Transforming growth factor-β-regulated mTOR activity preserves cellular metabolism to maintain long-term T cell responses in chronic infection

T cell exhaustion in human cancers

T cell exhaustion refers to a progressive state in which T cells become functionally impaired due to sustained antigenic stimulation, which is characterized by increased expression of immune inhibitory receptors, but weakened effector functions, reduced self-renewal capacity, altered epigenetics, transcriptional programme and metabolism. T cell exhaustion is one of the major causes leading to immune escape of cancer, creating an environment that supports tumor development and metastatic spread. In addition, T cell exhaustion plays a pivotal role to the efficacy of current immunotherapies for cancer. This review aims to provide a comprehensive view of roles of T cell exhaustion in cancer development and progression. We summerized the regulatory mechanisms that involved in T cell exhaustion, including transcription factors, epigenetic and metabolic reprogramming events, and various microenvironmental factors such as cytokines, microorganisms, and tumor autocrine substances. The paper also discussed the challenges posed by T cell exhaustion to cancer immunotherapies, including immune checkpoint blockade (ICB) therapies and chimeric antigen receptor T cell (CAR-T) therapy, highlightsing the obstacles encountered in ICB therapies and CAR-T therapies due to T cell exhaustion. Finally, the article provides an overview of current therapeutic options aimed to reversing or alleviating T cell exhaustion in ICB and CAR-T therapies. These therapeutic approaches seek to overcome T cell exhaustion and enhance the effectiveness of immunotherapies in treating tumors.

Aerobic glycolysis but not GLS1-dependent glutamine metabolism is critical for anti-tumor immunity and response to checkpoint inhibition

Tumor cells undergo uncontrolled proliferation driven by enhanced anabolic metabolism including glycolysis and glutaminolysis. Targeting these pathways to inhibit cancer growth is a strategy for cancer treatment. Critically, however, tumor-responsive T cells share metabolic features with cancer cells, making them susceptible to these treatments as well. Here, we assess the impact on anti-tumor T cell immunity and T cell exhaustion by genetic ablation of lactate dehydrogenase A (LDHA) and glutaminase1 (GLS1), key enzymes in aerobic glycolysis and glutaminolysis. Loss of LDHA severely impairs expansion of T cells in response to tumors and chronic infection. In contrast, T cells lacking GLS1 can compensate for impaired glutaminolysis by engaging alternative pathways, including upregulation of asparagine synthetase, and thus efficiently respond to tumor challenge and chronic infection as well as immune checkpoint blockade. Targeting GLS1-dependent glutaminolysis, but not aerobic glycolysis, may therefore be a successful strategy in cancer treatment, particularly in combination with immunotherapy.

PPARβ/δ-orchestrated metabolic reprogramming supports the formation and maintenance of memory CD8+ T cells

The formation of memory T cells is a fundamental feature of adaptative immunity, allowing the establishment of long-term protection against pathogens. Although emerging evidence suggests that metabolic reprogramming is crucial for memory T cell differentiation and survival, the underlying mechanisms that drive metabolic rewiring in memory T cells remain unclear. Here, we found that up-regulation of the nuclear receptor peroxisome proliferator-activated receptor β/δ (PPARβ/δ) instructs the metabolic reprogramming that occurs during the establishment of central memory CD8+ T cells. PPARβ/δ-regulated changes included suppression of aerobic glycolysis and enhancement of oxidative metabolism and fatty acid oxidation. Mechanistically, exposure to interleukin-15 and expression of T cell factor 1 facilitated activation of the PPARβ/δ pathway, counteracting apoptosis induced by antigen clearance and metabolic stress. Together, our findings indicate that PPARβ/δ is a master metabolic regulator orchestrating a metabolic switch that may be favorable for T cell longevity.

Cancer stem cell-derived exosomes in CD8+ T cell exhaustion

Tumor-derived extracellular vesicles (EVs) are one of the most important ways of intercellular communication and signaling. Cancer stem cells (CSCs) secrete EVs to modulate immune checkpoint molecules and evade immune surveillance. Activated CD8+ T cells known as cytotoxic T lymphocytes (CTLs) are the most powerful anti-cancer adaptive cells. Their activity is compromised upon encountering cells and signaling within the tumor microenvironment (TME), resulting in hyporesponsiveness called exhaustion. CSC-derived exosomes express programmed death ligand-1 (PD-L1) and upregulate programmed death-1 (PD-1) on CD8+ T cells to promote their exhaustion. PD-L1 expression on tumor-derived exosomes appears to be induced by CSC-derived exosomes containing transforming growth factor (TGF)-β. Tenascin-C is another constituent of CSC exosomes that acts on mammalian target of rapamycin (mTOR) signaling in T cells. Glycolysis is a metabolic event promoted by the inducing effect of CSC-derived exosomes on hypoxia-inducible factor-1α (HIF-1α). CSC interaction with CD8+ T cells is even more complex as the CSC-derived exosomes contain Notch1 to stimulate stemness in non-tumor cells, and the inducible effect of Notch1 on PD-1 promotes CD8+ T cell exhaustion. CSC exosome targeting has not been extensively studied yet. Advances in the field will open up new therapeutic windows and shape the future of cancer immunotherapy.

Stem-like CD8+ T cells in cancer

Stem-like CD8+ T cells (TSL) are a subset of immune cells with superior persistence and antitumor immunity. They are TCF1+ PD-1+ and important for the expansion of tumor specific CD8+ T cells in response to checkpoint blockade immunotherapy. In acute infections, naïve CD8+ T cells differentiate into effector and memory CD8+ T cells; in cancer and chronic infections, persistent antigen stimulation can lead to T cell exhaustion. Recent studies have highlighted the dichotomy between late dysfunctional (or exhausted) T cells (TLD) that are TCF1- PD-1+ and self-renewing TCF1+ PD-1+ TSL from which they derive. TCF1+ TSL cells are considered to have stem cell-like properties akin to memory T cell populations and can give rise to cytotoxic effector and transitory T cell phenotypes (TTE) which mediate tumor control. In this review, we will discuss recent advances made in research on the formation and expansion of TSL, as well as distinct niches required for their differentiation and maintenance in the setting of cancer. We will also discuss potential strategies to generate these cells, with clinical implications for stemness enhancement in vaccine design, immune checkpoint blockade (ICB), and adoptive T cell therapies.

Stem-like T cells in cancer and autoimmunity

Stem-like T cells are characterized by their ability to self-renew, survive long-term, and give rise to a heterogeneous pool of effector and memory T cells. Recent advances in single-cell RNA-sequencing (scRNA-seq) and lineage tracing technologies revealed an important role for stem-like T cells in both autoimmunity and cancer. In cancer, stem-like T cells constitute an important arm of the anti-tumor immune response by giving rise to effector T cells that mediate tumor control. In contrast, in autoimmunity stem-like T cells perform an unfavorable role by forming a reservoir of long-lived autoreactive cells that replenish the pathogenic, effector T-cell pool and thereby driving disease pathology. This review provides background on the discovery of stem-like T cells and their function in cancer and autoimmunity. Moreover, the influence of the microbiota and metabolism on the stem-like T-cell pool is summarized. Lastly, the implications of our knowledge about stem-like T cells for clinical treatment strategies for cancer and autoimmunity will be discussed.

