PD-1+ Tcf1+ CD8+ T cells from established chronic infection can form memory while retaining a stableimprint of persistent antigen exposure.

Virus-specific PD1+ Tcf1+ memory-like CD8+ T cells (TMLs) maintain the CD8+ T cell response during chronic viral infection. However, the fate of these cells following cessation of persistent antigen exposure has been unclear. Here, we find that TMLs persist upon transfer into antigen-free hosts and form memory following recall stimulation. Phenotypic, functional, and transcriptome analyses show that TML-derived memory cells resemble those arising in response to acute, resolved infection, but they retain features of chronically stimulated cells, including elevated PD-1 and Tox and reduced cytokine expression. This chronic infection imprint is largely accounted for by constitutive Tox expression. Virus-specific Tcf1+ CD8+ T cells that persist after clearance of systemic infection also display a chronic infection imprint. Notwithstanding, renewed virus exposure induces a recall response, which controls virus infection in part. Thus, cessation of chronic antigen exposure yields a memory CD8+ T cell compartment that reflects prior stimulation.

Conventional type I dendritic cells maintain a reservoir of proliferative tumor-antigen specific TCF-1+ CD8+ T cells in tumor-draining lymph nodes.

In tumors, a subset of CD8+ T cells expressing the transcription factor TCF-1 drives the response to immune checkpoint blockade. We examined the mechanisms that maintain these cells in an autochthonous model of lung adenocarcinoma. Longitudinal sampling and single-cell sequencing of tumor-antigen specific TCF-1+ CD8+ T cells revealed that while intratumoral TCF-1+ CD8+ T cells acquired dysfunctional features and decreased in number as tumors progressed, TCF-1+ CD8+ T cell frequency in the tumor draining LN (dLN) remained stable. Two discrete intratumoral TCF-1+ CD8+ T cell subsets developed over time-a proliferative SlamF6+ subset and a non-cycling SlamF6- subset. Blocking dLN egress decreased the frequency of intratumoral SlamF6+ TCF-1+ CD8+ T cells. Conventional type I dendritic cell (cDC1) in dLN decreased in number with tumor progression, and Flt3L+anti-CD40 treatment recovered SlamF6+ T cell frequencies and decreased tumor burden. Thus, cDC1s in tumor dLN maintain a reservoir of TCF-1+ CD8+ T cells and their decrease contributes to failed anti-tumor immunity.

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.

In Situ Maturation and Tissue Adaptation of Type 2 Innate Lymphoid Cell Progenitors.

Innate lymphoid cells (ILCs) are generated early during ontogeny and persist predominantly as tissue-resident cells. Here, we examined how ILCs are maintained and renewed within tissues. We generated a single cell atlas of lung ILC2s and found that Il18r1+ ILCs comprise circulating and tissue-resident ILC progenitors (ILCP) and effector-cells with heterogeneous expression of the transcription factors Tcf7 and Zbtb16, and CD103. Our analyses revealed a continuous differentiation trajectory from Il18r1+ ST2- ILCPs to Il18r- ST2+ ILC2s, which was experimentally validated. Upon helminth infection, recruited and BM-derived cells generated the entire spectrum of ILC2s in parabiotic and shield chimeric mice, consistent with their potential role in the renewal of tissue ILC2s. Our findings identify local ILCPs and reveal ILCP in situ differentiation and tissue adaptation as a mechanism of ILC maintenance and phenotypic diversification. Local niches, rather than progenitor origin, or the developmental window during ontogeny, may dominantly imprint ILC phenotypes in adult tissues.

TOX is expressed by exhausted and polyfunctional human effector memory CD8+ T cells.

