Persistent Antigen and Prolonged AKT-mTORC1 Activation Underlie Memory CD8 T Cell Impairment in the Absence of CD4 T Cells

Phenotypic and Immunometabolic Aspects on Stem Cell Memory and Resident Memory CD8+ T Cells

The immune system, smartly and surprisingly, saves the exposure of a particular pathogen in its memory and reacts to the pathogen very rapidly, preventing serious diseases.

Immunologists have long been fascinated by understanding the ability to recall and respond faster and more vigorously to a pathogen, known as “memory”.

T-cell populations can be better described by using more sophisticated techniques to define phenotype, transcriptional and epigenetic signatures and metabolic pathways (single-cell resolution), which uncovered the heterogeneity of the memory T-compartment. Phenotype, effector functions, maintenance, and metabolic pathways help identify these different subsets. Here, we examine recent developments in the characterization of the heterogeneity of the memory T cell compartment. In particular, we focus on the emerging role of CD8+ TRM and TSCM cells, providing evidence on how their immunometabolism or modulation can play a vital role in their generation and maintenance in chronic conditions such as infections or autoimmune diseases.

MicroRNA-7 overexpression positively regulates the CD8+ SP cell development via targeting PIK3R1

microRNA-7 (miR-7), a distinct miRNA family member, has been reported to be involved in the biological functions of immune cells. However, the potential role of miR-7 in the CD8⁺ T cell development remains to be elucidated. In this study, we estimated the potential effects of miR-7 overexpression in the thymic CD8⁺ SP cell development using miR-7 overexpression mice. Our results showed that compared with those in control wild type (WT) mice, the volume, weight and total cell numbers of thymus in miR-7 overexpression (OE) mice increased significantly. The absolute cell number of CD8⁺ SP cells in miR-7 OE mice increased and its ability of activation and proliferation enhanced. Futhermore, we clarified that miR-7 overexpression had an intrinsic promote role in CD8⁺ SP cell development by adoptive cell transfer assay. Mechanistically, the expression level of PIK3R1, a target of miR-7, decreased significantly in CD8⁺ SP cells of miR-7 OE mice. Moreover, the expression level of phosphorylated (p)-AKT and p-ERK changed inversely and indicating that miR-7 overexpression impaired the balance of AKE and ERK pathways. In summary, our work reveals an essential role of miR-7 in promoting CD8⁺ SP cell development through the regulation of PIK3R1 and balance of AKT and ERK pathways.

Emerging role of Tissue Resident Memory T cells in vitiligo: From pathogenesis to therapeutics

Vitiligo is an acquired depigmenting disorder which affects both skin and mucous membranes and autoimmunity has been strongly suggested to play a role in loss of melanocytes. The recurrence of skin macules at the same sites where they were observed prior to the treatment, suggests the existence of Tissue Resident Memory T cells (TRMs) that persist within the skin or peripheral tissues with a longer survivability. Emerging studies have shown that reactivation of these skin TRMs results into autoreactive TRM cells in various autoimmune diseases including vitiligo. This review focuses on different subsets (CD8⁺ TRMs and CD4⁺ TRMs) of TRM cells, their retention and survivability in the skin along with their pathomechanisms leading to melanocyte death and progression of vitiligo. In addition, the review describes the TRM cells as potential targets for developing effective therapeutics of vitiligo.

Helpless Priming Sends CD8+ T Cells on the Road to Exhaustion

Persistent antigen exposure in chronic infection and cancer has been proposed to lead to cytotoxic T lymphocyte (CTL) “exhaustion”, i.e., loss of effector function and disease control. Recent work identifies a population of poorly differentiated TCF-1⁺PD-1⁺ CD8⁺ T cells as precursors of the terminally exhausted CTL pool. These “predysfunctional” CTLs are suggested to respond to PD-1 targeted therapy by giving rise to a pool of functional CTLs. Supported by gene expression analyses, we present a model in which lack of CD4⁺ T cell help during CD8⁺ T cell priming results in the formation of predysfunctional CTLs. Our model implies that predysfunctional CTLs are formed during priming and that the remedy for CTL dysfunction is to provide “help” signals for generation of optimal CTL effectors. We substantiate that this may be achieved by engaging CD4⁺ T cells in new CD8⁺ T cell priming, or by combined PD-1 blocking and CD27 agonism with available immunotherapeutic antibodies.

