Effect of PD-1: PD-L1 in Invariant Natural Killer T-Cell Emigration and Chemotaxis Following Sepsis

invariant Natural Killer T Cells Modulate the Peritoneal Macrophage Response to Polymicrobial Sepsis

INTRODUCTION

A dysregulated immune system is a major driver of the mortality and long-term morbidity from sepsis. With respect to macrophages, it has been shown that phenotypic changes are critical to effector function in response to acute infections, including intra-abdominal sepsis. Invariant natural killer T cells (iNKT cells) have emerged as potential central regulators of the immune response to a variety of infectious insults. Specifically, various iNKT cell:macrophage interactions have been noted across a spectrum of diseases, including acute events such as sepsis. However, the potential for iNKT cells to affect peritoneal macrophages during an abdominal septic event is as yet unknown.

METHODS

Cecal ligation and puncture (CLP) was performed in both wild type (WT) and invariant natural killer T cell knockout (iNKT-/-) mice. 24 h following CLP or sham operation, peritoneal macrophages were collected for analysis. Analysis of macrophage phenotype and function was undertaken to include analysis of bactericidal activity and cytokine or superoxide production.

RESULTS

Within iNKT-/- mice, a greater degree of intraperitoneal macrophages in response to the sepsis was noted. Compared to WT mice, within iNKT-/- mice, CLP did induce an increase in CD86+ and CD206+, but no difference in CD11b+. Unlike WT mice, intra-abdominal sepsis within iNKT-/- mice induced an increase in Ly6C-int (5.2% versus 14.9%; P < 0.05) and a decrease in Ly6C-high on peritoneal macrophages. Unlike phagocytosis, iNKT cells did not affect macrophage bactericidal activity. Although iNKT cells did not affect interleukin-6 production, iNKT cells did affect IL-10 production and both nitrite and superoxide production from peritoneal macrophages.

CONCLUSIONS

The observations indicate that iNKT cells affect specific phenotypic and functional aspects of peritoneal macrophages during polymicrobial sepsis. Given that pharmacologic agents that affect iNKT cell functioning are currently in clinical trial, these findings may have the potential for translation to critically ill surgical patients with abdominal sepsis.

invariant Natural Killer T cell therapy as a novel therapeutic approach in hematological malignancies

Invariant Natural Killer T cell therapy is an emerging platform of immunotherapy for cancer treatment. This unique cell population is a promising candidate for cell therapy for cancer treatment because of its inherent cytotoxicity against CD1d positive cancers as well as its ability to induce host CD8 T cell cross priming. Substantial evidence supports that iNKT cells can modulate myelomonocytic populations in the tumor microenvironment to ameliorate immune dysregulation to antagonize tumor progression. iNKT cells can also protect from graft-versus-host disease (GVHD) through several mechanisms, including the expansion of regulatory T cells (Treg). Ultimately, iNKT cell-based therapy can retain antitumor activity while providing protection against GVHD simultaneously. Therefore, these biological properties render iNKT cells as a promising "off-the-shelf" therapy for diverse hematological malignancies and possible solid tumors. Further the introduction of a chimeric antigen recetor (CAR) can further target iNKT cells and enhance function. We foresee that improved vector design and other strategies such as combinatorial treatments with small molecules or immune checkpoint inhibitors could improve CAR iNKT in vivo persistence, functionality and leverage anti-tumor activity along with the abatement of iNKT cell dysfunction or exhaustion.

A higher number of exhausted local PD1+, but not TIM3+, NK cells in advanced endometriosis

Endometriosis (EMT) is a chronic inflammatory disease characterized by the presence and growth of endometrial-like glandular epithelial and stromal cells outside the uterus. Natural Killer (NK) cell dysfunction/exhaustion has been shown in patients with EMT. In this case-control study, we compared the frequency of exhausted PD-1 or TIM-3 positive NK cells in peripheral blood (PB) and peritoneal fluid (PF) of women with advanced endometriosis to control fertile women. PB and PF were collected from women aged 25-40 who underwent the laparoscopic procedure, including 13 stages III/IV endometriosis and 13 control samples. Multicolor flowcytometry was used to compare the frequency of PD-1 or TIM-3 positive NK (CD3-CD56+) cells in PB and PF of two groups. We demonstrated a higher percentage of PD-1+ NK cells in the peritoneal fluid of patients with endometriosis rather than controls (P-value = 0.039). This significance was related to stage IV of endometriosis (P-value = 0.047). We can not show any significant difference in the number of PD-1 or TIM-3 positive NK cells in peripheral blood. Our results suggest a local exhausted NK cell response in endometriosis that can be a leading factor in the endometriosis pathogenesis.