CD8+ T cell exhaustion is a hallmark of many cancers and chronic infections. In mice, T cell factor 1 (TCF-1) maintains exhausted CD8+ T cell responses, whereas thymocyte selection-associated HMG box (TOX) is required for the epigenetic remodeling and survival of exhausted CD8+ T cells. However, it has remained unclear to what extent these transcription factors play analogous roles in humans. In this study, we mapped the expression of TOX and TCF-1 as a function of differentiation and specificity in the human CD8+ T cell landscape. Here, we demonstrate that circulating TOX+ CD8+ T cells exist in most humans, but that TOX is not exclusively associated with exhaustion. Effector memory CD8+ T cells generally expressed TOX, whereas naive and early-differentiated memory CD8+ T cells generally expressed TCF-1. Cytolytic gene and protein expression signatures were also defined by the expression of TOX. In the context of a relentless immune challenge, exhausted HIV-specific CD8+ T cells commonly expressed TOX, often in clusters with various activation markers and inhibitory receptors, and expressed less TCF-1. However, polyfunctional memory CD8+ T cells specific for cytomegalovirus (CMV) or Epstein-Barr virus (EBV) also expressed TOX, either with or without TCF-1. A similar phenotype was observed among HIV-specific CD8+ T cells from individuals who maintained exceptional immune control of viral replication. Collectively, these data demonstrate that TOX is expressed by most circulating effector memory CD8+ T cell subsets and not exclusively linked to exhaustion.

IL-17A-producing T cells exacerbate fine particulate matter-induced lung inflammation and fibrosis by inhibiting PI3K/Akt/mTOR-mediated autophagy.

Fine particulate matter (PM2.5) is the primary air pollutant that is able to induce airway injury. Compelling evidence has shown the involvement of IL-17A in lung injury, while its contribution to PM2.5-induced lung injury remains largely unknown. Here, we probed into the possible role of IL-17A in mouse models of PM2.5-induced lung injury. Mice were instilled with PM2.5 to construct a lung injury model. Flow cytometry was carried out to isolate γδT and Th17 cells. ELISA was adopted to detect the expression of inflammatory factors in the supernatant of lavage fluid. Primary bronchial epithelial cells (mBECs) were extracted, and the expression of TGF signalling pathway-, autophagy- and PI3K/Akt/mTOR signalling pathway-related proteins in mBECs was detected by immunofluorescence assay and Western blot analysis. The mitochondrial function was also evaluated. PM2.5 aggravated the inflammatory response through enhancing the secretion of IL-17A by γδT/Th17 cells. Meanwhile, PM2.5 activated the TGF signalling pathway and induced EMT progression in bronchial epithelial cells, thereby contributing to pulmonary fibrosis. Besides, PM2.5 suppressed autophagy of bronchial epithelial cells by up-regulating IL-17A, which in turn activated the PI3K/Akt/mTOR signalling pathway. Furthermore, IL-17A impaired the energy metabolism of airway epithelial cells in the PM2.5-induced models. This study suggested that PM2.5 could inhibit autophagy of bronchial epithelial cells and promote pulmonary inflammation and fibrosis by inducing the secretion of IL-17A in γδT and Th17 cells and regulating the PI3K/Akt/mTOR signalling pathway.

HIV-1-induced cytokines deplete homeostatic innate lymphoid cells and expand TCF7-dependent memory NK cells.

Human immunodeficiency virus 1 (HIV-1) infection is associated with heightened inflammation and excess risk of cardiovascular disease, cancer and other complications. These pathologies persist despite antiretroviral therapy. In two independent cohorts, we found that innate lymphoid cells (ILCs) were depleted in the blood and gut of people with HIV-1, even with effective antiretroviral therapy. ILC depletion was associated with neutrophil infiltration of the gut lamina propria, type 1 interferon activation, increased microbial translocation and natural killer (NK) cell skewing towards an inflammatory state, with chromatin structure and phenotype typical of WNT transcription factor TCF7-dependent memory T cells. Cytokines that are elevated during acute HIV-1 infection reproduced the ILC and NK cell abnormalities ex vivo. These results show that inflammatory cytokines associated with HIV-1 infection irreversibly disrupt ILCs. This results in loss of gut epithelial integrity, microbial translocation and memory NK cells with heightened inflammatory potential, and explains the chronic inflammation in people with HIV-1.

The transcription factor c-Myb regulates CD8+ T cell stemness and antitumor immunity.

