Key words : C5a complement activation product, Kidney transplant, Liver transplant

Introduction

Organ transplantation is the gold standard therapy for patients with end-stage organ failure. Despite improvements in patient and graft survival,^1,2 inflam­mation and immune activation remain inevitable consequences of transplant that limit short- and long-term posttransplant outcomes.^3-6 Accumulating evidence suggests that both the innate and adaptive immune systems contribute to the immune response to transplantation. Components of these systems act in concert to cause immediate allograft injury and the development of immune memory against the allograft that predisposes to ongoing injury.^7-9
The complement cascade is a central component of the innate immune system that is implicated in immediate and delayed allograft injury.⁹ Complement activation is a well-recognized sequela of ischemia-reperfusion injury, contributing to inflammation and tissue injury that compromise early allograft function.^4,5,8,10 The complement system additionally plays a role in antigen presentation and can stimulate the development of adaptive immune responses against allograft tissue, leading to acute and chronic rejection.^8,9,11
Complement activation and inflammation begin­ning in the organ donor prior to transplant may contribute to suboptimal posttransplant outcomes.^12-14 It is well-known that brain death triggers a systemic inflammatory response, characterized in part by activation of the complement cascade.^15-17 In accordance with the pathophysiology of brain death, complement levels are elevated in serum and tissue samples from donation after brain death (DBD) organ donors and are associated with poor early and late graft function and a heightened incidence of acute rejection compared with levels found in organs from living donors.^14,18,19 Although DBD donors provide most of the organs for transplantation, use of donation after circulatory death (DCD) donor organs is increasing.²⁰ Limited evidence suggests that DCD donors exhibit a milder inflammatory phenotype compared with DBD donors, with relatively greater importance of apoptosis and hypoxia-related pathways.^21-24 Although several studies of com­plement activation in deceased donors have included both DBD and DCD donors,^13,25 the relative levels of complement activation in these 2 distinct popu­lations remain uncharacterized.
Accordingly, we aimed to characterize relative levels of systemic complement activation in DBD versus DCD donors. We measured serum levels of classical, lectin, alternative, and terminal pathway complement components to determine which of the 3 pathways are predominantly activated in each donor subgroup and explored the associations between levels of complement activation products and perioperative clinical outcomes in kidney and liver transplant recipients.

Materials and Methods

Study approval
This study was approved by the Duke University Institutional Review Board and by Carolina Donor Services (Durham, NC, USA). Signed written informed consent was received from study participants or authorized legal representatives for the use of samples for research purposes prior to inclusion in this study. None of the donors were prisoners at the time of donation. Donor data were obtained from the United Network for Organ Sharing and a research protocol approved by Carolina Donor Services.

Sample collection and processing
Peripheral blood was collected from healthy donors and deceased organ donors by venipuncture. Blood samples from deceased organ donors were collected in serum separator tubes (Beckton, Dickinson and Company, Franklin Lake, NJ, USA) in the operating room before organ procurement and were stored at 4 °C for less than 24 hours prior to processing. Serum was isolated by centrifugation at room temperature for 10 minutes at 500× gravity (g) to separate cells, followed by transfer to a 15-mL conical tube and subsequent centrifugation at 1200× g for 15 minutes to deplete platelets. Serum samples were aliquoted and stored at -80 °C until use.

Serum complement analysis
Serum concentrations of human complement factors were measured in duplicate using the Luminex platform with MILLIPLEX MAP Human Complement Panel 1 and Panel 2 (Millipore Sigma, Burlington, MA, USA). Assays were performed according to the manufacturer’s recommended protocol and read using a Bio-Plex 200 array reader (Bio-Rad, Hercules, CA, USA). Data were analyzed using Bio-Plex Manager software (Bio-Rad). Although complement component C5a has a particularly short serum half-life,²⁶ the assay manufacturer has reported consistent quantification of C5a above the limit of detection and stable concentrations with repeated thawing and freezing to -80 °C for sample processing and storage, respectively. Although some cross-reactivity with the stable metabolite C5a des arginine has been noted, this is thought to be minimal and has not yet been validated.

