Interleukin-2 programs mouse alpha beta T lymphocytes for apoptosis

Apoptosis, a Metabolic "Head-to-Head" between Tumor and T Cells: Implications for Immunotherapy

Induction of apoptosis represents a promising therapeutic approach to drive tumor cells to death. However, this poses challenges due to the intricate nature of cancer biology and the mechanisms employed by cancer cells to survive and escape immune surveillance. Furthermore, molecules released from apoptotic cells and phagocytes in the tumor microenvironment (TME) can facilitate cancer progression and immune evasion. Apoptosis is also a pivotal mechanism in modulating the strength and duration of anti-tumor T-cell responses. Combined strategies including molecular targeting of apoptosis, promoting immunogenic cell death, modulating immunosuppressive cells, and affecting energy pathways can potentially overcome resistance and enhance therapeutic outcomes. Thus, an effective approach for targeting apoptosis within the TME should delicately balance the selective induction of apoptosis in tumor cells, while safeguarding survival, metabolic changes, and functionality of T cells targeting crucial molecular pathways involved in T-cell apoptosis regulation. Enhancing the persistence and effectiveness of T cells may bolster a more resilient and enduring anti-tumor immune response, ultimately advancing therapeutic outcomes in cancer treatment. This review delves into the pivotal topics of this multifaceted issue and suggests drugs and druggable targets for possible combined therapies.

Diacylglycerol kinases: A look into the future of immunotherapy

Cancer still represents the second leading cause of death right after cardiovascular diseases. According to the World Health Organization (WHO), cancer provoked around 10 million deaths in 2020, with lung and colon tumors accounting for the deadliest forms of cancer. As tumor cells become resistant to traditional therapeutic approaches, immunotherapy has emerged as a novel strategy for tumor control. T lymphocytes are key players in immune responses against tumors. Immunosurveillance allows identification, targeting and later killing of cancerous cells. Nevertheless, tumors evolve through different strategies to evade the immune response and spread in a process called metastasis. The ineffectiveness of traditional strategies to control tumor growth and expansion has led to novel approaches considering modulation of T cell activation and effector functions. Program death receptor 1 (PD-1) and cytotoxic T-lymphocyte antigen 4 (CTLA-4) showed promising results in the early 90s and nowadays are still being exploited together with other drugs for several cancer types. Other negative regulators of T cell activation are diacylglycerol kinases (DGKs) a family of enzymes that catalyze the conversion of diacylglycerol (DAG) into phosphatidic acid (PA). In T cells, DGKα and DGKζ limit the PLCγ/Ras/ERK axis thus attenuating DAG mediated signaling and T cell effector functions. Upregulation of either of both isoforms results in impaired Ras activation and anergy induction, whereas germline knockdown mice showed enhanced antitumor properties and more effective immune responses against pathogens. Here we review the mechanisms used by DGKs to ameliorate T cell activation and how inhibition could be used to reinvigorate T cell functions in cancer context. A better knowledge of the molecular mechanisms involved upon T cell activation will help to improve current therapies with DAG promoting agents.

CD4 memory has a hierarchical structure created by requirements for infection-derived signals at an effector checkpoint

Our recent studies reveal that the persistence, location, and amount of both antigen and signals that induce pathogen recognition responses determine the number of CD4 memory cells, the subsets that develop, their location, and hence their protective efficacy. Non-replicating vaccines provide antigen that is short-lived and generate low levels of only some memory subsets that are mostly restricted to secondary lymphoid tissue. In contrast, exposure to long-lived replicating viruses and bacteria provides high levels of diverse antigens in sites of infection and induces strong pathogen recognition signals for extended periods of time, resulting in much higher levels of memory cells of diverse subsets in both lymphoid and nonlymphoid sites. These include memory subsets with highly potent functions such as T follicular helpers and cytotoxic CD4 effectors at sites of infection, where they can most effectively combat the pathogen early after re-infection. These effectors also do not develop without antigen and pathogen recognition signals at the effector stage, and both subsets must receive these signals in the tissue sites where they will become resident. We postulate that this leads to a hierarchical structure of memory, with the strongest memory induced only by replicating pathogens. This paradigm suggests a likely roadmap for markedly improving vaccine design.

Immune microenvironment of cervical cancer and the role of IL-2 in tumor promotion

The tumor microenvironment (TME) is a heterogeneous mixture of resident and tumor cells that maintain close communication through their secretion products. The composition of the TME is dynamic and complex among the different types of cancer, where the immune cells play a relevant role in the elimination of tumor cells, however, under certain circumstances they contribute to tumor development. In cervical cancer (CC) the human papilloma virus (HPV) shapes the microenvironment in order to mediate persistent infections that favors transformation and tumor development. Interleukin-2 (IL-2) is an important TME cytokine that induces CD8+ effector T cells and NKs to eliminate tumor cells, however, IL-2 can also suppress the immune response through Treg cells. Recent studies have shown that CC cells express the IL-2 receptor (IL-2R), that are induced to proliferate at low concentrations of exogenous IL-2 through alterations in the JAK/STAT pathway. This review provides an overview of the main immune cells that make up the TME in CC, as well as the participation of IL-2 in the tumor promotion. Finally, it is proposed that the low density of IL-2 produced by immunocompetent cells is used by tumor cells through its IL-2R as a mechanism to proliferate simultaneously depleting this molecule in order to evade immune response.

T Cells in Colorectal Cancer: Unravelling the Function of Different T Cell Subsets in the Tumor Microenvironment

Therapeutic options for metastatic colorectal cancer (mCRC) are very limited, and the prognosis using combination therapy with a chemotherapeutic drug and a targeted agent, e.g., epidermal growth factor receptor or tyrosine kinase, remains poor. Therefore, mCRC is associated with a poor median overall survival (mOS) of only 25-30 months. Current immunotherapies with checkpoint inhibitor blockade (ICB) have led to a substantial change in the treatment of several cancers, such as melanoma and non-small cell lung cancer. In CRC, ICB has only limited effects, except in patients with microsatellite instability-high (MSI-H) or mismatch repair-deficient (dMMR) tumors, which comprise about 15% of sporadic CRC patients and about 4% of patients with metastatic CRC. The vast majority of sporadic CRCs are microsatellite-stable (MSS) tumors with low levels of infiltrating immune cells, in which immunotherapy has no clinical benefit so far. Immunotherapy with checkpoint inhibitors requires the presence of infiltrating T cells into the tumor microenvironment (TME). This makes T cells the most important effector cells in the TME, as evidenced by the establishment of the immunoscore-a method to estimate the prognosis of CRC patients. The microenvironment of a tumor contains several types of T cells that are anti-tumorigenic, such as CD8⁺ T cells or pro-tumorigenic, such as regulatory T cells (Tregs) or T helper 17 (Th17) cells. However, even CD8⁺ T cells show marked heterogeneity, e.g., they can become exhausted, enter a state of hyporesponsiveness or become dysfunctional and express high levels of checkpoint molecules, the targets for ICB. To kill cancer cells, CD8⁺ T cells need the recognition of the MHC class I, which is often downregulated on colorectal cancer cells. In this case, a population of unconventional T cells with a γδ T cell receptor can overcome the limitations of the conventional CD8⁺ T cells with an αβT cell receptor. γδ T cells recognize antigens in an MHC-independent manner, thus acting as a bridge between innate and adaptive immunity. Here, we discuss the effects of different T cell subsets in colorectal cancer with a special emphasis on γδ T cells and the possibility of using them in CAR-T cell therapy. We explain T cell exclusion in microsatellite-stable colorectal cancer and the possibilities to overcome this exclusion to enable immunotherapy even in these "cold" tumors.

Viral reactivations and co-infections in COVID-19 patients: a systematic review

BACKGROUND

Viral reactivations and co-infections have been reported among COVID-19 patients. However, studies on the clinical outcomes of different viral reactivations and co-infections are currently in limit. Thus, the primary purpose of this review is to perform an overarching investigation on the cases of latent virus reactivation and co-infection in COVID-19 patients to build collective evidence contributing to improving patient health. The aim of the study was to conduct a literature review to compare the patient characteristics and outcomes of reactivations and co-infections of different viruses.

