Cutting edge: generation of memory precursors and functional memory CD8+ T cells depends on T cell factor-1 and lymphoid enhancer-binding factor-1

TCF1-positive and TCF1-negative TRM CD8 T cell subsets and cDC1s orchestrate melanoma protection and immunotherapy response

BACKGROUND

Melanoma, the most lethal form of skin cancer, has undergone a transformative treatment shift with the advent of checkpoint blockade immunotherapy (CBI). Understanding the intricate network of immune cells infiltrating the tumor and orchestrating the control of melanoma cells and the response to CBI is currently of utmost importance. There is evidence underscoring the significance of tissue-resident memory (TRM) CD8 T cells and classic dendritic cell type 1 (cDC1) in cancer protection. Transcriptomic studies also support the existence of a TCF7+ (encoding TCF1) T cell as the most important for immunotherapy response, although uncertainty exists about whether there is a TCF1+TRM T cell due to evidence indicating TCF1 downregulation for tissue residency activation.

METHODS

We used multiplexed immunofluorescence and spectral flow cytometry to evaluate TRM CD8 T cells and cDC1 in two melanoma patient cohorts: one immunotherapy-naive and the other receiving immunotherapy. The first cohort was divided between patients free of disease or with metastasis 2 years postdiagnosis while the second between CBI responders and non-responders.

RESULTS

Our study identifies two CD8+TRM subsets, TCF1+ and TCF1-, correlating with melanoma protection. TCF1+TRM cells show heightened expression of IFN-γ and Ki67 while TCF1- TRM cells exhibit increased expression of cytotoxic molecules. In metastatic patients, TRM subsets undergo a shift in marker expression, with the TCF1- subset displaying increased expression of exhaustion markers. We observed a close spatial correlation between cDC1s and TRMs, with TCF1+TRM/cDC1 pairs enriched in the stroma and TCF1- TRM/cDC1 pairs in tumor areas. Notably, these TCF1- TRMs express cytotoxic molecules and are associated with apoptotic melanoma cells. Both TCF1+ and TCF1- TRM subsets, alongside cDC1, prove relevant to CBI response.

CONCLUSIONS

Our study supports the importance of TRM CD8 T cells and cDC1 in melanoma protection while also highlighting the existence of functionally distinctive TCF1+ and TCF1- TRM subsets, both crucial for melanoma control and CBI response.

ER-associated degradation adapter Sel1L is required for CD8+ T cell function and memory formation following acute viral infection

The maintenance of antigen-specific CD8+ T cells underlies the efficacy of vaccines and immunotherapies. Pathways contributing to CD8+ T cell loss are not completely understood. Uncovering the pathways underlying the limited persistence of CD8+ T cells would be of significant benefit for developing novel strategies of promoting T cell persistence. Here, we demonstrate that murine CD8+ T cells experience endoplasmic reticulum (ER) stress following activation and that the ER-associated degradation (ERAD) adapter Sel1L is induced in activated CD8+ T cells. Sel1L loss limits CD8+ T cell function and memory formation following acute viral infection. Mechanistically, Sel1L is required for optimal bioenergetics and c-Myc expression. Finally, we demonstrate that human CD8+ T cells experience ER stress upon activation and that ER stress is negatively associated with improved T cell functionality in T cell-redirecting therapies. Together, these results demonstrate that ER stress and ERAD are important regulators of T cell function and persistence.

Pregnancy dedifferentiates memory CD8+ T cells into hypofunctional cells with exhaustion-enriched programs

Alloreactive memory, unlike naive, CD8+ T cells resist transplantation tolerance protocols and are a critical barrier to long-term graft acceptance in the clinic. We here show that semiallogeneic pregnancy successfully reprogrammed memory fetus/graft-specific CD8+ T cells (TFGS) toward hypofunction. Female C57BL/6 mice harboring memory CD8+ T cells generated by the rejection of BALB/c skin grafts and then mated with BALB/c males achieved rates of pregnancy comparable with naive controls. Postpartum CD8+ TFGS from skin-sensitized dams upregulated expression of T cell exhaustion (TEX) markers (Tox, Eomes, PD-1, TIGIT, and Lag3). Transcriptional analysis corroborated an enrichment of canonical TEX genes in postpartum memory TFGS and revealed a downregulation of a subset of memory-associated transcripts. Strikingly, pregnancy induced extensive epigenetic modifications of exhaustion- and memory-associated genes in memory TFGS, whereas minimal epigenetic modifications were observed in naive TFGS. Finally, postpartum memory TFGS durably expressed the exhaustion-enriched phenotype, and their susceptibility to transplantation tolerance was significantly restored compared with memory TFGS. These findings advance the concept of pregnancy as an epigenetic modulator inducing hypofunction in memory CD8+ T cells that has relevance not only for pregnancy and transplantation tolerance, but also for tumor immunity and chronic infections.

A novel engineered IL-21 receptor arms T-cell receptor-engineered T cells (TCR-T cells) against hepatocellular carcinoma

Strategies to improve T cell therapy efficacy in solid tumors such as hepatocellular carcinoma (HCC) are urgently needed. The common cytokine receptor γ chain (γc) family cytokines such as IL-2, IL-7, IL-15 and IL-21 play fundamental roles in T cell development, differentiation and effector phases. This study aims to determine the combination effects of IL-21 in T cell therapy against HCC and investigate optimized strategies to utilize the effect of IL-21 signal in T cell therapy. The antitumor function of AFP-specific T cell receptor-engineered T cells (TCR-T) was augmented by exogenous IL-21 in vitro and in vivo. IL-21 enhanced proliferation capacity, promoted memory differentiation, downregulated PD-1 expression and alleviated apoptosis in TCR-T after activation. A novel engineered IL-21 receptor was established, and TCR-T armed with the novel engineered IL-21 receptors (IL-21R-TCR-T) showed upregulated phosphorylated STAT3 expression without exogenous IL-21 ligand. IL-21R-TCR-T showed better proliferation upon activation and superior antitumor function in vitro and in vivo. IL-21R-TCR-T exhibited a less differentiated, exhausted and apoptotic phenotype than conventional TCR-T upon repetitive tumor antigen stimulation. The novel IL-21 receptor in our study programs powerful TCR-T and can avoid side effects induced by IL-21 systemic utilization. The novel IL-21 receptor creates new opportunities for next-generation TCR-T against HCC.

Microbiota-derived inosine programs protective CD8+ T cell responses against influenza in newborns

The immunological defects causing susceptibility to severe viral respiratory infections due to early-life dysbiosis remain ill-defined. Here, we show that influenza virus susceptibility in dysbiotic infant mice is caused by CD8+ T cell hyporesponsiveness and diminished persistence as tissue-resident memory cells. We describe a previously unknown role for nuclear factor interleukin 3 (NFIL3) in repression of memory differentiation of CD8+ T cells in dysbiotic mice involving epigenetic regulation of T cell factor 1 (TCF 1) expression. Pulmonary CD8+ T cells from dysbiotic human infants share these transcriptional signatures and functional phenotypes. Mechanistically, intestinal inosine was reduced in dysbiotic human infants and newborn mice, and inosine replacement reversed epigenetic dysregulation of Tcf7 and increased memory differentiation and responsiveness of pulmonary CD8+ T cells. Our data unveils new developmental layers controlling immune cell activation and identifies microbial metabolites that may be used therapeutically in the future to protect at-risk newborns.

