Decoding mTOR signalling heterogeneity in the tumour microenvironment using multiplexed imaging and graph convolutional networks

Evaluating the contribution of the tumour microenvironment (TME) in tumour progression has proven a complex challenge due to the intricate interactions within the TME. Multiplexed imaging is an emerging technology that allows concurrent assessment of multiple of these components simultaneously. Here we utilise a highly multiplexed dataset of 61 markers across 746 colorectal tumours to investigate how complex mTOR signalling in different tissue compartments influences patient prognosis. We found that the signalling of mTOR pathway can have heterogeneous activation patterns in tumour and immune compartments which correlate with patient prognosis. Using graph neural networks, we determined the most predictive features of mTOR activity in immune cells and identified relevant cellular subpopulations. We validated our observations using spatial transcriptomics data analysis in an independent patient cohort. Our work provides a framework for studying complex cell signalling and reveals important insights for developing mTOR-based therapies.

Opportunities for High-plex Spatial Transcriptomics in Solid Organ Transplantation

The last 5 y have seen the development and widespread adoption of high-plex spatial transcriptomic technology. This technique detects and quantifies mRNA transcripts in situ, meaning that transcriptomic signatures can be sampled from specific cells, structures, lesions, or anatomical regions while conserving the physical relationships that exist within complex tissues. These methods now frequently implement next-generation sequencing, enabling the simultaneous measurement of many targets, up to and including the whole mRNA transcriptome. To date, spatial transcriptomics has been foremost used in the fields of neuroscience and oncology, but there is potential for its use in transplantation sciences. Transplantation has a clear dependence on biopsies for diagnosis, monitoring, and research. Transplant patients represent a unique cohort with multiple organs of interest, clinical courses, demographics, and immunosuppressive regimens. Obtaining high complexity data on the disease processes underlying rejection, tolerance, infection, malignancy, and injury could identify new opportunities for therapeutic intervention and biomarker identification. In this review, we discuss currently available spatial transcriptomic technologies and how they can be applied to transplantation.

Regulatory T-cell therapy approaches

Regulatory T cells (Tregs) have enormous therapeutic potential to treat a variety of immunopathologies characterized by aberrant immune activation. Adoptive transfer of ex vivo expanded autologous Tregs continues to progress through mid- to late-phase clinical trials in several disease spaces and has generated promising preliminary safety and efficacy signals to date. However, the practicalities of this strategy outside of the clinical trial setting remain challenging. Here, we review the current landscape of regulatory T-cell therapy, considering emergent approaches and technologies presenting novel ways to engage Tregs, and reflect on the progress necessary to deliver their therapeutic potential to patients.

Spatial transcriptomic characterization of COVID-19 pneumonitis identifies immune circuits related to tissue injury

Severe lung damage resulting from COVID-19 involves complex interactions between diverse populations of immune and stromal cells. In this study, we used a spatial transcriptomics approach to delineate the cells, pathways, and genes present across the spectrum of histopathological damage in COVID-19-affected lung tissue. We applied correlation network-based approaches to deconvolve gene expression data from 46 areas of interest covering more than 62,000 cells within well-preserved lung samples from 3 patients. Despite substantial interpatient heterogeneity, we discovered evidence for a common immune-cell signaling circuit in areas of severe tissue that involves crosstalk between cytotoxic lymphocytes and pro-inflammatory macrophages. Expression of IFNG by cytotoxic lymphocytes was associated with induction of chemokines, including CXCL9, CXCL10, and CXCL11, which are known to promote the recruitment of CXCR3+ immune cells. The TNF superfamily members BAFF (TNFSF13B) and TRAIL (TNFSF10) were consistently upregulated in the areas with severe tissue damage. We used published spatial and single-cell SARS-CoV-2 data sets to validate our findings in the lung tissue from additional cohorts of patients with COVID-19. The resulting model of severe COVID-19 immune-mediated tissue pathology may inform future therapeutic strategies.

Barriers to Treg therapy in Europe: From production to regulation

There has been an increased interest in cell based therapies for a range of medical conditions in the last decade. This explosion in novel therapeutics research has led to the development of legislation specifically focused on cell and gene based therapies. In Europe, the European medicines agency (EMA) designates any medicines for human use which are based on genes, tissues, or cells as advanced therapy medicinal products or advanced therapy medicinal products (ATMPs). In this article we discuss the hurdles to widespread adoption of ATMPs in Europe, with a focus on regulatory T cells (Tregs). There are numerous barriers which must be overcome before mainstream adoption of Treg therapy becomes a reality. The source of the cells, whether to use autologous or allogenic cells, and the methods through which they are isolated and expanded, must all meet strict good manufacturing practice (GMP) standards to allow use of the products in humans. GMP compliance is costly, with the equipment and reagents providing a significant cost barrier and requiring specialized facilities and personnel. Conforming to the regulations set centrally by the EMA is difficult, and the different interpretations of the regulations across the various member states further complicates the regulatory approval process. The end products then require a complex and robust distribution network to ensure timely delivery of potentially life saving treatments to patients. In a European market whose logistics networks have been hammered by COVID and Brexit, ensuring rapid and reliable delivery systems is a more complex task than ever. In this article we will examine the impact of these barriers on the development and adoption of Tregs in Europe, and potential approaches which could facilitate more widespread use of Tregs, instead of its current concentration in a few very specialized centers.

A GMP Protocol for the Manufacture of Tregs for Clinical Application

Infusion of regulatory T cells is a promising therapeutic strategy in organ transplantation to modulate the immune system, prevent rejection, minimize the need for pharmaceutical immunosuppression, and improve long-term transplant outcomes. Here we describe a GMP-compliant method we have used for the manufacture of ex vivo expanded autologous regulatory T cells for use in clinical trials.

Low dose interleukin-2 selectively expands circulating regulatory T cells but fails to promote liver allograft tolerance in humans

BACKGROUND & AIMS

CD4+CD25+Foxp3+ regulatory T cells (Tregs) are essential to maintain immunological tolerance and have been shown to promote liver allograft tolerance in both rodents and humans. Low-dose IL-2 (LDIL-2) can expand human endogenous circulating Tregs in vivo, but its role in suppressing antigen-specific responses and promoting Treg trafficking to the sites of inflammation is unknown. Likewise, whether LDIL-2 facilitates the induction of allograft tolerance has not been investigated in humans.

METHODS

We conducted a clinical trial in stable liver transplant recipients 2-6 years post-transplant to determine the capacity of LDIL-2 to suppress allospecific immune responses and allow for the complete discontinuation of maintenance immunosuppression (ClinicalTrials.gov NCT02949492). One month after LDIL-2 was initiated, those exhibiting at least a 2-fold increase in circulating Tregs gradually discontinued immunosuppression over a 4-month period while continuing LDIL-2 for a total treatment duration of 6 months.

