Cytokine-mediated programmed proliferation of virus-specific CD8(+) memory T cells

Plasmodium falciparum infection induces T cell tolerance that is associated with decreased disease severity upon re-infection

Immunity to severe malaria is acquired quickly, operates independently of pathogen load, and represents a highly effective form of disease tolerance. The mechanism that underpins tolerance remains unknown. We used a human rechallenge model of falciparum malaria in which healthy adult volunteers were infected three times over a 12 mo period to track the development of disease tolerance in real-time. We found that parasitemia triggered a hardwired innate immune response that led to systemic inflammation, pyrexia, and hallmark symptoms of clinical malaria across the first three infections of life. In contrast, a single infection was sufficient to reprogram T cell activation and reduce the number and diversity of effector cells upon rechallenge. Crucially, this did not silence stem-like memory cells but instead prevented the generation of cytotoxic effectors associated with autoinflammatory disease. Tolerized hosts were thus able to prevent collateral tissue damage in the absence of antiparasite immunity.

Mechanisms governing bystander activation of T cells

The immune system is endowed with the capacity to distinguish between self and non-self, so-called immune tolerance or "consciousness of the immune system." This type of awareness is designed to achieve host protection by eliminating cells expressing a wide range of non-self antigens including microbial-derived peptides. Such a successful immune response is associated with the secretion of a whole spectrum of soluble mediators, e.g., cytokines and chemokines, which not only contribute to the clearance of infected host cells but also activate T cells that are not specific to the original cognate antigen. This kind of non-specific T-cell activation is called "bystander activation." Although it is well-established that this phenomenon is cytokine-dependent, there is evidence in the literature showing the involvement of peptide/MHC recognition depending on the type of T-cell subset (naive vs. memory). Here, we will summarize our current understanding of the mechanism(s) of bystander T-cell activation as well as its biological significance in a wide range of diseases including microbial infections, cancer, auto- and alloimmunity, and chronic inflammatory diseases such as atherosclerosis.

Regulatory T cells restrict immunity and pathology in distal tissue sites following a localized infection

Regulatory T cells (Tregs) are well-known to mediate peripheral tolerance at homeostasis, and there is a growing appreciation for their role in modulating infectious disease immunity. Following acute and chronic infections, Tregs can restrict pathogen-specific T cell responses to limit immunopathology. However, it is unclear if Tregs mediate control of pathology and immunity in distal tissue sites during localized infections. We investigated the role of Tregs in immunity and disease in various tissue compartments in the context of "mild" vaginal Zika virus infection. We found that Tregs are critical to generating robust virus-specific CD8 T cell responses in the initial infection site. Further, Tregs limit inflammatory cytokines and immunopathology during localized infection; a dysregulated immune response in Treg-depleted mice leads to increased T cell infiltrates and immunopathology in both the vagina and the central nervous system (CNS). Importantly, these CNS infiltrates are not present at the same magnitude during infection of Treg-sufficient mice, in which there is no CNS immunopathology. Our data suggest that Tregs are necessary to generate a robust virus-specific response at the mucosal site of infection, while Treg-mediated restriction of bystander inflammation limits immunopathology both at the site of infection as well as distal tissue sites.

p40 homodimers bridge ischemic tissue inflammation and heterologous alloimmunity in mice via IL-15 transpresentation

Virus-induced memory T cells often express functional cross-reactivity, or heterologous immunity, to other viruses and to allogeneic MHC molecules that is an important component of pathogenic responses to allogeneic transplants. During immune responses, antigen-reactive naive and central memory T cells proliferate in secondary lymphoid organs to achieve sufficient cell numbers to effectively respond, whereas effector memory T cell proliferation occurs directly within the peripheral inflammatory microenvironment. Mechanisms driving heterologous memory T cell proliferation and effector function expression within peripheral tissues remain poorly understood. Here, we dissected proliferation of heterologous donor-reactive memory CD8+ T cells and their effector functions following infiltration into heart allografts with low or high intensities of ischemic inflammation. Proliferation within both ischemic conditions required p40 homodimer-induced IL-15 transpresentation by graft DCs, but expression of effector functions mediating acute allograft injury occurred only in high-ischemic allografts. Transcriptional responses of heterologous donor-reactive memory CD8+ T cells were distinct from donor antigen-primed memory CD8+ T cells during early activation in allografts and at graft rejection. Overall, the results provide insights into mechanisms driving heterologous effector memory CD8+ T cell proliferation and the separation between proliferation and effector function that is dependent on the intensity of inflammation within the tissue microenvironment.

The Progress and Prospects of Immune Cell Therapy for the Treatment of Cancer

Immune cell therapy as a revolutionary treatment modality, significantly transformed cancer care. It is a specialized form of immunotherapy that utilizes living immune cells as therapeutic reagents for the treatment of cancer. Unlike traditional drugs, cell therapies are considered "living drugs," and these products are currently customized and require advanced manufacturing techniques. Although chimeric antigen receptor (CAR)-T cell therapies have received tremendous attention in the industry regarding the treatment of hematologic malignancies, their effectiveness in treating solid tumors is often restricted, leading to the emergence of alternative immune cell therapies. Tumor-infiltrating lymphocytes (TIL) cell therapy, cytokine-induced killer (CIK) cell therapy, dendritic cell (DC) vaccines, and DC/CIK cell therapy are designed to use the body's natural defense mechanisms to target and eliminate cancer cells, and usually have fewer side effects or risks. On the other hand, cell therapies, such as chimeric antigen receptor-T (CAR-T) cell, T cell receptor (TCR)-T, chimeric antigen receptor-natural killer (CAR-NK), or CAR-macrophages (CAR-M) typically utilize either autologous stem cells, allogeneic or xenogeneic cells, or genetically modified cells, which require higher levels of manipulation and are considered high risk. These high-risk cell therapies typically hold special characteristics in tumor targeting and signal transduction, triggering new anti-tumor immune responses. Recently, significant advances have been achieved in both basic and clinical researches on anti-tumor mechanisms, cell therapy product designs, and technological innovations. With swift technological integration and a high innovation landscape, key future development directions have emerged. To meet the demands of cell therapy technological advancements in treating cancer, we comprehensively and systematically investigate the technological innovation and clinical progress of immune cell therapies in this study. Based on the therapeutic mechanisms and methodological features of immune cell therapies, we analyzed the main technical advantages and clinical transformation risks associated with these therapies. We also analyzed and forecasted the application prospects, providing references for relevant enterprises with the necessary information to make informed decisions regarding their R&D direction selection.

New insights into the stemness of adoptively transferred T cells by γc family cytokines

T cell-based adoptive cell therapy (ACT) has exhibited excellent antitumoral efficacy exemplified by the clinical breakthrough of chimeric antigen receptor therapy (CAR-T) in hematologic malignancies. It relies on the pool of functional T cells to retain the developmental potential to serially kill targeted cells. However, failure in the continuous supply and persistence of functional T cells has been recognized as a critical barrier to sustainable responses. Conferring stemness on infused T cells, yielding stem cell-like memory T cells (TSCM) characterized by constant self-renewal and multilineage differentiation similar to pluripotent stem cells, is indeed necessary and promising for enhancing T cell function and sustaining antitumor immunity. Therefore, it is crucial to identify TSCM cell induction regulators and acquire more TSCM cells as resource cells during production and after infusion to improve antitumoral efficacy. Recently, four common cytokine receptor γ chain (γc) family cytokines, encompassing interleukin-2 (IL-2), IL-7, IL-15, and IL-21, have been widely used in the development of long-lived adoptively transferred TSCM in vitro. However, challenges, including their non-specific toxicities and off-target effects, have led to substantial efforts for the development of engineered versions to unleash their full potential in the induction and maintenance of T cell stemness in ACT. In this review, we summarize the roles of the four γc family cytokines in the orchestration of adoptively transferred T cell stemness, introduce their engineered versions that modulate TSCM cell formation and demonstrate the potential of their various combinations. Video Abstract.

