Association between lymphocyte count and neurological outcomes in post-cardiac arrest patients treated with mild therapeutic hypothermia

Glucocorticoid signaling mediates lymphopoiesis impairment after cardiac arrest in mice

Cardiac arrest (CA) is a life-threatening condition that requires immediate medical attention. Considerable advances in resuscitation have led to an increasing number of patients who survive the initial arrest event. However, among this growing patient population, morbidity and mortality rates remain strikingly high. This has been attributed to post-CA syndrome of which an imbalanced immune response is a crucial component. Using a murine CA model, we have shown that a profound immunosuppressive phase, characterized by severe lymphopenia, ensues following the initial pro-inflammatory response after CA. In the current study, we found that T and B lymphopoiesis was greatly impaired, as evidenced by the rapid and marked depletion of double-positive T cells and pre-B cells in the thymus and bone marrow, respectively. Our data then demonstrated that pharmacologic suppression of glucocorticoid signaling after CA significantly attenuated lymphopoiesis impairment, thereby mitigating post-CA lymphopenia. Lastly, we showed that specific deletion of the glucocorticoid receptor in T or B cells largely prevented the CA-induced depletion of immature lymphocyte populations in the thymus or bone marrow, respectively. Together, our findings indicate that glucocorticoid signaling mediates post-CA impairment of lymphopoiesis, a key contributor to post-CA immunosuppression.

Diverse NKT cells regulate early inflammation and neurological outcomes after cardiac arrest and resuscitation

Neurological injury drives most deaths and morbidity among patients hospitalized for out-of-hospital cardiac arrest (OHCA). Despite its clinical importance, there are no effective pharmacological therapies targeting post-cardiac arrest (CA) neurological injury. Here, we analyzed circulating immune cells from a large cohort of patients with OHCA, finding that lymphopenia independently associated with poor neurological outcomes. Single-cell RNA sequencing of immune cells showed that T cells with features of both innate T cells and natural killer (NK) cells were increased in patients with favorable neurological outcomes. We more specifically identified an early increase in circulating diverse NKT (dNKT) cells in a separate cohort of patients with OHCA who had good neurological outcomes. These cells harbored a diverse T cell receptor repertoire but were consistently specific for sulfatide antigen. In mice, we found that sulfatide-specific dNKT cells trafficked to the brain after CA and resuscitation. In the brains of mice lacking NKT cells (Cd1d-/-), we observed increased inflammatory chemokine and cytokine expression and accumulation of macrophages when compared with wild-type mice. Cd1d-/- mice also had increased neuronal injury, neurological dysfunction, and worse mortality after CA. To therapeutically enhance dNKT cell activity, we treated mice with sulfatide lipid after CA, showing that it improved neurological function. Together, these data show that sulfatide-specific dNKT cells are associated with good neurological outcomes after clinical OHCA and are neuroprotective in mice after CA. Strategies to enhance the number or function of dNKT cells may thus represent a treatment approach for CA.

Single-cell transcriptomics reveal a hyperacute cytokine and immune checkpoint axis after cardiac arrest in patients with poor neurological outcome

BACKGROUND

Most patients hospitalized after cardiac arrest (CA) die because of neurological injury. The systemic inflammatory response after CA is associated with neurological injury and mortality but remains poorly defined.

METHODS

We determine the innate immune network induced by clinical CA at single-cell resolution.

FINDINGS

Immune cell states diverge as early as 6 h post-CA between patients with good or poor neurological outcomes 30 days after CA. Nectin-2+ monocyte and Tim-3+ natural killer (NK) cell subpopulations are associated with poor outcomes, and interactome analysis highlights their crosstalk via cytokines and immune checkpoints. Ex vivo studies of peripheral blood cells from CA patients demonstrate that immune checkpoints are a compensatory mechanism against inflammation after CA. Interferon γ (IFNγ)/interleukin-10 (IL-10) induced Nectin-2 on monocytes; in a negative feedback loop, Nectin-2 suppresses IFNγ production by NK cells.

CONCLUSIONS

The initial hours after CA may represent a window for therapeutic intervention in the resolution of inflammation via immune checkpoints.

FUNDING

This work was supported by funding from the American Heart Association, Brigham and Women's Hospital Department of Medicine, the Evergreen Innovation Fund, and the National Institutes of Health.

Modulation of inflammation by treatment with tocilizumab after out-of-hospital cardiac arrest and associations with clinical status, myocardial- and brain injury

AIM

To investigate how the inflammatory response after out-of-hospital cardiac arrest (OHCA) is modulated by blocking IL-6-mediated signalling with tocilizumab, and to relate induced changes to clinical status, myocardial- and brain injury.

