- Open Access
How could we enhance translation of sepsis immunology to inform immunomodulation trials in sepsis?
Critical Care volume 21, Article number: 125 (2017)
The original article was published in Critical Care 2017 21:48
Sepsis results in complex alterations to the immune system. Our understanding of how these alterations in immune responses could help characterize extreme immune phenotypes, identify biomarkers with the ability to stratify patients for therapeutic interventions, surrogates in the causal pathway of clinical end-points, and treatable traits are still rudimentary. A methodologically rigorous, consensus-based approach should enrich sepsis immune subpopulations to increase the probability of successful trials.
Sepsis represents life-threatening organ dysfunction caused by a dysregulated host response to infection , which potentially affects every organ system. Susceptibility to damage, repair, and residual sequelae varies markedly between both individuals and organs , as do the risk for and outcomes from sepsis, which represent heterogeneity . Studying the temporal effects of sepsis on the immune system is challenging as numerous abnormalities differ between sepsis patients and within the same patient over time . Furthermore, the time between onset of infection to clinical presentation varies considerably, influenced by patient characteristics, infection site, pathogen virulence, and access to healthcare. While novel interventions are frequently discovered and tested, numerous trials are statistically negative . While these interventions may indeed be completely ineffective, it is perhaps more plausible that a benefitting subset is diluted by the overall lack of signal or even harm . Thus, reassessing our specialty’s approach to targeting the dysregulated immune system in sepsis is key.
Recently, Antonakos et al.  replicated the often reported finding that persistent impaired ex vivo cytokine production of monocytes and lymphocytes stimulated with either lipopolysaccharide (LPS) or Pam3 seen in sepsis patients differs by survival status [4, 7]. LPS is a conserved motif on Gram-negative bacteria. Pam3 is a Toll-like receptor agonist.
The causal reasoning here and in similar studies is that impaired cytokine production is a therapeutically modifiable surrogate endpoint that can improve outcomes in sepsis. This reasoning has not helped so far in bringing new therapies to routine clinical use . In this editorial, I suggest that enhanced translation and smarter interpretation of the sepsis immunology knowledge base should derive extreme immune phenotypes, clarify biomarkers’ purpose, identify surrogates in the causal pathway of clinical outcomes, and define treatable traits within sepsis cohorts (Table 1).
Extreme immune phenotypes in sepsis
The complex immune system alterations seen in sepsis separate into two patterns, primarily based on mechanisms contributing to late deaths [4, 7, 8]. In both these host response patterns, pro-inflammatory, anti-inflammatory, and immunosuppression responses are activated at onset of sepsis and early deaths occur because of excessive innate immune system-driven inflammation. Recovery in both patterns is characterised by resolution of inflammation and recovery of immune cell paresis. However, late deaths occur either due to progressive immune cell paresis resulting in secondary infections or due to intractable inflammation-induced organ injury or a combination of immunosuppression and persistent inflammation [4, 7, 8]. These patterns imply that there are at least two extreme immune phenotypes within sepsis cohorts. For example, Davenport et al.  identified two sepsis immune phenotypes in critically ill adults with sepsis using whole leukocyte transcriptomics. About 40% of patients had an immunosuppressed phenotype with impaired antigen processing ability suggested by endotoxin tolerance and T-cell exhaustion. This subgroup had a significantly higher mortality. However, are we to infer that the remainder of the cohort had no immunomodulation potential? Of note, much higher validation cohort mortality in this study exemplifies outcome heterogeneity in sepsis.
Biomarkers to stratify patients for interventions and treatable traits
It is imperative to clarify the ability of numerous biomarkers reported in sepsis literature  to either diagnose, predict, prognosticate, and/or act as surrogate outcomes . For example, in the trial by Meisel and colleagues  using granulocyte-monocyte colony stimulating factor (GM-CSF), HLD-DR is positioned as a diagnostic biomarker for immunosuppression and as a surrogate outcome for intervention, with a tenuous link to reported clinical outcomes. The clinical outcomes that improved were duration of mechanical ventilation and hospital stay . Interestingly 15% of patients in the control arm spontaneously restored their HLA-DR expression, which implies that HLA-DR also identifies placebo responders. Promising interventions in sepsis include interleukin-7, programmed cell death pathway specific antibodies, interferon-γ, and GM-CSF . These therapies will need different biomarkers for stratification, response prediction, and to work as surrogate outcomes. This also highlights the need to match intervention with treatable traits to accomplish precision medicine .
Surrogates in the causal pathway of clinical end-points
Causal models represent a directional link between variables and their associated probabilities for a given set of clinical circumstances. Therefore, it is important that when trials report surrogate outcome(s), similar inferences should be possible about likely clinical outcome(s). Let us consider nosocomial infection as an example to discuss this issue. Nosocomial infection is a difficult outcome to define, its risk varies with time, and it competes with mortality for event rate as it is associated with greater illness severity, more inflammation, and greater activation of endothelial markers . The attributable mortality when compared to non-sepsis controls is not significantly higher . Thus, the surrogate outcome should ideally mirror these relationships observed with clinical outcomes and should have a causal link.