Stem cells are maintained by transcriptional programs that promote self-renewal and repress differentiation. Here, we found that the transcription factor c-Myb was essential for generating and maintaining stem cells in the CD8+ T cell memory compartment. Following viral infection, CD8+ T cells lacking Myb underwent terminal differentiation and generated fewer stem cell-like central memory cells than did Myb-sufficient T cells. c-Myb acted both as a transcriptional activator of Tcf7 (which encodes the transcription factor Tcf1) to enhance memory development and as a repressor of Zeb2 (which encodes the transcription factor Zeb2) to hinder effector differentiation. Domain-mutagenesis experiments revealed that the transactivation domain of c-Myb was necessary for restraining differentiation, whereas its negative regulatory domain was critical for cell survival. Myb overexpression enhanced CD8+ T cell memory formation, polyfunctionality and recall responses that promoted curative antitumor immunity after adoptive transfer. These findings identify c-Myb as a pivotal regulator of CD8+ T cell stemness and highlight its therapeutic potential.

CD8+ T Cell Priming in Established Chronic Viral Infection Preferentially Directs Differentiation of Memory-like Cells for Sustained Immunity.

CD8+ T cell exhaustion impedes control of chronic viral infection; yet how new T cell responses are mounted during chronic infection is unclear. Unlike T cells primed at the onset of infection that rapidly differentiate into effectors and exhaust, we demonstrate that virus-specific CD8+ T cells primed after establishment of chronic LCMV infection preferentially generate memory-like transcription factor TCF1+ cells that were transcriptionally and proteomically distinct, less exhausted, and more responsive to immunotherapy. Mechanistically, adaptations of antigen-presenting cells and diminished T cell signaling intensity promoted differentiation of the memory-like subset at the expense of rapid effector cell differentiation, which was now highly dependent on IL-21-mediated CD4+ T cell help for its functional generation. Chronic viral infection similarly redirected de novo differentiation of tumor-specific CD8+ T cells, ultimately preventing cancer control. Thus, targeting these T cell stimulatory pathways could enable strategies to control chronic infection, tumors, and enhance immunotherapeutic efficacy.

Differential Requirements for Tcf1 Long Isoforms in CD8+ and CD4+ T Cell Responses to Acute Viral Infection.

In response to acute viral infection, activated naive T cells give rise to effector T cells that clear the pathogen and memory T cells that persist long-term and provide heightened protection. T cell factor 1 (Tcf1) is essential for several of these differentiation processes. Tcf1 is expressed in multiple isoforms, with all isoforms sharing the same HDAC and DNA-binding domains and the long isoforms containing a unique N-terminal ß-catenin-interacting domain. In this study, we specifically ablated Tcf1 long isoforms in mice, while retaining expression of Tcf1 short isoforms. During CD8+ T cell responses, Tcf1 long isoforms were dispensable for generating cytotoxic CD8+ effector T cells and maintaining memory CD8+ T cell pool size, but they contributed to optimal maturation of central memory CD8+ T cells and their optimal secondary expansion in a recall response. In contrast, Tcf1 long isoforms were required for differentiation of T follicular helper (TFH) cells, but not TH1 effectors, elicited by viral infection. Although Tcf1 short isoforms adequately supported Bcl6 and ICOS expression in TFH cells, Tcf1 long isoforms remained important for suppressing the expression of Blimp1 and TH1-associated genes and for positively regulating Id3 to restrain germinal center TFH cell differentiation. Furthermore, formation of memory TH1 and memory TFH cells strongly depended on Tcf1 long isoforms. These data reveal that Tcf1 long and short isoforms have distinct, yet complementary, functions and may represent an evolutionarily conserved means to ensure proper programming of CD8+ and CD4+ T cell responses to viral infection.

T cell factor-1 controls the lifetime of CD4+ CD8+ thymocytes in vivo and distal T cell receptor α-chain rearrangement required for NKT cell development.

