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Hematopoietic stem cells and multipotential progenitors emerge in multiple, overlapping waves of fetal development. Some of these populations seed the bone marrow and sustain adult B- and T-cell development long-term after birth. However, others are present transiently, but whether they are vestigial or generate B and T cells that contribute to the adult immune system is not well understood. We now report that transient fetal progenitors distinguished by expression of low levels of the PU.1 transcription factor generated activated and memory T and B cells that colonized and were maintained in secondary lymphoid tissues. These included the small and large intestines, where they may contribute to the maintenance of gut homeostasis through at least middle age. At least some of the activated/memory cells may have been the progeny of B-1 and marginal zone B cells, as transient PU.1low fetal progenitors efficiently generated those populations. Taken together, our data demonstrate the potential of B- and T-cell progeny of transient PU.1low fetal progenitors to make an early and long-term contribution to the adult immune system.

A major limitation of gene therapy for sickle cell disease (SCD) is the availability and access to a potentially curative one-time treatment, due to high treatment costs. We have developed a high-titer bifunctional lentiviral vector (LVV) in a vector backbone that has reduced size, high vector yields, and efficient gene transfer to human CD34+ hematopoietic stem and progenitor cells (HSPCs). This LVV contains locus control region cores expressing an anti-sickling βAS3-globin gene and two microRNA-adapted short hairpin RNA simultaneously targeting BCL11A and ZNF410 transcripts to maximally induce fetal hemoglobin (HbF) expression. This LVV induces high levels of anti-sickling hemoglobins (HbAAS3 + HbF), while concurrently decreasing sickle hemoglobin (HbS). The decrease in HbS and increased anti-sickling hemoglobin impedes deoxygenated HbS polymerization and red blood cell sickling at low vector copy per cell in transduced SCD patient CD34+ cells differentiated into erythrocytes. The dual alterations in red cell hemoglobins ameliorated the SCD phenotype in the SCD Berkeley mouse model in vivo. With high titer and enhanced transduction of HSPC at a low multiplicity of infection, this LVV will increase the number of patient doses of vector from production lots to decrease costs and help improve accessibility to gene therapy for SCD.

Clonal hematopoiesis (CH) is characterized by the acquisition of a somatic mutation in a hematopoietic stem cell that results in a clonal expansion. These driver mutations can be single nucleotide variants in cancer driver genes or larger structural rearrangements called mosaic chromosomal alterations (mCAs). The factors that influence the variations in mCA fitness and ultimately result in different clonal expansion rates are not well understood. We used the Passenger-Approximated Clonal Expansion Rate (PACER) method to estimate clonal expansion rate as PACER scores for 6,381 individuals in the NHLBI TOPMed cohort with gain, loss, and copy-neutral loss of heterozygosity mCAs. Our mCA fitness estimates, derived by aggregating per-individual PACER scores, were correlated (R2 = 0.49) with an alternative approach that estimated fitness of mCAs in the UK Biobank using population-level distributions of clonal fraction. Among individuals with JAK2 V617F clonal hematopoiesis of indeterminate potential or mCAs affecting the JAK2 gene on chromosome 9, PACER score was strongly correlated with erythrocyte count. In a cross-sectional analysis, genome-wide association study of estimates of mCA expansion rate identified a TCL1A locus variant associated with mCA clonal expansion rate, with suggestive variants in NRIP1 and TERT.

The developmental origin of blood-forming hematopoietic stem cells (HSCs) is a longstanding question. Here, our non-invasive genetic lineage tracing in mouse embryos pinpoints that artery endothelial cells generate HSCs. Arteries are transiently competent to generate HSCs for 2.5 days (∼E8.5-E11) but subsequently cease, delimiting a narrow time frame for HSC formation in vivo. Guided by the arterial origins of blood, we efficiently and rapidly differentiate human pluripotent stem cells (hPSCs) into posterior primitive streak, lateral mesoderm, artery endothelium, hemogenic endothelium, and >90% pure hematopoietic progenitors within 10 days. hPSC-derived hematopoietic progenitors generate T, B, NK, erythroid, and myeloid cells in vitro and, critically, express hallmark HSC transcription factors HLF and HOXA5-HOXA10, which were previously challenging to upregulate. We differentiated hPSCs into highly enriched HLF+ HOXA+ hematopoietic progenitors with near-stoichiometric efficiency by blocking formation of unwanted lineages at each differentiation step. hPSC-derived HLF+ HOXA+ hematopoietic progenitors could avail both basic research and cellular therapies.

Genome editing by homology directed repair (HDR) is leveraged to precisely modify the genome of therapeutically relevant hematopoietic stem and progenitor cells (HSPCs). Here, we present a new approach to increasing the frequency of HDR in human HSPCs by the delivery of an inhibitor of 53BP1 (named i53) as a recombinant peptide. We show that the use of i53 peptide effectively increases the frequency of HDR-mediated genome editing at a variety of therapeutically relevant loci in HSPCs as well as other primary human cell types. We show that incorporating the use of i53 recombinant protein allows high frequencies of HDR while lowering the amounts of AAV6 needed by 8-fold. HDR edited HSPCs were capable of long-term and bi-lineage hematopoietic reconstitution in NSG mice, suggesting that i53 recombinant protein might be safely integrated into the standard CRISPR/AAV6-mediated genome editing protocol to gain greater numbers of edited cells for transplantation of clinically meaningful cell populations.

Platelets are the terminal progeny of megakaryocytes, primarily produced in the bone marrow, and play critical roles in blood homeostasis, clotting, and wound healing. Traditionally, megakaryocytes and platelets are thought to arise from multipotent hematopoietic stem cells (HSCs) via multiple discrete progenitor populations with successive, lineage-restricting differentiation steps. However, this view has recently been challenged by studies suggesting that (1) some HSC clones are biased and/or restricted to the platelet lineage, (2) not all platelet generation follows the "canonical" megakaryocytic differentiation path of hematopoiesis, and (3) platelet output is the default program of steady-state hematopoiesis. Here, we specifically investigate the evidence that in vivo lineage tracing studies provide for the route(s) of platelet generation and investigate the involvement of various intermediate progenitor cell populations. We further identify the challenges that need to be overcome that are required to determine the presence, role, and kinetics of these possible alternate pathways.

Aims: There is limited real‐world data on cyclosporin A (CsA)‐induced liver injury (CILI). This study aims to investigate the incidence, clinical classification and risk factors of CILI, thereby providing evidence to inform the treatment of CILI. Methods: Inpatients receiving haematopoietic stem cell transplantation (HSCT) and treated with CsA were included. Patient information was collected to assess suspicious CILI by the Roussel Uclaf causality assessment method (RUCAM) scale. We evaluated the pattern and severity of CILI. The independent risk factors of CILI were identified by multivariable logistic regression. Results: A total of 216 allogeneic HSCT (allo‐HSCT) recipients were included in this study. The incidence of CILI was 15.3% (95% confidence interval [CI]: 10.4%–20.1%). Among these cases, 84.8% displayed a hepatocellular pattern, and 90.9% of CILI was of mild severity. Baseline alanine aminotransferase (ALT) level (OR = 1.030, 95% CI: 1.008–1.053, P =.008) and trough concentration level of CsA (OR = 1.007, 95% CI: 1.002–1.012, P =.009) were identified as independent risk factors for CILI. Conclusions: The incidence of CILI in allo‐HSCT recipients is notably high. Recipients with elevated baseline ALT levels and higher exposure to CsA are more susceptible to developing CILI. [ABSTRACT FROM AUTHOR]

