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.

CD4^＋ T-cell dependence of primary CD8^＋ T-cell response against vaccinia virus depends upon route of infection and viral dose

CD4^＋ T-cell help （CD4 help） plays a pivotal role in CD8^＋ T-cell responses against viral infections. However, the role in primary CD8^＋ T-cell responses remains controversial. We evaluated the effects of infection route and viral dose on primary CD8^＋ T-cell responses to vaccinia virus （VACV） in MHC class II^-/- mice. CD4 help deficiency diminished the generation of VACV-specific CD8^＋ T cells after intraperitoneal （i.p.） but not after intranasal （i.n.） infection. A large viral dose could not restore normal expansion of VACV-specific CD8^＋ T cells in i.p. infected MHC II-/- mice. In contrast, dependence on CD4 help was observed in i.n. infected MHC II-/- mice when a small viral dose was used. These data suggested that primary CD8~ T-cell responses are less dependent on CD4 help in i.n. infection compared to i.p. infection. Activated CD8~ T cells produced more I FN-y, TNF-a and granzyme B in i.n. infected mice than those in i.p. infected mice, regardless of CD4 help. IL-2 signaling via CD25 was not necessary to drive expansion of VACV-specific CD8~ T cells in i.n. infection, but it was crucial in i.p. infection. VACV-specific CD8^＋ T cells underwent increased apoptosis in the absence of CD4 help, but proliferated normally and had cytotoxic potential, regardless of infection route. Our results indicate that route of infection and viral dose are two determinants for CD4 help dependence, and intranasal infection induces more potent effector CD8^＋ T cells than i.D. infection.

The IL-1R/TLR signaling pathway is essential for efficient CD8+ T-cell responses against hepatitis B virus in the hydrodynamic injection mouse model

The outcome of hepatitis B viral(HBV)infection is determined by the complex interactions between replicating HBV and the immune system.While the role of the adaptive immune system in the resolution of HBV infection has been studied extensively,the contribution of innate immune mechanisms remains to be defined.Here we examined the role of the interleukin-1 receptor/Toll-like receptor(IL-1R/TLR)signaling pathway in adaptive immune responses and viral clearance by exploring the HBV mouse model.Hydrodynamic injection with a replication-competent HBV genome was performed in wild-type mice(WT)and a panel of mouse strains lacking specific innate immunity component expression.We found higher levels of HBV protein production and replication in Tlr2^(−/−),Tlr23479^(−/−),3d/Tlr24^(−/−),Myd88/Trif^(−/−)and Irak4^(−/−)mice,which was associated with reduced HBV-specific CD8+T-cell responses in these mice.Importantly,HBV clearance was delayed for more than 2 weeks in 3d/Tlr24^(−/−),Myd88/Trif^(−/−)and Irak4^(−/−)mice compared to WT mice.HBV-specific CD8+T-cell responses were functionally impaired for producing the cytokines IFN-γ,TNF-αand IL-2 in TLR signaling-deficient mice compared to WT mice.In conclusion,the IL-1R/TLR signaling pathway might contribute to controlling HBV infection by augmenting HBV-specific CD8+T-cell responses.

Activation or exhaustion of CD8^(+) T cells in patients with COVID-19

In addition to CD4^(+)T cells and neutralizing antibodies,CD8^(+)T cells contribute to protective immune responses against SARS-CoV-2 in patients with coronavirus disease 2019(COVID-19),an ongoing pandemic disease.In patients with COVID-19,CD8^(+)T cells exhibiting activated phenotypes are commonly observed,although the absolute number of CD8^(+)T cells is decreased.In addition,several studies have reported an upregulation of inhibitory immune checkpoint receptors,such as PD-1,and the expression of exhaustion-associated gene signatures in CD8^(+)T cells from patients with COVID-19.However,whether CD8^(+)T cells are truly exhausted during COVID-19 has been a controversial issue.In the present review,we summarize the current understanding of CD8^(+)T-cell exhaustion and describe the available knowledge on the phenotypes and functions of CD8^(+)T cells in the context of activation and exhaustion.We also summarize recent reports regarding phenotypical and functional analyses of SARS-CoV-2-specific CD8^(+)T cells and discuss long-term SARS-CoV-2-specific CD8^(+)T-cell memory.

