Early graft loss due to acute thrombotic microangiopathy accompanied by complement gene variants in living-related kidney transplantation: case series report

Currently, owing to improved screening regimens for transplant candidates and better immunosuppression, the short-term prognosis of kidney transplantation has greatly improved [1, 2], only 0.4% of patients had graft loss due to severe acute rejection during the first post-transplant year [2]. However, vascular thrombosis has become a common reason for early graft loss [2, 3]. TMA is a rare disease that is clinically characterized by hemolytic microangiopathic anemia, thrombocytopenia, and organ injuries due to the presence of thrombi in the capillaries and small arteries. Post-transplant TMA is relatively uncommon in the graft biopsy, with de novo and recurrent TMA being discovered in 0.8%-14% [4, 5] and 9%-29.4% [5, 6] of patients, respectively. Noteworthy, complement regulatory genetic variants have been observed to accelerate the development of TMA in renal allografts [7]. Patients with complement genetic variants had a higher risk of recurrence of TMA, whereas the highest risk of graft loss was observed in patients with both complement pathway variants and low C3 [8]. Le Quintrec et al. found that 7 out of 24 de novo TMA (29%) had complement factor H (CFH) or complement factor I (CFI) gene variants, two of whom had acute rejection and calcineurin inhibitor (CNI) toxicity, respectively [7]. In 2018, we reported a kidney recipient of concomitant C3 glomerulonephritis and TMA failed to respond to plasma exchange and had early graft loss who had two CFI genetic variations and low serum C3 level [9]. These two CFI genetic variants were not verified as pathogenic genes for TMA in a subsequent study with the CRISPR/Cas9 system to make mutant mouse lines that carried D288G and P467S variants in CFI in the mouse model [10].

Here we report 3 cases of fulminant TMA shortly after LKT accompanied by complement gene variants in donor-recipient pairs, leading to allograft loss within 3 months post-transplant in all cases.

The three cases presented in this case series all share the following similarities: (1) all the recipients who had unknown native kidney diseases received LKT from one of their parents, and both the recipients and the donors had genetic variants in the complement factors; (2) all cases were identified TMA in the renal allograft by biopsy; (3) the prognosis of these cases was poor, patients had allograft loss within 3 months post-transplant.

Multiple etiologies have been identified to trigger post-transplant TMA, including ABMR, CNI toxicity, viral infections, sepsis, pregnancy, malignancies, and surgery [11]. In our case series, ABMR cannot be ruled out as a trigger for TMA in case 1. Besides, next-generation sequencing confirmed that the patient had a CMV infection. Of note, previous studies have shown that CMV infection was associated with post-transplant TMA [12‐14]. CMV infection can cause endothelial cell injury indirectly and induce platelet adherence and von willebrand factor expression [15, 16]. Therefore, ABMR and CMV infection might act synergistically to cause TMA in the first case. The histological findings of case 2 showed tubular epithelial cell vacuolization and hyaline droplet degeneration in the adventitia of arterioles, suggesting that TMA may be induced by acute CNI toxicity. However, there was no improvement in Scr after conversion from tacrolimus to sirolimus. The first biopsy of case 3 showed typical ABMR [17], it was impossible to rule out the possibility of TMA caused by ABMR. Besides, cyclophosphamide metabolites are considered to cause direct endothelial capillary damage, inducing the cascade of thrombosis [18].

The interesting part of the current study is the observation of complement gene variants in both the donors and the recipients, which may lead to complement over-activation, potentially promoting TMA. The “multiple-hit hypothesis” for TMA argues that the combination of genetic predisposition and several trigger conditions work synergistically to provoke TMA in the allograft [19]. Genetic variants or acquired abnormality in CFH could induce uncontrolled complement activation amplifying. According to the American College of Medical Genetics and Genomics guideline classification [20], CFHR3 c.721C > T (p.P241S) is a variant of benign (BA1, BS1, BP4), CFH c.3572C > T (p.S1191L) is a likely pathogenic variant (PM1, PM2, PM5, BP4) and CFH c.3578C > G (p.T1193R) is evaluated as uncertain significance (PM1, PM2, BP4). Besides, all donors who carried the same variant of complement genes as the recipients were free of kidney disease. We suspected that external factors may be required to trigger TMA, and other undiscovered genetic variants of the recipients also contribute to the disease (Fig. 2). For example, patient 1 also had a heterozygous variant in the PROS1 gene, which has been reported to be associated with protein s deficiency and would increase the risk of thrombosis [21]. Therefore, the deficiency of triggers and absence of other potential deleterious genetic variants may have led to the different clinical manifestations.

The 2015 Kidney Disease: Improve Global Outcome (KDIGO) recommends that atypical hemolytic uremic syndrome (aHUS) recipients with identified genetic or acquired factors can only be considered for LKT from donors without these factors [22]. Patients with suspected aHUS are recommended to perform genetic testing in KDIGO 2021 guideline [23]. It has been suggested that genetic testing could reveal underlying conditions in patients with an unidentified cause of ESRD pre-transplant and help in improving pre- and post-transplant management [24‐26]. However, no studies have concluded that a complement genetic test is required for recipients with unknown primary disease before kidney transplantation. In our case series, recipients and donors both carried the complement genetic abnormality, which may contribute to the continuous injury of endothelial cells. Noteworthy, no abnormality was found in the routine screening program of recipients and donors, which led to the negligence of genetic testing pre-transplant. Therefore, for recipients with unknown causes of ESRD, appropriate complement genetic screening may be considered to identify potential risks with the consent of patients. Meanwhile, nephrologists should select the most suitable genetic test for the recipient [27]. The minimum set of genes that should be screened for complement genes includes CFH, CD46, CFI, CFB, THBD, CFHR1, CFHR5, and DGKE [22].

The prognosis of TMA in renal allografts is quite poor. Graft loss within 2 years of diagnosis was reported to occur in about 40% of cases, whereas 50% of patients died within 3 years after diagnosis [5]. Early anti-complement treatment is crucial to rescue renal function and avoid sequelae [22, 28]. Currently, eculizumab is the first-line effective therapy for the treatment and prevention of recurrent TMA [29‐32]. Pre-emptive eculizumab treatment is sufficient to prevent the recurrence of aHUS and to maintain long-term graft function in patients with complement genetic variants [33].

However, eculizumab is not approved by the State Food and Drug Administration in China. In this case, PE was recommended by the KDIGO workshop [22], which has been found to improve graft survival by removing platelet-aggregating factors and replenishing deficient factors [12, 34]. In our case series, case 1 and case 2 received PE, while case 2 was adjusted for immunosuppression since conversion from cyclosporine to tacrolimus is the preferred therapy for cyclosporine-associated TMA [4]. For CMV infection-related TMA, intravenous ganciclovir was noted to be effective in several case reports [12, 15]. However, all graft loss occurred within 3 months post-transplant. Such rapid progression of TMA may be associated with the lack of early use of eculizumab.

Our study has some limitations. Although the recipients carried the CFH gene variants, some tests such as CFH antibody, serum CFH level, ADAMTS13 activity, haptoglobin, and Shiga toxin testing were not performed. Our limited data are insufficient to recommend widespread testing for complement variants in recipients and donors scheduled for LKT. The hypothesis based on our case series requires further animal experiments to validate.

In conclusion, we reported 3 cases that had early graft loss due to fulminant TMA accompanied by complement gene variants in both donors and recipients. Simultaneous carriage of complement genetic variants by both the donors and recipients may increase the risk of TMA after LKT. Therefore, genetic testing of the complement pathway may be considered for selected patients with unknown causes of ESRD who are scheduled for LKT.