[Display omitted] Acute radiation syndrome encompasses a spectrum of pathological manifestations resulting from exposure to high doses of ionizing radiation. This syndrome typically progresses through three stages with a prodromal phase, a latency phase and a critical phase. Each of them varies in intensity and duration depending on the absorbed dose of radiation. Predominantly affecting the bone marrow, skin, and gastrointestinal tract, its clinical implications are profound and multiorgan failure must be considered. Radiation doses below 2 Gray generally result in insignificant clinical consequences, while exposures surpassing 12 Gray exceeds current therapeutic capacities. Survival outcomes for patients within this therapeutic range depend on their ability to withstand radiation-induced aplasia, compounded by an increased risk of bleeding and infection due to skin, gastrointestinal, and potentially combined radiation injuries. Assessing the degree of radiation exposure plays a pivotal role in tailoring patient management strategies and is based on a combination of clinical, biological, and physical parameters. Treatment approaches primarily include intensive hematologic support to manage symptomatic manifestations and etiologic treatment is now based on the administration of growth factors. The role of hematopoietic stem cell transplant (HSCT) will be carefully considered on an individual basis, especially for patients who do not respond following 3 weeks of cytokine therapy. This review highlights the pathophysiological mechanisms, assessment modalities, and therapeutic interventions crucial for managing acute radiation syndrome aiming to optimize patient outcomes and guide clinical practice. [ABSTRACT FROM AUTHOR]

Telocytes (TCs), a novel type of mesenchymal or interstitial cell with specific, very long and thin cellular prolongations, have been found in various mammalian organs and have potential biological functions. However, their existence during lung development is poorly understood. This study aimed to investigate the existence, morphological features, and role of CD34+ SCs/TCs in mouse lungs from foetal to postnatal life using primary cell culture, double immunofluorescence, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The immunofluorescence double staining profiles revealed positive expression of CD34 and PDGFR‐α, Sca‐1 or VEGFR‐3, and the expression of these markers differed among the age groups during lung development. Intriguingly, in the E18.5 stage of development, along with the CD34+ SCs/TCs, haematopoietic stem cells and angiogenic factors were also significantly increased in number compared with those in the E14.5, E16.5, P0 and P7. Subsequently, TEM confirmed that CD34+ SCs/TCs consisted of a small cell body with long telopodes (Tps) that projected from the cytoplasm. Tps consisted of alternating thin and thick segments known as podomers and podoms. TCs contain abundant endoplasmic reticulum, mitochondria and secretory vesicles and establish close connections with neighbouring cells. Furthermore, SEM revealed characteristic features, including triangular, oval, spherical, or fusiform cell bodies with extensive cellular prolongations, depending on the number of Tps. Our findings provide evidence for the existence of CD34+ SCs/TCs, which contribute to vasculogenesis, the formation of the air‒blood barrier, tissue organization during lung development and homoeostasis. [ABSTRACT FROM AUTHOR]

Ex vivo production of red blood cells (RBCs) represents a promising alternative for transfusion medicine. Several strategies have been described to generate erythroid cell lines from different sources, including embryonic, induced pluripotent, and hematopoietic stem cells. All these approaches have in common that they require elaborate differentiation cultures whereas the yield of enucleated RBCs is inefficient. We generated a human immortalized adult erythroid progenitor cell line derived from bone marrow CD71-positive erythroid progenitor cells (immortalized bone marrow erythroid progenitor adult, or imBMEP-A) by an inducible expression system, to shorten differentiation culture necessary for terminal erythroid differentiation. It is the first erythroid cell line that is generated from direct reticulocyte progenitors and demonstrates robust hemoglobin production in the immortalized state. Morphologic analysis of the immortalized cells showed that the preferred cell type of the imBMEP-A line corresponds to hemoglobin-producing basophilic erythroblasts. In addition, we were able to generate a stable cell line from a single cell clone with the triple knockout of RhAG, RhDCE and KELL. After removal of doxycycline, part of the cells differentiated into normoblasts and reticulocytes within 5–7 days. Our results demonstrate that the imBMEP-A cell line can serve as a stable and straightforward modifiable platform for RBC engineering in the future. [Display omitted] [ABSTRACT FROM AUTHOR]

Genetic manipulation of hematopoietic stem cells (HSCs) is being developed as a therapeutic strategy for several inherited disorders. This field is rapidly evolving with several novel tools and techniques being employed to achieve desired genetic changes. While commercial products are now available for sickle cell disease, transfusion-dependent β-thalassemia, metachromatic leukodystrophy and adrenoleukodystrophy, several challenges remain in patient selection, HSC mobilization and collection, genetic manipulation of stem cells, conditioning, hematologic recovery and post-transplant complications, financial issues, equity of access and institutional and global preparedness. In this report, we explore the current state of development of these therapies and provide a comprehensive assessment of the challenges these therapies face as well as potential solutions. [ABSTRACT FROM AUTHOR]

Introduction: Acute lymphoblastic leukemia is characterized by a disturbed maturation of hematopoietic stem cells (HSCs) resulting in development of a malignant clone. Despite relatively positive outcome, there are still instances of disease relapse occurring due to ineffective disease eradication or primary leukemic clone alterations. Unclear significance of stem cells in the course of ALL led us to investigate and establish crucial changes in two stem cell populations - very small embryonic-like stem cells (VSELs) and HSCs during the induction phase of treatment. Methods: In a retrospective study selected stem cells in peripheral blood and bone marrow of 60 pediatric ALL subjects and 48 healthy controls were subjected to flow cytometric analysis at 4 different time points. Results: Both VSELs and HSCs were elevated at the moment of ALL diagnosis compared to healthy controls, but profoundly decline until day 15. Further observations revealed an increase in HSCs with a concomitant depletion of VSELs until week 12. ALL patients with high HSCs showed positive correlation with bone marrow blasts at diagnosis. Patients with lower VSELs or HSCs at diagnosis had slightly improved response to applied therapy. We observed higher initial bone marrow lymphoblast values in patients with lower VSELs or higher HSCs in the high-risk group. The significance of VSELs in predicting treatment outcome can be illustrated by lower day 15 MRD level of patients with lower VSELs at diagnosis. ȩ Discussion: We found HSCs and VSELs to be valid participants in pediatric ALL with possible contribution in the neoplastic process and prediction of initial treatment outcome. [ABSTRACT FROM AUTHOR]

Introduction: Myelodysplastic syndromes/neoplasms (MDS) are a heterogeneous group of hematologic malignancies that are stratified into high-risk (HR-MDS) and low-risk (LR-MDS) categories. Until recently, LR-MDS has been typically managed by supportive measures and erythropoiesis-stimulating agents (ESAs); whereas management of HR-MDS typically included hypomethylating agents and allogeneic hematopoietic stem cell transplant. However, the limited rates and durations of response observed with these interventions prompted the search for targeted therapies to improve the outcomes among patients with MDS. Areas covered: Here, we review the current landscape of targeted therapies in MDS. These include pyruvate kinase and hypoxia-inducible factor (HIF) activators; TGF-beta, telomerase, BCL2 and isocitrate dehydrogenase (IDH) inhibitors; as well as novel approaches targeting inflammation, pyroptosis, immune evasion, and RNA splicing machinery. Expert opinion: This review highlights the progress and challenges in MDS treatment. Despite some promising results, many therapies remain in early development or have faced setbacks, emphasizing the need for a more comprehensive understanding of the disease's pathobiology. Continued research into targeted therapies, homogenous clinical trial designs, as well as increased incorporation of molecular prognostic tools and artificial intelligence into trial design are essential for developing effective treatments for MDS and improving patient outcomes. [ABSTRACT FROM AUTHOR]

Stem cell factors (SCFs) are pivotal factors existing in both soluble and membrane-bound forms, expressed by endothelial cells (ECs) and fibroblasts throughout the body. These factors enhance cell growth, viability, and migration in multipotent cell lineages. The preferential expression of SCF by arteriolar ECs indicates that arterioles create a unique microenvironment tailored to hematopoietic stem cells (HSCs). Insufficiency of SCF within bone marrow (BM)-derived adipose tissue results in decreased their overall cellularity, affecting HSCs and their immediate progenitors critical for generating diverse blood cells and maintaining the hematopoietic microenvironment. SCF deficiency disrupts BM function, impacting the production and differentiation of HSCs. Additionally, deleting SCF from adipocytes reduces lipogenesis, highlighting the crucial role of SCF/c-kit signaling in controlling lipid accumulation. This review elucidates the sources, roles, mechanisms, and molecular strategies of SCF in bone renewal, offering a comprehensive overview of recent advancements, challenges, and future directions for leveraging SCF as a key agent in regenerative medicine. [ABSTRACT FROM AUTHOR]