IL7 in combination with radiotherapy stimulates a memory T-cell response to improve outcomes in HNSCC models

Clinically approved head and neck squamous cell carcinoma (HNSCC) immunotherapies manipulate the immune checkpoint blockade (ICB) axis but have had limited success outside of recurrent/metastatic disease. Interleukin-7 (IL7) has been shown to be essential for effector T-cell survival, activation, and proliferation. Here, we show that IL7 in combination with radiotherapy (RT) is effective in activating CD8 + T-cells for reducing tumor growth. Our studies were conducted using both human papillomavirus related and unrelated orthotopic HNSCC murine models. Immune populations from the tumor, draining lymph nodes, and blood were compared between treatment groups and controls using flow cytometry, proteomics, immunofluorescence staining, and RNA sequencing. Treatment with RT and IL7 (RT + IL7) resulted in significant tumor growth reduction, high CD8 T-cell tumor infiltration, and increased proliferation of T-cell progenitors in the bone marrow. IL7 also expanded a memory-like subpopulation of CD8 T-cells. These results indicate that IL7 in combination with RT can serve as an effective immunotherapy strategy outside of the conventional ICB axis to drive the antitumor activity of CD8 T-cells.

Early-to-mid stage idiopathic Parkinson's disease shows enhanced cytotoxicity and differentiation in CD8 T-cells in females

Neuroinflammation in the brain contributes to the pathogenesis of Parkinson's disease (PD), but the potential dysregulation of peripheral immunity has not been systematically investigated for idiopathic PD (iPD). Here we showed an elevated peripheral cytotoxic immune milieu, with more terminally-differentiated effector memory (TEMRA) CD8 T, CD8+ NKT cells and circulating cytotoxic molecules in fresh blood of patients with early-to-mid iPD, especially females, after analyzing > 700 innate and adaptive immune features. This profile, also reflected by fewer CD8+FOXP3+ T cells, was confirmed in another subcohort. Co-expression between cytotoxic molecules was selectively enhanced in CD8 TEMRA and effector memory (TEM) cells. Single-cell RNA-sequencing analysis demonstrated the accelerated differentiation within CD8 compartments, enhanced cytotoxic pathways in CD8 TEMRA and TEM cells, while CD8 central memory (TCM) and naïve cells were already more-active and transcriptionally-reprogrammed. Our work provides a comprehensive map of dysregulated peripheral immunity in iPD, proposing candidates for early diagnosis and treatments.

Regulation of CD8+ T memory and exhaustion by the mTOR signals

CD8+ T cells are the key executioners of the adaptive immune arm, which mediates antitumor and antiviral immunity. Naïve CD8+ T cells develop in the thymus and are quickly activated in the periphery after encountering a cognate antigen, which induces these cells to proliferate and differentiate into effector cells that fight the initial infection. Simultaneously, a fraction of these cells become long-lived memory CD8+ T cells that combat future infections. Notably, the generation and maintenance of memory cells is profoundly affected by various in vivo conditions, such as the mode of primary activation (e.g., acute vs. chronic immunization) or fluctuations in host metabolic, inflammatory, or aging factors. Therefore, many T cells may be lost or become exhausted and no longer functional. Complicated intracellular signaling pathways, transcription factors, epigenetic modifications, and metabolic processes are involved in this process. Therefore, understanding the cellular and molecular basis for the generation and fate of memory and exhausted CD8+ cells is central for harnessing cellular immunity. In this review, we focus on mammalian target of rapamycin (mTOR), particularly signaling mediated by mTOR complex (mTORC) 2 in memory and exhausted CD8+ T cells at the molecular level.

Graded expression of the chemokine receptor CX3CR1 marks differentiation states of human and murine T cells and enables cross-species interpretation

T cells differentiate into functionally distinct states upon antigen encounter. These states are delineated by different cell surface markers for murine and human T cells, which hamper cross-species translation of T cell properties. We aimed to identify surface markers that reflect the graded nature of CD8+ T cell differentiation and delineate functionally comparable states in mice and humans. CITEseq analyses revealed that graded expression of CX3CR1, encoding the chemokine receptor CX3CR1, correlated with the CD8+ T cell differentiation gradient. CX3CR1 expression distinguished human and murine CD8+ and CD4+ T cell states, as defined by migratory and functional properties. Graded CX3CR1 expression, refined with CD62L, accurately captured the high-dimensional T cell differentiation continuum. Furthermore, the CX3CR1 expression gradient delineated states with comparable properties in humans and mice in steady state and on longitudinally tracked virus-specific CD8+ T cells in both species. Thus, graded CX3CR1 expression provides a strategy to translate the behavior of distinct T cell differentiation states across species.

DNA architectural protein CTCF facilitates subset-specific chromatin interactions to limit the formation of memory CD8+ T cells

Although the importance of genome organization for transcriptional regulation of cell-fate decisions and function is clear, the changes in chromatin architecture and how these impact effector and memory CD8+ T cell differentiation remain unknown. Using Hi-C, we studied how genome configuration is integrated with CD8+ T cell differentiation during infection and investigated the role of CTCF, a key chromatin remodeler, in modulating CD8+ T cell fates through CTCF knockdown approaches and perturbation of specific CTCF-binding sites. We observed subset-specific changes in chromatin organization and CTCF binding and revealed that weak-affinity CTCF binding promotes terminal differentiation of CD8+ T cells through the regulation of transcriptional programs. Further, patients with de novo CTCF mutations had reduced expression of the terminal-effector genes in peripheral blood lymphocytes. Therefore, in addition to establishing genome architecture, CTCF regulates effector CD8+ T cell heterogeneity through altering interactions that regulate the transcription factor landscape and transcriptome.

Primary role of type I interferons for the induction of functionally optimal antigen-specific CD8+ T cells in HIV infection

BACKGROUND

CD8⁺ T cells equipped with a full arsenal of antiviral effector functions are critical for effective immune control of HIV-1. It has nonetheless remained unclear how best to elicit such potent cellular immune responses in the context of immunotherapy or vaccination. HIV-2 has been associated with milder disease manifestations and more commonly elicits functionally replete virus-specific CD8⁺ T cell responses compared with HIV-1. We aimed to learn from this immunological dichotomy and to develop informed strategies that could enhance the induction of robust CD8⁺ T cell responses against HIV-1.

METHODS

We developed an unbiased in vitro system to compare the de novo induction of antigen-specific CD8⁺ T cell responses after exposure to HIV-1 or HIV-2. The functional properties of primed CD8⁺ T cells were assessed using flow cytometry and molecular analyses of gene transcription.

FINDINGS

HIV-2 primed functionally optimal antigen-specific CD8⁺ T cells with enhanced survival properties more effectively than HIV-1. This superior induction process was dependent on type I interferons (IFNs) and could be mimicked via the adjuvant delivery of cyclic GMP-AMP (cGAMP), a known agonist of the stimulator of interferon genes (STING). CD8⁺ T cells elicited in the presence of cGAMP were polyfunctional and highly sensitive to antigen stimulation, even after priming from people living with HIV-1.

INTERPRETATION

HIV-2 primes CD8⁺ T cells with potent antiviral functionality by activating the cyclic GMP-AMP synthase (cGAS)/STING pathway, which results in the production of type I IFNs. This process may be amenable to therapeutic development via the use of cGAMP or other STING agonists to bolster CD8⁺ T cell-mediated immunity against HIV-1.

FUNDING

This work was funded by INSERM, the Institut Curie, and the University of Bordeaux (Senior IdEx Chair) and by grants from Sidaction (17-1-AAE-11097, 17-1-FJC-11199, VIH2016126002, 20-2-AEQ-12822-2, and 22-2-AEQ-13411), the Agence Nationale de la Recherche sur le SIDA (ECTZ36691, ECTZ25472, ECTZ71745, and ECTZ118797), and the Fondation pour la Recherche Médicale (EQ U202103012774). D.A.P. was supported by a Wellcome Trust Senior Investigator Award (100326/Z/12/Z).

