Infusion of ex-vivo expanded human TCR-αβ+ double-negative regulatory T cells delays onset of xenogeneic graft-versus-host disease

Single-cell RNA sequencing of human double-negative T cells reveals a favorable cellular signature for cancer therapy

BACKGROUND

Allogeneic double-negative T-cell (DNT) therapy has emerged as a novel, off-the-shelf cellular treatment with clinical feasibility, safety, and promising efficacy against leukemia. However, the biology of DNTs is less well characterized, and how DNT therapy distinguishes from conventional γδ T-cell therapy remains unclear. Collectively, this hinders our ability to bolster DNT functionalities in cancer therapy. Here, we performed single-cell RNA sequencing with in vitro and in vivo functional analysis on DNTs. As a significant proportion of DNTs express Vγ9Vδ2 (Vδ2) TCR chain, we compared DNTs with donor-matched conventional Vδ2 T cells expanded with zoledronic acid.

METHODS

Healthy donor-derived allogeneic DNTs and Vδ2 T cells were expanded ex vivo. Single-cell RNA sequencing analysis was performed on both cellular products to identify the transcriptional landscape and inferred cellular interactions within DNTs, followed by comparisons with donor-matched Vδ2 T cells. Unique cellular subsets found only in DNTs were depleted to identify their contributions to the overall efficacy of DNTs against acute myeloid leukemia. The anti-leukemic activity and in vivo persistence of DNTs and Vδ2 T-cells were explored using flow cytometry-based cytotoxicity assays, memory phenotyping, and xenograft models.

RESULTS

Despite a shared Vδ2 expression between cellular products, we identified unique cellular compositions in DNTs that contribute to distinct transcriptional and cellular communication patterns relative to the donor-matched Vδ2 T cells, including higher expression of genes identified in chimeric antigen receptor T cells that persist in patients with durable cancer-remission. Vδ2- DNTs exhibited strong persistence characteristics, and their presence promoted the cytotoxic capabilities of Vδ2+ DNTs in repeated stimulation assays. This unique genetic signature and diverse cellular composition of DNTs resulted in better overall ex vivo expansion, prolonged persistence, and superior anti-leukemic activity compared with Vδ2 T cells in vitro and in vivo.

CONCLUSIONS

These results highlight the unique transcriptional, cellular, and functional profile of human DNTs and support the continued clinical investigation of allogeneic DNT therapy. The data also provide a reference gene signature that may help improve the efficacy of other types of allogeneic adoptive cellular therapies.

Bone marrow immune cells and drug resistance in acute myeloid leukemia

In recent years, the relationship between the immunosuppressive niche of the bone marrow and therapy resistance in acute myeloid leukemia (AML) has become a research focus. The abnormal number and function of immunosuppressive cells, including regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs), along with the dysfunction and exhaustion of immunological effector cells, including cytotoxic T lymphocytes (CTLs), dendritic cells (DCs) and natural killer cells (NKs), can induce immune escape of leukemia cells and are closely linked to therapy resistance in leukemia. This article reviews the research progress on the relationship between immune cells in the marrow microenvironment and chemoresistance in AML, aiming to provide new ideas for the immunotherapy of AML.

Purinergic signaling by TCRαβ+ double-negative T regulatory cells ameliorates liver ischemia-reperfusion injury

Hepatic ischemia-reperfusion injury (HIRI) is an important cause of liver injury following liver transplantation and major resections, and neutrophils are the key effector cells in HIRI. Double-negative T regulatory cells (DNT) are increasingly recognized as having critical regulatory functions in the immune system. Whether DNT expresses distinct immunoregulatory mechanisms to modulate neutrophils, as in HIRI, remains largely unknown. In this study, we found that murine and human DNT highly expressed CD39 that protected DNT from extracellular ATP-induced apoptosis and generated adenosine in tandem with CD73, to induce high levels of neutrophil apoptosis. Furthermore, extracellular adenosine enhanced DNT survival and suppressive function by upregulating survivin and NKG2D expression via the A2AR/pAKT/FOXO1 signaling pathway. Adoptive transfer of DNT ameliorated HIRI in mice through the inhibition of neutrophils in a CD39-dependent manner. Lastly, the adoptive transfer of A2ar-/- DNT validated the importance of adenosine/A2AR signaling, in promoting DNT survival and immunomodulatory function to protect against HIRI in vivo. In conclusion, purinergic signaling is crucial for DNT homeostasis in HIRI. Augmentation of CD39 or activation of A2AR signaling in DNT may provide novel therapeutic strategies to target innate immune disorders.