T cell receptor sequences are the dominant factor contributing to the phenotype of CD8+ T cells with specificities against immunogenic viral antigens

Antigen-specific CD8+ T cells mediate pathogen clearance. T cell phenotype is influenced by T cell receptor (TCR) sequences and environmental signals. Quantitative comparisons of these factors in human disease, while challenging to obtain, can provide foundational insights into basic T cell biology. Here, we investigate the phenotype kinetics of 679 CD8+ T cell clonotypes, each with specificity against one of three immunogenic viral antigens. Data were collected from a longitudinal study of 68 COVID-19 patients with antigens from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), cytomegalovirus (CMV), and influenza. Each antigen is associated with a different type of immune activation during COVID-19. We find TCR sequence to be by far the most important factor in shaping T cell phenotype and persistence for populations specific to any of these antigens. Our work demonstrates the important relationship between TCR sequence and T cell phenotype and persistence and helps explain why T cell phenotype often appears to be determined early in an infection.

A systematic analysis of the human immune response to Plasmodium vivax

BACKGROUNDThe biology of Plasmodium vivax is markedly different from that of P. falciparum; how this shapes the immune response to infection remains unclear. To address this shortfall, we inoculated human volunteers with a clonal field isolate of P. vivax and tracked their response through infection and convalescence.METHODSParticipants were injected intravenously with blood-stage parasites and infection dynamics were tracked in real time by quantitative PCR. Whole blood samples were used for high dimensional protein analysis, RNA sequencing, and cytometry by time of flight, and temporal changes in the host response to P. vivax were quantified by linear regression. Comparative analyses with P. falciparum were then undertaken using analogous data sets derived from prior controlled human malaria infection studies.RESULTSP. vivax rapidly induced a type I inflammatory response that coincided with hallmark features of clinical malaria. This acute-phase response shared remarkable overlap with that induced by P. falciparum but was significantly elevated (at RNA and protein levels), leading to an increased incidence of pyrexia. In contrast, T cell activation and terminal differentiation were significantly increased in volunteers infected with P. falciparum. Heterogeneous CD4+ T cells were found to dominate this adaptive response and phenotypic analysis revealed unexpected features normally associated with cytotoxicity and autoinflammatory disease.CONCLUSIONP. vivax triggers increased systemic interferon signaling (cf P. falciparum), which likely explains its reduced pyrogenic threshold. In contrast, P. falciparum drives T cell activation far in excess of P. vivax, which may partially explain why falciparum malaria more frequently causes severe disease.TRIAL REGISTRATIONClinicalTrials.gov NCT03797989.FUNDINGThe European Union's Horizon 2020 Research and Innovation programme, the Wellcome Trust, and the Royal Society.

Single-cycle influenza virus vaccine generates lung CD8+ Trm that cross-react against viral variants and subvert virus escape mutants

Influenza virus-specific tissue-resident memory (Trm) CD8+ T cells located along the respiratory tract provide cross-strain protection against a breadth of influenza viruses. We show that immunization with a single-cycle influenza virus vaccine candidate (S-FLU) results in the deposition of influenza virus nucleoprotein (NP)-specific CD8+ Trm along the respiratory tract that were more cross-reactive against viral variants and less likely to drive the development of cytotoxic T lymphocyte (CTL) escape mutants, as compared to the lung memory NP-specific CD8+ T cell pool established following influenza infection. This immune profile was linked to the limited inflammatory response evoked by S-FLU vaccination, which increased TCR repertoire diversity within the memory CD8+ T cell compartment. Cumulatively, this work shows that S-FLU vaccination evokes a clonally diverse, cross-reactive memory CD8+ T cell pool, which protects against severe disease without driving the virus to rapidly evolve and escape, and thus represents an attractive vaccine for use against rapidly mutating influenza viruses.

Cytolytic CD8+ T cell response to SARS-CoV-2 and non-SARS-CoV-2-related viruses is associated with severe manifestation of COVID-19

Little is known about the CD8+ T cell functionality in the coronavirus disease 2019 (COVID-19). Therefore, we examined twenty-five hospitalized COVID-19 patients with moderate (MD) or severe disease (SD) as well as seventeen SARS-CoV-2-unexposed persons regarding the cytolytic and cytokine-producing reactivity of their CD8+ T cells. Reactive CD8+ T cells were detectable in 90% of the unexposed persons, confirming high cross-reactive immune memory in the general population. Compared to unexposed persons and MD patients, SD patients had higher numbers of SARS-CoV-2 reactive CD8+ T cells with cytolytic function that can simultaneously produce inflammatory cytokines. In addition, SD patients showed higher CD8+ T cell reactivity against non-SARS-CoV-2-related viruses, which was mainly mediated by cytolytic response. Sequence alignments showed that cross-reactivities with the Spike protein could contribute to the expansion of such cells. Since insufficiently regulated cytolytic CD8+ T cells can damage peripheral and vascular tissue structures, high levels of both SARS-CoV-2-reactive and heterologously activated cytolytic CD8+ T cells could favor severe disease progression.

Advances in chimeric antigen receptor T cells therapy in the treatment of breast cancer

Breast cancer (BC) is the most frequently occurring cancer type seriously threatening the lives of women worldwide. Clinically, the high frequency of diverse resistance to current therapeutic strategies advocates a demand to develop novel and effective approaches for the efficient treatment of BC. The chimeric antigen receptor T (CAR-T) cells therapy, one of the immunotherapies, has displayed powerful capacity to specifically kill and eliminate tumors. Due to the success of CAR-T therapy achieved in treating hematological malignancy, the effect of CAR-T cells therapy has been tested in various human diseases including breast cancer. This review summarized and discussed the landscape of the CAR-T therapy for breast cancer, including the advances, challenge and countermeasure of CAR-T therapy in research and clinical application. The roles of potential antigen targets, tumor microenvironment, immune escape in regulating CAR-T therapy, the combination of CAR-T therapy with other therapeutic strategies to further enhance therapeutic efficacy of CAR-T treatment were also highlighted. Therefore, our review provided a comprehensive understanding of CAR-T cell therapy in breast cancer which will awake huge interests for future in-depth investigation of CAR-T based therapy in cancer treatment.

Memory T cells possess an innate-like function in local protection from mucosal infection

Mucosal infections pose a significant global health burden. Antigen-specific tissue-resident T cells are critical to maintaining barrier immunity. Previous studies in the context of systemic infection suggest that memory CD8+ T cells may also provide innate-like protection against antigenically unrelated pathogens independent of T cell receptor engagement. Whether bystander T cell activation is also an important defense mechanism in the mucosa is poorly understood. Here, we investigated whether innate-like memory CD8+ T cells could protect against a model mucosal virus infection, herpes simplex virus 2 (HSV-2). We found that immunization with an irrelevant antigen delayed disease progression from lethal HSV-2 challenge, suggesting that memory CD8+ T cells may mediate protection despite the lack of antigen specificity. Upon HSV-2 infection, we observed an early infiltration, rather than substantial local proliferation, of antigen-nonspecific CD8+ T cells, which became bystander-activated only within the infected mucosal tissue. Critically, we show that bystander-activated CD8+ T cells are sufficient to reduce early viral burden after HSV-2 infection. Finally, local cytokine cues within the tissue microenvironment after infection were sufficient for bystander activation of mucosal tissue memory CD8+ T cells from mice and humans. Altogether, our findings suggest that local bystander activation of CD8+ memory T cells contributes a fast and effective innate-like response to infection in mucosal tissue.