A transcriptionally distinct subset of influenza-specific effector memory B cells predicts long-lived antibody responses to vaccination in humans

Seasonal influenza vaccination elicits hemagglutinin (HA)-specific memory B (Bmem) cells, and although multiple Bmem cell populations have been characterized, considerable heterogeneity exists. We found that HA-specific human Bmem cells differed in the expression of surface marker FcRL5 and transcriptional factor T-bet. FcRL5+T-bet+ Bmem cells were transcriptionally similar to effector-like memory cells, while T-betnegFcRL5neg Bmem cells exhibited stem-like central memory properties. FcRL5+ Bmem cells did not express plasma-cell-commitment factors but did express transcriptional, epigenetic, metabolic, and functional programs that poised these cells for antibody production. Accordingly, HA+ T-bet+ Bmem cells at day 7 post-vaccination expressed intracellular immunoglobulin, and tonsil-derived FcRL5+ Bmem cells differentiated more rapidly into antibody-secreting cells (ASCs) in vitro. The T-bet+ Bmem cell response positively correlated with long-lived humoral immunity, and clonotypes from T-bet+ Bmem cells were represented in the secondary ASC response to repeat vaccination, suggesting that this effector-like population predicts influenza vaccine durability and recall potential.

Empowering the Potential of CAR-T Cell Immunotherapies by Epigenetic Reprogramming

T-cell-based, personalized immunotherapy can nowadays be considered the mainstream treatment for certain blood cancers, with a high potential for expanding indications. Chimeric antigen receptor T cells (CAR-Ts), an ex vivo genetically modified T-cell therapy product redirected to target an antigen of interest, have achieved unforeseen successes in patients with B-cell hematologic malignancies. Frequently, however, CAR-T cell therapies fail to provide durable responses while they have met with only limited success in treating solid cancers because unique, unaddressed challenges, including poor persistence, impaired trafficking to the tumor, and site penetration through a hostile microenvironment, impede their efficacy. Increasing evidence suggests that CAR-Ts' in vivo performance is associated with T-cell intrinsic features that may be epigenetically altered or dysregulated. In this review, we focus on the impact of epigenetic regulation on T-cell differentiation, exhaustion, and tumor infiltration and discuss how epigenetic reprogramming may enhance CAR-Ts' memory phenotype, trafficking, and fitness, contributing to the development of a new generation of potent CAR-T immunotherapies.

The degree of T cell stemness differentially impacts the potency of adoptive cancer immunotherapy in a Lef-1 and Tcf-1 dependent manner

Generating stem memory T cells (T _SCM ) is a key goal for improving cancer immunotherapy. Yet, the optimal way to modulate signaling pathways that enrich T _SCM properties remains elusive. Here, we discovered that the degree to which the PI3Kδ pathway is blocked pharmaceutically can generate T cells with differential levels of stemness properties. This observation was based on the progressive enrichment of transcriptional factors of stemness (Tcf-1 and Lef-1). Additional investigation revealed that T cells with high stemness features had enhanced metabolic plasticity, marked by heightened mitochondrial function and glucose uptake. Conversely, T cells with low or medium features of stemness expressed more inhibitory checkpoint receptors (Tim-3, CD39) and were vulnerable to antigen-induced cell death. Only TCR-antigen specific T cells with high stemness persisted following adoptive transfer in vivo and mounted protective immunity to melanoma tumors. Likewise, the strongest level of PI3Kδ blockade in vitro generated human tumor infiltrating lymphocytes (TILs) and CAR T cells with heightened stemness properties, in turn bolstering their capacity to regress human mesothelioma tumors. We find that the level of stemness T cells possess in vitro differentially impacts their potency upon transfer in three tumor models. Mechanistically, both Lef-1 and Tcf-1 sustain anti-tumor protection by high T _SCM , as deletion of either one compromised cellular therapy. Collectively, these findings highlight the therapeutic potential of carefully modulating PI3Kδ signaling in T cells to confer high stemness and mediate protective responses to solid tumors.

Chronic lymphocytic leukemia presence impairs antigen-specific CD8+ T-cell responses through epigenetic reprogramming towards short-lived effectors

T-cell dysregulation in chronic lymphocytic leukemia (CLL) associates with low response rates to autologous T cell-based therapies. How CLL affects antigen-specific T-cell responses remains largely unknown. We investigated (epi)genetic and functional consequences of antigen-specific T-cell responses in presence of CLL in vitro and in an adoptive-transfer murine model. Already at steady-state, antigen-experienced patient-derived T cells were skewed towards short-lived effector cells (SLEC) at the expense of memory-precursor effector cells (MPEC). Stimulation of these T cells in vitro showed rapid induction of effector genes and suppression of key memory transcription factors only in presence of CLL cells, indicating epigenetic regulation. This was investigated in vivo by following antigen-specific responses of naïve OT-I CD8⁺ cells to mCMV-OVA in presence/absence of TCL1 B-cell leukemia. Presence of leukemia resulted in increased SLEC formation, with disturbed inflammatory cytokine production. Chromatin and transcriptome profiling revealed strong epigenetic modifications, leading to activation of an effector and silencing of a memory profile through presence of CLL cells. Secondary challenge in vivo confirmed dysfunctional memory responses by antigen-experienced OT-I cells generated in presence of CLL. Altogether, we show that presence of CLL induces a short-lived effector phenotype and impaired memory responses by epigenetic reprogramming during primary responses.

LEF1 Drives a Central Memory Program and Supports Antitumor Activity of Natural Killer T Cells

Vα24-invariant natural killer T cells (NKT) possess innate antitumor properties that can be exploited for cancer immunotherapy. We have shown previously that the CD62L+ central memory-like subset of these cells drives the in vivo antitumor activity of NKTs, but molecular mediators of NKT central memory differentiation remain unknown. Here, we demonstrate that relative to CD62L- cells, CD62L+ NKTs express a higher level of the gene encoding the Wnt/β-catenin transcription factor lymphoid enhancer binding factor 1 (LEF1) and maintain active Wnt/β-catenin signaling. CRISPR/Cas9-mediated LEF1 knockout reduced CD62L+ frequency after antigenic stimulation, whereas Wnt/β-catenin activator Wnt3a ligand increased CD62L+ frequency. LEF1 overexpression promoted NKT expansion and limited exhaustion following serial tumor challenge and was sufficient to induce a central memory-like transcriptional program in NKTs. In mice, NKTs expressing a GD2-specific chimeric-antigen receptor (CAR) with LEF1 demonstrated superior control of neuroblastoma xenograft tumors compared with control CAR-NKTs. These results identify LEF1 as a transcriptional activator of the NKT central memory program and advance development of NKT cell-based immunotherapy. See related Spotlight by Van Kaer, p. 144.

RNA Therapeutics for Improving CAR T-cell Safety and Efficacy

Autologous chimeric antigen receptor (CAR) T cells have recently emerged as potent tools in the fight against cancer, with promising therapeutic efficacy against hematological malignancies. However, several limitations hamper their widespread clinical use, including availability of target antigen, severe toxic effects, primary and secondary resistance, heterogeneous quality of autologous T cells, variable persistence, and low activity against solid tumors. Development of allogeneic off-the-shelf CAR T cells could help address some of these limitations but is impeded by alloimmunity with either rejection and limited expansion of allo-CAR T cells or CAR T cells versus host reactions. RNA therapeutics, such as small interfering RNAs, microRNAs, and antisense oligonucleotides, are able to silence transcripts in a sequence-specific and proliferation-sensitive way, which may offer a way to overcome some of the challenges facing CAR T-cell development and clinical utility. Here, we review how different RNA therapeutics or a combination of RNA therapeutics and genetic engineering could be harnessed to improve the safety and efficacy of autologous and allogeneic CAR T-cell therapy.

