports medullary erythropoiesis and erythroid iron demand following burn injury through its activity on homeostatic iron recycling.

M-CSF receptor signaling supports the development and survival of mononuclear phagocytes and is thought to play a role in post burn anemia by promoting myeloid lineage bias. We found M-CSF secretion was increased in burn patients and a murine model of post burn ACI, so we neutralized M-CSF in ACI mice to determine if erythropoiesis was improved. Instead, M-CSF blockade further impaired erythropoiesis and erythroid cells access to iron. M-CSF blockade enhanced inflammatory cytokine secretion, further increased systemic neutrophil counts, and led to tissue iron sequestration that was dependent, in part, on augmented IL-6 secretion which induced hepcidin. Deleterious effects of post burn M-CSF blockade were associated with arrest of an iron recycling gene expression signature in the liver and spleen that included Spi-C transcription factor and heme oxygenase-1, which promote heme metabolism and confer a non-inflammatory tone in macrophages. Hepatic induction of these factors in ACI mice was consistent with a recovery of ferroportin gene expression and reflected an M-CSF dependent expansion and differentiation of Spi-C+ monocytes into Kupffer cells. Together, this data indicates M-CSF secretion supports a homeostatic iron recycling program that plays a key role in the maintenance of erythroid cells access to iron following burn injury.

Freeze-dried platelets are a promising alternative in bleeding thrombocytopenic patients with hematological malignancies.

Thrombosomes are trehalose-stabilized, freeze-dried group O platelets with a 3-year shelf life. They can be stockpiled, rapidly reconstituted, and infused regardless of the recipient's blood type. Thrombosomes thus represent a potential alternative platelet transfusion strategy. The present study assessed the safety and potential early signals of efficacy of Thrombosomes in bleeding thrombocytopenic patients. We performed an open-label, phase 1 study of single doses of allogeneic Thrombosomes at three dose levels in three cohorts, each consisting of eight patients who had hematologic malignancies, thrombocytopenia, and bleeding. Adverse events, dose-limiting toxicities (DLTs), World Health Organization (WHO) bleeding scores, and hematology values were assessed. No DLTs were reported. The median age was 59 years (24-71). Most patients had AML (58%) or ALL (29%), followed by MDS (8%) and myeloproliferative neoplasm (4%). The WHO scores of 22 patients who were actively bleeding at a total of 27 sites at baseline either improved (n = 17 [63%]) or stabilized (n = 10 [37%]) through day 6. Twenty-four hours after infusion, 12 patients (50%) had a clinically significant platelet count increase. Of eight patients who received no platelet transfusions for 6 days after Thrombosomes infusion, 5 had a clinically significant increase in platelet count of ≥5000 platelets/µL and 2 had platelet count normalization. Thrombosomes doses up to 3.78 × 108 particles/kg demonstrated safety in 24 bleeding, thrombocytopenic patients with hematological malignancies. Thrombosomes may represent an alternative to conventional platelets to treat bleeding. A phase 2 clinical trial in a similar patient population is underway.

Inhibition of the RacGEF VAV3 by the small molecule IODVA1 impedes RAC signaling and overcomes resistance to tyrosine kinase inhibition in acute lymphoblastic leukemia.

Aberrant RHO guanine nucleotide exchange factor (RhoGEF) activation is chief mechanism driving abnormal activation of their GTPase targets in transformation and tumorigenesis. Consequently, a small-molecule inhibitor of RhoGEF can make an anti-cancer drug. We used cellular, mouse, and humanized models of RAC-dependent BCR-ABL1-driven and Ph-like acute lymphoblastic leukemia to identify VAV3, a tyrosine phosphorylation-dependent RacGEF, as the target of the small molecule IODVA1. We show that through binding to VAV3, IODVA1 inhibits RAC activation and signaling and increases pro-apoptotic activity in BCR-ABL1-transformed cells. Consistent with this mechanism of action, cellular and animal models of BCR-ABL1-induced leukemia in Vav3-null background do not respond to IODVA1. By durably decreasing in vivo RAC signaling, IODVA1 eradicates leukemic propagating activity of TKI-resistant BCR-ABL1(T315I) B-ALL cells after treatment withdrawal. Importantly, IODVA1 suppresses the leukemic burden in the treatment refractory pediatric Ph+ and TKI-resistant Ph+ B-ALL patient-derived xenograft models better than standard-of-care dasatinib or ponatinib and provides a more durable response after treatment withdrawal. Pediatric leukemia samples with diverse genetic lesions show high sensitivity to IODVA1 ex vivo and this sensitivity is VAV3 dependent. IODVA1 thus spearheads a novel class of drugs that inhibits a RacGEF and holds promise as an anti-tumor therapy.

