Nonalloreactive T cells prevent donor lymphocyte infusion-induced graft-versus-host disease by controlling microbial stimuli

Tolerance in intestinal transplantation

Intestinal transplantation (ITx) is highly immunogenic, resulting in the need for high levels of immunosuppression, with frequent complications along with high rejection rates. Tolerance induction would provide a solution to these limitations. Detailed studies of alloreactive T cell clones as well as multiparameter flow cytometry in the graft and peripheral tissues have provided evidence for several tolerance mechanisms that occur spontaneously following ITx, which might provide targets for further interventions. These include the frequent occurrence of macrochimerism and engraftment in the recipient bone marrow of donor hematopoietic stem and progenitor cells carried in the allograft. These phenomena are seen most frequently in recipients of multivisceral transplants and are associated with reduced rejection rates. They reflect powerful graft-vs-host responses that enter the peripheral lymphoid system and bone marrow after expanding within and emigrating from the allograft. Several mechanisms of tolerance that may result from this lymphohematopoietic graft-vs-host response are discussed. Transcriptional profiling in quiescent allografts reveals tolerization of pre-existing host-vs-graft-reactive T cells that enter the allograft mucosa and become tissue-resident memory cells. Dissection of the pathways driving and maintaining this tolerant tissue-resident state among donor-reactive T cells will allow controlled tolerance induction through specific therapeutic approaches.

After Bone Marrow Transplantation, the Cell-Intrinsic Th2 Pathway Promotes Recipient T Lymphocyte Survival and Regulates Graft-versus-Host Disease

Recipient T cells can aggravate or regulate lethal and devastating graft-versus-host disease (GVHD) after bone marrow transplantation (BMT). In this context, we have shown before that intestinal immune conditioning with helminths is associated with survival of recipient T cells and Th2 pathway-dependent regulation of GVHD. We investigated the mechanism of survival of recipient T cells and their contribution to GVHD pathogenesis in this helminth infection and BMT model after myeloablative preparation with total body irradiation in mice. Our results indicate that the helminth-induced Th2 pathway directly promotes the survival of recipient T cells after total body irradiation. Th2 cells also directly stimulate recipient T cells to produce TGF-β, which is required to regulate donor T cell-mediated immune attack of GVHD and can thereby contribute to recipient T cell survival after BMT. Moreover, we show that recipient T cells, conditioned to produce Th2 cytokines and TGF-β after helminth infection, are fundamentally necessary for GVHD regulation. Taken together, reprogrammed or immune-conditioned recipient T cells after helminth infection are crucial elements of Th2- and TGF-β-dependent regulation of GVHD after BMT, and their survival is dependent on cell-intrinsic Th2 signaling.

Cytokine Overproduction and Immune System Dysregulation in alloHSCT and COVID-19 Patients

The COVID-19 pathomechanism depends on (i) the pathogenicity of the virus, (ii) ability of the immune system to respond to the cytopathic effect of the virus infection, (iii) co-morbidities. Inflammatory cytokine production constitutes a hallmark of COVID-19 that is facilitated by inability of adaptive immunity to control virus invasion. The effect of cytokine release syndrome is deleterious, but the severity of it depends on other confounding factors: age and comorbidities. In this study, we analyze the literature data on the post-transplant course of allogeneic hematopoietic stem cell transplanted (alloHSCT) patients, which is affected by generated inflammatory cytokines. The sequence of events boosting cytokine production was analyzed in relation to clinical and laboratory data highlighting the impact of cytokine generation on the post-transplant course. The collected data were compared to those from studies on COVID-19 patients. The similarities are: (i) the damage/pathogen-associated molecular pattern (DAMP/PAMP) stage is similar except for the initiation hit being sterile in alloHSCT (toxic damage of conditioning regimen) and viral in COVID-19; (ii) genetic host-derived factors play a role; (iii) adaptive immunity fails, DAMP signal(s) increases, over-production of cytokines occurs; (iv) monocytes lacking HLADR expression emerge, being suppressor cells hampering adaptive immunity; (v) immune system homeostasis is broken, the patient's status deteriorates to bed dependency, leading to hypo-oxygenation and malnutrition, which in turn stimulates the intracellular alert pathways with vigorous transcription of cytokine genes. All starts with the interaction between DAMPs with appropriate receptors, which leads to the production of pro-inflammatory cytokines, the inflammatory process spreads, tissue is damaged, DAMPs are released and a vicious cycle occurs. Attempts to modify intracellular signaling pathways in patients with post-alloHSCT graft vs host disease have already been undertaken. The similarities documented in this study show that this approach may also be used in COVID-19 patients for tuning signal transduction processes to interrupt the cycle that powers the cytokine overproduction.