METHODS

Our population of interest included confirmed COVID-19 patients who were diagnosed with a viral infection either concurrently or following their COVID-19 diagnosis. We extracted the relevant literature through a systematic search using the key terms in the online databases including the EMBASE, MEDLINE, Latin American Caribbean Health Sciences Literature (LILACS), from inception onwards up to June 2022. The authors independently extracted data from eligible studies and assessed the risk of bias using the Consensus-based Clinical Case Reporting (CARE) guidelines and the Newcastle-Ottawa Scale (NOS). Main patient characteristics, frequency of each manifestation, and diagnostic criteria used in studies were summarized in tables.

RESULTS

In total, 53 articles were included in this review. We identified 40 reactivation studies, 8 coinfection studies, and 5 studies where concomitant infection in COVID-19 patients was not distinguished as either reactivation or coinfection. Data were extracted for 12 viruses including IAV, IBV, EBV, CMV, VZV, HHV-1, HHV-2, HHV-6, HHV-7, HHV-8, HBV, and Parvovirus B19. EBV, HHV-1, and CMV were most frequently observed within the reactivation cohort, whereas IAV and EBV within the coinfection cohort. In both reactivation and coinfection groups, patients reported cardiovascular disease, diabetes, and immunosuppression as comorbidities, acute kidney injury as complication, and lymphopenia and elevated D-dimer and CRP levels from blood tests. Common pharmaceutical interventions in two groups included steroids and antivirals.

CONCLUSION

Overall, these findings expand our knowledge on the characteristics of COVID-19 patients with viral reactivations and co-infections. Our experience with current review indicates a need for further investigations on virus reactivation and coinfection among COVID-19 patients.

Mechanisms of antigen-induced reversal of CNS inflammation in experimental demyelinating disease

Autoimmune central nervous system (CNS) demyelinating diseases are a major public health burden and poorly controlled by current immunosuppressants. More precise immunotherapies with higher efficacy and fewer side effects are sought. We investigated the effectiveness and mechanism of an injectable myelin-based antigenic polyprotein MMPt (myelin oligodendrocyte glycoprotein, myelin basic protein and proteolipid protein, truncated). We find that it suppresses mouse experimental autoimmune encephalomyelitis without major side effects. MMPt induces rapid apoptosis of the encephalitogenic T cells and suppresses inflammation in the affected CNS. Intravital microscopy shows that MMPt is taken up by perivascular F4/80⁺ cells but not conventional antigen-presenting dendritic cells, B cells, or microglia. MMPt-stimulated F4/80⁺ cells induce reactive T cell immobilization and apoptosis in situ, resulting in reduced infiltration of inflammatory cells and chemokine production. Our study reveals alternative mechanisms that explain how cognate antigen suppresses CNS inflammation and may be applicable for effectively and safely treating demyelinating diseases.

A hydrogel platform for co-delivery of immunomodulatory proteins for pancreatic islet allografts

Type 1 diabetes (T1D), an autoimmune disorder in which the insulin-producing β-cells in the islets of Langerhans in the pancreas are destroyed, afflicts over 1.6 million Americans. Although pancreatic islet transplantation has shown promise in treating T1D, continuous use of required immunosuppression regimens limits clinical islet transplantation as it poses significant adverse effects on graft recipients and does not achieve consistent long-term graft survival with 50%-70% of recipients maintaining insulin independence at 5 years. T cells play a key role in graft rejection, and rebalancing pathogenic T effector and protective T regulatory cells can regulate autoimmune disorders and transplant rejection. The synergy of the interleukin-2 (IL-2) and Fas immunomodulatory pathways presents an avenue for eliminating the need for systemic immune suppression by exploiting IL-2's role in expanding regulatory T cells and leveraging Fas ligand (FasL) activity on antigen-induced cell death of effector T cells. Herein, we developed a hydrogel platform for co-delivering an analog of IL-2, IL-2D, and FasL-presenting microgels to achieve localized immunotolerance to pancreatic islets by targeting the upregulation of regulatory T cells and effector T cells simultaneously. Although this hydrogel provided for sustained, local delivery of active immunomodulatory proteins, indefinite allograft survival was not achieved. Immune profiling analysis revealed upregulation of target regulatory T cells but also increases in Granzyme B-expressing CD8+ T cells at the graft site. We attribute the failed establishment of allograft survival to these Granzyme B-expressing T cells. This study underscores the delicate balance of immunomodulatory components important for allograft survival - whose outcome can be dependent on timing, duration, modality of delivery, and disease model.

Cytokines and microRNAs in SARS-CoV-2: What do we know?

The coronavirus disease 2019 (COVID-19) pandemic constitutes a global health emergency. Currently, there are no completely effective therapeutic medications for the management of this outbreak. The cytokine storm is a hyperinflammatory medical condition due to excessive and uncontrolled release of pro-inflammatory cytokines in patients suffering from severe COVID-19, leading to the development of acute respiratory distress syndrome (ARDS) and multiple organ dysfunction syndrome (MODS) and even mortality. Understanding the pathophysiology of COVID-19 can be helpful for the treatment of patients. Evidence suggests that the levels of tumor necrosis factor alpha (TNF-α) and interleukin (IL)-1 and IL-6 are dramatically different between mild and severe patients, so they may be important contributors to the cytokine storm. Several serum markers can be predictors for the cytokine storm. This review discusses the cytokines involved in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, focusing on interferons (IFNs) and ILs, and whether they can be used in COVID-19 treatment. Moreover, we highlight several microRNAs that are involved in these cytokines and their role in the cytokine storm caused by COVID-19.

Colorectal Cancer-Infiltrating Regulatory T Cells: Functional Heterogeneity, Metabolic Adaptation, and Therapeutic Targeting

Colorectal cancer (CRC) is a heterogeneous disease with one of the highest rates of incidence and mortality among cancers worldwide. Understanding the CRC tumor microenvironment (TME) is essential to improve diagnosis and treatment. Within the CRC TME, tumor-infiltrating lymphocytes (TILs) consist of a heterogeneous mixture of adaptive immune cells composed of mainly anti-tumor effector T cells (CD4+ and CD8+ subpopulations), and suppressive regulatory CD4+ T (Treg) cells. The balance between these two populations is critical in anti-tumor immunity. In general, while tumor antigen-specific T cell responses are observed, tumor clearance frequently does not occur. Treg cells are considered to play an important role in tumor immune escape by hampering effective anti-tumor immune responses. Therefore, CRC-tumors with increased numbers of Treg cells have been associated with promoting tumor development, immunotherapy failure, and a poorer prognosis. Enrichment of Treg cells in CRC can have multiple causes including their differentiation, recruitment, and preferential transcriptional and metabolic adaptation to the TME. Targeting tumor-associated Treg cell may be an effective addition to current immunotherapy approaches. Strategies for depleting Treg cells, such as low-dose cyclophosphamide treatment, or targeting one or more checkpoint receptors such as CTLA-4 with PD-1 with monoclonal antibodies, have been explored. These have resulted in activation of anti-tumor immune responses in CRC-patients. Overall, it seems likely that CRC-associated Treg cells play an important role in determining the success of such therapeutic approaches. Here, we review our understanding of the role of Treg cells in CRC, the possible mechanisms that support their homeostasis in the tumor microenvironment, and current approaches for manipulating Treg cells function in cancer.

TNFR1 Contributes to Activation-Induced Cell Death of Pathological CD4+ T Lymphocytes During Ischemic Heart Failure

CD4⁺ T cells turn pathological during heart failure (HF). We show that the expression of tumor necrosis factor (TNF)-α and tumor necrosis factor receptor (TNFR1) increases in HF-activated CD4⁺ T cells. However, the role of the TNF-α/TNFR1 axis in T-cell activation/proliferation is unknown. We show that TNFR1 neutralization during T-cell activation (ex vivo) or the loss of TNFR1 in adoptively transferred HF-activated CD4⁺ T cells (in vivo) augments their prosurvival and proliferative signaling. Importantly, TNFR1 neutralization does not affect CD69 expression or the pathological activity of HF-activated TNFR1^-/- CD4⁺ T cells. These results show that during HF TNFR1 plays an important role in quelling prosurvival and proliferative signals in CD4⁺ T cells without altering their pathological activity.

