Circulating Nephrin Antibodies and Post-Transplant Recurrence of Diffuse Podocytopathies: A Systematic Review

Abstract

Recurrence of diffuse podocytopathy (DP), primarily focal segmental glomerulosclerosis and minimal change disease, after kidney transplantation threatens allograft survival. Circulating nephrin autoantibodies have been linked to disease activity, but posttransplant evidence remains limited. We performed a systematic review with patient-level data extraction, including kidney transplant recipients with DP as their native kidney disease from studies reporting serum nephrin antibody testing and posttransplant outcomes. Four studies including 63 recipients (23 pediatric and 40 adult) with DP were included, comprising 53 focal segmental glomerulosclerosis, 8 minimal change disease, and 2 steroid-resistant nephrotic syndrome cases. Nephrin antibodies were detected in 22 of 62 tested recipients (36%), either before transplantation or during posttransplant recurrence, including one patient in whom antibodies were detected 9 years after transplantation. Recurrence occurred in 34 of 63 recipients (54%), including 20 of 22 (91%) antibody-positive patients. Antibody positivity was strongly associated with recurrence (OR 20.8; 95% CI, 4.2-102.6; P < 0.001), with sensitivity of 61%, specificity of 93%, positive predictive value of 91%, and negative predictive value of 68%. Antibody titers correlated with disease activity and declined with remission. Nephrin autoantibodies are associated with posttransplant recurrence of DP and may inform pretransplant risk stratification and posttransplant monitoring. Standardized assays and larger validation studies are needed.

Diffuse podocytopathy (DP) is a spectrum of glomerular diseases characterized by diffuse podocyte injury and heavy proteinuria. It is commonly used to refer to minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS), although it is not limited to these entities.1, 2, 3 Posttransplant recurrence of DP remains a major challenge in kidney transplantation and is highly associated with allograft loss.⁴ Recurrence of primary FSGS occurs in approximately one third of adult patients (32%), leading to graft loss in 39% of those affected.^5,6

The pathogenesis of DP has been presumed to be driven by an unidentified circulating factor that injures the podocytes and disrupts the filtration barrier.^7,8 The discovery of anti-nephrin autoantibodies, which target the slit diaphragm protein nephrin, has shifted the understanding of this disease spectrum toward an autoimmune etiology.^7,9 Anti-nephrin autoantibodies have been identified in a substantial proportion of patients with active disease, including up to 44% of adults with MCD and 52% of children with idiopathic nephrotic syndrome.⁷ Experimental models showed that passive transfer of patient-derived IgG containing nephrin antibodies causes proteinuria and foot process effacement, supporting their pathogenicity.¹⁰ Nephrin antibodies also act as a marker of disease activity, as their circulating levels strongly correlate with the degree of proteinuria and typically decline upon clinical remission.^7,11

In the transplantation setting, recent evidence indicates that presence of serum nephrin antibodies is associated with a subgroup of patients who are at increased risk of recurrence of DP.^4,12 Nephrin antibodies have been consistently reported to be associated with characteristic histopathological changes, such as punctate IgG deposition co-localizing with nephrin in graft biopsies obtained as early as 1-hour post-perfusion, indicating early antibody-mediated injury and nephrin phosphorylation.^11,13

The emerging relationship between nephrin antibodies and post-transplant recurrence of DP highlights the need to clarify their clinical relevance. Furthermore, these antibodies have been detected even in immunosuppressed transplant patients, underscoring a knowledge gap. Because existing evidence is limited, a systematic review is warranted to synthesize the available data on circulating nephrin antibodies in kidney transplant recipients.

Methods

A comprehensive literature search was performed on October 6, 2025. No limits were placed on publication date or language. This systematic review was conducted and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines (Table S1).¹⁴ We searched Ovid MEDLINE (1946 to present, including Epub Ahead of Print and In-Process records), Ovid Embase (1974 to present), Ovid Cochrane Central Register of Controlled Trials (1991 to present), the Cochrane Database of Systematic Reviews (2005 to present), Web of Science (1975 to present), and Scopus (1970 to present). The search strategy was developed with a medical research librarian and combined controlled vocabulary (MeSH and Emtree) with free-text terms related to diffuse podocytopathy, focal segmental glomerulosclerosis, minimal change disease, nephrotic syndrome, nephrin, nephrin antibodies, and kidney transplantation. Full search strings and Boolean combinations are available in Item S1. The protocol was registered in PROSPERO (CRD420251251125).

