Emerging role of innate immunity in organ transplantation Part II: potential of damage-associated molecular patterns to generate immunostimulatory dendritic cells

Hypothermic oxygenated perfusion (HOPE) protects from biliary injury in a rodent model of DCD liver transplantation

BACKGROUND & AIMS

The use of livers from donors after cardiac arrest (DCD) is increasing in many countries to overcome organ shortage. Due to additional warm ischemia before preservation, those grafts are at higher risk of failure and bile duct injury. Several competing rescue strategies by machine perfusion techniques have been developed with, however, unclear effects on biliary injury. We analyze the impact of an end-ischemic Hypothermic Oxygenated PErfusion (HOPE) approach applied only through the portal vein for 1h before graft implantation.

METHODS

Rat livers were subjected to 30-min in situ warm ischemia, followed by subsequent 4-h cold storage, mimicking DCD-organ procurement and conventional organ transport. Livers in the HOPE group underwent also passive cold storage for 4h, but were subsequently machine perfused for 1h before implantation. Outcome was tested by liver transplantation (LT) at 12h after implantation (n=10 each group) and after 4 weeks (n=10 each group), focusing on early reperfusion injury, immune response, and later intrahepatic biliary injury.

RESULTS

All animals survived after LT. However, reperfusion injury was significantly decreased by HOPE treatment as tested by hepatocyte injury, Kupffer cell activation, and endothelial cell activation. Recipients receiving non-perfused DCD livers disclosed less body weight gain, increased bilirubin, and severe intrahepatic biliary fibrosis. In contrast, HOPE treated DCD livers were protected from biliary injury, as detected by cholestasis parameter and histology.

CONCLUSIONS

We demonstrate in a DCD liver transplant model that end-ischemic hypothermic oxygenated perfusion is a powerful strategy for protection against biliary injury.

Role of heat shock protein 70 in innate alloimmunity

This article briefly describes our own experience with the proven demonstration of heat shock protein 70 (HSP70) in reperfused renal allografts from brain-dead donors and reflects about its potential role as a typical damage-associated molecular pattern (DAMP) in the setting of innate alloimmunity. In fact, our group was able to demonstrate a dramatic up-regulation of HSP70 expression after postischemic reperfusion of renal allografts. Of note, up-regulation of this stress protein expression, although to a lesser extent, was already observed after cold storage of the organ indicating that this molecule is already induced in the stressed organism of a brain-dead donor. However, whether or not the dramatic up-regulation of HSP70 expression contributes to mounting an innate alloimmune response cannot be judged in view of these clinical findings. Nevertheless, HSP70, since generated in association with postischemic reperfusion-induced allograft injury, can be called a typical DAMP - as can every molecule be termed a DAMP that is generated in association with any stressful tissue injury regardless of its final positive or negative regulatory function within the innate immune response elicited by it. In fact, as we discuss in this article, the context-dependent, even contradistinctive activities of HSP70 reflect the biological phenomenon that, throughout evolution, mammals have developed an elaborate network of positive and negative regulatory mechanisms, which provide balance between defensive and protective measures against unwarranted destruction of the host. In this sense, up-regulated expression of HSP70 in an injured allograft might reflect a pure protective response against the severe oxidative injury of a reperfused donor organ. On the other hand, up-regulated expression of this stress protein in an injured allograft might reflect a (futile) attempt of the innate immune system to restore homeostasis with the aim to eliminate the "unwanted foreign allograft invader" by contributing to development of an adaptive alloimmune response. However, this adaptive immune response against donor histocompatibility alloantigens - in its evolutionary sense aimed to restore homeostasis - is by no means protective from a recipient's view point but tragically ends up with allograft rejection. Indeed: in this sense, allograft rejection is the result of a fateful confusion by the immune system of danger and benefit!