Oral Trypanosoma cruzi Acute Infection in Mice Targets Primary Lymphoid Organs and Triggers Extramedullary Hematopoiesis

During the acute phase of Chagas disease, Trypanosoma cruzi circulation through the bloodstream leads to high tissue parasitism in the host. In primary lymphoid organs, progenitor cell reduction paralleled transient immunosuppression. Herein we showed that acute oral infection in mice promotes diffuse parasitism in bone marrow cells at 14 and 21 days post-infection (dpi), with perivascular regions, intravascular regions, and regions near the bone being target sites of parasite replication. Phenotypic analysis of hematopoietic differentiation in the bone marrow of infected mice showed that the cell number in the tissue is decreased (lineage-negative and lineage-positive cells). Interestingly, analysis of hematopoietic branching points showed that hematopoietic stem and progenitor cells (HSPCs) were significantly increased at 14 dpi. In addition, the pool of progenitors with stem plasticity (HSC-MPP3), as well as multipotent progenitors (MPPs) such as MPP4, also showed this pattern of increase. In contrast, subsequent progenitors that arise from MPPs, such as common lymphoid progenitors (CLPs), lymphoid-primed MPPs (LMPPs), and myeloid progenitors, were not enhanced; conversely, all presented numeric decline. Annexin V staining revealed that cell death increase in the initial hematopoietic branching point probably is not linked to CLPs and that myeloid progenitors decreased at 14 and 21 dpi. In parallel, our investigation provided clues that myeloid progenitor decrease could be associated with an atypical expression of Sca-1 in this population leading to a remarkable increase on LSK-like cells at 14 dpi within the HSPC compartment. Finally, these results led us to investigate HSPC presence in the spleen as a phenomenon triggered during emergency hematopoiesis due to mobilization or expansion of these cells in extramedullary sites. Splenocyte analysis showed a progressive increase in HSPCs between 14 and 21 dpi. Altogether, our study shows that the bone marrow is a target tissue in T. cruzi orally infected mice, leading to a hematopoietic disturbance with LSK-like cell bias accounting on HSPCs possibly affecting myeloid progenitor numbers. The LMPP and CLP reduction converges with defective thymocyte development. Lastly, it is tempting to speculate that the extramedullary hematopoiesis seen in the spleen is a mechanism involved in the hematological maintenance reported during the acute phase of oral T. cruzi infection.

Activation-induced cell death in CAR-T cell therapy

Engineered T cells expressing chimeric antigen receptors (CARs) with tumor specificity have shown remarkable therapeutic effects on hematologic malignancies. However, CAR-T cells are less effective on solid tumors mainly due to the weak persistence of CAR-T cells, which might be caused by T cell death. Significant activation-induced cell death (AICD) of CAR-T cells was triggered by repeated antigen stimulation. AICD of T cell is characterized by the upregulation of death receptors and low persistence of T cells. Understanding the mechanism of AICD is crucial to improve the anti-tumor effect of CAR-T cells against solid tumors. Many approaches have been applied in CAR-T cell modification to enhance their anti-apoptosis ability. In this review, we summarized the molecular mechanisms of AICD in CAR-T cells and the progresses of anti-AICD in CAR-T cells therapy.

Infants with Down syndrome and congenital heart disease have altered peri-operative immune responses

BACKGROUND

Infants with Down syndrome (DS) have an altered immune response. We aimed to characterise the inflammatory response in infants with DS and congenital heart disease (CHD) peri-operatively in comparison to infants with CHD and a normal chromosomal complement, and to healthy infants pre-operatively.

METHODS

Infants with DS/CHD, infants without DS but with CHD (CHD only) and healthy infants were prospectively recruited and serial serum cytokines evaluated peri-operatively using multiplex ELISA: tumour necrosis factor (TNF)-α and TNF-β; interferon (IFN)-γ, interleukin (IL)-1α, IL-2, IL-6, IL-8, IL-18, IL-1β, IL-10, and IL-1ra; vascular endothelial growth factor (VEGF); granulocyte macrophage colony-stimulating factor (GM-CSF); and erythropoietin (EPO).

RESULTS

Ninety-four infants were recruited including age-matched controls (n = 10), DS/CHD (n = 55), and CHD only (n = 29). Children with DS/CHD had significantly lower concentrations of several cytokines (IL-10, IL-6, IL-8, IL-1β, VEGF) in the pre- and post-operatively vs CHD only and controls. EPO and GM-CSF were significantly higher in DS/CHD (p value <0.05).

CONCLUSIONS

Children with DS/CHD had significantly lower concentrations of several cytokines compared to controls or children with CHD only. EPO and GM-CSF were significantly higher in children with DS/CHD. The assessment of the immune response may be suitable for the predictable clinical outcomes in these children.

IMPACT

This study demonstrated that children with Down syndrome (DS) and congenital heart disease (CHD) have significant alterations in pro-inflammatory and anti-inflammatory immune responses peri-operatively. These changes may contribute to adverse clinical outcomes, including sepsis, chylothorax, and autoimmunity. They may impact the pathogenesis and outcome post-operatively and long term in this population. Children with DS and CHD have significantly lower cytokine concentrations, increased EPO and GM-CSF, and decreased VEGF pre- and post-operatively. Assessing their inflammatory state peri-operatively may facilitate the development of a predictive model that can inform tailored management of these infants using novel therapies including immunomodulation.

Lactose-binding lectin from Vatairea macrocarpa seeds induces in vivo angiogenesis via VEGF and TNF-ɑ expression and modulates in vitro doxorubicin-induced genotoxicity

Lactose-binding lectin from Vatairea macrocarpa seeds (VML) has attracted great attention due to its interesting biological activities, such as pro-inflammatory effects and macrophage activation. This study evaluated the cytotoxicity and genotoxicity/antigenotoxicity of VML in human lymphocytes using the CometChip assay, and angiogenic activity by the chick embryo chorioallantoic membrane (CAM) assay. In genotoxicity, lymphocytes were treated with different concentrations of VML (0.5, 2 and 8 μM). In antigenotoxicity, lymphocytes were treated with the same concentrations of VML concomitant doxorubicin (90 μM DXR). To evaluate angiogenesis, all CAM were treated with different concentrations of VML (0.5, 2 and 8 μM) alone or co-treated with lactose (0.1 M). Furthermore, the levels of vascular endothelial growth factor (VEGF) and tumor necrosis factor-alpha (TNF-α) in CAM were assessed by immunohistochemistry. The results showed that VML was cytotoxic to lymphocytes, genotoxic at the highest concentration (8 μM) and antigenotoxic at low concentrations (0.5, and 2 μM). Regarding the CAM assay and immunohistochemistry, VML was angiogenic and significantly increased VEGF and TNF-α levels. In contrast, co-treatment with lactose significantly reduced the angiogenic effect and VEGF levels. We propose that protein-carbohydrate interactions between VML and glycans in the cell membrane are probably the major events involved in these activities. It seems likely that VML elicits a pro-inflammatory response through VEGF and TNF-α expression, resulting in increased vascularization at the site of inflammation. Therefore, our results show novel information on the effects of VML on DNA, as well as provide data regarded the neovascularization process involving this lectin.

Evaluation of Immunoprotective Effects of Fusobacterium necrophorum Outer Membrane Proteins 43K OMP, Leukotoxin and Hemolysin Multi-Component Recombinant Subunit Vaccine in Mice

We evaluated the efficacy of three vaccine formulations containing different combinations of proteins (43K OMP, leukotoxin recombinant protein PL4 and hemolysin recombinant protein H2) and killed whole cell Fusobacterium necrophorum in preventing liver abscess. Four subcutaneous vaccines were formulated: vaccine 1 (43K OMP), vaccine 2 (PL4 and H2), vaccine 3 (43K OMP, PL4 and H2), and vaccine 4 (killed whole bacterial cell). 43K OMP, PL4, and H2 proteins were produced by using recombinant protein expression. To evaluate vaccine efficacy, we randomly allocated 50 BALB/c female mice to one of five different treatment groups: PBS control group, vaccine 1, vaccine 2, vaccine 3, and vaccine 4. Mice were vaccinated three times, with 14 days between each immunization. After immunization, the mice were challenged with F. necrophorum. The three key findings of this study are as follows: (1) Vaccine 3 has enabled mice to produce higher antibody titer following bacterial challenge, (2) in the liver pathology of mice, the vaccine 3 liver showed the least pathology, and (3) all four vaccines produced high levels of antibodies and cytokines in mice, but the level of vaccine 3 was the highest. Based on our results, it has been demonstrated that a mixture of F. necrophorum 43K OMP, PL4, and H2 proteins inoculated with mice can achieve protection against liver abscess in mice. Our research may therefore provide the basis for the development of a vaccine against F. necrophorum bovine infections.