Application of deep learning models on single-cell RNA sequencing analysis uncovers novel markers of double negative T cells

Double negative T (DNT) cells are a unique subset of CD3 + TCRαβ + T lymphocytes that lack CD4, CD8, or NK1.1 expression and constitute 3-5% of the total T cell population in C57BL/6 mice. They have increasingly gained recognition for their novel roles in the immune system, especially under autoimmune conditions. Conventional machine learning approaches such as principal component analysis have been employed in single-cell RNA sequencing (scRNA-seq) analysis to characterize DNT cells. However, advanced deep learning models such as Single Cell Variational Inference (scVI) have the capability to capture nonlinear gene expression patterns in the sequencing data. In this study, employing the deep learning methodology, we have revealed novel markers for splenic DNT cells in C57BL/6 mice which were validated with flow cytometry analysis. We classified DNT cells into two subgroups, naïve DNT (nDNT) cells differentiated by the expression of Ly6C and activated DNT (aDNT) cells differentiated by the expression of MHC-II. A prior study had predicted elevated expression of CD137/4-1BB encoded by Tnfrsf9 in nDNT cells; however, our analysis predicted and validated that CD137 was a marker for aDNT cells instead of nDNT cells. Innovatively, our data also identified CD30 encoded by Tnfrsf8 and CD153/CD30L encoded by Tnfsf8 as additional markers for aDNT cells. In addition, we classified three subgroups in nDNT cells and two subgroups in aDNT cells. Our scVI analysis suggested, and flow cytometry analysis confirmed, that Ly49G2 encoded by Slamf7 was a marker for the nDNT0 subgroup. Importantly, we validated that MHC-II was indeed expressed by a subset of human DNT cells suggesting the presence of a human aDNT population. Furthermore, we found increased expression of CD30, CD153, and CD137 on aDNT cells in MRL/lpr mice compared to those in C57BL/6 mice suggesting potential pathogenic roles of these molecules in autoimmunity. Together, our comprehensive analysis has uncovered and validated novel markers for different subpopulations of DNT cells that can be used in the phenotypic and/or functional characterization of these relatively rare cells in health and disease.

Identification of immune traits associated with neurodevelopmental disorders by two-sample Mendelian randomization analysis

BACKGROUND

One of the main causes of health-related issues in children is neurodevelopmental disorders (NDDs), which include attention-deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), and Tourette syndrome (TS). Nonetheless, there is relatively little prior research looking at the link between immunological inflammation and NDDs. Our work uses a two-sample Mendelian Randomization (MR) approach to provide a thorough evaluation of the causal effects of immune traits on ADHD, ASD, and TS.

METHODS

As exposures, 731 immunological traits' genetic associations were chosen, and the outcomes were genome-wide association data for ADHD, ASD, and TS. The inverse-variance weighted (IVW), weighted median (WM), and MR-Egger methods were used to conduct MR analysis. The results' robustness, heterogeneity, and horizontal pleiotropy were confirmed using extensive sensitivity analysis.

RESULTS

With single-nucleotide polymorphisms serving as instruments and false discovery rate (FDR) correction applied, the study found that significantly higher expression of CD62L on CD62L+ myeloid DC (IVW, OR: 0.926, 95% CI 0.896~0.958, P = 9.42 × 10-6, FDR = 0.007) and suggestively higher absolute cell count (AC) of CD28 + DN (CD4-CD8-) (IVW, OR: 0.852, 95% CI = 0.780 ∼ 0.932, P-value = 4.65 × 10-4, FDR = 0.170) was associated with a lower risk of ADHD. There was no pleiotropy, and the causal relationships were strong according to sensitivity, leave-one-out, and MR-Steiger directionality tests. For ASD and TS, no harmful or protective immune traits were observed.

CONCLUSIONS

The results of the study lend credence to the theory that deficiency in CD62L on CD62L+ myeloid DC and CD28 + DN (CD4-CD8) AC may contribute to the onset of ADHD.

CAR immunotherapy in autoimmune diseases: promises and challenges

In recent years, the use of chimeric antigen receptor (CAR)-T cells has emerged as a promising immunotherapy in multiple diseases. CAR-T cells are T cells genetically modified to express a surface receptor, known as CAR, for the targeting of cognate antigens on specific cells. The effectiveness of CAR-T cell therapy in hematologic malignancies including leukemia, myeloma, and non-Hodgkin's lymphoma has led to consider its use as a potential avenue of treatment for autoimmune diseases. However, broadening the use of CAR-T cell therapy to a large spectrum of autoimmune conditions is challenging particularly because of the possible development of side effects including cytokine release syndrome and neurotoxicity. The design of CAR therapy that include additional immune cells such as double-negative T cells, γδ T cells, T regulatory cells and natural killer cells has shown promising results in preclinical studies and clinical trials in oncology, suggesting a similar potential utility in the treatment of autoimmune diseases. This review examines the mechanisms, efficacy, and safety of CAR approaches with a focus on their use in autoimmune diseases including systemic lupus erythematosus, Sjögren's syndrome, systemic sclerosis, multiple sclerosis, myasthenia gravis, lupus nephritis and other autoimmune diseases. Advantages and disadvantages as compared to CAR-T cell therapy will also be discussed.

