Memory Phenotype CD8 Research Articles

Abstract 1030: Zeb2 Regulates Senescence And Cytotoxic Phenotype In Atherosclerotic Plaque CD8 T Cells

Circulating senescent CD8 + CD57 + T cells have been implicated in reduced post-myocardial infarction survival and impaired glucose homeostasis in type 2 diabetes (T2D) patients. Despite these associations, their specific role in human atherosclerotic plaques, particularly in the context of aggravated plaque pathology in T2D remains unknown. In this study, we analyzed single-cell transcriptomic data from 75,049 immune cells obtained from plaques from 12 T2D and 10 no diabetes patients enrolled in the ATHERO-IN study. We identified 14 clusters of CD8 + T cells clusters, revealing distinct subsets such cytotoxic CD8 + T cells with a terminally differentiated effector memory phenotype, cytotoxic/exhausted, naïve/CM and regulatory CD8 + T cells. These clusters expressed varying degrees of senescent genes, with a notable heightened senescent transcriptional signature in T2D patients. Fibrocalcific plaques, which were prevalent in T2D patients, showed significantly enrichment in cytotoxic, inflammatory, naïve/CM, and interferon response CD8 T cell clusters. In contrast, fibroatheroma samples were predominantly enriched in MAIT-like CD8 T cells and cytotoxic/exhausted clusters. Aged CD8 T cells expanded in T2D patients exhibited elevated senescence and cytotoxic score, manifested a senescence-associated secretory phenotype expressing cytotoxic, pro-inflammatory and proatherogenic genes. Trajectory analysis and regulatory network analysis, highlighted ZEB2— a GWAS gene associated to coronary artery disease and myocardial infarction— as a potential transcription factor driving the senescence phenotype. CRISPR-based studies corroborated this, demonstrating that ZEB2 KO CD8 T cells reduced senescence, cytotoxicity, and activation markers, underscoring the pivotal role of ZEB2 in driving the terminal differentiation and aging phenotype. In conclusion, our findings shed light on the intricate interplay between senescent CD8+ T cells and atherosclerotic plaque pathology in the context of T2D. The identification of ZEB2 as a key regulator of T cell senescence offers a potential target for therapeutic interventions aimed at mitigating the senescence-associated effects on plaque pathology and cardiovascular outcomes in T2D patients.

Unveiling the immune responses of ferrets inoculated with Ebola virus

Abstract Animal-based models continue to be important for investigating the immunological pathways involved with infections of emerging infectious diseases. Inoculation of Ebola virus (EBOV) in ferrets results in nearly uniformly fatal disease while also recapitulating numerous additional aspects associated with EBOV infection of nonhuman primates or humans. However, the underlying immune responses of EBOV-associated disease in ferrets is largely unknown due to a lack of available reagents. Thus, we designed and optimized a 10-color flow cytometry panel to investigate the adaptive and innate immune components of ferrets. Animals were inoculated with EBOV or mock virus, and circulating immune responses in whole blood were longitudinally examined by flow cytometry. Appreciable alterations in both the innate and adaptive immune responses during late-stage disease were observed. Animals were euthanized at 3 or 6-d post-exposure, and terminal tissues were examined. As expected, marked increases in the number and frequency of apoptotic and necrotic cells were noted. Interestingly, a significant loss of memory phenotype CD8+ T cells and activated CD11b+ cells was associated with advanced disease. In plasma, elevated circulating protein levels of multiple cytokines, commonly associated with EBOV infection, were found in a stepwise manner. Altogether, these tools add significant illumination of underlying immune responses in the ferret model.