Systems-level identification of key transcription factors in immune cell specification

Transcription factors (TFs) are crucial for regulating cell differentiation during the development of the immune system. However, the key TFs for orchestrating the specification of distinct immune cells are not fully understood. Here, we integrated the transcriptomic and epigenomic measurements in 73 mouse and 61 human primary cell types, respectively, that span the immune cell differentiation pathways. We constructed the cell-type-specific transcriptional regulatory network and assessed the global importance of TFs based on the Taiji framework, which is a method we have previously developed that can infer the global impact of TFs using integrated transcriptomic and epigenetic data. Integrative analysis across cell types revealed putative driver TFs in cell lineage-specific differentiation in both mouse and human systems. We have also identified TF combinations that play important roles in specific developmental stages. Furthermore, we validated the functions of predicted novel TFs in murine CD8+ T cell differentiation and showed the importance of Elf1 and Prdm9 in the effector versus memory T cell fate specification and Kdm2b and Tet3 in promoting differentiation of CD8+ tissue resident memory (Trm) cells, validating the approach. Thus, we have developed a bioinformatic approach that provides a global picture of the regulatory mechanisms that govern cellular differentiation in the immune system and aids the discovery of novel mechanisms in cell fate decisions.

Ceria nanoparticles prophylactic used for renal ischemia-reperfusion injury treatment by attenuating oxidative stress and inflammatory response

Renal ischemia-reperfusion (IR) injury (RIRI) is the leading cause of acute kidney injury (AKI), a common disease with high morbidity and mortality. However, due to the lack of effective diagnostic and therapeutic tools, patients have to resort to conservative treatment. To address this issue, we have developed a novel prophylactic strategy that involves the pre-treatment use of ceria nanoparticles (CNPs) before surgery. Based on our careful study of the three different sizes of CNPs that we synthesized, 46 nm (NP46), 81 nm (NP81), and 118 nm (NP118), we have found that NP118 can be used as effective prophylactic agents against RIRI and subsequent renal fibrosis. In our experiments, the CNPs exhibited excellent antioxidant and anti-inflammatory activities in vitro and effectively protected the kidney against RIRI and renal fibrosis in vivo, as proved by the decreases in renal lesions, serum creatinine, blood urea nitrogen, apoptotic cell, KIM-1 expression, and fibrotic area in CNPs treated samples relative to RIRI group. Mechanistically, not only did the CNPs reduce oxidative stress by regulating the Nrf2 pathway, but they also attenuated RIRI induced inflammatory response by decreasing macrophage infiltration and polarization to M1 phenotype, and reducing pro-inflammatory cytokine and chemokine production. In vitro results further confirmed that CNPs pre-treatment not only dramatically decreased intracellular ROS production in renal tubular epithelial cells and vascular endothelial cells, but also effectively attenuated lipopolysaccharide-induced inflammation in RAW264.7 cells. In addition, we found that one fourth of the NP118 persisted for more than 21 days in IR kidneys, and that out of the three sizes of CNPs, NP118 achieved the best results in all our experiments. Our study provides new insights into the usage and majorization of CNPs as a potential therapy to treat or prevent RIRI and renal fibrosis.

Id3 expression identifies CD4+ memory Th1 cells

Memory CD4⁺ T cells play a pivotal role in mediating long-term protective immunity, positioning them as an important target in vaccine development. However, multiple functionally distinct helper CD4⁺ T-cell subsets can arise in response to a single invading pathogen, complicating the identification of rare populations of memory precursor cells during the effector phase of infection and memory CD4⁺ T cells following pathogen clearance and the contraction phase of infection. Furthermore, current literature remains unclear regarding whether a single CD4⁺ memory T-cell lineage gives rise to secondary CD4⁺ T helper subsets or if there are unique memory precursor cells within each helper lineage. A majority of T follicular helper (Tfh) cells, which have established memory potential, express Id3, an inhibitor of E protein transcription factors, following acute viral infection. We show that expression of Id3 definitively identified a subset of cells within both the CD4⁺ Tfh and T helper 1 (Th1) lineages at memory time points that exhibited memory potential, with the capacity for significant re-expansion in response to secondary infection. Notably, we demonstrate that a subset of Th1 cells that survive into the memory phase were marked by Id3 expression and possessed the potential for enhanced expansion and generation of both Th1 and Tfh secondary effector cell populations in a secondary response to pathogen. Additionally, these cells exhibited enrichment of key molecules associated with memory potential when compared with Id3^lo Th1 cells. Therefore, we propose that Id3 expression serves as an important marker to indicate multipotent potential in memory CD4⁺ T cells.

The long noncoding RNA Malat1 regulates CD8+ T cell differentiation by mediating epigenetic repression

During an immune response to microbial infection, CD8+ T cells give rise to short-lived effector cells and memory cells that provide sustained protection. Although the transcriptional programs regulating CD8+ T cell differentiation have been extensively characterized, the role of long noncoding RNAs (lncRNAs) in this process remains poorly understood. Using a functional genetic knockdown screen, we identified the lncRNA Malat1 as a regulator of terminal effector cells and the terminal effector memory (t-TEM) circulating memory subset. Evaluation of chromatin-enriched lncRNAs revealed that Malat1 grouped with trans lncRNAs that exhibit increased RNA interactions at gene promoters and gene bodies. Moreover, we observed that Malat1 was associated with increased H3K27me3 deposition at a number of memory cell-associated genes through a direct interaction with Ezh2, thereby promoting terminal effector and t-TEM cell differentiation. Our findings suggest an important functional role of Malat1 in regulating CD8+ T cell differentiation and broaden the knowledge base of lncRNAs in CD8+ T cell biology.

TCF-1: a maverick in T cell development and function

The T cell-specific DNA-binding protein TCF-1 is a central regulator of T cell development and function along multiple stages and lineages. Because it interacts with β-catenin, TCF-1 has been classically viewed as a downstream effector of canonical Wnt signaling, although there is strong evidence for β-catenin-independent TCF-1 functions. TCF-1 co-binds accessible regulatory regions containing or lacking its conserved motif and cooperates with other nuclear factors to establish context-dependent epigenetic and transcription programs that are essential for T cell development and for regulating immune responses to infection, autoimmunity and cancer. Although it has mostly been associated with positive regulation of chromatin accessibility and gene expression, TCF-1 has the potential to reduce chromatin accessibility and thereby suppress gene expression. In addition, the binding of TCF-1 bends the DNA and affects the chromatin conformation genome wide. This Review discusses the current understanding of the multiple roles of TCF-1 in T cell development and function and their mechanistic underpinnings.

Dickkopf proteins in pathological inflammatory diseases

The human body encounters various challenges. Tissue repair and regeneration processes are augmented after tissue injury to reinstate tissue homeostasis. The Wnt pathway plays a crucial role in tissue repair since it induces target genes required for cell proliferation and differentiation. Since tissue injury causes inflammatory immune responses, it has become increasingly clear that the Wnt ligands can function as immunomodulators while critical for tissue homeostasis. The Wnt pathway and Wnt ligands have been studied extensively in cancer biology and developmental biology. While the Wnt ligands are being studied actively, how the Wnt antagonists and their regulatory mechanisms can modulate immune responses during chronic pathological inflammation remain elusive. This review summarizes DKK family proteins as immunomodulators, aiming to provide an overarching picture for tissue injury and repair. To this end, we first review the Wnt pathway components and DKK family proteins. Next, we will review DKK family proteins (DKK1, 2, and 3) as a new class of immunomodulatory protein in cancer and other chronic inflammatory diseases. Taken together, DKK family proteins and their immunomodulatory functions in chronic inflammatory disorders provide novel insights to understand immune diseases and make them attractive molecular targets for therapeutic intervention.