RESULTS

All participants achieved a marked and sustained increase in circulating Tregs. However, this was not associated with the preferential expansion of donor-reactive Tregs and did not promote the accumulation of intrahepatic Tregs. Furthermore, LDIL-2 induced a marked IFNγ-orchestrated transcriptional response in the liver even before immunosuppression weaning was initiated. The trial was terminated after the first 6 participants failed to reach the primary endpoint owing to rejection requiring reinstitution of immunosuppression.

CONCLUSIONS

The expansion of circulating Tregs in response to LDIL-2 is not sufficient to control alloimmunity and to promote liver allograft tolerance, due, at least in part, to off-target effects that increase liver immunogenicity. Our trial provides unique insight into the mechanisms of action of immunomodulatory therapies such as LDIL-2 and their limitations in promoting alloantigen-specific effects and immunological tolerance.

CLINICAL TRIALS REGISTRATION

The study is registered at ClinicalTrials.gov (NCT02949492).

IMPACT AND IMPLICATIONS

The administration of low-dose IL-2 is an effective way of increasing the number of circulating regulatory T cells (Tregs), an immunosuppressive lymphocyte subset that is key for the establishment of immunological tolerance, but its use to promote allograft tolerance in the setting of clinical liver transplantation had not been explored before. In liver transplant recipients on tacrolimus monotherapy, low-dose IL-2 effectively expanded circulating Tregs but did not increase the number of Tregs with donor specificity, nor did it promote their trafficking to the transplanted liver. Low-dose IL-2 did not facilitate the discontinuation of tacrolimus and elicited, as an off-target effect, an IFNγ-orchestrated inflammatory response in the liver that resembled T cell-mediated rejection. These results, supporting an unexpected role for IL-2 in regulating the immunogenicity of the liver, highlight the need to carefully evaluate systemic immunoregulatory strategies with investigations that are not restricted to the blood compartment and involve target tissues such as the liver.

Engineered human cytokine/antibody fusion proteins expand regulatory T cells and confer autoimmune disease protection

Low-dose human interleukin-2 (hIL-2) treatment is used clinically to treat autoimmune disorders due to the cytokine's preferential expansion of immunosuppressive regulatory T cells (Tregs). However, off-target immune cell activation and short serum half-life limit the clinical potential of IL-2 treatment. Recent work showed that complexes comprising hIL-2 and the anti-hIL-2 antibody F5111 overcome these limitations by preferentially stimulating Tregs over immune effector cells. Although promising, therapeutic translation of this approach is complicated by the need to optimize dosing ratios and by the instability of the cytokine/antibody complex. We leverage structural insights to engineer a single-chain hIL-2/F5111 antibody fusion protein, termed F5111 immunocytokine (IC), which potently and selectively activates and expands Tregs. F5111 IC confers protection in mouse models of colitis and checkpoint inhibitor-induced diabetes mellitus. These results provide a roadmap for IC design and establish a Treg-biased immunotherapy that could be clinically translated for autoimmune disease treatment.

Dampened Inflammatory Signalling and Myeloid-Derived Suppressor-Like Cell Accumulation Reduces Circulating Monocytic HLA-DR Density and May Associate With Malignancy Risk in Long-Term Renal Transplant Recipients

Background

Malignancy is a major cause of morbidity and mortality in transplant recipients. Identification of those at highest risk could facilitate pre-emptive intervention such as reduction of immunosuppression. Reduced circulating monocytic HLA-DR density is a marker of immune depression in the general population and associates with poorer outcome in critical illness. It has recently been used as a safety marker in adoptive cell therapy trials in renal transplantation. Despite its potential as a marker of dampened immune responses, factors that impact upon monocytic HLA-DR density and the long-term clinical sequelae of this have not been assessed in transplant recipients.

Methods

A cohort study of stable long-term renal transplant recipients was undertaken. Serial circulating monocytic HLA-DR density and other leucocyte populations were quantified by flow cytometry. Gene expression of monocytes was performed using the Nanostring nCounter platform, and 13-plex cytokine bead array used to quantify serum concentrations. The primary outcome was malignancy development during one-year follow-up. Risk of malignancy was calculated by univariate and multivariate proportionate hazards modelling with and without adjustment for competing risks.

Results

Monocytic HLA-DR density was stable in long-term renal transplant recipients (n=135) and similar to non-immunosuppressed controls (n=29), though was suppressed in recipients receiving prednisolone. Decreased mHLA-DRd was associated with accumulation of CD14+CD11b+CD33+HLA-DRlo monocytic myeloid-derived suppressor-like cells. Pathway analysis revealed downregulation of pathways relating to cytokine and chemokine signalling in monocytes with low HLA-DR density; however serum concentrations of major cytokines did not differ between these groups. There was an independent increase in malignancy risk during follow-up with decreased HLA-DR density.

Conclusions

Dampened chemokine and cytokine signalling drives a stable reduction in monocytic HLA-DR density in long-term transplant recipients and associates with subsequent malignancy risk. This may function as a novel marker of excess immunosuppression. Further study is needed to understand the mechanism behind this association.

Competing magnetic states andM-Hloop splitting in core-shell NiO nanoparticles

Magnetic relaxation in a nanoparticles system depends on the intra-particle interactions, reversal mechanism, the anisotropy field, easy axis distribution, particle volume, lattice defects, surface defects, materials composite, etc. Here we report the competing magnetic states between superparamagnetic blocking and Néel transition states in 14 nm core-shell NiO nanoparticles. A crossover temperature of 50 K was observed for both these states from the zero field cooled/field cooled magnetization curves taken at different fields. At crossover temperature, an interestingM-Hloop splitting is observed which is attributed to the slow spin relaxation. This anomalousM-Hloop splitting behaviour was found to be particle size dependent and suppressed for diameters above and below 14 nm which indicates a critical size for these competing magnetic states. Additional neutron diffraction experiments confirmed this observation. This experimental study provides a new insight for the understanding of intra-particle interactions in fine antiferromagnetic nanoparticles and obtained results are an important step towards deeper understanding of the competing/non-competing modes between superparamagnetic blocked and Néel transition states.

SARS-CoV-2-Specific T Cell Responses Are Not Associated with Protection against Reinfection in Hemodialysis Patients

Significance Statement

Patients on hemodialysis (HD) are vulnerable to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and mount poor neutralizing antibody responses after two-dose vaccination. Although serological responses have been associated with reduced rates of reinfection, the relationship between cellular immunogenicity and protection has not been established. We report, for the first time, high incidence of reinfection in patients on HD who are vaccine naive (25%), which identifies that T cell responses do not predict protection against reinfection. Instead, patients on HD who went on to become reinfected had mounted highly variable and sometimes robust proliferative T cell responses to a broad array of SARS-CoV-2 peptide pools during the primary infection. The understanding that SARS-CoV-2–specific T cell responses are not predictive of protection against future infection will be a critical issue when measuring clinical efficacy of vaccination in these vulnerable cohorts, particularly when facing rapidly emerging variants of concern.