Fanconi anemia (FA) is generally classified as a DNA repair disorder, conferring a genetic predisposition to cancer and prominent bone marrow failure (BMF) in early childhood. Corroborative human and murine studies point to a fetal origin of hematopoietic stem cell (HSC) attrition under replicative stress. Along with intriguing recent insights into non‐canonical roles and domain‐specific functions of FA proteins, these studies have raised the possibility of a DNA repair‐independent BMF etiology. However, deeper mechanistic insight is critical as current curative options of allogeneic stem cell transplantation and emerging gene therapy have limited eligibility, carry significant side effects, and involve complex procedures restricted to resource‐rich environments. To develop rational and broadly accessible therapies for FA patients, the field will need more faithful disease models that overcome the scarcity of patient samples, leverage technological advances, and adopt investigational clinical trial designs tailored for rare diseases. [ABSTRACT FROM AUTHOR]

AbstractEfforts to produce adoptive cell therapies in AML have been largely unfruitful, despite the success seen in lymphoid malignancies. Identifying targetable antigens on leukemic cells that are absent on normal progenitor cells remains a major obstacle, as is the hostile tumor microenvironment created by AML blasts. In this review, we summarize the challenges in the development of adoptive cell therapies such as CAR-T, CAR-NK, and TCR-T cells in AML, discussing both autologous and allogeneic therapies. We also discuss methods to address myelotoxicity associated with these therapies, including rapidly switchable CAR platforms and CRISPR-Cas9 genetic engineering of hematopoietic stem cells. Finally, we present the current clinical landscape in these areas, along with future directions in the field. [ABSTRACT FROM AUTHOR]

Hematopoietic stem cells (HSCs) obtained from patient-derived human induced pluripotent stem cells (iPSCs) are a promising tool for curing various hematological disorders. We previously demonstrated that enforced expression of the LIM-homeobox transcription factor Lhx2, which is essential for mouse embryonic hematopoiesis, leads to generation of engraftable and expandable hematopoietic stem cells (HSCs) from mouse iPSCs. However, it remained unknown whether Lhx2 can induce HSCs from human iPSCs. Here, we investigated the effect of Lhx2 overexpression on hematopoietic differentiation of human iPSCs. Unexpectedly, Lhx2 severely inhibited proliferation of human iPSC-derived hematopoietic cells. Thus, Lhx2 exhibited differential effects on mouse and human hematopoietic cells. Further studies implied that the inhibitory effect of Lhx2 on human iPSC-derived hematopoietic cells was due to insufficient transcriptional activation ability. Therefore, we modified Lhx2 to strengthen its activity as a transcriptional activator. This modified Lhx2 could induce ex vivo amplification of human iPSC-derived hematopoietic stem/progenitor cells (HSPCs). We believe that these findings will facilitate the development of a method to efficiently produce HSCs from human iPSCs. [ABSTRACT FROM AUTHOR]

Introduction: Immune checkpoint blockade (ICB) immunotherapy has revolutionized cancer treatment, demonstrating exceptional clinical responses in a wide range of cancers. Despite the success, a significant proportion of patients still fail to respond, highlighting the existence of unappreciated mechanisms of immunotherapy resistance. Delineating such mechanisms is paramount to minimize immunotherapy failures and optimize the clinical benefit. Methods: In this study, we treated tumour-bearing mice with PD-L1 blockage antibody (aPD-L1) immunotherapy, to investigate its effects on cancer-induced emergency myelopoiesis, focusing on bone marrow (BM) hematopoietic stem and progenitor cells (HSPCs). We examined the impact of aPD-L1 treatment on HSPC quiescence, proliferation, transcriptomic profile, and functionality. Results: Herein, we reveal that aPD-L1 in tumour-bearing mice targets the HSPCs in the BM, mediating their exit from quiescence and promoting their proliferation. Notably, disruption of the PDL1/PD1 axis induces transcriptomic reprogramming in HSPCs, observed in both individuals with Hodgkin lymphoma (HL) and tumour-bearing mice, shifting towards an inflammatory state. Furthermore, HSPCs from aPDL1-treated mice demonstrated resistance to cancer-induced emergency myelopoiesis, evidenced by a lower generation of MDSCs compared to control-treated mice. Discussion: Our findings shed light on unrecognized mechanisms of action of ICB immunotherapy in cancer, which involves targeting of BM-driven HSPCs and reprogramming of cancer-induced emergency myelopoiesis. [ABSTRACT FROM AUTHOR]

AbstractObjectiveMethodsResultsConclusionsThis retrospective, real-world claims database analysis described the clinical burden and healthcare resource utilization (HCRU) among patients with sickle cell disease (SCD) with recurrent vaso-occlusive crises (VOCs) in France.The French National Health Data System database (système national des données de santé) was used to identify eligible patients from 1 January 2012 to 1 March 2019. Inclusion criteria were a SCD diagnosis, ≥2 VOCs/year for ≥2 consecutive years following the diagnosis, and ≥1 year of follow-up data to 1 March 2020. Patients with hereditary persistence of fetal hemoglobin or hematopoietic stem cell transplant in their medical records were excluded. Clinical complications, mortality, treatment use, and HCRU were evaluated during follow-up.Overall, 4602 patients with SCD with recurrent VOCs were eligible; their mean (standard deviation [SD]) age was 19.8 (13.5) years, and 51.8% were female. Patients experienced a mean (SD) of 3.82 (3.57) VOCs per patient per year (PPPY). Prevalent complications were anemia or leukocytosis (44.1%), infections (42.0%), and organ failure (38.2%). In total, 101 (2.2%) patients died during follow-up (mean age of death [SD]: 39.3 [17.5] years; mortality rate: 0.64 deaths per 100 person-years). Most patients received opioids (89.1%) and hydroxycarbamide (72.8%). Patients had a mean of 5.7 inpatient hospitalizations, 6.0 emergency room visits, 6.6 outpatient visits, and 13.4 outpatient prescriptions PPPY.Patients with SCD with recurrent VOCs in France have substantial clinical complications, mortality, and HCRU despite currently available treatment options. Innovative treatments that reduce frequency of or eliminate VOCs are needed to alleviate the burden associated with SCD. [ABSTRACT FROM AUTHOR]

The Switch/Sugar non-fermenting (SWI/SNF) nucleosome remodeling complexes are essential for normal hematopoiesis. The Brg1/Brm associated factor (BAF) is a form of mammalian SWI/SNF that is distinguished by the presence of either ARID1A or ARID1B protein. In this study, we used hematopoietic specific Cre mouse models to assess the function of Arid1b in blood development. We found Arid1b loss did not affect steady state hematopoiesis or hematopoietic regeneration. Nonetheless, Arid1b null hematopoietic stem and progenitor cells have reduced ability to reconstitute hematopoietic system compared to wild type cells. Overall, our data indicate Arid1b is largely dispensable for normal hematopoiesis but impairs the regenerative ability of HSPCs. [ABSTRACT FROM AUTHOR]

Myelofibrosis (MF) is a complex myeloproliferative neoplasm characterized by abnormal hematopoietic stem cell proliferation and subsequent bone marrow (BM) fibrosis. First documented in the late 19th century, MF has since been extensively studied to unravel its pathophysiology, clinical phenotypes, and therapeutic interventions. MF can be classified into primary and secondary forms, both driven by mutations in genes such as JAK2, CALR, and MPL, which activate the JAK-STAT signaling pathway. These driver mutations are frequently accompanied by additional non-driver mutations in genes like TET2, SRSF2, and TP53, contributing to disease complexity. The BM microenvironment, consisting of stromal cells, extracellular matrix, and cytokines such as TGF-β and TNF-α, plays a critical role in fibrosis and aberrant hematopoiesis. Clinically, MF manifests with symptoms ranging from anemia, splenomegaly, and fatigue to severe complications such as leukemic transformation. Splenomegaly, caused by extramedullary hematopoiesis, leads to abdominal discomfort and early satiety. Current therapeutic strategies include JAK inhibitors like Ruxolitinib, which target the JAK-STAT pathway, alongside supportive treatments such as blood transfusions, erythropoiesis-stimulating agents and developing combinatorial approaches. Allogeneic hematopoietic stem cell transplantation remains the only curative option, though it is limited to younger, high-risk patients. Recently approved JAK inhibitors, including Fedratinib, Pacritinib, and Momelotinib, have expanded the therapeutic landscape. Spatially Resolved Transcriptomics (SRT) has revolutionized the study of gene expression within the spatial context of tissues, providing unprecedented insights into cellular heterogeneity, spatial gene regulation, and microenvironmental interactions, including stromal-hematopoietic dynamics. SRT enables high-resolution mapping of gene expression in the BM and spleen, revealing molecular signatures, spatial heterogeneity, and pathological niches that drive disease progression. These technologies elucidate the role of the spleen in MF, highlighting its transformation into a site of abnormal hematopoietic activity, fibrotic changes, and immune cell infiltration, functioning as a "tumor surrogate." By profiling diverse cell populations and molecular alterations within the BM and spleen, SRT facilitates a deeper understanding of MF pathophysiology, helping identify novel therapeutic targets and biomarkers. Ultimately, integrating spatial transcriptomics into MF research promises to enhance diagnostic precision and therapeutic innovation, addressing the multifaceted challenges of this disease. [ABSTRACT FROM AUTHOR]