Accelerating clinical-scale production of BCMA CAR T cells with defined maturation stages

The advent of CAR T cells targeting CD19 or BCMA on B cell neoplasm demonstrated remarkable efficacy, but rapid relapses and primary refractoriness remains challenging. A leading cause of CAR T cell failure is their lack of expansion and limited persistence. Long-lived, self-renewing multipotent T memory stem cells (T_SCM) and T central memory cells (T_CM) likely sustain superior tumor regression, but their low frequencies in blood from cancer patients impose a major hurdle for clinical CAR T production. We designed a clinically compliant protocol for generating BCMA CAR T cells starting with increased T_SCM/T_CM cell input. A CliniMACS Prodigy process was combined with flow cytometry-based enrichment of CD62L⁺CD95⁺ T cells. Although starting with only 15% of standard T cell input, the selected T_SCM/T_CM material was efficiently activated and transduced with a BCMA CAR-encoding retrovirus. Cultivation in the presence of IL-7/IL-15 enabled the harvest of CAR T cells containing an increased CD4⁺ T_SCM fraction and 70% T_SCM cells amongst CD8⁺. Strong cell proliferation yielded cell numbers sufficient for clinical application, while effector functions were maintained. Together, adaptation of a standard CliniMACS Prodigy protocol to low input numbers resulted in efficient retroviral transduction with a high CAR T cell yield.

TCF1 in T cell immunity: a broadened frontier

TCF1 and its homologue LEF1 are historically known as effector transcription factors downstream of the WNT signalling pathway and are essential for early T cell development. Recent advances bring TCF1 into the spotlight for its versatile, context-dependent functions in regulating mature T cell responses. In the cytotoxic T cell lineages, TCF1 is required for the self-renewal of stem-like CD8⁺ T cells generated in response to viral or tumour antigens, and for preserving heightened responses to checkpoint blockade immunotherapy. In the helper T cell lineages, TCF1 is indispensable for the differentiation of T follicular helper and T follicular regulatory cells, and crucially regulates immunosuppressive functions of regulatory T cells. Mechanistic investigations have also identified TCF1 as the first transcription factor that directly modifies histone acetylation, with the capacity to bridge transcriptional and epigenetic regulation. TCF1 also has the potential to become an important clinical biomarker for assessing the prognosis of tumour immunotherapy and the success of viral control in treating HIV and hepatitis C virus infection. Here, we summarize the key findings on TCF1 across the fields of T cell immunity and reflect on the possibility of exploring TCF1 and its downstream transcriptional programmes as therapeutic targets for improving antiviral and antitumour immunity.

In vivo genome-wide CRISPR screens identify SOCS1 as intrinsic checkpoint of CD4+ TH1 cell response

[Figure: see text].

Targeting Cbx3/HP1γ Induces LEF-1 and IL-21R to Promote Tumor-Infiltrating CD8 T-Cell Persistence

Immune checkpoint blockade (ICB) relieves CD8⁺ T-cell exhaustion in most mutated tumors, and TCF-1 is implicated in converting progenitor exhausted cells to functional effector cells. However, identifying mechanisms that can prevent functional senescence and potentiate CD8⁺ T-cell persistence for ICB non-responsive and resistant tumors remains elusive. We demonstrate that targeting Cbx3/HP1γ in CD8⁺ T cells augments transcription initiation and chromatin remodeling leading to increased transcriptional activity at Lef1 and Il21r. LEF-1 and IL-21R are necessary for Cbx3/HP1γ-deficient CD8⁺ effector T cells to persist and control ovarian cancer, melanoma, and neuroblastoma in preclinical models. The enhanced persistence of Cbx3/HP1γ-deficient CD8⁺ T cells facilitates remodeling of the tumor chemokine/receptor landscape ensuring their optimal invasion at the expense of CD4⁺ Tregs. Thus, CD8⁺ T cells heightened effector function consequent to Cbx3/HP1γ deficiency may be distinct from functional reactivation by ICB, implicating Cbx3/HP1γ as a viable cancer T-cell-based therapy target for ICB resistant, non-responsive solid tumors.

Ectopic activation of the miR-200c-EpCAM axis enhances antitumor T cell responses in models of adoptive cell therapy

Adoptive T cell therapy (ACT) is a promising strategy for treating cancer, but it often fails because of cell intrinsic regulatory programs that limit the degree or duration of T cell function. In this study, we found that ectopic expression of microRNA-200c (miR-200c) markedly enhanced the antitumor activity of CD8+ cytotoxic T lymphocytes (CTLs) during ACT in multiple mouse models. CTLs transduced with miR-200c exhibited reduced apoptosis during engraftment and enhanced in vivo persistence, accompanied by up-regulation of the transcriptional regulator T cell factor 1 (TCF1) and the inflammatory cytokine tumor necrosis factor (TNF). miR-200c elicited these changes by suppressing the transcription factor Zeb1 and thereby inducing genes characteristic of epithelial cells. Overexpression of one of these genes, Epcam, was sufficient to augment therapeutic T cell responses against both solid and liquid tumors. These results identify the miR-200c–EpCAM axis as an avenue for improving ACT and demonstrate that select genetic perturbations can produce phenotypically distinct T cells with advantageous therapeutic properties.

BATF regulates progenitor to cytolytic effector CD8+ T cell transition during chronic viral infection

During chronic viral infection, CD8⁺ T cells develop into three major phenotypically and functionally distinct subsets: Ly108⁺TCF-1⁺ progenitors, Ly108^-CX₃CR1^- terminally exhausted cells and the recently identified CX₃CR1⁺ cytotoxic effector cells. Nevertheless, how CX₃CR1⁺ effector cell differentiation is transcriptionally and epigenetically regulated remains elusive. Here, we identify distinct gene regulatory networks and epigenetic landscapes underpinning the formation of these subsets. Notably, our data demonstrate that CX₃CR1⁺ effector cells bear a striking similarity to short-lived effector cells during acute infection. Genetic deletion of Tbx21 significantly diminished formation of the CX₃CR1⁺ subset. Importantly, we further identify a previously unappreciated role for the transcription factor BATF in maintaining a permissive chromatin structure that allows the transition from TCF-1⁺ progenitors to CX₃CR1⁺ effector cells. BATF directly bound to regulatory regions near Tbx21 and Klf2, modulating their enhancer accessibility to facilitate the transition. These mechanistic insights can potentially be harnessed to overcome T cell exhaustion during chronic infection and cancer.

Role of TCF-1 in differentiation, exhaustion, and memory of CD8+ T cells: A review

T cell factor-1 (TCF-1) (encoded by the TCF7 gene) is a transcription factor that plays important role during the T cell development and differentiation for T cell to exercise its functions including producing memory T cells. Not only TCF-1 can modulate the T cell development but also exerts various effects on the differentiation and function of mature CD8⁺ T cells. In addition, it drives the production and maintenance of the immune response of CD8⁺ T cells after PD-1 checkpoint blockade therapy. TCF-1 can serve as a potential target of immunotherapy and may provide promising novel treatment strategies for patients with cancer and infections. Moreover, TCF-1 is a potential biomarker of CD8⁺ T cell functionality to predict the efficacy of immunotherapy in fighting against cancer and infections. Herein, we summarize the role of TCF-1 in T cell development and its applications in the treatment of cancer and infectious diseases.

TFH cells depend on Tcf1-intrinsic HDAC activity to suppress CTLA4 and guard B-cell help function

Precise regulation of coinhibitory receptors is essential for maintaining immune tolerance without interfering with protective immunity, yet the mechanism underlying such a balanced act remains poorly understood. In response to protein immunization, T follicular helper (T_FH) cells lacking Tcf1 and Lef1 transcription factors were phenotypically normal but failed to promote germinal center formation and antibody production. Transcriptomic profiling revealed that Tcf1/Lef1-deficient T_FH cells aberrantly up-regulated CTLA4 and LAG3 expression, and treatment with anti-CTLA4 alone or combined with anti-LAG3 substantially rectified B-cell help defects by Tcf1/Lef1-deficient T_FH cells. Mechanistically, Tcf1 and Lef1 restrain chromatin accessibility at the Ctla4 and Lag3 loci. Groucho/Tle corepressors, which are known to cooperate with Tcf/Lef factors, were essential for T_FH cell expansion but dispensable for repressing coinhibitory receptors. In contrast, mutating key amino acids in histone deacetylase (HDAC) domain in Tcf1 resulted in CTLA4 derepression in T_FH cells. These findings demonstrate that Tcf1-instrinsic HDAC activity is necessary for preventing excessive CTLA4 induction in protein immunization-elicited T_FH cells and hence guarding their B-cell help function.

