In the current pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a broad spectrum of renal manifestations of the disease has been observed on native kidneys.1 In a prospective study of 701 patients with a median age of 63 years, Cheng et al2 found that 43.9% had substantial proteinuria, 26.7% had hematuria, and acute kidney injury (AKI) occurred in 5.1% of patients during disease progression. Interestingly, kidney damage and patient survival were found to be closely related. These data were confirmed by Pei et al3 in a study of 333 patients, 75.4% of whom displayed renal disorders, including AKI, proteinuria, and hematuria. The pathophysiological processes underlying COVID-19-related kidney impairment seem to be multifactorial and promoted by hemodynamic instability, the direct infection of tubular cells in the parenchyma, interstitial infiltration, microthrombus formation, and acute glomerular injury.1 The pathological kidney lesions associated with AKI and proteinuria in patients infected with SARS-CoV-2 were initially described in postmortem study.4 In this study, the principal pathological lesions observed were acute tubular necrosis with prominent diffuse proximal tubular injury.4 Renal biopsies performed in patients with confirmed SARS-CoV-2 infection and nephrotic-range proteinuria subsequently suggested that collapsing glomerulopathy, a histological variant of focal segmental glomerulosclerosis (FSGS), may be a common finding in patients of African ancestry.5-10 Interestingly, in 4 cases tested for high-risk apolipoprotein L1 (APOL1) genetic variants,5,7,9 an association was found between these glomerular lesions and genetic susceptibility, suggesting that, as in other infectious diseases, such as HIV infection or malaria, SARS-CoV-2 infection may act as a trigger promoting FSGS/collapsing glomerulopathy lesions in patients of African ancestry.10 These data were confirmed in a biopsy series of 14 patients showing, in the setting of COVID-19, a strong association between FSGS collapsing glomerulopathy variant and APOL1 high-risk gene variant.11 It has recently been suggested that kidney transplant recipients have a higher risk of severe COVID-19.12-14 However, to date, in the setting of renal transplantation, biopsy-proven glomerular lesions potentially related to SARS-CoV-2 have been exceptionally described.15 We provide here a case report in this context, concerning a patient who developed laboratory-confirmed SARS-CoV-2 infection 2.5 months after a first renal transplantation, leading, 10 days later, to nephrotic syndrome with biopsy-proven FSGS lesions on the graft, which was obtained from a donor with a high-risk APOL1 variant.
A 49-year-old man of African origin was referred to our nephrology department on April 2020 for the assessment of nephrotic syndrome. His medical history included end-stage renal disease of presumed vascular origin that had required chronic intermittent hemodialysis since 2014. No renal biopsy was performed at the time of initial nephrologic evaluation, due to severely impaired renal function in a context of bilateral renal atrophy. At this time, urine protein/creatinine ratio (UPCR) and albumin levels were at 1100 mg/g and 43 g/L, respectively. The patient had no family history of renal disease or edema but had severe hypertension associated with hypertrophic cardiomyopathy. On January 2020, he underwent a first renal transplantation in which he received a kidney from a 45-year-old man who died in a road accident. There were 7 HLA mismatches (2A, 1B, 2C, 2DP) between donor and recipient. The patient’s pretransplantation panel reactive antibody level was 0%. Initial immunosuppressive treatment consisted of induction with antithymocyte globulin (thymoglobulin, Mérieux) for 5 days, combined with methylprednisolone pulses. The maintenance immunosuppressive regimen included tacrolimus (initiated on d 4, with trough concentrations maintained at 8–10 ng/mL) associated with mycophenolate mofetil (2 g/d, subsequently adjusted according to clinical safety criteria) and oral steroids. The posttransplantation period was unremarkable, and the patient was discharged 7 days after surgery, with a creatinine concentration of 1.84 mg/dL (estimated glomerular filtration rate [eGFR]: 42 mL/min/1.73 m2). Two weeks after transplantation, the patient developed noncompressive lymphocele with no signs of infection, which did not require surgery. Two months after transplantation, renal function was defined by a creatinine level of 1.47 mg/dL (eGFR of 52 mL/min/1.73 m2), and UPCR was considered to be in the normal range (201 mg/g). Five weeks after transplantation, the patient displayed a light cough and ageusia without dyspnea, fever, or diarrhea (Figure 1). These clinical manifestations were highly suggestive of the initial manifestations of COVID-19. Renal function initially remained stable, but we observed a substantial increase in UPCR (1380 mg/g; Figure 1). Two weeks later, we detected a significant worsening of renal function (creatinine level of 2.17 mg/dL, eGFR of 33 mL/min/1.73 m2), with an increase of proteinuria level. The patient was admitted to our department for renal graft biopsy (Figure 1). At this time, the patient presented a nephrotic syndrome with an albumin concentration of 27 g/L and a UPCR of 3270 mg/g, with a moderate inflammatory syndrome (C-reactive protein concentration of 19.2 mg/L) and lymphopenia (absolute lymphocyte count of 400 × 109/L and a CD4 T-cell count of 151/µL). Because of nephrotic syndrome occurring in a context of suspected COVID-19, a renal graft biopsy was performed.