Background: There is a need for therapies that can mitigate bone marrow dysfunction and organ toxicity that occur following myeloablative injury and reduced intensity conditioning regimens used in patients undergoing bone marrow transplantation (BMT). The pathogenesis of adverse effects from BMT conditioning has been linked to injury to the vascular endothelium, bone marrow (BM), and other organs. Objective: To evaluate the impact of the thrombopoietin mimetic drug JNJ-26366821 (TPOm) on BM vascular recovery in mice undergoing myeloablative radiation conditioning followed by BMT. Study design: TPOm (doses: 0 µg, 300 µg, 1000 µg per Kg body weight) was administered on Days 0 and 7 after BMT, in mice receiving a total body irradiation (TBI) conditioning regimen (5.5 Gy x 2) before congenic BMT. BM donner cell engraftment was analyzed using flow cytometry on Days 7, 14, and 30 post-BMT. The morphological and biophysical properties of the BM vasculature were evaluated by intravital multiphoton microscopy (MPM) and immunofluorescence confocal imaging. Herein, morphological properties involve microvascular density (MVD), vessel diameter, and vascular area, while biophysical properties include transfer rate (Ktrans) of contrast within the BM vascular niche, as well as the fractional volume (vec) of extracellular extravascular tissue (EES). Results: No significant difference in donor chimerism was observed at days 7, 14, and 30 post-BMT, between TPOm and PBS-treated mice. TPOm intervention improved BM vasculature regeneration in transplanted mice. The MVD, Ktrans, and BM vasculature as well as vascular endothelial growth factor receptor-2 (VEGFR2) in the BM, showed a dose dependent improvement inmice treated with TPOm. On day 14 post-BMT, the group receiving 1000 µg/Kg TPOm showed significant shifts (p-value < 0.05) in MVD, Ktrans, and VEGFR2 expression from their corresponding control types (TPOm dose 0 µg) towards levels comparable to healthy controls. Conclusion: TPOm intervention augments BM vascular structure and function, which may be important for hematopoietic recovery and bone marrow function in radiation conditioned hematopoietic stem cell transplant patients, in addition to enhancing platelet recovery. day 14 post-BMT, the group receiving 1000 µg/Kg TPOm showed significant shifts (p-value < 0.05) in MVD, Ktrans, and VEGFR2 expression from their corresponding control types (TPOm dose 0 µg) towards levels comparable to healthy controls. Conclusion: TPOm intervention augments BM vascular structure and function, which may be important for hematopoietic recovery and bone marrow function in radiation conditioned hematopoietic stem cell transplant patients, in addition to enhancing platelet recovery. [ABSTRACT FROM AUTHOR]

Cancer cohorts are now known to be associated with increased rates of clonal hematopoiesis (CH). We sort to characterize the hematopoietic compartment of patients with melanoma and non-small cell lung cancer (NSCLC) given our recent population level analysis reporting evolving rates of secondary leukemias. The advent of immune checkpoint blockade (ICB) has dramatically changed our understanding of cancer biology and has altered the standards of care for patients. However, the impact of ICB on hematopoietic myeloid clonal expansion remains to be determined. We studied if exposure to ICB therapy affects hematopoietic clonal architecture and if their evolution contributed to altered hematopoiesis. Blood samples from patients with melanoma and NSCLC (n = 142) demonstrated a high prevalence of CH. Serial samples (or post ICB exposure samples; n = 25) were evaluated in melanoma and NSCLC patients. Error-corrected sequencing of a targeted panel of genes recurrently mutated in CH was performed on peripheral blood genomic DNA. In serial sample analysis, we observed that mutations in DNMT3A and TET2 increased in size with longer ICB exposures in the melanoma cohort. We also noted that patients with larger size DNMT3A mutations with further post ICB clone size expansion had longer durations of ICB exposure. All serial samples in this cohort showed a statistically significant change in VAF from baseline. In the serial sample analysis of NSCLC patients, we observed similar epigenetic expansion, although not statistically significant. Our study generates a hypothesis for two important questions: (a) Can DNMT3A or TET2 CH serve as predictors of a response to ICB therapy and serve as a novel biomarker of response to ICB therapy? (b) As ICB-exposed patients continue to live longer, the myeloid clonal expansion may portend an increased risk for subsequent myeloid malignancy development. Until now, the selective pressure of ICB/T-cell activating therapies on hematopoietic stem cells were less known and we report preliminary evidence of clonal expansion in epigenetic modifier genes (also referred to as inflammatory CH genes). [ABSTRACT FROM AUTHOR]

Stem cell therapy constitutes a pivotal subject in contemporary discourse, with donor stem cells having been employed in research and clinical treatments for several decades. Primary cell transplantation encompasses diverse stem cell types, including ectomesenchymal stem cells, hematopoietic stem cells, and various stem cell derivatives such as vesicles and extracellular vesicles. Nevertheless, the emergence of cell engineering techniques has heralded a new epoch in stem cell therapy, markedly broadening their therapeutic potential. Induced pluripotent stem cells (iPSCs) epitomize a significant milestone in modern medical biology. This groundbreaking discovery offers significant potential in disciplines such as biology, pathophysiology, and cellular regenerative medicine. As a result, iPSCs derived differentiated cells have become a pioneering avenue for cell therapy research. Induced mesenchymal stem cells (iMSCs), derived from iPSCs, represent a novel frontier in MSCs related research. Empirical evidence suggests that iMSCs demonstrate enhanced proliferative capacities compared to natural MSCs, with diminished age-related variability and heterogeneity. Numerous clinical trials have highlighted the prospective superiority of iMSCs. This article synthesizes current basic research and clinical trials pertaining to iMSCs, aiming to provide a reference point for future research endeavors. [ABSTRACT FROM AUTHOR]

BIVV003 is a gene-edited autologous cell therapy in clinical development for the potential treatment of sickle cell disease (SCD). Hematopoietic stem cells (HSC) are genetically modified with mRNA encoding zinc finger nucleases (ZFN) that target and disrupt a specific regulatory GATAA motif in the BCL11A erythroid enhancer to reactivate fetal hemoglobin (HbF). We characterized ZFN-edited HSC from healthy donors and donors with SCD. Results of preclinical studies show that ZFN-mediated editing is highly efficient, with enriched biallelic editing and high frequency of on-target indels, producing HSC capable of long-term multilineage engraftment in vivo, and express HbF in erythroid progeny. Interim results from the Phase 1/2 PRECIZN-1 study demonstrated that BIVV003 was well-tolerated in seven participants with SCD, of whom five of the six with more than 3 months of follow-up displayed increased total hemoglobin and HbF, and no severe vaso-occlusive crises. Our data suggest BIVV003 represents a compelling and novel cell therapy for the potential treatment of SCD. [ABSTRACT FROM AUTHOR]