Resident memory T cells in tumor-distant tissues fortify against metastasis formation

As a critical machinery for rapid pathogen removal, resident memory T cells (T_RMs) are locally generated after the initial encounter. However, their development accompanying tumorigenesis remains elusive. Using a murine breast cancer model, we show that T_RMs develop in the tumor, the contralateral mammary mucosa, and the pre-metastatic lung. Single-cell RNA sequencing of T_RMs reveals two phenotypically distinct populations representing their active versus quiescent phases. These T_RMs in different tissue compartments share the same TCR clonotypes and transcriptomes with a subset of intratumoral effector/effector memory T cells (T_Eff/EMs), indicating their developmental ontogeny. Furthermore, CXCL16 is highly produced by tumor cells and CXCR6^- T_Eff/EMs are the major subset preferentially egressing the tumor to form distant T_RMs. Functionally, releasing CXCR6 retention in the primary tumor amplifies tumor-derived T_RMs in the lung and leads to superior protection against metastases. This immunologic fortification suggests a potential strategy to prevent metastasis in clinical oncology.

Divergent clonal differentiation trajectories establish CD8+ memory T cell heterogeneity during acute viral infections in humans

The CD8⁺ T cell response to an antigen is composed of many T cell clones with unique T cell receptors, together forming a heterogeneous repertoire of effector and memory cells. How individual T cell clones contribute to this heterogeneity throughout immune responses remains largely unknown. In this study, we longitudinally track human CD8⁺ T cell clones expanding in response to yellow fever virus (YFV) vaccination at the single-cell level. We observed a drop in clonal diversity in blood from the acute to memory phase, suggesting that clonal selection shapes the circulating memory repertoire. Clones in the memory phase display biased differentiation trajectories along a gradient from stem cell to terminally differentiated effector memory fates. In secondary responses, YFV- and influenza-specific CD8⁺ T cell clones are poised to recapitulate skewed differentiation trajectories. Collectively, we show that the sum of distinct clonal phenotypes results in the multifaceted human T cell response to acute viral infections.

E2A-regulated epigenetic landscape promotes memory CD8 T cell differentiation

During an acute viral infection, CD8 T cells encounter a myriad of antigenic and inflammatory signals of variable strength, which sets off individual T cells on their own differentiation trajectories. However, the developmental path for each of these cells will ultimately lead to one of only two potential outcomes after clearance of the infection-death or survival and development into memory CD8 T cells. How this cell fate decision is made remains incompletely understood. In this study, we explore the transcriptional changes during effector and memory CD8 T cell differentiation at the single-cell level. Using single-cell, transcriptome-derived gene regulatory network analysis, we identified two main groups of regulons that govern this differentiation process. These regulons function in concert with changes in the enhancer landscape to confer the establishment of the regulatory modules underlying the cell fate decision of CD8 T cells. Furthermore, we found that memory precursor effector cells maintain chromatin accessibility at enhancers for key memory-related genes and that these enhancers are highly enriched for E2A binding sites. Finally, we show that E2A directly regulates accessibility of enhancers of many memory-related genes and that its overexpression increases the frequency of memory precursor effector cells and accelerates memory cell formation while decreasing the frequency of short-lived effector cells. Overall, our results suggest that effector and memory CD8 T cell differentiation is largely regulated by two transcriptional circuits, with E2A serving as an important epigenetic regulator of the memory circuit.

Integrative Bulk and Single-Cell Profiling of Premanufacture T-cell Populations Reveals Factors Mediating Long-Term Persistence of CAR T-cell Therapy

The adoptive transfer of chimeric antigen receptor (CAR) T cells represents a breakthrough in clinical oncology, yet both between- and within-patient differences in autologously derived T cells are a major contributor to therapy failure. To interrogate the molecular determinants of clinical CAR T-cell persistence, we extensively characterized the premanufacture T cells of 71 patients with B-cell malignancies on trial to receive anti-CD19 CAR T-cell therapy. We performed RNA-sequencing analysis on sorted T-cell subsets from all 71 patients, followed by paired Cellular Indexing of Transcriptomes and Epitopes (CITE) sequencing and single-cell assay for transposase-accessible chromatin sequencing (scATAC-seq) on T cells from six of these patients. We found that chronic IFN signaling regulated by IRF7 was associated with poor CAR T-cell persistence across T-cell subsets, and that the TCF7 regulon not only associates with the favorable naïve T-cell state, but is maintained in effector T cells among patients with long-term CAR T-cell persistence. These findings provide key insights into the underlying molecular determinants of clinical CAR T-cell function. SIGNIFICANCE: To improve clinical outcomes for CAR T-cell therapy, there is a need to understand the molecular determinants of CAR T-cell persistence. These data represent the largest clinically annotated molecular atlas in CAR T-cell therapy to date, and significantly advance our understanding of the mechanisms underlying therapeutic efficacy.This article is highlighted in the In This Issue feature, p. 2113.

TCF-1 regulates HIV-specific CD8+ T cell expansion capacity

Although many HIV cure strategies seek to expand HIV-specific CD8+ T cells to control the virus, all are likely to fail if cellular exhaustion is not prevented. A loss in stem-like memory properties (i.e., the ability to proliferate and generate secondary effector cells) is a key feature of exhaustion; little is known, however, about how these properties are regulated in human virus-specific CD8+ T cells. We found that virus-specific CD8+ T cells from humans and nonhuman primates naturally controlling HIV/SIV infection express more of the transcription factor TCF-1 than noncontrollers. HIV-specific CD8+ T cell TCF-1 expression correlated with memory marker expression and expansion capacity and declined with antigenic stimulation. CRISPR-Cas9 editing of TCF-1 in human primary T cells demonstrated a direct role in regulating expansion capacity. Collectively, these data suggest that TCF-1 contributes to the regulation of the stem-like memory property of secondary expansion capacity of HIV-specific CD8+ T cells, and they provide a rationale for exploring the enhancement of this pathway in T cell-based therapeutic strategies for HIV.

Stem cell-like memory T cells: A perspective from the dark side

Much attention has been paid to a newly discovered subset of memory T (T_M) cells-stem cell-like memory T (T_SCM) cells for their high self-renewal ability, multi-differentiation potential and long-term effector function in adoptive therapy against tumors. Despite their application in cancer therapy, an excess of T_SCM cells also contributes to the persistence of autoimmune diseases for their immune memory and HIV infection as a long-lived HIV reservoir. Signaling pathways Wnt, AMPK/mTOR and NF-κB are key determinants for T_M cell generation, maintenance and proinflammatory effect. In this review, we focus on the phenotypic and functional characteristics of T_SCM cells and discuss their role in autoimmune diseases and HIV-1 chronic infection. Also, we explore the potential mechanism and signaling pathways involved in immune memory and look into the future therapy strategies of targeting long-lived T_M cells to suppress pathogenic immune memory.