In vivo genome-wide CRISPR screens identify SOCS1 as intrinsic checkpoint of CD4+ TH1 cell response

[Figure: see text].

Delivery of IL-2 to the T Cell Surface Through Phosphatidylserine Permits Robust Expansion of CD8 T Cells

The phospholipid phosphatidylserine (PS) is naturally maintained on the cytoplasmic side of the plasma membrane. Independent of apoptosis, PS is redistributed to the surface of CD8 T cells in response to TCR-mediated activation. Annexin V (AnnV) is a protein known to bind PS with high affinity and has been effectively utilized to anchor antigen to the surface of CD8 T cells. To expand these studies, we aimed to exploit TCR activation driven PS exposure as a target to deliver cytokine, namely interleukin-2 (IL-2), to the surface of CD8 T cells. This was accomplished using a novel chimeric fusion protein of annexin V and interleukin 2 (AnnV-IL2). In vitro analysis revealed that AnnV-IL2 is able to specifically bind PS on the T cell surface following TCR stimulation. Consequently, AnnV-IL2 proved to be significantly more effective at enhancing T cell activation compared to recombinant IL-2. In vivo, AnnV-IL2 promotes robust expansion of antigen-specific cells capable of interferon gamma (IFNγ) production when administered following peptide vaccination. Importantly, upon antigen rechallenge, AnnV-IL2 treatment mice demonstrated a stronger secondary expansion, indicating durability of AnnV-IL2 mediated responses. Our data supports the use of AnnV-IL2 to modulate antigen-specific T cell immunity and demonstrates that the PS-AnnV axis is a feasible mechanism to target diverse cargo to CD8 T cells.

Clean up by aisle 2: roles for IL-2 receptors in host defense and tolerance

Although IL-2 was first recognized as growth factor for T cells, it is now also appreciated to be a key regulator of T cells through its effects on regulatory T cells (Treg). The IL-2 receptor (IL-2R) subunits' different (i) ligand affinities, (ii) dimerization or trimerization relationships with other cytokine subunits, (iii) expression across multiple cell types, and (iv) downstream signaling effects, largely dictate cellular tolerance and antimicrobial processes. Defects in IL-2Rγ result in profound and almost universally fatal immune deficiency, unless treated with hematopoietic stem cell transplantation (HSCT). Defects in IL-2Rα and IL-2Rβ result in more limited infection susceptibility, particularly to herpesviruses. However, the most prominent clinical symptomatology for IL-2Rα and IL-2Rβ defects include multi-organ autoimmunity and inflammation, consistent with the critical role of IL-2 in establishing and maintaining immune tolerance. Here, we review how we have arrived at our current understanding of the complex roles of IL-2/2R in host defense and tolerance focusing on the insights gained from human clinical immunology.

Potential drug development and therapeutic approaches for clinical intervention in COVID-19

While the vaccination is now available to many countries and will slowly dissipate to others, effective therapeutics for COVID-19 is still illusive. The SARS-CoV-2 pandemic has posed an unprecedented challenge to researchers, scientists, and clinicians and affected the wellbeing of millions of people worldwide. Since the beginning of the pandemic, a multitude of existing anti-viral, antibiotic, antimalarial, and anticancer drugs have been tested, and some have shown potency in the treatment and management of COVID-19, albeit others failed to leave any positive impact and a few also became controversial as they showed mixed clinical outcomes. In the present article, we have brought together some of the candidate therapeutic drugs being repurposed or used in the clinical trials and discussed their clinical efficacy and safety for COVID-19.

Exploring the Pathogenic Role and Therapeutic Implications of Interleukin 2 in Autoimmune Hepatitis

Interleukin 2 is essential for the expansion of regulatory T cells, and low-dose recombinant interleukin 2 has improved the clinical manifestations of diverse autoimmune diseases in preliminary studies. The goals of this review are to describe the actions of interleukin 2 and its receptor, present preliminary experiences with low-dose interleukin 2 in the treatment of diverse autoimmune diseases, and evaluate its potential as a therapeutic intervention in autoimmune hepatitis. English abstracts were identified in PubMed by multiple search terms. Full-length articles were selected for review, and secondary and tertiary bibliographies were developed. Interleukin 2 is critical for the thymic selection, peripheral expansion, induction, and survival of regulatory T cells, and it is also a growth factor for activated T cells and natural killer cells. Interleukin 2 activates the signal transducer and activator of transcription 5 after binding with its trimeric receptor on regulatory T cells. Immune suppressor activity is increased; anti-inflammatory interleukin 10 is released; pro-inflammatory interferon-gamma is inhibited; and activation-induced apoptosis of CD8⁺ T cells is upregulated. Preliminary experiences with cyclic injections of low-dose recombinant interleukin 2 in diverse autoimmune diseases have demonstrated increased numbers of circulating regulatory T cells, preserved regulatory function, improved clinical manifestations, and excellent tolerance. Similar improvements have been recognized in one of two patients with refractory autoimmune hepatitis. In conclusion, interferon 2 has biological actions that favor the immune suppressor functions of regulatory T cells, and low-dose regimens in preliminary studies encourage its rigorous investigation in autoimmune hepatitis.

Severe COVID-19: Immunosuppression or Hyperinflammation?

ABSTRACT

The ongoing coronavirus disease 2019 (COVID-19) pandemic has swept over the world and causes thousands of deaths. Although the clinical features of COVID-19 become much clearer than before, there are still further problems with the pathophysiological process and treatments of severe patients. One primary problem is with the paradoxical immune states in severe patients with COVID-19. Studies indicate that Severe Acute Respiratory Syndrome Coronavirus 2 can attack the immune system, manifested as a state of immunosuppression with a decrease in lymphocytes, whereas a state of hyperinflammation, presenting as elevated cytokine levels, is also detected in COVID-19. Therefore, discussing the specific status of immunity in COVID-19 will contribute to the understanding of its pathophysiology and the search for appropriate treatments. Here, we review all the available literature concerning the different immune states in COVID-19 and the underlying pathophysiological mechanisms. In addition, the association between immune states and the development and severity of disease as well as the impact on the selection of immunotherapy strategies are discussed in our review.

TIM-3 drives temporal differences in restimulation-induced cell death sensitivity in effector CD8+ T cells in conjunction with CEACAM1

Immune homeostasis depends upon effective clearance of pathogens while simultaneously preventing autoimmunity and immunopathology in the host. Restimulation-induced cell death (RICD) is one such mechanism where by activated T cells receive subsequent antigenic stimulation, reach a critical signal threshold through the T cell receptor (TCR), and commit to apoptosis. Many details of this process remain unclear, including the role of co-stimulatory and co-inhibitory proteins that influence the TCR signaling cascade. Here we characterize the role of T cell immunoglobulin and mucin domain containing 3 (TIM-3) in RICD regulation. TIM-3 protected newly activated CD8+ effector T cells from premature RICD during clonal expansion. Surprisingly, however, we found that TIM-3 potentiated RICD in late-stage effector T cells. The presence of TIM-3 increased proximal TCR signaling and proapoptotic protein expression in late-stage effector T cells, with no consistent signaling effects noted in newly activated cells with or without TIM-3. To better explain these differences in TIM-3 function as T cells aged, we characterized the temporal pattern of TIM-3 expression in effector T cells. We found that TIM-3 was expressed on the surface of newly activated effector T cells, but remained largely intracellular in late-stage effector cells. Consistent with this, TIM-3 required a ligand to prevent early RICD, whereas ligand manipulation had no effects at later stages. Of the known TIM-3 ligands, carcinoembryonic antigen-related cell adhesion molecule (CEACAM1) showed the greatest difference in surface expression over time and also protected newly activated cells from premature RICD, with no measurable effects in late-stage effectors. Indeed, CEACAM1 enabled TIM-3 surface expression on T cells, implying a co-dependency for these proteins in protecting expanding T cells from premature RICD. Our findings suggest that co-signaling proteins like TIM-3 and CEACAM1 can alter RICD sensitivity at different stages of the effector T cell response, with important implications for checkpoint blockade therapy.