The pathogenesis and potential therapeutic targets in sepsis

Sepsis is defined as "a life-threatening organ dysfunction caused by dysregulated host systemic inflammatory and immune response to infection." At present, sepsis continues to pose a grave healthcare concern worldwide. Despite the use of supportive measures in treating traditional sepsis, such as intravenous fluids, vasoactive substances, and oxygen plus antibiotics to eradicate harmful pathogens, there is an ongoing increase in both the morbidity and mortality associated with sepsis during clinical interventions. Therefore, it is urgent to design specific pharmacologic agents for the treatment of sepsis and convert them into a novel targeted treatment strategy. Herein, we provide an overview of the molecular mechanisms that may be involved in sepsis, such as the inflammatory response, immune dysfunction, complement deactivation, mitochondrial damage, and endoplasmic reticulum stress. Additionally, we highlight important targets involved in sepsis-related regulatory mechanisms, including GSDMD, HMGB1, STING, and SQSTM1, among others. We summarize the latest advancements in potential therapeutic drugs that specifically target these signaling pathways and paramount targets, covering both preclinical studies and clinical trials. In addition, this review provides a detailed description of the crosstalk and function between signaling pathways and vital targets, which provides more opportunities for the clinical development of new treatments for sepsis.

SPLENIC INVARIANT NATURAL KILLER T CELLS PLAY A SIGNIFICANT ROLE IN THE RESPONSE TO POLYMICROBIAL SEPSIS

ABSTRACT

Background: Sepsis is marked by a dysregulated immune response to an infection. Invariant natural killer T cells ( i NKT cells) are a pluripotent lymphocyte subpopulation capable of affecting and coordinating the immune response to sepsis. The spleen is an important site of immune interactions in response to an infection. Splenic i NKT cells have emerged as important potential frontline mediators of chronic immune response. There are few data addressing the role splenic of i NKT cells in response to intra-abdominal polymicrobial sepsis. Methods: The cecal ligation and puncture model was used to create intra-abdominal sepsis in 8- to 12-week-old wild-type, i NKT -/- , or programmed cell death receptor-1 (PD-1) -/- mice. Twenty-four hours later, spleens were harvested. Flow cytometry was used for phenotyping using monoclonal antibodies. Cell sort was used to isolate i NKT cells. A macrophage cell line was used to assess i NKT cell-phagocyte interactions. Enzyme-linked immunosorbent assay was used for cytokine analysis. Results: Splenic i NKT-cell populations rapidly declined following induction of sepsis. Within i NKT-cell -/- mice, a distinct baseline hyperinflammatory environment was noted. Within wild type, sepsis induced an increase in splenic IL-6 and IL-10, whereas in i NKT -/- mice, there was no change in elevated IL-6 levels and a noted decrease in IL-10 expression. Further, following sepsis, PD-1 expression was increased upon spleen i NKT cells. With respect to PD-1 ligands upon phagocytes, PD-1 ligand expression was unaffected, whereas PD-L2 expression was significantly affected by the presence of PD-1. Conclusions: Invariant natural killer T cells play a distinct role in the spleen response to sepsis, an effect mediated by the checkpoint protein PD-1. Given that modulators are available in clinical trials, this offers a potential therapeutic target in the setting of sepsis-induced immune dysfunction.