Transcription tipping points for T follicular helper cell and T-helper 1 cell fate commitment

During viral infection, immune cells coordinate the induction of inflammatory responses that clear infection and humoral responses that promote protection. CD4⁺ T-cell differentiation sits at the center of this axis. Differentiation toward T-helper 1 (Th1) cells mediates inflammation and pathogen clearance, while T follicular helper (Tfh) cells facilitate germinal center (GC) reactions for the generation of high-affinity antibodies and immune memory. While Th1 and Tfh differentiation occurs in parallel, these CD4⁺ T-cell identities are mutually exclusive, and progression toward these ends is determined via the upregulation of T-bet and Bcl6, respectively. These lineage-defining transcription factors act in concert with multiple networks of transcriptional regulators that tip the T-bet and Bcl6 axis in CD4⁺ T-cell progenitors to either a Th1 or Tfh fate. It is now clear that these transcriptional networks are guided by cytokine cues that are not only varied between distinct viral infections but also dynamically altered throughout the duration of infection. Thus, multiple intrinsic and extrinsic factors combine to specify the fate, plasticity, and function of Th1 and Tfh cells during infection. Here, we review the current information on the mode of action of the lineage-defining transcription factors Bcl6 and T-bet and how they act individually and in complex to govern CD4⁺ T-cell ontogeny. Furthermore, we outline the multifaceted transcriptional regulatory networks that act upstream and downstream of Bcl6 and T-bet to tip the differentiation equilibrium toward either a Tfh or Th1 fate and how these are impacted by dynamic inflammatory cues.

Deletion of Nemo-like Kinase in T Cells Reduces Single-Positive CD8+ Thymocyte Population

The β-catenin/Wnt signaling pathway plays an important role in all stages of T cell development. Nemo-like kinase (NLK) is an evolutionary conserved serine/threonine kinase and a negative regulator of the Wnt signaling pathway. NLK can directly phosphorylate histone deacetylase 1 (HDAC1), as well as T cell factor/lymphoid enhancer-binding factor (TCF/LEF), causing subsequent repression of target gene transcription. By engineering mice lacking NLK in early stages of T cell development, we set out to characterize the role NLK plays in T cell development and found that deletion of NLK does not affect mouse health or lymphoid tissue development. Instead, these mice harbored a reduced number of single-positive (SP) CD8⁺ thymocytes without any defects in the SP CD4⁺ thymocyte population. The decrease in SP CD8⁺ thymocytes was not caused by a block in differentiation from double-positive CD4⁺CD8⁺ cells. Neither TCR signaling nor activation was altered in the absence of NLK. Instead, we observed a significant increase in cell death and reduced phosphorylation of LEF1 as well as HDAC1 among NLK-deleted SP CD8⁺ cells. Thus, NLK seems to play an important role in the survival of CD8⁺ thymocytes. Our data provide evidence for a new function for NLK with regard to its involvement in T cell development and supporting survival of SP CD8⁺ thymocytes.

TCF1 and LEF1 Control Treg Competitive Survival and Tfr Development to Prevent Autoimmune Diseases

CD4⁺ Foxp3⁺ T regulatory (Treg) cells are key players in preventing lethal autoimmunity. Tregs undertake differentiation processes and acquire diverse functional properties. However, how Treg’s differentiation and functional specification are regulated remains incompletely understood. Here, we report that gradient expression of TCF1 and LEF1 distinguishes Tregs into three distinct subpopulations, particularly highlighting a subset of activated Treg (aTreg) cells. Treg-specific ablation of TCF1 and LEF1 renders the mice susceptible to systemic autoimmunity. TCF1 and LEF1 are dispensable for Treg’s suppressive capacity but essential for maintaining a normal aTreg pool and promoting Treg’s competitive survival. As a consequence, the development of T follicular regulatory (Tfr) cells, which are a subset of aTreg, is abolished in TCF1/LEF1-conditional knockout mice, leading to unrestrained T follicular helper (Tfh) and germinal center B cell responses. Thus, TCF1 and LEF1 act redundantly to control the maintenance and functional specification of Treg subsets to prevent autoimmunity.

Transcriptional regulation of Treg differentiation and function remains incompletely understood. Yang et al. report that two TCF family transcription factors regulate the survival and functional specification of a subset of Treg cells to prevent autoimmunity.

Redundant and additive functions of the four Lef/Tcf transcription factors in lung epithelial progenitors

In multicellular organisms, paralogs from gene duplication survive purifying selection by evolving tissue-specific expression and function. Whether this genetic redundancy is also selected for within a single cell type is unclear for multimember paralogs, as exemplified by the four obligatory Lef/Tcf transcription factors of canonical Wnt signaling, mainly due to the complex genetics involved. Using the developing mouse lung as a model system, we generate two quadruple conditional knockouts, four triple mutants, and various combinations of double mutants, showing that the four Lef/Tcf genes function redundantly in the presence of at least two Lef/Tcf paralogs, but additively upon losing additional paralogs to specify and maintain lung epithelial progenitors. Prelung-specification, pan-epithelial double knockouts have no lung phenotype; triple knockouts have varying phenotypes, including defective branching and tracheoesophageal fistulas; and the quadruple knockout barely forms a lung, resembling the Ctnnb1 mutant. Postlung-specification deletion of all four Lef/Tcf genes leads to branching defects, down-regulation of progenitor genes, premature alveolar differentiation, and derepression of gastrointestinal genes, again phenocopying the corresponding Ctnnb1 mutant. Our study supports a monotonic, positive signaling relationship between CTNNB1 and Lef/Tcf in lung epithelial progenitors as opposed to reported repressor functions of Lef/Tcf, and represents a thorough in vivo analysis of cell-type-specific genetic redundancy among the four Lef/Tcf paralogs.

Re-defining T-Cell Exhaustion: Subset, Function, and Regulation

Acute viral infection or vaccination generates highly functional memory CD8 T cells following the Ag resolution. In contrast, persistent antigenic stimulation in chronic viral infection and cancer leads to a state of T-cell dysfunction termed T-cell exhaustion. We and other have recently identified a novel subset of exhausted CD8 T cells that act as stem cells for maintaining virus-specific CD8 T cells in a mouse model of chronic lymphocytic choriomeningitis virus infection. This stem cell-like CD8 T-cell subset has been also observed in both mouse and human tumor models. Most importantly, in both chronic viral infection and tumor models, the proliferative burst of Ag-specific CD8 T cells driven by PD-1-directed immunotherapy comes exclusively from this stem cell-like CD8 T-cell subset. Therefore, a better understanding of the mechanisms how CD8 T-cell subsets are regulated during chronic viral infection and cancer is required to improve the current immunotherapies that restore the function of exhausted CD8 T cells. In this review, we discuss the differentiation of virus-specific CD8 T cells during chronic viral infection, the characteristics and function of CD8 T-cell subsets, and the therapeutic intervention of PD-1-directed immunotherapy in cancer.

Ceria nanoparticles promoted the cytotoxic activity of CD8+ T cells by activating NF-κB signaling

Cytotoxic CD8+ T cells (CTLs) are crucial for controlling intracellular pathogens as well as cancer. However, how to promote the cytotoxic activity of CTL cells in vitro and in vivo remains largely unknown. On the other hand, ceria nanoparticles (CNPs) are widely used in biomedical fields, but the role of CNPs in CTL cells is still unclear. In this study, we found that the activated antigen-specific (P14) and nonspecific CD8+ T cells with CNP treatment both produced more cytokines, including interleukin-2 (IL-2) and tumor necrosis factor-α (TNF-α), and released more effector molecules, such as granzyme B and perforin, and then exhibited higher killing activity of P14 cells in vitro and stronger viral clearance capacity of CTL cells in vivo. Mechanistically, the activated P14 cells with CNP treatment inhibited the production of reactive oxygen species, and therefore promoted the activity of NF-κB signaling. Importantly, while the P14 cells were simultaneously treated by IMD-0354, a specific inhibitor of NF-κB signaling, the increases of IL-2 and TNF-α productions and granzyme B and perforin releases were remedied, and the P14 cells eventually exhibited the natural killing activity in vitro. Thus, our results demonstrated that CNP treatment promoted the cytotoxic activity of CTL cells and provide new ideas in the usage of CNPs and fascinating pharmacological potentials for clinical application, especially cancer immunotherapy.