Posttransplant clinical outcomes
All patients who underwent kidney or liver transplant with organs from donors who provided samples for the study were included. Pediatric (age <18 years) and multiorgan transplant recipients were included due to the small number of patients in the study.
Variables of interest were abstracted from patient charts and the United Network for Organ Sharing database. Recipient outcomes common to both kidney and liver transplant procedures included reintervention (surgical, endoscopic, radiologic, or biopsy) within 30 days of transplant, intensive care unit readmission within 30 days of discharge from the index hospitalization, hospital readmission within 30 days of discharge from the index hospitalization, mortality within 90 days of transplant, and the occurrence and timing of any biopsy-proven acute rejection episodes. Additional organ-specific peri­operative outcomes of interest included delayed graft function (DGF) and discharge with a Foley catheter for kidney transplant recipients and need for blood product transfusion within 72 hours posttransplant, occurrence of posttransplant medical complications (neurologic, cardiovascular, pulmonary, abdominal, renal, infectious), early allograft dysfunction, and primary allograft failure for liver transplant recipients. Delayed graft function was defined as the need for postoperative dialysis within 7 days of transplant. Early allograft dysfunction was defined as aspartate aminotransferase or alanine amino­transferase >2000 U/L within 7 days of transplant, international normalized ratio >1.6 on posttransplant day 7, or total bilirubin >10 mg/dL on posttransplant day 7.²⁷

Statistical analyses
Characteristics of DBD and DCD donors were compared using Wilcoxon rank-sum tests for continuous variables and chi-square and Fisher’s exact tests for categorical variables. Complement factor levels were compared between DBD, DCD, and healthy donor groups using Kruskal-Wallis with Dunn’s multiple comparison tests with a Bonferroni correction for multiple testing. Spearman correlation coefficients were used to determine associations between C5a levels and levels of all other complement factors in donor serum samples. Since C2, C4, and C4b are common to the classical and lectin pathways, the specific contributions of classical and lectin pathway activation to C5a generation were explored using partial correlation analysis, examining associations between levels of C5a versus C2, C4, and C4b, respectively, adjusting for C1q (independent contribution of the lectin pathway) and mannose-binding lectin (MBL) (independent contribution of the classical pathway).

For each clinical outcome, Wilcoxon rank-sum tests were used to compare levels of complement factors in donor serum samples between recipients with and without the outcome of interest. No adjustment for multiple comparisons was imple­mented as analyses of complement factor levels and clinical outcomes were primarily exploratory. A 2-sided P value less than .05 was considered statistically significant. All analyses were performed using R version 3.6.1 (Vienna, Austria).

Results

Study population
Characteristics of the donors included in this study have been described previously.12 Overall, samples were collected from 65 deceased donors of whom 55 met DBD criteria and 10 met DCD criteria. For comparison, samples were additionally collected from 10 living healthy donors. Demographic characteristics were similar between DBD and DCD groups as shown in Table 1.

Serum complement levels
To compare levels of complement activation between DBD, DCD, and healthy donors, we measured serum levels of classical, lectin, alternative, and terminal pathway complement components (Figure 1). As indicated in Table 2, we found significantly higher levels of C2, C5a, and properdin in both DBD and DCD donors compared with levels found in serum from healthy donors. Serum levels of C1q, C4b, C5, factor I, and factor B were significantly higher in DBD donors than in healthy donors but were similar between DCD donors and healthy donors. Compared with DBD donors, significantly lower levels of C2, C4b, and factor D adipsin were found in DCD donor serum. Conversely, serum levels of C3 were signifi­cantly higher among DCD donors and healthy donors compared with DBD donors.

Since production of C5a is common to the classical, lectin, and alternative pathways of complement activation, we examined correlations between levels of upstream complement factors and levels of C5a to determine the relative activation of each pathway in DBD and DCD donors. Among DBD donors, C2, C3b, C4, C4b, factor B, and factor H were positively correlated with C5a (all P < .05). Partial correlation showed that C2 was associated with C5a independent of MBL (C2/C5a corrected for MBL: r = 0.31, P = .02) and independent of C1q (C2/C5a corrected for C1q: r = 0.38, P = .005). C4 was associated with C5a independent of MBL (C4/C5a corrected for MBL: r = 0.27, P = .046) but not independent of C1q (C4/C5a corrected for C1q: r = 0.19, P = .2). Among DCD donors, only factor I, factor B, and factor H were significantly correlated with C5a (factor I/C5a: r = 0.77, P = .014; factor B/C5a: r = 0.76, P = .016; factor H/C5a: r = 0.72, P = .02) (Table 3).