Immunometabolism of CD8+ T cell differentiation in cancer

CD8+ cytotoxic T lymphocytes (CTLs) are central mediators of tumor immunity and immunotherapies. Upon tumor antigen recognition, CTLs differentiate from naive/memory-like toward terminally exhausted populations with more limited function against tumors. Such differentiation is regulated by both immune signals, including T cell receptors (TCRs), co-stimulation, and cytokines, and metabolism-associated processes. These immune signals shape the metabolic landscape via signaling, transcriptional and post-transcriptional mechanisms, while metabolic processes in turn exert spatiotemporal effects to modulate the strength and duration of immune signaling. Here, we review the bidirectional regulation between immune signals and metabolic processes, including nutrient uptake and intracellular metabolic pathways, in shaping CTL differentiation and exhaustion. We also discuss the mechanisms underlying how specific nutrient sources and metabolite-mediated signaling events orchestrate CTL biology. Understanding how metabolic programs and their interplay with immune signals instruct CTL differentiation and exhaustion is crucial to uncover tumor-immune interactions and design novel immunotherapies.

The role of transforming growth factor-β (TGF-β) in the formation of exhausted CD8 + T cells

CD8 + T cells exert a critical role in eliminating cancers and chronic infections, and can provide long-term protective immunity. However, under the exposure of persistent antigen, CD8 + T cells can differentiate into terminally exhausted CD8 + T cells and lose the ability of immune surveillance and disease clearance. New insights into the molecular mechanisms of T-cell exhaustion suggest that it is a potential way to improve the efficacy of immunotherapy by restoring the function of exhausted CD8 + T cells. Transforming growth factor-β (TGF-β) is an important executor of immune homeostasis and tolerance, inhibiting the expansion and function of many components of the immune system. Recent studies have shown that TGF-β is one of the drivers for the development of exhausted CD8 + T cells. In this review, we summarized the role and mechanisms of TGF-β in the formation of exhausted CD8 + T cells and discussed ways to target those to ultimately enhance the efficacy of immunotherapy.

Metabolic rewiring and communication in cancer immunity

The immune system shapes tumor development and progression. Although immunotherapy has transformed cancer treatment, its overall efficacy remains limited, underscoring the need to uncover mechanisms to improve therapeutic effects. Metabolism-associated processes, including intracellular metabolic reprogramming and intercellular metabolic crosstalk, are emerging as instructive signals for anti-tumor immunity. Here, we first summarize the roles of intracellular metabolic pathways in controlling immune cell function in the tumor microenvironment. How intercellular metabolic communication regulates anti-tumor immunity, and the impact of metabolites or nutrients on signaling events, are also discussed. We then describe how targeting metabolic pathways in tumor cells or intratumoral immune cells or via nutrient-based interventions may boost cancer immunotherapies. Finally, we conclude with discussions on profiling and functional perturbation methods of metabolic activity in intratumoral immune cells, and perspectives on future directions. Uncovering the mechanisms for metabolic rewiring and communication in the tumor microenvironment may enable development of novel cancer immunotherapies.

Induction of immortal-like and functional CAR T cells by defined factors

Long-term antitumor efficacy of chimeric antigen receptor (CAR) T cells depends on their functional persistence in vivo. T cells with stem-like properties show better persistence, but factors conferring bona fide stemness to T cells remain to be determined. Here, we demonstrate the induction of CAR T cells into an immortal-like and functional state, termed TIF. The induction of CARTIF cells depends on the repression of two factors, BCOR and ZC3H12A, and requires antigen or CAR tonic signaling. Reprogrammed CARTIF cells possess almost infinite stemness, similar to induced pluripotent stem cells while retaining the functionality of mature T cells, resulting in superior antitumor effects. Following the elimination of target cells, CARTIF cells enter a metabolically dormant state, persisting in vivo with a saturable niche and providing memory protection. TIF represents a novel state of T cells with unprecedented stemness, which confers long-term functional persistence of CAR T cells in vivo and holds broad potential in T cell therapies.

The TOPK Inhibitor HI-TOPK-032 Enhances CAR T-cell Therapy of Hepatocellular Carcinoma by Upregulating Memory T Cells

Chimeric antigen receptor (CAR) T cells are emerging as an effective antitumoral therapy. However, their therapeutic effects on solid tumors are limited because of their short survival time and the immunosuppressive tumor microenvironment. Memory T cells respond more vigorously and persist longer than their naïve/effector counterparts. Therefore, promoting CAR T-cell development into memory T cells could further enhance their antitumoral effects. HI-TOPK-032 is a T-LAK cell-originated protein kinase (TOPK)-specific inhibitor that moderately represses some types of tumors. However, it is unknown whether HI-TOPK-032 works on hepatocellular carcinoma (HCC) and whether it impacts antitumoral immunity. Using both subcutaneous and orthotopic xenograft tumor models of two human HCC cell lines, Huh-7 and HepG2, we found that HI-TOPK-032 significantly improved proliferation/persistence of CD8+ CAR T cells, as evidenced by an increase in CAR T-cell counts or frequency of Ki-67+CD8+ cells and a decrease in PD-1+LAG-3+TIM-3+CD8+ CAR T cells in vivo. Although HI-TOPK-032 did not significantly suppress HCC growth, it enhanced the capacity of CAR T cells to inhibit tumor growth. Moreover, HI-TOPK-032 augmented central memory CD8+ T cell (TCM) frequency while increasing eomesodermin expression in CD8+ CAR T cells in tumor-bearing mice. Moreover, it augmented CD8+ CAR TCM cells in vitro and reduced their expression of immune checkpoint molecules. Finally, HI-TOPK-032 inhibited mTOR activation in CAR T cells in vitro and in tumors, whereas overactivation of mTOR reversed the effects of HI-TOPK-032 on CD8+ TCM cells and tumor growth. Thus, our studies have revealed mechanisms underlying the antitumoral effects of HI-TOPK-032 while advancing CAR T-cell immunotherapy.

