The Mechanisms of CD8+ T Cells Exhaustion in the Tumor Microenvironment and Immune Therapy

In the tumor immune microenvironment, CD8+ T cells differentiate towards functional failure. The exhaustion of CD8+ T cells (Tex) showed varying degrees of effect dysfunction, loss of proliferation ability, and sustained high expression of a variety of inhibitory receptors, with metabolic and epigenetic changes. Tex cells are heterogeneous, including several subsets with different characteristics at different stages of differentiation. Immune checkpoint inhibitors (ICIs) can restore the effect or function of Tex cells, indicating that this T cell subset plays a key role in tumor immunotherapy. The understanding of the mechanism of CD8+ T cell exhaustion will be helpful to the implementation of tumor immunotherapy. This article reviews the production, differentiation and functional characteristics of Tex cells and their relationship with tumor immunotherapy.

Increased circulating level of interleukin-6 and CD8+T cell exhaustion are associated with progression of COVID-19

Background: Coronavirus disease 2019(COVID-19)is pandemic.It is critical to identify COVID-19 patients who are most likely to develop a severe disease.This study was designed to determine the clinical and epidemiological features of COVID-19 patients associated with the development of pneumonia and factors associated with disease progression.Methods:: Seventy consecutive patients with etiologically confirmed COVID-19 admitted to PLA General Hospital in Beijing,China from December 27,2019 to March 12,2020 were enrolled in this study and followed-up to March 16,2020.Differences in clinical and laboratory findings between COVID-19 patients with pneumonia and those without were determined by theχ2 test or the Fisher exact test(categorical variables)and independent group t test or Mann–Whitney U test(continuous variables).The Cox proportional hazard model and Generalized Estimating Equations were applied to evaluate factors that predicted the progression of COVID-19.Results: The mean incubation was 8.67(95%confidence interval,6.78–10.56)days.Mean duration from the first test severe acute respiratory syndrome coronavirus 2-positive to conversion was 11.38(9.86–12.90)days.Compared to pneumonia-free patients,pneumonia patients were 16.5 years older and had higher frequencies of having hypertension,fever,and cough and higher circulating levels of neutrophil proportion,interleukin-6,low count(<190/µl)of CD8+T cells,and neutrophil/lymphocyte ratio.Thirteen patients deteriorated during hospitalization.Cox regression analysis indicated that older age and higher serum levels of interleukin-6,C-reactive protein,procalcitonin,and lactate at admission significantly predicted the progression of COVID-19.During hospitalization,circulating counts of T lymphocytes,CD4+T cells,and CD8+T cells were lower,whereas neutrophil proportion,neutrophil/lymphocyte ratio,and the circulating levels of interleukin-6,C-reactive protein,and procalcitonin were higher,in pneumonia patients than in pneumonia-free patients.CD8+lymphocyte count in pneumonia patients did not recover when discharged.Conclusions: Older age and higher levels of C-reactive protein,procalcitionin,interleukin-6,and lactate might predict COVID-19 progression.T lymphocyte,especially CD8+cell-mediated immunity is critical in recovery of COVID-19.This study may help in predicting disease progression and designing immunotherapy for COVID-19.

Exhausted T cells and epigenetic status

Exhausted T cells are a group of dysfunctional T cells,which are present in chronic infections or tumors.The most significant characteristics of exhausted T cells are attenuated effector cytotoxicity,reduced cytokine production,and upregulation of multiple inhibitory molecular receptors(e.g.,PD-1,TIM-3,and LAG-3).The intracellular metabolic changes,altered expression of transcription factors,and a unique epigenetic landscape constitute the exhaustion program.Recently,researchers have made progress in understanding exhausted T cells,with the definition and identification of exhausted T cells changing from phenotypebased to being classified at the transcriptional and epigenetic levels.Recent studies have revealed that exhausted T cells can be separated into two subgroups,namely TCF1^(+)PD-1^(+)progenitor-like precursor exhausted cells and TCF1-PD-1^(+)terminally differentiated exhausted T cells.Moreover,the progenitor-like precursor cell population may be a subset of T cells that can respond to immunotherapy.Studies have also found that TOX initiates and dominates the development of exhausted T cells at the transcriptional and epigenetic levels.TOX also maintains T cell survival and may affect decisions regarding treatment strategies.In this review,we discuss the latest developments in T cell exhaustion in regards to definitions,subpopulations,development mechanisms,differences in diverse diseases,and treatment prospects for exhausted T cells.Furthermore,we hypothesize that the epigenetic state regulated by TOX might be the key point,which can determine the reversibility of exhaustion and the efficacy of immunotherapy.