IL-7-primed bystander CD8 tumor-infiltrating lymphocytes optimize the antitumor efficacy of T cell engager immunotherapy

Bispecific Tcell engagers (TCEs) show promising clinical efficacy in blood tumors, but their application to solid tumors remains challenging. Here, we show that Fc-fused IL-7 (rhIL-7-hyFc) changes the intratumoral CD8 Tcell landscape, enhancing the efficacy of TCE immunotherapy. rhIL-7-hyFc induces a dramatic increase in CD8 tumor-infiltrating lymphocytes (TILs) in various solid tumors, but the majority of these cells are PD-1-negative tumor non-responsive bystander Tcells. However, they are non-exhausted and central memory-phenotype CD8 Tcells with high Tcell receptor (TCR)-recall capacity that can be triggered by tumor antigen-specific TCEs to acquire tumoricidal activity. Single-cell transcriptome analysis reveals that rhIL-7-hyFc-induced bystander CD8 TILs transform into cycling transitional Tcells by TCE redirection with decreased memory markers and increased cytotoxic molecules. Notably, TCE treatment has no major effect on tumor-reactive CD8 TILs. Our results suggest that rhIL-7-hyFc treatment promotes the antitumor efficacy of TCE immunotherapy by increasing TCE-sensitive bystander CD8 TILs in solid tumors.

Regulatory T cells tonically inhibit spontaneous activation of naturally arising memory-phenotype CD4+ T lymphocytes

Abstract Foxp3- CD4+ T lymphocytes consist of naïve (CD44lo), foreign antigen-specific memory, and self antigen-driven memory-phenotype (MP; both CD44hi) cells at homeostasis. We recently showed that self-reactive MP cells spontaneously proliferate and differentiate into the T-bet+ subset. How excess proliferation and Th1 differentiation of MP cells are inhibited in steady state remains unclear. Regulatory T cells (Tregs) can inhibit several immune responses, posing a possibility that the same lymphocytes may suppress spontaneous MP cell activation. Here we show using Foxp3-diphtheria toxin receptor-transgenic mice that both preexisting MP and naïve CD4+ T cells spontaneously proliferate and differentiate into Th1 cells upon Treg depletion. MP as compared to naïve CD4+ T cells more rapidly proliferate and differentiate three to five days post Treg depletion whereas these responses are mainly attributed to by the latter T cells at a later time point. Moreover, we demonstrate that these early MP proliferation and differentiation are driven in a manner dependent on CD28 and IL-2 signals, respectively. Furthermore, our data suggest that such activation of MP and naïve CD4+ T cells contribute to development of multi-organ inflammation at early and later time points, respectively. Together our results argue that Tregs tonically inhibit early, spontaneous proliferation and Th1 differentiation of MP CD4+ T lymphocytes, thereby contributing to maintenance of T cell homeostasis.

Excess generation and activation of naturally arising memory-phenotype CD4+ T lymphocytes are inhibited by regulatory T cells in steady state.

Conventional CD4+ T lymphocytes consist of naïve, foreign antigen-specific memory, and self-antigen-driven memory-phenotype (MP) cell compartments at homeostasis. We recently showed that MP cells tonically proliferate in response to self-antigens and differentiate into the T-bet+ subset in steady state. How excess proliferation and differentiation of MP cells are inhibited remains unclear. Given immunosuppressive function of regulatory T cells (Tregs), it is possible that they are also involved in inhibition of spontaneous MP cell activation. Here we show using Foxp3-diphtheria toxin receptor-transgenic mice that both MP and naïve CD4+ T cells spontaneously proliferate and differentiate into Th1 cells upon acute Treg depletion. At an early time point post Treg depletion, MP as compared to naïve CD4+ T cells are preferentially activated while at a later stage, the response is dominated by activated cells originated from the naïve pool. Moreover, we argue that MP cell proliferation is driven by TCR and CD28 signaling whereas Th1 differentiation mediated by IL-2. Furthermore, our data indicate that such activation of MP and naïve CD4+ T lymphocytes contribute to development of multi-organ inflammation at early and later time points, respectively, after Treg ablation. Together our findings reveal that Tregs tonically inhibit early, spontaneous proliferation and Th1 differentiation of MP CD4+ T lymphocytes as well as late activation of naïve cells, thereby contributing to maintenance of T cell homeostasis.

Homeostatic cytokines reciprocally modulate the emergence of prenatal effector PLZF+CD4+ T cells in humans.