Patients heterozygous for germline CBL loss-of-function (LOF) variants can develop myeloid malignancy, autoinflammation, or both, if some or all of their leukocytes become homozygous for these variants through somatic loss of heterozygosity (LOH) via uniparental isodisomy. We observed an upregulation of the inflammatory gene expression signature in whole blood from these patients, mimicking monogenic inborn errors underlying autoinflammation. Remarkably, these patients had constitutively activated monocytes that secreted 10 to 100 times more inflammatory cytokines than those of healthy individuals and CBL LOF heterozygotes without LOH. CBL-LOH hematopoietic stem and progenitor cells (HSPCs) outgrew the other cells, accounting for the persistence of peripheral monocytes homozygous for the CBL LOF variant. ERK pathway activation was required for the excessive production of cytokines by both resting and stimulated CBL-LOF monocytes, as shown in monocytic cell lines. Finally, we found that about 1 in 10,000 individuals in the UK Biobank were heterozygous for CBL LOF variants and that these carriers were at high risk of hematological and inflammatory conditions. [ABSTRACT FROM AUTHOR]

Summary In recent years, large‐scale sequencing efforts have identified targetable driver mutations in haematopoietic stem cells. These efforts have led to the development and approval of nine novel agents for relapsed or refractory acute myelogenous leukaemia (R/R AML). However, despite an expansion in targeted therapies, achieving a durable remission in AML and high‐risk myelodysplastic syndrome (HR‐MDS) remains a significant challenge, and there is an urgent need for new effective treatments. Modulation of aberrant RNA splicing has emerged as a novel therapeutic approach in myeloid diseases. Aberrant splicing drives dysregulated gene expression that promotes tumourigenesis through increased proliferation and metastatic potential, immune evasion, decreased apoptosis, and chemotherapy resistance. Mutations in spliceosomal components have been identified in numerous cancer subtypes, with mutations in RNA binding proteins SF3B1, SRSF2, U2AF1, and ZRSR2 occurring frequently in AML and in up to 60% of patients with MDS, as well as in chronic myelomonocytic leukaemia and in 10% of patients with chronic lymphocytic leukaemia. In this review, we explore therapeutic strategies targeting aberrant splicing and the potential of these approaches to drive clinical responses. [ABSTRACT FROM AUTHOR]

Myeloproliferative neoplasms (MPNs) are characterized by an increased production of blood cells due to the acquisition of mutations such as JAK2V617F. TGF‐β, whose secretion is increased in MPN patients, is known to negatively regulate haematopoietic stem cell (HSC) proliferation. Using an isogenic JAK2V617F or JAK2 wild‐type UT‐7 cell line we observed that JAK2V617F cells resist to TGF‐β antiproliferative activity. Although TGF‐β receptors and SMAD2/3 expressions are similar in both cell types, TGF‐β‐induced phosphorylation of SMAD2/3 is reduced in UT‐7 JAK2V617F cells compared with JAK2 WT cells. We confirmed that JAK2V617F mutated cells are resistant to the antiproliferative effect of TGF‐β in a competitive assay as we observed a positive selection of JAK2V617F cells when exposed to TGF‐β. Using cell lines, CD34‐positive cells from MPN patients and bone marrow cells from JAK2V617F knock‐in mice we identified a down regulation of the SHP‐1 phosphatase, which is required for the regulation of HSC quiescence by TGF‐β. The transduction of SHP‐1 cDNA (but not a phosphatase inactive cDNA) restores the antiproliferative effect of TGF‐β in JAK2V617F mutated cells. Finally, SC‐1, a known agonist of SHP‐1, antagonized the selection of JAK2V617F mutated cells in the presence of TGF‐β. In conclusion, we show a JAK2‐dependent down regulation of SHP‐1 in MPN patients' cells which is related to their resistance to the antiproliferative effect of TGF‐β. This may participate in the clonal selection of cancer cells in MPNs. [ABSTRACT FROM AUTHOR]

Methyltransferase-like 3(METTL3), recognized as the primary N6-methyladenosine methyltransferase, influences cellular functions such as proliferation, migration, invasion, differentiation, and fate determination by regulating gene expression post-transcriptionally. Recent studies have highlighted the indispensability of METTL3 in various immune cells such as hematopoietic stem/progenitor cells, innate immune cells (monocytes, macrophages, dendritic cells), and adaptive immune cells (thymic epithelial cell, T cells, natural killer cells). However, a comprehensive summary and analysis of these findings to elucidate the relationship between METTL3 and the immune system is yet to be undertaken. Therefore, in this review, we systematically collate reports detailing themechanism underlying the role of METTL3 in regulating various immune processes and examine the modification of METTL3 and its potential implications. This review suggests that METTL3 plays an essential role in the immune system, ranging from maintaining homeostasis to regulating functions. Collectively, this review provides a comprehensive analysis of the relationship between METTL3 and the immune system, serving convenient researchers to understand the frontiers of immunological research and facilitate future clinical applications. [ABSTRACT FROM AUTHOR]

Background: Dysregulated innate immune responses underlie multiple inflammatory diseases, but clinical translation of preclinical innate immunity research in mice is hampered by the difficulty of studying human inflammatory reactions in an in vivo context. We therefore sought to establish in vivo human inflammatory responses in NSG-QUAD mice that express four human myelopoiesis transgenes to improve engraftment of a human innate immune system. Methods: We reconstituted NSG-QUAD mice with human hematopoietic stem and progenitor cells (HSPCs), after which we evaluated human myeloid cell development and subsequent human responses to systemic and local lipopolysaccharide (LPS) challenges. Results: NSG-QUAD mice already displayed engraftment of human monocytes, dendritic cells and granulocytes in peripheral blood, spleen and liver at 6 weeks after HSPC reconstitution, in which both classical, intermediate and non-classical monocytes were present. These huNSG-QUAD mice responded to intraperitoneal and intranasal LPS challenges with production of NF-kBdependent human cytokines, a human type I interferon response, as well as inflammasome-mediated production of human IL-1b and IL-18. The latter were specifically abrogated by the NLRP3 inhibitor MCC950, while LPS-induced human monocyte death was not altered. Besides providing proof-of-principle for small molecule testing of human inflammatory reactions in huNSG-QUAD mice, this observation suggests that LPS-induced in vivo release of human NLRP3 inflammasome-generated cytokines occurs in a cell death-independent manner. Conclusion: HuNSG-QUAD mice are competent for the NF-kB, interferon and inflammasome effectors of human innate immunity, and can thus be utilized to investigate signaling mechanisms and pharmacological targeting of human inflammatory responses in an in vivo setting. [ABSTRACT FROM AUTHOR]

X-linked chronic granulomatous disease (X-CGD) is an inborn error of immunity (IEI) resulting from genetic mutations in the cytochrome b-245 beta chain (CYBB) gene. The applicability of base editors (BEs) to correct mutations that cause X-CGD is constrained by the requirement of Cas enzymes to recognize specific protospacer adjacent motifs (PAMs). Our recently engineered PAMless Cas enzyme, SpRY, can overcome the PAM limitation. However, the efficiency, specificity, and applicability of SpRY-based BEs to correct mutations in human hematopoietic stem and progenitor cells (HSPCs) have not been thoroughly examined. Here, we demonstrated that the adenine BE ABE8e-SpRY can access a range of target sites in HSPCs to correct mutations causative of X-CGD. For the prototypical X-CGD mutation CYBB c.676C>T, ABE8e-SpRY achieved up to 70% correction, reaching efficiencies greater than three-and-one-half times higher than previous CRISPR nuclease and donor template approaches. We profiled potential off-target DNA edits, transcriptome-wide RNA edits, and chromosomal perturbations in base-edited HSPCs, which together revealed minimal off-target or bystander edits. Edited alleles persisted after transplantation of the base-edited HSPCs into immunodeficient mice. Together, these investigational new drug–enabling studies demonstrated efficient and precise correction of an X-CGD mutation with PAMless BEs, supporting a first-in-human clinical trial (NCT06325709) and providing a potential blueprint for treatment of other IEI mutations. Editor's summary: Gene therapy for the treatment of X-linked chronic granulomatous disease, using autologous hematopoietic stem and progenitor cells (HSPCs) transduced with lentiviruses containing the sequence of the corrected cytochrome b-245 beta chain (CYBB) gene, is limited by the use of a weak promoter to reduce the risk of transactivating nearby oncogenes and by a lack of physiological regulation of transgene expression. Base editing could overcome these concerns, but base editors use Cas9 enzymes that require the presence of a protospacer adjacent motif (PAM), limiting their use. Here, Bzhilyanskaya and colleagues optimized the PAMless Cas9 enzyme SpRY with the adenine base editor ABE8e, ultimately correcting two mutations in CYBB in patient HSPCs with high efficiency and specificity. This work underlies the ongoing clinical trial NCT06325709. —Melissa L. Norton [ABSTRACT FROM AUTHOR]

