Ablation of interferon regulatory factor 4 in T cells induces "memory" of transplant tolerance that is irreversible by immune checkpoint blockade

Vasoactive-Inotropic Score as a Promising Predictor of Acute Kidney Injury in Adult Patients Requiring Extracorporeal Membrane Oxygenation

Acute kidney injury (AKI) is a common complication in patients supported by extracorporeal membrane oxygenation (ECMO). Vasoactive-Inotropic Score (VIS) serves as an indicator of the extent of cardiovascular drug support provided. Our objective is to assess the relationship between the VIS and ECMO-associated AKI (EAKI). This single-center retrospective study extracted adult patients treated with ECMO between August 2016 and September 2022 from an intensive care unit (ICU) in a university hospital. A total of 126 patients requiring ECMO support were included in the study, of which 76% developed AKI. Multivariate logistic regression analysis identified VIS-max Day1 (odds ratio [OR]: 1.025, 95% confidence interval [CI]: 1.007-1.044, p = 0.006), VIS-max Day2 (OR: 1.038, 95% CI: 1.007-1.069, p = 0.015), VIS-mean Day1 (OR: 1.048, 95% CI: 1.013-1.084, p = 0.007), and VIS-mean Day2 (OR: 1.059, 95% CI: 1.014-1.107, p = 0.010) as independent risk factors for EAKI. VIS-max Day1 showing the best predictive effect (Area under the receiver operating characteristic curve (AUROC): 0.80, sensitivity: 71.87%, specificity: 80.00%) for EAKI with a cutoff value of 33.33. Surprisingly, VIS-mean Day2 was also excellent at predicting 7 day mortality (AUROC: 0.77, sensitivity: 87.50%, specificity: 56.38%) with a cutoff value of 8.67. In conclusion, VIS could independently predict EAKI and 7 day mortality in patients with ECMO implantation, which may help clinicians to recognize the poor prognosis in time for early intervention.

Inhibition of interferon regulatory factor 4 orchestrates T cell dysfunction, extending mouse cardiac allograft survival

BACKGROUND

T cell dysfunction, which includes exhaustion, anergy, and senescence, is a distinct T cell differentiation state that occurs after antigen exposure. Although T cell dysfunction has been a cornerstone of cancer immunotherapy, its potential in transplant research, while not yet as extensively explored, is attracting growing interest. Interferon regulatory factor 4 (IRF4) has been shown to play a pivotal role in inducing T cell dysfunction.

METHODS

A novel ultra-low-dose combination of Trametinib and Rapamycin, targeting IRF4 inhibition, was employed to investigate T cell proliferation, apoptosis, cytokine secretion, expression of T-cell dysfunction-associated molecules, effects of MAPK and mammalian target of Rapamycin (mTOR) signaling pathways, and allograft survival in both in vitro and BALB/c to C57BL/6 mouse cardiac transplantation models.

RESULTS

In vitro, blockade of IRF4 in T cells effectively inhibited T cell proliferation, increased apoptosis, and significantly upregulated the expression of programmed cell death protein 1 (PD-1), Helios, CD160, and cytotoxic T lymphocyte-associated antigen (CTLA-4), markers of T cell dysfunction. Furthermore, it suppressed the secretion of pro-inflammatory cytokines interferon (IFN)-γ and interleukin (IL)-17. Combining ultra-low-dose Trametinib (0.1 mg·kg-1·day-1) and Rapamycin (0.1 mg·kg-1·day-1) demonstrably extended graft survival, with 4 out of 5 mice exceeding 100 days post-transplantation. Moreover, analysis of grafts at day 7 confirmed sustained IFN regulatory factor 4 (IRF4) inhibition, enhanced PD-1 expression, and suppressed IFN-γ secretion, reinforcing the in vivo efficacy of this IRF4-targeting approach. The combination of Trametinib and Rapamycin synergistically inhibited the MAPK and mTOR signaling network, leading to a more pronounced suppression of IRF4 expression.

CONCLUSIONS

Targeting IRF4, a key regulator of T cell dysfunction, presents a promising avenue for inducing transplant immune tolerance. In this study, we demonstrate that a novel ultra-low-dose combination of Trametinib and Rapamycin synergistically suppresses the MAPK and mTOR signaling network, leading to profound IRF4 inhibition, promoting allograft acceptance, and offering a potential new therapeutic strategy for improved transplant outcomes. However, further research is necessary to elucidate the underlying pharmacological mechanisms and facilitate translation to clinical practice.