The development of human prenatal adaptive immunity progresses faster than previously appreciated, with the emergence of memory CD4+ T cells alongside regulatory T cells by midgestation. We previously identified a prenatal specific population of promyelocytic leukemia zinc finger-positive (PLZF+) CD4+ T cells with heightened effector potential that were enriched in the developing intestine and accumulated in the cord blood of infants exposed to prenatal inflammation. However, the signals that drive their tissue distribution and effector maturation are unknown. Here, we define the transcriptional and functional heterogeneity of human prenatal PLZF+CD4+ T cells and identify the compartmentalization of T helper-like (Th-like) effector function across the small intestine (SI) and mesenteric lymph nodes (MLNs). IL-7 was more abundant in the SI relative to the MLNs and drove the preferential expansion of naive PLZF+CD4+ T cells via enhanced STAT5 and MEK/ERK signaling. Exposure to IL-7 was sufficient to induce the acquisition of CD45RO expression and rapid effector function in a subset of PLZF+CD4+ T cells, identifying a human analog of memory phenotype CD4+ T cells. Further, IL-7 modulated the differentiation of Th1- and Th17-like PLZF+CD4+ T cells and thus likely contributes to the anatomic compartmentalization of human prenatal CD4+ T cell effector function.

Inhibition of TCR-MHC-II interactions abrogates Treg-mediated immune suppression and augments anti-tumor immunity.

Abstract CD4 +Foxp3 +Tregs play a non-redundant role in controlling autoimmunity. Continuous TCR signaling and the availability of exogenous IL-2 from CD4 +effectors regulate the size of the Treg pool and their suppressive function in the steady state. Homeostatic proliferation of Tregs and memory phenotype (MP) CD4 +Foxp3 −T cells depends on CD80/CD86-CD28 signaling. Acute blockade of TCR-MHC-II interactions in vivo by anti-MHC-II mAb significantly enhances memory phenotype (MP) Treg, CD4 +, and CD8 +T cell expansion by a CD28-dependent pathway. IL-15 trans presentation by APC also contributes to Treg, MP CD4 +and MP CD8 +proliferation following blockade of TCR-MHC-II interaction by a CD122-dependent pathway. Combined CD28 activation and IL-15 stimulation together with IL-2 deprivation secondary to MHCII-TCR blockade result in decreased expression of CD25, but enhancement of Foxp3 expression by Treg. In addition, Treg exhibit decreased pAKT/NFAT signaling, but enhanced pSTAT5/mTOR signaling. Mice transplanted with several different transplantable tumors manifest enhanced tumor immunity in the presence of MHCII-TCR inhibition. Our results demonstrate that in the absence of TCR-MHC-II interactions, Treg proliferate, but lose their identity and manifest disabled suppressor function resulting in enhanced innate and adaptive immunity against cancer progression. This work was supported by the Intramural Research Program of NIAID, NIH. This work was supported by the Intramural Research Program of NIAID, NIH.

Steady-state memory-phenotype conventional CD4+ T cells exacerbate autoimmune neuroinflammation in a bystander manner via the Bhlhe40/GM-CSF axis

Memory-phenotype (MP) CD4+ T cells are a substantial population of conventional T cells that exist in steady-state mice, yet their immunological roles in autoimmune disease remain unclear. In this work, we unveil a unique phenotype of MP CD4+ T cells determined by analyzing single-cell transcriptomic data and T cell receptor (TCR) repertoires. We found that steady-state MP CD4+ T cells in the spleen were composed of heterogeneous effector subpopulations and existed regardless of germ and food antigen exposure. Distinct subpopulations of MP CD4+ T cells were specifically activated by IL-1 family cytokines and STAT activators, revealing that the cells exerted TCR-independent bystander effector functions similar to innate lymphoid cells. In particular, CCR6high subpopulation of MP CD4+ T cells were major responders to IL-23 and IL-1β without MOG35-55 antigen reactivity, which gave them pathogenic Th17 characteristics and allowed them to contribute to autoimmune encephalomyelitis. We identified that Bhlhe40 in CCR6high MP CD4+ T cells as a key regulator of GM-CSF expression through IL-23 and IL-1β signaling, contributing to central nervous system (CNS) pathology in experimental autoimmune encephalomyelitis. Collectively, our findings reveal the clearly distinct effector-like heterogeneity of MP CD4+ T cells in the steady state and indicate that CCR6high MP CD4+ T cells exacerbate autoimmune neuroinflammation via the Bhlhe40/GM-CSF axis in a bystander manner.