Transplantation Without Overimmunosuppression (TWO) study protocol: a phase 2b randomised controlled single-centre trial of regulatory T cell therapy to facilitate immunosuppression reduction in living donor kidney transplant recipients

INTRODUCTION

Regulatory T cell (Treg) therapy has been demonstrated to facilitate long-term allograft survival in preclinical models of transplantation and may permit reduction of immunosuppression and its associated complications in the clinical setting. Phase 1 clinical trials have shown Treg therapy to be safe and feasible in clinical practice. Here we describe a protocol for the TWO study, a phase 2b randomised control trial of Treg therapy in living donor kidney transplant recipients that will confirm safety and explore efficacy of this novel treatment strategy.

METHODS AND ANALYSIS

60 patients will be randomised on a 1:1 basis to Treg therapy (TR001) or standard clinical care (control). Patients in the TR001 arm will receive an infusion of autologous polyclonal ex vivo expanded Tregs 5 days after transplantation instead of standard monoclonal antibody induction. Maintenance immunosuppression will be reduced over the course of the post-transplant period to low-dose tacrolimus monotherapy. Control participants will receive a standard basiliximab-based immunosuppression regimen with long-term tacrolimus and mycophenolate mofetil immunosuppression. The primary endpoint is biopsy proven acute rejection over 18 months; secondary endpoints include immunosuppression burden, chronic graft dysfunction and drug-related complications.

ETHICS AND DISSEMINATION

Ethical approval has been provided by the National Health Service Health Research Authority South Central-Oxford A Research Ethics Committee (reference 18/SC/0054). The study also received authorisation from the UK Medicines and Healthcare products Regulatory Agency and is being run in accordance with the principles of Good Clinical Practice, in collaboration with the registered trials unit Oxford Clinical Trials Research Unit. Results from the TWO study will be published in peer-reviewed scientific/medical journals and presented at scientific/clinical symposia and congresses.

TRIAL REGISTRATION NUMBER

ISRCTN: 11038572; Pre-results.

A non-coding RNA balancing act: miR-346-induced DNA damage is limited by the long non-coding RNA NORAD in prostate cancer

BACKGROUND

miR-346 was identified as an activator of Androgen Receptor (AR) signalling that associates with DNA damage response (DDR)-linked transcripts in prostate cancer (PC). We sought to delineate the impact of miR-346 on DNA damage, and its potential as a therapeutic agent.

METHODS

RNA-IP, RNA-seq, RNA-ISH, DNA fibre assays, in vivo xenograft studies and bioinformatics approaches were used alongside a novel method for amplification-free, single nucleotide-resolution genome-wide mapping of DNA breaks (INDUCE-seq).

RESULTS

miR-346 induces rapid and extensive DNA damage in PC cells - the first report of microRNA-induced DNA damage. Mechanistically, this is achieved through transcriptional hyperactivation, R-loop formation and replication stress, leading to checkpoint activation and cell cycle arrest. miR-346 also interacts with genome-protective lncRNA NORAD to disrupt its interaction with PUM2, leading to PUM2 stabilisation and its increased turnover of DNA damage response (DDR) transcripts. Confirming clinical relevance, NORAD expression and activity strongly correlate with poor PC clinical outcomes and increased DDR in biopsy RNA-seq studies. In contrast, miR-346 is associated with improved PC survival. INDUCE-seq reveals that miR-346-induced DSBs occur preferentially at binding sites of the most highly-transcriptionally active transcription factors in PC cells, including c-Myc, FOXA1, HOXB13, NKX3.1, and importantly, AR, resulting in target transcript downregulation. Further, RNA-seq reveals widespread miR-346 and shNORAD dysregulation of DNA damage, replication and cell cycle processes. NORAD drives target-directed miR decay (TDMD) of miR-346 as a novel genome protection mechanism: NORAD silencing increases mature miR-346 levels by several thousand-fold, and WT but not TDMD-mutant NORAD rescues miR-346-induced DNA damage. Importantly, miR-346 sensitises PC cells to DNA-damaging drugs including PARP inhibitor and chemotherapy, and induces tumour regression as a monotherapy in vivo, indicating that targeting miR-346:NORAD balance is a valid therapeutic strategy.

CONCLUSIONS

A balancing act between miR-346 and NORAD regulates DNA damage and repair in PC. miR-346 may be particularly effective as a therapeutic in the context of decreased NORAD observed in advanced PC, and in transcriptionally-hyperactive cancer cells.

Hermansky-Pudlak syndrome type 1 causes impaired anti-microbial immunity and inflammation due to dysregulated immunometabolism

Hermansky-Pudlak syndrome (HPS) types 1 and 4 are caused by defective vesicle trafficking. The mechanism for Crohn's disease-like inflammation, lung fibrosis, and macrophage lipid accumulation in these patients remains enigmatic. The aim of this study is to understand the cellular basis of inflammation in HPS-1. We performed mass cytometry, proteomic and transcriptomic analyses to investigate peripheral blood cells and serum of HPS-1 patients. Using spatial transcriptomics, granuloma-associated signatures in the tissue of an HPS-1 patient with granulomatous colitis were dissected. In vitro studies were conducted to investigate anti-microbial responses of HPS-1 patient macrophages and cell lines. Monocytes of HPS-1 patients exhibit an inflammatory phenotype associated with dysregulated TNF, IL-1α, OSM in serum, and monocyte-derived macrophages. Inflammatory macrophages accumulate in the intestine and granuloma-associated macrophages in HPS-1 show transcriptional signatures suggestive of a lipid storage and metabolic defect. We show that HPS1 deficiency leads to an altered metabolic program and Rab32-dependent amplified mTOR signaling, facilitated by the accumulation of mTOR on lysosomes. This pathogenic mechanism translates into aberrant bacterial clearance, which can be rescued with mTORC1 inhibition. Rab32-mediated mTOR signaling acts as an immuno-metabolic checkpoint, adding to the evidence that defective bioenergetics can drive hampered anti-microbial activity and contribute to inflammation.

Freezing Medium Containing 5% DMSO Enhances the Cell Viability and Recovery Rate After Cryopreservation of Regulatory T Cell Products ex vivo and in vivo

Cell therapies have significant therapeutic potential in diverse fields including regenerative medicine, transplantation tolerance, and autoimmunity. Within these fields, regulatory T cells (Treg) have been deployed to ameliorate aberrant immune responses with great success. However, translation of the cryopreservation strategies employed for other cell therapy products, such as effector T cell therapies, to Treg therapies has been challenging. The lack of an optimized cryopreservation strategy for Treg products presents a substantial obstacle to their broader application, particularly as administration of fresh cells limits the window available for sterility and functional assessment. In this study, we aimed to develop an optimized cryopreservation strategy for our CD4+CD25+Foxp3+ Treg clinical product. We investigate the effect of synthetic or organic cryoprotectants including different concentrations of DMSO on Treg recovery, viability, phenotype, cytokine production, suppressive capacity, and in vivo survival following GMP-compliant manufacture. We additionally assess the effect of adding the extracellular cryoprotectant polyethylene glycol (PEG), or priming cellular expression of heat shock proteins as strategies to improve viability. We find that cryopreservation in serum-free freezing medium supplemented with 10% human serum albumin and 5% DMSO facilitates improved Treg recovery and functionality and supports a reduced DMSO concentration in Treg cryopreservation protocols. This strategy may be easily incorporated into clinical manufacture protocols for future studies.