Molecular insight into T cell exhaustion in hepatocellular carcinoma

Hepatocellular carcinoma is one of the leading causes of cancer-related mortality globally. The emergence of immunotherapy has been shown to be a promising therapeutic approach for hepatocellular carcinoma in recent years. It has been well known that T cell plays a key role in current immunotherapy. However, sustained exposure to antigenic stimulation within the tumor microenvironment may lead to T cell exhaustion, which may cause treatment ineffectiveness. Therefore, reversing T cell exhaustion has been an important issue for the clinical application of immunotherapy, and a comprehensive understanding of the intricacies surrounding T cell exhaustion and its underlying mechanisms is imperative for devising strategies to overcome the T cell exhaustion during treatment. In this review, we summarized the reported drivers of T cell exhaustion in hepatocellular carcinoma and delineate potential ways to reverse it. Additionally, we discussed the interplay among metabolic plasticity, epigenetic regulation, and transcriptional factors in exhausted T cells in hepatocellular carcinoma, and their implication for future clinical applications.

TGF-β blockade drives a transitional effector phenotype in T cells reversing SIV latency and decreasing SIV reservoirs in vivo

HIV-1 persistence during ART is due to the establishment of long-lived viral reservoirs in resting immune cells. Using an NHP model of barcoded SIVmac239 intravenous infection and therapeutic dosing of anti-TGFBR1 inhibitor galunisertib (LY2157299), we confirm the latency reversal properties of in vivo TGF-β blockade, decrease viral reservoirs and stimulate immune responses. Treatment of eight female, SIV-infected macaques on ART with four 2-weeks cycles of galunisertib leads to viral reactivation as indicated by plasma viral load and immunoPET/CT with a 64Cu-DOTA-F(ab')2-p7D3-probe. Post-galunisertib, lymph nodes, gut and PBMC exhibit lower cell-associated (CA-)SIV DNA and lower intact pro-virus (PBMC). Galunisertib does not lead to systemic increase in inflammatory cytokines. High-dimensional cytometry, bulk, and single-cell (sc)RNAseq reveal a galunisertib-driven shift toward an effector phenotype in T and NK cells characterized by a progressive downregulation in TCF1. In summary, we demonstrate that galunisertib, a clinical stage TGF-β inhibitor, reverses SIV latency and decreases SIV reservoirs by driving T cells toward an effector phenotype, enhancing immune responses in vivo in absence of toxicity.

SHP-1 Regulates CD8+ T Cell Effector Function but Plays a Subtle Role with SHP-2 in T Cell Exhaustion Due to a Stage-Specific Nonredundant Functional Relay

SHP-1 (Src homology region 2 domain-containing phosphatase 1) is a well-known negative regulator of T cells, whereas its close homolog SHP-2 is the long-recognized main signaling mediator of the PD-1 inhibitory pathway. However, recent studies have challenged the requirement of SHP-2 in PD-1 signaling, and follow-up studies further questioned the alternative idea that SHP-1 may replace SHP-2 in its absence. In this study, we systematically investigate the role of SHP-1 alone or jointly with SHP-2 in CD8+ T cells in a series of gene knockout mice. We show that although SHP-1 negatively regulates CD8+ T cell effector function during acute lymphocytic choriomeningitis virus (LCMV) infection, it is dispensable for CD8+ T cell exhaustion during chronic LCMV infection. Moreover, in contrast to the mortality of PD-1 knockout mice upon chronic LCMV infection, mice double deficient for SHP-1 and SHP-2 in CD8+ T cells survived without immunopathology. Importantly, CD8+ T cells lacking both phosphatases still differentiate into exhausted cells and respond to PD-1 blockade. Finally, we found that SHP-1 and SHP-2 suppressed effector CD8+ T cell expansion at the early and late stages, respectively, during chronic LCMV infection.

The CUL5 E3 ligase complex negatively regulates central signaling pathways in CD8+ T cells

CD8+ T cells play an important role in anti-tumor immunity. Better understanding of their regulation could advance cancer immunotherapies. Here we identify, via stepwise CRISPR-based screening, that CUL5 is a negative regulator of the core signaling pathways of CD8+ T cells. Knocking out CUL5 in mouse CD8+ T cells significantly improves their tumor growth inhibiting ability, with significant proteomic alterations that broadly enhance TCR and cytokine signaling and their effector functions. Chemical inhibition of neddylation required by CUL5 activation, also enhances CD8 effector activities with CUL5 validated as a major target. Mechanistically, CUL5, which is upregulated by TCR stimulation, interacts with the SOCS-box-containing protein PCMTD2 and inhibits TCR and IL2 signaling. Additionally, CTLA4 is markedly upregulated by CUL5 knockout, and its inactivation further enhances the anti-tumor effect of CUL5 KO. These results together reveal a negative regulatory mechanism for CD8+ T cells and have strong translational implications in cancer immunotherapy.

De novo NAD+ synthesis contributes to CD8+ T cell metabolic fitness and antitumor function

The dysfunction and clonal constriction of tumor-infiltrating CD8+ T cells are accompanied by alterations in cellular metabolism; however, how the cell-intrinsic metabolic pathway specifies intratumoral CD8+ T cell features remains elusive. Here, we show that cell-autonomous generation of nicotinamide adenine dinucleotide (NAD+) via the kynurenine pathway (KP) contributes to the maintenance of intratumoral CD8+ T cell metabolic and functional fitness. De novo NAD+ synthesis is involved in CD8+ T cell metabolism and antitumor function. KP-derived NAD+ promotes PTEN deacetylation, thereby facilitating PTEN degradation and preventing PTEN-dependent metabolic defects. Importantly, impaired cell-autonomous NAD+ synthesis limits CD8+ T cell responses in human colorectal cancer samples. Our results reveal that KP-derived NAD+ regulates the CD8+ T cell metabolic and functional state by restricting PTEN activity and suggest that modulation of de novo NAD+ synthesis could restore CD8+ T cell metabolic fitness and antitumor function.

TGF-β blockade drives a transitional effector phenotype in T cells reversing SIV latency and decreasing SIV reservoirs in vivo

HIV-1 persistence during ART is due to the establishment of long-lived viral reservoirs in resting immune cells. Using an NHP model of barcoded SIVmac239 intravenous infection and therapeutic dosing of the anti-TGFBR1 inhibitor galunisertib (LY2157299), we confirmed the latency reversal properties of in vivo TGF-β blockade, decreased viral reservoirs and stimulated immune responses. Eight SIV-infected macaques on suppressive ART were treated with 4 2-week cycles of galunisertib. ART was discontinued 3 weeks after the last dose, and macaques euthanized 6 weeks after ART-interruption(ATI). One macaque did not rebound, while the remaining rebounded between week 2 and 6 post-ATI. Galunisertib led to viral reactivation as indicated by plasma viral load and immunoPET/CT with the 64Cu-DOTA-F(ab')2-p7D3-probe. Half to 1 Log decrease in cell-associated (CA-)SIV DNA was detected in lymph nodes, gut and PBMC, while intact pro-virus in PBMC decreased by 3-fold. No systemic increase in inflammatory cytokines was observed. High-dimensions cytometry, bulk and single-cell RNAseq revealed a shift toward an effector phenotype in T and NK cells. In summary, we demonstrated that galunisertib, a clinical stage TGFβ inhibitor, reverses SIV latency and decreases SIV reservoirs by driving T cells toward an effector phenotype, enhancing immune responses in vivo in absence of toxicity.