MATERIALS AND METHODS
Detection of the SARS-CoV-2 Genome
Nasopharyngeal swabs were collected, and samples were processed for RNA extraction with the QIA symphony platform. Real-time polymerase chain reaction (RT-PCR) was performed with a newly released commercial test kit (RealStar SARS-CoV-2 RT-PCR kit 1.0; Altona, Hamburg, Germany) on a LightCycler 480 plate-based real-time PCR platform. This kit uses probes conjugated with distinguishable dyes, making it possible to detect B-βCoV-specific and SARS-CoV-2-specific RNA simultaneously, together with an internal control to assess possible RT-PCR inhibition and to confirm the integrity of the RT-PCR. The cycle threshold (Ct) cutoff value is 40. A Ct value <40 indicates that the RT-PCR test is positive.
Analyses of Kidney Biopsy Specimen
The renal biopsy specimen was processed for light and immunofluorescence microscopy according to standard techniques. It was fixed in formol acetic alcohol, embedded in paraffin and sectioned. The sections were treated with hematoxylin and eosin, periodic acid-Schiff, Masson trichrome, and silver stains. Immunofluorescence was assessed on cryosections (3 μm), using fluorescein isothiocyanate–conjugated polyclonal antibodies directed against IgG, IgM, IgA, C3, C1q, and κ and λ light chains (Dako, Glostrup, Denmark). For electron microscopy, samples were fixed in 2.5% glutaraldehyde in 0.1 mmol/L cacodylate buffer (pH 7.4) at 4°C. Fragments were then postfixed in 1% osmium tetroxide, dehydrated using alcohol series, and embedded in epoxy resin. Semithin sections (0.5 µm) were stained using toluidine blue. Ultrastructure sections (80 nm) were contrast-enhanced using uranyl acetate and lead citrate, and they were examined using a JEOL 1010 electron microscope (JEOL, Ltd., Tokyo, Japan) with a MegaView III camera (Olympus Soft Imaging Systems GmbH, Munster, Germany).
High-risk APOL1 genotypes were defined as 2 risk alleles in any combination (homozygous G1/G1, homozygous G2/G2, or compound heterozygous G1/G2). As previously described, G1 variant allele consisting of 2 nonsynonymous coding mutations (S342G and I384M) and the G2 variant allele, a 6 base pair deletion that removes 2 amino acids (N388 and Y389) of gene encoding APOL1. DNA was extracted from peripheral blood leucocytes using the Maxwell 16 LEV Blood DNA Kit (Promega, Charbonnières-les-Bains, France) according to the recommendations of the manufacturer. APOL1 G1 haplotype (rs73885319 and rs60910145) and APOL1 G2 haplotype (rs71785313) were identified by allelic discrimination assays using TaqMan probes, on an ABI Prism Genetic Analyser System 9700 (Applied Biosystems, Thermo Fisher Scientific, Courtaboeuf, France). All investigations were performed in accordance with the Helsinki Declaration and was approved by our local institutional review board (IRB 412 Mondor No. 00003835) and by the Comité de Protection des Personnes d’Ile de France IV (No. 2016/25NICB).
Testing of Specimens for SARS-CoV-2 Infection
Nasopharyngeal swabs collected from the patient on day 2 after the onset of symptoms were tested positive for SARS-CoV-2 (low viral load, Ct values, 36). The patient’s clinical condition at this time did not require the administration of antibiotic or antiviral agents or hospitalization. Immunosuppressive treatment was left unmodified in the face of this not particularly worrying clinical presentation. A whole-body computerized tomographic scan revealed moderate bilateral pulmonary parenchymal ground-glass and other rare opacities. At the time of renal biopsy, SARS-CoV-2 PCR test results for nasal swabs remained positive, although the patient no longer had COVID-19 symptoms.