Association between donor complement levels and post-transplant clinical outcomes
A total of 15 kidney and 25 liver transplants were performed using organs from donors who provided samples for this study, including 1 simultaneous heart-kidney, 1 simultaneous pancreas-kidney, and 3 simultaneous liver-kidney transplants. Perioperative complications that occurred among recipients in the study are summarized in Table 4.

The associations between donor complement levels and perioperative complications in liver transplant recipients are summarized in Tables 5 to 8. Among kidney transplant recipients, donor complement levels were similar between those with and without clinical complications. Among liver transplant recipients, donor levels of C2 and MBL were significantly lower for patients who required blood product transfusion within 72 hours posttransplant compared with those who did not (median values were 9.1 vs 23.2 μg/mL for C2, P = .03, and 3.9 vs 10.0 µg/mL for MBL, P = .04) (Figure 2A and 2B; Table 5). Donor C4b levels were also significantly lower for patients who required posttransplant reintervention (median of 17.8 vs 22.3 μg/mL, P = .04) and those with acute rejection within 1 year (median of 12.8 vs 21.1 μg/mL, P = .015) (Figure 2C and 2D; Table 6 and Table 7). Donor levels of C3 and properdin were likewise significantly lower for recipients who were readmitted within 30 days of discharge from the transplant hospitalization (median of 171 vs 262 μg/mL for C3, P = .049, and 19.1 vs 29.5 μg/mL for properdin, P = .043) (Figure 2E and 2F; Table 8). No significant associations were found between donor complement levels and early allograft dysfunction, intensive care readmission within 30 days of discharge, or postoperative medical complications or biopsy-proven acute rejection within 30 days posttransplant.

Discussion

As we continue to face a critical shortage of organs for transplantation, use of DCD organs has increased in an attempt to maximize the potential donor pool.²⁰ While a growing body of evidence suggests that outcomes after DCD transplant are acceptable,^28,29 better understanding of DCD donor physiology is needed to optimize outcomes for recipients of these organs. Activation of the complement system in DBD donors contributes to allograft injury and is associated with poor graft function and acute rejection after kidney transplant.^13,14,18,19 To date, the role of the complement system in DCD donors and its contribution to perioperative outcomes in kidney and liver transplant recipients remain undefined and may be complicated by heterogeneity in underlying pathophysiology among DCD donors.

In this study, we found that serum levels of the downstream complement activation product C5a were significantly higher in DCD donors compared with living healthy controls. Serum samples from DCD donors demonstrated similar levels of C5a versus levels shown in DBD donors, suggesting that activation of the complement cascade occurs to similar degrees in both DCD and DBD donors.

Although DBD donor organ physiology is characterized in large part by a profound systemic inflammatory response to brain death,¹⁷ current understanding suggests that DCD donor organ physiology is characterized primarily by cell death and response to hypoxia that may result from warm ischemia that is unique to DCD organs.^21-23,30 Indeed, several studies of transcriptional profiles in DBD and DCD organs have identified upregulation of hypoxia response genes in DCD organs with comparatively lower levels of proinflammatory gene transcription compared with DBD organs.^21-23,30 These findings are further supported by studies demonstrating elevated levels of proinflammatory cytokines in serum samples from DBD versus DCD donors and demonstrating increased leukocyte infiltration in prereperfusion renal allograft biopsies from DBD versus DCD and living donor kidneys.^24,31 As a central component of the innate immune response to injury, the complement cascade is activated by both brain death and ischemia.^16,32 Our findings of comparable complement activation in DCD versus DBD donors suggests that, in the pretransplant setting, brain death and ischemia are both similarly potent activators of the complement cascade.