Towards regulatory cellular therapies in solid organ transplantation

Organ transplantation is a modern medical success story. However, since its inception it has been limited by the need for pharmacological immunosuppression. Regulatory cellular therapies offer an attractive solution to these challenges by controlling transplant alloresponses through multiple parallel suppressive mechanisms. A number of cell types have seen an accelerated development into human trials and are now on the threshold of a long-awaited breakthrough in personalized transplant therapeutics. Here we assess recent developments with a focus on the most likely candidates, some of which have already facilitated successful immunosuppression withdrawal in early clinical trials. We propose that this may constitute a promising approach in clinical transplantation but also evaluate outstanding issues in the field, providing cause for cautious optimism.

Therapeutically expanded human regulatory T-cells are super-suppressive due to HIF1A induced expression of CD73

The adoptive transfer of regulatory T-cells (Tregs) is a promising therapeutic approach in transplantation and autoimmunity. However, because large cell numbers are needed to achieve a therapeutic effect, in vitro expansion is required. By comparing their function, phenotype and transcriptomic profile against ex vivo Tregs, we demonstrate that expanded human Tregs switch their metabolism to aerobic glycolysis and show enhanced suppressive function through hypoxia-inducible factor 1-alpha (HIF1A) driven acquisition of CD73 expression. In conjunction with CD39, CD73 expression enables expanded Tregs to convert ATP to immunosuppressive adenosine. We conclude that for maximum therapeutic benefit, Treg expansion protocols should be optimised for CD39/CD73 co-expression.

Chimeric antigen receptor-modified human regulatory T cells that constitutively express IL-10 maintain their phenotype and are potently suppressive

Clinical trials of Treg therapy in transplantation are currently entering phases IIa and IIb, with the majority of these employing polyclonal Treg populations that harbor a broad specificity. Enhancing Treg specificity is possible with the use of chimeric antigen receptors (CARs), which can be customized to respond to a specific human leukocyte antigen (HLA). In this study, we build on our previous work in the development of HLA-A2 CAR-Tregs by further equipping cells with the constitutive expression of interleukin 10 (IL-10) and an imaging reporter as additional payloads. Cells were engineered to express combinations of these domains and assessed for phenotype and function. Cells expressing the full construct maintained a stable phenotype after transduction, were specifically activated by HLA-A2, and suppressed alloresponses potently. The addition of IL-10 provided an additional advantage to suppressive capacity. This study therefore provides an important proof-of-principle for this cell engineering approach for next-generation Treg therapy in transplantation.

Abstract 2362: Long non-coding RNA NORAD interaction with miR-346 impacts DNA damage response and anti-tumor immunity in prostate cancer

NORAD (NOn-Coding RNA Activated by DNA Damage) is a highly-abundant, evolutionarily-conserved lncRNA. It maintains mitosis, DNA damage repair (DDR), and chromosomal integrity through PUM1/2 sequestration (PUM1/2 activity increases turnover of DDR factors), and through formation of a TOPO2-containing complex critical for genome integrity. We show that NORAD activity is regulated by microRNA-346 (miR-346), which disrupts NORAD:PUM2, interaction, leading to PUM2 destabilization and derepression of PUM1/2 DDR targets in prostate cancer (PCa) cells. RNA-seq reveals widespread miR-346 dysregulation of DNA damage, DNA replication and cell cycle transcripts. A novel method for high resolution, amplification-free genome-wide mapping of double strand DNA breaks (DSBs) (INDUCE-seq) reveals miR-346 induces DSBs specifically at transcription start sites characterized by phospho-PolII/CTCF/ZFX binding - a phenomenon not previously described for any microRNA. Mechanistically, DSBs result from miR-346 activation of transcription, R-loop formation and replicative catastrophe. This results in rapid dose-dependent induction of DNA damage, leading to checkpoint activation and cytosolic DNA accumulation, rescuable by NORAD. This cytosolic DNA activates cytokine-inducing cGAS-STING/RIG-1 innate immune pathways. Indeed, RNA-seq analysis reveals the top NORAD-enriched pathway as interferon signaling, while cytokine arrays reveal secretion of pro-Treg, MDSC and TAM factors by NORAD-overexpressing cells. NORAD inversely correlates with tumor immune response in gene expression data sets, and expression-based immune infiltration scoring predicts increased M2 macrophages, and reduced NK, CD8+ve, Th1 and cytotoxic T cells in NORAD-high vs NORAD-low PCa, indicating an ‘immune-cold' microenvironment. Excitingly, NORAD silencing results in several thousand-fold increase in mature miR-346 without affecting pri-miR levels, supporting NORAD's ability to drive target-directed microRNA decay (TDMD) of miR-346 as a critical novel genome protection mechanism. However, miR-346-induced DNA damage is in part NORAD-independent, since miR-346 induces DSBs within 1h, and in contrast to most miRs is predominantly chromatin-bound (NORAD is cytoplasmic). Critically, miR-346 sensitizes PCa cells to DNA-damaging chemotherapy and PARP inhibition. MiR-346 expression is associated with improved PCa survival, and reduced in high vs low Gleason grade PCa. Notably, NORAD strongly correlates with DDR signatures in early-stage, but not advanced metastatic PCa. Despite its DDR-promoting activity, and in contrast to miR-346, it is associated with worse survival across multiple patient cohorts. In conclusion, these data demonstrate that the NORAD:miR-346 interaction determines DNA damage response and innate immune pathway activity to regulate tumor immune response in PCa.

Citation Format: Claire Fletcher, Lin Deng, Folake Orafidiya, Wei Yuan, Ines Figueiredo, Bora Gurel, Damien Leach, Fadi Issa, Antje Neeb, Denisa Bogdan, Felix Dobbs, Yiannis Philippou, Emma A. Murphy, Shuang G. Zhao, Joanna Hester, Richard J. Bryant, Simon H. Reed, Karen E. Knudsen, Ian G. Mills, Johann de Bono, Charlotte L. Bevan. Long non-coding RNA NORAD interaction with miR-346 impacts DNA damage response and anti-tumor immunity in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2362.