Targeted depletion of PD-1-expressing cells induces immune tolerance through peripheral clonal deletion

Thymic negative selection of the T cell receptor (TCR) repertoire is essential for establishing self-tolerance and acquired allograft tolerance following organ transplantation. However, it is unclear whether and how peripheral clonal deletion of alloreactive T cells induces transplantation tolerance. Here, we establish that programmed cell death protein 1 (PD-1) is a hallmark of alloreactive T cells and is associated with clonal expansion after alloantigen encounter. Moreover, we found that diphtheria toxin receptor (DTR)-mediated ablation of PD-1+ cells reshaped the TCR repertoire through peripheral clonal deletion of alloreactive T cells and promoted tolerance in mouse transplantation models. In addition, by using PD-1-specific depleting antibodies, we found that antibody-mediated depletion of PD-1+ cells prevented heart transplant rejection and the development of experimental autoimmune encephalomyelitis (EAE) in humanized PD-1 mice. Thus, these data suggest that PD-1 is an attractive target for peripheral clonal deletion and induction of immune tolerance.

CD4+ T cell immunity is dependent on an intrinsic stem-like program

CD4+ T cells are central to various immune responses, but the molecular programs that drive and maintain CD4+ T cell immunity are not entirely clear. Here we identify a stem-like program that governs the CD4+ T cell response in transplantation models. Single-cell-transcriptomic analysis revealed that naive alloantigen-specific CD4+ T cells develop into TCF1hi effector precursor (TEP) cells and TCF1-CXCR6+ effectors in transplant recipients. The TCF1-CXCR6+CD4+ effectors lose proliferation capacity and do not reject allografts upon adoptive transfer into secondary hosts. By contrast, the TCF1hiCD4+ TEP cells have dual features of self-renewal and effector differentiation potential, and allograft rejection depends on continuous replenishment of TCF1-CXCR6+ effectors from TCF1hiCD4+ TEP cells. Mechanistically, TCF1 sustains the CD4+ TEP cell population, whereas the transcription factor IRF4 and the glycolytic enzyme LDHA govern the effector differentiation potential of CD4+ TEP cells. Deletion of IRF4 or LDHA in T cells induces transplant acceptance. These findings unravel a stem-like program that controls the self-renewal capacity and effector differentiation potential of CD4+ TEP cells and have implications for T cell-related immunotherapies.

Continuous Expression of Interferon Regulatory Factor 4 Sustains CD8+ T Cell Immunity against Tumor

T-cell-based immunotherapy is gaining momentum in cancer treatment; however, our comprehension of the transcriptional regulation governing T cell antitumor activity remains constrained. The objective of this study was to explore the function of interferon regulatory factor 4 (IRF4) in antitumor CD8+ T cells using the TRAMP-C1 prostate cancer and B16F10 melanoma model. To achieve this, we generated an Irf4GFP-DTR mouse strain and discovered that CD8+ tumor-infiltrating lymphocytes (TILs) expressing high levels of IRF4.GFP exhibited a more differentiated PD-1high cell phenotype. By administering diphtheria toxin to tumor-bearing Irf4GFP-DTR mice, we partially depleted IRF4.GFP+ TILs and observed an accelerated tumor growth. To specifically explore the function of IRF4 in antitumor CD8+ T cells, we conducted 3 adoptive cell therapy (ACT) models. Firstly, depleting IRF4.GFP+ CD8+ TILs derived from ACT significantly accelerated tumor growth, emphasizing their crucial role in controlling tumor progression. Secondly, deleting the Irf4 gene in antitumor CD8+ T cells used for ACT led to a reduction in the frequency and effector differentiation of CD8+ TILs, completely abolishing the antitumor effects of ACT. Lastly, we performed a temporal deletion of the Irf4 gene in antitumor CD8+ T cells during ACT, starting from 20 days after tumor implantation, which significantly compromised tumor control. Therefore, sustained expression of IRF4 is essential for maintaining CD8+ T cell immunity in the melanoma model, and these findings carry noteworthy implications for the advancement of more potent immunotherapies for solid tumors.

