三浦 康生

Abstract Exposure to ionizing radiation can induce harmful biological effects on the human body, particularly in cases of high-dose γ-irradiation affecting the gastrointestinal tract, bone marrow, skin and lung. Such exposures lead to lethal outcomes as individuals experience a breakdown in their immune system’s ability to defend against pathogens, predisposing them to sepsis-induced multiple organ failures. Mesenchymal stromal/stem cells (MSCs) possess diverse biological characteristics, including immunomodulation, anti-inflammation and tissue regeneration. Off-the-shelf culture-expanded human bone marrow- or adipose tissue-derived MSCs are clinically available to treat graft-versus-host disease following hematopoietic cell transplantation and perianal fistulas in Crohn’s disease in Japan. While preclinical studies showcase encouraging outcomes in radiation-induced injuries, the effectiveness of MSC transplantation in addressing acute radiation syndrome affecting organs in irradiated individuals is limited. Recent studies have highlighted MSC-releasing extracellular vesicles as nanoparticle substances responsible for outlining the mechanism of action and have identified various components, including proteins and microRNA, that serve as functional molecules. MSC-releasing extracellular vesicle-based therapy emerges as a promising avenue, offering a potential solution to the challenges posed by radiation-induced injuries. However, further investigation is required, especially regarding whether MSC-releasing extracellular vesicles have regenerative effects on tissue-resident stem cells. These unresolved issues represent key aspects that need to be addressed to optimize the therapeutic potential of cell-based and extracellular vesicle-based MSC therapies for interventions in the context of radiation-induced injuries.

Extracellular vesicles (EVs) serve as an intrinsic system for delivering functional molecules within our body, playing significant roles in diverse physiological phenomena and diseases. Both native and engineered EVs are currently the subject of extensive research as promising therapeutics and drug delivery systems, primarily due to their remarkable attributes, such as targeting capabilities, biocompatibility, and low immunogenicity and mutagenicity. Nevertheless, their clinical application is still a long way off owing to multiple limitations. In this context, the Science Board of the Pharmaceuticals and Medical Devices Agency (PMDA) of Japan has conducted a comprehensive assessment to identify the current issues related to the quality and safety of EV-based therapeutic products. Furthermore, we have presented several examples of the state-of-the-art methodologies employed in EV manufacturing, along with guidelines for critical processes, such as production, purification, characterization, quality evaluation and control, safety assessment, and clinical development and evaluation of EV-based therapeutics. These endeavors aim to facilitate the clinical application of EVs and pave the way for their transformative impact in healthcare.

Abstract Cytopenia is a well-documented complication in the treatment of hematological malignancies with lenalidomide and pomalidomide. Although prior studies have highlighted direct effects on hematopoietic cells to explain this adverse effect, the involvement of hematopoietic-supportive stroma remains less understood. This study examined the effects of lenalidomide/pomalidomide on the expansion and differentiation of human CD34⁺ hematopoietic stem/progenitor cells (HSPCs) in vitro, in co-culture with human bone-marrow mesenchymal stromal/stem cells (MSCs). Our findings indicate that lenalidomide/pomalidomide increases the population of immature CD34⁺CD38⁻ cells while decreasing the number of mature CD34⁺CD38⁺ cells, suggesting a mechanism that inhibits early HSPC maturation. This effect persisted across myeloid, megakaryocytic, and erythroid lineages, with MSCs playing a key role in preserving immature progenitors and inhibiting their differentiation. Furthermore, in myeloid differentiation assays augmented by granulocyte-colony stimulating factor, lenalidomide/pomalidomide not only enhanced the presence of CD34⁺ cells with mature myeloid markers such as CD11b but also reduced the populations lacking CD34 yet positive for these markers, irrespective of MSC presence. Thus, while MSCs support the presence of these immature cell populations, they simultaneously inhibit their maturation. This finding provides novel mechanistic insights into lenalidomide- and pomalidomide-induced cytopenia, and could guide therapeutic strategies for its mitigation.