Because the physiologic basis for complement activation differs between DCD and DBD donors, it may reasonably be expected that the dominant pathways of complement activation differ between these groups. In studies of unstratified cohorts of deceased donors, all 3 of the classical, lectin, and alternative pathways have been shown to contribute to generation of the terminal membrane attack complex.^13,14 Consistent with these findings, levels of C5a in serum from DBD donors in our study were positively correlated with classical/lectin (C2, C4, C4b) and alternative (factor B, factor H) pathway factors, suggesting that all 3 pathways contributed to C5a generation in this group. Furthermore, C2 was associated with C5a independent of MBL and C1q, suggesting specific contributions from each of the classical and lectin pathways in DBD donors. Notably, current understanding suggests that C1q exhibits many anti-inflammatory and immune regulatory functions beyond the complement cascade; nonetheless, it continues to be recognized as a key initiator of the classical pathway, supporting our use of C1q as a means to separate the contribution of the classical pathway from that of the lectin pathway in DBD donors.³³

In contrast, levels of C5a in serum from DCD donors were only associated with factors B, H, and I, suggesting that the alternative pathway was the primary contributor to complement activation in this group. Despite statistical significance, levels of upstream complement components were weakly correlated with levels of C5a in DBD donors (all r < 0.4), whereas factors B, H, and I were strongly correlated with C5a in DCD donors (all r > 0.7). These findings may further emphasize the dominant contribution of the alternative pathway to complement activation in DCD donors, compared with a unified process involving the classical, lectin, and alternative pathways in DBD donors. Whereas damage- and pathogen-associated molecular patterns exposed during brain death may activate the classical pathway in DBD donors,^16,17 ischemic injury, which factors more prominently in DCD donor physiology, may preferentially activate the alternative pathway.¹⁴ Furthermore, in the absence of the potent immuno­genic stimuli associated with brain death, sole upregulation of the constitutively active alternative pathway in DCD donors may additionally explain the lower levels of upstream complement factors including C2 and C4b in this group. Improved understanding of the mechanisms of complement activation in DBD versus DCD donors may inform efforts to target inflammatory pathways in deceased donors to optimize allograft quality prior to organ donation.

Importantly, our findings of complement activa­tion via the alternative pathway in DCD donors may provide new understanding of the heightened occurrence of early posttransplant complications in recipients of organs from these donors. In particular, rates of DGF are significantly higher among recipients of DCD versus DBD donor kidneys, which may be attributed to the more severe ischemic insult associated with DCD organ donation.^30,34,35 However, in a rodent model of kidney transplant, Yu and colleagues found that treatment with a selective inhibitor of the alternative complement pathway improved posttransplant renal function and graft survival in treated versus untreated rodents.³² In light of these findings, our study suggests that complement activation via the alternative pathway in DCD donors may contribute to the heightened occurrence of DGF in recipients of these donor kidneys. However, further studies are needed to elucidate the relationship between ischemia, alterna­tive pathway activation, and DGF in the clinical setting.

Despite evidence of an association between donor complement activation and suboptimal outcomes after kidney transplant,^13,14,18,19 the relationship between donor complement activation and outcomes after liver transplant remains unclear. In this study, we found that donor complement levels were significantly lower for liver transplant recipients who required posttransplant blood product transfusion, reintervention, and hospital readmission and for those who had an episode of acute rejection within 1 year. In understanding these findings, it is worthwhile to note that the liver synthesizes the majority of the body’s soluble complement factors, which may complicate the relationship between systemic complement levels and liver-related adverse outcomes.³⁶ Indeed, in a study of complement levels in acute liver failure, Melgaco and colleagues found that serum levels of C3a were significantly lower in samples from patients with acute liver failure compared with healthy individuals.³⁷ Conversely, liver tissue samples from patients with acute liver failure demonstrated increased staining for complement factors, including C3a, C5a, and the membrane attack complex,^37,38 suggesting that complement activation in the setting of poor liver function may be reflected primarily by deposition in liver tissue. In liver transplant, positive staining for C4d in liver biopsies may help differentiate acute rejection from posttransplant viral hepatitis reactivation,^39,40 supporting an association between complement deposition in the liver allograft and immunologic posttransplant complications. Likewise, evidence from a rodent model of liver transplant suggests that the presence of terminal complement factors in donor livers at the time of transplant may increase the severity of ischemia-reperfusion injury, contributing to cell death, inflammation, and poor graft function regardless of recipient complement status.⁴¹ Our findings may be understood in the context of these studies, which suggest that, whereas complement levels were lower in donor serum samples for recipients who experienced clinical complications, complement deposition may have been present in corresponding donor liver tissue. Unfortunately, donor liver samples were unavailable in our study; future work should make specific provisions to obtain donor biopsy samples to test this hypothesis.