The transcription factor IRF4 determines the anti-tumor immunity of CD8+ T cells

Understanding the factors that regulate T cell infiltration and functional states in solid tumors is crucial for advancing cancer immunotherapies. Here, we discovered that the expression of interferon regulatory factor 4 (IRF4) was a critical T cell intrinsic requirement for effective anti-tumor immunity. Mice with T-cell-specific ablation of IRF4 showed significantly reduced T cell tumor infiltration and function, resulting in accelerated growth of subcutaneous syngeneic tumors and allowing the growth of allogeneic tumors. Additionally, engineered overexpression of IRF4 in anti-tumor CD8+ T cells that were adoptively transferred significantly promoted their tumor infiltration and transition from a naive/memory-like cell state into effector T cell states. As a result, IRF4-engineered anti-tumor T cells exhibited significantly improved anti-tumor efficacy, and inhibited tumor growth either alone or in combination with PD-L1 blockade. These findings identify IRF4 as a crucial cell-intrinsic driver of T cell infiltration and function in tumors, emphasizing the potential of IRF4-engineering as an immunotherapeutic approach.

MTHFD2 ablation in T cells protects against heart transplant rejection by perturbing IRF4/PD-1 pathway through the metabolic-epigenetic nexus

BACKGROUND

One-carbon metabolism supports the activation, proliferation, and function of multiple immune cells. However, researchers have not clearly determined whether and how one-carbon metabolic enzymes contribute to heart transplant rejection.

METHODS

We investigated the dynamic metabolic adaptation in grafts during heart transplant rejection by conducting transcriptomics, metabolomics and single-cell RNA sequencing studies of cardiac tissue from human and mouse heart transplant recipients. We also assessed the expression of the one-carbon metabolic enzyme methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) in cardiac grafts by immunofluorescence and flow cytometry assays. Then we constructed a murine heart transplant model with T cell-specific Mthfd2 knockout mice, analyzed T cells function by flow cytometry assays and enzyme-linked immunospot assays, and studied the mechanism by Cleavage Under Targets and Tagmentation assays. Finally, we studied the effect of a pharmacological inhibitor of MTHFD2 in humanized skin transplant model.

RESULTS

We revealed that the one-carbon metabolism enzyme MTHFD2 was a hallmark of alloreactive T cells and was linked to T cell proliferation and function after exposure to alloantigen. And, Mthfd2 ablation prevented murine heart transplant rejection. Mechanistically, we found Mthfd2 ablation affected the interferon regulatory factor 4/programmed death-1 pathway through a metabolic-epigenetic mechanism involving H3K4me3. Furthermore, we found that inhibiting MTHFD2 attenuated human allograft rejection in a humanized skin transplant model.

CONCLUSIONS

These data show that the one-carbon metabolic enzyme MTHFD2 serves as a metabolic checkpoint of alloreactive T cells and suggest that it may be a potential therapeutic target for heart transplant rejection.

Exosomes derived from LPS-preconditioned bone marrow-derived MSC modulate macrophage plasticity to promote allograft survival via the NF-κB/NLRP3 signaling pathway

OBJECTIVES

This study investigated whether exosomes from LPS pretreated bone marrow mesenchymal stem cells (LPS pre-MSCs) could prolong skin graft survival.

METHODS

The exosomes were isolated from the supernatant of MSCs pretreated with LPS. LPS pre-Exo and rapamycin were injected via the tail vein into C57BL/6 mice allografted with BALB/c skin; graft survival was observed and evaluated. The accumulation and polarization of macrophages were examined by immunohistochemistry. The differentiation of macrophages in the spleen was analyzed by flow cytometry. For in vitro, an inflammatory model was established. Specifically, bone marrow-derived macrophages (BMDMs) were isolated and cultured with LPS (100 ng/ml) for 3 h, and were further treated with LPS pre-Exo for 24 h or 48 h. The molecular signaling pathway responsible for modulating inflammation was examined by Western blotting. The expressions of downstream inflammatory cytokines were determined by Elisa, and the polarization of macrophages was analyzed by flow cytometry.

RESULTS

LPS pre-Exo could better ablate inflammation compared to untreated MSC-derived exosomes (BM-Exo). These loaded factors inhibited the expressions of inflammatory factors via a negative feedback mechanism. In vivo, LPS pre-Exo significantly attenuated inflammatory infiltration, thus improving the survival of allogeneic skin graft. Flow cytometric analysis of BMDMs showed that LPS pre-Exo were involved in the regulation of macrophage polarization and immune homeostasis during inflammation. Further investigation revealed that the NF-κB/NLRP3/procaspase-1/IL-1β signaling pathway played a key role in LPS pre-Exo-mediated regulation of macrophage polarization. Inhibiting NF-κB in BMDMs could abolish the LPS-induced activation of inflammatory pathways and the polarization of M1 macrophages while increasing the proportion of M2 cells.