4-Octyl itaconate regulates immune balance by activating Nrf2 and negatively regulating PD-L1 in a mouse model of sepsis

Introduction: Sepsis is a major global health challenge with high mortality rates and no effective treatment. Recent studies have suggested that sepsis may be associated with immune system dysfunction. Itaconate may exert anti-inflammatory effects via Nrf2 signaling. Although Nrf2 regulates oxidative/exogenous stress responses and inhibits inflammatory responses, the mechanism via which Nrf2 regulates immune checkpoints in sepsis remains unclear. Objectives: This study aimed to investigate the role of the Nrf2 signaling pathway in sepsis immunosuppression injury by exploring Nrf2 target genes in inflammatory macrophages in a mouse model of sepsis. Methods: We evaluated the effects of 4-octyl itaconate (OI) on pro-inflammatory and anti-inflammatory cytokines in a mouse model of sepsis and RAW264.7 cells. In addition, we investigated if OI could inhibit LPS-induced oxidative stress by activating Nrf2 signaling in vitro and in vivo. Results: OI reduced the release of pro-inflammatory cytokines and increased the release of anti-inflammatory cytokines, thereby inhibiting inflammation. OI increased glutathione synthase (GSS) expression by activating the Nrf2 signaling pathway to promote GSH synthesis, thus, inhibiting oxidative stress. OI inhibited the early release of inflammatory and oxidative stress-related factors to reduce tissue and organ injury in mice with sepsis, while Nrf2 interfered with PD-L1 induction and inhibited PD-L1 expression at an advanced stage to reduce the occurrence of sepsis immunosuppression. Conclusions: This study indicates that Nrf2 is a novel negative regulator of PD-L1 that functions at immune checkpoints and suggests an underlying mechanism for the anti-inflammatory process mediated by Nrf2.

A Peptide-Based Checkpoint Immunomodulator Alleviates Immune Dysfunction in Murine Polymicrobial Sepsis

ABSTRACT

Sepsis-induced immunosuppression involves both innate and adaptive immunity and is associated with the increased expression of checkpoint inhibitors, such as programmed cell-death protein 1 (PD-1). The expression of PD-1 is associated with poor outcomes in septic patients, and in models of sepsis, blocking PD-1 or its ligands with antibodies increased survival and alleviated immune suppression. While inhibitory antibodies are effective, they can lead to immune-related adverse events (irAEs), in part due to continual blockade of the PD-1 pathway, resulting in hyperactivation of the immune response. Peptide-based therapeutics are an alternative drug modality that provide a rapid pharmacokinetic profile, reducing the incidence of precipitating irAEs. We recently reported that the potent, peptide-based PD-1 checkpoint antagonist, LD01, improves T-cell responses. The goal of the current study was to determine whether LD01 treatment improved survival, bacterial clearance, and host immunity in the cecal-ligation and puncture (CLP)-induced murine polymicrobial sepsis model. LD01 treatment of CLP-induced sepsis significantly enhanced survival and decreased bacterial burden. Altered survival was associated with improved macrophage phagocytic activity and T-cell production of interferon-γ. Further, myeloperoxidase levels and esterase-positive cells were significantly reduced in LD01-treated mice. Taken together, these data establish that LD01 modulates host immunity and is a viable therapeutic candidate for alleviating immunosuppression that characterizes sepsis and other infectious diseases.

Cutaneous burn diminishes beneficial effect of intravenously administered mesenchymal stem cells on acute lung injury induced by smoke inhalation in sheep

OBJECTIVE

To investigate effects of intravenously administered allogeneic mesenchymal stem cells (MSCs) on burn/smoke-induced lung injury.

METHODS

Sheep were subjected to 40%, third-degree flame skin burn and smoke inhalation under deep anesthesia and analgesia. One-hour after injury, PlasmaLite A (control) or 200 million MSCs (treatment) were intravenously administered. Pulmonary oxygenation index, PaO2/FiO2 ratio, lung-lymph flow, and bloodless lung wet-to-dry weight ratio were measured. Distribution of MSCs and stromal cell-derived factor-1 (Sdf-1) protein level were determined in lung and skin tissues. Effects of burn exudate on MSCs migration were characterized.