Multifunctional oncolytic nanoparticles deliver self-replicating IL-12 RNA to eliminate established tumors and prime systemic immunity

Therapies that synergistically stimulate immunogenic cancer cell death (ICD), inflammation, and immune priming are of great interest for cancer immunotherapy. However, even multi-agent therapies often fail to trigger all of the steps necessary for self-sustaining anti-tumor immunity. Here we describe self-replicating RNAs encapsulated in lipid nanoparticles (LNP-replicons), which combine three key elements: (1) an LNP composition that potently promotes ICD, (2) RNA that stimulates danger sensors in transfected cells, and (3) RNA-encoded IL-12 for modulation of immune cells. Intratumoral administration of LNP-replicons led to high-level expression of IL-12, stimulation of a type I interferon response, and cancer cell ICD, resulting in a highly inflamed tumor microenvironment and priming of systemic anti-tumor immunity. In several mouse models of cancer, a single intratumoral injection of replicon-LNPs eradicated large established tumors, induced protective immune memory, and enabled regression of distal uninjected tumors. LNP-replicons are thus a promising multifunctional single-agent immunotherapeutic.

Self-assembled cGAMP-STINGΔTM signaling complex as a bioinspired platform for cGAMP delivery

The stimulator of interferon (IFN) genes (STING) pathway constitutes a highly important part of immune responses against various cancers and infections. Consequently, administration of STING agonists such as cyclic GMP-AMP (cGAMP) has been identified as a promising approach to target these diseases. In cancer cells, STING signaling is frequently impaired by epigenetic silencing of STING; hence, conventional delivery of only its agonist cGAMP may be insufficient to trigger STING signaling. In this work, while expression of STING lacking the transmembrane (TM) domain is known to be unresponsive to STING agonists and is dominant negative when coexpressed with the full-length STING inside cells, we observed that the recombinant TM-deficient STING protein complexed with cGAMP could effectively trigger STING signaling when delivered in vitro and in vivo, including in STING-deficient cell lines. Thus, this bioinspired method using TM-deficient STING may present a universally applicable platform for cGAMP delivery.

Vaccine-Induced Adverse Effects in Cultured Neuroblastoma 2A (N2A) Cells Duplicate Toxicity of Serum from Patients with Gulf War Illness (GWI) and Are Prevented in the Presence of Specific Anti-Vaccine Antibodies

Gulf War illness (GWI) is a chronic disease of unknown etiology affecting over 200,000 veterans with symptoms including neurocognitive problems. We previously demonstrated GWI serum toxicity on neural cell cultures manifested by compromised neural network function, decreased cell spreading, and enhanced cell apoptosis. These patients lacked six human leukocyte antigen (HLA) class II alleles, resulting in an inability to form antibodies. Therefore, we hypothesized that GWI patients have vaccine-derived, persistent pathogens, which contribute to the development of the disease. Here, we examined whether individual vaccines were toxic in cultured N2A cells. Moreover, we used antibodies against each of the 20 vaccines administered to Gulf War (GW) veterans, to examine the effects of these antibodies on cell spreading and apoptosis in N2A cells. Antibodies against cholera toxin, hepatitis B, hemagglutinin H1N1, H3N2, and B from influenza A and B strains, measles, and Salmonella Typhi polysaccharide Vi had a remarkable protective effect on both cell spreading and apoptosis, whereas none of the other antibodies administered to GW veterans had an effect. The in vitro observed adverse effects of GWI serum may be due in part to vaccine-derived pathogens, antibodies against which had a protective effect in N2A cell cultures.

iCa2+ Flux, ROS and IL-10 Determines Cytotoxic, and Suppressor T Cell Functions in Chronic Human Viral Infections

Exhaustion of CD8⁺ T cells and increased IL-10 production is well-known in chronic viral infections but mechanisms leading to loss of their cytotoxic capabilities and consequent exhaustion remain unclear. Exhausted CD8⁺T cells also called T suppressors are highly immune suppressive with altered T cell receptor signaling characteristics that mark it exclusively from their cytotoxic counterparts. Our study found that iCa²⁺ flux is reduced following T cell receptor activation in T suppressor cells when compared to their effector counterpart. Importantly chronic activation of murine cytotoxic CD8⁺ T cells lead to reduced iCa²⁺ influx, decreased IFN-γ and enhanced IL-10 production and this profile is mimicked in Tc1 cells upon reduction of iCa²⁺ flux by extracellular calcium channel inhibitors. Further reduced iCa²⁺ flux induced ROS which lead to IFN-γ reduction and increased IL-10 producing T suppressors through the STAT3—STAT5 axis. The above findings were substantiated by our human data where reduced iCa²⁺ flux in chronic Hepatitis infections displayed CD8⁺ T cells with low IFN-γ and increased IL-10 production. Importantly treatment with an antioxidant led to increased IFN-γ and reduced IL-10 production in human chronic Hep-B/C samples suggesting overall a proximal regulatory role for iCa²⁺ influx, ROS, and IL-10 in determining the effector/ suppressive axis of CD8⁺ T cells.