Crosstalk between IL-15Rα^(+)tumor-associated macrophages and breast cancer cells reduces CD8+T cell recruitment

Background:Interleukin-15(IL-15)is a promising immunotherapeutic agent owing to its powerful immune-activating effects.However,the clinical benefits of these treatments are limited.Crosstalk between tumor cells and immune cells plays an important role in immune escape and immunotherapy drug resistance.Herein,this study aimed to obtain in-depth understanding of crosstalk in the tumor microenvironment for providing potential therapeutic strategies to prevent tumor progression.Methods:T-cell killing assays and co-culture models were developed to determine the role of crosstalk between macrophages and tumor cells in breast cancer resistant to IL-15.Western blotting,histological analysis,CRISPR-Cas9 knockout,multi-parameter flow cytometry,and tumor cell-macrophage co-injection mouse models were developed to examine the mechanism by which IL-15Rα^(+)tumor-associated macrophages(TAMs)regulate breast cancer cell resistance to IL-15.Results:We found thatmacrophages contributed to the resistance of tumor cells to IL-15,and tumor cells induced macrophages to express high levels of theαsubunit of the IL-15 receptor(IL-15Rα).Further investigation showed that IL-15Rα^(+)TAMs reduced the protein levels of chemokine CX3C chemokine ligand 1(CX3CL1)in tumor cells to inhibit the recruitment of CD8^(+)T cells by releasing the IL-15/IL-15Rαcomplex(IL-15Rc).Administration of an IL-15Rc blocking peptide markedly suppressed breast tumor growth and overcame the resistance of cancer cells to anti-programmed cell death protein 1(PD-1)antibody immunotherapy.Interestingly,Granulocyte-macrophage colony-stimulating factor(GMCSF)inducedγchain(γc)expression to promote tumor cell-macrophage crosstalk,which facilitated tumor resistance to IL-15.Additionally,we observed that the non-transcriptional regulatory function of hypoxia inducible factor-1alpha(HIF-1α)was essential for IL-15Rc to regulateCX3CL1 expression in tumor cells.Conclusions:The IL-15Rc-HIF-1α-CX3CL1 signaling pathway serves as a crosstalk between macrophages and tumor cells in the tumormicroenvironment of breast cancer.Targeting this pathway may provide a potential therapeutic strategy for enhancing the efficacy of cancer immunotherapy.

Peripheral Tc17 and Tc17/Interferon-γ Cells are Increased and Associated with Lung Function in Patients with Chronic Obstructive Pulmonary Disease

Background：Chronic obstructive pulmonary disease （COPD） is characterized by progressive loss of lung function and local and systemic inflammation,in which CD8＋ T-cells are believed to play a key role.Activated CD8＋ T-cells differentiate into distinct subpopulations,including interferon-γ（IFN-γ）-producing Tc 1 and interleukin （IL）-17-producing Tc 1 7 cells.Recent evidence indicates that Tc 17 cells exhibit considerable plasticity and may convert into IL-17/IFN-γ-double producing （Tc1 7/IFN-γ） cells when driven by inflammatory conditions.The aim of this study was to investigate the Tc 17/IFN-γ subpopulation in peripheral blood of patients with COPD and to evaluate their potential roles in this disease.Methods：Peripheral blood samples were collected from 15 never-smokers,23 smokers with normal lung function,and 25 patients with COPD （Global Initiative for Chronic Obstructive Lung Disease 2-4）.Proportions of the IL-17/IFN-γ-double expressing subpopulation were assessed using flow cytometry.Plasma concentrations of cytokines favoring Tc 17/IFN-γ differentiation were measured by enzymelinked immunosorbent assay.Results：Patients with COPD had higher proportions of Tc17 cells and Tc17/IFN-γ cells in the peripheral blood than smokers and never-smokers.The plasticity of Tc 17 cells was higher than that of Th 17 cells.The percentages ofTc 17 cells and Tc 17/IFN-γcells showed negative correlations with forced expiratory volume in 1 s % predicted value （r =-0.418,P =0.03;r =-0.596,P =0.002,respectively）.The plasma concentrations of IL-6,transforming growth factor-β1,and IL-12 were significantly higher in patients with COPD compared with smokers and never-smokers.Conclusions：Peripheral Tc17 cells are increased and more likely to convert to Tc17/IFN-γ cells in COPD,suggesting that Tc17 cell plasticity may be involved in persistent inflammation of the disease.