RESULTS

MSCs did not attenuate pulmonary dysfunction. The number of MSCs was significantly higher in lungs of sheep with smoke inhalation compared with those with burn/smoke injury. In contrast, number of MSCs was significantly higher beneath burned skin in sheep with burn/smoke than in unburned skin of sheep with smoke inhalation only. Expression of Sdf-1 protein was increased in the burned skin compared to unburned skin. Effects of burn exudate on cultured MSCs proliferation differed depending on collection time.

CONCLUSION

Skin burn diminishes beneficial effects of MSCs on smoke-induced lung injury, by promoting migration of MSCs from the pulmonary tissue to the injured skin area, possibly via expression of Sdf-1 protein.

Increased attrition of memory T cells during sepsis requires 2B4

Recent seminal studies have revealed that laboratory mice differ from adult humans with regard to the frequency, number, and distribution of memory T cells. Because our data show that memory T cells are more susceptible to sepsis-induced death than naive T cells, in this study we developed a model in which mice possess a memory T cell compartment more similar to that of adult humans, to better study immune responses during sepsis in the more physiologically relevant context of high frequencies of memory T cells. Using this model, we found that CD44hi memory T cells significantly upregulated the coinhibitory molecule 2B4 during sepsis, and 2B4+ memory T cells coexpressed markers of both activation and exhaustion. Genetic deficiency in 2B4 resulted in decreased mortality during sepsis. Mechanistically, this decreased mortality was associated with reduced caspase-3/7+ apoptotic T cells in 2B4-/- relative to WT, septic hosts. These results were corroborated by analysis of PBMCs isolated from human patients with sepsis, which showed increased frequencies of caspase-3/7+ apoptotic cells among 2B4+ relative to 2B4- T cells. Thus, 2B4 plays a critical role in sepsis-induced apoptosis in both murine memory T cells and those isolated from human patients with sepsis.

A novel role for programmed cell death receptor ligand 2 in sepsis-induced hepatic dysfunction

The liver is an organ that, when dysfunctional in a septic patient, is strongly associated with morbidity and mortality. Understanding the pathophysiology of liver failure during sepsis may lead to improved diagnostics and potential therapeutic targets. Historically, programmed cell death receptor (PD) ligand 1 (PD-L1) has been considered the primary ligand for its checkpoint molecule counterpart, PD-1, with PD-L2 rarely in the immunopathological spotlight. PD-1 and PD-L1 contribute to liver dysfunction in a murine cecal ligation and puncture (CLP) model of sepsis, but virtually nothing is known about PD-L2's role in sepsis. Therefore, our central hypothesis was that sepsis-induced changes in hepatic PD-L2 expression contributed to worsened liver function and, subsequently, more pronounced morbidity and mortality. We found that although PD-L1 gene deficiency attenuated the hepatic dysfunction seen in wild-type mice after CLP, the loss of PD-L2 appeared to actually worsen indices of liver function along with a trend toward higher liver tissue vascular permeability. Conversely, some protective effects of PD-L2 gene deletion were noted, such as reduced liver/peritoneal bacterial load and reduced IL-6, IL-10, and macrophage inflammatory protein 2 levels following CLP. These diverse actions, as well as the unique expression pattern of PD-L2, may explain why no overt survival advantage could be witnessed in the septic PD-L2^-/- mice. Taken together, these data suggest that although PD-L2 has some selective effects on the hepatic response seen in the septic mouse, these factors are not sufficient to alter septic mortality in this adult murine model. NEW & NOTEWORTHY Our study shows not only that ligands of the checkpoint protein PD-1 respond inversely to a stressor such as septic challenge (PD-L2 declines, whereas PD-L1 rises) but also that aspects of liver dysfunction increase in septic mice lacking the PD-L2 gene. Furthermore, these differences in PD-L2 gene-deficient animals culminated in the abrogation of the survival advantage seen in the septic PD-L1-knockout mice, suggesting that PD-L2 may have roles beyond a simple immune tolerogen.

