Characterization of pulmonary immune responses to hyperoxia by high-dimensional mass cytometry analyses

Neurological outcomes and mortality following hyperoxemia in adult patients with acute brain injury: an updated meta-analysis and meta-regression

BACKGROUND

The aim of this study was to evaluate the association of arterial hyperoxemia with neurological outcomes and mortality in adults with acute brain injury (ABI).

METHODS

Six electronic databases, including MEDLINE, Embase and online registers of clinical trials, were systematically searched from inception to June 1 st, 2024. Studies comparing the effects of hyperoxemia versus no hyperoxemia on outcomes of hospitalized adult patients with ABI-related conditions (e.g. traumatic brain injury, post-cardiac arrest, subarachnoid hemorrhage, intracerebral hemorrhage, and ischemic stroke) were included according to PRISMA guidelines. Data were pooled using a random-effects model for unadjusted and covariate-adjusted odds ratios. The primary outcome was poor neurological outcome as defined by each individual study, and the secondary outcome was all-cause mortality. Subgroup analyses were conducted based on principal diagnosis, timing of outcome measures, oxygenation thresholds, among other factors. Meta-regression was applied to identify sources of heterogeneity.

RESULTS

After 7,849 nonduplicated records were screened, 66 studies fulfilled eligibility criteria for systematic review. The meta-analysis including 24 studies (16,635 patients) revealed that patients with hyperoxemia are 1.29 times more likely to develop poor neurological outcomes (unadjusted OR, 1.295; 95% Confidence Interval, CI 1.040-1.616) compared with those with no hyperoxemia, particularly in subarachnoid hemorrhage and ischemic stroke subgroups. The meta-analysis including 35 studies (98,207 patients) revealed that all-cause mortality is 1.13 times more likely (OR 1.13; 95% CI 1.002-1.282) in patients with hyperoxemia compared with no hyperoxemia.

CONCLUSIONS

In our study we found that hyperoxemia is significantly associated with an increased risk of poor neurological outcomes and mortality in patients with acute brain injury compared to those with no hyperoxemia. Our results suggest the importance of carefully adjusting oxygenation strategies in neurocritical ICUs.

Therapeutic characteristics of alveolar-like macrophages in mouse models of hyperoxia and LPS-induced lung inflammation

Acute respiratory distress syndrome (ARDS) is a severe lung disease of high mortality (30-50%). Patients require lifesaving supplemental oxygen therapy; however, hyperoxia can induce pulmonary inflammation and cellular damage. Although alveolar macrophages (AMs) are essential for lung immune homeostasis, they become compromised during inflammatory lung injury. To combat this, stem cell-derived alveolar-like macrophages (ALMs) are a prospective therapeutic for lung diseases like ARDS. Using in vitro and in vivo approaches, we investigated the impact of hyperoxia on murine ALMs during acute inflammation. In vitro, ALMs retained their viability, growth, and antimicrobial abilities when cultured at 60% O2, whereas they die at 90% O2. In contrast, ALMs instilled in mouse lungs remained viable during exposure of mice to 90% O2. The ability of the delivered ALMs to phagocytose Pseudomonas aeruginosa was not impaired by exposure to 60 or 90% O2. Furthermore, ALMs remained immunologically stable in a murine model of LPS-induced lung inflammation when exposed to 60 and 90% O2 and effectively attenuated the accumulation of CD11b+ inflammatory cells in the airways. These results support the potential use of ALMs in patients with ARDS receiving supplemental oxygen therapy.NEW & NOTEWORTHY The current findings support the prospective use of stem cell-derived alveolar-like macrophages (ALMs) as a therapeutic for inflammatory lung disease such as acute respiratory distress syndrome (ARDS) during supplemental oxygen therapy where lungs are exposed to high levels of oxygen. Alveolar-like macrophages directly delivered to mouse lungs were found to remain viable, immunologically stable, phagocytic toward live Pseudomonas aeruginosa, and effective in reducing CD11b+ inflammatory cell numbers in LPS-challenged lungs during moderate and extreme hyperoxic exposure.