Studies were eligible if they included kidney transplant recipients with FSGS, MCD, or presumed DP nephrotic syndrome as the native disease, performed serum nephrin antibody testing, and reported post-transplant outcomes such as recurrence or graft failure. We excluded studies that duplicated previously published data, did not include nephrin antibody testing or outcome information, or were review articles or meta-analyses.

From each study, we extracted author and publication year; study design; patient characteristics; sample size; sex distribution; native disease; age at onset and at transplantation; pretransplant dialysis status; treatment before transplantation; donor type; immunosuppression regimen; antibody status and method of detection; use of any antibody-depletion approach; recurrence and its timing; treatment of recurrence; graft failure; clinical course; length of follow-up; and biopsy findings. Recurrence was recorded as defined by the original authors.

Case reports were assessed using the JBI case report checklist, and cohort studies with the Newcastle–Ottawa scale, which covers selection, comparability, and outcome domains. Two investigators (N.A. and W.C.) independently screened articles, extracted data, and evaluated risk of bias. Disagreements were resolved through discussion by all investigators (N.A., C.T., and W.C.) until consensus was reached.

Statistical Analysis

Descriptive statistics were used to summarize baseline and clinical characteristics. Continuous measures are presented as medians with interquartile ranges, while categorical variables are shown as counts and percentages. For studies in which individual patient data could be extracted, we planned to analyze 2 × 2 tables to examine the relationship between nephrin antibody status and post-transplant recurrence. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated with 95% confidence intervals (CIs) using the Clopper–Pearson exact method. Because predictive values depend on disease prevalence, we used Bayes’ theorem to recalculate predictive values at assumed recurrence risks of 30%, representing recurrence rates reported in a high-quality study of primary FSGS,⁵ and 10%, representing a lower-risk cohort, based on published data.¹⁵ The receiver operating characteristic (ROC) curve analysis was performed when sufficient data were available. Quantitative values would be used when reported and when data were comparable across studies; however, if only binary antibody results (positive or negative) could be extracted, ROC analysis would be conducted using the dichotomous classification. The association between antibody positivity and recurrence was assessed by logistic regression, yielding odds ratios with 95% CIs. When sufficient individual-level covariables were available, we planned to perform multivariable logistic regression to adjust confounders. A 2-sided P value of < 0.05 was considered statistically significant. Statistical analysis was performed using IBM SPSS Statistics version 26.0 (IBM Corp.).

Results

Clinical Characteristics

Four eligible studies from 428 screened records were included (Fig 1). These comprised one North American/European multicenter adult cohort study,⁴ one European pediatric case report,¹¹ one Japanese pediatric cohort study,¹² and one Japanese adult case report.¹⁶

Figure 1.

Flowchart of search methodology. A total of 428 studies were identified through database searching. After removal of 9 duplicates and exclusion of 375 records that were reviews, meta-analyses, conference abstracts, or otherwise irrelevant, 44 studies underwent full-text assessment. Of these, 22 were excluded because serum nephrin antibody measurements were not performed or reported, 10 were excluded because they did not involve kidney transplant recipients, 7 were excluded for lacking post-transplant outcome data, and 1 was excluded because of cohort overlap with a subsequently published larger cohort. Four studies met all eligibility criteria and were included in the systematic review.

A total of 63 kidney transplant recipients with DP were identified, including 23 pediatric and 40 adult patients. The underlying native kidney diagnoses included focal segmental glomerulosclerosis (FSGS, n = 53; 8 genetic), MCD (n = 8), and steroid-resistant nephrotic syndrome (SRNS, n = 2). Among all patients, 35 (56%) were male, and 34 (54%) received living-donor kidney transplants. Twenty-three patients were Japanese, and 40 patients were North American or European (Table 1).

Table 1.

