Ex Vivo Evaluation of the Function of Hematopoietic Stem Cells in Toxicology of Metals.

A variety of metals, e.g., lead (Pb), cadmium (Cd), and lithium (Li), are in the environment and are toxic to humans. Hematopoietic stem cells (HSCs) reside at the apex of hematopoiesis and are capable of generating all kinds of blood cells and self-renew to maintain the HSC pool. HSCs are sensitive to environmental stimuli. Metals may influence the function of HSCs by directly acting on HSCs or indirectly by affecting the surrounding microenvironment for HSCs in the bone marrow (BM) or niche, including cellular and extracellular components. Investigating the impact of direct and/or indirect actions of metals on HSCs contributes to the understanding of immunological and hematopoietic toxicology of metals. Treatment of HSCs with metals ex vivo, and the ensuing HSC transplantation assays, are useful for evaluating the impacts of the direct actions of metals on the function of HSCs. Investigating the mechanisms involved, given the rarity of HSCs, methods that require large numbers of cells are not suitable for signal screening; however, flow cytometry is a useful tool for signal screening HSCs. After targeting signaling pathways, interventions ex vivo and HSCs transplantation are required to confirm the roles of the signaling pathways in regulating the function of HSCs exposed to metals. Here, we describe protocols to evaluate the mechanisms of direct and indirect action of metals on HSCs. © 2024 Wiley Periodicals LLC. Basic Protocol 1: Identify the impact of a metal on the competence of HSCs Basic Protocol 2: Identify the impact of a metal on the lineage bias of HSC differentiation Basic Protocol 3: Screen the potential signaling molecules in HSCs during metal exposure Alternate Protocol 1: Ex vivo treatment with a metal on purified HSCs Alternate Protocol 2: Ex vivo intervention of the signaling pathway regulating the function of HSCs during metal exposure.

CNS-wide repopulation by hematopoietic-derived microglia-like cells corrects progranulin deficiency in mice.

Hematopoietic stem cell transplantation can deliver therapeutic proteins to the central nervous system (CNS) through transplant-derived microglia-like cells. However, current conditioning approaches result in low and slow engraftment of transplanted cells in the CNS. Here we optimized a brain conditioning regimen that leads to rapid, robust, and persistent microglia replacement without adverse effects on neurobehavior or hematopoiesis. This regimen combines busulfan myeloablation and six days of Colony-stimulating factor 1 receptor inhibitor PLX3397. Single-cell analyses revealed unappreciated heterogeneity of microglia-like cells with most cells expressing genes characteristic of homeostatic microglia, brain-border-associated macrophages, and unique markers. Cytokine analysis in the CNS showed transient inductions of myeloproliferative and chemoattractant cytokines that help repopulate the microglia niche. Bone marrow transplant of progranulin-deficient mice conditioned with busulfan and PLX3397 restored progranulin in the brain and eyes and normalized brain lipofuscin storage, proteostasis, and lipid metabolism. This study advances our understanding of CNS repopulation by hematopoietic-derived cells and demonstrates its therapeutic potential for treating progranulin-dependent neurodegeneration.

Hematopoietic stem and progenitor cell membrane-coated vesicles for bone marrow-targeted leukaemia drug delivery.

Leukemia is a kind of hematological malignancy originating from bone marrow, which provides essential signals for initiation, progression, and recurrence of leukemia. However, how to specifically deliver drugs to the bone marrow remains elusive. Here, we develop biomimetic vesicles by infusing hematopoietic stem and progenitor cell (HSPC) membrane with liposomes (HSPC liposomes), which migrate to the bone marrow of leukemic mice via hyaluronic acid-CD44 axis. Moreover, the biomimetic vesicles exhibit superior binding affinity to leukemia cells through intercellular cell adhesion molecule-1 (ICAM-1)/integrin ß2 (ITGB2) interaction. Further experiments validate that the vesicles carrying chemotherapy drug cytarabine (Ara-C@HSPC-Lipo) markedly inhibit proliferation, induce apoptosis and differentiation of leukemia cells, and decrease number of leukemia stem cells. Mechanically, RNA-seq reveals that Ara-C@HSPC-Lipo treatment induces apoptosis and differentiation and inhibits the oncogenic pathways. Finally, we verify that HSPC liposomes are safe in mice. This study provides a method for targeting bone marrow and treating leukemia.

