Transient antibody targeting of CD45RC inhibits the development of graft-versus-host disease

Simple, Rapid, Reproducible and Biomarker-Validated Clinical Grading System for Murine Models of Xenogeneic Graft-Versus-Host Disease

Experiment models of xenogeneic graft-versus-host disease (xeno-GVHD), in which human immune cells are injected into immunodeficient mice, are increasingly used to study human immune cell behavior in vivo and to test therapeutic approaches. Today, the main, and more commonly accepted clinical parameters used to characterize xeno-GVHD are weight loss and mortality. These criteria do not provide an accurate and subtle assessment of the disease intensity, nor do they reflect the great variability of xeno-GVHD, which depends on the donor. Relying on previous work in which we described an original clinical grading system for assessing GVHD in mice, we propose an adaptation of this system for xeno-GVHD models. This simple, solid, and reproducible scoring system of xeno-GVHD is constituted of the binary (yes or no) evaluation of 4 easy-to-evaluate parameters that reflect the complexity of the disease without the need to sacrifice the mice. This scoring system is consistent with the gold standard histological grading of human GVHD and with numerous biomarkers characteristic of the disease. We propose this new clinical grading system to evaluate and compare the results obtained with a common tool, regardless of the experimenters and laboratories where the experiments would have been carried out and whatever the therapeutic strategy evaluated.

Pathophysiology and preclinical relevance of experimental graft-versus-host disease in humanized mice

Graft-versus-host disease (GVHD) is a life-threatening complication of allogeneic hematopoietic cell transplantations (allo-HCT) used for the treatment of hematological malignancies and other blood-related disorders. Until recently, the discovery of actionable molecular targets to treat GVHD and their preclinical testing was almost exclusively based on modeling allo-HCT in mice by transplanting bone marrow and splenocytes from donor mice into MHC-mismatched recipient animals. However, due to fundamental differences between human and mouse immunology, the translation of these molecular targets into the clinic can be limited. Therefore, humanized mouse models of GVHD were developed to circumvent this limitation. In these models, following the transplantation of human peripheral blood mononuclear cells (PBMCs) into immunodeficient mice, T cells recognize and attack mouse organs, inducing GVHD. Thereby, humanized mice provide a platform for the evaluation of the effects of candidate therapies on GVHD mediated by human immune cells in vivo. Understanding the pathophysiology of this xenogeneic GVHD is therefore crucial for the design and interpretation of experiments performed with this model. In this article, we comprehensively review the cellular and molecular mechanisms governing GVHD in the most commonly used model of xenogeneic GVHD: PBMC-engrafted NOD/LtSz-PrkdcscidIL2rγtm1Wjl (NSG) mice. By re-analyzing public sequencing data, we also show that the clonal expansion and the transcriptional program of T cells in humanized mice closely reflect those in humans. Finally, we highlight the strengths and limitations of this model, as well as arguments in favor of its biological relevance for studying T-cell reactions against healthy tissues or cancer cells.

Renal graft function in transplanted patients correlates with CD45RC T cell phenotypic signature

Biomarkers that could predict the evolution of the graft in transplanted patients and that could allow to adapt the care of the patients would be an invaluable tool. Additionally, certain biomarkers can be target of treatments and help to stratify patients. Potential effective biomarkers have been identified but still need to be confirmed. CD45RC, one of the splicing variants of the CD45 molecule, a tyrosine phosphatase that is critical in negatively or positively regulating the TCR and the BCR signaling, is one marker already described. The frequency of CD8+ T cells expressing high levels of CD45RC before transplantation is increased in patients with an increased risk of acute rejection. However, single biomarkers have limited predictive reliability and the correlation of the expression levels of CD45RC with other cell markers was not reported. In this study, we performed a fluorescent-based high dimensional immunophenotyping of T cells on a cohort of 69 kidney transplant patients either with stable graft function or having experienced acute transplant rejection during the first year after transplantation or at the time of rejection. We identified combinations of markers and cell subsets associated with activation/inflammation or Tregs/tolerance (HLA-DR, PD-1, IFNγ, CD28) as significant biomarkers associated to transplant outcome, and showed the importance of cell segregation based on the CD45RC marker to identify the signature of a stable graft function. Our study highlights potential reliable biomarkers in transplantation to predict and/or monitor easily graft-directed immune responses and adapt immunosuppression treatments to mitigate adverse effects.

