Notch signaling drives intestinal graft-versus-host disease in mice and nonhuman primates

Early Notch signals from fibroblastic reticular cells program effector CD8+ T cell differentiation

A better understanding of the mechanisms regulating CD8+ T cell differentiation is essential to develop new strategies to fight infections and cancer. Using genetic mouse models and blocking antibodies, we uncovered cellular and molecular mechanisms by which Notch signaling favors the efficient generation of effector CD8+ T cells. Fibroblastic reticular cells from secondary lymphoid organs, but not dendritic cells, were the dominant source of Notch signals in T cells via Delta-like1/4 ligands within the first 3 days of immune responses to vaccination or infection. Using transcriptional and epigenetic studies, we identified a unique Notch-driven T cell-specific signature. Early Notch signals were associated with chromatin opening in regions occupied by bZIP transcription factors, specifically BATF, known to be important for CD8+ T cell differentiation. Overall, we show that fibroblastic reticular cell niches control the ultimate molecular and functional fate of CD8+ T cells after vaccination or infection through the delivery of early Notch signals.

Targeting the chemokines in acute graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) constitutes a critical therapeutic approach for patients with malignant hematological disorders. Nevertheless, acute graft-versus-host disease (GVHD), one of the most prevalent complications associated with HSCT, remains a leading contributor to non-relapse mortality. In recent years, there has been an increasing focus on the interplay between chemokines and their receptors in the context of acute GVHD. Chemokines exert substantial effects across various pathological conditions, including autoimmune diseases, inflammatory processes, tumorigenesis, and metastatic dissemination. In this review, we aim to elucidate the role of chemokines in the pathogenesis of acute GVHD and further understand their potential as diagnostic biomarkers. We also present both preclinical and clinical insights into the application of chemokines in preventing and treating acute GVHD. The objective of this review is to offer novel perspectives on the clinical diagnosis and management strategies for acute GVHD.

Exosomes derived from umbilical cord mesenchymal stem cells ameliorate ischemic brain injury in mice by regulating AAK1 via miR-664a-5p

OBJECTIVE

To identify the molecular targets of mesenchymal stem cell (MSC)-derived exosomes in treating cerebral ischemia and elucidate their therapeutic mechanisms.

METHODS

We utilized a mouse model of middle cerebral artery occlusion and treated mice with umbilical cord mesenchymal stem cells derived exosomes. Proteomic analysis identified AAK1(AP2 associated kinase 1) as a key target protein. Functional studies confirmed that AAK1 modulates the NF-κB signaling pathway in ischemic stroke. MicroRNA profiling, bioinformatic prediction and cell experiments identified miR-664a-5p as the specific microRNA regulating AAK1 expression. Finally, we validated the therapeutic effects of umbilical cord mesenchymal stem cell-derived exosomes using engineered miR-664a-5p-deficient exosomes.

RESULTS

Our findings demonstrate that umbilical cord mesenchymal stem cells-derived exosomes exert neuroprotective effects in ischemic stroke by modulating the AAK1/NF-κB axis via miR-664a-5p.

CONCLUSION

This study provides novel insights into the therapeutic mechanism of mesenchymal stem cell-derived exosomes in ischemic stroke, highlighting their potential for developing exosome-based therapies.

Cellular Strategies for Separating GvHD from GvL in Haploidentical Transplantation

GvHD still remains, despite the continuous improvement of transplantation platforms, a fearful complication of transplantation from allogeneic donors. Being able to separate GvHD from GvL represents the greatest challenge in the allogeneic transplant setting. This may be possible through continuous improvement of cell therapy techniques. In this review, current cell therapies are taken into consideration, which are based on the use of TCR alpha/beta depletion, CD45RA depletion, T regulatory cell enrichment, NK-cell-based immunotherapies, and suicide gene therapies in order to prevent GvHD and maximally amplify the GvL effect in the setting of haploidentical transplantation.