Feasibility, long-term safety, and immune monitoring of regulatory T cell therapy in living donor kidney transplant recipients

Short-term outcomes in kidney transplantation are marred by progressive transplant failure and mortality secondary to immunosuppression toxicity. Immune modulation with autologous polyclonal regulatory T cell (Treg) therapy may facilitate immunosuppression reduction promoting better long-term clinical outcomes. In a Phase I clinical trial, 12 kidney transplant recipients received 1-10 × 10⁶ Treg per kg at Day +5 posttransplantation in lieu of induction immunosuppression (Treg Therapy cohort). Nineteen patients received standard immunosuppression (Reference cohort). Primary outcomes were rejection-free and patient survival. Patient and transplant survival was 100%; acute rejection-free survival was 100% in the Treg Therapy versus 78.9% in the reference cohort at 48 months posttransplant. Treg therapy revealed no excess safety concerns. Four patients in the Treg Therapy cohort had mycophenolate mofetil withdrawn successfully and remain on tacrolimus monotherapy. Treg infusion resulted in a long-lasting dose-dependent increase in peripheral blood Tregs together with an increase in marginal zone B cell numbers. We identified a pretransplantation immune phenotype suggesting a high risk of unsuccessful ex-vivo Treg expansion. Autologous Treg therapy is feasible, safe, and is potentially associated with a lower rejection rate than standard immunosuppression. Treg therapy may provide an exciting opportunity to minimize immunosuppression therapy and improve long-term outcomes.

Development of LT-HSC-Reconstituted Non-Irradiated NBSGW Mice for the Study of Human Hematopoiesis In Vivo

Humanized immune system (HIS) mouse models are useful tools for the in vivo investigation of human hematopoiesis. However, the majority of HIS models currently in use are biased towards lymphocyte development and fail to support long-term multilineage leucocytes and erythrocytes. Those that achieve successful multilineage reconstitution often require preconditioning steps which are expensive, cause animal morbidity, are technically demanding, and poorly reproducible. In this study, we address this challenge by using HSPC-NBSGW mice, in which NOD,B6.SCID IL-2rγ-/-KitW41/W41 (NBSGW) mice are engrafted with human CD133+ hematopoietic stem and progenitor cells (HSPCs) without the need for preconditioning by sublethal irradiation. These HSPCs are enriched in long-term hematopoietic stem cells (LT-HSCs), while NBSGW mice are permissive to human hematopoietic stem cell (HSC) engraftment, thus reducing the cell number required for successful HIS development. B cells reconstitute with the greatest efficiency, including mature B cells capable of class-switching following allogeneic stimulation and, within lymphoid organs and peripheral blood, T cells at a spectrum of stages of maturation. In the thymus, human thymocytes are identified at all major stages of development. Phenotypically distinct subsets of myeloid cells, including dendritic cells and mature monocytes, engraft to a variable degree in the bone marrow and spleen, and circulate in peripheral blood. Finally, we observe human erythrocytes which persist in the periphery at high levels following macrophage clearance. The HSPC-NBSGW model therefore provides a useful platform for the study of human hematological and immunological processes and pathologies.

Immune Monitoring for Advanced Cell Therapy Trials in Transplantation: Which Assays and When?

A number of immune regulatory cellular therapies, including regulatory T cells and mesenchymal stromal cells, have emerged as novel alternative therapies for the control of transplant alloresponses. Clinical studies have demonstrated their feasibility and safety, however developing our understanding of the impact of cellular therapeutics in vivo requires advanced immune monitoring strategies. To accurately monitor the immune response, a combination of complementary methods is required to measure the cellular and molecular phenotype as well as the function of cells involved. In this review we focus on the current immune monitoring strategies and discuss which methods may be utilized in the future.

IL-33 drives the production of mouse regulatory T cells with enhanced in vivo suppressive activity in skin transplantation

Regulatory T cells (Tregs) are crucial mediators of immune homeostasis with the ability to modulate allogeneic response and control transplant rejection. Although Treg-based cell therapies have shown immense promise, methods to optimize current strategies are critical for successful implementation within the clinic. IL-33 is a cytokine with pleiotropic properties and effects on Treg function and development. In this study, we explored the unique properties of Treg populations activated through the IL-33/ST2 pathway, aiming to exploit their tolerogenic properties for cell therapy. We show that treatment with exogenous IL-33 results in a generalized downregulation of genes critical to T cell biology together with an upregulation of Treg-associated genes. Tregs that develop in response to IL-33 upregulate critical Treg-associated markers, yet without developing enhanced in vitro suppressive capacity. Conversely, these Tregs display potent regulatory activity in vivo, promoting long-term skin allograft survival in a stringent transplantation model. Detailed transcriptomic and immunophenotypic analyses of IL-33-expanded Tregs reveal an enhancement in graft-homing chemokine receptors, which may be partly responsible for their superior in vivo activity that is not reflected in vitro. IL-33 treatment is therefore an attractive adjunctive strategy for patients receiving Treg cell therapeutics.

Recent advances in our understanding of the allograft response

Organ transplantation is a life-saving treatment for end-stage organ failure. However, despite advances in immunosuppression, donor matching, tissue typing, and organ preservation, many organs are still lost each year to rejection. Ultimately, tolerance in the absence of immunosuppression is the goal, and although this seldom occurs spontaneously, a deeper understanding of alloimmunity may provide avenues for future therapies which aid in its establishment. Here, we highlight the recent key advances in our understanding of the allograft response. On the innate side, recent work has highlighted the previously unrecognised role of innate lymphoid cells as well as natural killer cells in promoting the alloresponse. The two major routes of allorecognition have recently been joined by a third newly identified pathway, semi-direct allorecognition, which is proving to be a key active pathway in transplantation. Through this review, we detail these newly defined areas in the allograft response and highlight areas for potential future therapeutic intervention.

The Oxford Classic Links Epithelial-to-Mesenchymal Transition to Immunosuppression in Poor Prognosis Ovarian Cancers

PURPOSE

Using RNA sequencing, we recently developed the 52-gene-based Oxford classifier of carcinoma of the ovary (Oxford Classic, OxC) for molecular stratification of serous ovarian cancers (SOCs) based on the molecular profiles of their cell of origin in the fallopian tube epithelium. Here, we developed a 52-gene NanoString panel for the OxC to test the robustness of the classifier.

EXPERIMENTAL DESIGN

We measured the expression of the 52 genes in an independent cohort of prospectively collected SOC samples (n = 150) from a homogenous cohort who were treated with maximal debulking surgery and chemotherapy. We performed data mining of published expression profiles of SOCs and validated the classifier results on tissue arrays comprising 137 SOCs.

RESULTS

We found evidence of profound nongenetic heterogeneity in SOCs. Approximately 20% of SOCs were classified as epithelial-to-mesenchymal transition-high (EMT-high) tumors, which were associated with poor survival. This was independent of established prognostic factors, such as tumor stage, tumor grade, and residual disease after surgery (HR, 3.3; P = 0.02). Mining expression data of 593 patients revealed a significant association between the EMT scores of tumors and the estimated fraction of alternatively activated macrophages (M2; P < 0.0001), suggesting a mechanistic link between immunosuppression and poor prognosis in EMT-high tumors.

CONCLUSIONS

The OxC-defined EMT-high SOCs carry particularly poor prognosis independent of established clinical parameters. These tumors are associated with high frequency of immunosuppressive macrophages, suggesting a potential therapeutic target to improve clinical outcome.