Targeting IGF2BP1 alleviated benzene hematotoxicity by reprogramming BCAA metabolism and fatty acid oxidation.

Benzene is the main environmental pollutant and risk factor of childhood leukemia and chronic benzene poisoning. Benzene exposure leads to hematopoietic stem and progenitor cell (HSPC) dysfunction and abnormal blood cell counts. However, the key regulatory targets and mechanisms of benzene hematotoxicity are unclear. In this study, we constructed a benzene-induced hematopoietic damage mouse model to explore the underlying mechanisms. We identified that Insulin like growth factor 2 mRNA binding protein 1 (IGF2BP1) was significantly reduced in benzene-exposed mice. Moreover, targeting IGF2BP1 effectively mitigated damages to hematopoietic function and hematopoietic molecule expression caused by benzene in mice. On the mechanics, by metabolomics and transcriptomics, we discovered that branched-chain amino acid (BCAA) metabolism and fatty acid oxidation were key metabolic pathways, and Branched-chain amino acid transaminase 1 (BCAT1) and Carnitine palmitoyltransferase 1a (CPT1A) were critical metabolic enzymes involved in IGF2BP1-mediated hematopoietic injury process. The expression of the above molecules in the benzene exposure population was also examined and consistent with animal experiments. In conclusion, targeting IGF2BP1 alleviated hematopoietic injury caused by benzene exposure, possibly due to the reprogramming of BCAA metabolism and fatty acid oxidation via BCAT1 and CPT1A metabolic enzymes. IGF2BP1 is a potential regulatory and therapeutic target for benzene hematotoxicity.

Endogenous stem cell mobilization and localized immunosuppression synergistically ameliorate DSS-induced Colitis in mice.

BACKGROUND: Stem cell therapy is a promising alternative for inflammatory diseases and tissue injury treatment. Exogenous delivery of mesenchymal stem cells is associated with instant blood-mediated inflammatory reactions, mechanical stress during administration, and replicative senescence or change in phenotype during long-term culture in vitro. In this study, we aimed to mobilize endogenous hematopoietic stem cells (HSCs) using AMD-3100 and provide local immune suppression using FK506, an immunosuppressive drug, for the treatment of inflammatory bowel diseases. METHODS: Reactive oxygen species (ROS)-responsive FK506-loaded thioketal microspheres were prepared by emulsification solvent-evaporation method. Thioketal vehicle based FK506 microspheres and AMD3100 were co-administered into male C57BL6/J mice with dextran sulfate sodium (DSS) induced colitis. The effect of FK506-loaded thioketal microspheres in colitis mice were evaluated using disease severity index, myeloperoxidase activity, histology, flow cytometry, and gene expression by qRT-PCR. RESULTS: The delivery of AMD-3100 enhanced mobilization of HSCs from the bone marrow into the inflamed colon of mice. Furthermore, targeted oral delivery of FK506 in an inflamed colon inhibited the immune activation in the colon. In the DSS-induced colitis mouse model, the combination of AMD-3100 and FK506-loaded thioketal microspheres ameliorated the disease, decreased immune cell infiltration and activation, and improved body weight, colon length, and epithelial healing process. CONCLUSION: This study shows that the significant increase in the percentage of mobilized hematopoietic stem cells in the combination therapy of AMD and oral FK506 microspheres may contribute to a synergistic therapeutic effect. Thus, low-dose local delivery of FK506 combined with AMD3100 could be a promising alternative treatment for inflammatory bowel diseases.

Single-cell transcriptional profile of CD34+ hematopoietic progenitor cells from del(5q) myelodysplastic syndromes and impact of lenalidomide.