Study Characteristics and Patient Population of Kidney Transplant Recipients With Diffuse Podocytopathy and Nephrin Antibody Testing

First Author (Y)	Study Type and Population	Subjects (n, male)	Native Kidney	Age at DP Onset	Age at TX Onset	TX Type	Immunosuppression (Induction; Maintenance)
Shirai, et al12 (2024)	Multicenter cohort of Japanese pediatric patients with FSGS	11 (7 male) with recurrent FSGS	FSGS	2.1 (1.5-4.8)	8.1 (6.9-15.0)	7 LDKT (64%) 4 DDKT (36%)	100% basiliximab; Tac/MMF/steroids
		3 patients (all male) with nonrecurrent FSGS	FSGS	5.5 (4.8-6.4)	12.4 (10.8-12.8)	3/3 LDKT (100%)	100% basiliximab; Tac/MMF/steroids
		8 genetic FSGS (4 male)	FSGS	3.2 (2.8-4.4)	12.3 (9.2-15.5)	7 LDKT (88%)	7/8 (88%) basiliximab; Tac/MMF/steroids. 1/8 used CsA instead of Tac
Batal, et al4 (2024)	Retrospective multicenter cohort of North American and European adults with DP; 82% identified as White	39 patients total, 20 of 39 (51%) were male	Total cohort (n=39)	NR	35 (26-51)	24/39 DDKT (62%); 38% had prior KT; median donor age 44 (31-58) with 46% male	NR
			FSGS (30)
			MCD (7)
Habbig, et al11 (2025)	Case report of a European pediatric case	1 female	FSGS	14	15	Pre-emptive LDKT	Basiliximab; Tac/MMF/steroids
Miyazaki, et al16 (2025)	Case report of a Japanese adult	1 male	MCD	15	49	LDKT	NR

Note: Values for age are median (IQR) in years unless otherwise noted.

Abbreviations: Ab, antibody; CsA, cyclosporine A; DP, diffuse podocytopathy; DDKT, deceased-donor kidney transplantation; FSGS, focal segmental glomerulosclerosis; LDKT, living-donor kidney transplantation; MCD, minimal change disease; MMF, mycophenolate mofetil; NR, not reported; TX, transplantation; Tac, tacrolimus.

Pediatric Populations

All pediatric subjects had FSGS. Fifteen of 23 were presumed primary FSGS, and the remaining 8 had genetically confirmed FSGS. Eighteen of the 23 pediatric recipients underwent living-donor kidney transplantation. Nearly all children received basiliximab induction, followed by maintenance immunosuppression with tacrolimus, mycophenolate mofetil, and corticosteroids.

Pediatric cases were reported predominantly from Japan, with disease onset typically from 2 to 3 years of age and kidney transplantation occurring from 7 to 12 years. Individuals who developed recurrence tended to have a younger age of onset and become dialysis dependent before transplantation. In Shirai et al,¹² all 11 pediatric patients with recurrent FSGS were anti-nephrin positive. All genetically confirmed FSGS patients tested negative for nephrin antibodies with no post-transplant recurrence reported.

Another pediatric case report from Germany described a 14-year-old, nondialysis-dependent patient with high anti-nephrin antibody levels who underwent a living-donor kidney transplant. This patient did not develop recurrent FSGS, likely due to the immediate peri-transplant antibody-depletion therapy, and achieved excellent graft function¹¹ (Tables 1 and 2).

Table 2.

Nephrin Antibody Findings and Post-Transplant Clinical Outcomes in Recipients With Diffuse Podocytopathy