Human Immune System Mice With Autologous Tumor for Modeling Cancer Immunotherapies

Mouse models are the most commonly used in vivo system for biomedical research, in which immune-related diseases and therapies can be investigated in syngeneic and immunologically intact hosts. However, because there are significant differences between rodent and human, most findings from conventional mouse models cannot be applied to humans. The humanized mouse with a functional human immune system, also referred to as human immune system (HIS) mouse, is the only model available to date for in vivo studies in real-time of human immune function under physiological and pathological conditions. HIS mice with human tumor xenografts are considered an emerging and promising in vivo model for modeling human cancer immunotherapy. In this review, we briefly discuss the protocols to construct HIS mice and elaborate their pros and cons. Particular attention is given to HIS mouse models with human tumor that is autologous or genetically identical to the human immune system, which are discussed with examples of their usefulness in modeling human cancer immunotherapies.

Recommendations on Selection and Processing of RBC Components for Pediatric Patients From the Pediatric Critical Care Transfusion and Anemia Expertise Initiative

OBJECTIVES

To present the recommendations and supporting literature for selection and processing of RBC products in critically ill children developed by the Pediatric Critical Care Transfusion and Anemia Expertise Initiative.

DESIGN

Consensus conference series of international, multidisciplinary experts in RBC transfusion management of critically ill children METHODS:: The panel of 38 experts developed evidence-based, and when evidence was lacking, expert-based clinical recommendations as well as research priorities for RBC transfusions in critically ill children. The RBC processing subgroup included five experts. Electronic searches were conducted using PubMed, EMBASE, and Cochrane Library databases from 1980 to May 2017. Agreement was obtained using the Research and Development/UCLA Appropriateness Method. Results were summarized using the Grading of Recommendations Assessment, Development, and Evaluation method.

RESULTS

Five recommendations reached agreement (> 80%). Irradiated cellular products are recommended for children at risk of transfusion-associated graft versus host disease due to severe congenital or acquired causes of immune deficiency or when the blood donor is a blood relative. Washed cellular blood components and avoidance of other plasma-containing products are recommended for critically ill children with history of severe allergic reactions or anaphylaxis to blood transfusions, although patient factors appear to be important in the pathogenesis of reactions. For children with history of severe allergic transfusion reactions, evaluation for allergic stigmata prior to transfusion is recommended. In children with severe immunoglobulin A deficiency with evidence of antiimmunoglobulin A antibodies and/or a history of a severe transfusion reaction, immunoglobulin A-deficient blood components obtained either from an immunoglobulin A-deficient donor and/or washed cellular components is recommended.

CONCLUSIONS

The Transfusion and Anemia Expertise Initiative consensus conference developed recommendations for selection and processing of RBC units for critically ill children. Recommendations in this area are largely based on pediatric and adult case report data.

CTLA4-CD28 chimera gene modification of T cells enhances the therapeutic efficacy of donor lymphocyte infusion for hematological malignancy

Donor lymphocyte infusion (DLI) followed by hematopoietic stem cell transplantation has served as an effective prevention/treatment modality against the relapse of some hematologic tumors, such as chronic myeloid leukemia (CML). However, the therapeutic efficacies of DLI for other types of leukemia, including acute lymphocytic leukemia (ALL), have been limited thus far. Therefore, we examined whether increasing the reactivity of donor T cells by gene modification could enhance the therapeutic efficacy of DLI in a murine model of ALL. When a CTLA4-CD28 chimera gene (CTC28) in which the intracellular signaling domain of CTLA4 was replaced with the CD28 signaling domain was introduced into CD4 and CD8 T cells in DLI, the graft-versus-tumor (GVT) effect was significantly increased. This effect was correlated with an increased expansion of donor CD8 T cells in vivo, and the depletion of CD8 T cells abolished this effect. The CD8 T cell expansion and the enhanced GVT effect were dependent on the transduction of both CD4 and CD8 T cells with CTC28, which emphasizes the role of dual modification in this therapeutic effect. The CTC28-transduced T cells that expanded in vivo also exhibited enhanced functionality. Although the potentiation of the GVT effect mediated by the CTC28 gene modification of T cells was accompanied by an increase of graft-versus-host disease (GVHD), the GVHD was not lethal and was mitigated by treatment with IL-10 gene-modified third-party mesenchymal stem cells. Thus, the combined genetic modification of CD4 and CD8 donor T cells with CTC28 could be a promising strategy for enhancing the therapeutic efficacy of DLI.