Localization, tissue biology and T cell state - implications for cancer immunotherapy

Tissue localization is a critical determinant of T cell immunity. CD8+ T cells are contact-dependent killers, which requires them to physically be within the tissue of interest to kill peptide-MHC class I-bearing target cells. Following their migration and extravasation into tissues, T cells receive many extrinsic cues from the local microenvironment, and these signals shape T cell differentiation, fate and function. Because major organ systems are variable in their functions and compositions, they apply disparate pressures on T cells to adapt to the local microenvironment. Additional complexity arises in the context of malignant lesions (either primary or metastatic), and this has made understanding the factors that dictate T cell function and longevity in tumours challenging. Moreover, T cell differentiation state influences how cues from the microenvironment are interpreted by tissue-infiltrating T cells, highlighting the importance of T cell state in the context of tissue biology. Here, we review the intertwined nature of T cell differentiation state, location, survival and function, and explain how dysfunctional T cell populations can adopt features of tissue-resident memory T cells to persist in tumours. Finally, we discuss how these factors have shaped responses to cancer immunotherapy.

Latent transforming growth factor beta binding protein 4: A regulator of mitochondrial function in acute kidney injury

Recently, latent transforming growth factor beta binding protein 4 (LTBP4) was implicated in the pathogenesis of renal damage through its modulation of mitochondrial dynamics. The seminal article written by Su et al. entitled "LTBP4 (Latent Transforming Growth Factor Beta Binding Protein 4) Protects Against Renal Fibrosis via Mitochondrial and Vascular Impacts" uncovers LTBP4's renoprotective role against acute kidney injury via modulating mitochondrial dynamics. Recently, LTBP4 has emerged as a driver in the mitochondrial-dependent modulation of age-related organ pathologies. This article aims to expand our understanding of LTBP4's diverse roles in these diseases in the context of these recent findings.

Stem-like exhausted and memory CD8+ T cells in cancer

T cells can acquire a broad spectrum of differentiation states following activation. At the extreme ends of this continuum are short-lived cells equipped with effector machinery and more quiescent, long-lived cells with heightened proliferative potential and stem cell-like developmental plasticity. The latter encompass stem-like exhausted T cells and memory T cells, both of which have recently emerged as key determinants of cancer immunity and response to immunotherapy. Here, we discuss key similarities and differences in the regulation and function of stem-like exhausted CD8+ T cells and memory CD8+ T cells, and consider their context-specific contributions to protective immunity in diverse outcomes of cancer, including tumour escape, long-term control and eradication. Finally, we emphasize how recent advances in the understanding of the molecular regulation of stem-like exhausted T cells and memory T cells are being explored for clinical benefit in cancer immunotherapies such as checkpoint inhibition, adoptive cell therapy and vaccination.

Mitochondrial dysfunction promotes the transition of precursor to terminally exhausted T cells through HIF-1α-mediated glycolytic reprogramming

T cell exhaustion is a hallmark of cancer and persistent infections, marked by inhibitory receptor upregulation, diminished cytokine secretion, and impaired cytolytic activity. Terminally exhausted T cells are steadily replenished by a precursor population (Tpex), but the metabolic principles governing Tpex maintenance and the regulatory circuits that control their exhaustion remain incompletely understood. Using a combination of gene-deficient mice, single-cell transcriptomics, and metabolomic analyses, we show that mitochondrial insufficiency is a cell-intrinsic trigger that initiates the functional exhaustion of T cells. At the molecular level, we find that mitochondrial dysfunction causes redox stress, which inhibits the proteasomal degradation of hypoxia-inducible factor 1α (HIF-1α) and promotes the transcriptional and metabolic reprogramming of Tpex cells into terminally exhausted T cells. Our findings also bear clinical significance, as metabolic engineering of chimeric antigen receptor (CAR) T cells is a promising strategy to enhance the stemness and functionality of Tpex cells for cancer immunotherapy.

Regulation of T cells by myeloid-derived suppressor cells: emerging immunosuppressor in lung cancer

Myeloid-derived suppressor cells (MDSCs), major components maintaining the immune suppressive microenvironment in lung cancer, are relevant to the invasion, metastasis, and poor prognosis of lung cancer, through the regulation of epithelial-mesenchymal transition, remodeling of the immune microenvironment, and regulation of angiogenesis. MDSCs regulate T-cell immune functions by maintaining a strong immunosuppressive microenvironment and promoting tumor invasion. This raises the question of whether reversing the immunosuppressive effect of MDSCs on T cells can improve lung cancer treatment. To understand this further, this review explores the interactions and specific mechanisms of different MDSCs subsets, including regulatory T cells, T helper cells, CD8 + T cells, natural killer T cells, and exhausted T cells, as part of the lung cancer immune microenvironment. Second, it focuses on the guiding significance confirmed via clinical liquid biopsy and tissue biopsy that different MDSC subsets improve the prognosis of lung cancer. Finally, we conclude that targeting MDSCs through action targets or signaling pathways can help regulate T-cell immune functions and suppress T-cell exhaustion. In addition, immune checkpoint inhibitors targeting MDSCs may serve as a new approach for enhancing the efficiency of immunotherapy and targeted therapy for lung cancer in the future, providing better comprehensive options for lung cancer treatment.

CD8+ T cells in the cancer-immunity cycle

CD8+ T cells are end effectors of cancer immunity. Most forms of effective cancer immunotherapy involve CD8+ T cell effector function. Here, we review the current understanding of T cell function in cancer, focusing on key CD8+ T cell subtypes and states. We discuss factors that influence CD8+ T cell differentiation and function in cancer through a framework that incorporates the classic three-signal model and a fourth signal-metabolism-and also consider the impact of the tumor microenvironment from a T cell perspective. We argue for the notion of immunotherapies as "pro-drugs" that act to augment or modulate T cells, which ultimately serve as the drug in vivo, and for the importance of overall immune health in cancer treatment and prevention. The progress in understanding T cell function in cancer has and will continue to improve harnessing of the immune system across broader tumor types to benefit more patients.