A study published in the Blood Cancer Journal highlights an increased risk and incidence of acute lymphoblastic leukemia (ALL) in patients with multiple myeloma (MM) who were treated with lenalidomide. The study conducted a systematic review and safety meta-analysis of randomized controlled trials (RCTs) and analyzed data from the World Health Organization's pharmacovigilance database. The findings suggest that lenalidomide-associated ALL should be considered as a specific entity and may require better monitoring and patient information. Further research is needed to determine the risk and incidence of lenalidomide-associated ALL in non-MM diseases and to identify potential drug combinations that could increase this risk. [Extracted from the article]

CRISPR-based genome editing of pseudogene-associated disorders, such as p47phox-deficient chronic granulomatous disease (p47 CGD), is challenged by chromosomal rearrangements due to presence of multiple targets. We report that interactions between highly homologous sequences that are localized on the same chromosome contribute substantially to post-editing chromosomal rearrangements. We successfully employed editing approaches at the NCF1 gene and its pseudogenes, NCF1B and NCF1C, in a human cell line model of p47 CGD and in patient-derived human hematopoietic stem and progenitor cells. Upon genetic engineering, a droplet digital PCR-based method identified cells with altered copy numbers, spanning megabases from the edited loci. We attributed the high aberration frequency to the interaction between repetitive sequences and their predisposition to recombination events. Our findings emphasize the need for careful evaluation of the target-specific genomic context, such as the presence of homologous regions, whose instability can constitute a risk factor for chromosomal rearrangements upon genome editing. Simultaneous editing of the NCF1 and its pseudogenes in p47phox-deficient chronic granulomatous disease is associated with homologous recombination and chromosomal rearrangements due to presence of multiple targets of high sequence similarity. [ABSTRACT FROM AUTHOR]

MGTA-145 or GROβT, a CXCR2 agonist, has shown promising activity for hematopoietic stem cell (HSC) mobilization with plerixafor in pre-clinical studies and healthy volunteers. Twenty-five patients with multiple myeloma enrolled in a phase 2 trial evaluating MGTA-145 and plerixafor for HSC mobilization (NCT04552743). Plerixafor was given subcutaneously followed 2 h later by MGTA-145 (0.03 mg/kg) intravenously with same day apheresis. Mobilization/apheresis could be repeated for a second day in patients who collected <6 ×106 CD34+ cells/kg. Lenalidomide and anti-CD38 antibody were part of induction therapy in 92% (n = 23) and 24% (n = 6) of patients, respectively. Median total HSC cell yield (CD34+ cells/kg × 106) was 5.0 (range: 1.1–16.2) and day 1 yield was 3.4 (range: 0.3–16.2). 88% (n = 22) of patients met the primary endpoint of collecting 2 ×106 CD34+ cells/kg in ≤ two days, 68% (n = 17) in one day. Secondary endpoints of collecting 4 and 6 × 106 CD34+ cells/kg in ≤ two days were met in 68% (n = 17) and 40% (n = 10) patients. Grade 1 or 2 adverse events (AE) were seen in 60% of patients, the most common AE being grade 1 pain, usually self-limited. All 19 patients who underwent transplant with MGTA-145 and plerixafor mobilized HSCs engrafted successfully, with durable engraftment at day 100. 74% (17 of 23) of grafts with this regimen were minimal residual disease negative by next generation flow cytometry. Graft composition for HSCs and immune cells were similar to a contemporaneous cohort mobilized with G-CSF and plerixafor. [ABSTRACT FROM AUTHOR]

Hematopoietic stem cell (HSC)-independent lymphopoiesis has been elucidated in murine embryos. However, our understanding regarding human embryonic counterparts remains limited. Here, we demonstrated the presence of human yolk sac-derived lymphoid-biased progenitors (YSLPs) expressing CD34 , IL7R , LTB , and IRF8 at Carnegie stage 10, much earlier than the first HSC emergence. The number and lymphopoietic potential of these progenitors were both significantly higher in the yolk sac than the embryo proper at this early stage. Importantly, single-cell/bulk culture and CITE-seq have elucidated the tendency of YSLP to differentiate into innate lymphoid cells and dendritic cells. Notably, lymphoid progenitors in fetal liver before and after HSC seeding displayed distinct transcriptional features, with the former closely resembling those of YSLPs. Overall, our data identified the origin, potential, and migratory dynamics of innate lymphoid-biased multipotent progenitors in human yolk sac before HSC emergence, providing insights for understanding the stepwise establishment of innate immune system in humans. [Display omitted] • Progenitors with non-NK lymphoid potential exist in human yolk sac before HSC onset • Human yolk sac lymphoid progenitors before HSC emergence show ILC and DC potential • ILC potential before HSC onset is stronger in human yolk sac than in embryo proper • Early fetal liver lymphoid progenitors share characteristics with those from yolk sac Liu et al. demonstrated the presence of yolk sac-derived lymphoid progenitors expressing IL7R and IRF8 well before HSC emergence in human embryos, which showed differentiation bias toward innate lymphoid cells and dendritic cells. They shared transcriptional profiles with lymphoid progenitors in the fetal liver before HSC colonization. [ABSTRACT FROM AUTHOR]

The B cell lineage tree encapsulates the successive phases of B cell differentiation and maturation, transitioning from hematopoietic stem cells to mature, antibody-secreting cells within the immune system. Mathematically, this lineage can be conceptualized as an evolutionary tree, where each node represents a distinct stage in B cell development, and the edges reflect the differentiation pathways. To compare these lineage trees, a rigorous mathematical metric is essential. Analyzing B cell lineage trees mathematically and quantifying changes in lineage attributes over time necessitates a comparison methodology capable of accurately assessing and measuring these changes. Addressing the intricacies of multiple B cell lineage tree comparisons, this study introduces a novel metric that enhances the precision of comparative analysis. This metric is formulated on principles of metric theory and evolutionary biology, quantifying the dissimilarities between lineage trees by measuring branch length distance and weight. By providing a framework for systematically classifying lineage trees, this metric facilitates the development of predictive models that are crucial for the creation of targeted immunotherapy and vaccines. To validate the effectiveness of this new metric, synthetic datasets that mimic the complexity and variability of real B cell lineage structures are employed. We demonstrated the ability of the new metric method to accurately capture the evolutionary nuances of B cell lineages. [ABSTRACT FROM AUTHOR]

Certain immune cells, including neutrophils, macrophages, dendritic cells, B cells, Breg cells, CD4+ T cells, CD8+ T cells, and Treg cells, establish enduring residency within the bone marrow. Their distinctive interactions with hematopoiesis and the bone marrow microenvironment are becoming increasingly recognized alongside their multifaceted immune functions. These cells play a dual role in shaping hematopoiesis. They directly influence the quiescence, self-renewal, and multi-lineage differentiation of hematopoietic stem and progenitor cells through either direct cell-to-cell interactions or the secretion of various factors known for their immunological functions. Additionally, they actively engage with the cellular constituents of the bone marrow niche, particularly mesenchymal stem cells, endothelial cells, osteoblasts, and osteoclasts, to promote their survival and contribute to tissue repair, thereby fostering a supportive environment for hematopoietic stem and progenitor cells. Importantly, these bone marrow immune cells function synergistically, both locally and functionally, rather than in isolation. In summary, immune cells residing in the bone marrow are pivotal components of a sophisticated network of regulating hematopoiesis. [ABSTRACT FROM AUTHOR]