Mechanisms and Effects of Macrophage Polarization and Its Specifics in Pulmonary Environment

Macrophages are a specific group of cells found in all body tissues. They have specific characteristics in each of the tissues that correspond to the functional needs of the specific environment. These cells are involved in a wide range of processes, both pro-inflammatory and anti-inflammatory ("wound healing"). This is due to their specific capacity for so-called polarization, a phenotypic change that is, moreover, partially reversible compared to other differentiated cells of the human body. This promises a wide range of possibilities for its influence and thus therapeutic use. In this article, we therefore review the mechanisms that cause polarization, the basic classification of polarized macrophages, their characteristic markers and the effects that accompany these phenotypic changes. Since the study of pulmonary (and among them mainly alveolar) macrophages is currently the focus of scientific interest of many researchers and these macrophages are found in very specific environments, given mainly by the extremely high partial pressure of oxygen compared to other locations, which specifically affects their behavior, we will focus our review on this group.

Revisiting transplant immunology through the lens of single-cell technologies

Solid organ transplantation (SOT) is the standard of care for end-stage organ disease. The most frequent complication of SOT involves allograft rejection, which may occur via T cell- and/or antibody-mediated mechanisms. Diagnosis of rejection in the clinical setting requires an invasive biopsy as there are currently no reliable biomarkers to detect rejection episodes. Likewise, it is virtually impossible to identify patients who exhibit operational tolerance and may be candidates for reduced or complete withdrawal of immunosuppression. Emerging single-cell technologies, including cytometry by time-of-flight (CyTOF), imaging mass cytometry, and single-cell RNA sequencing, represent a new opportunity for deep characterization of pathogenic immune populations involved in both allograft rejection and tolerance in clinical samples. These techniques enable examination of both individual cellular phenotypes and cell-to-cell interactions, ultimately providing new insights into the complex pathophysiology of allograft rejection. However, working with these large, highly dimensional datasets requires expertise in advanced data processing and analysis using computational biology techniques. Machine learning algorithms represent an optimal strategy to analyze and create predictive models using these complex datasets and will likely be essential for future clinical application of patient level results based on single-cell data. Herein, we review the existing literature on single-cell techniques in the context of SOT.

Implications of Hyperoxia over the Tumor Microenvironment: An Overview Highlighting the Importance of the Immune System

Hyperoxia is used in order to counteract hypoxia effects in the TME (tumor microenvironment), which are described to boost the malignant tumor phenotype and poor prognosis. The reduction of tumor hypoxic state through the formation of a non-aberrant vasculature or an increase in the toxicity of the therapeutic agent improves the efficacy of therapies such as chemotherapy. Radiotherapy efficacy has also improved, where apoptotic mechanisms seem to be implicated. Moreover, hyperoxia increases the antitumor immunity through diverse pathways, leading to an immunopermissive TME. Although hyperoxia is an approved treatment for preventing and treating hypoxemia, it has harmful side-effects. Prolonged exposure to high oxygen levels may cause acute lung injury, characterized by an exacerbated immune response, and the destruction of the alveolar-capillary barrier. Furthermore, under this situation, the high concentration of ROS may cause toxicity that will lead not only to cell death but also to an increase in chemoattractant and proinflammatory cytokine secretion. This would end in a lung leukocyte recruitment and, therefore, lung damage. Moreover, unregulated inflammation causes different consequences promoting tumor development and metastasis. This process is known as protumor inflammation, where different cell types and molecules are implicated; for instance, IL-1β has been described as a key cytokine. Although current results show benefits over cancer therapies using hyperoxia, further studies need to be conducted, not only to improve tumor regression, but also to prevent its collateral damage.

The Effect of Conservative Oxygen Therapy in Reducing Mortality in Critical Care Patients: A Meta-Analysis and Trial Sequential Analysis

Background: Conservative oxygen therapy can prevent both hypoxemia and hyperoxemia, but the effect on the prognosis of patients admitted to the intensive care unit (ICU) remains controversial.

Methods: All controlled studies comparing conservative oxygen therapy and conventional oxygen therapy in adult patients admitted to the ICU were searched. The primary outcome was mortality, and the secondary outcomes were length of ICU stay (ICU LOS), length of hospital stay (hospital LOS), length of mechanical ventilation (MV) hours, new organ failure during ICU stay, and new infections during ICU stay.

Results: Nine trials with a total of 5,759 patients were pooled in our final studies. Compared with conventional oxygen therapy, conservative oxygen therapy did not reduce overall mortality (Z = 0.31, p = 0.75) or ICU LOS (Z = 0.17, p = 0.86), with firm evidence from trial sequential analysis, or hospital LOS (Z = 1.98, p = 0.05) or new infections during the ICU stay (Z = 1.45, p = 0.15). However, conservative oxygen therapy was associated with a shorter MV time (Z = 5.05, p < 0.00001), reduction of new organ failure during the ICU stay (Z = 2.15, p = 0.03) and lower risk of renal replacement therapy (RRT) (Z = 2.18, p = 0.03).