Biomarker and surrogate development in vascularised composite allograft transplantation: Current progress and future challenges

Vascularised composite allograft (VCA) transplantation is now a feasible reconstructive option for patients who have suffered significant soft tissue injuries. However, despite numerous technical advances in the field over two decades, a number of challenges remain, not least the management of transplant rejection. Part of the difficulty faced by clinicians is the early recognition and prevention of acute rejection episodes. Whilst this is potentially easier in VCAs than solid organ transplants, due to their visible skin component, at present the only validated method for the diagnosis of acute rejection is histological examination of a tissue biopsy. The aim of this review article is to provide an evidence-based overview of progress in the field of VCA biomarker discovery, including immune cell subsets, immune cell effector pathways, and circulating markers of allograft damage, and to discuss future challenges in the field.

Magnetic homogeneity in Fe-Mn co-doped NiO nanoparticles

The effect of Fe and Mn co-doping on the magnetic properties of the antiferromagnetic (AFM) NiO nanoparticles which offer large potential for different magnetic applications have been studied. The Rietveld refinement fitting of powder x-ray diffractometry (XRD) patterns confirmed the phase formation of face-centred cubic crystal structure of NiO and average crystallite size lies in the short range of 32-38 nm. The cavity and broadband ferromagnetic resonance (FMR) measurements taken at room temperature demonstrate the smaller local magnetic inhomogeneity for 4%Mn-4%Fe co-doped NiO nanoparticles as compared to undoped, single doped and co-doped with different concentration NiO nanoparticles. The M-H loops revealed the room temperature ferromagnetism-like behaviour for higher Fe doping concentration and lower Mn doping concentration. This can be attributed to the double exchange interaction. The zero field cooled (ZFC) and field cooled (FC) dc magnetization curves showed a small surface freezing peak (at[Formula: see text] at low temperatures and a blocking peak (at [Formula: see text] at higher temperatures. For samples with 4%Mn-4%Fe and 2%Mn-6%Fe, the blocking peak was found at a relatively high temperature in comparison to other samples. This can be attributed to the presence of magnetic exchange interactions which block the magnetic spins against a thermal increase. The ZFC AC-susceptibility showed three peaks; a surface freezing peak at T_f, a blocking peak at T_B peak and an anomalous peak at T_x in between [Formula: see text] and [Formula: see text], which was found to be most prominent for the 4%Mn-4%Fe co-doped nanoparticles. The neutron diffraction pattern confirmed the AFM order of the core of the 4%Mn-4%Fe co-doped nanoparticles, which indicates an AFM coupling between the Fe²⁺ and Mn²⁺ ions and the Ni²⁺ ions through super-exchange interaction. Therefore, the origin of T_X peak can be attributed to the ferromagnetic coupling between the Fe²⁺ and Mn²⁺ ions which has a maximum strength at equal concentration. Thus, small and equal doping concentration of Fe and Mn in NiO nanoparticles increase the magnetic homogeneity which makes them attractive for magnetic applications.

Regulatory B cells in transplantation: roadmaps to clinic

Over the last two decades, an additional and important role for B cells has been established in immune regulation. Preclinical studies demonstrate that regulatory B cells (Breg) can prolong allograft survival in animal models and induce regulatory T cells. Operationally tolerant human kidney transplant recipients demonstrate B-cell-associated gene signatures of immune tolerance, and novel therapeutic agents can induce Bregs in phase I clinical trials in transplantation. Our rapidly expanding appreciation of this novel B-cell subtype has made the road to clinical application a reality. Here, we outline several translational pathways by which Bregs could soon be introduced to the transplant clinic.

CD70 expression determines the therapeutic efficacy of expanded human regulatory T cells

Regulatory T cells (Tregs) are critical mediators of immune homeostasis. The co-stimulatory molecule CD27 is a marker of highly suppressive Tregs, although the role of the CD27-CD70 receptor-ligand interaction in Tregs is not clear. Here we show that after prolonged in vitro stimulation, a significant proportion of human Tregs gain stable CD70 expression while losing CD27. The expression of CD70 in expanded Tregs is associated with a profound loss of regulatory function and an unusual ability to provide CD70-directed co-stimulation to TCR-activated conventional T cells. Genetic deletion of CD70 or its blockade prevents Tregs from delivering this co-stimulatory signal, thus maintaining their regulatory activity. High resolution targeted single-cell RNA sequencing of human peripheral blood confirms the presence of CD27-CD70+ Treg cells. These findings have important implications for Treg-based clinical studies where cells are expanded over extended periods in order to achieve sufficient treatment doses.

Distinct metabolic pathways mediate regulatory T cell differentiation and function

Investigation of the cellular metabolic pathways of immune cells, or immunometabolism, is a field of increasing interest. An understanding of immunometabolism provides routes to modifying T cell function for therapeutic purposes. Here, we review immunometabolism with a specific focus on regulatory T cells (Tregs). While T cells are known to switch their metabolic profile from oxidative phosphorylation to aerobic glycolysis upon activation, in vitro-induced Tregs display alternate metabolic characteristics which may be related to their specialised suppressive function. Recent data suggest that the preferential pathways employed by Tregs differ in vivo and ex vivo. Metabolic 'harshness', particularly the deterioration of glycolysis, positively affects Treg differentiation and function, while negatively correlating with Treg clonal expansion and migratory capacity. These context-dependent findings provide new insights into the behaviour of Tregs with implications for both tumour immunology and autoimmunity. This review examines the field in detail, offering an overview of our current understanding of Treg immunometabolism.

Systemic silencing of PHD2 causes reversible immune regulatory dysfunction

Physiological effects of cellular hypoxia are sensed by prolyl hydroxylase (PHD) enzymes which regulate HIFs. Genetic interventions on HIF/PHD pathways reveal multiple phenotypes that extend the known biology of hypoxia. Recent studies unexpectedly implicate HIF in aspects of multiple immune and inflammatory pathways. However such studies are often limited by systemic lethal effects and/or use tissue-specific recombination systems, which are inherently irreversible, un-physiologically restricted and difficult to time. To study these processes better we developed recombinant mice which express tetracycline-regulated shRNAs broadly targeting the main components of the HIF/PHD pathway, permitting timed bi-directional intervention. We have shown that stabilization of HIF levels in adult mice through PHD2 enzyme silencing by RNA interference, or inducible recombination of floxed alleles, results in multi-lineage leukocytosis and features of autoimmunity. This phenotype was rapidly normalized on re-establishment of the hypoxia-sensing machinery when shRNA expression was discontinued. In both situations these effects were mediated principally through the Hif2a isoform. Assessment of cells bearing regulatory T cell markers from these mice revealed defective function and pro-inflammatory effects in vivo. We believe our findings have shown a new role for the PHD2/Hif2a couple in the reversible regulation of T cell and immune activity.