Circulating effector γδ T cell populations are associated with acute coronavirus disease 19 in unvaccinated individuals

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection causes severe coronavirus disease 2019 (COVID-19) in a small proportion of infected individuals. The immune system plays an important role in the defense against SARS-CoV-2, but our understanding of the cellular immune parameters that contribute to severe COVID-19 disease is incomplete. Here, we show that populations of effector γδ T cells are associated with COVID-19 in unvaccinated patients with acute disease. We found that circulating CD27^neg CD45RA⁺ CX3CR1⁺ Vδ1_effector cells expressing Granzymes (Gzms) were enriched in COVID-19 patients with acute disease. Moreover, higher frequencies of GzmB⁺ Vδ2⁺ T cells were observed in acute COVID-19 patients. SARS-CoV-2 infection did not alter the γδ T cell receptor repertoire of either Vδ1⁺ or Vδ2⁺ subsets. Our work demonstrates an association between effector populations of γδ T cells and acute COVID-19 in unvaccinated individuals.

IL-12 conditioning of peripheral blood mononuclear cells from breast cancer patients promotes the zoledronate-induced expansion of γδ T cells in vitro and enhances their cytotoxic activity and cytokine production

BACKGROUND

In a series of our preclinical studies, we have reported that conditioning of α/β CD8+ T cells in vitro with interleukin-12 (IL-12) during their expansion improves their homing phenotype and anti-tumor cytolytic function upon their adoptive transfer in vivo. Vγ9+Vδ2+ T cells can also be expanded in vitro with amino bisphosphonates such as zoledronate (ZOL) for the purpose of adoptive therapy.

AIM

We aimed in this study to use IL-12 to enhance the expansion and cytotoxic functions of ZOL-expanded Vγ9+Vδ2+T cells.

MATERIALS AND METHODS

Peripheral blood mononuclear cells (PBMCs) were separated from healthy donors and stage II breast cancer patients. PBMCs (1 × 106 cells/mL) were cultured and treated with ZOL/IL2, ZOL/IL2/IL12, or IL2/IL12. Cultured cells were harvested on days 7 and 14 of culture and their numbers, phenotype, and cytolytic activity were assessed. The levels of pro- and inflammatory cytokines/chemokines in the plasma and supernatants of the cultured cells were analyzed by Luminex.

RESULTS

In healthy subjects, the addition of IL-12 to ZOL/IL2-stimulated PBMCs increased the expansion and the cytotoxic activity of Vγ9+Vδ2+ T cells on days 7 and 14 of culture. The latter was measured by the expression level of the cytolytic molecules granzyme B (GZB) and perforin (PER). Of note, αβ CD8 + T cells were also activated under the same condition but with a lesser extent addition of IL-12 to ZOL/IL2-stimulated PBMCs from cancer patients also induced similar effects but were lower than in control subjects. Interestingly, ZOL/IL2/IL12-treated PBMCs showed higher levels of cytokines/chemokines, in particular, CCL, CCL4, GM-CSF, IL-1rα; IL-12, IL-13, TNF, and IFNγ measured on days 7 and 14.

CONCLUSION

The addition of IL12 at the start of the expansion protocol can enhance the activity of γδ T cells which might be mediated in part by the activation of αβ T cells.

Inflammatory Cytokines That Enhance Antigen Responsiveness of Naïve CD8+ T Lymphocytes Modulate Chromatin Accessibility of Genes Impacted by Antigen Stimulation

Naïve CD8⁺ T lymphocytes exposed to certain inflammatory cytokines undergo proliferation and display increased sensitivity to antigens. Such 'cytokine priming' can promote the activation of potentially autoreactive and antitumor CD8⁺ T cells by weak tissue antigens and tumor antigens. To elucidate the molecular mechanisms of cytokine priming, naïve PMEL-1 TCR transgenic CD8⁺ T lymphocytes were stimulated with IL-15 and IL-21, and chromatin accessibility was assessed using the assay for transposase-accessible chromatin (ATAC) sequencing. PMEL-1 cells stimulated by the cognate antigenic peptide mgp100_25-33 served as controls. Cytokine-primed cells showed a limited number of opening and closing chromatin accessibility peaks compared to antigen-stimulated cells. However, the ATACseq peaks in cytokine-primed cells substantially overlapped with those of antigen-stimulated cells and mapped to several genes implicated in T cell signaling, activation, effector differentiation, negative regulation and exhaustion. Nonetheless, the expression of most of these genes was remarkably different between cytokine-primed and antigen-stimulated cells. In addition, cytokine priming impacted the expression of several genes following antigen stimulation in a synergistic or antagonistic manner. Our findings indicate that chromatin accessibility changes in cytokine-primed naïve CD8⁺ T cells not only underlie their increased antigen responsiveness but may also enhance their functional fitness by reducing exhaustion without compromising regulatory controls.

Herpes simplex virus lymphadenitis is associated with tumor reduction in a patient with chronic lymphocytic leukemia

BackgroundHerpes simplex virus lymphadenitis (HSVL) is an unusual presentation of HSV reactivation in patients with chronic lymphocytic leukemia (CLL) and is characterized by systemic symptoms and no herpetic lesions. The immune responses during HSVL have not, to our knowledge, been studied.MethodsPeripheral blood and lymph node (LN) samples were obtained from a patient with HSVL. HSV-2 viral load, antibody levels, B and T cell responses, cytokine levels, and tumor burden were measured.ResultsThe patient showed HSV-2 viremia for at least 6 weeks. During this period, she had a robust HSV-specific antibody response with neutralizing and antibody-dependent cellular phagocytotic activity. Activated (HLA-DR+, CD38+) CD4+ and CD8+ T cells increased 18-fold, and HSV-specific CD8+ T cells in the blood were detected at higher numbers. HSV-specific B and T cell responses were also detected in the LN. Markedly elevated levels of proinflammatory cytokines in the blood were also observed. Surprisingly, a sustained decrease in CLL tumor burden without CLL-directed therapy was observed with this and also a prior episode of HSVL.ConclusionHSVL should be considered part of the differential diagnosis in patients with CLL who present with signs and symptoms of aggressive lymphoma transformation. An interesting finding was the sustained tumor control after 2 episodes of HSVL in this patient. A possible explanation for the reduction in tumor burden may be that the HSV-specific response served as an adjuvant for the activation of tumor-specific or bystander T cells. Studies in additional patients with CLL are needed to confirm and extend these findings.FundingNIH grants 4T32CA160040, UL1TR002378, and 5U19AI057266 and NIH contracts 75N93019C00063 and HHSN261200800001E. Neil W. and William S. Elkin Fellowship (Winship Cancer Institute).

Significance of bystander T cell activation in microbial infection

During microbial infection, pre-existing memory CD8⁺ T cells that are not specific for the infecting pathogens can be activated by cytokines without cognate antigens, termed bystander activation. Studies in mouse models and human patients demonstrate bystander activation of memory CD8⁺ T cells, which exerts either protective or detrimental effects on the host, depending on the infection model or disease. Research has elucidated mechanisms underlying the bystander activation of CD8⁺ T cells in terms of the responsible cytokines and the effector mechanisms of bystander-activated CD8⁺ T cells. In this Review, we describe the history of research on bystander CD8⁺ T cell activation as well as evidence of bystander activation. We also discuss the mechanisms and immunopathological roles of bystander activation in various microbial infections.

Unique molecular signatures typify skin inflammation induced by chemical allergens and irritants

BACKGROUND

Skin exposure to chemicals may induce an inflammatory disease known as contact dermatitis (CD). Distinguishing the allergic and irritant forms of CD often proves challenging in the clinic.

METHODS

To characterize the molecular signatures of chemical-induced skin inflammation, we conducted a comprehensive transcriptomic analysis on the skin lesions of 47 patients with positive patch tests to reference contact allergens and nonallergenic irritants.