TGFβ signaling links early life endocrine-disrupting chemicals exposure to suppression of nucleotide excision repair in rat myometrial stem cells

Environmental exposure to endocrine-disrupting chemicals (EDCs) is linked to the development of uterine fibroids (UFs) in women. UFs, non-cancerous tumors, are thought to originate from abnormal myometrial stem cells (MMSCs). Defective DNA repair capacity may contribute to the emergence of mutations that promote tumor growth. The multifunctional cytokine TGFβ1 is associated with UF progression and DNA damage repair pathways. To investigate the impact of EDC exposure on TGFβ1 and nucleotide excision repair (NER) pathways, we isolated MMSCs from 5-month-old Eker rats exposed neonatally to diethylstilbestrol (DES), an EDC, or to vehicle (VEH). EDC-MMSCs exhibited overactivated TGFβ1 signaling and reduced mRNA and protein levels of NER pathway components compared to VEH-MMSCs. EDC-MMSCs also demonstrated impaired NER capacity. Exposing VEH-MMSCs to TGFβ1 decreased NER capacity while inhibiting TGFβ signaling in EDC-MMSCs restored it. RNA-seq analysis and further validation revealed decreased expression of Uvrag, a tumor suppressor gene involved in DNA damage recognition, in VEH-MMSCs treated with TGFβ1, but increased expression in EDC-MMSCs after TGFβ signaling inhibition. Overall, we demonstrated that the overactivation of the TGFβ pathway links early life exposure to EDCs with impaired NER capacity, which would lead to increased genetic instability, arise of mutations, and fibroid tumorigenesis. We demonstrated that the overactivation of the TGFβ pathway links early life exposure to EDCs with impaired NER capacity, which would lead to increased fibroid incidence.

ILC1-derived IFN-γ regulates macrophage activation in colon cancer

BACKGROUND

Tumor-associated macrophages (TAMs) are an important subset of innate immune cells in the tumor microenvironment, and they are pivotal regulators of tumor-promoting inflammation and tumor progression. Evidence has proven that TAM numbers are substantially increased in cancers, and most of these TAMs are polarized toward the alternatively activated M2 phenotype; Thus, these TAMs strongly promote the progression of cancer diseases. Type 1 innate lymphocytes (ILC1s) are present in high numbers in intestinal tissues and are characterized by the expression of the transcription factor T-bet and the secretion of interferon (IFN)-γ, which can promote macrophages to polarize toward the classically activated antitumor M1 phenotype. However, the relationship between these two cell subsets in colon cancer remains unclear.

METHODS

Flow cytometry was used to determine the percentages of M1-like macrophages, M2-like macrophages and ILC1s in colon cancer tissues and paracancerous healthy colon tissues in the AOM/DSS-induced mouse model of colon cancer. Furthermore, ILC1s were isolated and bone marrow-derived macrophages were generated to analyze the crosstalk that occurred between these cells when cocultured in vitro. Moreover, ILC1s were adoptively transferred or inhibited in vivo to explore the effects of ILC1s on tumor-infiltrating macrophages and tumor growth.

RESULTS

We found that the percentages of M1-like macrophages and ILC1s were decreased in colon cancer tissues, and these populations were positively correlated. ILC1s promoted the polarization of macrophages toward the classically activated M1-like phenotype in vitro, and this effect could be blocked by an anti-IFN-γ antibody. The in vivo results showed that the administration of the Group 1 innate lymphocyte-blocking anti-NK1.1 antibody decreased the number of M1-like macrophages in the tumor tissues of MC38 tumor-bearing mice and promoted tumor growth, and adoptive transfer of ILC1s inhibited tumors and increased the percentage of M1-like macrophages in MC38 tumor-bearing mice.

CONCLUSIONS

Our studies preliminarily prove for the first time that ILC1s promote the activation of M1-like macrophages by secreting IFN-γ and inhibit the progression of colon cancer, which may provide insight into immunotherapeutic approaches for colon cancer.

Stem-like CD4+ T cells in perivascular tertiary lymphoid structures sustain autoimmune vasculitis

Autoimmune vasculitis of the medium and large elastic arteries can cause blindness, stroke, aortic arch syndrome, and aortic aneurysm. The disease is often refractory to immunosuppressive therapy and progresses over decades as smoldering aortitis. How the granulomatous infiltrates in the vessel wall are maintained and how tissue-infiltrating T cells and macrophages are replenished are unknown. Single-cell and whole-tissue transcriptomic studies of immune cell populations in vasculitic arteries identified a CD4+ T cell population with stem cell-like features. CD4+ T cells supplying the tissue-infiltrating and tissue-damaging effector T cells survived in tertiary lymphoid structures around adventitial vasa vasora, expressed the transcription factor T cell factor 1 (TCF1), had high proliferative potential, and gave rise to two effector populations, Eomesodermin (EOMES)+ cytotoxic T cells and B cell lymphoma 6 (BCL6)+ T follicular helper-like cells. TCF1hiCD4+ T cells expressing the interleukin 7 receptor (IL-7R) sustained vasculitis in serial transplantation experiments. Thus, TCF1hiCD4+ T cells function as disease stem cells and promote chronicity and autonomy of autoimmune tissue inflammation. Remission-inducing therapies will require targeting stem-like CD4+ T cells instead of only effector T cells.

Cellular and molecular waypoints along the path of T cell exhaustion

Thirty years of foundational research investigating molecular and cellular mechanisms promoting T cell exhaustion are now enabling rational design of T cell-based therapies for the treatment of chronic infections and cancer. Once described as a static cell fate, it is now well appreciated that the developmental path toward exhaustion is composed of a heterogeneous pool of cells with varying degrees of effector potential that ultimately converge on a terminally differentiated state. Recent description of the developmental stages along the differentiation trajectory of T cell exhaustion has provided insight into past immunotherapeutic success and future opportunities. Here, we discuss the hallmarks of distinct developmental stages occurring along the path to T cell dysfunction and the impact of these discrete CD8+ T cell fates on cancer immunotherapy.

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.

Signaling Pathways Leading to mTOR Activation Downstream Cytokine Receptors in Lymphocytes in Health and Disease

CD8+ T cells and Natural Killer (NK) cells are cytotoxic lymphocytes important in the response to intracellular pathogens and cancer. Their activity depends on the integration of a large set of intracellular and environmental cues, including antigenic signals, cytokine stimulation and nutrient availability. This integration is achieved by signaling hubs, such as the mechanistic target of rapamycin (mTOR). mTOR is a conserved protein kinase that controls cellular growth and metabolism in eukaryotic cells and, therefore, is essential for lymphocyte development and maturation. However, our current understanding of mTOR signaling comes mostly from studies performed in transformed cell lines, which constitute a poor model for comprehending metabolic pathway regulation. Therefore, it is only quite recently that the regulation of mTOR in primary cells has been assessed. Here, we review the signaling pathways leading to mTOR activation in CD8+ T and NK cells, focusing on activation by cytokines. We also discuss how this knowledge can contribute to immunotherapy development, particularly for cancer treatment.