Preclinical proof of concept for VivoVec, a lentiviral-based platform for in vivo CAR T-cell engineering

BACKGROUND

Chimeric antigen receptor (CAR) T-cell therapies have demonstrated transformational outcomes in the treatment of B-cell malignancies, but their widespread use is hindered by technical and logistical challenges associated with ex vivo cell manufacturing. To overcome these challenges, we developed VivoVec, a lentiviral vector-based platform for in vivo engineering of T cells. UB-VV100, a VivoVec clinical candidate for the treatment of B-cell malignancies, displays an anti-CD3 single-chain variable fragment (scFv) on the surface and delivers a genetic payload that encodes a second-generation CD19-targeted CAR along with a rapamycin-activated cytokine receptor (RACR) system designed to overcome the need for lymphodepleting chemotherapy in supporting successful CAR T-cell expansion and persistence. In the presence of exogenous rapamycin, non-transduced immune cells are suppressed, while the RACR system in transduced cells converts rapamycin binding to an interleukin (IL)-2/IL-15 signal to promote proliferation.

METHODS

UB-VV100 was administered to peripheral blood mononuclear cells (PBMCs) from healthy donors and from patients with B-cell malignancy without additional stimulation. Cultures were assessed for CAR T-cell transduction and function. Biodistribution was evaluated in CD34-humanized mice and in canines. In vivo efficacy was evaluated against normal B cells in CD34-humanized mice and against systemic tumor xenografts in PBMC-humanized mice.

RESULTS

In vitro, administration of UB-VV100 resulted in dose-dependent and anti-CD3 scFv-dependent T-cell activation and CAR T-cell transduction. The resulting CAR T cells exhibited selective expansion in rapamycin and antigen-dependent activity against malignant B-cell targets. In humanized mouse and canine studies, UB-VV100 demonstrated a favorable biodistribution profile, with transduction events limited to the immune compartment after intranodal or intraperitoneal administration. Administration of UB-VV100 to humanized mice engrafted with B-cell tumors resulted in CAR T-cell transduction, expansion, and elimination of systemic malignancy.

CONCLUSIONS

These findings demonstrate that UB-VV100 generates functional CAR T cells in vivo, which could expand patient access to CAR T technology in both hematological and solid tumors without the need for ex vivo cell manufacturing.

Neuroinflammation: Extinguishing a blaze of T cells

Inflammation is a biological process that dynamically alters the surrounding microenvironment, including participating immune cells. As a well-protected organ surrounded by specialized barriers and with immune privilege properties, the central nervous system (CNS) tightly regulates immune responses. Yet in neuroinflammatory conditions, pathogenic immunity can disrupt CNS structure and function. T cells in particular play a key role in promoting and restricting neuroinflammatory responses, while the inflamed CNS microenvironment can influence and reshape T cell function and identity. Still, the contraction of aberrant T cell responses within the CNS is not well understood. Using autoimmunity as a model, here we address the contribution of CD4 T helper (Th) cell subsets in promoting neuropathology and disease. To address the mechanisms antagonizing neuroinflammation, we focus on the control of the immune response by regulatory T cells (Tregs) and describe the counteracting processes that preserve their identity under inflammatory challenges. Finally, given the influence of the local microenvironment on immune regulation, we address how CNS-intrinsic signals reshape T cell function to mitigate abnormal immune T cell responses.

Federation of Clinical Immunology Societies Goes South 2021: advanced course on molecular and cellular translational immunology

The Federation of Clinical Immunology Societies (FOCIS) regularly organizes scientific meetings to foster advances in immunology. A new event of this type is FOCIS Goes South, a course and workshop organized by FOCIS Centers of Excellence (FCEs) from across Latin America, which consists of a course on advanced immunology, a flow cytometry workshop and seminars on cutting-edge research in autoimmunity, tolerance, cancer, infectious diseases and vaccines. Due to the COVID-19 pandemic, the second version of FOCIS Goes South, hosted by the Millennium Institute on Immunology and Immunotherapy in Chile, took place virtually from 15 to 18 November 2021, with more than 950 registered participants. The present article summarizes the key findings and insights discussed at FOCIS Goes South 2021.