Background: The roles of Lenalidomide (Len) and Daratumumab (Dara) in multiple myeloma treatment are well-established, yet their influences on hematopoietic stem cell harvesting and reconstitution remain disputed. Methods: We conducted a systematic database review to identify cohort studies or RCTs evaluating the effect of the use of Len or Dara on hematopoietic stem cell collection and peripheral blood count recovery in multiple myeloma patients. Effects on hematopoietic collection or reconstitution were estimated by comparing standardized mean differences (SMD) and mean differences (MD), or median differences. Results: Eighteen relevant studies were identified, summarizing mobilization results. For Len, data from 13 studies were summarized, including total CD34+ cell yield, collection failure rate, and time to neutrophil and platelet engraftment. Results indicated that Len exposure led to decreased stem cell collection [SMD=-0.23, 95% CI (-0.34, -0.12)]. However, collection failure (<2×106) could be mitigated by plerixafor [OR=2.14, 95% CI (0.96, 4.77)]. For Dara, two RCTs and three cohort studies were included, showing that Dara exposure resulted in a reduction in total stem cells even with optimized plerixafor mobilization [SMD=-0.75, 95% CI (-1.26, -0.23)], and delayed platelet engraftment recovery [MD=1.20, 95% CI (0.73, 1.66)]. Conclusions: Our meta-analysis offers a comprehensive view of Len and Dara's impacts on hematopoietic stem cell collection and reconstitution in multiple myeloma. Len usage could lead to reduced stem cell collection, counteracted by plerixafor mobilization. Dara usage could result in diminished stem cell collection and delayed platelet engraftment. [ABSTRACT FROM AUTHOR]

Hematopoietic stem cell transplant (HSCT) is now recognized as a standard treatment option for people with HIV (PWH) who develop high-risk hematologic malignancies. However, the involved polypharmacy can lead to complications from drug interactions and toxicities, affecting the efficacy and safety of chemotherapy and antiretroviral therapy (ART). Managing these patients requires a personalized approach, including the careful selection of ART based on previous therapies and potential interactions, alongside risk assessment for infections. This discussion will address the history of HSCT in PWH and management considerations for this group. [ABSTRACT FROM AUTHOR]

Among patients with hematopoietic stem cell transplants, infections, particularly multidrug‐resistant infections, pose a grave threat. In this setting, penicillin allergy labels are both common and harmful. Though the majority of patients who report penicillin allergy can actually tolerate penicillin, penicillin allergy labels are associated with use of alternative antibiotics, which are often more broad spectrum, less effective, and more toxic. In turn, they are associated with more severe infections, multidrug‐resistant infections, Clostridium difficile, and increased mortality. Evaluating penicillin allergy labels can immediately expand access to preferred therapeutic options, which are critical to care in patients with recent hematopoietic stem cell transplants. Point‐of‐care assessment and clinical decision tools now exist to aid the nonallergist in assessment of penicillin allergy. This can aid in expanding use of other beta‐lactam antibiotics and assist in risk‐stratifying patients to determine a testing strategy. In patients with low‐risk reaction histories, direct oral challenges can be employed to efficiently delabel patients across clinical care settings. We advocate for multidisciplinary efforts to evaluate patients with penicillin allergy labels prior to transplantation. [ABSTRACT FROM AUTHOR]

Background: Peripheral blood‐derived hematopoietic stem cells (HSCs) are widely used for various adult stem cell transplants. To obtain sufficient HSCs from healthy volunteer donors during the apheresis process and ensure that the donors are exposed to fewer apheresis‐related side effects, calculation methods have been developed for the prediction of processed blood volume or CD34+ count. However, there is no consensus on a formula to predict the volume of blood to be processed or the number of stem cells to be obtained. Objective: This study aimed to estimate the predicted blood volume and CD34+ cell counts using collection efficiency (CE)‐based formulas and evaluate their accuracy compared to the actual CD34+ cell counts. It also seeks to identify the factors that affect CE. Methods: Data from 397 healthy, unrelated stem cell donors were retrospectively analyzed. An algorithm using four different CE2 metrics (1st quartile, mean, 3rd quartile, and median) was developed to predict the volume of blood to be processed using the Spectra Optia continuous mononuclear cell collection procedure. Results: When employing the mean CE2 algorithm, the results revealed a strong correlation (r =.894, p <.001) between predicted and actual CD34+ values. The study also identified strong associations between pre‐apheresis CD34+, pre‐apheresis leukocyte count, the use of two doses of G‐CSF, and low CE2. Conclusion: These findings suggest that the mean CE2 algorithm could be a potent, straightforward, and accurate tool for predicting CD34+ stem cell counts in healthy allogeneic stem cell donors and potentially optimizing stem cell collection procedures. [ABSTRACT FROM AUTHOR]

We aimed to characterize the population pharmacokinetics (PK) of vedolizumab for acute graft‐versus‐host disease prophylaxis in adults undergoing allogeneic hematopoietic stem cell transplantation (allo‐HSCT) and assess potential clinically relevant covariates. Dosing, patient characteristics, and PK from a phase 1b, open‐label, dose‐finding study of vedolizumab 75 mg initial dose escalated to 300 mg and a phase 3 study of vedolizumab 300 mg in patients receiving allo‐HSCT were analyzed using a two‐compartment population PK model with linear elimination. Covariates included age, race, weight, sex, albumin, lymphocyte count, GvHD type, and concomitant medications. Weight, albumin, and lymphocyte count were time‐varying covariates. Model selection was driven by goodness‐of‐fit criteria, precision of parameter estimates, and visual predictive checks. In 193 patients undergoing allo‐HSCT, vedolizumab PK were well described by a two‐compartment, linear PK model. Using reference covariate values, final parameter estimates (95% confidence intervals [CI]) were: clearance, 0.148 (0.136, 0.162) L/day; central volume of distribution, 3.12 (3.03, 3.21) L; intercompartmental clearance, 0.500 (0.408, 0.612) L/day; and peripheral volume of distribution, 3.95 (3.52, 4.44) L. Weight and albumin were the most important predictors of vedolizumab PK, with clearance decreasing by ≈20% for low body weight/high albumin and increasing by ≈30% for high body weight/low albumin. There was an inverse relationship between vedolizumab clearance and age, but no detectable effect for lymphocyte count or GvHD type. Post hoc analyses did not detect any relationship between vedolizumab PK and concomitant medications. In summary, the covariates studied did not have a clinically meaningful effect on the PK of vedolizumab. [ABSTRACT FROM AUTHOR]

Objectives The optimal dosing regimen of caspofungin in adolescents undergoing allogeneic haematopoietic stem cell transplantation against Candida spp. is unknown. The study aimed to compare body surface area (BSA)-based and fixed dosing regimens through population pharmacokinetic (PPK) analysis and to optimize dosing regimens likely to achieve therapeutic exposures. Methods Opportunistic sampling was used to collect plasma concentrations through a prospective observational pharmacokinetic study. PPK analysis and Monte Carlo simulations (n  = 1000) were performed using NONMEM. Results A total of 86 samples of 30 adolescents (12–17 years old) were best described by a two-compartment pharmacokinetic model. BSA is the only covariate on clearance and central volume of distribution. For Candida glabrata and Candida albicans , a standard dosing regimen could achieve at least a 90% probability of target attainment for the indicator of AUC0–24/MIC90. Dosing regimen simulations identified a BSA cut-off value of 1.3 m2, where a fixed loading dose (LD) is preferred when BSA ≥ 1.3 m2 and a BSA-based LD is preferred when BSA < 1.3 m2. For maintenance dose (MD), however, the BSA-based dose was proposed, regardless of BSA. The current maximum dosing regimen of LD 70 mg/day and MD 70 mg/day could not result in sufficient antifungal exposure for Candida parapsilosis with MIC90 of 1 mg/L. Furthermore, an LD of 70 mg/day and MD of 60 mg/m2/day rendered 90.4% steady-state trough concentration (C trough) over 1 mg/L in the virtual population. Conclusions Our study proposed optimized dosing regimens of caspofungin based on AUC0–24/MIC90 or C trough, which may support further individualized treatment. [ABSTRACT FROM AUTHOR]