Combined PD-L1/TGFβ blockade allows expansion and differentiation of stem cell-like CD8 T cells in immune excluded tumors

TGFβ signaling is associated with non-response to immune checkpoint blockade in patients with advanced cancers, particularly in the immune-excluded phenotype. While previous work demonstrates that converting tumors from excluded to inflamed phenotypes requires attenuation of PD-L1 and TGFβ signaling, the underlying cellular mechanisms remain unclear. Here, we show that TGFβ and PD-L1 restrain intratumoral stem cell-like CD8 T cell (TSCL) expansion and replacement of progenitor-exhausted and dysfunctional CD8 T cells with non-exhausted T effector cells in the EMT6 tumor model in female mice. Upon combined TGFβ/PD-L1 blockade IFNγhi CD8 T effector cells show enhanced motility and accumulate in the tumor. Ensuing IFNγ signaling transforms myeloid, stromal, and tumor niches to yield an immune-supportive ecosystem. Blocking IFNγ abolishes the anti-PD-L1/anti-TGFβ therapy efficacy. Our data suggest that TGFβ works with PD-L1 to prevent TSCL expansion and replacement of exhausted CD8 T cells, thereby maintaining the T cell compartment in a dysfunctional state.

PD-1 blockade increases the self-renewal of stem-like CD8 T cells to compensate for their accelerated differentiation into effectors

PD-1+TCF-1+ stem-like CD8 T cells act as critical resource cells for maintaining T cell immunity in chronic viral infections and cancer. In addition, they provide the proliferative burst of effector CD8 T cells after programmed death protein 1 (PD-1)-directed immunotherapy. However, it is not known whether checkpoint blockade diminishes the number of these stem-like progenitor cells as effector cell differentiation increases. To investigate this, we used the mouse model of chronic lymphocytic choriomeningitis virus (LCMV) infection. Treatment of chronically infected mice with either αPD-1 or αPD-L1 antibody not only increased effector cell differentiation from the virus-specific stem-like CD8 T cells but also increased their proliferation so their numbers were maintained. The increased self-renewal of LCMV-specific stem-like CD8 T cells was mTOR dependent. We used microscopy to understand the division of these progenitor cells and found that after PD-1 blockade, an individual dividing cell could give rise to a differentiated TCF-1- daughter cell alongside a self-renewing TCF-1+ sister cell. This asymmetric division helped to preserve the number of stem-like cells. Moreover, we found that the PD-1+TCF-1+ stem-like CD8 T cells retained their transcriptional program and their in vivo functionality in terms of responding to viral infection and to repeat PD-1 blockade. Together, our results demonstrate that PD-1 blockade does not deplete the stem-like population despite increasing effector differentiation. These findings have implications for PD-1-directed immunotherapy in humans.

Sustained CD28 costimulation is required for self-renewal and differentiation of TCF-1+ PD-1+ CD8 T cells

During persistent antigen stimulation, such as in chronic infections and cancer, CD8 T cells differentiate into a hypofunctional programmed death protein 1-positive (PD-1+) exhausted state. Exhausted CD8 T cell responses are maintained by precursors (Tpex) that express the transcription factor T cell factor 1 (TCF-1) and high levels of the costimulatory molecule CD28. Here, we demonstrate that sustained CD28 costimulation is required for maintenance of antiviral T cells during chronic infection. Low-level CD28 engagement preserved mitochondrial fitness and self-renewal of Tpex, whereas stronger CD28 signaling enhanced glycolysis and promoted Tpex differentiation into TCF-1neg exhausted CD8 T cells (Tex). Furthermore, enhanced differentiation by CD28 engagement did not reduce the Tpex pool. Together, these findings demonstrate that continuous CD28 engagement is needed to sustain PD-1+ CD8 T cells and suggest that increasing CD28 signaling promotes Tpex differentiation into more functional effector-like Tex, possibly without compromising long-term responses.

Identification of ligand-receptor pairs that drive human astrocyte development

Extrinsic signaling between diverse cell types is crucial for nervous system development. Ligand binding is a key driver of developmental processes. Nevertheless, it remains a significant challenge to disentangle which and how extrinsic signals act cooperatively to affect changes in recipient cells. In the developing human brain, cortical progenitors transition from neurogenesis to gliogenesis in a stereotyped sequence that is in part influenced by extrinsic ligands. Here we used published transcriptomic data to identify and functionally test five ligand-receptor pairs that synergistically drive human astrogenesis. We validate the synergistic contributions of TGFβ2, NLGN1, TSLP, DKK1 and BMP4 ligands on astrocyte development in both hCOs and primary fetal tissue. We confirm that the cooperative capabilities of these five ligands are greater than their individual capacities. Additionally, we discovered that their combinatorial effects converge in part on the mTORC1 signaling pathway, resulting in transcriptomic and morphological features of astrocyte development. Our data-driven framework can leverage single-cell and bulk genomic data to generate and test functional hypotheses surrounding cell-cell communication regulating neurodevelopmental processes.

Metabolites and Immune Response in Tumor Microenvironments

The remodeled cancer cell metabolism affects the tumor microenvironment and promotes an immunosuppressive state by changing the levels of macro- and micronutrients and by releasing hormones and cytokines that recruit immunosuppressive immune cells. Novel dietary interventions such as amino acid restriction and periodic fasting mimicking diets can prevent or dampen the formation of an immunosuppressive microenvironment by acting systemically on the release of hormones and growth factors, inhibiting the release of proinflammatory cytokines, and remodeling the tumor vasculature and extracellular matrix. Here, we discuss the latest research on the effects of these therapeutic interventions on immunometabolism and tumor immune response and future scenarios pertaining to how dietary interventions could contribute to cancer therapy.

Immune response and treatment targets of chronic hepatitis B virus infection: innate and adaptive immunity

Chronic hepatitis B virus (HBV) infection is a major global public health risk that threatens human life and health, although the number of vaccinated people has increased. The clinical outcome of HBV infection depends on the complex interplay between viral replication and the host immune response. Innate immunity plays an important role in the early stages of the disease but retains no long-term immune memory. However, HBV evades detection by the host innate immune system through stealth. Therefore, adaptive immunity involving T and B cells is crucial for controlling and clearing HBV infections that lead to liver inflammation and damage. The persistence of HBV leads to immune tolerance owing to immune cell dysfunction, T cell exhaustion, and an increase in suppressor cells and cytokines. Although significant progress has been made in HBV treatment in recent years, the balance between immune tolerance, immune activation, inflammation, and fibrosis in chronic hepatitis B remains unknown, making a functional cure difficult to achieve. Therefore, this review focuses on the important cells involved in the innate and adaptive immunity of chronic hepatitis B that target the host immune system and identifies treatment strategies.