In light of the associations between donor complement activation and posttransplant compli­cations, pharmacologic inhibition of the complement cascade in deceased donors prior to transplant may represent a promising therapeutic avenue by which to improve posttransplant outcomes. Recipient treatment with complement-targeted therapeutics, including eculizumab, an anti-C5 monoclonal antibody, and C1 esterase inhibitor (C1-INH), has previously been explored as a means to prevent ischemia-reperfusion injury and DGF after kidney transplant.^42-44 In 2 randomized controlled trials, neither eculizumab nor C1-INH reduced rates of DGF in treated versus untreated recipients; however, patients who received C1-INH and developed DGF required fewer hemodialysis sessions after the first posttransplant week, suggesting that although C1-INH administration in transplant recipients may not prevent DGF, it may reduce DGF duration, facilitate renal recovery, and portend sustained benefits in graft function over time.^42-44 More recently, Danobeitia and colleagues found that in a nonhuman primate model of kidney transplant, recipients of kidneys from donors treated with C1-INH experienced significantly lower rates of DGF and demonstrated superior posttransplant renal function compared with recipients of untreated donor kidneys.⁴⁵ These results suggest that although complement inhibition in transplant recipients may improve renal function over time, complement inhibition in deceased donors may not only improve renal function, but may additionally prevent DGF from occurring altogether. Furthermore, in contrast to eculizumab, C1-INH acts upstream on the classical pathway, blocking the generation of complement activation products, including C3a and C4b, mediators that were associated with posttransplant complications in our study.⁴⁶ Although complement therapeutics remain an area of active investigation, our findings suggest that agents such as C1-INH that inhibit upstream complement activation and consequent generation of complement activation products may offer a novel means by which to optimize allograft function and quality in the deceased donor prior to transplant.

There are several limitations to our study that warrant discussion. First, we did not have access to DCD-specific data, such as duration of pretransplant warm ischemia, which may influence complement activation and posttransplant outcomes. In addition, as previously noted, donor tissue samples were not available, which limited our ability to comment on the association between local donor complement levels and posttransplant outcomes in both kidney and liver transplant recipients. Although future studies should examine the association between donor tissue complement levels and posttransplant outcomes, additional consideration of the association between tissue complement levels and evidence of tissue injury, including apoptosis or necrosis, is needed to understand how complement activation in the deceased donor may affect allograft quality prior to transplant. Finally, given the relatively small number of transplant recipients and perioperative complications in our study, we may have been underpowered to detect differences in donor complement levels between patients who did and did not have complications of interest. Additionally, multiorgan transplant recipients may be more likely to have complex posttransplant courses with a higher rate of clinical complications, which may have contributed to the complications that were seen in our study. Further studies examining a larger cohort of deceased donors and corresponding isolated kidney or liver transplant recipients may help clarify these associations, providing evidence to direct management decisions such as the use of complement-targeted therapeutics to optimize posttransplant outcomes.¹⁵

Conclusions

To our knowledge, this is the first study to define the relative activity of the complement system in DCD versus DBD donors. We have demonstrated that the complement cascade in DCD donors is activated to a similar extent compared with that shown in DBD donors and occurs primarily via the alternative pathway. While our study also provides preliminary evidence to support an association between decreased systemic donor complement activation and peri­operative complications after liver transplant, further investigation is warranted to better understand the relative contributions of systemic and local donor complement activation to outcomes after liver transplant, as well as to elucidate specific associations between DCD donor complement activation and posttransplant outcomes in the clinical setting.