First Author (Y)	Serum Nephrin Ab	Timing of Nephrin Ab	Detection Method	Pre-TX Ab Depletion	Recurrence (n, %)	Recurrence Timing	Treatment	Allograft Failure	Clinical Course	Follow-up Duration
Shirai, et al12 (2024)	11/11 (100%); median 899 (831-1,292 U/mL)	Before TX or during recurrence (within 1 day post-TX)	ELISA with cutoff 231 U/mL against mouse myeloma cell (NS0)-derived extracellular domain of recombinant human nephrin (R&D)	4/11 (36%) PLEX only; 3/11 (27%) PLEX+RTX	11/14 (79%) among nongenetic FSGS	Immediate/early within 1 day	PLEX 9 (82%) ± rituximab 3 (27%)	2 (18%)	Anti-nephrin levels fell to 155 (53-367) U/mL in 5 with remission. 1 achieved spontaneous remission; another responded to pMP	NR
	1/3 (33%); median 165 (153-244)			3/3 (100%) received PLEX+RTX		NR	NR	NR	NR	NR
	Negative			3/8 (38%) PLEX	None	NR	NR	None	NR	NR
Batal, et al4 (2024)	8/38 (21%)	Pre-TX	ELISA with cutpoint >187 U/mL against extracellular domain of recombinant human nephrin (hNephrinG1059)	21 (4 PLEX+RTX, 17 PLEX only)	22/39 (56%) recurred; 8/21 (38%) of them were anti-nephrin positive, whereas none of the nonrecurrent cases were positive	8 (6-20) days in nephrin Ab positive; 20 (9-39) days in nephrin Ab negative	PLEX alone 2 (9%) PLEX + IVIG (± others) 7 (32%) PLEX + rituximab (± others) 3 (14%) PLEX + obinutuzumab (± others) 3 (14%) PLEX + CsA (± others) 7 (32%) Multi-drug (PLEX + ≥3 agents) 5 (23%)	12 (31%); 10 due to recurrent DP, 2 due to rejection (time to graft failure 30 (13-48) months)	Four died with functioning graft	43 (8-79) mo
	3/30 (10%)			15 (3 PLEX+RTX, 12 PLEX only)	15 of 30 in FSGS			7 (23%); 5 due to recurrent DP, 2 due to rejection	Three died with functioning graft
	3/7 (43%)			4 (1 PLEX+RTX, 3 PLEX only)	5 of 7 in MCD			3 (43%) due to recurrence	One died with functioning graft
Habbig, et al11 (2025)	Positive at 100-200 RU/mL before RTX and PLEX	Before and after TX	ELISA, WB, and immunoprecipitation using R&D mouse and human, and SinoBio human cells	RTX + PLEX	No	NR	NR	No	Immediate graft function after nephrin Ab cleared	Over 1 y
Miyazaki, et al16 (2025)	Positive at 1,645 and 517 U/mL (cutoff >226), before and after LDL apheresis, respectively	9 years post-TX	NR	NR	Yes; biopsy-confirmed MCD	Three and 9 years post-TX	LDL-C apheresis then switched to pMP + single RTX	No	Refractory to LDL-C apheresis × 4 courses. Quickly responded to pMP + single RTX; nephrin Ab became undetectable and proteinuria resolved	188 d

Note: Values for age are median (IQR) in years unless otherwise noted.

Abbreviations: Ab, antibody; CsA, cyclosporine A; DP, diffuse podocytopathy; ELISA, enzyme-linked immunosorbent assay; FSGS, focal segmental glomerulosclerosis; IVIG, intravenous immunoglobulin; LDL-C, low-density lipoprotein cholesterol; MCD, minimal change disease; MMF, mycophenolate mofetil; PLEX, plasma exchange; pMP, pulse methylprednisolone; RTX, rituximab; TX, transplantation; Tac, tacrolimus; WB, Western blot; NR, not reported.

Adult Populations

The largest dataset came from Batal et al,⁴ a retrospective multicenter cohort of 39 North American and European kidney transplant recipients with DP. The median age at transplantation was 35 years, 51% were male, 82% were White, the median follow-up duration was 43 months (8-79), and most had native kidney disease attributed to FSGS (77%), followed by MCD (18%) and SRNS (5%). Most recipients underwent deceased-donor kidney transplantation (62%), and 38% had received a previous kidney transplant. Twenty-two subjects developed recurrent DP. Pretransplant nephrin antibodies were detected in 8 of 38 tested patients (21%). Antibody positivity differed by diagnosis (10% in FSGS, 43% in MCD, and 100% in SRNS). Anti-nephrin antibodies were detected in 8 of 21 patients with recurrent DP (38%), but in none of the 17 patients who did not recur. Prior native-disease treatments were heterogeneous and included corticosteroids, calcineurin inhibitors, mycophenolate mofetil, adrenocorticotropic hormone, and rituximab. Dialysis-dependent status and detailed maintenance immunosuppression regimens were not consistently reported. Twenty-one patients received pretransplant antibody-depletion therapy, predominantly therapeutic plasma exchange, with or without rituximab.⁴

Another adult case was described by Miyazaki et al¹⁶ and involved a Japanese man with childhood-onset MCD who later progressed to steroid-resistant nephrotic syndrome requiring dialysis before transplantation. He received a living-donor kidney and developed late recurrent podocytopathy 9 years post-transplant, accompanied by markedly elevated nephrin antibody titers (up to 1,645 IU/mL, cutoff > 226 IU/mL). Treatment with corticosteroids, rituximab, and low-density lipoprotein (LDL)-apheresis led to clinical improvement and parallel reduction in antibody levels¹⁶ (Tables 1 and 2).

