Successful living kidney transplantation in a T-cell flow cytometry crossmatch-positive patient with atypical hemolytic uremic syndrome treated with an anti-C5 antibody: a case report

Abstract

Atypical hemolytic uremic syndrome (aHUS) is an intravascular hemolytic disorder caused by complement dysregulation. A 41-year-old female patient with end-stage kidney disease and a history of glomerulonephritis had been receiving frequent blood transfusions for anemia and thrombocytopenia with hemolytic findings. She came to our hospital for a living donor kidney transplant from her mother, and a preoperative evaluation revealed ABO incompatibility and strong positivity in the T-cell flow cytometry crossmatch (FCXM) due to broad anti-HLA antibodies sensitized by previous blood transfusions. Since her clinical course and genetic testing led to the diagnosis of aHUS, treatment with eculizumab was started prior to kidney transplantation. She received desensitization therapy with intravenous immunoglobulin, plasma exchange, and rituximab along with regular eculizumab treatment, and then underwent living donor kidney transplantation. She achieved stable renal function without developing antibody-mediated rejection (ABMR) or the recurrence of thrombotic microangiopathy (TMA). Kidney graft biopsies 3 months and 1 year after transplantation showed no ABMR or TMA, with stable renal function. We herein report a positive FCXM case with aHUS that safely underwent living donor kidney transplantation without ABMR or the recurrence of TMA by starting eculizumab and desensitization therapy before surgery.

Introduction

Atypical hemolytic uremic syndrome (aHUS) is a complement-mediated thrombotic microangiopathy (TMA) caused by complement dysregulation [1], and is known for its high recurrence rate of TMA in transplanted kidneys and an increased risk of graft loss [2–4].

In addition, the risk of developing antibody-mediated rejection (ABMR) after transplantation is high in cases with a positive flow cytometry crossmatch (FCXM). These cases must be treated with improved desensitization protocols [5]. We herein describe a positive T-cell FCXM case with aHUS that safely underwent living donor kidney transplantation without ABMR or the recurrence of TMA by starting eculizumab and desensitization therapy before surgery.

Case report

A 40-year-old woman was referred to our hospital with anemia, hypertension, and end-stage kidney disease. She had no history of abnormal urinalysis findings during school health check-ups. At approximately 20 years old, she started to experience episodes of gross hematuria during upper respiratory infections but did not undergo detailed examinations. After being transferred to our hospital, peritoneal dialysis was initiated. However, a few months after the initiation of peritoneal dialysis, she began to exhibit anemia with hemolytic findings and thrombocytopenia, which worsened during episodes of menorrhagia, upper respiratory infections, hypertension, or fluid overload. Anemia exacerbation was accompanied by headaches, necessitating red blood cell transfusions on ten occasions. She was switched to hemodialysis one year after the initiation of peritoneal dialysis due to persistent fluid overload and hypertensive emergencies, which required hospitalization. Even with aggressive fluid and blood pressure management, hemolytic anemia persisted. Microangiopathic hemolysis was confirmed by episodic decreases in hemoglobin and platelet count, concomitant elevation of lactate dehydrogenase, and reduced haptoglobin levels. Other potential causes of hemolysis were systematically evaluated. Bone marrow examination demonstrated erythroid hyperplasia, which was consistent with a hemolytic process and did not suggest an alternative hematologic disorder. Detailed longitudinal changes in laboratory parameters during the clinical course are summarized in Table 1.

Table 1.

Longitudinal changes in laboratory parameters

	Reference range	Pre-PD	1-month post-PD	Hemolytic episode	Pre-Ecu	1-month post-Ecu	Pre-Tx	1-month post-Tx
Hb (g/dL)	11.6–14.8	9.2	10.6	7.0	8.1	8.4	9.4	11.1
Plt (× 104/μL)	15.8–34.8	15.6	13.6	13.2	20.5	21.3	13.0	29.3
LDH (U/L)	124–222	156	172	318	248	154	195	239
T-Bil (mg/dL)	0.4–1.5	0.30	0.28	0.23	0.37	0.35	0.57	0.42
Cr (mg/dL)	0.46–0.79	14.75	11.08	12.67	6.88	7.58	6.94	1.18
Haptoglobin (mg/dL)	19–170	N.D	N.D	< 5	< 5	18	30	40
D-dimer (μg/mL)	0.0–0.9	5.0	N.D	3.9	0.7	0.6	N.D	1.3
CH50 (U/mL)	30–50	N.D	N.D	N.D	34.6	< 5.0	< 5.0	< 5.0

Hb Hemoglobin, Plt Platelet count, LDH Lactate dehydrogenase, T-Bil Total bilirubin, Cr Serum creatinine, CH50 Total hemolytic complement activity, PD Peritoneal dialysis, Ecu Eculizumab, Tx Kidney transplantation, N.D. Not determined