Off-the-Shelf Third-Party Virus-Specific T Cell Therapy to Treat JC Polyomavirus Infection in Hematopoietic Stem Cell Transplantation Recipients.

Progressive multifocal leukoencephalopathy (PML) is a progressive and generally fatal demyelinating neurologic disease that occurs in profoundly immunocompromised patients due to infection with the human polyomavirus JC virus (JCPyV). Treatment options are limited and are largely focused on restoring T cell immunity, and outcomes are historically poor. Control of JCPyV in the setting of an immunocompromised patient by adoptive transfer of third-party virus specific T cells (VSTs) has been described in a small number of cases. To investigate treatment response and outcomes in recipients of hematopoietic stem cell transplantation (HSCT) with PML treated with third-party VSTs directed against the BK virus, a highly homologous polyoma virus that shares immunogenic epitopes with JCPyV. A retrospective chart review was performed on 4 patients who received VSTs for the treatment of PML at Cincinnati Children's Hospital Medical Center since 2019. VSTs were administered safely, with no cases of graft-versus-host disease and no infusion reactions. One patient who was treated almost immediately after diagnosis was able to clear JCPyV from blood and cerebrospinal fluid, with resultant stabilization of neurologic decline. IFN-γ enzyme-linked immunospot (ELISpot) analysis demonstrated VSTs in the peripheral blood following infusion. Response was maintained through repeat infusions. Three other patients, all of whom had a longer delay between diagnosis and infusion, exhibited progressive neurologic decline despite varying degrees of improvement in viral load. PML is a rare but often fatal complication following HSCT for which few treatment options are available. BK-directed, JCPyV cross-reactive VSTs are a safe and viable therapeutic option, and prompt administration should be considered once PML is diagnosed. © 2021 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

Virus-specific T cells for adenovirus infection after stem cell transplantation are highly effective and class II HLA restricted.

Infection with adenoviruses is a common and significant complication in pediatric patients after allogeneic hematopoietic stem cell transplantation. Treatment options with traditional antivirals are limited by poor efficacy and significant toxicities. T-cell reconstitution is critical for the management of adenoviral infections, but it generally takes place months after transplantation. Ex vivo-generated virus-specific T cells (VSTs) are an alternative approach for viral control and can be rapidly generated from either a stem cell donor or a healthy third-party donor. In the context of a single-center phase 1/2 clinical trial, we treated 30 patients with a total of 43 infusions of VSTs for adenoviremia and/or adenoviral disease. Seven patients received donor-derived VSTs, 21 patients received third-party VSTs, and 2 received VSTs from both donor sources. Clinical responses were observed in 81% of patients, with a complete response in 58%. Epitope prediction and potential epitope identification for common HLA molecules helped elucidate HLA restriction in a subset of patients receiving third-party products. Intracellular interferon-γ expression in T cells in response to single peptides and response to cell lines stably transfected with a single HLA molecule demonstrated HLA-restricted CD4+ T-cell response, and these results correlated with clinical outcomes. Taken together, these data suggest that VSTs are a highly safe and effective therapy for the management of adenoviral infection in immunocompromised hosts. The trials were registered at www.clinicaltrials.gov as #NCT02048332 and #NCT02532452.

Inflammation rapidly recruits mammalian GMP and MDP from bone marrow into regional lymphatics.