Renal Graft Pathological Findings
The renal biopsy specimen consisted of renal cortex tissues with 8 glomeruli, none of which was globally sclerotic. One glomerulus displayed FSGS not otherwise specified with segmental lesion of the glomerular tuft and hypertrophy of the overlying epithelial cells (Figure 2A). Acute proximal tubular injury was severe, with a diffuse flattened tubular epithelium and frank focal necrosis (Figure 2B). No microcystic tubular dilation, interstitial edema, or inflammation were observed. Interstitial fibrosis was mild (ci1; according to Banff classification), and vessels were normal. There was no evidence of thrombotic microangiopathy or rejection. Immunofluorescence assays on glomeruli were negative for IgG, IgM, IgA, C3, C1q, Kappa, and Lambda. Tests for C4d on peritubular capillaries were also negative. Electron microscopy analysis revealed severe podocyte injury characterized by foot process effacement (Figure 3A). We also observed glomerular endothelial changes, consisting on endothelial swelling and numerous tubuloreticular inclusions in glomerular capillaries (Figure 3B).
Screening for Underlying Cause of De Novo Focal and Segmental Glomerulosclerosis and Outcome
Serological tests for HIV and for other viruses (tests performed for hepatitis B and C viruses) were negative. Search for cytomegalovirus, Epstein Barr virus, parvovirus B19, and BK virus blood replication was negative. No donor-specific antibodies were detected. Immunological tests for antineutrophil cytoplasm, antinuclear, and anti-DNA antibodies were negative. Serum complement levels were within the normal range. Serum protein electrophoresis showed total protein concentration to be decreased (55 g/L) without monoclonal immunoglobulin spike on immunoelectrophoresis. Given this case of biopsy-proven FSGS in a renal graft 2.5 months after renal transplantation in a context of COVID-19, we investigated whether the donor had an APOL1 risk allele (using a blood sample collected at the time of kidney donation). The donor was found to have a homozygous G2/G2 genotype. After renal biopsy, the patient developed macroscopic hematuria, associated with a worsening of renal function (due to hypovolemia and postrenal AKI), necessitating blood transfusion and bladder catheterization. Strikingly, without specific treatment (steroid, introduction of new immunosuppressive agent) apart from introduction of a low dose of angiotensin–converting enzyme inhibitor, renal function progressively improved and proteinuria level decreased. At the patient’s most recent follow-up visit (10 wk after renal biopsy), creatinine level had returned to baseline values (1.64 mg/dL, eGFR of 48 mL/min/1.73 m2) and proteinuria level was at 1610 mg/g (Figure 1).
Patients who have undergone kidney transplantation may be particularly susceptible to COVID-19 because many morbid conditions, including hypertension, diabetes, and cardiovascular disease, are common in this population.12-14 The initial clinical presentation of COVID-19 in kidney transplant recipients seems to be quite similar that that in the general population.9,10 In a study performed in the framework of the Columbia University Kidney Transplant Program, the authors found that 6 transplant recipients displayed AKI, but the level of proteinuria was not specified and none of the patients underwent graft biopsies to determine the nature of the underlying histological lesions of the kidney.13 However, Kadosh et al16 recently described the case of a patient receiving immunosuppressive agents for heart transplantation who developed collapsing glomerulopathy after COVID-19. We provide here one of the first descriptions of biopsy-proven FSGS occurring in a context of AKI and nephrotic syndrome in a kidney transplant recipient with laboratory-confirmed SARS-CoV-2 infection. Even if we cannot definitely rule out that initial renal disease may be due to primary FSGS, medical history, clinical, and biological data were not consistent with this diagnosis at the time of the first nephrologic assessment. In addition, electron microscopy findings showing endothelial tubuloreticular inclusions are highly suggestive of FSGS related to COVID-19.6 As observed in our patient, severe kidney injury may occur in patients with only moderate lung symptoms and may persist even after the pulmonary symptoms have resolved.10 Two weeks after renal biopsy, with the exception of renal graft parameters (no improvement of the nephrotic syndrome), the patient’s clinical condition remains unchanged, with no reduction of immunosuppression. Strikingly, 10 weeks after post-COVID-19 FSGS diagnosis, without specific therapeutic intervention and exclusively