While myelodysplastic syndromes with del(5q) (del(5q) MDS) comprises a well-defined hematological subgroup, the molecular basis underlying its origin remains unknown. Using single cell RNA-seq (scRNA-seq) on CD34+ progenitors from del(5q) MDS patients, we have identified cells harboring the deletion, characterizing the transcriptional impact of this genetic insult on disease pathogenesis and treatment response. Interestingly, both del(5q) and non-del(5q) cells present similar transcriptional lesions, indicating that all cells, and not only those harboring the deletion, may contribute to aberrant hematopoietic differentiation. However, gene regulatory network (GRN) analyses reveal a group of regulons showing aberrant activity that could trigger altered hematopoiesis exclusively in del(5q) cells, pointing to a more prominent role of these cells in disease phenotype. In del(5q) MDS patients achieving hematological response upon lenalidomide treatment, the drug reverts several transcriptional alterations in both del(5q) and non-del(5q) cells, but other lesions remain, which may be responsible for potential future relapses. Moreover, lack of hematological response is associated with the inability of lenalidomide to reverse transcriptional alterations. Collectively, this study reveals transcriptional alterations that could contribute to the pathogenesis and treatment response of del(5q) MDS.

BF170 hydrochloride enhances the emergence of hematopoietic stem and progenitor cells.

Generation of hematopoietic stem and progenitor cells (HSPCs) ex vivo and in vivo, especially the generation of safe therapeutic HSPCs, still remains inefficient. In this study, we have identified compound BF170 hydrochloride as a previously unreported pro-hematopoiesis molecule, using the differentiation assays of primary zebrafish blastomere cell culture and mouse embryoid bodies (EBs), and we demonstrate that BF170 hydrochloride promoted definitive hematopoiesis in vivo. During zebrafish definitive hematopoiesis, BF170 hydrochloride increases blood flow, expands hemogenic endothelium (HE) cells and promotes HSPC emergence. Mechanistically, the primary cilia-Ca2+-Notch/NO signaling pathway, which is downstream of the blood flow, mediated the effects of BF170 hydrochloride on HSPC induction in vivo. Our findings, for the first time, reveal that BF170 hydrochloride is a compound that enhances HSPC induction and may be applied to the ex vivo expansion of HSPCs.

Long-term combination therapy with metformin and oxymetholone in a Fanconi anemia mouse model.

Fanconi anemia (FA) is a disease caused by defective deoxyribonucleic acid (DNA) repair that manifests as bone marrow failure, cancer predisposition, and developmental defects. We previously reported that monotherapy with either metformin (MET) or oxymetholone (OXM) improved peripheral blood (PB) counts and the number and functionality of bone marrow hematopoietic stem progenitor cells (HSPCs) number in Fancd2-/- mice. To evaluate whether the combination treatment of these drugs has a synergistic effect to prevent bone marrow failure in FA, we treated cohorts of Fancd2-/- mice and wildtype controls with either MET alone, OXM alone, MET+OXM, or placebo diet from age 3 weeks to 18 months. The OXM treated animals showed modest improvements in blood parameters including platelet count (p = .01) and hemoglobin levels (p < .05). In addition, the percentage of quiescent hematopoietic stem cell (HSC) (LSK [Lin-Sca+c-Kit+]) was significantly increased (p = .001) by long-term treatment with MET alone. The combination of metformin and oxymetholone did not result in a significant synergistic effect in any hematopoietic parameter. Gene expression analysis of liver tissue from these animals showed that some of the expression changes caused by Fancd2 deletion were partially normalized by metformin treatment. Importantly, no adverse effects of the individual or combination therapies were observed, despite the long-term administration. We conclude that androgen therapy is not a contraindication to concurrent metformin administration in clinical trials. HIGHLIGHTS: Long-term coadministration of metformin in combination with oxymetholone is well tolerated by Fancd2-/- mice. Hematopoietic stem cell quiescence in mutant mice was enhanced by treatment with metformin alone. Metformin treatment caused a partial normalization of gene expression in the livers of mutant mice.

Targeting MCL1-driven anti-apoptotic pathways overcomes blast progression after hypomethylating agent failure in chronic myelomonocytic leukemia.