Cytokine-driven integrin expression controls CD8 T cell homeostasis

Abstract The peripheral CD8 T cell pool comprises a mixture of naïve and memory-phenotype (MP) cells. While naïve CD8 T cells are continuously produced and supplied through thymic export, MP CD8 T cells are mostly generated by antigen activation or cytokine-mediated differentiation and maintained by homeostatic cytokines, such as IL-15. Both naïve and MP CD8 T cells are necessary to mount vigorous immune responses against new and reoccurring pathogens. But, the mechanisms through which MP CD8 T cells would avoid competing with naïve CD8 T cells for limited space and survival cues remain largely unsolved. Here, we report that integrin CD103 plays a critical role in this process. CD103 is highly expressed on naïve CD8 T cells to mediate adhesion to cells and tissues that are abundant for its ligand, E-cadherin. Interestingly, homeostatic cytokine signaling that drives MP CD8 T cell differentiation potently downregulated the expression of CD103, dissociating them from potential competition with CD103-positive naïve CD8 T cells. Conversely, the forced expression of CD103 on MP CD8 T cells resulted in the accumulation of MP CD8 T cells and selective loss of naïve CD8 T cells. Mechanistically, we identified a subset of dendritic cells that expresses E-cadherin (E-cad +DCs), that would interact with CD103-positive CD8 T cells to provide survival signals and control their maintenance. Collectively, our results suggest that IL-15-mediated downregulation of CD103 contributes to balancing the size and composition of the peripheral CD8 T cell pool, revealing a previously unappreciated role of cytokine-driven integrin expression in controlling CD8 T cell homeostasis. This work was supported by the Intramural Research Program of the NIH, National Cancer Institute, Center for Cancer Research.

Exploring the Role of T VMCells in Age-Related CD8 +T Cell Dysfunction through ATAC-seq and RNA-seq Analysis

Abstract Virtual memory T (T VM) cells are a unique subset of CD8 +T cells that have both classical memory and innate-like immune function. Unlike other CD8 +T cell subsets, T VMcells are highly dependent on cytokines for their homeostasis and are selectively depleted in mice lacking IL-15. In aged mice and humans, T VMcells acquire T cell receptor-associated defects, which may contribute to the decline in overall CD8 +T cell function seen with aging. T VMcells make up a large proportion of the naive CD8 +T cell pool in aged individuals, making them an ideal target for age-specific therapeutic interventions. In this study, we performed ATAC-seq and RNA-seq analysis on young and aged mouse CD8 +T cell subsets and identified several key signatures associated with age-related dysfunction specifically in T VMcells. These signatures reveal a bifurcation in the aging process whereby memory-phenotype CD8 +T cells are affected differently by the aging environment. The aged-specific T VMsignature is distinct from that of conventional memory CD8 +T cells and results in the upregulation of immunomodulatory molecules such as Fcgr2b, which encodes the low-affinity inhibitory Fcγ receptor. Expression of FcγRIIB on CD8 +T cells has been shown to play a role in suppressing anti-tumor immunity and mitigating graft-versus-host disease. We show that a subset of aged T VMcells upregulate FcγRIIB independently of antigen exposure and are prone to apoptosis in vitro. Blockade of FcγRIIB has been shown to augment CD8 +T cell responses in vivo, making it a potential therapeutic target for restoring function in aged T VMcells. These findings provide insight into the mechanisms of age-related immune dysfunction and potential strategies for targeting T VMcells in the elderly. Supported by grants from NHMRC/ARC

CD127 and Sca1 mark self-driven memory-phenotype CD4 +T cells that differ from foreign antigen-specific memory cells and possess inflammatogenic and anti-tumor activities