The treatment of human immunodeficiency virus (HIV-1) has evolved since the establishment of combination antiretroviral therapy (ART) in the 1990s, providing HIV-infected individuals with approaches that suppress viral replication, prevent acquired immunodeficiency syndrome (AIDS) throughout their lifetime with continuous therapy, and halt HIV transmission. However, despite the success of these regimens, the global HIV epidemic persists, prompting a comprehensive exploration of potential strategies for an HIV cure. Here, we offer a consolidated overview of cell-based therapies for HIV-1, focusing on CAR-T cell approaches, gene editing, and immune modulation. Persistent challenges, including CAR-T cell susceptibility to HIV infection, stability, and viral reservoir control, underscore the need for continued research. This review synthesizes current knowledge, highlighting the potential of cellular therapies to address persistent challenges in the pursuit of an HIV cure.

SARS-CoV-2 infection has been reported to be associated with a positive direct antiglobulin test (DAT). In this study, an analysis of 40 consecutive coronavirus disease 2019 (COVID-19) cases from December 2020 to September 2021 in Japan revealed that patients of 70 years and over were predisposed to a positive DAT. DAT positivity was related to a decrease in the hemoglobin level. Anemia in DAT-positive COVID-19 patients was attributed to hemolysis, which was corroborated by high reticulocyte counts and an increase in the red blood cell distribution width. Human leukocyte antigen (HLA)-DRB1*12:01 and DRB1*12:02 were exclusively found in DAT-positive COVID-19 patients. In silico assays for the Spike protein of SARS-CoV-2 predicted several common core peptides that met the criteria for a B cell epitope and strong binding to both HLA-DRB1*12:01 and DRB1*12:02. Among these peptides, the amino acids sequence TSNFR, which is found within the S1 subunit of SARS-CoV-2 Spike protein, is shared by human blood group antigen Rhesus (Rh) CE polypeptides. In vitro analysis showed that the expression of HLA-DR in CD4+ T cells and CD8+ T cells from a DAT-positive patient was increased after pulsation with TSNFR-sequence-containing peptides. In summary, positive DAT is related to enhanced anemia and to HLA-DR12 in the Japanese population. A peptide sequence within SARS-CoV-2 Spike protein may act as an epitope for IgG binding to RBCs in DAT-positive COVID-19 patients.

© 2017 The Authors Stem Cells published by Wiley Periodicals, Inc. on behalf of AlphaMed Press A substantial proportion of patients with acute graft-versus-host disease (aGVHD) respond to cell therapy with culture-expanded human bone marrow mesenchymal stromal/stem cells (BM-MSCs). However, the mechanisms by which these cells can ameliorate aGVHD-associated complications remain to be clarified. We show here that BM-MSC-derived extracellular vesicles (EVs) recapitulated the therapeutic effects of BM-MSCs against aGVHD. Systemic infusion of human BM-MSC-derived EVs prolonged the survival of mice with aGVHD and reduced the pathologic damage in multiple GVHD-targeted organs. In EV-treated GVHD mice, CD4+ and CD8+ T cells were suppressed. Importantly, the ratio of CD62L-CD44+ to CD62L + CD44- T cells was decreased, suggesting that BM-MSC-derived EVs suppressed the functional differentiation of T cells from a naive to an effector phenotype. BM-MSC-derived EVs also preserved CD4 + CD25 + Foxp3+ regulatory T cell populations. In a culture of CD3/CD28-stimulated human peripheral blood mononuclear cells with BM-MSC-derived EVs, CD3+ T cell activation was suppressed. However, these cells were not suppressed in cultures with EVs derived from normal human dermal fibroblasts (NHDFs). NHDF-derived EVs did not ameliorate the clinical or pathological characteristics of aGVHD in mice, suggesting an immunoregulatory function unique to BM-MSC-derived EVs. Microarray analysis of microRNAs in BM-MSC-derived EVs versus NHDF-derived EVs showed upregulation of miR-125a-3p and downregulation of cell proliferative processes, as identified by Gene Ontology enrichment analysis. Collectively, our findings provide the first evidence that amelioration of aGVHD by therapeutic infusion of BM-MSC-derived EVs is associated with the preservation of circulating naive T cells, possibly due to the unique microRNA profiles of BM-MSC-derived EVs. Stem Cells 2018;36:434–445.