Higher PD-1 expression concurrent with exhausted CD8+ T cells in patients with de novo acute myeloid leukemia

Objective： To investigate the association between the T cell inhibitory receptor programmed death 1（PD-1）and T cell exhaustion status in T cells from patients with de novo acute myeloid leukemia（AML） and AML in complete remission（CR）.Methods：Surface expression of PD-1 and the exhaustion and immunosenescence markers CD244 and CD57 on CD3＋,CD4＋ and CD8＋ T cells from peripheral blood samples from 20 newly diagnosed,untreated AML patients and 10 cases with AML in CR was analyzed by flow cytometry.Twenty-three healthy individuals served as control.Results：A significantly higher percentage of PD-1＋ cells were found for CD3＋ T cells in the de novo AML group compared with healthy controls.In addition,an increased level of PD-1＋ CD8＋ T cells,but not PD-1＋ CD4＋,was found for CD3＋ T cells in the de novo AML and AML-CR samples.A higher percentage of CD244＋ CD4＋,CD244＋ CD8＋,CD57＋ CD4＋ and CD57＋ CD8＋ T cells was found in CD3＋ T cells in samples from those with de novo AML compared with those from healthy controls.Strong increased PD-1＋ CD244＋ and PD-1＋ CD57＋ coexpression was found for CD4＋ and CD8＋ T cells in the de novo AML group compared with healthy controls.Conclusions：We characterized the major T cell defects,including co-expression of PD-1 and CD244,CD57-exhausted T cells in patients with de novo AML,and found a particular influence on CD8＋ T cells,suggesting a poor anti-leukemia immune response in these patients.

T cells in pancreatic cancer stroma

Pancreatic ductal adenocarcinoma(PDAC)is a highly devastating disease with a dismal 5-year survival rate.PDAC has a complex tumour microenvironment;characterised by a robust desmoplastic stroma,extensive infiltration of immunesuppressive cells such as immature myeloid cells,tumour-associated macrophages,neutrophils and regulatory T cells,and the presence of exhausted and senescent T cells.The cross-talk between cells in this fibrotic tumour establishes an immune-privileged microenvironment that supports tumour cell escape from immune-surveillance,disease progression and spread to distant organs.PDAC tumours,considered to be non-immunogenic or cold,express low mutation burden,low infiltration of CD8+cytotoxic lymphocytes that are localised along the invasive margin of the tumour border in the surrounding fibrotic tissue,and often display an exhausted phenotype.Here,we review the role of T cells in pancreatic cancer,examine the complex interactions of these crucial effector units within pancreatic cancer stroma and shed light on the increasingly attractive use of T cells as therapy.

Predictive value of co-expression patterns of immune checkpoint molecules for clinical outcomes of hematological malignancies

Co-expression of immune checkpoint(IC)molecules can exacerbate T cell exhaustion in patients with hematological malignancies(HMs)and contribute to the immune escape of tumor cells,which is related to poor clinical outcome.It is worth establishing and optimizing an ideal prediction model based on the co-expression patterns of IC molecules to evaluate the immune status of HM patients and predict their clinical outcome.In this perspective,we summarize the co-expression patterns of IC molecules and their importance as biomarkers that predict the prognosis of patients with different HMs,providing new insights for designing dual IC blockades(ICBs).

Immunomodulatory Function of Pien Tze Huang in T Cell-Mediated Anti-tumor Activity against B16-F10,MC38 and Hep1-6 Tumor Models

Objective To investigate the anti-tumor effects of Pien Tze Huang(PZH)in mouse models of B16–F10 melanoma,MC38 colorectal cancer,Hep1-6 hepatocellular carcinoma and chemically induced hepatocellular carcinoma model.Methods Various tumor models,including B16–F10,MC38 and Hep1-6 tumor hypodermic inoculation models,B16–F10 and Hep1-6 pulmonary metastasis models,Hep1-6 orthotopic implantation model,and chemically induced hepatocellular carcinoma model,were utilized to evaluate the anti-tumor function of PZH.Tumor growth was assessed by measuring tumor size and weight of solid tumors isolated from C57BL/6 mice.For cell proliferation and death of tumor cells in vitro,as well as T cell activation markers,cytokine production and immune checkpoints analysis,single-cell suspensions were prepared from mouse spleen,lymph nodes,and tumors after PZH treatment.Results PZH demonstrated significant therapeutic efficacy in inhibiting tumor growth(P<0.01).Treatment with PZH resulted in a reduction in tumor size in subcutaneous MC38 colon adenocarcinoma and B16–F10 melanoma models,and decreased pulmonary metastasis of B16–F10 melanoma and Hep1-6 hepatoma(P<0.01).However,in vitro experiments showed that PZH only had slight impact on the cell proliferation and survival of tumor cells(P>0.05).Nevertheless,PZH exhibited a remarkable ability to enhance T cell activation and the production of interferon gamma,tumor necrosis factor alpha,and interleukin 2 in CD4^(+)T cells in vitro(P<0.01 or P<0.05).Importantly,PZH substantially inhibited T cell exhaustion and boosted cytokine production by tumor-infiltrating CD8^(+)T cells(P<0.01 or P<0.05).Conclusion This study has confirmed a novel immunomodulatory function of PZH in T cell-mediated anti-tumor immunity,indicating that PZH holds promise as a potential therapeutic agent for cancer treatment.