References:

1. Hart A, Smith JM, Skeans MA, et al. OPTN/SRTR 2018 Annual Data Report: Kidney. Am J Transplant. 2020;20 Suppl s1:20-130. doi:10.1111/ajt.15672
   CrossRef - PubMed
   
2. Kwong A, Kim WR, Lake JR, et al. OPTN/SRTR 2018 Annual Data Report: Liver. Am J Transplant. 2020;20 Suppl s1:193-299. doi:10.1111/ajt.15674
   CrossRef - PubMed
   
3. Zhao H, Alam A, Soo AP, George AJT, Ma D. Ischemia-reperfusion injury reduces long term renal graft survival: mechanism and beyond. EBioMedicine. 2018;28:31-42. doi:10.1016/j.ebiom.2018.01.025
   CrossRef - PubMed
   
4. Menke J, Sollinger D, Schamberger B, Heemann U, Lutz J. The effect of ischemia/reperfusion on the kidney graft. Curr Opin Organ Transplant. 2014;19(4):395-400. doi:10.1097/MOT.0000000000000090
   CrossRef - PubMed
   
5. Lutz J, Thurmel K, Heemann U. Anti-inflammatory treatment strategies for ischemia/reperfusion injury in transplantation. J Inflamm (Lond). 2010;7:27. doi:10.1186/1476-9255-7-27
   CrossRef - PubMed
   
6. Mori DN, Kreisel D, Fullerton JN, Gilroy DW, Goldstein DR. Inflammatory triggers of acute rejection of organ allografts. Immunol Rev. 2014;258(1):132-144. doi:10.1111/imr.12146
   CrossRef - PubMed
   
7. Brennan TV, Lunsford KE, Kuo PC. Innate pathways of immune activation in transplantation. J Transplant. 2010;2010: 826240. doi:10.1155/2010/826240
   CrossRef - PubMed
   
8. Nieuwenhuijs-Moeke GJ, Pischke SE, Berger SP, et al. Ischemia and reperfusion injury in kidney transplantation: relevant mechanisms in injury and repair. J Clin Med. 2020;9(1):253. doi:10.3390/jcm9010253
   CrossRef - PubMed
   
9. Grafals M, Thurman JM. The role of complement in organ transplantation. Front Immunol. 2019;10:2380. doi:10.3389/fimmu.2019.02380
   CrossRef - PubMed
   
10. Thorgersen EB, Barratt-Due A, Haugaa H, et al. The role of complement in liver injury, regeneration, and transplantation. Hepatology. 2019;70(2):725-736. doi:10.1002/hep.30508
    CrossRef - PubMed
    
11. Rogers NJ, Lechler RI. Allorecognition. Am J Transplant. 2001;1(2):97-102
    CrossRef - PubMed
    
12. Pollara J, Edwards RW, Lin L, Bendersky VA, Brennan TV. Circulating mitochondria in deceased organ donors are associated with immune activation and early allograft dysfunction. JCI Insight. 2018;3(15):e121622. doi:10.1172/jci.insight.121622
    CrossRef - PubMed
    
13. Damman J, Seelen MA, Moers C, et al. Systemic complement activation in deceased donors is associated with acute rejection after renal transplantation in the recipient. Transplantation. 2011;92(2):163-169. doi:10.1097/TP.0b013e318222c9a0
    CrossRef - PubMed
    
14. Naesens M, Li L, Ying L, et al. Expression of complement components differs between kidney allografts from living and deceased donors. J Am Soc Nephrol. 2009;20(8):1839-1851. doi:10.1681/ASN.2008111145
    CrossRef - PubMed
    
15. van Zanden JE, Jager NM, Daha MR, Erasmus ME, Leuvenink HGD, Seelen MA. Complement therapeutics in the multi-organ donor: Do or Don't Front Immunol. 2019;10:329. doi:10.3389/fimmu.2019.00329
    CrossRef - PubMed
    
16. Poppelaars F, Seelen MA. Complement-mediated inflammation and injury in brain dead organ donors. Mol Immunol. 2017;84:77-83. doi:10.1016/j.molimm.2016.11.004
    CrossRef - PubMed
    
17. Watts RP, Thom O, Fraser JF. Inflammatory signalling associated with brain dead organ donation: from brain injury to brain stem death and posttransplant ischaemia reperfusion injury. J Transplant. 2013;2013:521369. doi:10.1155/2013/521369
    CrossRef - PubMed
    
18. Damman J, Nijboer WN, Schuurs TA, et al. Local renal complement C3 induction by donor brain death is associated with reduced renal allograft function after transplantation. Nephrol Dial Transplant. 2011;26(7):2345-2354. doi:10.1093/ndt/gfq717
    CrossRef - PubMed
    