Background/Objectives: Integrating the cytotoxic drug busulfan into a high-dose chemotherapy regimen prior to autologous hematopoietic stem cell rescue in patients with high-risk neuroblastoma has improved the survival of children battling this deadly disease. Busulfan-induced toxicities can, however, be severe. Here, we describe the diagnosis and successful treatment of acute pulmonary injury by total-body-weight-adjusted busulfan therapy in two children with high-risk neuroblastoma. Case series: Patient 1 developed life-threatening biphasic acute respiratory failure on days +60 and +100 after busulfan therapy, requiring intubation and invasive mechanical ventilation. Despite intensive anti-inflammatory and immunomodulatory therapy, including systemic corticosteroids, topical inhalation regimens, azithromycin, nintedanib and extracorporal photopheresis, patient 1 required extended intensive care measures and non-invasive respiratory support for a total of 20 months. High-resolution computed tomography showed diffuse intra-alveolar and interstitial patterns. Patient 2 developed partial respiratory failure with insufficient oxygen saturation and dyspnea on day +52 after busulfan therapy. Symptoms were resolved after 6 months of systemic corticosteroids, topical inhalation regimens and azithromycin. High-resolution computed tomography showed atypical pneumonic changes with ground-glass opacities. While both patients fully recovered without evidence of pulmonary fibrosis, cancer therapy had to be paused and then modified until full recovery from busulfan-induced lung injury. Conclusions: Busulfan-induced lung injury requires prompt diagnosis and intervention. Symptoms and signs are nonspecific and difficult to differentiate from other causes. Therapeutic busulfan drug level monitoring and the identification of patients at risk for drug overdosing through promoter polymorphisms in the glutathione S-transferase alpha 1 gene encoding the main enzyme in busulfan metabolism are expected to reduce the risk of busulfan-induced toxicities. [ABSTRACT FROM AUTHOR]

Background/Objectives: Changes in muscle mass and bone density are common in multiple myeloma (MM) patients. Dual-energy X-ray absorptiometry (DXA) offers precise, non-invasive insights into a patient's physical condition before autologous stem cell transplantation (autoHSCT). This study examines how pre-transplant body composition impacts treatment outcomes and early complications in MM patients undergoing autoHSCT. Methods: This study is a single-center, retrospective analysis of patients with MM who were treated with first or second autoHSCT and underwent DXA pre-transplant between 11 August 2019 and 12 June 2024. Results: We conducted a study of pre-transplant body composition in 127 patients with MM. Among them, 108 (85%) qualified for first autoHSCT, while 19 (15%) qualified for a second. The median age of the patients was 64 years (range 50–73). In the Cox proportional hazards regression conducted in the group of women, Total Body %Fat was a statistically significant predictor for progression-free survival (PFS) (HR = 0.07, 95% CI = 0.01,0.6, p = 0.0157). In the Mann–Whitney U test conducted on males, Lean Mass/Height2 and Appen. Lean Height2 were statistically significant predictors of early infections after autoHSCT (Z = 1.98, p = 0.0473 and Z = 2.32, p = 0.0204, respectively). In males, Fat Mass/Height2 was a significant predictor of non-infectious toxicity related to treatment (Z = −1.98, p = 0.0476). Conclusions: In women, higher levels of adipose tissue initially appear to exert a protective effect; however, this benefit diminishes over time, with greater fat mass eventually correlating with an increased risk of disease progression. In men, muscle mass has been identified as a significant predictor of early infection risk post-autoHSCT. Furthermore, our findings indicate that an increased amount of adipose tissue in men is statistically associated with a higher risk of non-infectious treatment-related toxicity. These conclusions highlight the critical need for further investigation into the role of body composition. [ABSTRACT FROM AUTHOR]

Hematopoietic stem cells (HSCs) reside in specific microenvironments that facilitate their regulation through both internal mechanisms and external cues. Bone marrow endothelial cells (BMECs), which are found in one of these microenvironments, play a vital role in controlling the self-renewal and differentiation of HSCs during hematological stress. We previously showed that 27-hydroxycholesterol (27HC) administration of exogenous 27HC negatively affected the population of HSCs and progenitor cells by increasing the reactive oxygen species levels in the bone marrow. However, the effect of 27HC on BMECs is unclear. To determine the function of 27HC in BMECs, we employed magnetic-activated cell sorting to isolate CD31+ BMECs and CD31− cells. We demonstrated the effect of 27HC on CD31+ BMECs and HSCs. Treatment with exogenous 27HC led to a decrease in the number of BMECs and reduced the expression of adhesion molecules that are crucial for maintaining HSCs. Our results demonstrate that BMECs are sensitively affected by 27HC and are crucial for HSC survival. [ABSTRACT FROM AUTHOR]

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potential cure for myelodysplastic neoplasms (MDSs) and other hematologic malignancies. This study investigates post-transplantation genetic evolution and telomere dynamics in hematopoietic cells, with a focus on clonal hematopoiesis (CH). We conducted a longitudinal analysis of 21 MDS patients who underwent allo-HSCT between September 2009 and February 2015. Genetic profiles of hematopoietic cells from both recipients and donors were compared at equivalent pre- and post-transplantation time points. Targeted sequencing identified CH-associated mutations, and real-time quantitative PCR measured telomere length. Furthermore, we compared CH incidence between recipients and age-matched controls from the GENIE cohort from routine health checkups. Post-allo-HSCT, 38% of recipients developed somatic mutations not detected before transplantation, indicating de novo CH originating from donor cells. Compared to age-matched healthy controls, recipients showed a significantly higher incidence of CH, suggesting increased susceptibility to genetic changes post-transplant. Telomere length analysis also revealed accelerated shortening in transplanted cells, highlighting the heightened stress and proliferation demands in the new microenvironment. Our findings reveal a notable incidence of donor-derived CH in allo-HSCT recipients, alongside significant telomere attrition. This suggests the potential influence of the marrow microenvironment on genetic and molecular changes in hematopoietic cells. [ABSTRACT FROM AUTHOR]

Simple Summary: Daratumumab (DARA) plus bortezomib, thalidomide, and dexamethasone (D-VTd) represent the standard of induction care in Europe for autologous stem cell transplantation (auto-SCT)-eligible, newly diagnosed multiple myeloma (NDMM) patients. This study aimed to investigate the possible impact of D-VTd induction therapy on hematopoietic engraftment after auto-SCT. Our findings indicate that patients treated with D-VTd experienced longer neutrophil and platelet engraftment times than those treated with VTd. Additionally, D-VTd treatment was associated with a higher incidence of febrile neutropenia and grade 2 or higher diarrhea. However, no significant differences were observed in the median number of days to discharge. The conclusion we can draw from our real-life study is that a four-drug induction therapy containing DARA does not impact transplant safety outcomes. Background: This real-life study aimed to investigate the possible impact of D-VTd induction therapy on hematopoietic engraftment after autologous stem cell transplantation (auto-SCT). Methods: Sixty consecutive NDMM patients received four cycles of induction therapy with D-VTd. The conditioning regimen consisted of melphalan 200 mg/m2. These patients were compared with a historical control group of 80 patients who received four cycles of VTd as induction therapy. Results: The median days to reach neutrophil and platelet engraftment significantly differed between patients treated with D-VTd (11 and 13 days, respectively) and VTd (10 and 12 days). Univariate Cox analyses show that patients treated with D-VTd had a hazard ratio of neutrophil engraftment that was 42% significantly lower than those in the VTd arm (HR: 0.58, p = 0.002), and a multivariate model confirmed this result. Patients treated with D-VTd developed FN more frequently. Univariate and multivariate logistic regressions revealed an association between D-VTd and FN. Delayed engraftment did not correlate with more extended hospitalization. No patients died in the first six months after transplantation. Conclusions: Our real-life study showed that a four-drug induction therapy containing DARA does not impact transplant safety outcomes. [ABSTRACT FROM AUTHOR]

Aged hematopoietic stem cells (HSCs) show reduced reconstitution potential, limiting their use in transplantation settings in the clinic. We demonstrate here that exposure of aged HSCs ex vivo to a pH of 6.9 instead of the commonly used pH of 7.4 results in enhanced HSCs potential that is consistent with rejuvenation, including attenuation of the myeloid bias of aged HSC and restoration of a youthful frequency of epigenetic polarity. Rejuvenation of aged HSCs by pH 6.9 is, at least in part, due to alterations in the polyamine/methionine pathway within pH 6.9 HSCs, and consequently, attenuation of the production of spermidine also attenuated aging of HSCs. Exposure of aged HSCs to pH 6.9, or pharmacological targeting of the polyamine pathway, might thus extend the use of HSCs from aged donors for therapeutic applications. [ABSTRACT FROM AUTHOR]