At the age of 41 years, she expressed a desire to undergo living donor kidney transplantation from her mother. Preoperative immunological evaluations revealed ABO incompatibility, with the donor having blood type AB and the recipient blood type B and an anti-A IgG antibody titer of 1:4, as well as strong positivity in T- and B-cell FCXM due to broad anti-HLA antibodies sensitized by previous blood transfusions. LABScreen single antigen™ (LSSA) (One Lambda, Canoga Park, LA, USA) showed a high mean fluorescence intensity (MFI) of 15,884 against HLA B*04:06, a donor-specific anti-HLA antibody (DSA). Based on her clinical history, aHUS was suspected and genetic testing was performed using targeted next-generation sequencing with a hybrid capture method. The analyzed gene panel included CFH, CFI, CD46, C3, CFB, THBD, and DGKE, covering all protein-coding exons and exon–intron boundaries (up to 10 bp into intronic regions). The obtained sequences were compared with the human reference genome (GRCh38/hg38), and single nucleotide variants and short insertions/deletions were analyzed. Variants not listed in public databases or with a minor allele frequency ≤ 0.5% were reported. Three heterozygous variants of CFH (NM_000186.4) were identified: c.1935G > T (p.Thr645 =), c.2509G > A (p.Val837Ile), and c.2637A > G (p.Gly879 =). Two were synonymous variants, and the missense variant (c.2509G > A) has a relatively high allele frequency in the Japanese population and is classified as Benign/Likely benign in ClinVar. Therefore, all variants were considered non-pathogenic. There was no family history suggestive of aHUS. However, crossmatch-positive kidney transplantation is associated with a high risk of developing antibody-mediated rejection even after desensitization therapy, and we considered that it could represent a sufficient second hit to trigger aHUS, even in the presence of variants with low pathogenicity. In consideration of her clinical course, she was diagnosed with aHUS.

Two months before the scheduled living donor kidney transplant, eculizumab therapy was initiated, which attenuated symptoms, such as headache and fatigue, normalized blood pressure, and decreased her lactate dehydrogenase level (Table 1). Eculizumab was selected rather than ravulizumab prior to transplantation because its pharmacodynamic effect can be reliably monitored using CH50 levels, which was considered essential for perioperative management. Immunosuppressive therapy was started 28 days before transplantation and consisted of tacrolimus extended-release, mycophenolate mofetil, methylprednisolone, and basiliximab. Desensitization therapy with intravenous immunoglobulin (IVIG), plasma exchange (PE), and rituximab was performed in conjunction with continued eculizumab therapy. Supplemental eculizumab dosing was primarily administered according to a pre-planned strategy, with an additional 600 mg given after each PE or IVIG session to maintain adequate complement blockade. However, when PE and IVIG were performed on the same day, CH50 levels became detectable despite this strategy. Therefore, during the final sessions in which PE and IVIG were administered on the same day, an additional 600 mg of eculizumab was administered after each procedure to ensure sufficient complement inhibition. CH50 was confirmed to be below detectable levels on the day of surgery and, thus, living donor kidney transplantation was performed (Fig. 1). Two days before surgery, during IVIG treatment, analyses of LSSA using HLA Fusion™ Software 4.7. (One Lambda, Canoga Park, LA, USA) revealed that the levels of the eplets 76ESN and 71TTS, which were included in DSA against HLA B*04:06, were sufficiently reduced (Fig. 2).

Fig. 1.

Desensitization and induction immunosuppression therapy during eculizumab treatment. PE Plasma exchange, IVIG Intravenous globulin, TacER Tacrolimus extended-release, MMF Mycophenolate mofetil, MP Methylprednisolone

Fig. 2.

Anti-HLA class I antibody levels before and after desensitization analyzed with HLA Fusion™ Software 4.7. Based on mean fluorescence intensity (MFI) against the recipient HLA allele after intravenous globulin administration, the DSA eplets 76ESN and 71TTS were generally distributed and near background levels

Biopsy 1 h after revascularization showed no deposits of C1q or its downstream components C3, C4d, or C5b-9 in the transplanted kidney (Fig. 3). This finding supported DSA being almost completely removed by desensitization.

Fig. 3.

Immunofluorescence staining of kidney graft biopsy samples 0 and 1 h after reperfusion

The postoperative course was uneventful, without clinical TMA findings or rejection. The patient was discharged on postoperative day 14 with a serum creatinine level of 0.87 mg/dL. One month after transplantation, eculizumab was switched to ravulizumab in an outpatient setting, and treatment has been ongoing. After switching to ravulizumab, CH50 levels increased to a detectable range. Graft biopsies performed 3 months and 1 year after transplantation showed no signs of ABMR or TMA (Fig. 4), and renal function has remained stable.