CONCLUSION

LPS pre-Exo are able to switch the polarization of macrophages and enhance the resolution of inflammation. This type of exosomes provides an improved immunotherapeutic potential in prolonging graft survival.

T cell specific deletion of IRF4 with Ox40-Cre impairs effector and memory T cell responses in heart transplantation

BACKGROUND

IRF4 is the pioneer factor for effector T cell maturation. Here we investigated the function of IRF4 in maintaining OX40-related T cell responses following alloantigen activation in a mouse heart transplantation model.

METHODS

Irf4^flox/flox mice were bred with Ox40^cre/+ mice to generate Irf4^flox/floxOx40^cre/+ mice. Wild type C57BL/6, Irf4^flox/floxOx40^cre/+ mice were transplanted with BALB/c heart allografts, with or without BALB/c skin-sensitization. CD4⁺ TEa T cells co-transfer experiments and flow cytometric analysis were conducted to investigate the amount of CD4⁺ T cells and the percentage of the T effector subset.

RESULTS

Irf4^flox/floxOx40^cre/+ and Irf4^flox/floxOx40^cre/+ TEa mice were constructed successfully. IRF4 ablation in activated OX40-mediated alloantigen specific CD4⁺ TEa T cells reduced effector T cell differentiation (CD44^hiCD62L^lo, Ki67, IFN-γ), which caused long-term allograft survival (> 100 d) in the chronic rejection model. In the donor skin-sensitized heart transplantation model, the formation and function of alloantigen-specific memory CD4⁺ TEa cells were also impaired in Irf4^flox/floxOx40^cre/+ mice. Additionally, deletion of IRF4 after T cell activation in Irf4^flox/floxOx40^cre/+ mice reduced T cell reactivation in vitro.

CONCLUSIONS

IRF4 ablation after OX40-related T cell activation could reduce effector and memory T cell formation and inhibit their function in response to alloantigen stimulation. These findings could have significant implications in targeting activated T cells to induce transplant tolerance.

Reduced Satb1 expression predisposes CD4+ T conventional cells to Treg suppression and promotes transplant survival

Limiting CD4+ T cell responses is important to prevent solid organ transplant rejection. In a mouse model of costimulation blockade-dependent cardiac allograft tolerance, we previously reported that alloreactive CD4+ conventional T cells (Tconvs) develop dysfunction, losing proliferative capacity. In parallel, induction of transplantation tolerance is dependent on the presence of regulatory T cells (Tregs). Whether susceptibility of CD4+ Tconvs to Treg suppression is modulated during tolerance induction is unknown. We found that alloreactive Tconvs from transplant tolerant mice had augmented sensitivity to Treg suppression when compared with memory T cells from rejector mice and expressed a transcriptional profile distinct from these memory T cells, including down-regulated expression of the transcription factor Special AT-rich sequence-binding protein 1 (Satb1). Mechanistically, Satb1 deficiency in CD4+ T cells limited their expression of CD25 and IL-2, and addition of Tregs, which express higher levels of CD25 than Satb1-deficient Tconvs and successfully competed for IL-2, resulted in greater suppression of Satb1-deficient than wild-type Tconvs in vitro. In vivo, Satb1-deficient Tconvs were more susceptible to Treg suppression, resulting in significantly prolonged skin allograft survival. Overall, our study reveals that transplantation tolerance is associated with Tconvs' susceptibility to Treg suppression, via modulated expression of Tconv-intrinsic Satb1. Targeting Satb1 in the context of Treg-sparing immunosuppressive therapies might be exploited to improve transplant outcomes.