Cancer immunotherapy with envelopedself-amplifying mRNA CARG-2020 thatmodulates IL-12,IL-17 and PD-L1 pathways toprevent tumor recurrence

Targeting multiple immune mechanisms may overcome therapy resistance and further improve cancer immunotherapy for humans.Here,we describe the application of virus-like vesicles(VLV)for delivery of three immunomodulators alone and in combination,as a promising approach for cancer immunotherapy.VLV vectors were designed to deliver single chain interleukin(IL)-12,shorthairpin RNA(shRNA)targeting programmed death ligand 1(PD-L1),and a dominant-negative form of IL-17 receptor A(dn-IL17RA)as a single payload or as a combination payload.Intralesional delivery of the VLV vector expressing IL-12 alone,as well as the trivalent vector(designated CARG-2020)eradicated large established tumors.However,only CARG-2020 prevented tumor recurrence and provided long-term survival benefit to the tumor-bearing mice,indicating a benefit of the combined immunomodulation.The abscopal effects of CARG-2020 on the non-injected contralateral tumors,as well as protection from the tumor cell re-challenge,suggest immune-mediated mechanism of protection and establishment of immunological memory.Mechanistically,CARG-2020 potently activates Th1 immune mechanisms and inhibits expression of genes related to T cell exhaustion and cancer-promoting inflammation.The ability of CARG-2020 to prevent tumor recurrence and to provide survival benefit makes it a promising candidate for its development for human cancer immunotherapy.

Ectopic Tcf1 expression instills a stem-like program in exhausted CD8^(+) T cells to enhance viral and tumor immunity

Exhausted CD8^(+)T(Tex)cells are dysfunctional due to persistent antigen exposure in chronic viral infection and tumor contexts.A stem cell-like Tex(Tex-stem)subset can self-renew and differentiate into terminally exhausted(Tex-term)cells.Here,we show that ectopic Tcf1 expression potently promoted the generation of Tex-stem cells in both a chronic viral infection and preclinical tumor models.Tcf1 overexpression diminished coinhibitory receptor expression and enhanced polycytokine-producing capacity while retaining a heightened responses to checkpoint blockade,leading to enhanced viral and tumor control.Mechanistically,ectopically expressed Tcf1 exploited existing and novel chromatin accessible sites as transcriptional enhancers or repressors and modulated the transcriptome by enforcing pre-existing expression patterns in Tex-stem cells,such as enhanced suppression of Blimp1 and Bim and acquisition of new downstream genes,including Mx1,Tox2,and Runx3.These findings reveal a pronounced impact of ectopic Tcf1 expression on Tex functional restoration and highlight the therapeutic potential of harnessing Tcf1-enforced transcriptional programs.

Efficient control of chronic LCMV infection by a CD4 T cell epitope-based heterologous prime-boost vaccination in a murine model

CD4^(+)T cells are essential for sustaining CD8^(+)T cell responses during a chronic infection.The adoptive transfer of virus-specific CD4^(+)T cells has been shown to efficiently rescue exhausted CD8^(+)T cells.However,the question of whether endogenous virus-specific CD4^(+)T cell responses can be enhanced by certain vaccination strategies and subsequently reinvigorate exhausted CD8^(+)T cells remains unexplored.In this study,we developed a CD4^(+)T cell epitope-based heterologous prime-boost immunization strategy and examined the efficacy of this strategy using a mouse model of chronic lymphocytic choriomeningitis virus(LCMV)infection.We primed chronically LCMV-infected mice with a Listeria monocytogenes vector that expressed the LCMV glycoprotein-specific I-Ab-restricted CD4^(+)T cell epitope GP61–80(LM-GP61)and subsequently boosted the primed mice with an influenza virus A(PR8 strain)vector that expressed the same CD4^(+)T cell epitope(IAV-GP61).This heterologous prime-boost vaccination strategy elicited strong anti-viral CD4^(+)T cell responses,which further improved both the quantity and quality of the virusspecific CD8^(+)T cells and led to better control of the viral loads.The combination of this strategy and the blockade of the programmed cell death-1(PD-1)inhibitory pathway further enhanced the anti-viral CD8^(+)T cell responses and viral clearance.Thus,a heterologous prime-boost immunization that selectively induces virus-specific CD4^(+)T cell responses in conjunction with blockade of the inhibitory pathway may represent a promising therapeutic approach to treating patients with chronic viral infections.