In summary, our understanding of intervention-matched extreme immune phenotypes and outcomes in sepsis trials is not sophisticated enough to yield positive results. Whilst a moratorium on trials is unreasonable, a consensus towards study designs using fundamental principles of population epidemiology and biological response characterisation for immunomodulation trials is not.
Granulocyte-monocyte colony stimulating factor
Human leukocyte antigen
Singer M, Deutschman CS, Seymour CW, Shankar-Hari M, Annane D, Bauer M, Bellomo R, Bernard GR, Chiche JD, Coopersmith CM, et al. The Third international consensus definitions for sepsis and septic shock (Sepsis-3). JAMA. 2016;315(8):801–10.
Medzhitov R, Schneider DS, Soares MP. Disease tolerance as a defense strategy. Science. 2012;335(6071):936–41.
Shankar-Hari M, Rubenfeld GD. The use of enrichment to reduce statistically indeterminate or negative trials in critical care. Anaesthesia. 2017;72(5):560–5.
Hotchkiss RS, Monneret G, Payen D. Sepsis-induced immunosuppression: from cellular dysfunctions to immunotherapy. Nat Rev Immunol. 2013;13(12):862–74.
Marshall JC. Why have clinical trials in sepsis failed? Trends Mol Med. 2014;20(4):195–203.
Antonakos N, Tsaganos T, Oberle V, Tsangaris I, Lada M, Pistiki A, Machairas N, Souli M, Bauer M, Giamarellos-Bourboulis EJ. Decreased cytokine production by mononuclear cells after severe gram-negative infections: early clinical signs and association with final outcome. Crit Care. 2017;21(1):48.
Boomer JS, To K, Chang KC, Takasu O, Osborne DF, Walton AH, Bricker TL, Jarman II SD, Kreisel D, Krupnick AS, et al. Immunosuppression in patients who die of sepsis and multiple organ failure. JAMA. 2011;306(23):2594–605.
Xiao W, Mindrinos MN, Seok J, Cuschieri J, Cuenca AG, Gao H, Hayden DL, Hennessy L, Moore EE, Minei JP, et al. A genomic storm in critically injured humans. J Exp Med. 2011;208(13):2581–90.
Davenport EE, Burnham KL, Radhakrishnan J, Humburg P, Hutton P, Mills TC, Rautanen A, Gordon AC, Garrard C, Hill AV, et al. Genomic landscape of the individual host response and outcomes in sepsis: a prospective cohort study. Lancet Respir Med. 2016;4(4):259–71.
Pierrakos C, Vincent JL. Sepsis biomarkers: a review. Crit Care. 2010;14(1):R15.
Ballman KV. Biomarker: predictive or prognostic? J Clin Oncol. 2015;33(33):3968–71.
Meisel C, Schefold JC, Pschowski R, Baumann T, Hetzger K, Gregor J, Weber-Carstens S, Hasper D, Keh D, Zuckermann H, et al. Granulocyte-macrophage colony-stimulating factor to reverse sepsis-associated immunosuppression: a double-blind, randomized, placebo-controlled multicenter trial. Am J Respir Crit Care Med. 2009;180(7):640–8.
van Vught LA, Wiewel MA, Hoogendijk AJ, Frencken JF, Scicluna BP, Klein Klouwenberg PM, Zwinderman AH, Lutter R, Horn J, Schultz MJ, et al. The host response in sepsis patients developing intensive care unit-acquired secondary infections. Am J Respir Crit Care Med. 2017;20. doi:10.1164/rccm.201606-1225OC. [Epub ahead of print]
van Vught LA, Klein Klouwenberg PM, Spitoni C, Scicluna BP, Wiewel MA, Horn J, Schultz MJ, Nurnberg P, Bonten MJ, Cremer OL, et al. Incidence, risk factors, and attributable mortality of secondary infections in the intensive care unit after admission for sepsis. JAMA. 2016;315(14):1469–79.
MS-H is supported by the National Institute for Health Research Clinician Scientist Award (NIHR-CS-2016-16-011). The views expressed in this publication are those of the author(s) and not necessarily those of the NHS, the UK National Institute for Health Research, or the Department of Health.
Availability of data and materials
MSH wrote and revised the manuscript.
The author declares that they have no competing interests.
Consent for publication
Ethics approval and consent to participate
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
See related research by Antonakos et al., https://ccforum.biomedcentral.com/articles/10.1186/s13054-017-1625-1.
About this article
Cite this article
Shankar-Hari, M. How could we enhance translation of sepsis immunology to inform immunomodulation trials in sepsis?. Crit Care 21, 125 (2017). https://doi.org/10.1186/s13054-017-1715-0
- Host response