#4443 INNATE IMMUNE MEMORY DETERMINES LONG-TERM KIDNEY ALLOGRAFT SURVIVAL
Authors: Jonkman Inge , Jacobs Maaike , Yanginlar Cansu , Martens Joost , Baltissen Marijke , Netea Mihai , Van Der Vlag Johan , Hilbrands Luuk , Rother Nils , Duivenvoorden Raphael 
Published: June 2023

Abstract

Background and Aims
Historically, transplant medicine has focused primarily on the adaptive immune system, while the role of innate immune cells in the complex graft-reactive immune response has been understudied. The recently emerging concept of “trained immunity” is of particular interest in this regard. Trained immunity is a phenomenon in which innate immune cells develop a long-lasting memory in response to an initial stimulus, thereby reprogramming cells for a stronger inflammatory response to future stimuli. We hypothesized that damage-associated molecular patterns (DAMPs), released during ischemia-reperfusion injury, and immunosuppressive medication can affect trained immunity, and investigated in a cohort of kidney transplant patients if trained immunity is associated with long-term allograft survival.

Method
An established in vitro trained immunity assay was used in which human peripheral blood mononuclear cells (PBMCs) were stimulated. After five days of rest, cells were restimulated with lipopolysaccharide (LPS), and IL-6 and TNF were measured in the supernatant as a readout of the trained immunity response (Fig. 1A). We tested a library of DAMPs, and immunosuppressive drugs commonly used in kidney transplantation, to determine their effect on trained immunity. Of 96 kidney transplant recipients, with a follow-up for graft survival &gt;8 years, serum was obtained before- and one week after transplantation. Patient sera were used to stimulate healthy PBMCs in the trained immunity assay. The relationship between serum induced trained immunity and long-term allograft survival was analyzed by Kaplan-Meier and Cox regression analysis.

Results
We found that DAMPs can affect trained immunity, causing either an enhanced (HMGB1, histones, IL-1β) or suppressed (vimentin, ATP, and C1q) cytokine response after LPS restimulation (Fig. 1B). Prednisone and tacrolimus potently suppressed trained immunity (Fig. 1C). In the kidney transplant patient cohort, cells stimulated with patients’ serum showed considerable heterogeneity in the IL-6 and TNF production after LPS restimulation. The IL-6 and TNF response of cells stimulated with serum obtained one week post-transplantation was lower compared to cells stimulated with serum obtained before transplantation (Difference of 463 ± 428 pg/mL, p&lt;0.001 for IL-6; 1215 ± 1078 pg/mL, p&lt;0.001 for TNF). The trained immunity response to post-transplant obtained serum was strongly associated with long-term death-censored graft survival (p = 0.005 for IL-6 tertials, and p = 0.037 for TNF tertials in a Kaplan-Meier analysis), and remained significant after adjusting for potential confounders.

Conclusion
Trained immunity can be affected by stimulation with DAMPs, which are released during ischemia-reperfusion injury during transplantation, and by immunosuppressive drugs used in kidney transplantation. The net effect of patients' serum taken one week after transplantation, containing a mixture of DAMPs and immunosuppressive drugs, has a suppressive effect on trained immunity compared with patients' pre-transplant serum. Interestingly, the trained immunity response to post-transplant serum is strongly associated with long-term allograft survival. Thereby we have identified trained immunity as a novel and relevant immunological mechanism in organ transplantation.