Innate immune cellular effectors are actively consumed during systemic inflammation, but the systemic traffic and the mechanisms that support their replenishment remain unknown. Here, we demonstrate that acute systemic inflammation induces the emergent activation of a previously unrecognized system of rapid migration of granulocyte-macrophage progenitors and committed macrophage-dendritic progenitors, but not other progenitors or stem cells, from bone marrow (BM) to regional lymphatic capillaries. The progenitor traffic to the systemic lymphatic circulation is mediated by Ccl19/Ccr7 and is NF-κB independent, Traf6/IκB-kinase/SNAP23 activation dependent, and is responsible for the secretion of pre-stored Ccl19 by a subpopulation of CD205+/CD172a+ conventional dendritic cells type 2 and upregulation of BM myeloid progenitor Ccr7 signaling. Mature myeloid Traf6 signaling is anti-inflammatory and necessary for lymph node myeloid cell development. This report unveils the existence and the mechanistic basis of a very early direct traffic of myeloid progenitors from BM to lymphatics during inflammation.

When the body becomes infected with disease-causing pathogens, such as bacteria, the immune system activates various mechanisms which help to fight off the infection. One of the immune system's first lines of defense is to launch an inflammatory response that helps remove the pathogen and recruit other immune cells. However, this response can become overactivated, leading to severe inflammatory conditions that damage healthy cells and tissues. A second group of cells counteract this over inflammation and are different to the ones involved in the early inflammatory response. Both types of cells ­ inflammatory and anti-inflammatory ­ develop from committed progenitors, which, unlike stem cells, are already destined to become a certain type of cell. These committed progenitors reside in the bone marrow and then rapidly travel to secondary lymphoid organs, such as the lymph nodes, where they mature into functioning immune cells. During this journey, committed progenitors pass from the bone marrow to the lymphatic vessels that connect up the different secondary lymphoid organs, and then spread to all tissues in the body. Yet, it is not fully understood what exact route these cells take and what guides them towards these lymphatic tissues during inflammation. To investigate this, Serrano-Lopez, Hegde et al. used a combination of techniques to examine the migration of progenitor cells in mice that had been treated with lethal doses of a bacterial product that triggers inflammation. This revealed that as early as one to three hours after the onset of infection, progenitor cells were already starting to travel from the bone marrow towards lymphatic vessels. Serrano-Lopez, Hegde et al. found that a chemical released by an "alarm" immune cell already residing in secondary lymphoid organs attracted these progenitor cells towards the lymphatic tissue. Further experiments showed that the progenitor cells travelling to secondary lymphoid organs were already activated by bacterial products. They then follow the chemical released by alarm immune cells ready to respond to the immune challenge and suppress inflammation. These committed progenitors were also found in the inflamed lymph nodes of patients. These findings suggest this rapid circulation of progenitors is a mechanism of defense that contributes to the fight against severe inflammation. Altering how these cells migrate from the bone marrow to secondary lymphoid organs could provide a more effective treatment for inflammatory conditions and severe infections. However, these approaches would need to be tested further in the laboratory and in clinical trials.

Mitochondria Transfer in Bone Marrow Hematopoietic Activity.

Purpose of Review: The well-established crosstalk between hematopoietic stem cells (HSC) and bone marrow (BM) microenvironment is critical for the homeostasis and hematopoietic regeneration in response to blood formation emergencies. Past decade has witnessed that the intercellular communication mediated by the transfer of cytoplasmic material and organelles between cells can regenerate and/or repair the damaged cells. Mitochondria have recently emerged as a potential regulator of HSC fate. This review intends to discuss recent advances in the understanding of the mitochondrial dynamics, specifically focused on the role of mitochondrial transfer, in the maintenance of HSC activity with clear implications in stem cell transplantation and regenerative medicine. Recent Findings: HSC are highly heterogeneous in their mitochondrial metabolism, and the quiescence and potency of HSC depend on the status of mitochondrial dynamics and the clearance of damaged mitochondria. Recent evidence has shown that in stress response, BM stromal cells transfer healthy mitochondria to HSC, facilitate HSC bioenergetics shift towards oxidative phosphorylation, and subsequently stimulate leukocyte expansion. Furthermore, metabolic rewiring following mitochondria transfer from HSPC to BM stromal cells likely to repair the damaged BM niche and accelerate limiting HSC transplantation post myeloablative conditioning.