Tissue-resident memory CAR T cells with stem-like characteristics display enhanced efficacy against solid and liquid tumors

Chimeric antigen receptor (CAR) T cells demonstrate remarkable success in treating hematological malignancies, but their effectiveness in non-hematopoietic cancers remains limited. This study proposes enhancing CAR T cell function and localization in solid tumors by modifying the epigenome governing tissue-residency adaptation and early memory differentiation. We identify that a key factor in human tissue-resident memory CAR T cell (CAR-TRM) formation is activation in the presence of the pleotropic cytokine, transforming growth factor β (TGF-β), which enforces a core program of both "stemness" and sustained tissue residency by mediating chromatin remodeling and concurrent transcriptional changes. This approach leads to a practical and clinically actionable in vitro production method for engineering peripheral blood T cells into a large number of "stem-like" CAR-TRM cells resistant to tumor-associated dysfunction, possessing an enhanced ability to accumulate in situ and rapidly eliminate cancer cells for more effective immunotherapy.

Hierarchical transcriptional network governing heterogeneous T cell exhaustion and its implications for immune checkpoint blockade

The fundamental principle of immune checkpoint blockade (ICB) is to protect tumor-infiltrating T cells from being exhausted. Despite the remarkable success achieved by ICB treatment, only a small group of patients benefit from it. Characterized by a hypofunctional state with the expression of multiple inhibitory receptors, exhausted T (Tex) cells are a major obstacle in improving ICB. T cell exhaustion is a progressive process which adapts to persistent antigen stimulation in chronic infections and cancers. In this review, we elucidate the heterogeneity of Tex cells and offer new insights into the hierarchical transcriptional regulation of T cell exhaustion. Factors and signaling pathways that induce and promote exhaustion are also summarized. Moreover, we review the epigenetic and metabolic alterations of Tex cells and discuss how PD-1 signaling affects the balance between T cell activation and exhaustion, aiming to provide more therapeutic targets for applications of combinational immunotherapies.

The role of mitochondria in the resistance of melanoma to PD-1 inhibitors

Malignant melanoma is one of the most common tumours and has the highest mortality rate of all types of skin cancers worldwide. Traditional and novel therapeutic approaches, including surgery, targeted therapy and immunotherapy, have shown good efficacy in the treatment of melanoma. At present, the mainstay of treatment for melanoma is immunotherapy combined with other treatment strategies. However, immune checkpoint inhibitors, such as PD-1 inhibitors, are not particularly effective in the clinical treatment of patients with melanoma. Changes in mitochondrial function may affect the development of melanoma and the efficacy of PD-1 inhibitors. To elucidate the role of mitochondria in the resistance of melanoma to PD-1 inhibitors, this review comprehensively summarises the role of mitochondria in the occurrence and development of melanoma, targets related to the function of mitochondria in melanoma cells and changes in mitochondrial function in different cells in melanoma resistant to PD-1 inhibitors. This review may help to develop therapeutic strategies for improving the clinical response rate of PD-1 inhibitors and prolonging the survival of patients by activating mitochondrial function in tumour and T cells.

Extremely Differentiated T Cell Subsets Contribute to Tissue Deterioration During Aging

There is a dramatic remodeling of the T cell compartment during aging. The most notorious changes are the reduction of the naive T cell pool and the accumulation of memory-like T cells. Memory-like T cells in older people acquire a phenotype of terminally differentiated cells, lose the expression of costimulatory molecules, and acquire properties of senescent cells. In this review, we focus on the different subsets of age-associated T cells that accumulate during aging. These subsets include extremely cytotoxic T cells with natural killer properties, exhausted T cells with altered cytokine production, and regulatory T cells that gain proinflammatory features. Importantly, all of these subsets lose their lymph node homing capacity and migrate preferentially to nonlymphoid tissues, where they contribute to tissue deterioration and inflammaging.

Integrated analysis of multi-omics data reveals T cell exhaustion in sepsis

Background

Sepsis is a heterogeneous disease, therefore the single-gene-based biomarker is not sufficient to fully understand the disease. Higher-level biomarkers need to be explored to identify important pathways related to sepsis and evaluate their clinical significance.

Methods

Gene Set Enrichment Analysis (GSEA) was used to analyze the sepsis transcriptome to obtain the pathway-level expression. Limma was used to identify differentially expressed pathways. Tumor IMmune Estimation Resource (TIMER) was applied to estimate immune cell abundance. The Spearman correlation coefficient was used to find the relationships between pathways and immune cell abundance. Methylation and single-cell transcriptome data were also employed to identify important pathway genes. Log-rank test was performed to test the prognostic significance of pathways for patient survival probability. DSigDB was used to mine candidate drugs based on pathways. PyMol was used for 3-D structure visualization. LigPlot was used to plot the 2-D pose view for receptor-ligand interaction.

Results

Eighty-four KEGG pathways were differentially expressed in sepsis patients compared to healthy controls. Of those, 10 pathways were associated with 28-day survival. Some pathways were significantly correlated with immune cell abundance and five pathways could be used to distinguish between systemic inflammatory response syndrome (SIRS), bacterial sepsis, and viral sepsis with Area Under the Curve (AUC) above 0.80. Seven related drugs were screened using survival-related pathways.

Conclusion

Sepsis-related pathways can be utilized for disease subtyping, diagnosis, prognosis, and drug screening.

T cell exhaustion in malignant gliomas

Despite advances in understanding tumor biology, malignant gliomas remain incurable. While immunotherapy has improved outcomes in other cancer types, comparable efficacy has not yet been demonstrated for primary cancers of the central nervous system (CNS). T cell exhaustion, defined as a progressive decrease in effector function, sustained expression of inhibitory receptors, metabolic dysfunction, and distinct epigenetic and transcriptional alterations, contributes to the failure of immunotherapy in the CNS. Herein, we describe recent advances in understanding the drivers of T cell exhaustion in the glioma microenvironment. We discuss the extrinsic and intrinsic factors that contribute to exhaustion and highlight potential avenues for reversing this phenotype. Our ability to directly target specific immunosuppressive drivers in brain cancers would be a major advance in immunotherapy.

Neuraminidase 1 promotes renal fibrosis development in male mice

The functions of the influenza virus neuraminidase has been well documented but those of the mammalian neuraminidases remain less explored. Here, we characterize the role of neuraminidase 1 (NEU1) in unilateral ureteral obstruction (UUO) and folic acid (FA)-induced renal fibrosis mouse models. We find that NEU1 is significantly upregulated in the fibrotic kidneys of patients and mice. Functionally, tubular epithelial cell-specific NEU1 knockout inhibits epithelial-to-mesenchymal transition, inflammatory cytokines production, and collagen deposition in mice. Conversely, NEU1 overexpression exacerbates progressive renal fibrosis. Mechanistically, NEU1 interacts with TGFβ type I receptor ALK5 at the 160-200aa region and stabilizes ALK5 leading to SMAD2/3 activation. Salvianolic acid B, a component of Salvia miltiorrhiza, is found to strongly bind to NEU1 and effectively protect mice from renal fibrosis in a NEU1-dependent manner. Collectively, this study characterizes a promotor role for NEU1 in renal fibrosis and suggests a potential avenue of targeting NEU1 to treat kidney diseases.