RAS pathway mutations, which are present in 30% of patients with chronic myelomonocytic leukemia (CMML) at diagnosis, confer a high risk of resistance to and progression after hypomethylating agent (HMA) therapy, the current standard of care for the disease. Here, using single-cell, multi-omics technologies, we seek to dissect the biological mechanisms underlying the initiation and progression of RAS pathway-mutated CMML. We identify that RAS pathway mutations induce transcriptional reprogramming of hematopoietic stem and progenitor cells (HSPCs) and downstream monocytic populations in response to cell-intrinsic and -extrinsic inflammatory signaling that also impair the functions of immune cells. HSPCs expand at disease progression after therapy with HMA or the BCL2 inhibitor venetoclax and rely on the NF-κB pathway effector MCL1 to maintain survival. Our study has implications for the development of therapies to improve the survival of patients with RAS pathway-mutated CMML.

Selective haematological cancer eradication with preserved haematopoiesis.

Haematopoietic stem cell (HSC) transplantation (HSCT) is the only curative treatment for a broad range of haematological malignancies, but the standard of care relies on untargeted chemotherapies and limited possibilities to treat malignant cells after HSCT without affecting the transplanted healthy cells1. Antigen-specific cell-depleting therapies hold the promise of much more targeted elimination of diseased cells, as witnessed in the past decade by the revolution of clinical practice for B cell malignancies2. However, target selection is complex and limited to antigens expressed on subsets of haematopoietic cells, resulting in a fragmented therapy landscape with high development costs2-5. Here we demonstrate that an antibody-drug conjugate (ADC) targeting the pan-haematopoietic marker CD45 enables the antigen-specific depletion of the entire haematopoietic system, including HSCs. Pairing this ADC with the transplantation of human HSCs engineered to be shielded from the CD45-targeting ADC enables the selective eradication of leukaemic cells with preserved haematopoiesis. The combination of CD45-targeting ADCs and engineered HSCs creates an almost universal strategy to replace a diseased haematopoietic system, irrespective of disease aetiology or originating cell type. We propose that this approach could have broad implications beyond haematological malignancies.

Cigarette smoke impairs the hematopoietic supportive property of mesenchymal stem cells via the production of reactive oxygen species and NLRP3 activation.

BACKGROUND: Mesenchymal stem cells (MSCs) play important roles in tissue homeostasis by providing a supportive microenvironmental niche for the hematopoietic system. Cigarette smoking induces systemic abnormalities, including an impeded recovery process after hematopoietic stem cell transplantation. However, the role of cigarette smoking-mediated alterations in MSC niche function have not been investigated. METHODS: In the present study, we investigated whether exposure to cigarette smoking extract (CSE) disrupts the hematopoietic niche function of MSCs, and pathways impacted. To investigate the effects on bone marrow (BM)-derived MSCs and support of hematopoietic stem and progenitor cells (HSPCs), mice were repeatedly infused with the CSE named 3R4F, and hematopoietic stem and progenitor cells (HSPCs) supporting function was determined. The impact of 3R4F on MSCs at cellular level were screened by bulk-RNA sequencing and subsequently validated through qRT-PCR. Specific inhibitors were treated to verify the ROS or NLRP3-specific effects, and the cells were then transplanted into the animal model or subjected to coculture with HSPCs. RESULTS: Both direct ex vivo and systemic in vivo MSC exposure to 3R4F resulted in impaired engraftment in a humanized mouse model. Furthermore, transcriptomic profile analysis showed significantly upregulated signaling pathways related to reactive oxygen species (ROS), inflammation, and aging in 3R4F-treated MSCs. Notably, ingenuity pathway analysis revealed the activation of NLRP3 inflammasome signaling pathway in 3R4F-treated MSCs, and pretreatment with the NLRP3 inhibitor MCC950 rescued the HSPC-supporting ability of 3R4F-treated MSCs. CONCLUSION: In conclusion, these findings indicate that exposure to CSE reduces HSPCs supportive function of MSCs by inducing robust ROS production and subsequent NLRP3 activation.

Establishment of human hematopoietic organoids for evaluation of hematopoietic injury and regeneration effect.