Distinct characteristics of unique immunoregulatory canine non-conventional TCRαβpos CD4negCD8αneg double-negative T cell subpopulations

Conventional CD4pos regulatory T (Treg) cells characterized by expression of the key transcription factor forkhead box P3 (FoxP3) are crucial to control immune responses, thereby maintaining homeostasis and self-tolerance. Within the substantial population of non-conventional T cell receptor (TCR)αβpos CD4negCD8αneg double-negative (dn) T cells of dogs, a novel FoxP3pos Treg-like subset was described that, similar to conventional CD4pos Treg cells, is characterized by high expression of CD25. Noteworthy, human and murine TCRαβpos regulatory dn T cells lack FoxP3. Immunosuppressive capacity of canine dn T cells was hypothesized based on expression of inhibitory molecules (interleukin (IL)-10, cytotoxic T-lymphocyte associated protein 4, CTLA4). Here, to verify their regulatory function, the dnCD25pos (enriched for FoxP3pos Treg-like cells) and the dnCD25neg fraction, were isolated by fluorescence-activated cell sorting from peripheral blood mononuclear cells (PBMC) of Beagle dogs and analyzed in an in vitro suppression assay in comparison to conventional CD4posCD25pos Treg cells (positive control) and CD4posCD25neg T cells (negative control). Canine dnCD25pos T cells suppressed the Concanavalin A-driven proliferation of responder PBMC to a similar extent as conventional CD4posCD25pos Treg cells. Albeit to a lesser extent than FoxP3-enriched dn and CD4posCD25pos populations, even dnCD25neg T cells reduced the proliferation of responder cells. This is remarkable, as dnCD25neg T cells have a FoxP3neg phenotype comparable to non-suppressive CD4posCD25neg T cells. Both, CD25pos and CD25neg dn T cells, can mediate suppression independent of cell-cell contact and do not require additional signals from CD4posCD25neg T cells to secrete inhibitory factors in contrast to CD4posCD25pos T cells. Neutralization of IL-10 completely abrogated the suppression by dnCD25pos and CD4posCD25pos Treg cells in a Transwell™ system, while it only partially reduced suppression by dnCD25neg T cells. Taken together, unique canine non-conventional dnCD25pos FoxP3pos Treg-like cells are potent suppressor cells in vitro. Moreover, inhibition of proliferation of responder T cells by the dnCD25neg fraction indicates suppressive function of a subset of dn T cells even in the absence of FoxP3. The identification of unique immunoregulatory non-conventional dn T cell subpopulations of the dog in vitro is of high relevance, given the immunotherapeutic potential of manipulating regulatory T cell responses in vivo.

CD19-CAR-DNT cells (RJMty19) in patients with relapsed or refractory large B-cell lymphoma: a phase 1, first-in-human study

Background

Current approved chimeric antigen receptor (CAR) T-cell products are autologous cell therapies that are costly and poorly accessible to patients. We aimed to evaluate the safety and antitumor activity of a novel off-the-shelf anti-CD19 CAR-engineered allogeneic double-negative T cells (RJMty19) in patients with relapsed/refractory large B-cell lymphoma. We report the results from a first-in-human, open-label, single-dose, phase 1 study of allogeneic CD19-specific CAR double-negative T (CAR-DNT) cells.

Methods

Eligibility criteria included the presence of measurable lesions, at least 2 lines of prior immunochemotherapy, and an ECOG score of 0-1. We evaluated four dose levels (DL) of RJMty19 in a 3 + 3 dose-escalation scheme: 1 × 106, 3 × 106, 9 × 106 and 2 × 107 CAR-DNT cells per kilogram of body weight. All patients received lymphodepleting chemotherapy with fludarabine and cyclophosphamide. The primary endpoints were dose-limiting toxicities (DLTs), incidence of adverse events (AEs), and clinically significant laboratory abnormalities. Secondary endpoints included evaluation of standard cellular pharmacokinetic parameters, immunogenicity, objective response rates (ORR), and disease control rate (DCR) per Lugano 2014 criteria.