with usual renal-protective measures, renal function progressively improved and proteinuria decreased. Since no second renal biopsy was performed at this time, and due to lacking data in the literature, regarding the long-term follow-up of COVID-19-related glomerulopathy, this finding suggesting a possible spontaneous partial recovery remains intriguing and should to be cautiously interpreted. The principal renal histopathological lesions observed in the native kidneys of patients with COVID-19 are tubular injuries, glomerular fibrin thrombi, and collapsing glomerulopathy lesions.1,5-11 The precise mechanisms by which SARS-CoV-2 induces kidney damage remain poorly understood. Angiotensin-converting enzyme 2, which may play a determinant role in intracellular invasion, is expressed on the brush border of the proximal tubule and in podocytes.1 Retrospective postmortem study analyzing kidneys from patients who died from severe COVID-19 previously reported the in situ expression of viral nucleocapsid protein antigen in the tubular compartment.4 Puelles et al17 detected SARS-CoV-2 protein and RNA in glomerular epithelial and tubular cells from autopsy samples, with elegant high-spatial resolution techniques. Of particular interest, Puelles et al17 reported that some patients had normal kidney function despite evidence of direct kidney infection. As SARS-CoV-2 displays renal tropism, these data suggest that the kidney may act as a reservoir of the virus during COVID-19. Conversely, several reports have shown that patients with COVID-19 may present AKI and heavy proteinuria due to collapsing glomerulopathy with no evidence of kidney infection, in the absence of SARS-CoV-2 RNA detection by in situ hybridization.5,7 In the present case, immunohistochemistry against SARS-CoV-2 nucleocapsid protein and SARS-CoV-2 in situ hybridization were not available to assess for the absence or presence of SARS-CoV-2 in renal cells. These data suggest a role for indirect mechanisms in the pathogenesis of COVID-19-related kidney injury. Our case, as previously reported for native kidneys from patients of African ancestry,5,7,9,11 highlights the importance of checking a DNA sample from the donor for high-risk APOL1 variants in the specific context of COVID-19 and renal transplantation. In native kidneys, Afro-Caribbean individuals carrying APOL1 risk alleles have a higher risk of developing FSGS lesions, and collapsing glomerulopathy in particular, as observed in HIV-associated nephropathy or systemic lupus erythematosus-associated collapsing glomerulopathy.18 Kidney allografts from donors with high-risk APOL1 variants also have a shorter survival.19,20 After renal transplantation, APOL1 risk alleles are independent predictors of a poor outcome, with a higher rate of occurrence for de novo collapsing glomerulopathy.21 Our patient was not infected with BK, cytomegalovirus, or parvovirus B19, all of which can act as second hits favoring the occurrence of FSGS and collapsing glomerulopathy in kidney transplant recipients with grafts from donors carrying 2 high-risk APOL1 alleles.22 Interestingly, in the case published by Lazareth et al,15 collapsing glomerulopathy occurred later (5 y after kidney transplantation) and the donor APOL1 genotype was considered as “low risk” (G0/G2). The APOL1 protein has been detected in human glomeruli, and there is growing experimental evidence to suggest that kidney-specific expression of the APOL1 G1 and APOL1 G2 risk variants may interfere with normal podocyte homeostasis.23 Tubuloreticular inclusions, frequently identified in patients with autoimmune and viral infections, are considered as a marker of systemic stimulation by endogenous or exogenous interferons. The presence of tubuloreticular inclusions in endothelial cells during COVID-19-associated collapsing glomerulopathy suggests a possible enhancement of the type I interferon response.6 Interferon stimulates APOL1 expression in vitro, causing severe podocyte injury, and collapsing glomerulopathy has been described in patients receiving interferon treatment.24 However, an inappropriate inflammatory response, with low levels of type I and type III interferon and high levels of IL-6 expression, has been reported in patients with COVID-19.25
In conclusion, our case supports the hypothesis that SARS-CoV-2 infection can be considered a second hit for FSGS after renal transplantation in patients with grafts originating from donors with genetic susceptibility factors. Further reports and analyses of the specific signaling pathways involved in COVID-19-induced glomerular damage are required to confirm this hypothesis.
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