Distinct fibroblast functions associated with fibrotic and immune-mediated inflammatory diseases and their implications for therapeutic development

Fibroblasts are ubiquitous cells that can adopt many functional states. As tissue-resident sentinels, they respond to acute damage signals and shape the earliest events in fibrotic and immune-mediated inflammatory diseases. Upon sensing an insult, fibroblasts produce chemokines and growth factors to organize and support the response. Depending on the size and composition of the resulting infiltrate, these activated fibroblasts may also begin to contract or relax thus changing local stiffness within the tissue. These early events likely contribute to the divergent clinical manifestations of fibrotic and immune-mediated inflammatory diseases. Further, distinct changes to the cellular composition and signaling dialogue in these diseases drive progressive fibroblasts specialization. In fibrotic diseases, fibroblasts support the survival, activation and differentiation of myeloid cells, granulocytes and innate lymphocytes, and produce most of the pathogenic extracellular matrix proteins. Whereas, in immune-mediated inflammatory diseases, sequential accumulation of dendritic cells, T cells and B cells programs fibroblasts to support local, destructive adaptive immune responses. Fibroblast specialization has clear implications for the development of effective induction and maintenance therapies for patients with these clinically distinct diseases.

Protective fibroblastic niches in secondary lymphoid organs

Fibroblastic reticular cells (FRCs) are specialized fibroblasts of secondary lymphoid organs that provide the structural foundation of the tissue. Moreover, FRCs guide immune cells to dedicated microenvironmental niches where they provide lymphocytes and myeloid cells with homeostatic growth and differentiation factors. Inflammatory processes, including infection with pathogens, induce rapid morphological and functional adaptations that are critical for the priming and regulation of protective immune responses. However, adverse FRC reprogramming can promote immunopathological tissue damage during infection and autoimmune conditions and subvert antitumor immune responses. Here, we review recent findings on molecular pathways that regulate FRC-immune cell crosstalk in specialized niches during the generation of protective immune responses in the course of pathogen encounters. In addition, we discuss how FRCs integrate immune cell-derived signals to ensure protective immunity during infection and how therapies for inflammatory diseases and cancer can be developed through improved understanding of FRC-immune cell interactions.

Regulation of immune cell development, differentiation and function by stromal Notch ligands

In multicellular organisms, cell-to-cell communication is critical for the regulation of tissue organization. Notch signaling relies on direct interactions between Notch receptors on signal-receiving cells and Notch ligands on adjacent cells. Notch evolved to mediate local cellular interactions that are responsive to spatial cues via dosage-sensitive short-lived signals. Immune cells utilize these unique properties of Notch signaling to direct their development, differentiation, and function. In this review, we explore how immune cells interact through Notch receptors with stromal cells in specialized niches of lymphohematopoietic organs that express Notch-activating ligands. We emphasize factors that control these interactions and focus on how Notch signals communicate spatial, quantitative, and temporal information to program the function of signal-receiving cells in the immune system.

Having it both ways: how STAT3 deficiency blocks graft-versus-host disease while preserving graft-versus-leukemia activity

Allogeneic hematopoietic cell transplantation can cure patients with high-risk leukemia through graft-versus-leukemia (GVL) effects, the process by which malignant leukemic cells are cleared by donor-derived immune cells from the graft. The problem of harnessing GVL effects while controlling inflammation and host-organ damage linked with graft-versus-host disease (GVHD) has been the most formidable hurdle facing allogeneic hematopoietic cell transplantation. This powerful, curative-intent therapy remains among the most toxic treatments in the hematologist's armamentarium due to the combined risks of GVHD-related morbidity, infections, and leukemia relapse. In this issue of the JCI, Li, Wang, et al. report that T cell Stat3 deficiency can extricate GVL effects from GVHD through tissue-specific programmed death-ligand 1/programmed cell death protein 1-dependent (PD-L1/PD-1-dependent) bioenergetic alterations that blunt harmful T cell effects in GVHD target organs, while preserving their beneficial antitumor activity in lymphohematopoietic tissues.