Natural killer T (NKT) cells are a component of innate and adaptive immune systems implicated in immune, autoimmune responses and in the control of obesity and cancer. NKT cells develop from common CD4+ CD8+ double positive (DP) thymocyte precursors after the rearrangement and expression of T cell receptor (TCR) Vα14-Jα18 gene. Temporal regulation and late appearance of Vα14-Jα18 rearrangement in immature DP thymocytes has been demonstrated. However, the precise control of lifetime of DP thymocytes in vivo that enables distal rearrangements remains incompletely defined. Here we demonstrate that T cell factor (TCF)-1, encoded by the Tcf7 gene, is critical for the extended lifetime of DP thymocytes. TCF-1-deficient DP thymocytes fail to undergo TCR Vα14-Jα18 rearrangement and produce significantly fewer NKT cells. Ectopic expression of Bcl-xL permits Vα14-Jα18 rearrangement and rescues NKT cell development. We report that TCF-1 regulates expression of RORγt, which regulates DP thymocyte survival by controlling expression of Bcl-xL. We posit that TCF-1 along with its cofactors controls the lifetime of DP thymocytes in vivo.

Differentiation of CD8 memory T cells depends on Foxo1.

The forkhead O transcription factors (FOXO) integrate a range of extracellular signals, including growth factor signaling, inflammation, oxidative stress, and nutrient availability, to substantially alter the program of gene expression and modulate cell survival, cell cycle progression, and many yet to be unraveled cell type-specific responses. Naive antigen-specific CD8(+) T cells undergo a rapid expansion and arming of effector function within days of pathogen exposure. In addition, by the peak of expansion, they form precursors to memory T cells capable of self-renewal and indefinite survival. Using lymphocytic choriomeningitis virus Armstrong to probe the response to infection, we found that Foxo1(-/-) CD8(+) T cells expand normally with no defects in effector differentiation, but continue to exhibit characteristics of effector T cells long after antigen clearance. The KLRG1(lo) CD8(+) T cells that are normally enriched for memory-precursor cells retain Granzyme B and CD69 expression, and fail to up-regulate TCF7, EOMES, and other memory signature genes. As a correlate, Foxo1(-/-) CD8(+) T cells were virtually unable to expand upon secondary infection. Collectively, these results demonstrate an intrinsic role for FOXO1 in establishing the post-effector memory program that is essential to forming long-lived memory cells capable of immune reactivation.

Id2-mediated inhibition of E2A represses memory CD8+ T cell differentiation.

The transcription factor inhibitor of DNA binding (Id)2 modulates T cell fate decisions, but the molecular mechanism underpinning this regulation is unclear. In this study we show that loss of Id2 cripples effector differentiation and instead programs CD8(+) T cells to adopt a memory fate with increased Eomesodermin and Tcf7 expression. We demonstrate that Id2 restrains CD8(+) T cell memory differentiation by inhibiting E2A-mediated direct activation of Tcf7 and that Id2 expression level mirrors T cell memory recall capacity. As a result of the defective effector differentiation, Id2-deficient CD8(+) T cells fail to induce sufficient Tbx21 expression to generate short-lived effector CD8(+) T cells. Our findings reveal that the Id2/E2A axis orchestrates T cell differentiation through the induction or repression of downstream transcription factors essential for effector and memory T cell differentiation.

The TCF-1 and LEF-1 transcription factors have cooperative and opposing roles in T cell development and malignancy.

The TCF-1 and LEF-1 transcription factors are known to play critical roles in normal thymocyte development. Unexpectedly, we found that TCF-1-deficient (Tcf7(-/-)) mice developed aggressive T cell malignancy, resembling human T cell acute lymphoblastic leukemia (T-ALL). LEF-1 was aberrantly upregulated in premalignant Tcf7(-/-) early thymocytes and lymphoma cells. We further demonstrated that TCF-1 directly repressed LEF-1 expression in early thymocytes and that conditional inactivation of Lef1 greatly delayed or prevented T cell malignancy in Tcf7(-/-) mice. In human T-ALLs, an early thymic progenitor (ETP) subtype was associated with diminished TCF7 expression, and two of the ETP-ALL cases harbored TCF7 gene deletions. We also showed that TCF-1 and LEF-1 were dispensable for T cell lineage commitment but instead were required for early thymocytes to mature beyond the CD4(-)CD8(-) stage. TCF-1 thus has dual roles, i.e., acting cooperatively with LEF-1 to promote thymocyte maturation while restraining LEF-1 expression to prevent malignant transformation of developing thymocytes.

p27(Kip1) negatively regulates the magnitude and persistence of CD4 T cell memory.