19. Damman J, Hoeger S, Boneschansker L, et al. Targeting complement activation in brain-dead donors improves renal function after transplantation. Transpl Immunol. 2011;24(4):233-237. doi:10.1016/j.trim.2011.03.001
    CrossRef - PubMed
    
20. Israni AK, Zaun D, Hadley N, et al. OPTN/SRTR 2018 Annual Data Report: Deceased Organ Donation. Am J Transplant. 2020;20 Suppl s1:509-541. doi:10.1111/ajt.15678
    CrossRef - PubMed
    
21. Damman J, Bloks VW, Daha MR, et al. Hypoxia and complement-and-coagulation pathways in the deceased organ donor as the major target for intervention to improve renal allograft outcome. Transplantation. 2015;99(6):1293-1300. doi:10.1097/TP.0000000000000500
    CrossRef - PubMed
    
22. Saat TC, Susa D, Roest HP, et al. A comparison of inflammatory, cytoprotective and injury gene expression profiles in kidneys from brain death and cardiac death donors. Transplantation. 2014;98(1):15-21. doi:10.1097/TP.0000000000000136
    CrossRef - PubMed
    
23. Kang CH, Anraku M, Cypel M, et al. Transcriptional signatures in donor lungs from donation after cardiac death vs after brain death: a functional pathway analysis. J Heart Lung Transplant. 2011;30(3):289-298. doi:10.1016/j.healun.2010.09.004
    CrossRef - PubMed
    
24. Sandiumenge A, Bello I, Coll E, Franco C, Pérez M, Crowley S, et al. Multicenter study of inflammation markers in lung transplant (LT): comparison of donation after cardiac death (cDCD) and brain death (DBD) DACMECITOS Study. J Heart Lung Transplant. 2020;39(4):S380.
    CrossRef - PubMed
    
25. de Vries DK, van der Pol P, van Anken GE, et al. Acute but transient release of terminal complement complex after reperfusion in clinical kidney transplantation. Transplantation. 2013;95(6):816-820. doi:10.1097/TP.0b013e31827e31c9
    CrossRef - PubMed
    
26. Reis ES, Chen H, Sfyroera G, et al. C5a receptor-dependent cell activation by physiological concentrations of desarginated C5a: insights from a novel label-free cellular assay. J Immunol. 2012;189(10):4797-4805. doi:10.4049/jimmunol.1200834
    CrossRef - PubMed
    
27. Olthoff KM, Kulik L, Samstein B, et al. Validation of a current definition of early allograft dysfunction in liver transplant recipients and analysis of risk factors. Liver Transpl. 2010;16(8):943-949. doi:10.1002/lt.22091
    CrossRef - PubMed
    
28. Schaapherder A, Wijermars LGM, de Vries DK, et al. Equivalent long-term transplantation outcomes for kidneys donated after brain death and cardiac death: conclusions from a nationwide evaluation. EClinicalMedicine. 2018;4-5:25-31. doi:10.1016/j.eclinm.2018.09.007
    CrossRef - PubMed
    
29. Kollmann D, Sapisochin G, Goldaracena N, et al. Expanding the donor pool: Donation after circulatory death and living liver donation do not compromise the results of liver transplantation. Liver Transpl. 2018;24(6):779-789. doi:10.1002/lt.25068
    CrossRef - PubMed
    
30. de Kok MJ, McGuinness D, Shiels PG, et al. The neglectable impact of delayed graft function on long-term graft survival in kidneys donated after circulatory death associates with superior organ resilience. Ann Surg. 2019;270(5):877-883. doi:10.1097/SLA.0000000000003515
    CrossRef - PubMed
    
31. de Vries DK, Lindeman JH, Ringers J, Reinders ME, Rabelink TJ, Schaapherder AF. Donor brain death predisposes human kidney grafts to a proinflammatory reaction after transplantation. Am J Transplant. 2011;11(5):1064-1070. doi:10.1111/j.1600-6143.2011.03466.x
    CrossRef - PubMed
    
32. Yu ZX, Qi S, Lasaro MA, et al. Targeting complement pathways during cold ischemia and reperfusion prevents delayed graft function. Am J Transplant. 2016;16(9):2589-2597. doi:10.1111/ajt.13797
    CrossRef - PubMed
    