Conclusion: Conservative oxygen therapy did not reduce mortality but did decrease MV time, new organ failure and risk of RRT in critically ill patients.

Systematic Review Registration: identifier [CRD42020171055].

CyTOF: An Emerging Technology for Single-Cell Proteomics in the Mouse

The ability to analyze the proteome of single cells is critical for the advancement of studies of steady-state and pathological processes. Mass cytometry, or CyTOF, combines principles of mass spectrometry and flow cytometry to enable single-cell analysis of protein expression. CyTOF can simultaneously assess DNA content and proteins and has the capacity to measure 40 to 100 parameters in each cell. Applying this technology to tissues or cells on slides, termed imaging mass cytometry (IMC), allows for visualization of normal and diseased tissues in situ. The high-dimensional proteomic analysis that can be undertaken with CyTOF and IMC has the potential to enhance our understanding of complex and heterogeneous developmental and disease pathways. This article will describe the CyTOF experimental workflow, including reagent selection, sample preparation, and data analysis. CyTOF is compared to flow cytometry, focusing on the strengths and weaknesses of these powerful techniques. Importantly, we review key studies in mouse models of human disease that highlight the strength of CyTOF and IMC to drive discovery research and therapeutic advancement. © 2021 Wiley Periodicals LLC.

Increase in tumour PD-L1 expression in non-small cell lung cancer following bronchoscopic thermal vapour ablation

Limited early evidence indicates thermal ablation of non-small cell lung cancer (NSCLC) may induce alterations to the immune response that could enhance the efficacy of immunotherapy with immune checkpoint inhibitor therapy. This study reports pilot data demonstrating increased programmed death-ligand 1 (PD-L1) expression on tumour cells in response to bronchoscopic thermal vapour ablation. Five patients underwent bronchoscopic thermal vapour ablation under a treat-and-resect protocol, as part of a clinical safety and feasibility study, with lobectomy performed five days after thermal vapour ablation. PD-L1 (clone SP263) immunohistochemistry (IHC) tumour proportion score (TPS) was assessed on both baseline diagnostic biopsy specimens, and post-ablation resection specimens in five patients with stage I NSCLC. Two areas of the resection sample defined as viable tumour and injured tumour were examined. All tumours demonstrated 0% PD-L1 TPS at baseline. Three of five (60%) patients demonstrated an increase in PD-L1 TPS in areas of injured tumour to 20%, 30% and 50%. One patient demonstrated an increase in PD-L1 expression in an area of viable tumour to 5%. Changes in PD-L1 expression did not correlate with measures of systemic inflammation. Our findings comprise the first evidence that thermal ablation of NSCLC may induce PD-L1 expression. Further investigation is required to determine the extent of an adaptive immune response, and confirm the potential for augmentation of clinical response to immune check point inhibitor therapy in NSCLC.

Thermal ablation in non-small cell lung cancer: a review of treatment modalities and the evidence for combination with immune checkpoint inhibitors

Lung cancer is the leading cause of cancer death worldwide, with approximately 1.6 million cancer related deaths each year. Prognosis is best in patients with early stage disease, though even then five-year survival is only 55% in some groups. Median survival for advanced non-small cell lung cancer (NSCLC) is 8–12 months with conventional treatment. Immune checkpoint inhibitor (ICI) therapy has revolutionised the treatment of NSCLC with significant long-term improvements in survival demonstrated in some patients with advanced NSCLC. However, only a small proportion of patients respond to ICI, suggesting the need for further techniques to harness the potential of ICI therapy. Thermal ablation utilizes the extremes of temperature to cause tumour destruction. Commonly used modalities are radiofrequency ablation (RFA), cryoablation and microwave ablation (MWA). At present thermal ablation is reserved for curative-intent therapy in patients with localized NSCLC who are unable to undergo surgical resection or stereotactic ablative body radiotherapy (SABR). Limited evidence suggests that thermal ablative modalities can upregulate an anticancer immune response in NSCLC. It is postulated that thermal ablation can increase tumour antigen release, which would initiate and upregulated steps in the cancer immunity cycle required to elicit an anticancer immune response. This article will review the current thermal ablative techniques and their ability to modulate an anti-cancer immune response with a view of using thermal ablation in conjunction with ICI therapy.