Abstract Under steady-state conditions, conventional CD4 +T lymphocytes are divided into naïve (CD44 loCD62L hi) and memory (CD44 hiCD62L lo) cell compartments. While the latter population is presumed to comprise a mixture of explicit foreign antigen (Ag)-specific “authentic” memory and foreign Ag-independent memory-phenotype (MP) cells, phenotypic markers differentially expressed in these two cell types have yet to be identified. Moreover, it is unknown whether MP cells consist of distinct subsets defined by marker expression. In this study we demonstrate using combined single cell RNA sequencing and flow cytometric approaches that self-driven MP CD4 +T lymphocytes are divided into CD127 hiSca1 lo, CD127 hiSca1 hi, CD127 loSca1 hi, and CD127 loSca1 losubpopulations that are Bcl2 lowhile foreign Ag-specific memory cells are CD127 hiSca1 hiBcl2 hi. We further show that amongst the four MP subsets, CD127 hiSca1 hilymphocytes represent the most quiescent, cell division-experienced subpopulation derived from peripheral naïve precursors. Finally, we provide new evidence arguing that the CD127 hiSca1 hiMP subpopulation tonically expresses T-bet and possesses the capacity to trigger systemic inflammation including colitis, interstitial pneumonia, and nephritis as well as to exert anti-tumor activity against malignant lymphoma. Together our findings define MP CD4 +T lymphocytes as a unique, self-driven population consisting of distinct subsets that differ from conventional foreign Ag-specific memory cells in marker expression and reveal the inflammatogenic nature of the mature CD127 hiSca1 hiMP cells.

Global inhibition of Ly-49/MHC-I interactions by anti-MHC-I augments innate and adaptive immunity against cancer metastasis.

Abstract We have identified an pan-anti-MHC-I mAb (M1/42), which blocks the interaction of NK cell inhibitory receptors (Ly-49 antigens) with MHC-I, but does not inhibit antigen presentation by MHC-I. Administration of M1/42 in vivo markedly activated IFNg-producing NK cells. NK cell-derived IFNg stimulated APC to produce IL-12/-15/-18 cytokine cascades that further drove the proliferation of NK cells and memory phenotype (MP) T cells. M1/42 treatments profoundly augmented innate and adaptive immunity against PD-1-sensitive and -resistant transplanted tumors. Given that NK cells are critical to control of cancer metastases, we evaluated the effects of M1/42 therapy in several metastatic cancer models. M1/42 treatments successfully constrained B16F10 lung metastasis by enhancing CD8 +T cell infiltration and inducing melanoma-specific MP CD8 +T cell expansion and activation. In contrast, treatment with conventional checkpoint inhibitors (anti-PD-1/PD-L1, anti-CTLA-4 and anti-NKG2A) had no therapeutic effect. scRNAseq analysis of B16F10 lung melanoma tumor infiltrating lymphocytes revealed that M1/42 treatment significantly enhanced the expression of multiple genes associated with NK cell proliferation and activation. M1/42 also enhanced Th1-type innate and adaptive immune responses, and greatly restricted liver and lung metastasis produced by pancreatic adenocarcinoma cell line via intrasplenic or intravenous injection. Thus, the global inhibition of Ly-49/MHC-I interactions by M1/42 results in activation of a potent innate and adaptive immune response that restrains the growth of both transplanted tumors and cancer metastasis produced by intrasplenic or intravenous injection of tumor cells. This work was supported by the Intramural Research Program of NIAID, NIH.

Self antigen-driven, undifferentiated memory-phenotype CD4 T lymphocytes can induce mild and systemic inflammation by differentiating into effector and regulatory T cells