Nephrin Antibodies and Clinical Outcomes

Posttransplant recurrence of DP occurred in 34 of 63 patients (54.0%), and among those with available antibody data, 20 of 33 (60.6%) were anti-nephrin positive. Posttransplant recurrence was defined as nephrotic-range proteinuria (urine protein-to-creatinine ratio > 2 g/g) and/or diffuse foot process effacement on graft biopsy in pediatric cohort.¹² Diffuse podocytopathy was defined by nephrotic syndrome (proteinuria > 3.5 g/day with serum albumin < 3.5 g/dL) and required >80% foot process effacement when electron microscopy was available in adult multicenter cohort.⁴

Nephrin antibodies were detected in 22 of 62 tested patients (35.5%). In 21 patients, antibodies were detected before transplantation or within the first posttransplant day; in the remaining adult patient, antibodies were detected at the time of late recurrence 9 years posttransplant, and pretransplant antibody status was not reported.¹⁶

Positive serum anti-nephrin antibodies identified 20 of 33 recurrent cases, corresponding to a sensitivity of 60.6% (95% CI, 42.1%-77.1%). Specificity was 93.1% (95% CI, 77.2%-99.2%), correctly classifying 27 of 29 nonrecurrent patients. The PPV was 90.9% (95% CI, 70.8%-98.9%), whereas the NPV was 67.5% (95% CI, 50.9%-81.4%). When recalculated using Bayes’ theorem at lower assumed recurrence risks, the PPV decreased to 79% at a 30% recurrence risk and 49% at a 10% recurrence risk, whereas the NPV increased to 85% and 96%, respectively. Two false-positive results were identified. One patient had a nephrin antibody level marginally above the positivity threshold (231 U/mL) but did not experience posttransplant recurrence.¹² A second antinephrin-positive case remained recurrence-free following transplantation after receiving antibody-depletion therapy, including rituximab and repeated therapeutic plasma exchanges, administered in response to the detected antibody level¹¹ (Table 3).

Table 3.

Diagnostic Accuracy of Nephrin Antibodies for Detecting Recurrence of Diffuse Podocytopathy in Kidney Transplant Recipients

Anti-Nephrin Status	Recurrence	No recurrence	Total
Positive	20	2	22
Negative	13	27	40
Total	33	29	62

Nephrin antibody positivity identified 20 of 33 recurrent cases, corresponding to a sensitivity of 0.61 (95% CI, 0.42-0.77). Specificity was high at 0.93 (95% CI, 0.77-0.99), correctly classifying 27 of 29 nonrecurrent patients. The positive predictive value (PPV) was 0.91 (95% CI, 0.71-0.99), whereas the negative predictive value (NPV) was 0.68 (95% CI, 0.51-0.81). At recurrence risks of 30% and 10%, PPV decreased to 0.79 and 0.49, while NPV increased to 0.85 and 0.96, respectively. Two false-positive cases were observed: one with minimally elevated anti-nephrin levels (likely nonpathogenic), and one from a patient who received pre-emptive intensive immunotherapy, which may have clinically suppressed recurrence of DP despite antibody detection.

The ROC analysis, performed using the binary antibody result (positive or negative), yielded an AUC of 0.77 (95% CI, 0.65-0.89). However, cutoff points were study-specific, and no standardized threshold was established (Fig 2). Circulating anti-nephrin antibodies were associated with a 20.8-fold higher odds of recurrent disease (crude OR 20.8; 95% CI, 4.2-102.6; P < 0.001). Multivariable analysis could not be performed because key covariates were inconsistently reported at the individual patient level.

Figure 2.

Receiver operating characteristic curve for nephrin antibodies in detecting recurrence of diffuse podocytopathy in kidney transplant recipients. The ROC curve illustrates the diagnostic performance of nephrin antibody for identifying recurrence of diffuse podocytopathy in kidney transplant recipients. Using binary antibody status, the area under the curve (AUC) was 0.77 (95% CI, 0.65-0.89), indicating moderate discriminative performance. Of note, cutoff points were study-specific, not standardized. ROC, receiver operating characteristic.

Recurrent cases typically presented with detectable antibodies before or immediately after transplantation, with titers declining after treatments, including therapeutic plasma exchange, rituximab, pulse steroids, and LDL-apheresis.^11,16 Clinical improvement was documented in many treated cases; however, the degree of remission was difficult to assess because outcomes and follow-up duration were not consistently reported across studies. A total of 12 patients developed graft failure due to recurrent DP, including 5 who were antibody positive. An additional 2 graft failures were attributed to rejection.

