Immune system homeostasis in people with multiple long-term conditions determines susceptibility to organ injury and mortality following cardiac surgery

Background People with Multiple Long-Term Conditions (MLTC) experience higher rates of organ failure and death following cardiac surgery. The aim of this study was to identify disease processes in MLTC associated with increased susceptibility to organ injury post-surgery. Methods Unsupervised machine learning methods were applied to pre-surgery biomarkers of haematological, cardiac, liver, and renal disease from four intensively phenotyped cardiac surgery cohorts. The resulting MLTC clusters were then matched to a fifth cohort where single nuclei RNA sequencing (snRNAseq) was performed on atrial biopsies collected at surgery. Results K-means clustering identified two MLTC clusters. Cluster 1 had lower rates of chronic kidney disease and anaemia and increased immune system activation pre-surgery. Cluster 2 had more severe cardiorenal disease, anaemia, and elevated biomarkers of immunological ageing pre-surgery. Cluster 2 had significantly higher rates of organ injury relative to Cluster 1. The results were consistent across internal and external validation analyses. Analysis of snRNAseq data in biopsies from Cluster 1 demonstrated enrichment for immune response genes in cardiomyocytes, naive T/B lymphocytes and progenitor cells, and activation of non-tissue resident macrophages relative to Cluster 2. Cluster 2 showed enrichment for senescent/ effector memory T cells, dysregulated activation of tissue-resident macrophages, and cardiomyocyte dedifferentiation relative to Cluster 1. In UK Biobank, genetic modification of genes differentially expressed between the two MLTC phenotypes altered 90-day mortality post-surgery. Conclusions Immune system homeostasis determines susceptibility to organ injury and death in people with MLTC undergoing cardiac surgery and represents a previously unrecognised target for organ protection interventions. ### Competing Interest Statement GJM has received consultancy fees from Pharmacosmos. All other authors declare no competing interests. ### Clinical Protocols ### Funding Statement The study was supported by British Heart Foundation grants RG/13/6/29947, CH/12/1/29419, and AA18/3/34220, and the Leicester NIHR Biomedical Research Centre. MR is a NIHR Clinical Lecturer. TC is an NIHR Academic Clinical fellow. FL is currently an employee for GlaxoSmithKline, but was an employee of the University of Leicester when this research was undertaken, supported by the British Heart Foundation grant CH/12/1/29419. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: UK HRA ethics approvals for the primary studies were 09/H0104/53, 12/EM/0475, 13/EM/0383, 15/YH/0489, and 16/NW/0494, and, and for the secondary clustering analyses and UK Biobank analyses were 18/WS/0148, 21/NW/0157 and 21/SC/0118. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available through approved governance processes from the University of Leicester.