Genetically targeting the BATF family transcription factors BATF and BATF3 in the mouse abrogates effector T cell activities and enables long-term heart allograft survival

T cells must be activated and become effectors first before executing allograft rejection, a process that is regulated by diverse signals and transcription factors. In this study, we studied the basic leucine zipper ATF-like transcription factor (BATF) family members in regulating T cell activities in a heart transplant model and found that mice deficient for both BATF and BATF3 (Batf-/- Batf3-/- mice) spontaneously accept the heart allografts long-term without tolerizing therapies. Similarly, adoptive transfer of wild type T cells into Rag1-/- hosts induced prompt rejection of heart and skin allografts, whereas the Batf-/- Batf3-/- T cells failed to do so. Analyses of graft-infiltrating cells showed that Batf-/- Batf3-/- T cells infiltrate the graft but fail to acquire an effector phenotype (CD44high KLRG1+ ). Co-transfer experiments in a T cell receptor transgenic TEa model revealed that the Batf-/- Batf3-/- T cells fail to expand in vivo, retain a quiescent phenotype (CD62L+ CD127+ ), and unable to produce effector cytokines to alloantigen stimulation, which contrasted sharply to that of wild type T cells. Together, our data demonstrate that the BATF and BATF3 are critical regulators of T effector functions, thus making them attractive targets for therapeutic interventions in transplant settings.

Transgenic Expression of a Mutant Ribonuclease Regnase-1 in T Cells Disturbs T Cell Development and Functions

Regnase-1 is an RNA-binding protein with ribonuclease activities, and once induced it controls diverse immune responses by degrading mRNAs that encode inflammatory cytokines and costimulatory molecules, thus exerting potent anti-inflammatory functions. However, Regnase-1 is extremely sensitive to degradation by proteases and therefore short-lived. Here, we constructed a mutant Regnase-1 that is resistant to degradation and expressed this mutant in vivo as a transgene specifically in T cells. We found that the mutant Regnase-1 transgenic mice exhibited profound lymphopenia in the periphery despite grossly normal spleen and lymph nodes, and spontaneously accepted skin allografts without any treatment. Mechanistic studies showed that in the transgenic mice thymic T cell development was disrupted, such that most of the developing thymocytes were arrested at the double positive stage, with few mature CD4⁺ and CD8⁺ T cells in the thymus and periphery. Our findings suggest that interfering with the dynamic Regnase-1 expression in T cells disrupts T cell development and functions and further studies are warranted to uncover the mechanisms involved.

IRF4 ablation in B cells abrogates allogeneic B cell responses and prevents chronic transplant rejection

BACKGOUND

B cells contribute to chronic transplant rejection by producing donor-specific antibodies and promoting T cell response, but how these processes are regulated at the transcriptional level remains unclear. Herein, we investigate the role of transcription factor interferon regulatory factor 4 (IRF4) in controlling B cell response during chronic transplant rejection.

METHODS

We generated the Irf4^gfp reporter mice to determine IRF4 expression in B cell lineage. We then used mice with B cell-specific IRF4 deletion to define the role of IRF4 in B cell response after NP-KLH immunization or allogeneic heart transplantation. In particular, graft survival and histology, as well as B and T cell responses, were evaluated after transplantation.

RESULTS

IRF4 is dynamically expressed at different stages of B cell development and is absent in germinal center (GC) B cells. However, IRF4 ablation in the B cell lineage primarily eliminates GC B cells in both naïve and NP-KLH immunized mice. In the transplantation setting, IRF4 functions intrinsically in B cells and governs allogeneic B cell responses at multiple levels, including GC B cell generation, plasma cell differentiation, donor-specific antibody production, and support of T cell response. B cell-specific IRF4 deletion combined with transient CTLA4-Ig treatment abrogates acute and chronic cardiac allograft rejection in naïve recipient mice but not in donor skin-sensitized recipients.

CONCLUSIONS

B cells require IRF4 to mediate chronic transplant rejection. IRF4 ablation in B cells abrogates allogeneic B cell responses and may also inhibit the ability of B cells to prime allogenic T cells. Targeting IRF4 in B cells represents a potential therapeutic strategy for eliminating chronic transplant rejection.