BACKGROUND: Human hematopoietic organoids have a wide application value for modeling human bone marrow diseases, such as acute hematopoietic radiation injury. However, the manufacturing of human hematopoietic organoids is an unaddressed challenge because of the complexity of hematopoietic tissues. METHODS: To manufacture hematopoietic organoids, we obtained CD34+ hematopoietic stem and progenitor cells (HSPCs) from human embryonic stem cells (hESCs) using stepwise induction and immunomagnetic bead-sorting. We then mixed these CD34+ HSPCs with niche-related cells in Gelatin-methacryloyl (GelMA) to form a three-dimensional (3D) hematopoietic organoid. Additionally, we investigated the effects of radiation damage and response to granulocyte colony-stimulating factor (G-CSF) in hematopoietic organoids. RESULTS: The GelMA hydrogel maintained the undifferentiated state of hESCs-derived HSPCs by reducing intracellular reactive oxygen species (ROS) levels. The established hematopoietic organoids in GelMA with niche-related cells were composed of HSPCs and multilineage blood cells and demonstrated the adherence of hematopoietic cells to niche cells. Notably, these hematopoietic organoids exhibited radiation-induced hematopoietic cell injury effect, including increased intracellular ROS levels, γ-H2AX positive cell percentages, and hematopoietic cell apoptosis percentages. Moreover, G-CSF supplementation in the culture medium significantly improved the survival of HSPCs and enhanced myeloid cell regeneration in these hematopoietic organoids after radiation. CONCLUSIONS: These findings substantiate the successful manufacture of a preliminary 3D hematopoietic organoid from hESCs-derived HSPCs, which was utilized for modeling hematopoietic radiation injury and assessing the radiation-mitigating effects of G-CSF in vitro. Our study provides opportunities to further aid in the standard and scalable production of hematopoietic organoids for disease modeling and drug testing.

Thrombopoietin mimetic stimulates bone marrow vascular and stromal niches to mitigate acute radiation syndrome.

BACKGROUND: Acute radiation syndrome (ARS) manifests after exposure to high doses of radiation in the instances of radiologic accidents or incidents. Facilitating regeneration of the bone marrow (BM), namely the hematopoietic stem and progenitor cells (HSPCs), is key in mitigating ARS and multi-organ failure. JNJ-26366821, a PEGylated thrombopoietin mimetic (TPOm) peptide, has been shown as an effective medical countermeasure (MCM) to treat hematopoietic-ARS (H-ARS) in mice. However, the activity of TPOm on regulating BM vascular and stromal niches to support HSPC regeneration has yet to be elucidated. METHODS: C57BL/6J mice (9-14 weeks old) received sublethal or lethal total body irradiation (TBI), a model for H-ARS, by 137Cs or X-rays. At 24 h post-irradiation, mice were subcutaneously injected with a single dose of TPOm (0.3 mg/kg or 1.0 mg/kg) or PBS (vehicle). At homeostasis and on days 4, 7, 10, 14, 18, and 21 post-TBI with and without TPOm treatment, BM was harvested for histology, BM flow cytometry of HSPCs, endothelial (EC) and mesenchymal stromal cells (MSC), and whole-mount confocal microscopy. For survival, irradiated mice were monitored and weighed for 30 days. Lastly, BM triple negative cells (TNC; CD45-, TER-119-, CD31-) were sorted for single-cell RNA-sequencing to examine transcriptomics after TBI with or without TPOm treatment. RESULTS: At homeostasis, TPOm expanded the number of circulating platelets and HSPCs, ECs, and MSCs in the BM. Following sublethal TBI, TPOm improved BM architecture and promoted recovery of HSPCs, ECs, and MSCs. Furthermore, TPOm elevated VEGF-C levels in normal and irradiated mice. Following lethal irradiation, mice improved body weight recovery and 30-day survival when treated with TPOm after 137Cs and X-ray exposure. Additionally, TPOm reduced vascular dilation and permeability. Finally, single-cell RNA-seq analysis indicated that TPOm increased the expression of collagens in MSCs to enhance their interaction with other progenitors in BM and upregulated the regeneration pathway in MSCs. CONCLUSIONS: TPOm interacts with BM vascular and stromal niches to locally support hematopoietic reconstitution and systemically improve survival in mice after TBI. Therefore, this work warrants the development of TPOm as a potent radiation MCM for the treatment of ARS.

Loss of Dnmt3a increases self-renewal and resistance to pegIFN-α in JAK2-V617F-positive myeloproliferative neoplasms.