RESULTS

A clear segregation was observed between allergen- and irritant-induced gene profiles. Distinct modules pertaining to the epidermal compartment, metabolism, and proliferation were induced by both contact allergens and irritants; whereas only contact allergens prompted strong activation of adaptive immunity, notably of cytotoxic T-cell responses. Our results also confirmed that: (a) unique pathways characterize allergen- and irritant-induced dermatitis; (b) the intensity of the clinical reaction correlates with the magnitude of immune activation. Finally, using a machine-learning approach, we identified and validated several minimal combinations of biomarkers to distinguish contact allergy from irritation.

CONCLUSION

These results highlight the value of molecular profiling of chemical-induced skin inflammation for improving the diagnosis of allergic versus irritant contact dermatitis.

Selective IL-1 activity on CD8+ T cells empowers antitumor immunity and synergizes with neovasculature-targeted TNF for full tumor eradication

Background

Clinical success of therapeutic cancer vaccines depends on the ability to mount strong and durable antitumor T cell responses. To achieve this, potent cellular adjuvants are highly needed. Interleukin-1β (IL-1β) acts on CD8⁺ T cells and promotes their expansion and effector differentiation, but toxicity and undesired tumor-promoting side effects hamper efficient clinical application of this cytokine.

Methods

This ‘cytokine problem’ can be solved by use of AcTakines (Activity-on-Target cytokines), which represent fusions between low-activity cytokine mutants and cell type-specific single-domain antibodies. AcTakines deliver cytokine activity to a priori selected cell types and as such evade toxicity and unwanted off-target side effects. Here, we employ subcutaneous melanoma and lung carcinoma models to evaluate the antitumor effects of AcTakines.

Results

In this work, we use an IL-1β-based AcTakine to drive proliferation and effector functionality of antitumor CD8⁺ T cells without inducing measurable toxicity. AcTakine treatment enhances diversity of the T cell receptor repertoire and empowers adoptive T cell transfer. Combination treatment with a neovasculature-targeted tumor necrosis factor (TNF) AcTakine mediates full tumor eradication and establishes immunological memory that protects against secondary tumor challenge. Interferon-γ was found to empower this AcTakine synergy by sensitizing the tumor microenvironment to TNF.

Conclusions

Our data illustrate that anticancer cellular immunity can be safely promoted with an IL-1β-based AcTakine, which synergizes with other immunotherapies for efficient tumor destruction.

Memory CD8+ T cells mediate early pathogen-specific protection via localized delivery of chemokines and IFNγ to clusters of monocytes

While cognate antigen drives clonal expansion of memory CD8+ T (CD8+ TM) cells to achieve sterilizing immunity in immunized hosts, not much is known on how cognate antigen contributes to early protection before clonal expansion occurs. Here, using distinct models of immunization, we establish that cognate antigen recognition by CD8+ TM cells on dendritic cells initiates their rapid and coordinated production of a burst of CCL3, CCL4, and XCL1 chemokines under the transcriptional control of interferon (IFN) regulatory factor 4. Using intravital microscopy imaging, we reveal that CD8+ TM cells undergo antigen-dependent arrest in splenic red pulp clusters of CCR2+Ly6C+ monocytes to which they deliver IFNγ and chemokines. IFNγ enables chemokine-induced microbicidal activities in monocytes for protection. Thus, rapid and effective CD8+ TM cell responses require spatially and temporally coordinated events that quickly restrict microbial pathogen growth through the local delivery of activating chemokines to CCR2+Ly6C+ monocytes.

Th2 cells lacking T-bet suppress naive and memory T cell responses via IL-10

Exacerbated immune responses and loss of self-tolerance lead to the development of autoimmunity and immunopathology. Novel therapies to target autoreactive T cells are still needed. Here, we report that Th2-polarized T cells lacking the transcription factor T-bet harbor strong immunomodulatory potential and suppress antigen-specific CD8+ T cells via IL-10. Tbx21-/- Th2 cells protected mice against virus-induced type 1 diabetes development and suppressed not only naive but also memory CD8+ T cell responses. IL-10-producing, but not IL-10-deficient Tbx21-/- Th2 cells down-regulated costimulatory molecules on dendritic cells and reduced their IL-12 production after lymphocytic choriomeningitis virus infection. Impaired dendritic cell activation hindered effector and cytotoxic CD8+ T cell development after infection. These findings indicate that Tbx21-/- Th2 cells strongly suppress proinflammatory responses of naive and memory T cells via IL-10. Thus, in vivo IL-10-secreting Th2 cells could harbor a therapeutic potential for the treatment of T cell-mediated inflammatory disorders.

Two nanoformulations induce reactive oxygen species and immunogenetic cell death for synergistic chemo-immunotherapy eradicating colorectal cancer and hepatocellular carcinoma

BACKGROUND

FOLFOX is a combinational regimen of folinic acid (FnA, FOL), fluorouracil (5-Fu, F) and oxaliplatin (OxP, OX), and has been long considered as the standard treatment of colorectal cancer (CRC) and hepatocellular carcinoma (HCC). Recent developments of nano delivery systems have provided profound promise for improving anticancer efficacy and alleviating side effects of FOLFOX. Previously, a nanoformulation (termed Nano-Folox) containing OxP derivative and FnA was developed in our laboratory using nanoprecipitation technique. Nano-Folox induced OxP-mediated immunogenic cell death (ICD)-associated antitumor immunity, which significantly suppressed tumor growth in the orthotopic CRC mouse model when administrated in combination with free 5-Fu.

METHODS

A nanoformulation (termed Nano-FdUMP) containing FdUMP (5-Fu active metabolite) was newly developed using nanoprecipitation technique and used in combination with Nano-Folox for CRC and HCC therapies.

RESULTS

Synergistic efficacy was achieved in orthotopic CRC and HCC mouse models. It resulted mainly from the fact that Nano-FdUMP mediated the formation of reactive oxygen species (ROS), which promoted the efficacy of ICD elicited by Nano-Folox. In addition, combination of Nano-Folox/Nano-FdUMP and anti-PD-L1 antibody significantly inhibited CRC liver metastasis, leading to long-term survival in mice.

CONCLUSION

This study provides proof of concept that combination of two nano delivery systems can result in successful FOLFOX-associated CRC and HCC therapies. Further optimization in terms of dosing and timing will enhance clinical potential of this combination strategy for patients.

The downregulation of IL-18R defines bona fide kidney-resident CD8+ T cells

Stepwise induction of CD69 and CD103 marks distinct differentiation stages of mucosal Trms. But the majority of non-mucosal Trm lacks CD103 expression. The expression of CD69 alone cannot faithfully define Trm cells in heavily vascularized non-mucosal tissues, such as the kidney. Here, we found that a subset of kidney Trms downregulated IL-18 receptor during differentiation. Via global transcriptional analysis and parabiosis experiments, we have discovered that the downregulation of interleukin-18 receptor (IL-18R) is associated with the establishment of tissue residency. Together with the expression of CD69, IL-18R^lo exclusively identify tissue-resident cells whereas IL-18R^hi population contains both tissue-resident and migratory ones. Local cytokines including transforming growth factor β (TGF-β) and interferon α (IFN-α)/β as well as TGF-β-dependent suppression of transcription factor Tcf-1 are essential for IL-18R downregulation during kidney Trm differentiation. Together, we identified a convenient surface marker to distinguish bona fide kidney-resident CD8⁺ T cells as well as underlying molecular mechanisms controlling this differentiation process.