CD4+ T cell exhaustion leads to adoptive transfer therapy failure which can be prevented by immune checkpoint blockade

Cytotoxic CD8⁺ T cell exhaustion is one of the mechanisms underlying the tumor immune escape. The paradigm-shifting immune checkpoint therapy can mitigate CD8⁺ T lymphocyte exhaustion, reinvigorate the anticancer immunity, and achieve durable tumor regression for some patients. Emerging evidence indicates that CD4⁺ T lymphocytes also have a critical role in anticancer immunity, either by directly applying cytotoxicity toward cancer cells or as a helper to augment CD8⁺ T cell cytotoxicity. Whether anticancer CD4⁺ T lymphocytes undergo exhaustion during immunotherapy of solid tumors remains unknown. Here we report that melanoma antigen TRP-1/gp75-specific CD4⁺ T lymphocytes exhibit an exhaustion phenotype after being adoptively transferred into mice bearing large subcutaneous melanoma. Exhaustion of these CD4⁺ T lymphocytes is accompanied with reduced cytokine release and increased expression of inhibitory receptors, resulting in loss of tumor control. Importantly, we demonstrate that PD-L1 immune checkpoint blockade can prevent exhaustion, induce proliferation of the CD4⁺ T lymphocytes, and consequently prevent tumor recurrence. Therefore, when encountering an excessive amount of tumor antigens, tumor-reactive CD4⁺ T lymphocytes also enter the exhaustion state, which can be prevented by immune checkpoint blockade. Our results highlight the importance of tumor-specific CD4⁺ T lymphocytes in antitumor immunity and suggest that the current immune checkpoint blockade therapy may achieve durable anticancer efficacy by rejuvenating both tumor antigen-specific CD8⁺ T lymphocytes and CD4⁺ T lymphocytes.

Interferon regulatory factor 4 deficiency in CD8+ T cells abrogates terminal effector differentiation and promotes transplant acceptance

Allogeneic CD8⁺ cytotoxic T cells play an essential role in rejecting transplanted allografts, but how their effector function is regulated on a transcriptional level remains unclear. Herein, we investigate the role of interferon regulatory factor 4 (IRF4) in controlling CD8⁺ T-cell function in response to transplant. B6.Rag1^-/- mice were adoptively transferred with CD8⁺ T cells isolated from either Irf4^fl/fl Cd4-Cre (T-cell-specific Irf4-deficient) or Irf4^fl/fl control mice, followed by BALB/c skin transplantation. Recipients that received Irf4-deficient CD8⁺ T cells permanently accepted the skin allografts, whereas recipients that received control CD8⁺ T cells acutely rejected the transplanted skins. Mechanistically, compared with the transferred control CD8⁺ T cells in B6.Rag1^-/- recipients, the transferred Irf4-deficient CD8⁺ T cells lost the capacity to differentiate into CD127^- KLRG1⁺ terminal effector cells, barely produced effector cytokines and cytotoxic molecules (e.g. IL-2, IFN-γ, TNF-α, granzyme A and granzyme B), and displayed defect in proliferative capacity, evident by their decreased Ki67 expression and lower frequencies. Moreover, the transferred Irf4-deficient CD8⁺ T cells displayed low expression of transcription factors ID2 and T-bet that govern the terminal effector T-cell programmes, and high expression of transcription factor TCF1 that maintains the naïve-memory T-cell programmes. Hence, IRF4 deficiency in CD8⁺ T cells abrogates their terminal effector differentiation and promotes transplant acceptance. These findings suggest that targeting IRF4 expression represents an attractive and promising therapeutic approach for inducing transplant acceptance.

T cell exhaustion is associated with antigen abundance and promotes transplant acceptance

Exhaustion of T cells limits their ability to clear chronic infections or eradicate tumors. Here, in the context of transplant, we investigated whether T cell exhaustion occurs and has a role in determining transplant outcome. A peptide/MHC tetramer-based approach was used to track exhausted CD8⁺ T cells in a male-to-female skin transplant model. Transplant of large whole-tail skins, but not small tail skins (0.8 cm × 0.8 cm), led to exhaustion of anti-male tetramer⁺ CD8⁺ T cells and subsequently the acceptance of skin grafts. To study CD4⁺ T cell exhaustion, we used the TCR-transgenic B6 TEa cells that recognize a major transplant antigen I-Eα from Balb/c mice. TEa cells were adoptively transferred either into B6 recipients that received Balb/c donor skins or into CB6F1 mice that contained an excessive amount of I-Eα antigen. Adoptively transferred TEa cells in skin-graft recipients were not exhausted. By contrast, virtually all adoptively transferred TEa cells were exhausted in CB6F1 mice. Those exhausted TEa cells lost ability to reject Balb/c skins upon further transfer into lymphopenic B6.Rag1^-/- mice. Hence, T cell exhaustion develops in the presence of abundant antigen and promotes transplant acceptance. These findings are essential for better understanding the nature of transplant tolerance.