ABSTRACT: Pegylated interferon alfa (pegIFN-α) can induce molecular remissions in patients with JAK2-V617F-positive myeloproliferative neoplasms (MPNs) by targeting long-term hematopoietic stem cells (LT-HSCs). Additional somatic mutations in genes regulating LT-HSC self-renewal, such as DNMT3A, have been reported to have poorer responses to pegIFN-α. We investigated whether DNMT3A loss leads to alterations in JAK2-V617F LT-HSC functions conferring resistance to pegIFN-α treatment in a mouse model of MPN and in hematopoietic progenitors from patients with MPN. Long-term treatment with pegIFN-α normalized blood parameters and reduced splenomegaly and JAK2-V617F chimerism in single-mutant JAK2-V617F (VF) mice. However, pegIFN-α in VF;Dnmt3aΔ/Δ (VF;DmΔ/Δ) mice worsened splenomegaly and failed to reduce JAK2-V617F chimerism. Furthermore, LT-HSCs from VF;DmΔ/Δ mice compared with VF were less prone to accumulate DNA damage and exit dormancy upon pegIFN-α treatment. RNA sequencing showed that IFN-α induced stronger upregulation of inflammatory pathways in LT-HSCs from VF;DmΔ/Δ than from VF mice, indicating that the resistance of VF;DmΔ/Δ LT-HSC was not due to failure in IFN-α signaling. Transplantations of bone marrow from pegIFN-α-treated VF;DmΔ/Δ mice gave rise to more aggressive disease in secondary and tertiary recipients. Liquid cultures of hematopoietic progenitors from patients with MPN with JAK2-V617F and DNMT3A mutation showed increased percentages of JAK2-V617F-positive colonies upon IFN-α exposure, whereas in patients with JAK2-V617F alone, the percentages of JAK2-V617F-positive colonies decreased or remained unchanged. PegIFN-α combined with 5-azacytidine only partially overcame resistance in VF;DmΔ/Δ mice. However, this combination strongly decreased the JAK2-mutant allele burden in mice carrying VF mutation only, showing potential to inflict substantial damage preferentially to the JAK2-mutant clone.

Anti-CD45 PBD-based antibody-drug conjugates are effective targeted conditioning agents for gene therapy and stem cell transplant.

Stem cell gene therapy and hematopoietic stem cell transplantation (SCT) require conditioning to ablate the recipient's hematopoietic stem cells (HSCs) and create a niche for gene-corrected/donor HSCs. Conventional conditioning agents are non-specific, leading to off-target toxicities and resulting in significant morbidity and mortality. We developed tissue-specific anti-human CD45 antibody-drug conjugates (ADCs), using rat IgG2b anti-human CD45 antibody clones YTH24.5 and YTH54.12, conjugated to cytotoxic pyrrolobenzodiazepine (PBD) dimer payloads with cleavable (SG3249) or non-cleavable (SG3376) linkers. In vitro, these ADCs internalized to lysosomes for drug release, resulting in potent and specific killing of human CD45+ cells. In humanized NSG mice, the ADCs completely ablated human HSCs without toxicity to non-hematopoietic tissues, enabling successful engraftment of gene-modified autologous and allogeneic human HSCs. The ADCs also delayed leukemia onset and improved survival in CD45+ tumor models. These data provide proof of concept that conditioning with anti-human CD45-PBD ADCs allows engraftment of donor/gene-corrected HSCs with minimal toxicity to non-hematopoietic tissues. Our anti-CD45-PBDs or similar agents could potentially shift the paradigm in transplantation medicine that intensive chemo/radiotherapy is required for HSC engraftment after gene therapy and allogeneic SCT. Targeted conditioning both improve the safety and minimize late effects of these procedures, which would greatly increase their applicability.

Impacts of cationic lipid-DNA complexes on immune cells and hematopoietic cells in vivo.