Biopsy Findings

Biopsy findings reflected nephrin antibody status. Recurrent diffuse podocytopathy showed consistent structural injury patterns. Early posttransplant biopsies in Shirai et al¹² demonstrated a rapid shift from linear to granular nephrin staining within 1 hour of reperfusion, accompanied by diffuse foot process effacement, supporting immediate antibody-mediated podocyte injury. In adults, Batal et al⁴ reported significantly higher frequencies of punctate nephrin staining and IgG-nephrin colocalization in recurrent cases compared with non-recurrent controls, whereas Miyazaki et al¹⁶ similarly showed diffuse effacement on EM despite MCD-like histology. We did not observe clear differences between pediatric and adult cohorts; biopsy patterns appeared broadly similar across age groups.

Treatment of Recurrence and Clinical Response

Across the 4 studies, treatment of recurrent DP primarily relied on plasma exchange, rituximab, and high-dose corticosteroids, often used in combination. In the pediatric cohorts, early initiation of plasma exchange frequently reduced proteinuria and corresponded with improvement in podocyte structural changes on biopsy.¹² Batal et al⁴ similarly reported that recurrent adult cases treated with plasma exchange, with or without rituximab, showed partial or complete remission in a substantial proportion of patients. Habbig et al¹¹ demonstrated a clear titer response relationship, with anti-nephrin antibody levels declining following combined PLEX and rituximab therapy, paralleling clinical remission. A similar pattern was seen in Miyazaki et al,¹⁶ in which elevated antibody titers at relapse decreased with steroid pulse therapy and rituximab, accompanied by recovery of normal nephrin localization on repeat biopsy (Table 2).

Antibody Detection Methods

All included studies used serum-based assays with recombinant human nephrin but differed in platform, antigen source, and timing of sampling. In Shirai et al,¹² anti-nephrin antibodies were measured by ELISA using a commercially available nonsecreting mouse myeloma cell (NS0)-derived recombinant extracellular domain of human nephrin. Habbig et al¹¹ measured anti-nephrin antibodies by ELISA using 3 recombinant extracellular domains of human nephrin: an NS0 (mouse myeloma cell)-derived protein (R&D 9399-NN), a HEK293 (human embryonic kidney 293)-derived protein from Sino Biological (17757-H08H), and a custom HEK293-derived protein from R&D Systems. Positive findings were further evaluated using immunoprecipitation, Western blotting, and immunofluorescence. Batal et al⁴ used a validated indirect ELISA against recombinant human nephrin extracellular domain (hNephrinG1059), with pretransplant sera collected a median of 4 days before transplantation. Miyazaki et al¹⁶ reported anti-nephrin antibody positivity, with titers markedly elevated at relapse (517 IU/mL; cutoff 226 IU/mL) and declining in parallel with clinical remission, although the assay methodology was not described.

Methodological Quality

Overall methodological quality ranged from moderate to high across included studies. Among case reports, both Habbig et al¹¹ and Miyazaki et al¹⁶ showed high reporting quality. For cohort studies, Batal et al⁴ achieved a high-quality rating (7/9 on the NOS), reflecting robust cohort selection and outcome assessment with only minor limitations in confounder adjustment and follow-up reporting. Shirai et al¹² scored 5/9, indicating moderate quality due to limited control of confounding and some uncertainty regarding the timing of exposure measurement. The variations in study quality were considered when interpreting the overall evidence (Tables S2 and S3).

Discussion

Recurrence of DP after kidney transplantation is a major threat to allograft survival, and reliable biomarkers to guide risk stratification and preventive strategies remain limited. In this systematic review, more than half (54.0%) of kidney transplant recipients with DP had recurrence after transplantation, and serum nephrin antibodies were associated with recurrence. However, the small number of graft failure events limits definitive conclusion. Across pediatric and adult studies, antibody positivity before or early after transplantation correlated with early heavy proteinuria and characteristic pathologic findings, including punctate IgG nephrin colocalization and granular redistribution of nephrin.

Our study showed that anti-nephrin antibodies have high specificity and PPV but moderate sensitivity and NPV for predicting recurrence of DP. Their presence suggests a high likelihood of recurrence, supporting a pathogenic role in a distinct immunologic subtype of the disease. Anti-nephrin antibodies do not account for all cases of recurrence, indicating that the mechanisms underlying recurrent DP are heterogeneous. Identification of additional autoantibodies targeting slit diaphragm or podocytes is needed to further elucidate the pathogenesis of primary DP. Anti-podocin and anti-Kirrel1 IgG have been described in nephrotic cohorts,¹⁷ and Habbig et al,¹¹ demonstrated concurrent anti-NEPH3 reactivity. These findings suggest that a subset of nephrin-negative transplant recurrences may still reflect antibody-mediated mechanisms targeting other slit-diaphragm proteins.