Rethinking peripheral T cell tolerance: checkpoints across a T cell's journey

Following their exit from the thymus, T cells are endowed with potent effector functions but must spare host tissue from harm. The fate of these cells is dictated by a series of checkpoints that regulate the quality and magnitude of T cell-mediated immunity, known as tolerance checkpoints. In this Perspective, we discuss the mediators and networks that control the six main peripheral tolerance checkpoints throughout the life of a T cell: quiescence, ignorance, anergy, exhaustion, senescence and death. At the naive T cell stage, two intrinsic checkpoints that actively maintain tolerance are quiescence and ignorance. In the presence of co-stimulation-deficient T cell activation, anergy is a dominant hallmark that mandates T cell unresponsiveness. When T cells are successfully stimulated and reach the effector stage, exhaustion and senescence can limit excessive inflammation and prevent immunopathology. At every stage of the T cell's journey, cell death exists as a checkpoint to limit clonal expansion and to terminate unrestrained responses. Here, we compare and contrast the T cell tolerance checkpoints and discuss their specific roles, with the aim of providing an integrated view of T cell peripheral tolerance and fate regulation.

Long-Acting Human Interleukin 2 Bioconjugate Modified with Fatty Acids by Sortase A

Human Interleukin 2 (IL-2) has already achieved impressive results as a therapeutic agent for cancer and autoimmune diseases. However, one of the limitations associated with the clinical application of IL-2 is its short half-life owing to rapid clearance by the kidneys. Modification with fatty acids, as an albumin noncovalent ligand with the advantage of deep penetration into tissues and high activity-to-mass ratio, is a commonly used approach to improve the half-life of native peptides and proteins. In this investigation, we attempted to extend the half-life of IL-2 through conjugation with a fatty acid using sortase A (srtA). We initially designed and optimized three IL-2 analogues with different peptide linkers between the C-terminus of IL-2 and srtA recognition sequence (LPETG). Among these, analogue A3 was validated as the optimal IL-2 analogue for further modification. Next, six fatty acid moieties with the same fatty acid and different hydrophilic spacers were conjugated to A3 through srtA. The six bioconjugates generated were screened for in vitro biological activity, among which bioconjugate B6 was identified as near-optimal to IL-2. Additionally, B6 could effectively bind albumin through the conjugated fatty acid, which contributed to a significant improvement in its pharmacokinetic properties in vivo. In summary, we have developed a novel IL-2 bioconjugate, B6, modified with fatty acids using srtA, which may effectively serve as a new-generation long-acting IL-2 immunotherapeutic agent.

Heterodimeric IL-15 in Cancer Immunotherapy

Simple Summary

The rapidly expanding field of cancer immunotherapy uses diverse technologies, including cytokines, T cells, and antibody administration, with the aim to induce effective immune responses leading to tumor control. Interleukin-15 (IL-15), a cytokine discovered in 1994, supports the homeostasis of cytotoxic immune cells and shows promise as an anti-tumor agent. Many studies have elucidated IL-15 synthesis, regulation and biological function and explored its therapeutic efficacy in preclinical cancer models. Escherichia coli-derived single-chain IL-15 was tested in the first in-human trial in cancer patients. Its effects were limited by the biology of IL-15, which in vivo comprises a complex of the IL-15 chain with the IL-15 receptor alpha (IL-15Rα) chain, together forming the IL-15 heterodimer (hetIL-15). Currently, single-chain IL-15 and several heterodimeric IL-15:IL-15Rα variants (hetIL-15, N-803 and RLI) are being tested in clinical trials. This review presents a summary of contemporary preclinical and clinical research on IL-15.

Abstract

Immunotherapy has emerged as a valuable strategy for the treatment of many cancer types. Interleukin-15 (IL-15) promotes the growth and function of cytotoxic CD8⁺ T and natural killer (NK) cells. It also enhances leukocyte trafficking and stimulates tumor-infiltrating lymphocytes expansion and activity. Bioactive IL-15 is produced in the body as a heterodimeric cytokine, comprising the IL-15 and the so-called IL-15 receptor alpha chain that are together termed “heterodimeric IL-15” (hetIL-15). hetIL-15, closely resembling the natural form of the cytokine produced in vivo, and IL-15:IL-15Rα complex variants, such as hetIL-15Fc, N-803 and RLI, are the currently available IL-15 agents. These molecules have showed favorable pharmacokinetics and biological function in vivo in comparison to single-chain recombinant IL-15. Preclinical animal studies have supported their anti-tumor activity, suggesting IL-15 as a general method to convert “cold” tumors into “hot”, by promoting tumor lymphocyte infiltration. In clinical trials, IL-15-based therapies are overall well-tolerated and result in the expansion and activation of NK and memory CD8⁺ T cells. Combinations with other immunotherapies are being investigated to improve the anti-tumor efficacy of IL-15 agents in the clinic.

Optimized gene engineering of murine CAR-T cells reveals the beneficial effects of IL-15 coexpression

Limited clinical benefit has been demonstrated for chimeric antigen receptor (CAR) therapy of solid tumors, but coengineering strategies to generate so-called fourth-generation (4G) CAR-T cells are advancing toward overcoming barriers in the tumor microenvironment (TME) for improved responses. In large part due to technical challenges, there are relatively few preclinical CAR therapy studies in immunocompetent, syngeneic tumor-bearing mice. Here, we describe optimized methods for the efficient retroviral transduction and expansion of murine T lymphocytes of a predominantly central memory T cell (T_CM cell) phenotype. We present a bicistronic retroviral vector encoding both a tumor vasculature–targeted CAR and murine interleukin-15 (mIL-15), conferring enhanced effector functions, engraftment, tumor control, and TME reprogramming, including NK cell activation and reduced presence of M2 macrophages. The 4G-CAR-T cells coexpressing mIL-15 were further characterized by up-regulation of the antiapoptotic marker Bcl-2 and lower cell-surface expression of the inhibitory receptor PD-1. Overall, this work introduces robust tools for the development and evaluation of 4G-CAR-T cells in immunocompetent mice, an important step toward the acceleration of effective therapies reaching the clinic.

The Surprising Story of IL-2: From Experimental Models to Clinical Application

Equilibrium in the immune system is maintained by a balance between activation, which generates effector and memory cells, and suppression, which is mediated mainly by regulatory T cells. Understanding this balance and how to exploit it therapeutically is one of the dominant themes of modern immunology. The cytokine IL-2 was discovered as a growth factor for T cells and thus a key component of immune activation. It was initially used to boost immune responses in patients with cancer. Studies in experimental models and humans showed that the major function of IL-2 is to maintain functional regulatory T cells, and thus its essential function is in immune suppression. How the same cytokine can serve two opposing roles is a subject of current investigation. Because of these advances, IL-2 is now being tested as a cytokine for suppressing pathologic immune responses in autoimmune diseases and graft rejection. Fully understanding the biology of IL-2 may enable us to custom-design this cytokine for different applications in humans.

Induction Phase of Spontaneous Liver Transplant Tolerance

The liver has long been known to possess tolerogenic properties. Early experiments in liver transplantation demonstrated that in animal models, hepatic allografts could be accepted across MHC-mismatch without the use of immunosuppression, and that transplantation of livers from the same donor was capable of inducing tolerance to other solid organs that would normally otherwise be rejected. Although this phenomenon is less pronounced in human liver transplantation, lower levels of immunosuppression are nevertheless required for graft acceptance than for other solid organs, and in a minority of individuals immunosuppression can be discontinued in the longer term. The mechanisms underlying this unique hepatic property have not yet been fully delineated, however it is clear that immunological events in the early period post-liver transplant are key to generation of hepatic allograft tolerance. Both the hepatic parenchyma and the large number of donor passenger leukocytes contained within the liver allograft have been demonstrated to contribute to the generation of donor-specific tolerance in the early post-transplant phase. In particular, the unique nature of hepatic-leukocyte interactions appears to play a crucial role in the ability of the liver to silence the recipient alloimmune response. In this review, we will summarize the evidence regarding the potential mechanisms that mediate the critical early phase in the generation of hepatic allograft tolerance.