The inability to systemic administration of nanoparticles, particularly cationic nanoparticles, has been a significant barrier to their clinical translation due to toxicity concerns. Understanding the in vivo behavior of cationic lipids is crucial, given their potential impact on critical biological components such as immune cells and hematopoietic stem cells (HSC). These cells are essential for maintaining the body's homeostasis, and their interaction with cationic lipids is a key factor in determining the safety and efficacy of these nanoparticles. In this study, we focused on the cytotoxic effects of cationic lipid/DNA complexes (CLN/DNA). Significantly, we observed that the most substantial cytotoxic effects, including a marked increase in numbers of long-term hematopoietic stem cells (LT-HSC), occurred 24 h post-CLN/DNA treatment in mice. Furthermore, we found that CLN/DNA-induced HSC expansion in bone marrow (BM) led to a notable decrease in the ability to reestablish blood cell production. Our study provides crucial insights into the interaction between cationic lipids and vital cellular components of the immune and hematopoietic systems.

Neutrophil Granulopoiesis Optimized Through Ex Vivo Expansion of Hematopoietic Progenitors in Engineered 3D Gelatin Methacrylate Hydrogels.

Neutrophils are the first line of defense of the innate immune system. In response to methicillin-resistant Staphylococcus aureus infection in the skin, hematopoietic stem, and progenitor cells (HSPCs) traffic to wounds and undergo extramedullary granulopoiesis, producing neutrophils necessary to resolve the infection. This prompted the engineering of a gelatin methacrylate (GelMA) hydrogel that encapsulates HSPCs within a matrix amenable to subcutaneous delivery. The authors study the influence of hydrogel mechanical properties to produce an artificial niche for granulocyte-monocyte progenitors (GMPs) to efficiently expand into functional neutrophils that can populate infected tissue. Lin-cKIT+ HSPCs, harvested from fluorescent neutrophil reporter mice, are encapsulated in GelMA hydrogels of varying polymer concentration and UV-crosslinked to produce HSPC-laden gels of specific stiffness and mesh sizes. Softer 5% GelMA gels yield the most viable progenitors and effective cell-matrix interactions. Compared to suspension culture, 5% GelMA results in a twofold expansion of mature neutrophils that retain antimicrobial functions including degranulation, phagocytosis, and ROS production. When implanted dermally in C57BL/6J mice, luciferase-expressing neutrophils expanded in GelMA hydrogels are visualized at the site of implantation for over 5 days. They demonstrate the potential of GelMA hydrogels for delivering HSPCs directly to the site of skin infection to promote local granulopoiesis.

Impact of lower concentrations of dimethyl sulfoxide on cryopreservation of autologous hematopoietic stem cells: a systematic review and meta-analysis of controlled clinical studies.

BACKGROUND AIMS: Cryopreservation of hematopoietic stem cells (HSCs) is crucial for autologous transplantation, cord blood banking and other special circumstances. Dimethyl sulfoxide (DMSO) is used most commonly for cryopreserving HSC products but can cause infusional toxicities and affect cell viability and engraftment after transplant. A systematic review of controlled studies using lower concentrations of DMSO to cryopreserve HSC products in clinical transplant studies is needed to determine the effect of reducing DMSO concentrations on post-thaw cell viability, initial engraftment and adverse effects on patient health. METHODS: All studies identified in our systematic search (to July 11, 2023) examining the use of cryopreserved peripheral blood stem cells (PBSCs) for autologous stem cell transplantation (AHCT) were included. Meta-analysis was performed to determine how varying the concentration of DMSO during cryopreservation effects post-thaw cell viability, initial engraftment and adverse effects on patient health. RESULTS: A total of 1547 studies were identified in our systematic search, with seven published articles meeting eligibility for inclusion in meta-analysis. All patients underwent AHCT using (PBSCs) to treat hematologic malignancies. The viability of CD34+ cells post thaw was greater when cryopreserved with 5% DMSO compared with 10% DMSO, with lower rates of adverse side effects in patients. DMSO concentration had minimal impact on rates of initial engraftment. Significant heterogeneity in outcome reporting was observed and the potential for bias was identified in all studies. CONCLUSIONS: Reducing the concentration of DMSO from 10% to 5% during cryopreservation of autologous PBSCs may improve cell viability and reduce DMSO-associated adverse effects in patients undergoing AHCT. Data from more studies with similar patients and standard outcome reporting are needed to increase confidence in our initial observations. PROTOCOL REGISTRATION: PROSPERO; registration number CRD42023476809 registered November 8, 2023.