Findings

A total of 12 patients were enrolled between 22 July 2022 and 27 July 2023. Among these patients, 66% were classified as stage IV, 75% had an IPI score of 3 or higher, representing an intermediate risk or worse. The maximum tolerated dose was not reached because no DLT was observed. Four patient experienced grade 1 or 2 cytokine release syndrome and dizziness. The most common AEs were hematologic toxicities, including neutropenia (N = 12, 100%), leukopenia (N = 12, 100%), lymphopenia (N = 10, 83%), thrombocytopenia (N = 6, 50%), febrile neutropenia (N = 3, 25%), and anemia (N = 3, 25%). Seven subjects died till the cut-off date, five of them died of disease progression and two of them died of COVID 19. In all patients (N = 12), the ORR was 25% and CRR was 8.3%. DL1 and DL2 patients benefited less from the therapy (ORR: 17%, N = 1; DCR: 33%, N = 2). However, all DL3 patients achieved disease control (N = 3, 100%), and all DL4 patients achieved objective response (N = 3, 100%).

Interpretation

Our results demonstrate that CD19-CAR-DNT cells appear to be well tolerated with promising antitumor activity in LBCL patients. Further study of this product with a larger sample size is warranted. This phase 1 study is registered on clinicaltrials.gov (NCT05453669).

Funding

Wyze Biotech. Co., Ltd.

Double-Negative T (DNT) Cells in Patients with Systemic Lupus Erythematosus

Double-negative T (DNT) cells are a rare and unconventional T-lymphocyte subpopulation lacking both CD4 and CD8 markers. Their immunopathological roles and clinical relevance have yet to be elucidated. Beyond autoimmune lymphoproliferative syndrome (ALPS), these cells may also play a role in rheumatic disorders, including systemic lupus erythematosus (SLE); indeed, these two diseases share several autoimmune manifestations (including nephritis). Moreover, one of the main experimental murine models used to investigate lupus, namely the MRL/lpr mouse, is characterized by an expansion of DNT cells, which can support the production of pathogenic autoantibodies and/or modulate the immune response in this context. However, lupus murine models are not completely consistent with their human SLE counterpart, of course. In this mini review, we summarize and analyze the most relevant clinical studies investigating the DNT cell population in SLE patients. Overall, based on the present literature review and analysis, DNT cell homeostasis seems to be altered in patients with SLE. Indeed, most of the available clinical studies (which include both adults and children) reported an increased DNT cell percentage in SLE patients, especially during the active phases, even though no clear correlation with disease activity and/or inflammatory parameters has been clearly established. Well-designed, standardized, and longitudinal clinical studies focused on DNT cell population are needed, in order to further elucidate the actual contribution of these cells in SLE pathogenesis and their interactions with other immune cells (also implicated and/or altered in SLE, such as basophils), and clarify whether their expansion and/or immunophenotypic aspects may have any immunopathological relevance (and, then, represent potential disease markers and, in perspective, even therapeutic targets) or are just an unspecific epiphenomenon of autoimmunity.

Targeting T-cell malignancies using allogeneic double-negative CD4-CAR-T cells

BACKGROUND

Patients with relapsed/refractory T-cell malignancies have limited treatment options. The use of chimeric antigen receptor (CAR)-T cell therapy for T-cell malignancies is challenging due to possible blast contamination of autologous T-cell products and fratricide of CAR-T cells targeting T-lineage antigens. Recently, allogeneic double-negative T cells (DNTs) have been shown to be safe as an off-the-shelf adoptive cell therapy and to be amendable for CAR transduction. Here, we explore the antitumor activity of allogeneic DNTs against T-cell malignancies and the potential of using anti-CD4-CAR (CAR4)-DNTs as adoptive cell therapy for T-cell malignancies.

METHODS

Healthy donor-derived allogeneic DNTs were ex vivo expanded with or without CAR4 transduction. The antitumor activity of DNTs and CAR4-DNTs against T-cell acute lymphoblastic leukemia (T-ALL) and peripheral T-cell lymphoma (PTCL) were examined using flow cytometry-based cytotoxicity assays and xenograft models. Mechanisms of action were investigated using transwell assays and blocking assays.

RESULTS

Allogeneic DNTs induced endogenous antitumor cytotoxicity against T-ALL and PTCL in vitro, but high doses of DNTs were required to attain therapeutic effects in vivo. The potency of DNTs against T-cell malignancies was significantly enhanced by transducing DNTs with a third-generation CAR4. CAR4-DNTs were manufactured without fratricide and showed superior cytotoxicity against CD4+ T-ALL and PTCL in vitro and in vivo relative to empty-vector transduced-DNTs. CAR4-DNTs eliminated T-ALL and PTCL cell lines and primary T-ALL blasts in vitro. CAR4-DNTs effectively infiltrated tumors, delayed tumor progression, and prolonged the survival of T-ALL and PTCL xenografts. Further, pretreatment of CAR4-DNTs with PI3Kδ inhibitor idelalisib promoted memory phenotype of CAR4-DNTs and enhanced their persistence and antileukemic efficacy in vivo. Mechanistically, LFA-1, NKG2D, and perforin/granzyme B degranulation pathways were involved in the DNT-mediated and CAR4-DNT-mediated killing of T-ALL and PTCL.