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CD8⁺ Trm cells downregulate IL-18 receptor during differentiation

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IL-18R^hi population is composed of both migratory and resident subsets

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IL-18R^lo population is exclusively tissue-resident

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TGF-β promotes, whereas IFN-α/β inhibits, IL-18R downregulation

Microbiota stimulation generates LCMV-specific memory CD8+ T cells in SPF mice and determines their TCR repertoire during LCMV infection

Both mouse and human harbour memory phenotype CD8⁺ T cells specific for antigens in hosts that have not been previously exposed to these antigens. The origin and the nature of the stimuli responsible for generation of CD44^hi CD8⁺ T cells in specific pathogen-free (SPF) mice remain controversial. It is known that microbiota plays a crucial role in the prevention and resolution of systemic infections by influencing myelopoiesis, regulating dendritic cells, inflammasome activation and promoting the production of type I and II interferons. By contrast, here we suggest that microbiota has a direct effect on generation of memory phenotype CD44^hiGP33⁺CD8⁺ T cells. In SPF mice, it generates a novel GP33⁺CD44^hiCD8⁺ T cell sub-population associating the properties of innate and genuine memory cells. These cells are highly enriched in the bone marrow, proliferate rapidly and express immediate effector functions. They dominate the response to LCMV and express particular TCRβ chains. The sequence of these selected TCRβ chains overlaps with that of GP33⁺CD8⁺ T cells directly selected by microbiota in the gut epithelium of SPF mice, demonstrating a common selection mechanism in gut and peripheral CD8⁺ T cell pool. Therefore microbiota has a direct role in priming T cell immunity in SPF mice and in the selection of TCRβ repertoires during systemic infection. We identify a mechanism that primes T cell immunity in SPF mice and may have a major role in colonization resistance and protection from infection.

Relaxin-FOLFOX-IL-12 triple combination therapy engages memory response and achieves long-term survival in colorectal cancer liver metastasis

Induction of memory T cell response is inefficient in colorectal cancer (CRC) liver metastasis following existing therapies due to abundant stroma and immunosuppressive environment within the metastatic liver, which leads to fast disease progression, high recurrence rate, and short survival. Two fundamental steps are involved to elicit extensive memory T cell response: stimulation of naive T cells with robust and persistent antigen signals; and maintenance of differentiated memory T cells with survival factors. Here, we demonstrate a rational design of triple combination regimen, including relaxin (RLN), FOLFOX (combination of 5-fluorouracil, leucovorin, and oxaliplatin), and IL-12, successfully stimulates central memory T cells and achieves long-term survival in an aggressive experimental CRC liver metastasis model. Sequential administration of FOLFOX and IL-12 gene therapy following stromal deactivation by RLN gene therapy completely cured established CRC liver metastases in ~50% of mice and provided long-lasting protection against tumor recurrence. The study here may highlight the potential of evoking memory response as a curative therapy for the treatment of CRC liver metastasis.

Unique Type I Interferon, Expansion/Survival Cytokines, and JAK/STAT Gene Signatures of Multifunctional Herpes Simplex Virus-Specific Effector Memory CD8+ TEM Cells Are Associated with Asymptomatic Herpes in Humans

A large proportion of the world population harbors herpes simplex virus 1 (HSV-1), a major cause of infectious corneal blindness. HSV-specific CD8⁺ T cells protect from herpesvirus infection and disease. However, the genomic, phenotypic, and functional characteristics of CD8⁺ T cells associated with the protection seen in asymptomatic (ASYMP) individuals, who, despite being infected, never experienced any recurrent herpetic disease, remains to be fully elucidated. In this investigation, we compared the phenotype, function, and level of expression of a comprehensive panel of 579 immune genes of memory CD8⁺ T cells, sharing the same HSV-1 epitope specificities, and freshly isolated peripheral blood from well-characterized cohorts of protected ASYMP and nonprotected symptomatic (SYMP) individuals, with a history of numerous episodes of recurrent herpetic disease, using the high-throughput digital NanoString nCounter system and flow cytometry. Interestingly, our results demonstrated that memory CD8⁺ T cells from ASYMP individuals expressed a unique set of genes involved in expansion and survival, type I interferon (IFN-I), and JAK/STAT pathways. Frequent multifunctional HSV-specific effector memory CD62L^low CD44^high CD8⁺ T_EM cells were detected in ASYMP individuals compared to more of monofunctional central memory CD62L^high CD44^high CD8⁺ T_CM cells in SYMP individuals. Shedding light on the genotype, phenotype, and function of antiviral CD8⁺ T cells from "naturally protected" ASYMP individuals will help design future T-cell-based ocular herpes immunotherapeutic vaccines.IMPORTANCE A staggering number of the world population harbors herpes simplex virus 1 (HSV-1) potentially leading to blinding recurrent herpetic disease. While the majority are asymptomatic (ASYMP) individuals who never experienced any recurrent herpetic disease, symptomatic (SYMP) individuals have a history of numerous episodes of recurrent ocular herpetic disease. This study elucidates the phenotype, the effector function, and the gene signatures of memory CD8⁺ T-cell populations associated with protection seen in ASYMP individuals. Frequent multifunctional HSV-specific effector memory CD8⁺ T_EM cells were detected in ASYMP individuals. In contrast, nonprotected SYMP individuals had more central memory CD8⁺ T_CM cells. The memory CD8⁺ T_EM cells from ASYMP individuals expressed unique gene signatures characterized by higher levels of type I interferon (IFN), expansion and expansion/survival cytokines, and JAK/STAT pathways. Future studies on the genotype, phenotype, and function of antiviral CD8⁺ T cells from "naturally protected" ASYMP individuals will help in the potential design of T-cell-based ocular herpes vaccines.

Induction of anti-leukemic responses by stimulation of leukemic CD3+ cells with allogeneic stimulator cells

Background

Immunotherapeutic protocols have focused on identification of stimuli that induce effective anti-leukemic immune responses. One potent immune stimulus is the encounter with allogeneic cells. Our group previously showed that the infusion of haploidentical donor white blood cells (1-2 × 10⁸ CD3+ cells/kg) into patients with refractory hematological malignancies induced responses of varying magnitude in over half of the patients. Because donor cells were eliminated within 2 weeks in these patients, it is presumed that the responses of recipient lymphocytes were critically important in achieving prolonged anti-leukemic responses.

Methods

The role of patient CD3+ cells in anti-leukemic responses was examined by isolating peripheral blood mononuclear cells from newly diagnosed leukemic patients. Immunophenotyping was performed on these peripheral blood mononuclear cells. CD3+ cells were isolated from the peripheral blood mononuclear cells and tested for their ability to proliferate and lyse autologous leukemic cells when stimulated with unrelated allogeneic cells.

Results

Allostimulated CD3+ cells effectively generated cytolytic responses to autologous CD3-cells in 11/21 patients. Increased numbers of CD4+ cells expressing high levels of granzyme A, B and perforin and CD8+CD39+ cells were found in nonresponsive CD3+ cells.

Conclusions

These results indicate that CD3+ cells from leukemic patients are capable of generating anti-leukemic responses when stimulated with unrelated allogeneic cells. This model can be used to identify approaches using alloreactive responses by patient lymphocytes to enhance in vivo anti-leukemic responses.

T cell exhaustion implications during transplantation

Exhaustion of lymphocyte function, particularly T cell exhaustion, due to prolonged exposure to a high load of foreign antigen is commonly seen during chronic viral infection as well as antitumor immune responses. This phenomenon has been associated with a determined molecular mechanism and phenotypic manifestations on the cell surface. In spite of investigation of exhaustion, mostly about CD8 responses toward viral infections, recent studies have reported that chronic exposure to antigen may develop exhaustion in CD4 + T cells, B cells, and NK cells. Little is known with respect to lymphocyte exhaustion during transplantation and its effect on aberrant anti-graft responses. Through a same mechanobiology observed during chronic exposure of foreign viral antigens, alloantigen persistence mediated by allograft could develop a favorable circumstance for exhaustion of T cells responding to allograft. However, to achieve better manipulation approaches of this event to reduce the complications during transplantation, we need to be armed with a bulk of knowledge with regard to quality and quantity of T cell exhaustion occurring in various allografts, the kinetics of exhaustion development, the impression of immunosuppressive agents on the exhaustion, and the influence of exhaustion on graft survival and immune tolerance.