Anti-CD45RC antibody immunotherapy prevents and treats experimental Autoimmune PolyEndocrinopathy Candidiasis Ectodermal Dystrophy syndrome

Targeted monoclonal antibody (mAb) therapies show great promise for the treatment of transplant rejection and autoimmune diseases by inducing more specific immunomodulatory effects than broadly immunosuppressive drugs routinely used. We recently described the therapeutic advantage of targeting CD45RC, expressed at high levels by conventional T cells (Tconv, CD45RChigh), their precursors and terminally differentiated T (TEMRA) cells, but not by regulatory T cells (Tregs, CD45RClow/-). We demonstrated efficacy of anti-CD45RC mAb treatment in transplantation but its potential has not been examined in autoimmune diseases. APECED is a rare genetic syndrome caused by loss-of-function mutations of the key central tolerance mediator, autoimmune regulator (AIRE) leading to abnormal auto-reactive T cell responses and autoantibodies production. Herein, we showed that, in a rat model of APECED syndrome, anti-CD45RC mAb was effective both as prevention and treatment of autoimmune manifestations and inhibited autoantibody development. Anti-CD45RC mAb intervention depleted CD45RChigh T cells, inhibited CD45RChigh B cells, and restored the Treg/Tconv ratio and the altered Tregs transcriptomic profile. In APECED patients, CD45RC was significantly increased in peripheral blood T cells and lesioned organs from APECED patients were infiltrated by CD45RChigh cells. Our observations highlight the potential role for CD45RChigh cells in the pathogenesis of experimental and human APECED syndrome and the potential of anti-CD45RC antibody treatment.

Comprehensive analysis of the immunomodulatory effects of rapamycin on human T cells in graft-versus-host disease prophylaxis

Graft-versus-host disease (GVHD) is a major cause of toxicity after allogeneic hematopoietic cell transplantation (allo-HCT). While rapamycin (RAPA) is commonly used in GVHD prophylaxis in combination with a calcineurin inhibitor (CNI), the understanding of its mechanism of action on human T cells is still incomplete. Here, we performed an extensive analysis of RAPA effects on human T cells in a humanized mouse model of GVHD, in ex-vivo T cell cultures and in patients given RAPA plus tacrolimus as GVHD prophylaxis after nonmyeloablative allo-HCT. We demonstrate that RAPA mitigates GVHD by decreasing T cell engraftment and differentiation, inhibiting CD8⁺ T cell activation and increasing the long-term IL-2 secretion, thereby supporting regulatory T cell (Treg) proliferation. In contrast, graft-versus-leukemia effects were not abrogated, as RAPA-treated T cells had increased resistance to apoptosis and retained their effector function and proliferative capacity upon re-stimulation. Importantly, we found that RAPA impact on Treg and CD8⁺ T cells was closely dependent upon IL-2 signaling and that therapeutic options interfering with IL-2, such as calcineurin inhibitors, antagonize the IL-2-dependent promotion of Treg mediated by RAPA. Our results suggest that RAPA immunological efficacy could be improved in combination with drugs having possible synergistic effects such as the hypomethylating agent 5-azacytidine.

Itacitinib prevents xenogeneic GVHD in humanized mice

We assessed the impact of the Janus Kinase (JAK) 1 inhibitor itacitinib on xenogeneic graft-versus-host disease (xGVHD). XGVHD was induced by i.v. injection 20 × 10⁶ human peripheral blood mononuclear cells (hPBMC) in NSG mice on day 0. Itacitinib (3 mg, ≈120 mg/kg) or methylcellulose was administered by force-feeding twice a day from day 3 to day 28. Mice were followed for xGVHD score and survival. In addition, human T-cell engraftment and as well as human T-cell subtypes were monitored in blood on days 14, 21, and 28 after transplantation. We observed that itacitinib-treated mice had significantly longer survival than control mice (median 45 versus 33 days; P < 0.001). Further, they also had lower absolute numbers of human CD4⁺ T cells on days 21 and 28 after transplantation as well as of human CD8⁺ T cells on days 14, 21, and 28 after transplantation. In addition, itacitinib-treated mice had higher frequencies of human regulatory T cells (Treg) on days 21 and 28 after transplantation. In summary, our data indicate that itacitinib decreases human T-cell engraftment, increases Treg frequencies and attenuates xGVHD in NSG mice transplanted with hPBMC.

Diversity, localization, and (patho)physiology of mature lymphocyte populations in the bone marrow

The bone marrow (BM) is responsible for generating and maintaining lifelong output of blood and immune cells. In addition to its key hematopoietic function, the BM acts as an important lymphoid organ, hosting a large variety of mature lymphocyte populations, including B cells, T cells, natural killer T cells, and innate lymphoid cells. Many of these cell types are thought to visit the BM only transiently, but for others, like plasma cells and memory T cells, the BM provides supportive niches that promote their long-term survival. Interestingly, accumulating evidence points toward an important role for mature lymphocytes in the regulation of hematopoietic stem cells (HSCs) and hematopoiesis in health and disease. In this review, we describe the diversity, migration, localization, and function of mature lymphocyte populations in murine and human BM, focusing on their role in immunity and hematopoiesis. We also address how various BM lymphocyte subsets contribute to the development of aplastic anemia and immune thrombocytopenia, illustrating the complexity of these BM disorders and the underlying similarities and differences in their disease pathophysiology. Finally, we summarize the interactions between mature lymphocytes and BM resident cells in HSC transplantation and graft-versus-host disease. A better understanding of the mechanisms by which mature lymphocyte populations regulate BM function will likely improve future therapies for patients with benign and malignant hematologic disorders.