Much is known about the differentiation of naive T cells into distinct lineages of effector cells, but the molecular mechanisms underlying the generation and maintenance of CD4 T cell memory are poorly characterized. Our studies ascribe a novel role for the cell cycle regulator p27(Kip1) as a prominent negative regulator of the establishment and long-term maintenance of Th1 CD4 T cell memory. We demonstrate that p27(Kip1) might restrict the differentiation and survival of memory precursors by increasing the T-bet/Bcl-6 ratio in effector CD4 T cells. By promoting apoptosis and contraction of effector CD4 T cells by mechanisms that are at least in part T cell intrinsic, p27(Kip1) markedly limits the abundance of memory CD4 T cells. Furthermore, we causally link p27(Kip1)-dependent apoptosis to the decay of CD4 T cell memory, possibly by repressing the expression of γ-chain receptors and the downstream effector of the Wnt/ß-catenin signaling pathway, Tcf-1. We extend these findings by showing that the antagonistic effects of p27(Kip1) on CD4 T cell memory require its cyclin-dependent kinase-binding domain. Collectively, these findings provide key insights into the mechanisms underlying the governance of peripheral CD4 T cell homeostasis and identify p27(Kip1) as a target to enhance vaccine-induced CD4 T cell memory.

T cell factor-1 and ß-catenin control the development of memory-like CD8 thymocytes.

Innate memory-like CD8 thymocytes develop and acquire effector function during maturation in the absence of encounter with Ags. In this study, we demonstrate that enhanced function of transcription factors T cell factor (TCF)-1 and ß-catenin regulate the frequency of promyelocytic leukemia zinc finger (PLZF)-expressing, IL-4-producing thymocytes that promote the generation of eomesodermin-expressing memory-like CD8 thymocytes in trans. In contrast, TCF1-deficient mice do not have PLZF-expressing thymocytes and eomesodermin-expressing memory-like CD8 thymocytes. Generation of TCF1 and ß-catenin-dependent memory-like CD8 thymocytes is non-cell-intrinsic and requires the expression of IL-4 and IL-4R. CD8 memory-like thymocytes migrate to the peripheral lymphoid organs, and the memory-like CD8 T cells rapidly produce IFN-γ. Thus, TCF1 and ß-catenin regulate the generation of PLZF-expressing thymocytes and thereby facilitate the generation of memory-like CD8 T cells in the thymus.

T cell factor 1 regulates thymocyte survival via a RORγt-dependent pathway.

Survival of CD4(+)CD8(+) double-positive (DP) thymocytes plays a critical role in shaping the peripheral T cell repertoire. However, the mechanisms responsible for the regulation of DP thymocyte lifespan remain poorly understood. In this work, we demonstrate that T cell factor (TCF)-1 regulates DP thymocyte survival by upregulating RORγt. Microarray analysis revealed that RORγt was significantly downregulated in TCF-1(-/-) thymocytes that underwent accelerated apoptosis, whereas RORγt was greatly upregulated in thymocytes that had enhanced survival due to transgenic expression of a stabilized ß-catenin (ß-cat(Tg)), a TCF-1 activator. Both TCF-1(-/-) and RORγt(-/-) DP thymocytes underwent similar accelerated apoptosis. Forced expression of RORγt successfully rescued TCF-1(-/-) DP thymocytes from apoptosis, whereas ectopically expressed TCF-1 was not able to rescue the defective T cell development because of the lack of RORγt-supported survival. Furthermore, activation of TCF-1 by stabilized ß-catenin was able to enhance DP thymocyte survival only in the presence of RORγt, indicating that RORγt acts downstream of TCF-1 in the regulation of DP thymocyte survival. Moreover, ß-catenin/TCF-1 directly interacted with the RORγt promoter region and stimulated its activity. Therefore, our data demonstrated that TCF-1 enhances DP thymocyte survival through transcriptional upregulation of RORγt, which we previously showed is an essential prosurvival molecule for DP thymocytes.