The proportion of transplant recipients who tested positive for nephrin antibodies in this review (36%) falls within the range reported in nontransplant populations, in which antibodies are detected in 44% of patients with active MCD, 52% in childhood idiopathic nephrotic syndrome, and 9% in primary FSGS.⁷ The high PPV and moderate NPV may be influenced by the high disease prevalence in our study. With a recurrence prevalence of 54%, the PPV is likely overestimated. To enhance generalizability, we performed a Bayes’ theorem analysis to estimate test performance at different levels of prevalence. Using published recurrence estimates for primary FSGS in transplant populations, including the general-risk⁵ and lower-risk groups,¹⁵ the modeled PPV declined to 79% at a 30% recurrence risk and 49% at a 10% recurrence risk, and the modeled NPV increased to 85% at a 30% recurrence risk and to 96% at 10% recurrence risk. Therefore, antibody status should be interpreted in conjunction with local disease prevalence and individual clinical risk factors. This higher recurrence in the transplant setting may reflect a subgroup with more severe or aggressive native disease, as patients who progress to advanced chronic kidney disease and ultimately require transplantation often represent those with refractory or high-risk clinical courses. This pattern is illustrated by the Japanese recurrent FSGS case series, in which all dialysis-dependent patients were anti-nephrin positive.¹² Because of the variability in assay platforms and the lack of standardized quantitative thresholds across studies, ROC analysis was performed using the dichotomized antibody status (center-specific positive vs negative). This approach limits the power of the ROC analysis. The resulting AUC of 0.77 indicates moderate discriminatory ability.

The overall crude OR showed a strong association between the presence of nephrin antibody and recurrence, and this pattern was consistent with the adjusted hazard ratio reported in the largest adult cohort,⁴ which identified nephrin antibodies as an independent predictor of recurrence. These observations support the concept that immune-mediated podocyte injury can recur in the allograft through antibody-driven pathways. The crude odds ratio may overestimate the true effect size due to the nature of odds ratios, the absence of multivariable adjustment, and the small sample size from limited published data. We were unable to perform a multivariable logistic regression adjusting for antibody-depletion prophylaxis and other relevant factors because individual-level data were limited. The true predictive effect of anti-nephrin antibodies could be attenuated after adjustment for these factors.

Regarding the 2 false-positive cases, the low-level antibody signal in the Shirai et al¹² case is unlikely to represent a truly pathogenic response, as the magnitude was closer to that observed in disease controls than in recurrent DP. In contrast, the absence of recurrence in the Habbig et al¹¹case likely reflects the effectiveness of antibody-depletion therapy rather than a true false-positive result. Importantly, rare nephrin reactivity has been reported in a pediatric control subject with a concurrent upper respiratory infection and in cases of nonprimary FSGS and PLA2R-associated membranous nephropathy. These observations raise the possibility of cross-reactivity, overlapping disease, or epitope spreading and underscore the importance of clinical correlation when evaluating anti-nephrin antibody results.⁷

In contrast to the primary DP population, genetically confirmed FSGS in the Japanese studies showed consistently negative anti-nephrin serology and no posttransplant recurrence, despite similar exposure to immunosuppression. This pattern is consistent with the underlying biology of genetic podocytopathies, which are not driven by circulating factors. The absence of both nephrin autoantibodies and recurrence in genetic FSGS thus provides an internal negative control that strengthens the observed association between anti-nephrin autoimmunity and recurrent DP in primary cases.

Anti-nephrin antibody assays remain technically heterogeneous, with no FDA-approved commercial kit, no universally validated cutoff, and no standardized antigen construct. Limitations appear to arise from the biological properties of nephrin autoantibodies themselves. Anti-nephrin antibodies were biologically potent and structurally complex.¹⁷ The experimental data suggest that even low concentrations of the antibodies may disrupt slit diaphragm integrity and induce podocyte injury, making clinically relevant thresholds difficult to define.⁷ The included studies used heterogeneous detection techniques, including ELISA alone, ELISA with Western blot and immunoprecipitation, and multimodal approaches incorporating immunofluorescence. Antigen sources also varied, with nephrin fragments expressed in HEK293 (human embryonic kidney 293) or NS0 (mouse myeloma) systems. A subsequent re-evaluation of the Shirai cohort using a HEK-derived recombinant nephrin ectodomain reclassified one recurrent and one non-recurrent antibody-positive patient as antibody negative, while all other classifications remained unchanged.¹⁸ A sensitivity analysis incorporating these reclassifications yielded similar estimates and did not significantly alter the overall findings (Table S4). These assay-to-assay discrepancies may influence diagnostic accuracy. Recent validation work has shown that mouse-myeloma–derived ectodomains can yield nonspecific reactivity, whereas HEK-derived ectodomains with immunoprecipitation-Western blotting detection more reliably identify true anti-nephrin antibodies.^19,20

