Preserving myocardium and regulating inflammation by ex vivo perfusion

Abstract

Heart transplantation is a lifesaving therapy required by patients with end stage heart failure, yet there are a number of caveats to long term success. Primary amongst these is the immunological rejection of the donor graft by recipient leucocytes. The transfer of passenger leucocytes from the donor organ is important in stimulating this response, although the cardiac immune content is currently unknown. Despite the increase in demand for transplantation there is a shortfall in the number of suitable donor organs. This programme of work aimed to profile the cardiac immune reservoir and to establish whether novel ex vivo perfusion devices could be used for the preservation and evaluation of donor hearts. The effect of preservation and evaluation on the donor cardiac immune reservoir was then established. The findings presented herein provide novel evidence that the heart contains a significant immune reservoir capable of mobilisation upon reperfusion. Moreover, traditional static cold storage is associated with endothelial and myocardial injury, as well as broad inflammatory cytokine release. Such injury can be avoided for at least 8 hours by preserving the heart using hypothermic cardioplegic perfusion. Such preservation diminishes ischaemia-reperfusion related protein signalling, demonstrating a protective effect in the acute period. This method provides auxiliary benefits by mediating the significant immunodepletion of the donor organ, diminishing the population able to be transferred into the recipient. Importantly, hypothermic perfusion is also associated with an interferon gamma driven inflammatory storm, which promotes the upregulation of a protective immune checkpoint molecule. This may confer the ability to delete or anergise recipient T cells. Perfused organs that were subsequently transplanted initially displayed improved graft infiltration although this could not be confirmed in a larger study. Finally, this thesis demonstrates that donor hearts can undergo a thorough and sustained ex vivo functional evaluation over a four hour period without imparting myocardial injury. Surprisingly, this method of perfusion was not associated with large immune mobilisation from the heart, although it did stimulate a significant inflammatory response on the circuit. Overall, this work demonstrates that ex vivo perfusion can play a dual role in enhancing access to and improving outcomes of transplantation. This can be achieved by extended preservation, impaired direct allorecognition as a result of immunodepletion and improved evaluation of marginal organs.

Date of Award	31 Dec 2017
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Steven Shaw (Supervisor), James Fildes (Supervisor) & Elizabeth Clare Mills (Supervisor)