Transiently Activated Human Regulatory T Cells Upregulate BCL-XL Expression and Acquire a Functional Advantage in vivo

Regulatory T cells (Tregs) can control excessive or undesirable immune responses toward autoantigens, alloantigens, and pathogens. In transplantation, host immune responses against the allograft are suppressed through the use of immunosuppressive drugs, however this often results in life-threatening side effects including nephrotoxicity and an increased incidence of cancer and opportunistic infections. Tregs can control graft-vs.-host disease and transplant rejection in experimental models, providing impetus for the use of Tregs as a cellular therapy in clinical transplantation. One of the major barriers to the widespread use of Treg cellular therapy is the requirement to expand cells ex vivo to large numbers in order to alter the overall balance between regulatory and effector cells. Methods that enhance suppressive capacity thereby reducing the need for expansion are therefore of interest. Here, we have compared the function of freshly-isolated and ex vivo-manipulated human Tregs in a pre-clinical humanized mouse model of skin transplantation. Sorted human CD127^loCD25⁺CD4⁺ Tregs were assessed in three different conditions: freshly-isolated, following transient in vitro activation with antiCD3/antiCD28 beads or after ex vivo-expansion for 2 weeks in the presence of antiCD3/antiCD28 beads and recombinant human IL2. While ex vivo-expansion of human Tregs increased their suppressive function moderately, transient in vitro-activation of freshly isolated Tregs resulted in a powerful enhancement of Treg activity sufficient to promote long-term graft survival of all transplants in vivo. In order to investigate the mechanisms responsible for these effects, we measured the expression of Treg-associated markers and susceptibility to apoptosis in activated Tregs. Transiently activated Tregs displayed enhanced survival and proliferation in vitro and in vivo. On a molecular level, Treg activation resulted in an increased expression of anti-apoptotic BCL2L1 (encoding BCL-XL) which may be at least partially responsible for the observed enhancement in function. Our results suggest that in vitro activation of human Tregs arms them with superior proliferative and survival abilities, enabling them to more effectively control alloresponses. Importantly, this transient activation results in a rapid functional enhancement of freshly-isolated Tregs, thereby providing an opportunity to eliminate the need for in vitro expansion in select circumstances. A protocol employing this technique would therefore benefit from a reduced requirement for large cell numbers for effective therapy.

Isolation of Human Regulatory T Lymphocytes by Fluorescence-Activated Cell Sorting

Regulatory T cells (Tregs) are a population of lymphocytes that exerts suppressive effects upon the immune system. In human peripheral blood, the major population of T lymphocytes with suppressive capacity are defined by expression of the T cell co-receptor CD4 and the interleukin-2 receptor α-chain (CD25), combined with minimal expression of the interleukin-7 receptor α subunit (CD127). We begin by outlining the method for isolating peripheral blood mononuclear cells (PBMCs) from human blood by centrifugation of whole blood overlayed on a hydrophilic polysaccharide, with an additional erythrocyte lysis step. The protocol that follows utilizes Fluorescence-Activated Cell Sorting (FACS) for the isolation of this CD4⁺CD25⁺CD127^lo population of regulatory T cells, with high yield and purity, from immunostained PBMCs. Prior to FACS isolation, this protocol exploits magnetic immunoselection for pre-enrichment of CD25⁺ PBMC, which reduces the duration of the subsequent FACS isolation.

Deciphering the Contribution of γδ T Cells to Outcomes in Transplantation

γδ T cells are a subpopulation of lymphocytes expressing heterodimeric T-cell receptors composed of γ and δ chains. They are morphologically and functionally heterogeneous, innate yet also adaptive in behavior, and exhibit diverse activities spanning immunosurveillance, immunomodulation, and direct cytotoxicity. The specific responses of γδ T cells to allografts are yet to be fully elucidated with evidence of both detrimental and tolerogenic roles in different settings. Here we present an overview of γδ T-cell literature, consider ways in which their functional heterogeneity contributes to the outcomes after transplantation, and reflect on methods to harness their beneficial properties.

Seronegative antibody-mediated neurology after immune checkpoint inhibitors

Checkpoint inhibitor medications have revolutionized oncology practice, but frequently induce immune‐related adverse events. During autoimmune neurology practice over 20 months, we prospectively identified four patients with likely antibody‐mediated neurological diseases after checkpoint inhibitors: longitudinally extensive transverse myelitis, Guillain–Barré syndrome, and myasthenia gravis. All patients shared three characteristics: symptoms commenced 4 weeks after drug administration, responses to conventional immunotherapies were excellent, and autoantibodies traditionally associated with their syndrome were absent. However, serum immunoglobulins from the myelitis and Guillain–Barré syndrome patients showed novel patterns of tissue reactivity. Vigilance is required for antibody‐mediated neurology after checkpoint inhibitor administration. This phenomenon may inform the immunobiology of antibody‐mediated diseases.

Minimum Information about T Regulatory Cells: A Step toward Reproducibility and Standardization

Cellular therapies with CD4+ T regulatory cells (Tregs) hold promise of efficacious treatment for the variety of autoimmune and allergic diseases as well as posttransplant complications. Nevertheless, current manufacturing of Tregs as a cellular medicinal product varies between different laboratories, which in turn hampers precise comparisons of the results between the studies performed. While the number of clinical trials testing Tregs is already substantial, it seems to be crucial to provide some standardized characteristics of Treg products in order to minimize the problem. We have previously developed reporting guidelines called minimum information about tolerogenic antigen-presenting cells, which allows the comparison between different preparations of tolerance-inducing antigen-presenting cells. Having this experience, here we describe another minimum information about Tregs (MITREG). It is important to note that MITREG does not dictate how investigators should generate or characterize Tregs, but it does require investigators to report their Treg data in a consistent and transparent manner. We hope this will, therefore, be a useful tool facilitating standardized reporting on the manufacturing of Tregs, either for research purposes or for clinical application. This way MITREG might also be an important step toward more standardized and reproducible testing of the Tregs preparations in clinical applications.

Selective blockade of CD28 on human T cells facilitates regulation of alloimmune responses

T cells are central to the detrimental alloresponses that develop in autoimmunity and transplantation, with CD28 costimulatory signals being key to T cell activation and proliferation. CTLA4-Ig molecules that bind CD80/86 and inhibit CD28 costimulation offer an alternative immunosuppressive treatment, free from some of the chronic toxicities associated with calcineurin inhibition. However, CD80/86 blockade by CTLA4-Ig also results in the loss of coinhibitory CTLA4 signals that are critical to the regulation of T cell activation. Here, we show that a nonactivating monovalent anti-CD28 that spares CTLA4 signaling is an effective immunosuppressant in a clinically relevant humanized mouse transplant model. We demonstrate that selective CD28 blockade prolongs human skin allograft survival through a mechanism that includes a reduction in the cellular graft infiltrate. Critically, selective CD28 blockade promotes Treg function in vivo and synergizes with adoptive Treg therapy to promote transplant survival. In contrast to CTLA4-Ig treatment, selective CD28 blockade promotes regulation of alloimmune responses and facilitates Treg-based cellular therapy.