CONCLUSIONS

These results demonstrate that CAR4-DNTs can effectively target T-ALL and PTCL and support allogeneic CAR4-DNTs as adoptive cell therapy for T-cell malignancies.

IL-33 promotes double negative T cell survival via the NF-κB pathway

IL-33, which is a crucial modulator of adaptive immune responses far beyond type 2 response, can enhance the function of several T cell subsets and maintain the immune homeostasis. However, the contribution of IL-33 to double negative T (DNT) cell remains unappreciated. Here, we demonstrated that the IL-33 receptor ST2 was expressed on DNT cells, and that IL-33 stimulation increased DNT cells proliferation and survival in vivo and in vitro. Transcriptome sequencing analysis also demonstrated that IL-33 enhanced the biological function of DNT cells, especially effects on proliferation and survival. IL-33 promoted DNT cells survival by regulating Bcl-2, Bcl-xl and Survivin expression. IL-33-TRAF4/6-NF-κB axis activation promoted the transmission of essential division and survival signals in DNT cells. However, IL-33 failed to enhance the expression of immunoregulatory molecules in DNT cells. DNT cells therapy combined with IL-33 inhibited T cells survival and further ameliorated ConA-induced liver injury, which mainly depended on the proliferative effect of IL-33 on DNT cells in vivo. Finally, we stimulated human DNT cells with IL-33, and similar results were observed. In conclusion, we revealed a cell intrinsic role of IL-33 in the regulation of DNT cells, thereby identifying a previously unappreciated pathway supporting the expansion of DNT cells in the immune environment.

Adoptive Cell Therapy for T-Cell Malignancies

T-cell malignancies are often aggressive and associated with poor prognoses. Adoptive cell therapy has recently shown promise as a new line of therapy for patients with hematological malignancies. However, there are currently challenges in applying adoptive cell therapy to T-cell malignancies. Various approaches have been examined in preclinical and clinical studies to overcome these obstacles. This review aims to provide an overview of the recent progress on adoptive cell therapy for T-cell malignancies. The benefits and drawbacks of different types of adoptive cell therapy are discussed. The potential advantages and current applications of innate immune cell-based adoptive cell therapy for T cell malignancies are emphasized.

Insights into mechanisms of graft-versus-host disease through humanised mouse models

Graft-versus-host disease (GVHD) is a major complication that occurs following allogeneic haematopoietic stem cell transplantation (HSCT) for the treatment of haematological cancers and other blood-related disorders. GVHD is an inflammatory disorder, where the transplanted donor immune cells can mediate an immune response against the recipient and attack host tissues. Despite over 60 years of research, broad-range immune suppression is still used to prevent or treat GVHD, leading to an increased risk of cancer relapse and infection. Therefore, further insights into the disease mechanisms and development of predictive and prognostic biomarkers are key to improving outcomes and reducing GVHD development following allogeneic HSCT. An important preclinical tool to examine the pathophysiology of GVHD and to understand the key mechanisms that lead to GVHD development are preclinical humanised mouse models. Such models of GVHD are now well-established and can provide valuable insights into disease development. This review will focus on models where human peripheral blood mononuclear cells are injected into immune-deficient non-obese diabetic (NOD)-scid-interleukin-2(IL-2)Rγ mutant (NOD-scid-IL2Rγ^null) mice. Humanised mouse models of GVHD can mimic the clinical setting for GVHD development, with disease progression and tissues impacted like that observed in humans. This review will highlight key findings from preclinical humanised mouse models regarding the role of donor human immune cells, the function of cytokines and cell signalling molecules and their impact on specific target tissues and GVHD development. Further, specific therapeutic strategies tested in these preclinical models reveal key molecular pathways important in reducing the burden of GVHD following allogeneic HSCT.

Expansion of Double-Negative T Cells in Patients before Liver Transplantation Correlates with Post-Transplant Infections

Liver transplantation (LTx) is currently the only effective therapy for patients with end-stage liver diseases, but post-transplant infection is a key issue for morbidity and mortality. In this study, we found that pre-transplant patients with an expansion of double-negative T (DNT) cells (CD3+CD4-CD8- T cells) had an increased incidence of infections within the first 6 months after LTx. These DNT cells also negatively correlated with their CD4/CD8 ratio. Compared to patients who had no infections after LTx, these DNT cells expressed more CD25, especially in the memory compartment. The receiver operating characteristic (ROC) analysis showed that the threshold area under the ROC curve of DNT cells which could be used to distinguish LTx patients with post-transplant infections from patients without infections after LTx was 0.8353 (95% CI: 0.6591-1.000). The cut-off for the pre-LTx DNT cell level was 11.35%. Although patients with post-transplant infections had decreased levels of CD4/CD8 T cells, CD8+ T cells in these patients were more exhausted, with higher PD-1 expression and lower IFNγ secretion. The increased levels of DNT cells in patients with post-transplant infections were still observed 2 weeks after LTx, with higher proportions of memory DNT cells. In conclusion, increased levels of DNT cells in pre-LTx patients may be valuable for the prognosis of post-transplant infections, especially within the first 6 months after LTx.

