Opening a Life-Saving Therapeutic Window in Critical Illness

Mortality in trauma patients is often caused not by the initial insult but by secondary complications such as sepsis and multiple organ failure. The current protocols for the treatment of septic patients are mostly supportive and unspecific, often ineffective and uniformly expensive. Both traumatic injury and sepsis activate the complement system concurrently with the innate immune response. After trauma, the complement system initially supports immune defenses by induction of chemotaxis and phagocytosis, triggering the release of inflammatory mediators and induction of cell lysis via the membrane attack complex. The localized immune response, however, may rapidly develop into a detrimental systemic hyper-inflammation quickly followed by a prolonged period of severe immunosuppression. The above predisposes patients for various secondary complications including sepsis. One of the key complement components is C5a, a potent anaphylatoxin that is released during inflammation and may decisively contribute to the deregulation of immune-inflammatory responses exaggerated and suppressed alike. Therefore, we hypothesize that trauma/hemorrhage (TH) trigger detrimental modulation of the complement system by an excessive C5a release before and during 2ndary sepsis and blockage of C5aR improves survival in the mouse model of post-traumatic sepsis. The proposed Aim I will investigate the dynamics of complement system derangements and the link to the trauma/hemorrhage-induced immunosuppression. More precisely, we will focus on the activation of complement system and the potential role of C5a on the development of post-TH immunosuppression. Aim II will in turn explore potential benefits of global and broad versus targeted and individualized inhibition of C5a mediated signaling. The 2-hit polytrauma model is comprised of femur fracture, explorative laparotomy and hemorrhage (TH) as 1st hit followed by cecal ligation and puncture (CLP) sepsis (2nd hit; 48h later) that simulates polymicrobial peritonitis in patients. A daily monitoring approach by the low-volume sampling technique will be used to characterize TH-CLP responses in the blood and to minimize repeated sacrifice of animals. Additionally, by blocking the anaphylatoxin C5a receptor with its specific antagonist, PMX-53, we will attempt to improve long-term TH-CLP outcomes. Based on different time-points and tactics, three specific treatment approaches will be employed including a targeted, individualized administration of PMX-53 in TH-CLP mice stratified into homogenous high and low-risk-of-death cohorts. If successful, our findings will provide 1) a characterization of the role of complement system/C5a dynamics on immunosuppression after trauma/hemorrhage and post-traumatic sepsis and 2) a comprehensive verification of therapeutic efficacy of PMX-53 in various TH- CLP phases. Overall, this project promotes an ideology that a timely and accurate treatment of trauma/septic patients based on their well-defined disease fingerprints has the highest life saving potential. Using our clinically relevant model, we intend to show that targeted treatment can successfully be applied in the unforgiving and very dynamic field of critical care medicine.

In the context of the main goal posited in the Hertha-Firnberg project, we discovered that in mice, the complement component C5a (a side-product of the innate immune system activation), is not a key mediator of the fatal immunosuppression induced by severe physical trauma. We reached this conclusion by employing three different treatment scenarios for the inhibition of C5a after trauma and in post-traumatic sepsis: a) single treatment b) blanket treatment and c) personalized treatment for high-risk individuals. Surprisingly, none of those approaches improved the survival of mice with post-traumatic sepsis. Overall, the project was based on the following rationale: severe traumatic injuries initially induce a localized activation of the innate immunity and the complement system, which can spread and trigger a generalized immune response affecting the whole body. This overwhelming activation may finally lead to a state of immune dysfunction, predisposing these patients for secondary sepsis. Sepsis belongs to the most frequent causes of death after trauma and CDC has recently declared sepsis as medical emergency (i.e. August 13, 2016) encouraging raising sepsis awareness, prevention and research. This project specifically aimed to understand the impaired immune system and the role C5a plays in the specific post-traumatic sepsis scenario. We initially relied on a well-known pre-clinical model of haemorrhagic-traumatic shock followed by sepsis to emulate the respective clinical scenario. In the course of the project, we further modified the existing model (e.g. by removal of the spleen; splenectomy) to better recapitulate the severity of the immune-dysfunction encountered by trauma patients. This led to a surprising finding that the splenectomy- reprogramming of the immune response in trauma was highly protective in post-traumatic sepsis. This experimental finding matches data of a recent large clinical trial (28,000 patients) demonstrating that trauma patients with splenectomy had shorter hospital stay and better secondary outcomes. Summarizing our findings, we showed a) that complement component C5a is not an appropriate target to modulate immunosuppression induced by trauma and sepsis, and b) we delineated immuno-inflammatory re-programming after trauma and traumatic spleen; both findings ultimately advance the understanding of trauma-induced immune-dysfunctions in post-traumatic sepsis in utility of this modelling setup in pre-clinical sepsis research.