Measurement of T Cell Alloreactivity Using Imaging Flow Cytometry

The measurement of immunological reactivity to donor antigens in transplant recipients is likely to be crucial for the successful reduction or withdrawal of immunosuppression. The mixed leukocyte reaction (MLR), limiting dilution assays, and trans-vivo delayed-type hypersensitivity (DTH) assay have all been applied to this question, but these methods have limited predictive ability and/or significant practical limitations that reduce their usefulness.Imaging flow cytometry is a technique that combines the multiparametric quantitative powers of flow cytometry with the imaging capabilities of fluorescent microscopy. We recently made use of an imaging flow cytometry approach to define the proportion of recipient T cells capable of forming mature immune synapses with donor antigen-presenting cells (APCs). Using a well-characterized mouse heart transplant model, we have shown that the frequency of in vitro immune synapses among T-APC membrane contact events strongly predicted allograft outcome in rejection, tolerance, and a situation where transplant survival depends on induced regulatory T cells.The frequency of T-APC contacts increased with T cells from mice during acute rejection and decreased with T cells from mice rendered unresponsive to alloantigen. The addition of regulatory T cells to the in vitro system reduced prolonged T-APC contacts. Critically, this effect was also seen with human polyclonally expanded, naturally occurring regulatory T cells, which are known to control the rejection of human tissues in humanized mouse models. Further development of this approach may allow for a deeper characterization of the alloreactive T-cell compartment in transplant recipients. In the future, further development and evaluation of this method using human cells may form the basis for assays used to select patients for immunosuppression minimization, and it can be used to measure the impact of tolerogenic therapies in the clinic.

Quantification of CD4(+) T Cell Alloreactivity and Its Control by Regulatory T Cells Using Time-Lapse Microscopy and Immune Synapse Detection

Assays designed to select transplant recipients for immunosuppression withdrawal have met with limited success, perhaps because they measure events downstream of T cell-alloantigen interactions. Using in vitro time-lapse microscopy in a mouse transplant model, we investigated whether transplant outcome would result in changes in the proportion of CD4(+) T cells forming prolonged interactions with donor dendritic cells. By blocking CD4-MHC class II and CD28-B7 interactions, we defined immunologically relevant interactions as those ≥500 s. Using this threshold, T cell-dendritic cell (T-DC) interactions were examined in rejection, tolerance and T cell control mediated by regulatory T cells. The frequency of T-DC contacts ≥500 s increased with T cells from mice during acute rejection and decreased with T cells from mice rendered unresponsive to alloantigen. Regulatory T cells reduced prolonged T-DC contacts. Importantly, this effect was replicated with human polyclonally expanded naturally occurring regulatory T cells, which we have previously shown can control rejection of human tissues in humanized mouse models. Finally, in a proof-of-concept translational context, we were able to visualize differential allogeneic immune synapse formation in polyclonal CD4(+) T cells using high-throughput imaging flow cytometry.

Induction of transplantation tolerance through regulatory cells: from mice to men

Organ transplantation results in the activation of both innate and adaptive immune responses to the foreign antigens. While these responses can be limited with the use of systemic immunosuppressants, the induction of regulatory cell populations may be a novel strategy for the maintenance of specific immunological unresponsiveness that can reduce the severity of the detrimental side effects of current therapies. Our group has extensively researched different regulatory T-cell induction protocols for use as cellular therapy in transplantation. In this review, we address the cellular and molecular mechanisms behind regulatory T-cell suppression and their stability following induction protocols. We further discuss the use of different hematopoietically derived regulatory cell populations, including regulatory B cells, regulatory macrophages, tolerogenic dendritic cells, and myeloid-derived suppressor cells, for the induction of transplantation tolerance in light of new clinical trials developing therapies with some of these populations.

Homing of regulatory T cells to human skin is important for the prevention of alloimmune-mediated pathology in an in vivo cellular therapy model

Regulatory T cell (Treg) therapy for immune modulation is a promising therapeutic strategy for the treatment and prevention of autoimmune disease and graft-versus-host disease (GvHD) after bone marrow transplantation. However, Treg are heterogeneous and express a variety of chemokine receptor molecules. The optimal subpopulation of Treg for therapeutic use may vary according to the pathological target. Indeed, clinical trials of Treg for the prevention of GvHD where the skin is a major target of the anti-host response have employed Treg derived from a variety of different sources. We postulated that for the effective treatment of GvHD-related skin pathology, Treg must be able to migrate to skin in order to regulate local alloimmune responses efficiently. To test the hypothesis that different populations of Treg display distinct efficacy in vivo based on their expression of tissue-specific homing molecules, we evaluated the activity of human Treg derived from two disparate sources in a model of human skin transplantation. Treg were derived from adult blood or cord blood and expanded in vitro. While Treg from both sources displayed similar in vitro suppressive efficacy, they exhibited marked differences in the expression of skin homing molecules. Importantly, only adult-derived Treg were able to prevent alloimmune-mediated human skin destruction in vivo, by virtue of their improved migration to skin. The presence of Treg within the skin was sufficient to prevent its alloimmune-mediated destruction. Additionally, Treg expressing the skin homing cutaneous lymphocyte antigen (CLA) were more efficient at preventing skin destruction than their CLA-deficient counterparts. Our findings highlight the importance of the careful selection of an effective subpopulation of Treg for clinical use according to the pathology of interest.

Conversion to sirolimus in kidney transplant recipients with squamous cell cancer and changes in immune phenotype

BACKGROUND

Conversion to sirolimus from calcineurin inhibitor- (CNI), azathioprine- (AZA) and mycophenolate-based regimens reduces the risk of development of squamous cell carcinoma of the skin (SCC) in kidney transplant recipients (KTRs). Sirolimus conversion may also be protective by permitting beneficial changes in immune phenotype. It is not known how sirolimus will affect immune phenotype in KTRs with SCC.

METHODS

Thirty-two KTRs with SCC were enrolled into this single-blinded randomized study and 13 KTRs randomized to sirolimus (4-10 ng/mL) and prednisolone 5 mg/day.

RESULTS

Six-month post conversion to sirolimus FOXP3(+) CD127(low)CD25(high)CD69(-), the number of T cells (putative Treg) increased significantly (P = 0.008). Natural killer (NK) and CD56(bright) NK cells also increased significantly (P = 0.039 and 0.02). T-cell number only significantly increased in those KTRs where CNI was ceased as part of the conversion to mammalian target of rapamycin inhibitors (mTORi's) (P = 0.031) implying CNI cessation rather than mTORi initiation induced an increase in T-cell number. Increases in the NK cell number was only significant in those KTRs where AZA was ceased (P = 0.040), implying AZA cessation rather than mTORi initiation caused the NK cell number to increase. At 6 months, sirolimus conversion reduces new SCC/year, rate ratio 0.49 (95%CI: 0.15-1.63), P = 0.276. On therapy analysis and intention-to-treat analysis over 24 months, the rate ratios were 0.84 and 0.87, respectively, and did not reach significance.

CONCLUSIONS

Conversion to mTORi from CNI may reveal a pre-existing high Treg phenotype by unmasking CNI inhibition of FOXP3 expression. Cessation of AZA leads to increased NK cell number. High FOXP3(+) T-cell number on conversion to mTORi may predict those KTRs who continue to accrue SCC.