Modeling Human Leukemia Immunotherapy in Humanized Mice

The currently available human tumor xenograft models permit modeling of human cancers in vivo, but in immunocompromised hosts. Here we report a humanized mouse (hu-mouse) model made by transplantation of human fetal thymic tissue plus hematopoietic stem cells transduced with a leukemia-associated fusion gene MLL-AF9. In addition to normal human lymphohematopoietic reconstitution as seen in non-leukemic hu-mice, these hu-mice showed spontaneous development of B-cell acute lymphoblastic leukemia (B-ALL), which was transplantable to secondary recipients with an autologous human immune system. Using this model, we show that lymphopenia markedly improves the antitumor efficacy of recipient leukocyte infusion (RLI), a GVHD-free immunotherapy that induces antitumor responses in association with rejection of donor chimerism in mixed allogeneic chimeras. Our data demonstrate the potential of this leukemic hu-mouse model in modeling leukemia immunotherapy, and suggest that RLI may offer a safe treatment option for leukemia patients with severe lymphopenia.

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NSG mice grafted with thymus/oncogenic HSC develop human immune system and leukemia.

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Leukemia transfer to mice with autologous immunity suffices to model immunotherapy.

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Lymphopenia enhances RLI-mediated HVGR and anti-leukemia activity in mixed chimeras.

This study establishes a humanized mouse model with human immunity and autologous leukemia. Using this model, the authors demonstrate that lymphopenia promotes the rejection of donor hematopoietic chimerism and the associated anti-leukemia response by recipient leukocyte infusion in mixed allogeneic chimeras.

Immune tolerance in recipients of combined haploidentical bone marrow and kidney transplantation

The success of allogeneic hematopoietic cell transplantation (HCT) has been limited by transplant-associated toxicities related to the conditioning regimens used and to graft-vs-host disease (GVHD). The frequency and severity of GVHD observed when extensive HLA barriers are transgressed has greatly impeded the routine use of extensively HLA-mismatched HCT. Allogeneic HCT also has potential as an approach to organ allograft tolerance induction, but this potential has not been previously realized because of the toxicity associated with traditional conditioning. This paper reviews an approach to HCT involving reduced intensity conditioning that demonstrated sufficient safety in patients with hematologic malignancies, even in the HLA-mismatched transplant setting, to be applied for the induction of kidney allograft tolerance in humans with no other indication for HCT. These studies provided the first successful example of intentional organ allograft tolerance induction across HLA barriers in humans. Current data and hypotheses on the mechanisms of tolerance in these patients are reviewed.

Innate allorecognition

Vertebrates mount strong adaptive immune responses to transplanted organs (allografts), but the mechanisms by which the innate immune system initiates this response are not completely understood. In anti-microbial immunity, non-self molecules associated with pathogens but not present in the host induce the maturation of innate antigen-presenting cells (APCs) by binding to germ-line-encoded receptors. Mature APCs then initiate the adaptive immune response by presenting microbial antigen and providing costimulatory signals to T cells. How allografts activate APCs, however, is less clear, because allografts are presumably sterile. A widely accepted view is that inflammatory or 'danger' molecules released by dying graft cells at the time of transplantation trigger APC maturation and the T-cell response that follows. Alternatively, it has been proposed that the introduction of microbial products during the surgical procedure could also alert the innate immune system to the presence of the transplanted organ. Here, we review why these hypotheses fail to fully explain how the alloimmune response is initiated after transplantation and summarize evidence that recognition of allogeneic non-self by monocytes is a key event in triggering alloimmunity and graft rejection.

Induction of tolerance through mixed chimerism

"Mixed chimerism" refers to a state in which the lymphohematopoietic system of the recipient of allogeneic hematopoietic stem cells comprises a mixture of host and donor cells. This state is usually attained through either bone marrow or mobilized peripheral blood stem cell transplantation. Although numerous treatment regimens have led to transplantation tolerance in mice, the induction of mixed chimerism is currently the only treatment modality that has been successfully extended to large animals and to the clinic. Here we describe and compare the use of mixed chimerism to establish transplantation tolerance in mice, pigs, monkeys, and in the clinic. We also attempt to correlate the mechanisms involved in achieving tolerance with the nature of the tolerance that has resulted in each case.