33. Thielens NM, Tedesco F, Bohlson SS, Gaboriaud C, Tenner AJ. C1q: A fresh look upon an old molecule. Mol Immunol. 2017;89:73-83. doi:10.1016/j.molimm.2017.05.025
    CrossRef - PubMed
    
34. Singh RP, Farney AC, Rogers J, et al. Kidney transplantation from donation after cardiac death donors: lack of impact of delayed graft function on post-transplant outcomes. Clin Transplant. 2011;25(2):255-264. doi:10.1111/j.1399-0012.2010.01241.x
    CrossRef - PubMed
    
35. Nagaraja P, Roberts GW, Stephens M, et al. Influence of delayed graft function and acute rejection on outcomes after kidney transplantation from donors after cardiac death. Transplantation. 2012;94(12):1218-1223. doi:10.1097/TP.0b013e3182708e30
    CrossRef - PubMed
    
36. Qin X, Gao B. The complement system in liver diseases. Cell Mol Immunol. 2006;3(5):333-340
    CrossRef - PubMed
    
37. Melgaco JG, Veloso CE, Pacheco-Moreira LF, Vitral CL, Pinto MA. Complement system as a target for therapies to control liver regeneration/damage in acute liver failure induced by viral hepatitis. J Immunol Res. 2018;2018:3917032. doi:10.1155/2018/3917032
    CrossRef - PubMed
    
38. Pham BN, Mosnier JF, Durand F, et al. Immunostaining for membrane attack complex of complement is related to cell necrosis in fulminant and acute hepatitis. Gastroenterology. 1995;108(2):495-504. doi:10.1016/0016-5085(95)90079-9
    CrossRef - PubMed
    
39. Schmeding M, Dankof A, Krenn V, et al. C4d in acute rejection after liver transplantation--a valuable tool in differential diagnosis to hepatitis C recurrence. Am J Transplant. 2006;6(3):523-530. doi:10.1111/j.1600-6143.2005.01180.x
    CrossRef - PubMed
    
40. Bu X, Zheng Z, Yu Y, Zeng L, Jiang Y. Significance of C4d deposition in the diagnosis of rejection after liver transplantation. Transplant Proc. 2006;38(5):1418-1421. doi:10.1016/j.transproceed.2006.03.018
    CrossRef - PubMed
    
41. Fondevila C, Shen XD, Tsuchihashi S, et al. The membrane attack complex (C5b-9) in liver cold ischemia and reperfusion injury. Liver Transpl. 2008;14(8):1133-1141. doi:10.1002/lt.21496
    CrossRef - PubMed
    
42. Jordan SC, Choi J, Aubert O, et al. A phase I/II, double-blind, placebo-controlled study assessing safety and efficacy of C1 esterase inhibitor for prevention of delayed graft function in deceased donor kidney transplant recipients. Am J Transplant. 2018;18(12):2955-2964. doi:10.1111/ajt.14767
    CrossRef - PubMed
    
43. Huang E, Vo A, Choi J, et al. Three-year outcomes of a randomized, double-blind, placebo-controlled study assessing safety and efficacy of C1 esterase inhibitor for prevention of delayed graft function in deceased donor kidney transplant recipients. Clin J Am Soc Nephrol. 2020;15(1):109-116. doi:10.2215/CJN.04840419
    CrossRef - PubMed
    
44. Schroppel B, Akalin E, Baweja M, et al. Peritransplant eculizumab does not prevent delayed graft function in deceased donor kidney transplant recipients: Results of two randomized controlled pilot trials. Am J Transplant. 2020;20(2):564-572. doi:10.1111/ajt.15580
    CrossRef - PubMed
    
45. Danobeitia JS, Zens TJ, Chlebeck PJ, et al. Targeted donor complement blockade after brain death prevents delayed graft function in a nonhuman primate model of kidney transplantation. Am J Transplant. 2020;20(6):1513-1526. doi:10.1111/ajt.15777
    CrossRef - PubMed
    
46. Berger M, Lefaucheur C, Jordan SC. Update on C1 esterase inhibitor in human solid organ transplantation. Transplantation. 2019;103(9):1763-1775. doi:10.1097/TP.0000000000002717
    CrossRef - PubMed