Abstract In adaptive immune responses, naïve CD4 +T lymphocytes that have T cell receptors (TCRs) reactive to challenged foreign antigens are activated to differentiate into antigen-specific effector and memory cells. We have recently reported that in steady state, peripheral naïve precursors can also recognize self antigens to spontaneously acquire a memory phenotype (MP) and that such naturally arising “MP cells” can exert innate immune function in host defense. Given the self-reactivity of MP cells, it is likely that the same T lymphocyte population also has the capacity to induce autoimmune and/or inflammatory disease. Here we show that in lymphopenic environment, self antigen-driven MP cells can evoke mild and persistent inflammation in various organs including colon, lungs, kidneys, and liver. The MP cell-driven colitis is dependent on commensal microbiota as well as cytokines IFN-γ and IL-17A while inflammation in the other organs is independent of these factors. On the other hand, we demonstrate using combined single cell RNA sequencing, TCR sequencing, and flow cytometric approaches that MP as compared to naïve CD4 +T lymphocytes more efficiently differentiate into regulatory T (Treg) cells in a TGF-β-dependent fashion, thereby partially ameliorating inflammation. We further provide evidence arguing that these Th1, Th17, and Treg cells are generated from preexisting, undifferentiated T-bet −rather than T-bet +MP subset. Altogether, our results identify self-driven T-bet −MP cells as a multi-potent CD4 +T lymphocyte population that can induce systemic and mild inflammation by differentiating into Th1 and Th17 effector as well as Treg cells. This work was supported by the Japan Society for the Promotion of Science, Astellas Foundation for Research on Metabolic Disorders, Bristol-Myers Squibb, Cell Science Research Foundation, Chemo-Sero-Therapeutic Research Institute, Daiichi Sankyo Foundation of Life Science, GlaxoSmithKline, Gonryo Foundation for the Promotion of Medical Science, G-7 Scholarship Foundation, Harmonic Ito Foundation, Ichiro Kanehara Foundation for the Promotion of Medical Sciences and Medical Care, Inamori Foundation, Intelligent Cosmos Foundation, Japan Allergy Foundation, Japan Intractable Diseases Research Foundation, Kanae Foundation for the Promotion of Medical Science, Kobayashi Foundation, Life Science Foundation of Japan, Mitsubishi Foundation, Mochida Memorial Foundation for Medical and Pharmaceutical Research, MSD Life Science Foundation, Nakajima Foundation, Nakayama Foundation for Human Science, Ohyama Health Foundation, Okinaka Memorial Institute for Medical Research, Pharmacodynamics Research Foundation, Senri Life Science Foundation, Senshin Medical Research Foundation, Sumitomo Foundation, Takeda Science Foundation, Ube Industries Foundation, Uehara Memorial Foundation, and Waksman Foundation of Japan. Akihisa Kawajiri was supported by the PhD Scholarship (Kibou Project) from Japanese Society for Immunology.

Redefining the Foreign Antigen and Self-Driven Memory CD4+ T-Cell Compartments via Transcriptomic, Phenotypic, and Functional Analyses.

Under steady-state conditions, conventional CD4+ T lymphocytes are classically divided into naïve (CD44lo CD62Lhi) and memory (CD44hi CD62Llo) cell compartments. While the latter population is presumed to comprise a mixture of distinct subpopulations of explicit foreign antigen (Ag)-specific “authentic” memory and foreign Ag-independent memory-phenotype (MP) cells, phenotypic markers differentially expressed in these two cell types have yet to be identified. Moreover, while MP cells themselves have been previously described as heterogeneous, it is unknown whether they consist of distinct subsets defined by marker expression. In this study, we demonstrate using combined single-cell RNA sequencing and flow cytometric approaches that self-driven MP CD4+ T lymphocytes are divided into CD127hi Sca1lo, CD127hi Sca1hi, CD127lo Sca1hi, and CD127lo Sca1lo subpopulations that are Bcl2lo, while foreign Ag-specific memory cells are CD127hi Sca1hi Bcl2hi. We further show that among the four MP subsets, CD127hi Sca1hi lymphocytes represent the most mature and cell division-experienced subpopulation derived from peripheral naïve precursors. Finally, we provide evidence arguing that this MP subpopulation exerts the highest responsiveness to Th1-differentiating cytokines and can induce colitis. Together, our findings define MP CD4+ T lymphocytes as a unique, self-driven population consisting of distinct subsets that differ from conventional foreign Ag-specific memory cells in marker expression and establish functional relevance for the mature subset of CD127hi Sca1hi MP cells.