METHODS

This is a preplanned substudy of the IMICA trial (ClinicalTrials.gov, NCT03863015). Upon admission 80 comatose OHCA patients were randomized to infusion of tocilizumab or placebo. Inflammation was characterized by a cytokine assay, CRP, and leukocyte differential count; myocardial injury by TnT and NT-proBNP; brain injury by neuron-specific enolase (NSE) and Neurofilament Light chain (NFL), while sequential organ assessment (SOFA) score and Vasoactive-Inotropic Score (VIS) represented overall clinical status.

RESULTS

Responses for IL-5, IL-6, IL-17, neutrophil as well as monocyte counts, and VIS were affected by tocilizumab treatment (all p < 0.05), while there was no effect on levels of NFL. IL-5 and IL-6 were substantially increased by tocilizumab, while IL-17 was lowered. Neutrophils and monocytes were lower at 24 and 48 hours, and VIS was lower at 24 hours, for the tocilizumab group compared to placebo. Multiple correlations were identified for markers of organ injury and clinical status versus inflammatory markers; this included correlations of neutrophils and monocytes with TnT, NSE, NFL, SOFA- and VIS score for the tocilizumab but not the placebo group. NT-proBNP, NFL and SOFA score correlated with CRP in both groups.

CONCLUSIONS

Treatment with tocilizumab after OHCA modulated the inflammatory response with notable increases for IL-5, IL-6, and decreases for neutrophils and monocytes, as well as reduced vasopressor and inotropy requirements.

Systemic immune derangements are shared across various CNS pathologies and reflect novel mechanisms of immune privilege

Background

The nervous and immune systems interact in a reciprocal manner, both under physiologic and pathologic conditions. Literature spanning various CNS pathologies including brain tumors, stroke, traumatic brain injury and de-myelinating diseases describes a number of associated systemic immunologic changes, particularly in the T-cell compartment. These immunologic changes include severe T-cell lymphopenia, lymphoid organ contraction, and T-cell sequestration within the bone marrow.

Methods

We performed an in-depth systematic review of the literature and discussed pathologies that involve brain insults and systemic immune derangements.

Conclusions

In this review, we propose that the same immunologic changes hereafter termed 'systemic immune derangements', are present across CNS pathologies and may represent a novel, systemic mechanism of immune privilege for the CNS. We further demonstrate that systemic immune derangements are transient when associated with isolated insults such as stroke and TBI but persist in the setting of chronic CNS insults such as brain tumors. Systemic immune derangements have vast implications for informed treatment modalities and outcomes of various neurologic pathologies.

Skin sympathetic nerve activity as a biomarker for neurologic recovery during therapeutic hypothermia for cardiac arrest

BACKGROUND

Targeted temperature management (TTM) improves neurologic outcome after cardiac arrest. However, better neurologic prognostication is needed.

OBJECTIVE

The purpose of this study was to test the hypothesis that noninvasive recording of skin sympathetic nerve activity (SKNA) and its association with heart rate (HR) during TTM may serve as a biomarker of neurologic status.

METHODS

SKNA recordings were analyzed from 29 patients undergoing TTM. Patients were grouped based on Clinical Performance Category (CPC) score into group 1 (CPC 1-2) representing a good neurologic outcome and group 2 (CPC 3-5) representing a poor neurologic outcome.

RESULTS

Of the 29 study participants, 18 (62%) were deemed to have poor neurologic outcome. At all timepoints, low average skin sympathetic nerve activity (aSKNA) was associated with poor neurologic outcome (odds ratio 22.69; P = .002) and remained significant (P = .03) even when adjusting for presenting clinical factors. The changes in aSKNA and HR during warming in group 1 were significantly correlated (ρ = 0.49; P <.001), even when adjusting for corresponding temperature and mean arterial pressure measurements (P = .017), whereas this correlation was not observed in group 2. Corresponding to high aSKNA, there was increased nerve burst activity during warming in group 1 compared to group 2 (0.739 ± 0.451 vs 0.176 ± 0.231; P = .013).

CONCLUSION

Neurologic recovery was retrospectively associated with SKNA. Patients undergoing TTM who did not achieve neurologic recovery were associated with low SKNA and lacked a significant correlation between SKNA and HR. These preliminary results indicate that SKNA may potentially be a useful biomarker to predict neurologic status in patients undergoing TTM.