Reported prevalence across transplant cohorts must be interpreted with caution, as methodological variation almost certainly contributes to inconsistent detection rates. The antibody titers fluctuate with disease activity and fall rapidly after antibody-depleting or immunosuppressive therapy, and heavy proteinuria may further reduce measurable levels. Transplant-related factors such as previous transplantation, immunosuppression, or transfusions can also alter humoral responses. These limitations highlight the need for standardized assays, consistent testing protocol, and validated cutoffs before anti-nephrin testing can be used reliably in clinical practice.

Despite the limitations, clinically meaningful points were noted. First, early antibody detection may help identify patients at high risk for recurrence. Whether transplantation should be deferred until antibody levels become undetectable remains uncertain and requires prospective evaluation. The study by Batal et al⁴ showed that pre-transplant nephrin positivity predicted early recurrence and poor graft survival, whereas The case reported by Habbig et al¹¹ illustrated that serial antibody monitoring can guide pretransplant depletion strategies and prevent recurrence. These observations raise the possibility that antibody-guided prophylaxis, such as targeted and aggressive peri-transplant plasmapheresis or rituximab, could reduce recurrence risk and improve graft outcomes, although prospective trials are needed. Second, expansion of testing to include multiple slit-diaphragm antigens may improve diagnostic sensitivity and refine classification of immune podocytopathy after transplantation. Third, antibody detectability is influenced by disease activity, exposure to immunosuppression, and possibly concurrent infection, emphasizing the importance of testing during active disease and before antibody-depleting therapy, with results interpreted in the proper clinical context.

Limitations

This systematic review has several limitations. Methodological heterogeneity is a major concern. The included studies differed in antigen source, assay design, and the threshold used to define a positive result. There was no consistent protocol regarding the timing of sample collection, and in several reports, testing was performed after antibody depleting or immunosuppressive therapy, which can lead to false negative findings. In contrast, there was a case that received intensive antibody depletion immediately after a positive test, which may prevent recurrence and make the initial antibody result appear falsely positive. Quantitative titers were not comparable due to assay variability across studies, preventing more detailed analyses, including quantitative ROC modeling. ROC analysis should be interpreted cautiously because most studies reported only dichotomized antibody status rather than harmonized quantitative titers. Consequently, the calculated AUC reflects discrimination based on a single binary operating point and does not represent threshold optimization across continuous assay values. Only 4 studies were eligible, and many provided limited individual-level data. Important variables such as age, sex, immunosuppression, previous transplants, rejection history, donor type, genetic testing, biopsy timing, and details of plasmapheresis or rituximab were often missing or incompletely described at the individual level. Because of this, multivariable analyses were not possible, and we could not identify independent predictors of recurrence. Follow-up duration also varied widely and was inconsistently reported, making long-term outcomes difficult to assess. In addition, the cohort likely represents a selected population with more aggressive disease progressing to transplantation, resulting in a higher recurrence prevalence and antibody positivity that may not reflect the overall DP population. Sex-specific analyses could not be performed due to limited individual-level data.

Conclusion

Circulating nephrin antibodies appear to be a promising biomarker, as it demonstrates an association with recurrent primary DP after kidney transplantation across both pediatric and adult populations. Their detection, typically before or early after transplantation, correlates with early structural injury on graft biopsy and with recurrence of DP. However, antibody detectability is influenced by disease activity, immunosuppressive exposure, and assay methodology, and interpretation is currently limited by technical heterogeneity, lack of standardization, and restricted availability. Test results should be interpreted cautiously within the clinical context. Further development of standardized nephrin antibody assays and prospective transplant cohorts will be essential to determine whether pretransplant interventions can significantly reduce recurrence risk and improve graft survival.

Supplementary Material

Supplementary File (PDF)

Item S1; Table S1-S4.