Single-cell analysis by mass cytometry reveals CD19 CAR T cell spatiotemporal plasticity in patients

ABSTRACT The adaptive T cell immune response requires cellular plasticity to generate distinct subsets with diverse functional and migratory capacities. Studies of CAR T cells have primarily focused on a limited number of phenotypic markers in blood, representing an incomplete view of CAR T cell complexity. Here, we adapted mass cytometry to simultaneously analyze trafficking and functional proteins expression in CD19 CAR T cells across patients’ tissues, including leukapheresis T cells, CAR product, CAR T cells in peripheral blood, bone marrow, and cerebrospinal fluid post infusion and correlate them with phenotypes. This approach revealed spatiotemporal plasticity of CAR T cells. Patients’ CAR product revealed upregulation in many trafficking and activation molecules compared to leukapheresis T cells as baseline. Including statistically significant upregulation in CD4 and CD8 integrin-β7, CD4 granzyme B, and CD11a as well as CD8 CD25 and CD95. Moreover, patients’ tissues showed spatiotemporal alteration in trafficking, activation, maturation, and exhaustion features, with a distinct signature in the central nervous system niche. Compared to peripheral blood samples, cerebrospinal fluid samples were statistically significant enriched in CD4 and CD8 trafficking and memory phenotype proteins integrin β7, CCR7, CXCR4, and CD8 CD69. Our data provide a potential framework to remodel CAR T cells and enhance immunotherapy efficacy.

Control of Memory Phenotype T Lymphocyte Homeostasis: Role of Costimulation.

Foxp3+ T regulatory cells (Tregs), CD4+Foxp3- T cells, and CD8+ T cells are composed of naive phenotype (NP) and memory phenotype (MP) subsets. Ten to 20% of each MP T cell population are cycling (Ki-67+) in vivo. We investigated the contribution of costimulatory (CD28) and coinhibitory (CTLA-4, PD-1) receptors on MP T cell homeostatic proliferation in vivo in the mouse. Blockade of CD28-CD80/CD86 signaling completely abolished MP Tregs and profoundly inhibited MP CD4+Foxp3- T cell proliferation, but it did not affect MP CD8+ T cell proliferation. Marked enhancement of homeostatic proliferation of MP Tregs and MP CD4+Foxp3- T cells was seen after blocking CTLA4-CD80/CD86 interactions and PD-1-PD-L1/2 interactions, and greater enhancement was seen with blockade of both pathways. The CD28 pathway also played an important role in the expansion of Tregs and MP T cells after treatment of mice with agonistic Abs to members of the TNF receptor superfamily, which can act directly (anti-GITR, anti-OX40, anti-4-1BB) or indirectly (anti-CD40) on T cells. Induction of a cytokine storm by blocking the interaction of NK inhibitory receptors with MHC class I had no effect on Treg homeostasis, enhanced MP CD4+ proliferation, and expansion in a CD28-dependent manner, but it enhanced MP CD8+ T cell proliferation in a CD28-independent manner. Because MP T cells exert potent biologic effects primarily before the induction of adaptive immune responses, these findings have important implications for the use of biologic agents designed to suppress autoimmune disease or enhance T effector function in cancer that may have negative effects on MP T cells.

Turnover of Murine Cytomegalovirus-Expanded CD8+ T Cells Is Similar to That of Memory Phenotype T Cells and Independent of the Magnitude of the Response.

The potential of memory T cells to provide protection against reinfection is beyond question. Yet, it remains debated whether long-term T cell memory is due to long-lived memory cells. There is ample evidence that blood-derived memory phenotype CD8+ T cells maintain themselves through cell division, rather than through longevity of individual cells. It has recently been proposed, however, that there may be heterogeneity in the lifespans of memory T cells, depending on factors such as exposure to cognate Ag. CMV infection induces not only conventional, contracting T cell responses, but also inflationary CD8+ T cell responses, which are maintained at unusually high numbers, and are even thought to continue to expand over time. It has been proposed that such inflating T cell responses result from the accumulation of relatively long-lived CMV-specific memory CD8+ T cells. Using in vivo deuterium labeling and mathematical modeling, we found that the average production rates and expected lifespans of mouse CMV-specific CD8+ T cells are very similar to those of bulk memory-phenotype CD8+ T cells. Even CMV-specific inflationary CD8+ T cell responses that differ 3-fold in size were found to turn over at similar rates.