The poor prognosis of adults with B cell precursor acute lymphoblastic leukemia (BCP-ALL) is attributed to leukemia cells that are protected by the bone marrow (BM) microenvironment. In the present study, we explored the pharmacological targeting of mesenchymal stromal/stem cells in BM (BM-MSCs) to eliminate chemoresistant BCP-ALL cells. Human BCP-ALL cells (NALM-6 cells) that adhered to human BM-MSCs (NALM-6/Ad) were highly resistant to multiple anti-cancer drugs, and exhibited pro-survival characteristics, such as an enhanced Akt/Bcl-2 pathway and increased populations in the G0 and G2/S/M cell cycle stages. Bortezomib, a proteasome inhibitor, interfered with adhesion between BM-MSCs and NALM-6 cells and up-regulated the matricellular protein SPARC (secreted protein acidic and rich in cysteine) in BM-MSCs, thereby reducing the NALM-6/Ad population. Inhibition of SPARC expression in BM-MSCs using a small interfering RNA enhanced adhesion of NALM-6 cells. Conversely, recombinant SPARC protein interfered with adhesion of NALM-6 cells. These results suggest that SPARC disrupts adhesion between BM-MSCs and NALM-6 cells. Co-treatment with bortezomib and doxorubicin prolonged the survival of BCP-ALL xenograft mice, with a significant reduction of leukemia cells in BM. Our findings demonstrate that bortezomib contributes to the elimination of BCP-ALL cells through disruption of their adhesion to BM-MSCs, and offer a novel therapeutic strategy for BCP-ALL through targeting of BM-MSCs.

Bone marrow-derived mesenchymal stem cells (BMMSCs) are multipotent postnatal stem cells that have been used for the treatment of bone defects and graft-versus-host diseases in clinics. In this study, we found that subcutaneously transplanted human BMMSCs are capable of organizing hematopoietic progenitors of recipient origin. These hematopoietic cells expressed multiple lineages of hematopoietic cell associated markers and were able to rescue lethally irradiated mice, with successful engraftment in the recipient, suggesting a potential bone marrow (BM) resource for stem cell therapies. Furthermore, we found that platelet-derived growth factor (PDGF) promotes the formation of BMMSC-generated BM niches through upregulation of beta-catenin, implying that the PDGF pathway contributes to the formation of ectopic BM. These results indicate that the BMMSC-organized BM niche system represents a unique hematopoietic progenitor resource possessing potential clinical value.

Osteogenesis by the bone marrow stromal stem cells (BMSSCs) supports continuous bone formation and the homeostasis of the bone marrow microenvironment. The mechanism that controls the proliferation and differentiation of BMSSCs is not fully understood. Here, we report that CD18, a surface protein present primarily on hematopoietic cells, but not on differentiated mesenchymal cells, is expressed by the stromal stem cells and plays a critical role in the osteogenic process. Constitutive expression of CD18 on BMSSCs using a retroviral promoter significantly enhances bone formation in vivo , whereas genetic inactivation of CD18 in mice leads to defective osteogenesis due to decreased expression of the osteogenic master regulator Runx2/Cbfa1. The defective osteogenesis of the CD18-null BMSSCs can be restored by expressing full-length, but not cytoplasmic domain-truncated, CD18. Radiographic analyses with dual-energy x-ray absorptiometry and 3D microcomputed tomography show that mice lacking CD18 have decreased bone mineral density and exhibit certain features of osteoporosis. Altogether, this work demonstrates that CD18 functions critically in the osteogenesis of BMSSCs, and thus lack of CD18 expression in the leukocyte adhesion deficiency patients may predispose them to osteoporosis.