Cytokine-mediated activation of human ex vivo-expanded Vγ9Vδ2 T cells

Vγ9Vδ2 T cells, the major subset of the human peripheral blood γδ T-cell, respond to microbial infection and stressed cells through the recognition of phosphoantigens. In contrast to the growing knowledge of antigen-mediated activation mechanisms, the antigen-independent and cytokine-mediated activation mechanisms of Vγ9Vδ2 T cells are poorly understood. Here, we show that interleukin (IL) -12 and IL-18 synergize to activate human ex vivo-expanded Vγ9Vδ2 T cells. Vγ9Vδ2 T cells treated with IL-12 and IL-18 enhanced effector functions, including the expression of IFN-γ and granzyme B, and cytotoxicity. These enhanced effector responses following IL-12 and IL-18 treatment were associated with homotypic aggregation, enhanced expression of ICAM-1 and decreased expression of the B- and T-lymphocyte attenuator (BTLA), a co-inhibitory receptor. IL-12 and IL-18 also induced the antigen-independent proliferation of Vγ9Vδ2 T cells. Increased expression of IκBζ, IL-12Rβ2 and IL-18Rα following IL-12 and IL-18 stimulation resulted in sustained activation of STAT4 and NF-κB. The enhanced production of IFN-γ and cytotoxic activity are critical for cancer immunotherapy using Vγ9Vδ2 T cells. Thus, the combined treatment of ex vivo-expanded Vγ9Vδ2 T cells with IL-12 and IL-18 may serve as a new strategy for the therapeutic activation of these cells.

Influence of Inflammation in the Process of T Lymphocyte Differentiation: Proliferative, Metabolic, and Oxidative Changes

T lymphocytes, from their first encounter with their specific antigen as naïve cell until the last stages of their differentiation, in a replicative state of senescence, go through a series of phases. In several of these stages, T lymphocytes are subjected to exponential growth in successive encounters with the same antigen. This entire process occurs throughout the life of a human individual and, earlier, in patients with chronic infections/pathologies through inflammatory mediators, first acutely and later in a chronic form. This process plays a fundamental role in amplifying the activating signals on T lymphocytes and directing their clonal proliferation. The mechanisms that control cell growth are high levels of telomerase activity and maintenance of telomeric length that are far superior to other cell types, as well as metabolic adaptation and redox control. Large numbers of highly differentiated memory cells are accumulated in the immunological niches where they will contribute in a significant way to increase the levels of inflammatory mediators that will perpetuate the new state at the systemic level. These levels of inflammation greatly influence the process of T lymphocyte differentiation from naïve T lymphocyte, even before, until the arrival of exhaustion or cell death. The changes observed during lymphocyte differentiation are correlated with changes in cellular metabolism and these in turn are influenced by the inflammatory state of the environment where the cell is located. Reactive oxygen species (ROS) exert a dual action in the population of T lymphocytes. Exposure to high levels of ROS decreases the capacity of activation and T lymphocyte proliferation; however, intermediate levels of oxidation are necessary for the lymphocyte activation, differentiation, and effector functions. In conclusion, we can affirm that the inflammatory levels in the environment greatly influence the differentiation and activity of T lymphocyte populations. However, little is known about the mechanisms involved in these processes. The elucidation of these mechanisms would be of great help in the advance of improvements in pathologies with a large inflammatory base such as rheumatoid arthritis, intestinal inflammatory diseases, several infectious diseases and even, cancerous processes.

Mechanisms regulating expansion of CD8+ T cells during HIV-1 infection

Abnormal immune activation and expansion of CD8+ T cells, especially of memory and effector phenotypes, take place during HIV-1 infection, and these abnormal features persist during administration of antiretroviral therapy (ART) to infected patients. The molecular mechanisms for CD8+ T-cell expansion remain poorly characterized. In this article, we review the literature addressing features of CD8+ T-cell immune pathology and present an integrated view on the mechanisms leading to abnormal CD8+ T-cell expansion during HIV-1 infection. The expression of molecules important for directing the homing of CD8+ T cells between the circulation and lymphoid tissues, in particular CCR5 and CXCR3, is increased in CD8+ T cells in circulation and in inflamed tissues during HIV-1 infection; these disturbances in the homing capacity of CD8+ T cells have been linked to increased CD8+ T-cell proliferation. The production of IL-15, a cytokine responsible for physiological proliferation of CD8+ T cells, is increased in lymphoid tissues during HIV-1 infection as result of microbial translocation and severe inflammation. IL-15, and additional inflammatory cytokines, may lead to deregulated proliferation of CD8+ T cells and explain the accumulation of CD8+ T cells in circulation. The decreased capacity of CD8+ T cells to localize to gut-associated lymphoid tissue also contributes to the accumulation of these cells in blood. Control of inflammation, through ART administration during primary HIV-1 infection or therapies aimed at controlling inflammation during HIV-1 infection, is pivotal to prevent abnormal expansion of CD8+ T cells during HIV-1 infection.

Allograft dendritic cell p40 homodimers activate donor-reactive memory CD8+ T cells

Recipient endogenous memory T cells with donor reactivity pose an important barrier to successful transplantation and costimulatory blockade-induced graft tolerance. Longer ischemic storage times prior to organ transplantation increase early posttransplant inflammation and negatively impact early graft function and long-term graft outcome. Little is known about the mechanisms enhancing endogenous memory T cell activation to mediate tissue injury within the increased inflammatory environment of allografts subjected to prolonged cold ischemic storage (CIS). Endogenous memory CD4+ and CD8+ T cell activation is markedly increased within complete MHC-mismatched cardiac allografts subjected to prolonged versus minimal CIS, and the memory CD8+ T cells directly mediate CTLA-4Ig-resistant allograft rejection. Memory CD8+ T cell activation within allografts subjected to prolonged CIS requires memory CD4+ T cell stimulation of graft DCs to produce p40 homodimers, but not IL-12 p40/p35 heterodimers. Targeting p40 abrogates memory CD8+ T cell proliferation within the allografts and their ability to mediate CTLA-4Ig-resistant allograft rejection. These findings indicate a critical role for memory CD4+ T cell-graft DC interactions to increase the intensity of endogenous memory CD8+ T cell activation needed to mediate rejection of higher-risk allografts subjected to increased CIS.

Immune system and melanoma biology: a balance between immunosurveillance and immune escape

Melanoma is one of the most immunogenic tumors and its relationship with host immune system is currently under investigation. Many immunomodulatory mechanisms, favoring melanomagenesis and progression, have been described to interfere with the disablement of melanoma recognition and attack by immune cells resulting in immune resistance and immunosuppression. This knowledge produced therapeutic advantages, such as immunotherapy, aiming to overcome the immune evasion.

Here, we review the current advances in cancer immunoediting and focus on melanoma immunology, which involves a dynamic interplay between melanoma and immune system, as well as on effects of “targeted therapies” on tumor microenvironment for combination strategies.

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.

Cytokine response to Hantaan virus infection in patients with hemorrhagic fever with renal syndrome

Hantaan virus (HTNV) infection of the human body causes a severe acute infectious disease known as hemorrhagic fever renal syndrome (HFRS). The aim of this study was to correlate patient cytokine profiles to HFRS severity. In this study, we discuss the clinical significance of evaluating HFRS treatment outcomes using cytokine information. The levels of 18 cytokines were quantitatively determined in three groups: 34 HTNV IgM+ cases, 63 HTNV IgM- negative cases, and 78 healthy volunteers. The level of 14 serum cytokines were higher in the patient group than that in the healthy control group. In the 34 HTNV IgM+ patient sera, a set of 27 cytokines was further assessed. The cytokines of TNF-β, IL-1ra, and IL-6 were detected at higher level in the IgM+ group than that in the IgM- group. The deterioration of HFRS was accompanied with multiple cytokines increased, such as IL-1ra, IL-12p70, IL-10, IP-10, IL-17, IL-2, and IL-6. Our data indicate that serum cytokine levels are associated with the progression of HFRS.