Allogeneic double-negative CAR-T cells inhibit tumor growth without off-tumor toxicities

The development of autologous chimeric antigen receptor T (CAR-T) cell therapies has revolutionized cancer treatment. Nevertheless, the delivery of CAR-T cell therapy faces challenges, including high costs, lengthy production times, and manufacturing failures. To overcome this, attempts have been made to develop allogeneic CAR-T cells using donor-derived conventional CD4⁺ or CD8⁺ T cells (T_convs), but severe graft-versus-host disease (GvHD) and host immune rejection have made this challenging. CD3⁺CD4^-CD8^- double-negative T cells (DNTs) are a rare subset of mature T cells shown to fulfill the requirements of an off-the-shelf cellular therapy, including scalability, cryopreservability, donor-independent anticancer function, resistance to rejection, and no observed off-tumor toxicity including GvHD. To overcome the challenges faced with CAR-T_convs, we evaluated the feasibility, safety, and efficacy of using healthy donor-derived allogeneic DNTs as a CAR-T cell therapy platform. We successfully transduced DNTs with a second-generation anti-CD19-CAR (CAR19) without hampering their endogenous characteristics or off-the-shelf properties. CAR19-DNTs induced antigen-specific cytotoxicity against B cell acute lymphoblastic leukemia (B-ALL). In addition, CAR19-DNTs showed effective infiltration and tumor control against lung cancer genetically modified to express CD19 in xenograft models. CAR19-DNT efficacy was comparable with that of CAR19-T_convs. However, unlike CAR19-T_convs, CAR19-DNTs did not cause alloreactivity or xenogeneic GvHD-related mortality in xenograft models. These studies demonstrate the potential of using allogeneic DNTs as a platform for CAR technology to provide a safe, effective, and patient-accessible CAR-T cell treatment option.

CD3+CD4-CD8- (Double-Negative) T Cells in Inflammation, Immune Disorders and Cancer

The crucial role of CD4⁺ and CD8⁺ T cells in shaping and controlling immune responses during immune disease and cancer development has been well established and used to achieve marked clinical benefits. CD3⁺CD4^-CD8^- double-negative (DN) T cells, although constituting a rare subset of peripheral T cells, are gaining interest for their roles in inflammation, immune disease and cancer. Herein, we comprehensively review the origin, distribution and functions of this unique T cell subgroup. First, we focused on characterizing multifunctional DN T cells in various immune responses. DN regulatory T cells have the capacity to prevent graft-versus-host disease and have therapeutic value for autoimmune disease. T helper-like DN T cells protect against or promote inflammation and virus infection depending on the specific settings and promote certain autoimmune disease. Notably, we clarified the role of DN tumor-infiltrating lymphocytes and outlined the potential for malignant proliferation of DN T cells. Finally, we reviewed the recent advances in the applications of DN T cell-based therapy for cancer. In conclusion, a better understanding of the heterogeneity and functions of DN T cells may help to develop DN T cells as a potential therapeutic tool for inflammation, immune disorders and cancer.

Double-negative T cells: Setting the stage for disease control or progression

Double-negative (DN) T cells are present at relatively low frequencies in human peripheral blood, and are characterized as expressing the alpha-beta or gamma-delta T-cell receptor (TCR), but not the CD4 nor the CD8 co-receptors. Despite their low frequencies, these cells are potent producers of cytokines and, thus, are key orchestrators of immune responses. DN T cells were initially associated with induction of peripheral immunological tolerance and immunomodulatory activities related to disease prevention. However, other studies demonstrated that these cells can also display effector functions associated with pathology development. This apparent contradiction highlighted the heterogeneity of the DN T-cell population. Here, we review phenotypic and functional characteristics of DN T cells, emphasizing their role in human diseases. The need for developing biomarkers to facilitate the translation of studies from animal models to humans will also be discussed. Finally, we will examine DN T cells as promising therapeutic targets to prevent or inhibit human disease development.