A Review of Immunomodulatory Effects of Fluoroquinolones

Past researches indicate that some types of antibiotics, apart from their antimicrobial effects, have some other important effects which indirectly are exerted by modulating and regulating the immune system's mediators. Among the compounds with antimicrobial effects, fluoroquinolones (FQs) are known as synthetic antibiotics, which exhibit the property of decomposing of DNA and prevent bacterial growth by inactivating the enzymes involved in DNA twisting, including topoisomerase II (DNA gyrase) and IV. Interestingly, immune responses are indirectly modulated by FQs through suppressing pro-inflammatory cytokines, such as interleukin 1 (IL-1), IL-6, tumor necrosis factor-alpha (TNF-α), and super-inducing IL-2, which tend to increase both the growth and activity of T and B lymphocytes. In addition, they affect the development of immune responses by influencing of expression of other cytokines and mediators. This study aims to review past research on the immunomodulatory effects of FQs on the expression of cytokines, especially IL-2 and to discuss controversial investigations.

Soluble IL-2 Receptor in Dermatomyositis: Its Associations with Skin Ulcers and Disease Activity

Objective

To investigate the role of soluble interleukin-2R (sIL-2R) in idiopathic inflammatory myopathies (IIM).

Methods

Serum sIL-2R levels were measured in 74 dermatomyositis (DM), 16 immune-mediated necrotizing myopathy (IMNM), 24 rheumatoid arthritis (RA), 20 systemic lupus erythematosus (SLE), and 20 healthy controls (HCs) by chemiluminescent immunometric assay. Clinical features and laboratory data were collected from electronic medical record. Disease activity was evaluated by using physician global disease activity and myositis disease activity assessment visual analog scale (MYOACT) on admission. 20 DM patients were followed. Serum sIL-2R levels were analyzed and compared with clinical features, laboratory data, and measures of disease activity.

Results

Serum sIL-2R levels were significantly higher in DM patients than in IMNM patients and HCs (648.8 ± 433.1 U/ml vs. 352.3 ± 126.0 U/ml and 648.8 ± 433.1 U/ml vs. 285.8 ± 101.9 U/ml, respectively; all P < 0.001), while there was no significant difference between IMNM and HCs. There were also no significant differences of sIL-2R levels in DM, SLE, and RA. Importantly, serum sIL-2R levels were significantly higher in treatment-naïve or active DM patients than those that are not (1100.9 ± 550.4 U/ml vs. 615.6 ± 330.4 U/ml, P = 0.006; 808.8 ± 421.6 U/ml vs. 339.8 ± 103.4 U/ml, P < 0.001). DM patients with skin ulcers had significantly higher sIL-2R levels than those without (889.3 ± 509.9 U/ml vs. 640.0 ± 368.7 U/ml, P = 0.023). Cross-sectional analysis in DM showed that sIL-2R levels positively correlated with CK, ESR, CRP, ferritin, physician VAS, and MYOACT scores (rho = 0.278, rho = 0.474, rho = 0.469, rho = 0.454, r = 0.646, and r = 0.600, respectively; all P < 0.05), negatively correlated with T cell counts and MMT8 scores (r = −0.380, P = 0.002; rho = −0.394, P = 0.001). Follow-up study showed that changes in sIL-2R levels after treatment correlated with changes in physician VAS and MYOACT scores (r = 0.823 and r = 0.695, respectively; all P < 0.01).

Conclusion

Serum sIL-2R levels were elevated in DM but not in IMNM. Serum sIL-2R could act as a disease activity marker and be associated with ulcerative skin lesions in DM.

Relevance of Regulatory T Cells during Colorectal Cancer Development

In recent years, there has been a significant increase in the study of own and foreign human factors favoring the development of different types of cancer, including genetic and environmental ones. However, the fact that the immune response plays a fundamental role in the development of immunity and susceptibility to colorectal cancer (CRC) is much stronger. Among the many cell populations of the immune system that participate in restricting or favoring CRC development, regulatory T cells (Treg) play a major role in orchestrating immunomodulation during CRC. In this review, we established concrete evidence supporting the fact that Treg cells have an important role in the promotion of tumor development during CRC, mediating an increasing suppressive capacity which controls the effector immune response, and generating protection for tumors. Furthermore, Treg cells go through a process called "phenotypic plasticity", where they co-express transcription factors that promote an inflammatory profile. We reunited evidence that describes the interaction between the different effector populations of the immune response and its modulation by Treg cells adapted to the tumor microenvironment, including the mechanisms used by Treg cells to suppress the protective immune response, as well as the different subpopulations of Treg cells participating in tumor progression, generating susceptibility during CRC development. Finally, we discussed whether Treg cells might or might not be a therapeutic target for an effective reduction in the morbidity and mortality caused by CRC.

Common gamma chain cytokines and CD8 T cells in cancer

Overcoming exhaustion-associated dysfunctions and generating antigen-specific CD8 T cells with the ability to persist in the host and mediate effective long-term anti-tumor immunity is the final aim of cancer immunotherapy. To achieve this goal, immuno-modulatory properties of the common gamma-chain (γ_c) family of cytokines, that includes IL-2, IL-7, IL-15 and IL-21, have been used to fine-tune and/or complement current immunotherapeutic protocols. These agents potentiate CD8 T cell expansion and functions particularly in the context of immune checkpoint (IC) blockade, shape their differentiation, improve their persistence in vivo and alternatively, influence distinct aspects of the T cell exhaustion program. Despite these properties, the intrinsic impact of cytokines on CD8 T cell exhaustion has remained largely unexplored impeding optimal therapeutic use of these agents. In this review, we will discuss current knowledge regarding the influence of relevant γ_c cytokines on CD8 T cell differentiation and function based on clinical data and preclinical studies in murine models of cancer and chronic viral infection. We will restate the place of these agents in current immunotherapeutic regimens such as IC checkpoint blockade and adoptive cell therapy. Finally, we will discuss how γ_c cytokine signaling pathways regulate T cell immunity during cancer and whether targeting these pathways may sustain an effective and durable T cell response in patients.

A role for cell-autocrine interleukin-2 in regulatory T-cell homeostasis

Activated T-cells make both interleukin-2 (IL2) and its high-affinity receptor component CD25. Regulatory CD4 T-cells (Treg cells) do not make IL2, and the IL2-CD25 circuit is considered a paracrine circuit crucial in their generation and maintenance. Yet, all T-cells are capable of making IL2 at some stage during differentiation, making a cell-intrinsic autocrine circuit additionally possible. When we re-visited experiments with mixed bone marrow chimeras using a wide range of ratios of wild-type (WT) and IL2-/- genotype progenitors, we found that, as expected, thymic Treg cells were almost equivalent between WT and IL2-/- genotypes at ratios with WT prominence. However, at WT-limiting ratios, the IL2-/- genotype showed lower thymic Treg frequencies, indicating a role for cell-intrinsic autocrine IL2 in thymic Treg generation under IL2-limiting conditions. Further, peripheral IL2-/- naive CD4 T-cells showed poor conversion to inducible Tregs (pTregs) both in vivo and in vitro, again indicating a significant role for cell-intrinsic autocrine IL2 in their generation. Peripherally, the IL2-/- genotype was less prominent at all WT:IL2-/- ratios among both thymic Tregs (tTregs) and pTregs, adoptively transferred IL2-/- Tregs showed poorer survival than WT Tregs did, and RNA-seq analysis of WT and IL2-/- Tregs showed interesting differences in the T-cell receptor and transforming growth factor-beta-bone morphogenetic protein-JNK pathways between them, suggesting a non-titrating role for cell-intrinsic autocrine IL2 in Treg programming. These data indicate that cell-intrinsic autocrine IL2 plays significant roles in Treg generation and maintenance.