Autophagy-lysosome inhibitor chloroquine prevents CTLA-4 degradation of T cells and attenuates acute rejection in murine skin and heart transplantation

Background: The immune checkpoint cytotoxic T lymphocyte antigen-4 (CTLA-4), induced upon T cell activation but degraded quickly, has been targeted in the clinical therapy of advanced cancers and autoimmune diseases. However, whether inhibiting CTLA-4 degradation ameliorates transplant rejection remains unknown.

Methods: The CTLA-4 expression in activated murine T cells treated with the inhibitors mediating protein degradation was detected by flow cytometry (FCM). CD45.1 mice, which received TEa T cells and underwent heart transplantation, were administrated with the inhibitor. Subsequently, CTLA-4 expression of TEa T cells was analyzed. Murine skin and heart transplantation models were built, then the survival and histopathology of the allografts, and T cell subsets in the spleens of each group were compared.

Results: Chloroquine (CQ) was identified as an inhibitor of CTLA-4 degradation, which augmented both surface and total CTLA-4 expression in T cells. It considerably prolonged the skin and heart allograft survival time and reduced the infiltration of inflammatory cells in allografts. Besides decreasing the frequencies of the CD4⁺ and CD8⁺ effector T cells, especially IFN-γ producing T cells, CQ also increased the proportion of regulatory T cells in the spleen. The CTLA-4 blockade abrogated the benefits of CQ on the survival of heart allografts. Moreover, CQ enhanced CTLA-4 expression in activated human T cells and reduced the secretion of IFN-γ in human mixed lymphocyte reaction.

Conclusion: Targeting CTLA-4 degradation provides a novel means to prevent transplant rejection and induce transplant tolerance.

Programmed T cell differentiation: Implications for transplantation

While T cells play a critical role in protective immunity against infection, they are also responsible for graft rejection in the setting of transplantation. T cell differentiation is regulated by both intrinsic transcriptional pathways as well as extrinsic factors such as antigen encounter and the cytokine milieu. Herein, we review recent discoveries in the transcriptional regulation of T cell differentiation and their impact on the field of transplantation. Recent studies uncovering context-dependent differentiation programs that differ in the setting of infection or transplantation will also be discussed. Understanding the key transcriptional pathways that underlie T cell responses in transplantation has important clinical implications, including development of novel therapeutic agents to mitigate graft rejection.

T follicular helper and memory cell responses and the mTOR pathway in murine heart transplantation

BACKGROUND

The mammalian target of rapamycin (mTOR) inhibitors are valuable immunosuppressants in clinical transplantation; however, the mTOR regulation of allogeneic T-cell responses is not fully understood yet. Therefore, the objective of this study is to investigate the effects of T-cell-specific mTOR deletion on the allogeneic T-cell responses and heart transplant survival.

METHODS

BALB/c heart allografts, with or without BALB/c skin sensitization, were transplanted in the wild-type C57BL/6, Mtor^fl/flCd4-Cre, Stat3^fl/flCd4-Cre, and Mtor^fl/flStat3^fl/flCd4-Cre mice. Graft survival and histology, as well as T-cell frequencies and phenotypes, were evaluated after transplantation.

RESULTS

In the absence of donor skin sensitization, long-term heart allograft survival was achieved in the Mtor^fl/flCd4-Cre recipients, which was associated with significantly decreased frequencies of CD62L^-CD44⁺ effector T cells and BCL-6⁺CXCR5⁺ T follicular helper (Tfh) cells in the periphery. Long-term heart allograft survival was also achieved in the donor skin-sensitized Mtor^fl/flStat3^fl/flCd4-Cre mice, whereas the heart allograft survival was prolonged in the donor skin-sensitized Mtor^fl/flCd4-Cre and Stat3^fl/flCd4-Cre mice.

CONCLUSIONS

mTOR is required for Tfh cell response in murine heart transplantation. T-cell-specific deletion of both mTOR and Stat3 abrogates the memory response to heart transplants. These findings help us to better understand the molecular mechanisms underlying the T cell immunity to transplanted organs.