Memory-phenotype CD4+ T Lymphocytes: A Novel Therapeutic Target in Infectious or Autoimmune Diseases?

Infectious diseases are posing threats to the world. Although several types of antibiotics and antivirals have been created to treat the diseases, emerging/re-emerging infectious diseases, as well as those caused by pathogens with multidrug resistance, remain to be significant challenges. As a new therapeutic approach, “host-directed therapy” that enhances immune responses of host cells has been proposed. Nevertheless, the agents used in this strategy often lead to a side effect of hyperinflammation, posing a challenge in developing safe and effective drugs. In this review, I suggest boosting a novel CD4+ T lymphocyte population called “memory-phenotype (MP) cells” as a target of the host-directed therapy. MP cells are homeostatically generated from peripheral naïve precursors via recognition of self rather than foreign antigens and are maintained via rapid proliferation in steady state. Surprisingly, MP cells possess innate immune function; they can respond to an inflammatory cytokine IL-12 in the absence of antigen recognition to produce IFN-γ, thereby contributing to host defense against Toxoplasma and Mycobacterium. In this article, I summarize our current understanding of the mechanisms of generation, maintenance, differentiation, and innate effector function of MP CD4+ T lymphocytes and further discuss how we can target these cells as a new therapeutic strategy to infectious and autoimmune/inflammatory diseases.

Memory-phenotype CD4+ T cells: a naturally arising T lymphocyte population possessing innate immune function.

In conventional adaptive immune responses, upon recognition of foreign antigens, naive CD4+ T lymphocytes are activated to differentiate into effector/memory cells. In addition, emerging evidence suggests that in the steady state, naive CD4+ T cells spontaneously proliferate in response to self-antigens to acquire a memory phenotype (MP) through homeostatic proliferation. This expansion is particularly profound in lymphopenic environments but also occurs in lymphoreplete, normal conditions. The 'MP T lymphocytes' generated in this manner are maintained by rapid proliferation in the periphery and they tonically differentiate into T-bet-expressing 'MP1' cells. Such MP1 CD4+ T lymphocytes can exert innate effector function, producing IFN-γ in response to IL-12 in the absence of antigen recognition, thereby contributing to host defense. In this review, we will discuss our current understanding of how MP T lymphocytes are generated and persist in steady-state conditions, their populational heterogeneity as well as the evidence for their effector function. We will also compare these properties with those of a similar population of innate memory cells previously identified in the CD8+ T lymphocyte lineage.

Egr2 and 3 control inflammation, but maintain homeostasis, of PD-1high memory phenotype CD4 T cells.

The transcription factors Egr2 and 3 are essential for controlling inflammatory autoimmune responses of memory phenotype (MP) CD4 T cells. However, the mechanism is still unclear. We have now found that the Egr2+ subset (PD-1high MP) of MP CD4 T cells expresses high levels of checkpoint molecules (PD-1 and Lag3) and also markers of effector T cells (CXCR3 and ICAM-1). Egr2/3 are not required for PD-1high MP CD4 cell development but mediate a unique transcriptional programme that effectively controls their inflammatory responses, while promoting homeostatic proliferation and adaptive responses. Egr2 negative PD-1high MP CD4 T cells are impaired in homeostatic proliferation and adaptive responses against viral infection but display inflammatory responses to innate stimulation such as IL-12. PD-1high MP CD4 T cells have recently been implicated in rheumatoid arthritis pathogenesis, and we have now found that Egr2 expression is reduced in PD-1high MP CD4 T cells from patients with active rheumatoid arthritis compared with healthy controls. These findings demonstrate that Egr2/3 control the inflammatory responses of PD-1high MP CD4 T cells and maintain their adaptive immune fitness.