Tissue-resident memory T cells and their biological characteristics in the recurrence of inflammatory skin disorders

The skin is the largest organ of the body. The establishment of immunological memory in the skin is a crucial component of the adaptive immune response. Once naive T cells are activated by antigen-presenting cells, a small fraction of them differentiate into precursor memory T cells. These precursor cells ultimately develop into several subsets of memory T cells, including central memory T (T_CM) cells, effector memory T (T_EM) cells, and tissue resident memory T (T_RM) cells. T_RM cells have a unique transcriptional profile, and their most striking characteristics are their long-term survival (longevity) and low migration in peripheral tissues, including the skin. Under physiological conditions, T_RM cells that reside in the skin can respond rapidly to pathogenic challenges. However, there is emerging evidence to support the vital role of T_RM cells in the recurrence of chronic inflammatory skin disorders, including psoriasis, vitiligo, and fixed drug eruption, under pathological or uncontrolled conditions. Clarifying and characterizing the mechanisms that are involved in skin T_RM cells will help provide promising strategies for reducing the frequency and magnitude of skin inflammation recurrence. Here, we discuss recent insights into the generation, homing, retention, and survival of T_RM cells and share our perspectives on the biological characteristics of T_RM cells in the recurrence of inflammatory skin disorders.

Differential Kinase Activation in Peripheral Blood Mononuclear Cells from Non-Small-Cell Lung Cancer Patients Treated with Nivolumab

In the era of precision medicine, research of biomarkers for identification of responders to nivolumab therapy is a major challenge. Peripheral blood mononuclear cells (PBMC) could be an interesting surrogate tissue for identifying pharmacodynamic biomarkers. The aim of this exploratory study was to investigate the global serine/threonine kinase (STK) activity in PBMC from non-small-cell lung cancer (NSCLC) patients using a high throughput kinomic profiling method. PamChip^® microarrays were used to explore the STK kinomic profile in PBMC from 28 NSCLC patients before nivolumab initiation (D0) and on day 14 (D14) of the first administration. Two clusters of patients (A and B) were identified at D0, median overall survival (OS) tended to be longer in cluster A than in B (402 vs. 112.5 days, respectively; p = 0.15). Interestingly, the PD-L1 tumor cell score (p = 0.045), the count of CD8+ cells (p = 0.023) and the total body weight (p = 0.038) were statistically different between the clusters. On D14, clusters C and D were identified. Greater activity of most STK, especially those of the PI3K/Akt signaling pathway, was noticed among cluster C. No significant difference between C and D was observed regarding OS. Considering the small number of patients, results from this preliminary study are not conclusive. However, the 4-fold longer median OS in cluster A paves the way to further investigate, in a larger cohort of NSCLC patients, the benefit of basal STK kinomic profile in PBMC to identify responders to nivolumab therapy.

In vitro evolution of enhanced RNA replicons for immunotherapy

Self-replicating (replicon) RNA is a promising new platform for gene therapy, but applications are still limited by short persistence of expression in most cell types and low levels of transgene expression in vivo. To address these shortcomings, we developed an in vitro evolution strategy and identified six mutations in nonstructural proteins (nsPs) of Venezuelan equine encephalitis (VEE) replicon that promoted subgenome expression in cells. Two mutations in nsP2 and nsP3 enhanced transgene expression, while three mutations in nsP3 regulated this expression. Replicons containing the most effective mutation combinations showed enhanced duration and cargo gene expression in vivo. In comparison to wildtype replicon, mutants expressing IL-2 injected into murine B16F10 melanoma showed 5.5-fold increase in intratumoral IL-2 and 2.1-fold increase in infiltrating CD8 T cells, resulting in significantly slowed tumor growth. Thus, these mutant replicons may be useful for improving RNA therapeutics for vaccination, cancer immunotherapy, and gene therapy.

The spectrum of T cell metabolism in health and disease

In healthy individuals, metabolically quiescent T cells survey lymph nodes and peripheral tissues in search of cognate antigens. During infection, T cells that encounter cognate antigens are activated and - in a context-specific manner - proliferate and/or differentiate to become effector T cells. This process is accompanied by important changes in cellular metabolism (known as metabolic reprogramming). The magnitude and spectrum of metabolic reprogramming as it occurs in T cells in the context of acute infection ensure host survival. By contrast, altered T cell metabolism, and hence function, is also observed in various disease states, in which T cells actively contribute to pathology. In this Review, we introduce the idea that the spectrum of immune cell metabolic states can provide a basis for categorizing human diseases. Specifically, we first summarize the metabolic and interlinked signalling requirements of T cells responding to acute infection. We then discuss how metabolic reprogramming of T cells is linked to disease.