Targeting alveolar-specific succinate dehydrogenase A attenuates pulmonary inflammation during acute lung injury

Acute lung injury (ALI) is an inflammatory lung disease, which manifests itself in patients as acute respiratory distress syndrome (ARDS). Previous studies have implicated alveolar-epithelial succinate in ALI protection. Therefore, we hypothesized that targeting alveolar succinate dehydrogenase SDH A would result in elevated succinate levels and concomitant lung protection. Wild-type (WT) mice or transgenic mice with targeted alveolar-epithelial Sdha or hypoxia-inducible transcription factor Hif1a deletion were exposed to ALI induced by mechanical ventilation. Succinate metabolism was assessed in alveolar-epithelial via mass spectrometry as well as redox measurements and evaluation of lung injury. In WT mice, ALI induced by mechanical ventilation decreased SDHA activity and increased succinate in alveolar-epithelial. In vitro, cell-permeable succinate decreased epithelial inflammation during stretch injury. Mice with inducible alveolar-epithelial Sdha deletion (Sdha^loxp/loxp SPC-CreER mice) revealed reduced lung inflammation, improved alveolar barrier function, and attenuated histologic injury. Consistent with a functional role of succinate to stabilize HIF, Sdha^loxp/loxp SPC-CreER experienced enhanced Hif1a levels during hypoxia or ALI. Conversely, Hif1a^loxp/loxp SPC-CreER showed increased inflammation with ALI induced by mechanical ventilation. Finally, wild-type mice treated with intra-tracheal dimethlysuccinate were protected during ALI. These data suggest that targeting alveolar-epithelial SDHA dampens ALI via succinate-mediated stabilization of HIF1A. Translational extensions of our studies implicate succinate treatment in attenuating alveolar inflammation in patients suffering from ARDS.

Soluble PD-L1 improved direct ARDS by reducing monocyte-derived macrophages

Acute respiratory distress syndrome (ARDS) is common in intensive care units (ICUs), although it is associated with high mortality, no effective pharmacological treatments are currently available. Despite being poorly understood, the role of programmed cell death protein 1 (PD-1) and PD-ligand 1 (PD-L1) axis in ARDS may provide significant insights into the immunosuppressive mechanisms that occur after ARDS. In the present study, we observed that the level of soluble PD-L1 (sPD-L1), a potential activator of the PD-1 pathway, was upregulated in survivors of direct ARDS than in non-survivors. Administration of sPD-L1 in mice with direct ARDS relieved inflammatory lung injury and improved the survival rate, indicating the protective role of sPD-L1 in direct ARDS. Using high-throughput mass cytometry, we found a marked decrease in the number of lung monocyte-derived macrophages (MDMs) with proinflammatory markers, and the protective role of sPD-L1 diminished in ARDS mice with monocyte/macrophage depletion. Furthermore, PD-1 expression increased in the MDMs of patients and mice with direct ARDS. Finally, we showed that sPD-L1 induced MDM apoptosis in patients with direct ARDS. Taken together, our results demonstrated that the engagement of sPD-L1 on PD-1 expressing macrophages resulted in a decrease in pro-inflammatory macrophages and eventually improved direct ARDS. Our study identified a prognostic indicator for patients with direct ARDS and a potential target for therapeutic development in direct ARDS.

Hyperoxia and modulation of pulmonary vascular and immune responses in COVID-19

Oxygen is the most commonly used therapy in hospitalized patients with COVID-19. In those patients who develop worsening pneumonia and acute respiratory distress syndrome (ARDS), high concentrations of oxygen may need to be administered for prolonged time periods, often together with mechanical ventilation. Hyperoxia, although lifesaving and essential for maintaining adequate oxygenation in the short term, may have adverse long-term consequences upon lung parenchymal structure and function. How hyperoxia per se impacts lung disease in COVID-19 has remained largely unexplored. Numbers of experimental studies have previously established that hyperoxia is associated with deleterious outcomes inclusive of perturbations in immunologic responses, abnormal metabolic function, and alterations in hemodynamics and alveolar barrier function. Such changes may ultimately progress into clinically evident lung injury and adverse remodeling and result in parenchymal fibrosis when exposure is prolonged. Given that significant exposure to hyperoxia in patients with severe COVID-19 may be unavoidable to preserve life, these sequelae of hyperoxia, superimposed on the cytopathic effects of SARS-CoV-2 virus, may well impact pathogenesis of COVID-19-induced ARDS.