The lineage-defining factors T-bet and Bcl-6 collaborate to regulate Th1 gene expression patterns.

The T-box transcription factor T-bet is important for the differentiation of naive CD4(+) T helper cells (Th cells) into the Th1 phenotype. Much is known about T-bet's role as a transcriptional activator, but less is known about the mechanisms by which T-bet functionally represses alternative Th cell genetic programs. In this study, we first identify Socs1, Socs3, and Tcf7 (TCF-1) as gene targets that are negatively regulated by T-bet. Significantly, T-bet's role in the repression of these genes is through a direct interaction with their promoters. Consistent with this, we identified two T-bet DNA-binding elements in the Socs1 promoter that are functionally used to down-regulate transcription in primary Th1 cells. Importantly, T-bet's novel role in transcriptional repression is because of its ability to physically associate with, and functionally recruit, the transcriptional repressor Bcl-6 to a subset of promoters. Furthermore, T-bet functionally recruits Bcl-6 to the Ifng locus in late stages of Th1 differentiation to repress its activity, possibly to prevent the overproduction of IFN-γ, which could result in autoimmunity. Collectively, these data establish a novel mechanism for T-bet-mediated gene repression in which two lineage-defining transcription factors, one a classical activator and one a repressor, collaborate to promote and properly regulate Th1 development.

Inhibition of suppressive T cell factor 1 (TCF-1) isoforms in naive CD4+ T cells is mediated by IL-4/STAT6 signaling.

The Wnt pathway transcription factor T cell factor 1 (TCF-1) plays essential roles in the control of several developmental processes, including T cell development in the thymus. Although previously regarded as being required only during early T cell development, recent studies demonstrate an important role for TCF-1 in T helper 2 (Th2) cell polarization. TCF-1 was shown to activate expression of the Th2 transcription factor GATA-binding protein 3 (GATA3) and thus to promote the development of IL-4-producing Th2 cells independent of STAT6 signaling. In this study, we show that TCF-1 is down-regulated in human naive CD4(+) T cells cultured under Th2-polarizing conditions. The down-regulation is largely due to the polarizing cytokine IL-4 because IL-4 alone is sufficient to substantially inhibit TCF-1 expression. The IL-4-induced suppression of TCF-1 is mediated by STAT6, as shown by electrophoretic mobility shift assays, chromatin immunoprecipitation, and STAT6 knockdown experiments. Moreover, we found that IL-4/STAT6 predominantly inhibits the shorter, dominant-negative TCF-1 isoforms, which were reported to inhibit IL-4 transcription. Thus, this study provides a model for an IL-4/STAT6-dependent fine tuning mechanism of TCF-1-driven T helper cell polarization.

Differentiation and persistence of memory CD8(+) T cells depend on T cell factor 1.

T cell factor 1 (TCF-1) is a transcription factor known to act downstream of the canonical Wnt pathway and is essential for normal T cell development. However, its physiological roles in mature CD8(+) T cell responses are unknown. Here we showed that TCF-1 deficiency limited proliferation of CD8(+) effector T cells and impaired their differentiation toward a central memory phenotype. Moreover, TCF-1-deficient memory CD8(+) T cells were progressively lost over time, exhibiting reduced expression of the antiapoptotic molecule Bcl-2 and interleukin-2 receptor beta chain and diminished IL-15-driven proliferation. TCF-1 was directly associated with the Eomes allele and the Wnt-TCF-1 pathway was necessary and sufficient for optimal Eomes expression in naive and memory CD8(+) T cells. Importantly, forced expression of Eomes partly protected TCF-1-deficient memory CD8(+) T cells from time-dependent attrition. Our studies thus identify TCF-1 as a critical player in a transcriptional program that regulates memory CD8 differentiation and longevity.