Dedicator of cytokinesis protein 2 couples with lymphoid enhancer-binding factor 1 to regulate expression of CD21 and B-cell differentiation

BACKGROUND

B-cell receptor (BCR) signaling, combined with CD19 and CD21 signals, imparts specific control of B-cell responses. Dedicator of cytokinesis protein 2 (DOCK2) is critical for the migration and motility of lymphocytes. Although absence of DOCK2 leads to lymphopenia, little is known about the signaling mechanisms and physiologic functions of DOCK2 in B cells.

OBJECTIVE

We sought to determine the underlying molecular mechanism of how DOCK2 regulates BCR signaling and peripheral B-cell differentiation.

METHODS

In this study we used genetic models for DOCK2, Wiskott-Aldrich syndrome protein (WASP), and lymphoid enhancer-binding factor 1 deficiency to study their interplay in BCR signaling and B-cell differentiation.

RESULTS

We found that the absence of DOCK2 led to downregulation of proximal and distal BCR signaling molecules, including CD19, but upregulation of SH2-containing inositol 5 phosphatase 1, a negative signaling molecule. Interestingly, DOCK2 deficiency reduced CD19 and CD21 expression at the mRNA and/or protein levels and was associated with reduced numbers of marginal zone B cells. Additionally, loss of DOCK2 reduced activation of WASP and accelerated degradation of WASP, resulting into reduced actin accumulation and early activation of B cells. Mechanistically, the absence of DOCK2 upregulates the expression of lymphoid enhancer-binding factor 1. These differences were associated with altered humoral responses in the absence of DOCK2.

CONCLUSIONS

Overall, our study has provided a novel underlying molecular mechanism of how DOCK2 deficiency regulates surface expression of CD21, which leads to downregulation of CD19-mediated BCR signaling and marginal zone B-cell differentiation.

The Role of WNT Signaling in Mature T Cells: T Cell Factor Is Coming Home

T cell factor, the effector transcription factor of the WNT signaling pathway, was so named because of the primary observation that it is indispensable for T cell development in the thymus. Since this discovery, the role of this signaling pathway has been extensively studied in T cell development, hematopoiesis, and stem cells; however, its functional role in mature T cells has remained relatively underinvestigated. Over the last few years, various studies have demonstrated that T cell factor can directly influence T cell function and the differentiation of Th1, Th2, Th17, regulatory T cell, follicular helper CD4⁺ T cell subsets, and CD8⁺ memory T cells. In this paper, we discuss the molecular mechanisms underlying these observations and place them in the general context of immune responses. Furthermore, we explore the implications and limitations of these findings for WNT manipulation as a therapeutic approach for treating immune-related diseases.

Cutting Edge: Transcription Factor BCL6 Is Required for the Generation, but Not Maintenance, of Memory CD8+ T Cells in Acute Viral Infection

The differentiation of memory CD8⁺ T cells is critical to the long-term cellular immunity. The transcription factor BCL6 has been reportedly important for the generation and maintenance of memory CD8⁺ T cells; however, using the newly established BCL6 conditional knockout mouse model, we demonstrate that BCL6 is dispensable for the maintenance of established memory CD8⁺ T cell pool, although BCL6 is still required for the generation of CD8⁺ memory precursors upon acute viral infection. In addition, BCL6 promotes the expression of TCF-1 via directly binding to the Tcf7 (gene symbol for TCF-1) allele in CD8⁺ memory precursors and forced expression of TCF-1 restores the generation of BCL6-deficient memory precursors. Thus, our findings clarify that BCL6 is dispensable for the maintenance of memory CD8⁺ T cells, but functions as an important upstream of TCF-1 to regulate the generation of memory precursors in acute viral infection.

TCF1 expression marks self-renewing human CD8+ T cells

Expression of the transcription factor T-cell factor 1 (TCF1) identifies antigen-experienced murine CD8⁺ T cells that retain potential for lymphoid recirculation and the ability to self-renew while producing more differentiated effector cells. We found that CD8⁺ T cells in the blood of both healthy and chronically infected humans expressed TCF1 at 3 distinct levels: high (TCF1-hi), intermediate (TCF1-int), and low (TCF1-lo). TCF1-hi cells could be found within both the naive and memory compartments and were characterized by relative quiescence and lack of immediate effector function. A substantial fraction of TCF1-int cells were found among memory cells, and TCF1-int cells exhibited robust immediate effector functions. TCF1-lo cells were most enriched in effector memory cells that expressed the senescence marker CD57. Following reactivation, TCF1-hi cells gave rise to TCF1-lo descendants while self-renewing the TCF1-hi progenitor. By contrast, reactivation of TCF1-lo cells produced more TCF1-lo cells without evidence of de-differentiating into TCF1-hi cells. Flow cytometric analyses of TCF1 expression from patient specimens may become a useful biomarker for adaptive immune function in response to vaccination, infection, autoimmunity, and cancer.

Tcf1 and Lef1 are required for the immunosuppressive function of regulatory T cells

Tcf1 and Lef1 are underexpressed in T reg cells compared with conventional CD4⁺ T cells. Xing et al. demonstrate that genetic ablation of both factors impairs immunosuppressive function of T reg cells and leads to spontaneous multi-organ autoimmunity.

Tcf1 and Lef1 have versatile functions in regulating T cell development and differentiation, but intrinsic requirements for these factors in regulatory T (T reg) cells remain to be unequivocally defined. Specific ablation of Tcf1 and Lef1 in T reg cells resulted in spontaneous multi-organ autoimmunity that became more evident with age. Tcf1/Lef1-deficient T regs showed reduced protection against experimentally induced colitis, indicative of diminished immuno-suppressive capacity. Transcriptomic analysis revealed that Tcf1 and Lef1 were responsible for positive regulation of a subset of T reg–overrepresented signature genes such as Ikzf4 and Izumo1r. Unexpectedly, Tcf1 and Lef1 were necessary for restraining expression of cytotoxic CD8⁺ effector T cell–associated genes in T reg cells, including Prdm1 and Ifng. Tcf1 ChIP-seq revealed substantial overlap between Tcf1 and Foxp3 binding peaks in the T reg cell genome, with Tcf1-Foxp3 cooccupancy observed at key T reg signature and cytotoxic effector genes. Our data collectively indicate that Tcf1 and Lef1 are critical for sustaining T reg suppressive functions and preventing loss of self-tolerance.

Cloning and characterization of the LEF/TCF gene family in grass carp (Ctenopharyngodon idella) and their expression profiles in response to grass carp reovirus infection

T-cell factor/lymphoid enhancer-binding factor (TCF/LEF) proteins from the High Mobility Group (HMG) box family act as the main downstream effectors of the Wnt signaling pathway. HMGB proteins play multifaceted roles in the immune system of mammals. To clarify the immunological characteristics of LEF/TCF genes in grass carp (Ctenopharyngodon idella), five LEF/TCF genes (TCF7, LEF1, TCF7L1A, TCF7L1B, and TCF7L2) were identified and characterized. All five LEF/TCF proteins contained two characteristic domains: a HMG-BOX domain and a CTNNB1_binding region. Phylogenetic tree analysis revealed that the LEF/TCF proteins were represented different lineages. These results of subcellular localization showed that four of the LEF/TCF genes were localized exclusively within the nucleus, while TCF7L2 was localized in the cytoplasm and nucleus. The mRNA expression profiles of these LEF/TCF family genes differed across different tissues. The mRNA expression levels of TCF7, TCF7L1A, and TCF7L2 changed significantly in liver after grass carp reovirus (GCRV) challenge; TCF7 and TCF7L1A responded early while TCF7L2 responded late. This suggests that these genes may participate in GCRV-related immune responses. Moreover, TCF7 promoted Bcl6 transcription in response to the GCRV challenge. These findings further our understanding of the function of LEF/TCF genes in teleosts.