Group 2 Innate Lymphoid Cells (ILC2s) Are Key Mediators of the Inflammatory Response in Polymicrobial Sepsis

Sepsis remains a major public health concern, characterized by marked immune dysfunction. Innate lymphoid cells develop from a common lymphoid precursor but have a role in orchestrating inflammation during innate response to infection. Here, we investigate the pathologic contribution of the group 2 innate lymphoid cells (ILC2s) in a murine model of acute septic shock (cecal ligation and puncture). Flow cytometric data revealed that ILC2s increase in number and percentage in the small intestine and in the peritoneal cells and inversely decline in the liver at 24 hours after septic insult. Sepsis also resulted in changes in ILC2 effector cytokine (IL-13) and activating cytokine (IL-33) in the plasma of mice and human patients in septic shock. Of interest, the sepsis-induced changes in cytokines were abrogated in mice deficient in functionally invariant natural killer T cells. Mice deficient in IL-13-producing cells, including ILC2s, had a survival advantage after sepsis along with decreased morphologic evidence of tissue injury and reduced IL-10 levels in the peritoneal fluid. Administration of a suppressor of tumorigenicity 2 (IL-33R) receptor-blocking antibody led to a transient survival advantage. Taken together, these findings suggest that ILC2s may play an unappreciated role in mediating the inflammatory response in both mice and humans; further, modulating ILC2 response in vivo may allow development of immunomodulatory strategies directed against sepsis.

A novel role for coinhibitory receptors/checkpoint proteins in the immunopathology of sepsis

Coinhibitory molecules, such as PD-1, CTLA-4, 2B4, and BTLA, are an important new family of mediators in the pathophysiology of severe bacterial and/or fungal infection, as well as the combined insults of shock and sepsis. Further, the expression of these molecules may serve as indicators of the immune status of the septic individual. Using PD-1:PD-L as an example, we discuss in this review how such checkpoint molecules may affect the host response to infection by mediating the balance between effective immune defense and immune-mediated tissue injury. Additionally, we explore how the up-regulation of PD-1 and/or PD-L1 expression on not only adaptive immune cells (e.g., T cells), but also on innate immune cells (e.g., macrophages, monocytes, and neutrophils), as well as nonimmune cells during sepsis and/or shock contributes to functional alterations often with detrimental sequelae.

Pre-existing malignancy results in increased prevalence of distinct populations of CD4+ T cells during sepsis

The presence of pre-existing malignancy in murine hosts results in increased immune dysregulation and risk of mortality following a septic insult. Based on the known systemic immunologic changes that occur in cancer hosts, we hypothesized that the presence of pre-existing malignancy would result in phenotypic and functional changes in CD4⁺ T cell responses following sepsis. In order to conduct a non-biased, unsupervised analysis of phenotypic differences between CD4⁺ T cell compartments, cohorts of mice were injected with LLC1 tumor cells and tumors were allowed to grow for 3 weeks. These cancer hosts and age-matched non-cancer controls were then subjected to CLP. Splenocytes were harvested at 24h post CLP and flow cytometry and SPADE (Spanning-tree Progression Analysis of Density-normalized Events) were used to analyze populations of CD4⁺ cells most different between the two groups. Results indicated that relative to non-cancer controls, cancer mice contained more resting memory CD4⁺ T cells, more activated CD4⁺ effectors, and fewer naïve CD4⁺ T cells during sepsis, suggesting that the CD4⁺ T cell compartment in cancer septic hosts is one of increased activation and differentiation. Moreover, cancer septic animals exhibited expansion of two distinct subsets of CD4⁺ T cells relative to previously healthy septic controls. Specifically, we identified increases in both a PD-1^hi population and a distinct 2B4^hi BTLA^hi LAG-3^hi population in cancer septic animals. By combining phenotypic analysis of exhaustion markers with functional analysis of cytokine production, we found that PD-1⁺ CD4⁺ cells in cancer hosts failed to make any cytokines following CLP, while the 2B4⁺ PD-1^lo cells in cancer mice secreted increased TNF during sepsis. In sum, the immunophenotypic landscape of cancer septic animals is characterized by both increased CD4⁺ T cell activation and exhaustion, findings that may underlie the observed increased mortality in mice with pre-existing malignancy following sepsis.