Purinergic Signalling in Allogeneic Haematopoietic Stem Cell Transplantation and Graft-versus-Host Disease

Allogeneic haematopoietic stem cell transplantation (allo-HSCT) is a curative therapy for blood cancers and other haematological disorders. However, allo-HSCT leads to graft-versus-host disease (GVHD), a severe and often lethal immunological response, in the majority of transplant recipients. Current therapies for GVHD are limited and often reduce the effectiveness of allo-HSCT. Therefore, pro- and anti-inflammatory factors contributing to disease need to be explored in order to identify new treatment targets. Purinergic signalling plays important roles in haematopoiesis, inflammation and immunity, and recent evidence suggests that it can also affect haematopoietic stem cell transplantation and GVHD development. This review provides a detailed assessment of the emerging roles of purinergic receptors, most notably P2X7, P2Y2 and A2A receptors, and ectoenzymes, CD39 and CD73, in GVHD.

Immunometabolism in haematopoietic stem cell transplantation and adoptive cellular therapies

PURPOSE OF REVIEW

Controlling T cell activity through metabolic manipulation has become a prominent feature in immunology and practitioners of both adoptive cellular therapy (ACT) and haematopoietic stem cell transplantation (HSCT) have utilized metabolic interventions to control T cell function. This review will survey recent metabolic research efforts in HSCT and ACT to paint a broad picture of immunometabolism and highlight advances in each area.

RECENT FINDINGS

In HSCT, recent publications have focused on modifying reactive oxygen species, sirtuin signalling or the NAD salvage pathway within alloreactive T cells and regulatory T cells. In ACT, metabolic interventions that bolster memory T cell development, increase mitochondrial density and function, or block regulatory signals in the tumour microenvironment (TME) have recently been published.

SUMMARY

Metabolic interventions control immune responses. In ACT, efforts seek to improve the in-vivo metabolic fitness of T cells, while in HSCT energies have focused on blocking alloreactive T cell expansion or promoting regulatory T cells. Methods to identify new, metabolically targetable pathways, as well as the ability of metabolic biomarkers to predict disease onset and therapeutic response, will continue to advance the field towards clinically applicable interventions.

Post-transplant cyclophosphamide limits reactive donor T cells and delays the development of graft-versus-host disease in a humanized mouse model

Graft-versus-host disease (GVHD) is a major complication of allogeneic haematopoietic stem cell transplantation (allo-HSCT) that develops when donor T cells in the graft become reactive against the host. Post-transplant cyclophosphamide (PTCy) is increasingly used in mismatched allo-HSCT, but how PTCy impacts donor T cells and reduces GVHD is unclear. This study aimed to determine the effect of PTCy on reactive human donor T cells and GVHD development in a preclinical humanized mouse model. Immunodeficient NOD-scid-IL2Rγ^null mice were injected intraperitoneally (i.p.) with 20 × 10⁶ human peripheral blood mononuclear cells stained with carboxyfluorescein succinimidyl ester (CFSE) (day 0). Mice were subsequently injected (i.p.) with PTCy (33 mg kg^-1 ) (PTCy-mice) or saline (saline-mice) (days 3 and 4). Mice were assessed for T-cell depletion on day 6 and monitored for GVHD for up to 10 weeks. Flow cytometric analysis of livers at day 6 revealed lower proportions of reactive (CFSE^low ) human (h) CD3⁺ T cells in PTCy-mice compared with saline-mice. Over 10 weeks, PTCy-mice showed reduced weight loss and clinical GVHD, with prolonged survival and reduced histological liver GVHD compared with saline-mice. PTCy-mice also demonstrated increased splenic hCD4⁺ :hCD8⁺ T-cell ratios and reduced splenic Tregs (hCD4⁺  hCD25⁺  hCD127^lo ) compared with saline-mice. This study demonstrates that PTCy reduces GVHD in a preclinical humanized mouse model. This corresponded to depletion of reactive human donor T cells, but fewer human Tregs.

Transcriptome landscape of double negative T cells by single-cell RNA sequencing

CD4 and CD8 coreceptor double negative TCRαβ⁺ T (DNT) cells are increasingly being recognized for their critical and diverse roles in the immune system. However, their molecular and functional signatures remain poorly understood and controversial. Moreover, the majority of studies are descriptive because of the relative low frequency of cells and non-standardized definition of this lineage. In this study, we performed single-cell RNA sequencing on 28,835 single immune cells isolated from mixed splenocytes of male C57BL/6 mice using strict fluorescence-activated cell sorting. The data was replicated in a subsequent study. Our analysis revealed five transcriptionally distinct naïve DNT cell clusters, which expressed unique sets of genes and primarily performed T helper, cytotoxic and innate immune functions. Anti-CD3/CD28 activation enhanced their T helper and cytotoxic functions. Moreover, in comparison with CD4⁺, CD8⁺ T cells and NK cells, Ikzf2 was highly expressed by both naïve and activated cytotoxic DNT cells. In conclusion, we provide a map of the heterogeneity in naïve and active DNT cells, addresses the controversy about DNT cells, and provides potential transcription signatures of DNT cells. The landscape approach herein will eventually become more feasible through newer high throughput methods and will enable clustering data to be fed into a systems analysis approach. Thus the approach should become the "backdrop" of similar studies in the myriad murine models of autoimmunity, potentially highlighting the importance of DNT cells and other minor lineage of cells in immune homeostasis. The clear characterization of functional DNT subsets into helper DNT, cytotoxic DNT and innate DNT will help to better understand the intrinsic roles of different functional DNT subsets in the development and progression of autoimmune diseases and transplant rejection, and thereby may facilitate diagnosis and therapy.