FOXP3 protects conventional human T cells from premature restimulation-induced cell death

The adaptive immune response relies on specific apoptotic programs to maintain homeostasis. Conventional effector T cell (Tcon) expansion is constrained by both forkhead box P3 (FOXP3)⁺-regulatory T cells (Tregs) and restimulation-induced cell death (RICD), a propriocidal apoptosis pathway triggered by repeated stimulation through the T-cell receptor (TCR). Constitutive FOXP3 expression protects Tregs from RICD by suppressing SLAM-associated protein (SAP), a key adaptor protein that amplifies TCR signaling strength. The role of transient FOXP3 induction in activated human CD4 and CD8 Tcons remains unresolved, but its expression is inversely correlated with acquired RICD sensitivity. Here, we describe a novel role for FOXP3 in protecting human Tcons from premature RICD during expansion. Unlike FOXP3-mediated protection from RICD in Tregs, FOXP3 protects Tcons through a distinct mechanism requiring de novo transcription that does not require SAP suppression. Transcriptome profiling and functional analyses of expanding Tcons revealed that FOXP3 enhances expression of the SLAM family receptor CD48, which in turn sustains basal autophagy and suppresses pro-apoptotic p53 signaling. Both CD48 and FOXP3 expression reduced p53 accumulation upon TCR restimulation. Furthermore, silencing FOXP3 expression or blocking CD48 decreased the mitochondrial membrane potential in expanding Tcons with a concomitant reduction in basal autophagy. Our findings suggest that FOXP3 governs a distinct transcriptional program in early-stage effector Tcons that maintains RICD resistance via CD48-dependent protective autophagy and p53 suppression.

Fatty Acid Synthase Contributes to Restimulation-Induced Cell Death of Human CD4 T Cells

Restimulation-induced cell death (RICD) is an apoptotic pathway triggered in activated effector T cells after T cell receptor (TCR) re-engagement. RICD operates at the peak of the immune response to ensure T cell expansion remains in check to maintain immune homeostasis. Understanding the biochemical regulation of RICD sensitivity may provide strategies for tuning the magnitude of an effector T cell response. Metabolic reprogramming in activated T cells is not only critical for T cell differentiation and effector functions, but also influences apoptosis sensitivity. We previously demonstrated that aerobic glycolysis correlates with optimum RICD sensitivity in human effector CD8 T cells. However, metabolic programming in CD4 T cells has not been investigated in this context. We employed a pharmacological approach to explore the effects of fatty acid and glycolytic metabolism on RICD sensitivity in primary human CD4 T cells. Blockade of fatty acid synthase (FASN) with the compound C75 significantly protected CD4 effector T cells from RICD, suggesting that fatty acid biosynthesis contributes to RICD sensitivity. Interestingly, sphingolipid synthesis and fatty acid oxidation (FAO) were dispensable for RICD. Disruption of glycolysis did not protect CD4 T cells from RICD unless glyceraldehyde-3-phosphate dehydrogenase (GAPDH) enzymatic activity was targeted specifically, highlighting important differences in the metabolic control of RICD in effector CD4 vs. CD8 T cell populations. Moreover, C75 treatment protected effector CD4 T cells derived from naïve, effector memory, and central memory T cell subsets. Decreased RICD in C75-treated CD4 T cells correlated with markedly reduced FAS ligand (FASL) induction and a Th2-skewed phenotype, consistent with RICD-resistant CD4 T cells. These findings highlight FASN as a critical metabolic potentiator of RICD in human effector CD4 T cells.

Daclizumab Therapy for Multiple Sclerosis

Daclizumab is a humanized monoclonal antibody that prevents formation of high-affinity interleukin (IL)-2 receptor (IL-2R). Because activated T cells up-regulate high-affinity IL-2R and IL-2 is used to grow activated T cells in vitro, daclizumab was envisioned to selectively inhibit activated T cells. However, the mechanism of action (MOA) of daclizumab is surprisingly broad and it includes many unanticipated effects on innate immunity. Specifically, daclizumab modulates the development of innate lymphoid cells, leading to expansion of immunoregulatory CD56^bright natural killer (NK) cells. Activated CD56^bright NK cells migrate to the intrathecal compartment in multiple sclerosis (MS) and regulate autoreactive T cells via cytotoxicity. Finally, daclizumab also restricts initial steps of T-cell activation by blocking trans-presentation of IL-2 by dendritic cells to antigen-specific T cells. In conclusion, daclizumab has complex immunomodulatory effects with resultant inhibition of central nervous system inflammation in MS.

Relationship between various cytokines implicated in asthma

Asthma is a complex disorder involving immunologic, environmental, genetic and other factors. Today, asthma is the most common disease encountered in clinical medicine in both children and adults worldwide. Asthma is characterized by increased responsiveness of the tracheobronchial tree resulting in chronic swelling and inflammation of the airways recognized to be controlled by the T-helper 2 (Th2) lymphocytes, which secrete cytokines to increase the production of IgE by B cells. There are many cytokines implicated in the development of the chronic inflammatory processes that are often observed in asthma. Ultimately, these cytokines cause the release of mediators such as histamine and leukotrienes (LT), which in turn promote airway remodeling, bronchial hyperresponsiveness and bronchoconstriction. The CD4⁺ T-lymphocytes from the airways of asthmatics express a panel of cytokines that represent the Th2 cells. The knowledge derived from numerous experimental and clinical studies have allowed physicians and scientists to understand the normal functions of these cytokines and their roles in the pathogenesis of asthma. The main focus of this review is to accentuate the relationship between various cytokines implicated in human asthma. However, some key findings from animal models will be highlighted to support the discoveries from clinical studies.

Human interleukin-2 receptor β mutations associated with defects in immunity and peripheral tolerance

Zhang et al. identify human IL-2Rβ deficiency as a cause of severe immune dysregulation. The hypomorphic gene mutations reveal variable IL-2Rβ expression and function between different lymphocyte subsets as a means of selectively modulating immune responses.

Interleukin-2, which conveys essential signals for immunity, operates through a heterotrimeric receptor. Here we identify human interleukin-2 receptor (IL-2R) β chain (IL2RB) gene defects as a cause of life-threatening immune dysregulation. We report three homozygous mutations in the IL2RB gene of eight individuals from four consanguineous families that cause disease by distinct mechanisms. Nearly all patients presented with autoantibodies, hypergammaglobulinemia, bowel inflammation, dermatological abnormalities, lymphadenopathy, and cytomegalovirus disease. Patient T lymphocytes lacked surface expression of IL-2Rβ and were unable to respond to IL-2 stimulation. By contrast, natural killer cells retained partial IL-2Rβ expression and function. IL-2Rβ loss of function was recapitulated in a recombinant system in which IL2RB mutations caused reduced surface expression and IL-2 binding. Stem cell transplant ameliorated clinical symptoms in one patient; forced expression of wild-type IL-2Rβ also increased the IL-2 responsiveness of patient T lymphocytes in vitro. Insights from these patients can inform the development of IL-2–based therapeutics for immunological diseases and cancer.

Daclizumab: Mechanisms of Action, Therapeutic Efficacy, Adverse Events and Its Uncovering the Potential Role of Innate Immune System Recruitment as a Treatment Strategy for Relapsing Multiple Sclerosis

Daclizumab (DAC) is a humanized, monoclonal antibody that blocks CD25, a critical element of the high-affinity interleukin-2 receptor (IL-2R). DAC HYP blockade of CD25 inhibits effector T cell activation, regulatory T cell expansion and survival, and activation-induced T-cell apoptosis. Because CD25 blockade reduces IL-2 consumption by effector T cells, it increases IL-2 bioavailability allowing for greater interaction with the intermediate-affinity IL-2R, and therefore drives the expansion of CD56^bright natural killer (NK) cells. Furthermore, there appears to be a direct correlation between CD56^bright NK cell expansion and DAC HYP efficacy in reducing relapses and MRI evidence of disease activity in patients with RMS in phase II and phase III double-blind, placebo- and active comparator-controlled trials. Therapeutic efficacy was maintained during open-label extension studies. However, treatment was associated with an increased risk of rare adverse events, including cutaneous inflammation, autoimmune hepatitis, central nervous system Drug Reaction with Eosinophilia Systemic Symptoms (DRESS) syndrome, and autoimmune Glial Fibrillary Acidic Protein (GFAP) alpha immunoglobulin-associated encephalitis. As a result, DAC HYP was removed from clinical use in 2018. The lingering importance of DAC is that its use led to a deeper understanding of the underappreciated role of innate immunity in the potential treatment of autoimmune disease.