Program Cell Death Receptor-1-Mediated Invariant Natural Killer T-Cell Control of Peritoneal Macrophage Modulates Survival in Neonatal Sepsis

We have shown that invariant natural killer T (iNKT) cells mediate sepsis-induced end-organ changes and immune responses, including macrophage bacterial phagocytosis, a finding regulated by the check point protein program cell death receptor-1 (PD-1). Furthermore, PD-1 mediates mortality in both adult and neonatal murine sepsis as well as in surgical patients. Given our previous findings, we hypothesize that iNKT cells will also modulate neonatal sepsis survival, and that this effect is regulated in part through PD-1. We utilized a polymicrobial intra-peritoneal cecal slurry (CS) sepsis model in wild type (WT), iNKT^−/− or PD-1^−/− 5–7 day old neonatal pups. Typically, tissues were harvested at 24 h for various bioassays/histology and, in some cases, survival was assessed for up to 7 days. Interestingly, similar to what we recently reported for PD-1^−/− mice following CS, iNKT^−/−-deficient animals exhibit a markedly improved survival vs. WT. Histologically, minor alterations in liver architectural, which were noted in WT pups, were attenuated in both iNKT^−/− and PD-1^−/− pups. Following CS, PECAM-1 expression was unchanged in the WT pups but increased in both iNKT^−/− and PD-1^−/− pups. In WT, following CS the emergence of a Ly6C^low subpopulation was noted among the influxed peritoneal macrophage population. Conversely, within iNKT^−/− pups, there were fewer peritoneal macrophages and a greater percentage of Ly6C^high macrophages. We show not only a key role for iNKT cells in affecting end-organ damage as well as alterations in phagocytes phenotypes in neonatal sepsis but that this iNKT cell mediated effect is driven by the central checkpoint protein PD-1.

Improved survival after induction of sepsis by cecal slurry in PD-1 knockout murine neonates

BACKGROUND

Sepsis and the ensuing immune dysfunction continue to be major contributors to neonatal morbidity and mortality. Neonatal sepsis also is associated with profound immune dysfunction. We have recently identified a role for a family of coinhibitory molecules that are altered in murine sepsis and in critically ill adult patients, which may be a target for development of novel therapies. There is, however, a paucity of data pertaining to the role of coinhibitory checkpoint proteins in the control and modulation of neonatal sepsis.

METHODS

The cecal slurry model consists of harvesting the cecal content of an adult, wild-type, male mouse and combining it with 5% dextrose to create a cecal slurry with a concentration of 80 mg/mL (LD₇₀ at 7 days). Neonatal mice (5-7 days of age) underwent intraperitoneal injection of the cecal slurry or 0.9% saline for the sham procedure. Wild-type (C57BL/6) or PD-1^-/- mice were used; a 7-day survival study was undertaken. Cytometric bead array was used for cytokine expression. Blood and peritoneal fluid was cultured for bacterial burden. Flow cytometry was used to assess the peritoneal cavity cell populations.

RESULTS

There was no mortality after the sham procedure in either wild-type or PD-1^-/- pups. PD-1 markedly affected sepsis survival with significantly improved survival in the PD-1^-/- pups (40% vs 80%; P < .01). This survival improvement was not associated with any difference in bacterial clearance. The bacterial burden was equivalent between wild-type and PD-1^-/- pups at 24 hours after cecal slurry. However, PD-1^-/- pups did display an increased circulating cytokine response to the cecal slurry compared with wild type, with increased expression of IL-6, IL-10, and TNF-α levels. Within the peritoneal cavity, sepsis induced an influx of neutrophils, a finding that was increased in PD-1^-/- pups. Although the T-cell response was unaffected by PD-1, it was noted that cecal slurry induced a loss of peritoneal B cells in WT, while the peritoneal B-cell population was preserved in PD-1^-/- pups.

CONCLUSION

Our data suggest that the checkpoint protein, PD-1, plays an important role in controlling the immune response to sepsis in the neonate, ultimately affecting sepsis-related mortality in this neonatal murine model of sepsis. Akin to adult studies, these data further emphasize the potential therapeutic target for PD-1 across a spectrum of septic patients.