Resilience of T cell-intrinsic dysfunction in transplantation tolerance

Following antigen stimulation, naïve T cells differentiate into memory cells that mediate antigen clearance more efficiently upon repeat encounter. Donor-specific tolerance can be achieved in a subset of transplant recipients, but some of these grafts are rejected after years of stability, often following infections. Whether T cell memory can develop from a tolerant state and whether these formerly tolerant patients develop antidonor memory is not known. Using a mouse model of cardiac transplantation in which donor-specific tolerance is induced with costimulation blockade (CoB) plus donor-specific transfusion (DST), we have previously shown that systemic infection with Listeria monocytogenes (Lm) months after transplantation can erode or transiently abrogate established tolerance. In this study, we tracked donor-reactive T cells to investigate whether memory can be induced when alloreactive T cells are activated in the setting of tolerance. We show alloreactive T cells persist after induction of cardiac transplantation tolerance, but fail to acquire a memory phenotype despite becoming antigen experienced. Instead, donor-reactive T cells develop T cell-intrinsic dysfunction evidenced when removed from the tolerant environment. Notably, Lm infection after tolerance did not rescue alloreactive T cell memory differentiation or functionality. CoB and antigen persistence were sufficient together but not separately to achieve alloreactive T cell dysfunction, and conventional immunosuppression could substitute for CoB. Antigen persistence was required, as early but not late surgical allograft removal precluded the acquisition of T cell dysfunction. Our results demonstrate transplant tolerance-associated T cell-intrinsic dysfunction that is resistant to memory development even after Lm-mediated disruption of tolerance.

Incidence and Impact of Acute Kidney Injury in Patients Receiving Extracorporeal Membrane Oxygenation: A Meta-Analysis

BACKGROUND

Although acute kidney injury (AKI) is a frequent complication in patients receiving extracorporeal membrane oxygenation (ECMO), the incidence and impact of AKI on mortality among patients on ECMO remain unclear. We conducted this systematic review to summarize the incidence and impact of AKI on mortality risk among adult patients on ECMO.

METHODS

A literature search was performed using EMBASE, Ovid MEDLINE, and Cochrane Databases from inception until March 2019 to identify studies assessing the incidence of AKI (using a standard AKI definition), severe AKI requiring renal replacement therapy (RRT), and the impact of AKI among adult patients on ECMO. Effect estimates from the individual studies were obtained and combined utilizing random-effects, generic inverse variance method of DerSimonian-Laird. The protocol for this systematic review is registered with PROSPERO (no. CRD42018103527).

RESULTS

41 cohort studies with a total of 10,282 adult patients receiving ECMO were enrolled. Overall, the pooled estimated incidence of AKI and severe AKI requiring RRT were 62.8% (95%CI: 52.1%-72.4%) and 44.9% (95%CI: 40.8%-49.0%), respectively. Meta-regression showed that the year of study did not significantly affect the incidence of AKI (p = 0.67) or AKI requiring RRT (p = 0.83). The pooled odds ratio (OR) of hospital mortality among patients receiving ECMO with AKI on RRT was 3.73 (95% CI, 2.87-4.85). When the analysis was limited to studies with confounder-adjusted analysis, increased hospital mortality remained significant among patients receiving ECMO with AKI requiring RRT with pooled OR of 3.32 (95% CI, 2.21-4.99). There was no publication bias as evaluated by the funnel plot and Egger's regression asymmetry test with p = 0.62 and p = 0.17 for the incidence of AKI and severe AKI requiring RRT, respectively.

CONCLUSION

Among patients receiving ECMO, the incidence rates of AKI and severe AKI requiring RRT are high, which has not changed over time. Patients who develop AKI requiring RRT while on ECMO carry 3.7-fold higher hospital mortality.

The pursuit of transplantation tolerance: new mechanistic insights

Donor-specific transplantation tolerance that enables weaning from immunosuppressive drugs but retains immune competence to non-graft antigens has been a lasting pursuit since the discovery of neonatal tolerance. More recently, efforts have been devoted not only to understanding how transplantation tolerance can be induced but also the mechanisms necessary to maintain it as well as how inflammatory exposure challenges its durability. This review focuses on recent advances regarding key peripheral mechanisms of T cell tolerance, with the underlying hypothesis that a combination of several of these mechanisms may afford a more robust and durable tolerance and that a better understanding of these individual pathways may permit longitudinal tracking of tolerance following clinical transplantation to serve as biomarkers. This review may enable a personalized assessment of the degree of tolerance in individual patients and the opportunity to strengthen the robustness of peripheral tolerance.