Revisiting IL-2: Biology and therapeutic prospects

Interleukin-2 (IL-2), the first cytokine that was molecularly cloned, was shown to be a T cell growth factor essential for the proliferation of T cells and the generation of effector and memory cells. On the basis of this activity, the earliest therapeutic application of IL-2 was to boost immune responses in cancer patients. Therefore, it was a surprise that genetic deletion of the cytokine or its receptor led not only to the expected immune deficiency but also to systemic autoimmunity and lymphoproliferation. Subsequent studies established that IL-2 is essential for the maintenance of Foxp3⁺ regulatory T cells (T_reg cells), and in its absence, there is a profound deficiency of T_reg cells and resulting autoimmunity. We now know that IL-2 promotes the generation, survival, and functional activity of T_reg cells and thus has dual and opposing functions: maintaining T_reg cells to control immune responses and stimulating conventional T cells to promote immune responses. It is well documented that certain IL-2 conformations result in selective targeting of T_reg cells by increasing reliance on CD25 binding while compromising CD122 binding. Recent therapeutic strategies have emerged to use IL-2, monoclonal antibodies to IL-2, or IL-2 variants to boost T_reg cell numbers and function to treat autoimmune diseases while dealing with the continuing challenges to minimize the generation of effector and memory cells, natural killer cells, and other innate lymphoid populations.

Fueling Cancer Immunotherapy With Common Gamma Chain Cytokines

Adoptive T cell transfer therapy (ACT) using tumor infiltrating lymphocytes or lymphocytes redirected with antigen receptors (CAR or TCR) has revolutionized the field of cancer immunotherapy. Although CAR T cell therapy mediates robust responses in patients with hematological malignancies, this approach has been less effective for treating patients with solid tumors. Additionally, toxicities post T cell infusion highlight the need for safer ACT protocols. Current protocols traditionally expand T lymphocytes isolated from patient tumors or from peripheral blood to large magnitudes in the presence of high dose IL-2 prior to infusion. Unfortunately, this expansion protocol differentiates T cells to a full effector or terminal phenotype in vitro, consequently reducing their long-term survival and antitumor effectiveness in vivo. Post-infusion, T cells face further obstacles limiting their persistence and function within the suppressive tumor microenvironment. Therapeutic manipulation of T cells with common γ chain cytokines, which are critical growth factors for T cells, may be the key to bypass such immunological hurdles. Herein, we discuss the primary functions of the common γ chain cytokines impacting T cell survival and memory and then elaborate on how these distinct cytokines have been used to augment T cell-based cancer immunotherapy.

Structural Basis for Signaling Through Shared Common γ Chain Cytokines

The common γ chain (γ_c) family of hematopoietic cytokines consists of six distinct four α-helix bundle soluble ligands that signal through receptors which include the shared γ_c subunit to coordinate a wide range of physiological processes, in particular, those related to innate and adaptive immune function. Since the first crystallographic structure of a γ_c family cytokine/receptor signaling complex (the active Interleukin-2 [IL-2] quaternary complex) was determined in 2005 [1], tremendous progress has been made in the structural characterization of this protein family, transforming our understanding of the molecular mechanisms underlying immune activity. Although many conserved features of γ_c family cytokine complex architecture have emerged, distinguishing details have been observed for individual cytokine complexes that rationalize their unique functional properties. Much work remains to be done in the molecular characterization of γ_c family signaling, particularly with regard to intracellular activation events, and looking forward, new technologies in structural biophysics will offer further insight into the biology of cytokine signaling to inform the design of targeted therapeutics for treatment of immune-linked diseases such as cancer, infection, and autoimmune disorders.

The effects of interleukin-2 on immune response regulation

The immune system has many adaptive and dynamic components that are regulated to ensure appropriate, precise and rapid response to a foreign pathogen. A delayed or inadequate immune response can lead to prolonged disease, while an excessive or under-regulated response can lead to autoimmunity. The cytokine, interleukin-2 (IL-2) and its receptor IL-2R play an important role in maintaining this balance.The IL-2 receptor transduces pSTAT5 signal through both the intermediate and high affinity receptors, which differ from each other by the presence of CD25 chain in IL-2 receptor. We present experimental data on the kinetics of pSTAT5 signalling through both of the receptors and develop a model that captures this kinetics. We then use this model to parameterize key aspects of two additional models in which we propose and study two different mechanisms by which IL-2 receptor can transduce distinct signals leading to either an activated or a non-activated cell state. We speculate that this initial state differentiation, perhaps enhanced by downstream feedbacks, may eventually lead to differential cell fates.Our result shows that non-linear dynamical models can suggest resolution of a puzzling array of seemingly contradictory experimental results on IL-2 effect on proliferation and differentiation of T-cells.

The Common Cytokine Receptor γ Chain Family of Cytokines

Interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15, and IL-21 form a family of cytokines based on their sharing the common cytokine receptor γ chain (γc), which was originally discovered as the third receptor component of the IL-2 receptor, IL-2Rγ. The IL2RG gene is located on the X chromosome and is mutated in humans with X-linked severe combined immunodeficiency (XSCID). The breadth of the defects in XSCID could not be explained solely by defects in IL-2 signaling, and it is now clear that γc is a shared receptor component of the six cytokines noted above, making XSCID a disease of defective cytokine signaling. Janus kinase (JAK)3 associates with γc, and JAK3-deficient SCID phenocopies XSCID, findings that served to stimulate the development of JAK3 inhibitors as immunosuppressants. γc family cytokines collectively control broad aspects of lymphocyte development, growth, differentiation, and survival, and these cytokines are clinically important, related to allergic and autoimmune diseases and cancer as well as immunodeficiency. In this review, we discuss the actions of these cytokines, their critical biological roles and signaling pathways, focusing mainly on JAK/STAT (signal transducers and activators of transcription) signaling, and how this information is now being used in clinical therapeutic efforts.

T Cells and Regulated Cell Death: Kill or Be Killed

Cell death plays two major complementary roles in T cell biology: mediating the removal of cells that are targeted by T cells and the removal of T cells themselves. T cells serve as major actors in the adaptive immune response and function by selectively killing cells which are infected or dysfunctional. This feature is highly involved during homeostatic maintenance, and is relied upon and modulated in the context of cancer immunotherapy. The vital recognition and elimination of both autoreactive T cells and cells which are unable to recognize threats is a highly selective and regulated process. Moreover, detection of potential threats will result in the activation and expansion of T cells, which on resolution of the immune response will need to be eliminated. The culling of these T cells can be executed via a multitude of cell death pathways which are used in context-specific manners. Failure of these processes may result in an accumulation of misdirected or dysfunctional T cells, leading to complications such as autoimmunity or cancer. This review will focus on the role of cell death regulation in the maintenance of T cell homeostasis, as well as T cell-mediated elimination of infected or dysfunctional cells, and will summarize and discuss the current knowledge of the cellular mechanisms which are implicated in these processes.

Contemporary Strategies and Barriers to Transplantation Tolerance

The purpose of this review is to discuss immunologic tolerance as it applies to solid organ transplantation and to identify barriers that hinder the achievement of this long-term goal. First, the definition of tolerance and an introduction of mechanisms by which tolerance exists or can be achieved will be discussed. Next, a review of contemporary attempts at achieving transplant tolerance will be described. Finally, a discussion of the humoral barriers to transplantation tolerance and potential ways to overcome these barriers will be presented.

Beyond Cell Death: New Functions for TNF Family Cytokines in Autoimmunity and Tumor Immunotherapy

Originally discovered as an inducer of apoptosis, the TNF-family receptor Fas (CD95, APO-1, TNFRSF6) has more recently been found to have functions beyond cell death, including T cell co-stimulation and promoting terminal differentiation of CD4⁺ and CD8⁺ T cells. Other TNF family members also discovered as apoptosis inducers, such as TRAIL (APO-2L, TNFSF10), can promote inflammation through caspase-8. Surprisingly, non-apoptotic signaling through Fas can protect from the autoimmunity seen in Fas deficiency independently from the cell death inducing functions of the receptor. Non-apoptotic Fas signaling can induce tumor cell growth and migration, and impair the efficacy of T cell adoptive immunotherapy. Blocking of non-apoptotic functions of these receptors may be a novel strategy to regulate autoimmunity and inflammation, and enhance antitumor immunity.