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Competing Interests: Declaration of competing interest None.

Background: Polycythemia Vera (PV) is a well-defined disorder of erythroid hyperproliferation that can result in life-threatening thromboembolic and hemorrhagic events. It is most prevalent in adults and is caused by mutations in Janus Kinase 2 (JAK2). Predominantly, PV is caused by a JAK2V617F mutation on exon 14., Observations: A rare case of PV in a 9-year-old, driven by an uncommon, p.Glu543_Asp544del, JAK2 exon 12 mutation. Despite management with phlebotomy, aspirin and hydroxyurea, the patient suffered a dural sinus venous thrombosis, prompting a change in therapy to Ruxolitinib., Conclusions: This is the first description of the successful use of ruxolitnib to treat a pediatric patient with PV caused by a JAK2 exon 12 mutation., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)

Thoracic outlet syndrome (TOS), a rare condition, results from the compression of neurovascular structures traversing from the neck through the thoracic outlet into the axilla. It can develop from chronic repetitive activities of the upper extremities, commonly reported in athletes playing sports involving vigorous use of arms and shoulders. While symptoms of neurovascular compression can occur, stroke due to TOS in children is not commonly reported. We describe a rare case of a healthy 14-year-old boy, a competitive violinist, with acute limb ischemia from extensive occlusive thrombi involving several arteries in the right upper extremity as well as the right vertebral artery, which ultimately caused infarcts in the bilateral posterior circulation. The etiology was determined to be TOS leading to impingement of the right subclavian artery by a fused cervical rib aggravated by patient's prolonged violin practice. This case represents the first description of stroke from TOS in an adolescent violinist., Competing Interests: None

Graft-versus-host disease (GVHD) limits the success of allogeneic hematopoietic cell transplantation (allo-HCT). Lysosomal acid lipase (LAL) mediates the intrinsic lipolysis of cells to generate free fatty acids (FFAs), which play an essential role in the development, proliferation, and function of T cells. Here, we find that LAL is essential for donor T cells to induce GVHD in murine models of allo-HCT. Specifically, LAL is required for donor T cell survival, differentiation, and alloreactivity in GVHD target organs, but not in lymphoid organs. LAL induces the differentiation of donor T cells toward GVHD pathogenic Th1/Tc1 and Th17 while suppressing regulatory T cell generation. LAL -/- T cells succumb to oxidative stress and become anergic in target organs. Pharmacologically targeting LAL effectively prevents GVHD development while preserving the GVL activity. Thus, the present study reveals the role of LAL in T cell alloresponse and pathogenicity and validates LAL as a target for controlling GVHD and tumor relapse after allo-HCT., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Purpose: Application of allogeneic hematopoietic cell transplantation (allo-HCT) for patients with hematologic disorders is limited by the development of GVHD. Separation of GVHD and graft-versus-leukemia (GVL) remains a great challenge in the field. We investigated the contribution of individual pathways involved in the complement cascade in GVH and GVL responses to identify specific targets by which to separate these two processes., Experimental Design: We used multiple preclinical murine and human-to-mouse xenograft models involving allo-HCT recipients lacking components of the alternative pathway (AP) or classical pathway (CP)/lectin pathway (LP) to dissect the role of each individual pathway in GVHD pathogenesis and the GVL effect. For translational purposes, we used the AP-specific complement inhibitor, CR2-fH, which localizes in injured target organs to allow specific blockade of complement activation at sites of inflammation., Results: Complement deposition was evident in intestines of mice and patients with GVHD. In a preclinical setting, ablation of the AP, but not the CP/LP, significantly improved GVHD outcomes. Complement activation through the AP in host hematopoietic cells, and specifically dendritic cells (DC), was required for GVHD progression. AP deficiency in recipients decreased donor T-cell migration and Th1/Th2 differentiation, while increasing the generation of regulatory T cells. This was because of decreased activation and stimulatory activity of recipient DCs in GVHD target organs. Treatment with CR2-fH effectively prevented GVHD while preserving GVL activity., Conclusions: This study highlights the AP as a new therapeutic target to prevent GVHD and tumor relapse after allo-HCT. Targeting the AP by CR2-fH represents a promising therapeutic approach for GVHD treatment., (©2020 American Association for Cancer Research.)

Graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic cell transplantation (HCT). DCs play critical roles in GVHD induction. Modulating autophagy represents a promising therapeutic strategy for the treatment of immunological diseases. Complement receptors C3aR/C5aR expressed on DCs regulate immune responses by translating extracellular signals into intracellular activity. In the current study, we found that C3aR/C5aR deficiency enhanced ceramide-dependent lethal mitophagy (CDLM) in DCs. Cotransfer of host-type C3aR-/-/C5aR-/- DCs in the recipients significantly improved GVHD outcome after allogeneic HCT, primarily through enhancing CDLM in DCs. C3aR/C5aR deficiency in the host hematopoietic compartment significantly reduced GVHD severity via impairing Th1 differentiation and donor T cell glycolytic activity while enhancing Treg generation. Prophylactic treatment with C3aR/C5aR antagonists effectively alleviated GVHD while maintaining the graft-versus-leukemia (GVL) effect. Altogether, we demonstrate that inhibiting C3aR/C5aR induces lethal mitophagy in DCs, which represents a potential therapeutic approach to control GVHD while preserving the GVL effect.

Metabolism, including catabolism and anabolism, is a basic cellular process necessary for cell survival. T lymphocytes have a distinct metabolism that can determine both fate and function. T-cell activation depends on glycolysis to obtain materials and energy for proliferation and effector function. Importantly, T cells utilize different metabolic processes under different conditions and diseases. Allogeneic hematopoietic cell transplantation (allo-HCT) is a classic immunotherapy for hematological malignancies; however, the development of graft-versus-host disease (GVHD) is a major factor limiting the success of allo-HCT. T cells in the donor graft drive GVHD by mounting a robust immunological attack against recipient normal tissues. Hence, understanding T-cell metabolism after allo-HCT would provide potential metabolic targets for the control of GVHD and primary tumor relapse. The purpose of the current review is to highlight the key metabolic pathways involved in alloantigen-activated T cells and to discuss how manipulating these pathways can serve as potential new therapeutic strategies to induce immune tolerance after allo-transplantation. We will also summarize the recent progress in regulating T-cell metabolism in bone marrow transplantation by targeting novel metabolic regulators or immune checkpoint molecules.