Antioxidant prevents clearance of hemostatically competent platelets after long-term cold storage.

BACKGROUND: Cold storage of platelets (PLTs) has the potential advantage of prolonging storage time while reducing posttransfusion infection given the decreased likelihood of bacterial outgrowth during storage and possibly beneficial effects in treating bleeding patients. However, cold storage reduces PLT survival through the induction of complex storage lesions, which are more accentuated when storage is prolonged. STUDY DESIGN AND METHODS: Whole blood-derived PLT-rich plasma concentrates from seven PLT pools (n = 5 donors per pool). PLT additive solution was added (67%/33% plasma) and the product was split into 50-mL bags. Split units were stored in the presence or absence of 1 mM of N-acetylcysteine (NAC) under agitation for up to 14 days at room temperature or in the cold and were analyzed for PLT activation, fibrinogen-dependent spreading, microparticle formation, mitochondrial respiratory activity, reactive oxygen species (ROS) generation, as well as in vivo survival and bleeding time correction in immunodeficient mice. RESULTS: Cold storage of PLTs for 7 days or longer induces significant PLT activation, cytoskeletal damage, impaired fibrinogen spreading, enhances mitochondrial metabolic decoupling and ROS generation, and increases macrophage-dependent phagocytosis and macrophage-independent clearance. Addition of NAC prevents PLT clearance and allows a correction of the prolonged bleeding time in thrombocytopenic, aspirin-treated, immunodeficient mice. CONCLUSIONS: Long-term cold storage induces mitochondrial uncoupling and increased proton leak and ROS generation. The resulting ROS is a crucial contributor to the increased macrophage-dependent and -independent clearance of functional PLTs and can be prevented by the antioxidant NAC in a magnesium-containing additive solution.

Frozen Platelets-Development and Future Directions.

Storage requirements and outdating of platelets represent a continued challenge for blood banks. These hurdles are confounded for rural area hospitals or in military deployments. Over 60 years of research and development into frozen platelets have generated a stable and reproducible product. Valeri's method to freeze platelets in 6% dimethyl sulfoxide (DMSO) and storage at -80°C allows for long-term storage alleviating burdens placed on blood banks. Clinical studies show that frozen platelet transfusions are safe with no related thrombotic or other serious adverse events. There are ongoing efforts to demonstrate cryopreserved platelet (CPP) superiority in efficacy studies designed in trauma or cardiac surgery patients. Technical advances in CPP manufacturing including closed system manufacturing, applications of pathogen reduction technology and potency standard characterization add to the appeal of CPP as an alternative to traditional liquid-stored platelets (LP) in settings of supply shortages, mass casualty, active bleeding, rapid provision of HLA-compatible platelets, and remote care.

Virus-specific T-cell therapy to treat BK polyomavirus infection in bone marrow and solid organ transplant recipients.

BK polyomavirus (BKPyV) infection is a major complication of hematopoietic stem cell transplant (HSCT) and solid organ transplant (SOT). Treatment options are limited, poorly effective, and have significant toxicities. Cellular therapy using T cells directed against BKPyV is an emerging therapy, and we report efficacy in controlling BKPyV-associated disease in highly immunocompromised patients. Virus-specific T cells (VSTs) against BKPyV were manufactured using either blood from the patient's stem cell donor (donor-derived VSTs) or from unrelated donors (third-party VSTs). VSTs were used to treat BKPyV in 38 HSCT recipients and 3 SOT recipients between June 2017 and December 2019. Overall response rate was 86% in patients treated for BK viremia, 100% in patients treated for hemorrhagic cystitis, and 87% in patients treated for both BK viremia and hemorrhagic cystitis. No infusional toxicity, de novo graft-versus-host disease, or rejection of the organ occurred attributable to the VST infusion. BKPyV-specific immune responses were demonstrated by interferon-γ production by peripheral blood mononuclear cells postinfusion in response to BKPyV antigens. VSTs are a safe and potentially effective strategy to treat BKPyV and associated symptoms in recipients of HSCT and SOT. Cellular therapy should be considered for all patients with BKPyV and underlying immune suppression at risk of complications. This trial was registered at www.clinicaltrials.gov as #NCT02532452.