Regulation of T Cell Activation and Metabolism by Transforming Growth Factor-Beta

Transforming growth factor beta (TGFβ) receptor signalling regulates T cell development, differentiation and effector function. Expression of the immune-associated isoform of this cytokine, TGFβ1, is absolutely required for the maintenance of immunological tolerance in both mice and humans, whilst context-dependent TGFβ1 signalling regulates the differentiation of both anti- and pro-inflammatory T cell effector populations. Thus, distinct TGFβ-dependent T cell responses are implicated in the suppression or initiation of inflammatory and autoimmune diseases. In cancer settings, TGFβ signals contribute to the blockade of anti-tumour immune responses and disease progression. Given the key functions of TGFβ in the regulation of immune responses and the potential for therapeutic targeting of TGFβ-dependent pathways, the mechanisms underpinning these pleiotropic effects have been the subject of much investigation. This review focuses on accumulating evidence suggesting that modulation of T cell metabolism represents a major mechanism by which TGFβ influences T cell immunity.

Distinct tissue niches direct lung immunopathology via CCL18 and CCL21 in severe COVID-19

Prolonged lung pathology has been associated with COVID-19, yet the cellular and molecular mechanisms behind this chronic inflammatory disease are poorly understood. In this study, we combine advanced imaging and spatial transcriptomics to shed light on the local immune response in severe COVID-19. We show that activated adventitial niches are crucial microenvironments contributing to the orchestration of prolonged lung immunopathology. Up-regulation of the chemokines CCL21 and CCL18 associates to endothelial-to-mesenchymal transition and tissue fibrosis within these niches. CCL21 over-expression additionally links to the local accumulation of T cells expressing the cognate receptor CCR7. These T cells are imprinted with an exhausted phenotype and form lymphoid aggregates that can organize in ectopic lymphoid structures. Our work proposes immune-stromal interaction mechanisms promoting a self-sustained and non-resolving local immune response that extends beyond active viral infection and perpetuates tissue remodeling.

Deletion of SNX9 alleviates CD8 T cell exhaustion for effective cellular cancer immunotherapy

Tumor-specific T cells are frequently exhausted by chronic antigenic stimulation. We here report on a human antigen-specific ex vivo model to explore new therapeutic options for T cell immunotherapies. T cells generated with this model resemble tumor-infiltrating exhausted T cells on a phenotypic and transcriptional level. Using a targeted pooled CRISPR-Cas9 screen and individual gene knockout validation experiments, we uncover sorting nexin-9 (SNX9) as a mediator of T cell exhaustion. Upon TCR/CD28 stimulation, deletion of SNX9 in CD8 T cells decreases PLCγ1, Ca²⁺, and NFATc2-mediated T cell signaling and reduces expression of NR4A1/3 and TOX. SNX9 knockout enhances memory differentiation and IFNγ secretion of adoptively transferred T cells and results in improved anti-tumor efficacy of human chimeric antigen receptor T cells in vivo. Our findings highlight that targeting SNX9 is a strategy to prevent T cell exhaustion and enhance anti-tumor immunity.

Rebalancing TGFβ1/BMP signals in exhausted T cells unlocks responsiveness to immune checkpoint blockade therapy

T cell dysfunctionality prevents the clearance of chronic infections and cancer. Furthermore, epigenetic programming in dysfunctional CD8+ T cells limits their response to immunotherapies, including immune checkpoint blockade (ICB). However, it is unclear which upstream signals drive acquisition of dysfunctional epigenetic programs, and whether therapeutically targeting these signals can remodel terminally dysfunctional T cells to an ICB-responsive state. Here we innovate an in vitro model system of stable human T cell dysfunction and show that chronic TGFβ1 signaling in posteffector CD8+ T cells accelerates their terminal dysfunction through stable epigenetic changes. Conversely, boosting bone morphogenetic protein (BMP) signaling while blocking TGFβ1 preserved effector and memory programs in chronically stimulated human CD8+ T cells, inducing superior responses to tumors and synergizing the ICB responses during chronic viral infection. Thus, rebalancing TGFβ1/BMP signals provides an exciting new approach to unleash dysfunctional CD8+ T cells and enhance T cell immunotherapies.

Engaging stemness improves cancer immunotherapy

Intra-tumoral immune cells promote the stemness of cancer stem cells (CSCs) in the tumor microenvironment (TME). CSCs promote tumor progression, relapse, and resistance to immunotherapy. Cancer stemness induces the expression of neoantigens and neo-properties in CSCs, creating an opportunity for targeted immunotherapies. Isolation of stem-like T cells or retaining stemness in T clonotypes strategies produces exhaustion-resistance T cells with superior re-expansion capacity and long-lasting responses after adoptive cell therapies. Stem cells-derived NK cells may be the next generation of NK cell products for immunotherapy. Here, we have reviewed mechanisms by which stemness factors modulated the immunoediting of the TME and summarized the potentials of CSCs in the development of immunotherapy regimens, including CAR-T cells, CAR-NK cells, cancer vaccines, and monoclonal antibodies. We have discussed the natural or genetically engineered stem-like T cells and stem cell-derived NK cells with increased cytotoxicity to tumor cells. Finally, we have provided a perspective on approaches that may improve the therapeutic efficacy of these novel adoptive cell-based products in targeting immunosuppressive TME.

mTOR regulates T cell exhaustion and PD-1-targeted immunotherapy response during chronic viral infection

T cell exhaustion is a state of T cell dysfunction associated with expression of programmed death 1 (PD-1). Exhausted CD8+ T cells are maintained by self-renewing stem-like T cells that provide differentiated TIM3+ cells, a part of which possesses effector-like properties. PD-1-targeted therapies enhance T cell response by promoting differentiation of stem-like T cells toward TIM3+ cells, but the role of mTOR during T cell exhaustion remains elusive. Here, we showed that mTOR inhibition has distinct outcomes during the beginning of and after the establishment of chronic viral infection. Blocking mTOR during the T cell expansion phase enhanced the T cell response by causing accumulation of stem-like T cells, leading to improved efficacy of PD-1 immunotherapy; whereas, after exhaustion progressed, mTOR inhibition caused immunosuppression, characterized by decreased TIM3+ cells and increased viral load with minimal changes in stem-like T cells. Mechanistically, a cell-intrinsic mTOR signal was vital for differentiation of stem-like T cells into the TIM3+ state in the early and late phases of chronic infection as well as during PD-1 immunotherapy. Thus, PD-1 blockade worked after cessation of mTOR inhibition, but simultaneous treatment failed to induce functional TIM3+ cells, reducing efficacy of PD-1 immunotherapy. Our data demonstrate that mTOR regulates T cell exhaustion and have important implications for combination cancer therapies with PD-1 blockade.