Fig. 4.

Protocol kidney graft biopsies performed 3 months and 1 year after transplantation showed no signs of antibody-mediated rejection or recurrent thrombotic microangiopathy. MT Masson trichrome, PAM Periodic acid-methenamine silver

Discussion

aHUS is defined as an intravascular hemolytic disorder caused by complement abnormalities that presents with clinical features such as microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury, while excluding other TMA, such as Shiga toxin-producing Escherichia coli-associated hemolytic uremic syndrome and thrombotic thrombocytopenic purpura [1]. Genetic testing and the confirmation of complement activation serve as diagnostic adjuncts when available. Although three CFH variants were detected in the present case, none were classified as pathogenic or likely pathogenic according to ACMG guidelines, and their contribution to the present disease was therefore considered unlikely. However, previous studies reported that pathogenic genetic variants were not present in 30–50% of aHUS cases [6–8]. This case demonstrated persistent findings of chronic TMA and anemia requiring frequent blood transfusions, leading to a diagnosis of aHUS, for which anti-C5 antibody therapy with eculizumab was initiated. Furthermore, when undergoing kidney transplantation, there is a risk that even minor genetic abnormalities may cause the abnormal activation of the complement system due to various external factors caused by kidney transplantation [9].

Eculizumab is a terminal complement inhibitor with high affinity and specificity for complement protein C5, preventing its cleavage into C5a and C5b and thereby inhibiting the formation of the terminal complement complex C5b-9 [10]. Indications for eculizumab include aHUS, paroxysmal nocturnal hemoglobinuria, myasthenia gravis, and other complement-related disorders; however, its use as desensitization therapy before transplantation is not currently approved. However, safe and successful kidney transplants have been achieved using eculizumab as preoperative desensitization for HLA-incompatible or ABO-incompatible kidney transplantations [11, 12].

Kidney transplantation in patients with aHUS is associated with a high risk of TMA recurrence in the graft and a high rate of graft failure [13]. Patients treated with eculizumab showed a long-term reduction in DSA and became negative for a crossmatch even without desensitization therapy [14]. In the present case, the patient exhibited high DSA due to frequent blood transfusions, posing a significant risk of ABMR postoperatively, as well as the potential recurrence of aHUS and post-transplant TMA. The preoperative administration of IVIG, PE, and rituximab, along with eculizumab therapy for aHUS, is considered to have contributed to controlling not only the recurrence of aHUS, but also ABMR.

The clinical course of the present case suggests the potential effectiveness of a multifaceted treatment strategy, including eculizumab, for patients highly sensitized to HLA and at risk of aHUS recurrence. In this context, a pre-planned supplemental eculizumab dosing strategy with additional adjustment based on CH50 monitoring was considered important to maintain adequate terminal complement inhibition during intensive desensitization.

The novelty of this report lies in the successful preemptive use of eculizumab combined with intensive desensitization in a strongly T-cell FCXM–positive aHUS patient, enabling living donor kidney transplantation without ABMR or TMA recurrence. This case further demonstrates that initiating terminal complement inhibition before transplantation, together with CH50-guided perioperative management, can facilitate safe transplantation in patients facing both high immunological risk and complement-mediated TMA risk. It should be noted that, because the present case showed a relatively indolent clinical course and lacked pathogenic complement gene variants, the favorable outcome may not be generalizable to patients with more severe aHUS or clearly pathogenic genetic variants. However, due to the high cost and infectious risks associated with eculizumab, further randomized controlled trials are necessary to confirm its efficacy and safety. Additionally, increasing the diagnostic accuracy of aHUS without detectable genetic abnormalities and establishing optimal protocols for preventing post-transplant TMA recurrence remain challenges for the future.

Conclusion

The present case developed a highly sensitized state due to frequent blood transfusions, resulting in strongly positive T-cell FCXM findings. ABMR observed in the transplanted kidney progressed through activation of the complement cascade via the classical pathway when DSA bound to vascular endothelial cells. In patients with aHUS who are highly sensitized to HLA, the addition of anti-C5 antibody therapy to desensitization consisting of IVIG, PE, and rituximab successfully blocks the terminal pathway of the complement cascade, thereby preventing ABMR.

Declarations

Conflict of interest

Consultancies: Masayoshi Okumi (Alexion Pharmaceuticals Inc.), Honoraria: Masayoshi Okumi (Astellas Pharm Inc. and Alexion Pharmaceuticals Inc.). The remaining authors have declared that no conflict of interest exists.

Ethical approval

This article does not contain any studies with human participants or animals performed by any of the authors.

Informed consent

Informed consent was obtained from the patient in this report.