Cytoplasm-Translocated Ku70/80 Complex Sensing of HBV DNA Induces Hepatitis-Associated Chemokine Secretion

Chronic hepatitis B virus (HBV) infection remains a serious disease, mainly due to its severe pathological consequences, which are difficult to cure using current therapies. When the immune system responds to hepatocytes experiencing rapid HBV replication, effector cells (such as HBV-specific CD8+ T cells, NK cells, NKT cells, and other subtypes of immune cells) infiltrate the liver and cause hepatitis. However, the precise recruitment of these cells remains unclear. In the present study, we found that the cytoplasm-translocated Ku70/80 complex in liver-derived cells sensed cytosolic HBV DNA and promoted hepatitis-associated chemokine secretion. Upon sensing HBV DNA, DNA-dependent protein kinase catalytic subunit and PARP1 were assembled. Then, IRF1 was activated and translocated into the nucleus, which upregulated CCL3 and CCL5 expression. Because CCR5, a major chemokine receptor for CCL3 and CCL5, is known to be critical in hepatitis B, Ku70/80 sensing of HBV DNA likely plays a critical role in immune cell recruitment in response to HBV infection.

Immune signatures of protective spleen memory CD8 T cells

Memory CD8 T lymphocyte populations are remarkably heterogeneous and differ in their ability to protect the host. In order to identify the whole range of qualities uniquely associated with protective memory cells we compared the gene expression signatures of two qualities of memory CD8 T cells sharing the same antigenic-specificity: protective (Influenza-induced, Flu-TM) and non-protective (peptide-induced, TIM) spleen memory CD8 T cells. Although Flu-TM and TIM express classical phenotypic memory markers and are polyfunctional, only Flu-TM protects against a lethal viral challenge. Protective memory CD8 T cells express a unique set of genes involved in migration and survival that correlate with their unique capacity to rapidly migrate within the infected lung parenchyma in response to influenza infection. We also enlighten a new set of poised genes expressed by protective cells that is strongly enriched in cytokines and chemokines such as Ccl1, Ccl9 and Gm-csf. CCL1 and GM-CSF genes are also poised in human memory CD8 T cells. These immune signatures are also induced by two other pathogens (vaccinia virus and Listeria monocytogenes). The immune signatures associated with immune protection were identified on circulating cells, i.e. those that are easily accessible for immuno-monitoring and could help predict vaccines efficacy.

Pretreatment of activated human CD8 T cells with IL-12 leads to enhanced TCR-induced signaling and cytokine production

During the immune response to pathogens and autoantigens, CD8T cells are exposed to numerous inflammatory agents including the cytokine IL-12. Previous studies have focused on how IL-12 regulates T cell functions when present during or after the activation of the T cell receptor (TCR). However, recent studies suggest that prior exposure to IL-12 also alters the TCR responsiveness of murine T cells. Whether similar phenomena occur in human activated CD8T cells and the mechanisms mediating these effects remain unexplored. In this study, we observed that pretreatment of human activated CD8T cells with IL-12 results in increased cytokine mRNA and protein production following subsequent TCR challenge. The potentiation of TCR-mediated cytokine release was transient and required low doses of IL-12 for at least 24h. Mechanistically, prior exposure to IL-12 increased the TCR induced activation of select MAPKs and AKT without altering the activation of more proximal TCR signaling molecules, suggesting that the IL-12 mediated changes in TCR signaling are responsible for the increased production of cytokines. Our data suggest that prior treatment with IL-12 potentiates human CD8T cell responses at sites of infection and inflammation, expanding our understanding of the function of this clinically important cytokine.

TCR independent suppression of CD8(+) T cell cytokine production mediated by IFNγ in vivo

CD8(+) memory T cells produce IFNγ within hours of secondary infection, but this is quickly terminated in vivo despite the presence of stimulatory viral antigen, suggesting that active suppression occurs. Herein, we investigated the in vivo effector function of CD8(+) memory T cells during successive encounters with viral antigen. CD8(+) T cells in immune mice receiving prior viral or peptide challenge failed to reproduce IFNγ during LCMV rechallenge. Surprisingly, this refractory state was induced even in memory cells that had not encountered their cognate antigen, indicating that the silencing of CD8(+) T cell responses is TCR-independent. Direct injection of IFNγ also suppressed the ability of virus-specific memory cells to respond to subsequent viral challenge. We propose the existence of a negative feedback loop whereby IFNγ, produced by memory CD8(+) T cells to combat viral challenge, acts - directly or indirectly - to limit its further production.

Memory CD8+ T Cells: Orchestrators and Key Players of Innate Immunity?

Over the past decades, the dichotomy between innate and adaptive immune responses has largely dominated our understanding of immunology. Upon primary encounter with microbial pathogens, differentiation of adaptive immune cells into functional effectors usually takes several days or even longer, making them contribute to host protection only late during primary infection. However, once generated, antigen-experienced T lymphocytes can persist in the organism and constitute a pool of memory cells that mediate fast and effective protection to a recall infection with the same microbial pathogen. Herein, we challenge this classical paradigm by highlighting the “innate nature” of memory CD8⁺ T cells. First, within the thymus or in the periphery, naïve CD8⁺ T cells may acquire phenotypic and functional characteristics of memory CD8⁺ T cells independently of challenge with foreign antigens. Second, both the “unconventional” and the “conventional” memory cells can rapidly express protective effector functions in response to sets of inflammatory cytokines and chemokines signals, independent of cognate antigen triggering. Third, memory CD8⁺ T cells can act by orchestrating the recruitment, activation, and licensing of innate cells, leading to broad antimicrobial states. Thus, collectively, memory CD8⁺ T cells may represent important actors of innate immune defenses.

Regulatory T Cell Numbers in Inflamed Skin Are Controlled by Local Inflammatory Cues That Upregulate CD25 and Facilitate Antigen-Driven Local Proliferation

CD4(+)Foxp3(+) regulatory T cells (Tregs) are key immune suppressors that regulate immunity in diverse tissues. The tissue and/or inflammatory signals that influence the magnitude of the Treg response remain unclear. To define signals that promote Treg accumulation, we developed a simple system of skin inflammation using defined Ags and adjuvants that induce distinct cytokine milieus: OVA protein in CFA, aluminum salts (Alum), and Schistosoma mansoni eggs (Sm Egg). Polyclonal and Ag-specific Treg accumulation in the skin differed significantly between adjuvants. CFA and Alum led to robust Treg accumulation, with >50% of all skin CD4(+) T cells being Foxp3(+) In contrast, Tregs accumulated poorly in the Sm Egg-inflamed skin. Surprisingly, we found no evidence of inflammation-specific changes to the Treg gene program between adjuvant-inflamed skin types, suggesting a lack of selective recruitment or adaptation to the inflammatory milieu. Instead, Treg accumulation patterns were linked to differences in CD80/CD86 expression by APC and the regulation of CD25 expression, specifically in the inflamed skin. Inflammatory cues alone, without cognate Ag, differentially supported CD25 upregulation (CFA and Alum > Sm Egg). Only in inflammatory milieus that upregulated CD25 did the provision of Ag enhance local Treg proliferation. Reduced IL-33 in the Sm Egg-inflamed environment was shown to contribute to the failure to upregulate CD25. Thus, the magnitude of the Treg response in inflamed tissues is controlled at two interdependent levels: inflammatory signals that support the upregulation of the important Treg survival factor CD25 and Ag signals that drive local expansion.