Regulatory T cells and transplantation tolerance: Emerging from the darkness?

The field of tissue transplantation has revolutionized the treatment of patients with failing organs. Its success, thus far, has depended on combinations of immunosuppressive drugs that damp host immunity, while also imposing numerous unwanted side-effects. There is a longstanding recognition that better treatment outcomes, will come from replacing these drugs, fully or in part, by taking advantage of tractable physiological mechanisms of self-tolerance. The past 50 years have seen many advances in the field of self-tolerance, but perhaps, the most tractable of these has been the more recent discovery of a subset T-cells (Treg) whose role is to regulate or damp immunity. This article is intended to first provide the reader with some historical background to explain why we have been slow to identify these cells, despite numerous clues to their existence, and also to indicate how little we know about how they achieve their regulatory function in averting transplant rejection. However, as is often the case in immunology, the therapeutic needs often dictate that our advances move to translation even before detailed explanations of the science are available. The final part of the article will briefly summarize how Treg are being harnessed as agents to interface with or perhaps, replace current drug combinations.

Genetic engineering of human and mouse CD4+ and CD8+ Tregs using lentiviral vectors encoding chimeric antigen receptors

The last decade has seen a significant increase of cell therapy protocols using effector T cells (Teffs) in particular, but also, more recently, non-engineered and expanded polyclonal regulatory T cells (Tregs) to control pathological immune responses such as cancer, autoimmune diseases, or transplantation rejection. However, limitations, such as stability, migration, and specificity of the cell products, have been seen. Thus, genetic engineering of these cell subsets is expected to provide the next generation of T cell therapy products. Lentiviral vectors are commonly used to modify Teffs; however, Tregs are more sensitive to mechanical stress and require specific culture conditions. Also, there is a lack of reproducible and efficient protocols to expand and genetically modify Tregs without affecting their growth and function. Due to smaller number of cells and poorer viability upon culture in vitro, mouse Tregs are more difficult to transduce and amplify in vitro than human Tregs. Here we propose a step-by-step protocol to produce both human and mouse genetically modified CD8⁺ and CD4⁺ Tregs in sufficient amounts to assess their therapeutic efficacy in humanized immunocompromised mouse models and murine models of disease and to establish pre-clinical proofs of concept. We report, for the first time, an efficient and reproducible method to isolate Tregs from human blood or mouse spleen, transduce with a lentiviral vector, and culture, in parallel, CD8⁺ and CD4⁺ Tregs while preserving their function. Beyond chimeric antigen receptor (CAR)-Treg cell therapy, this protocol will promote the development of potential new engineered T cell therapies to treat autoimmune diseases and transplantation rejection.

AIRE deficiency, from preclinical models to human APECED disease

Autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED) is a rare life-threatening autoimmune disease that attacks multiple organs and has its onset in childhood. It is an inherited condition caused by a variety of mutations in the autoimmune regulator (AIRE) gene that encodes a protein whose function has been uncovered by the generation and study of Aire-KO mice. These provided invaluable insights into the link between AIRE expression in medullary thymic epithelial cells (mTECs), and the broad spectrum of self-antigens that these cells express and present to the developing thymocytes. However, these murine models poorly recapitulate all phenotypic aspects of human APECED. Unlike Aire-KO mice, the recently generated Aire-KO rat model presents visual features, organ lymphocytic infiltrations and production of autoantibodies that resemble those observed in APECED patients, making the rat model a main research asset. In addition, ex vivo models of AIRE-dependent self-antigen expression in primary mTECs have been successfully set up. Thymus organoids based on pluripotent stem cell-derived TECs from APECED patients are also emerging, and constitute a promising tool to engineer AIRE-corrected mTECs and restore the generation of regulatory T cells. Eventually, these new models will undoubtedly lead to main advances in the identification and assessment of specific and efficient new therapeutic strategies aiming to restore immunological tolerance in APECED patients.