Cellular therapies for graft-versus-host disease: a tale of tissue repair and tolerance

The success of allogeneic hematopoietic cell transplantation depends heavily on the delicate balance between the activity of the donor immune system against malignant and nonmalignant cells of the recipient. Abrogation of alloreactivity will lead to disease relapse, whereas untamed allo-immune responses will lead to lethal graft-versus-host disease (GVHD). A number of cell types have been identified that can be used to suppress alloreactive immune cells and prevent lethal GVHD in mice. Of those, mesenchymal stromal cells and, to a lesser extent, regulatory T cells have demonstrated efficacy in humans. Ideally, cellular therapy for GVHD will not affect alloreactive immune responses against tumor cells. The importance of tissue damage in the pathophysiology of GVHD rationalizes the development of cells that support tissue homeostasis and repair, such as innate lymphoid cells. We discuss recent developments in the field of cellular therapy to prevent and treat acute and chronic GVHD, in the context of GVHD pathophysiology.

DNT Cell-based Immunotherapy: Progress and Applications

Cancer immunotherapy has firmly established a dominant status in recent years. Adoptive cellular immunotherapy (ACI) is the main branch of immunotherapy. Recently, the immune effector cells of ACI, such as T cells, NK cells, and genetically engineered cells, have been used to achieve significant clinical benefits in the treatment of malignant tumors. However, the clinical applications have limitations, including toxicity, unexpectedly low efficiency, high costs and strict technical requirements. More exploration is needed to optimize ACI for cancer patients. CD3+CD4-CD8- double negative T cells (DNTs) have emerged as functional antitumor effector cells, according to the definition of adoptive immunotherapy. They constitute a kind of T cell subset that mediates nontumor antigen-restricted immunity and has important immune regulatory functions. Preclinical experiments showed that DNTs had a dual effect by killing tumor cells and inhibiting graft-versus-host disease. Notably, DNTs can be acquired from healthy donors and expanded in vitro; thus, allogeneic DNTs may be provided as “off-the-shelf” cellular products that can be readily available for direct clinical application. We review the progress and application of DNTs in immunotherapy. DNTs may provide some novel perspectives on cancer immunotherapy.

Human Double-Negative Regulatory T-Cells Induce a Metabolic and Functional Switch in Effector T-Cells by Suppressing mTOR Activity

The recently discovered population of TCRαβ+ CD4–/CD8– (double-negative, DN) T-cells are highly potent suppressor cells in mice and humans. In preclinical transplantation models, adoptive transfer of DN T-cells specifically inhibits alloreactive T-cells and prevents transplant rejection or graft-vs.-host disease (GvHD). Interestingly, clinical studies in patients who underwent allogeneic stem cell transplantation reveal an inverse correlation between the frequency of circulating DN T-cells and the severity of GvHD, suggesting a therapeutic potential of human DN T-cells. However, their exact mode of action has not been elucidated yet. Investigating the impact of DN T-cells on conventional T-cells, we found that human DN T-cells selectively inhibit mTOR signaling in CD4 T-cells. Given that mTOR is a critical regulator of cellular metabolism, we further determined the impact of DN T-cells on the metabolic framework of T-cells. Intriguingly, DN T-cells diminished expression of glucose transporters and glucose uptake, whereas fatty acid uptake was not modified, indicating that DN T-cells prevent metabolic adaptation of CD4 T-cells upon activation (i.e., glycolytic switch) thereby contributing to their suppression. Further analyses demonstrated that CD4 T-cells also do not upregulate homing receptors associated with inflammatory processes. In contrast, expression of central memory-cell associated cell surface markers and transcription factors were increased by DN T-cells. Moreover, CD4 T-cells failed to produce inflammatory cytokines after co-culture with DN T-cells, whereas IL-2 secretion was enhanced. Taken together DN T-cells impair metabolic reprogramming of conventional CD4 T-cells by abrogating mTOR signaling, thereby modulating CD4 T-cell functionality. These results uncover a new mechanism of DN T-cell-mediated suppression, pointing out that DN T-cells could serve as cell-based therapy to limit alloreactive immune response.