Protein Translation Activity: A New Measure of Host Immune Cell Activation

We describe the in vivo ribopuromycylation (RPM) method, which uses a puromycin-specific Ab to fluorescently label ribosome-bound puromycylated nascent chains, enabling measurement of translational activity via immunohistochemistry or flow cytometry. Tissue staining provides a unique view of virus-induced activation of adaptive, innate, and stromal immune cells. RPM flow precisely quantitates virus-induced activation of lymphocytes and innate immune cells, and it provides a unique measure of immune cell deactivation and quiescence. Using RPM we find that high endothelial cells in draining lymph nodes rapidly increase translation in the first day of vaccinia virus infection. We also find a population of constitutively activated splenic T cells in naive mice and further that most bone marrow T cells activate 3 d after vaccinia virus infection. Bone marrow T cell activation is nonspecific, IL-12-dependent, and induces innate memory T cell phenotypic markers. Thus, RPM measures translational activity to uniquely identify cell populations that participate in the immune response to pathogens, other foreign substances, and autoantigens.

Brain-resident memory T cells represent an autonomous cytotoxic barrier to viral infection

During viral infections, brain tissue–resident memory T cells (bTRM) prevent fatal brain infection after acquiring perforin- and IFN-γ–dependent effector functions through a pathway that involves presentation of cognate antigen on MHC-I.

Tissue-resident memory T cells (T_RM) persist at sites of prior infection and have been shown to enhance pathogen clearance by recruiting circulating immune cells and providing bystander activation. Here, we characterize the functioning of brain-resident memory T cells (bT_RM) in an animal model of viral infection. bT_RM were subject to spontaneous homeostatic proliferation and were largely refractory to systemic immune cell depletion. After viral reinfection in mice, bT_RM rapidly acquired cytotoxic effector function and prevented fatal brain infection, even in the absence of circulating CD8⁺ memory T cells. Presentation of cognate antigen on MHC-I was essential for bT_RM-mediated protective immunity, which involved perforin- and IFN-γ–dependent effector mechanisms. These findings identify bT_RM as an organ-autonomous defense system serving as a paradigm for T_RM functioning as a self-sufficient first line of adaptive immunity.

Attrition of memory CD8 T cells during sepsis requires LFA-1

CD8 T cell loss and dysfunction have been implicated in the increased susceptibility to opportunistic infections during the later immunosuppressive phase of sepsis, but CD8 T cell activation and attrition in early sepsis remain incompletely understood. With the use of a CLP model, we assessed CD8 T cell activation at 5 consecutive time points and found that activation after sepsis results in a distinct phenotype (CD69⁺CD25^intCD62L^HI) independent of cognate antigen recognition and TCR engagement and likely through bystander-mediated cytokine effects. Additionally, we observed that sepsis concurrently results in the preferential depletion of a subset of memory-phenotype CD8 T cells that remain "unactivated" (i.e., fail to up-regulate activation markers) by apoptosis. Unactivated CD44^HI OT-I cells were spared from sepsis-induced attrition, as were memory-phenotype CD8 T cells of mice treated with anti-LFA-1 mAb, 1 h after CLP. Perhaps most importantly, we demonstrate that attrition of memory phenotype cells may have a pathologic significance, as elevated IL-6 levels were associated with decreased numbers of memory-phenotype CD8 T cells in septic mice, and preservation of this subset after administration of anti-LFA-1 mAb conferred improved survival at 7 d. Taken together, these data identify potentially modifiable responses of memory-phenotype CD8 T cells in early sepsis and may be particularly important in the application of immunomodulatory therapies in sepsis.

Exposure of Human CD4 T Cells to IL-12 Results in Enhanced TCR-Induced Cytokine Production, Altered TCR Signaling, and Increased Oxidative Metabolism

Human CD4 T cells are constantly exposed to IL-12 during infections and certain autoimmune disorders. The current paradigm is that IL-12 promotes the differentiation of naïve CD4 T cells into Th1 cells, but recent studies suggest IL-12 may play a more complex role in T cell biology. We examined if exposure to IL-12 alters human CD4 T cell responses to subsequent TCR stimulation. We found that IL-12 pretreatment increased TCR-induced IFN-γ, TNF-α, IL-13, IL-4 and IL-10 production. This suggests that prior exposure to IL-12 potentiates the TCR-induced release of a range of cytokines. We observed that IL-12 mediated its effects through both transcriptional and post-transcriptional mechanisms. IL-12 pretreatment increased the phosphorylation of AKT, p38 and LCK following TCR stimulation without altering other TCR signaling molecules, potentially mediating the increase in transcription of cytokines. In addition, the IL-12-mediated enhancement of cytokines that are not transcriptionally regulated was partially driven by increased oxidative metabolism. Our data uncover a novel function of IL-12 in human CD4 T cells; specifically, it enhances the release of a range of cytokines potentially by altering TCR signaling pathways and by enhancing oxidative metabolism.

Memory CD8(+) T Cells: Innate-Like Sensors and Orchestrators of Protection

Recent findings have revealed roles for systemic and mucosa-resident memory CD8(+) T cells in the orchestration of innate immune responses critical to host defense upon microbial infection. Here we integrate these findings into the current understanding of the molecular and cellular signals controlling memory CD8(+) T cell reactivation and the mechanisms by which these cells mediate effective protection in vivo. The picture that emerges presents memory CD8(+) T cells as early sensors of danger signals, mediating protective immunity both through licensing of cellular effectors of the innate immune system and via the canonical functions associated with memory T cells. We discuss implications for the development of T cell vaccines and therapies and highlight important areas in need of further investigation.

Exploiting cytokines in adoptive T-cell therapy of cancer

Adoptive immunotherapy with tumor-reactive autologous T cells, either expanded from tumor specimens or genetically engineered to express tumor-reactive T-cell receptors and chimeric antigen receptors, is holding promising results in clinical trials. Several critical issues have been identified and results underline the possibility to exploit cytokines to further ameliorate the efficacy of current treatment protocols, also encompassing adoptive T-cell therapy. Here we review latest developments on the use of cytokines to better direct the nature of the T-cell infusion product, T-cell function and persistence in vivo, as well as to modulate the tumor microenvironment.

Genetic Influence on the Peripheral Blood CD4+ T-cell Differentiation Status in CMV Infection

A latent infection with cytomegalovirus (CMV), a ubiquitous beta herpesvirus, is associated with an accumulation of late-differentiated memory T-cells, often accompanied by a reciprocal reduced frequency of early-differentiated cells (commonly also referred to as "naïve"). However, this impact of CMV on T-cell phenotypes is variable between individuals. Our previous findings in a subgroup of participants in the Leiden familial Longevity Study indicated an important role of genetics. For further testing, we have analyzed middle-aged monozygotic (MZ, n = 42) and dizygotic (DZ, n = 39) twin pairs from the Danish Twin Registry for their T-cell differentiation status, assessed by surface expression of CD27, CD28, CD57, and KLRG-1. We observed a significant intraclass correlation between cotwins of MZ, but not DZ pairs for the differentiation status of CD4⁺ and CD8⁺ subsets. Classical heritability analysis confirmed a substantial contribution of genetics to the differentiation status of T-cells in CMV infection. The humoral (IgG) response to different CMV antigens also seems to be genetically influenced, suggesting that a similar degree of immune control of the virus in MZ twins might be responsible for their similar T-cell differentiation status. Thus, the way T-cells differentiate in the face of a latent CMV infection, and the parallel humoral responses, both controlling the virus, are genetically influenced.

Regulation of effector and memory CD8(+) T cell function by inflammatory cytokines

Cells communicate with each other through the production and secretion of cytokines, which are integral to the host response to infection. Once recognized by specific cytokine receptors expressed on the cell surface, these exogenous signals direct the biological function of a cell in order to adapt to their microenvironment. CD8(+) T cells are critical immune cells that play an important role in the control and elimination of intracellular pathogens. Current findings have demonstrated that cytokines influence all aspects of the CD8(+) T cell response to infection or immunization. The cytokine milieu induced at the time of activation impacts the overall magnitude and function of the effector CD8(+) T cell response and the generation of functional memory CD8(+) T cells. This review will focus on the impact of inflammatory cytokines on different aspects of CD8(+) T cell biology.