Dual anti-CD20/anti-CD38 therapy for severe recurrent FSGS with longitudinal anti-nephrin assessment

To the Editor,

Primary focal segmental glomerulosclerosis (FSGS) recurs in approximately 30%–40% of patients after kidney transplantation and is associated with early graft dysfunction and accelerated graft loss. Its pathophysiology remains incompletely understood, and no approved therapies are available. Accumulating evidence, such as the clinical efficacy of therapies targeting B cells and long-lived plasma cells, implicates antibodies and/or B cell/plasma cell secreting factors in disease pathogenesis [1].

Autoantibodies directed against the glomerular slit diaphragm, including nephrin, have been proposed as potential mediators of post-transplant recurrence [2–7]. In addition, natural immunoglobulin M (IgM) targeting endothelial antigens may also play a role in FSGS progression [8], but data in post-transplant FSGS recurrence (rFSGS) remain limited.

Here, we report a case of early rFSGS associated with anti-nephrin antibody that was successfully treated by combined B-cell and plasma-cell targeting therapy.

A 27-year-old patient with ESKD secondary to FSGS, negative for known monogenic variants of FSGS and presenting as frequently relapsing and multidrug-dependent FSGS, received a kidney transplant from a deceased donor. Induction immunosuppression consisted of anti-thymocyte globulin (3.5 mg/kg) and steroids, followed by maintenance therapy with steroids, tacrolimus and mycophenolate mofetil. Urine output recovered immediately after transplant, but early-onset of severe, nephrotic-range proteinuria (28.5 g/day) developed on post-transplant Day 1. On Day 3, the patient developed oliguria followed by anuria, requiring hemodialysis (HD) on Day 5. The following day, a severe peri-graft bleeding occurred during HD: imaging with ultrasound and computed tomography revealed a large and persistent perirenal hematoma (20 × 5 cm). Due to hemodynamic instability and poor graft accessibility related to the extensive perirenal collection, a kidney biopsy was contraindicated. Doppler ultrasound demonstrated preserved graft vascularization with diffusely increased intrarenal resistive indices (0.7–0.8). Recurrent FSGS, acute ischemic injury secondary to severe hypoperfusion and acute rejection were all considered plausible contributors to the persistent anuria.

However, serum samples collected the day before transplant and on post-operative Day 1 were retrospectively analyzed after the onset of anuria and tested positive for anti-nephrin antibodies using enzyme-linked immunosorbent (ELISA) and immunoprecipitation assays, as previously described [9] (see online Supplementary Material). In the absence of risk factors for acute rejection (donor-specific antibodies were negative), we interpreted the clinical course secondary to a severe rFSGS, despite the lack of a histological documentation because contraindicated. Therefore, plasma exchange (PEX) and anti-CD20 therapy with the humanized monoclonal antibody obinutuzumab was initiated (Fig. 1; see online Supplementary Material for clinical details). To drain the perirenal hematoma, the patient underwent two surgical re-interventions and multiple blood transfusions.

Figure 1:

Longitudinal clinical, biochemical and serological course following kidney transplantation. Temporal relationship between proteinuria (ProtU, g/day), serum creatinine (mg/dL), urine output, renal replacement therapy, therapeutic interventions and anti-nephrin antibody levels during the early post-transplant period. Immediate post-transplant nephrotic-range proteinuria and subsequent anuria were followed by hemorrhagic complications requiring surgical re-interventions and HD. PEX sessions and administration of obinutuzumab (Obi, anti-CD20) and daratumumab (Dara, anti-CD38) are indicated. Longitudinal serological assessment by ELISA and immunoprecipitation (IP) shows the progressive decline and eventual negativization of anti-nephrin antibodies, paralleling reduction in proteinuria and recovery of graft function. KTx, kidney transplantation.

Over this period, PEX was continued (for a total of six treatments) and anti-CD38 monoclonal antibody daratumumab was initiated based on our prior data showing the efficacy of anti-CD20/anti-CD38 therapy in rFSGS [10–12]. On post-operative Day 21, urine output recovered, followed by improvement in kidney function from Day 24, which allowed discontinuation of dialysis. Serial measurements of anti-nephrin antibody (always measured prior to PEX and monoclonal infusions) showed a progressive decline. PEX and daratumumab infusions (administered at a distance from PEX), were continued until Day 33, when serum anti-nephrin antibody became definitively negative (Fig. 1). At Day 60 post-transplantation, proteinuria is 0.2 g/day, eGFR is 76 mL/min/1.73 m² and anti-nephrin antibodies are undetectable in the circulation.

This is the first reported case of rFSGS in whom combined PEX, anti-CD20 and anti-CD38 therapy was guided by anti-nephrin antibody. Despite the dramatic course of the disease, such treatment safely promoted a full recovery of graft function.

Anti-nephrin antibody positivity supported the diagnosis of rFSGS even in the absence of a histological documentation of rFSGS and guided the duration of treatment. In this patient, serial monitoring of such antibodies is currently ongoing to detect relapses early and allow for timely treatment.

The combined use of anti-CD20 and anti-CD38 therapies does not allow us to conclude whether the source of anti-nephrin antibodies was B cells or plasma cells. Also, the fact that changes in anti-nephrin and total IgG followed similar trends leaves open the possibility that IgG with other targets played a pathogenic role in this patient. Intriguingly, IgM were also rapidly depleted, suggesting that also this immune globulin might have played a role in disease activity (Fig. 2A), as previously reported in native disease [13]. In our biobank, we had stored serum samples collected throughout the patient’s clinical course (the diagnosis was made at 6 years of age). To further examine the association between anti-nephrin antibodies and disease activity, we quantified these antibodies in seven samples obtained between the ages of 9 and 19 years, during periods of active disease or remission and at different time points related to the immunosuppressive therapy (Fig. 2B). Immunofluorescence staining on native kidney biopsy, performed at the age of 9 years, showed no IgG deposition (Supplementary data, Fig. S1).

Figure 2:

IgG, IgM trends and anti-nephrin antibody trends during native kidney disease and after kidney transplantation. (A) Serial changes in proteinuria and serum immunoglobulin levels, highlighting a closer temporal association with IgM than with total IgG, in the pre-transplant phase. (B) Longitudinal analysis of anti-nephrin antibody levels during native kidney disease, evaluated by ELISA and immunoprecipitation, showing dissociation from clinical disease activity.

Notably, only one sample tested positive for anti-nephrin IgG, without a clear correlation between antibody presence and disease activity. This finding suggests that fluctuations in serum anti-nephrin antibody levels may occur independently of clinical activity, particularly in the later phases of the disease. Interestingly, the pre-transplant serum sample was strongly positive, despite the patient having been on HD for more than 2 years.

An additional hypothesis proposed by others is that anti-nephrin antibodies may arise secondary to other slit diaphragm–targeting antibodies through molecular epitope spreading [5, 14, 15]. Overall, these data suggest that repeated measurements may be warranted in the immediate pre-transplant period in cases where suspicion for an autoimmune pathophysiology remains high. However, these observations should be interpreted with caution, as ELISA-based assays for anti-nephrin antibodies have been reported to show variable sensitivity and specificity [9], which may partly contribute to the apparent inconsistency.

The doses of obinuzuzumab and daratumumab we used are significantly lower than those adopted for hematological indications. The effective levels of these biologics might be further reduced by urinary losses in the presence of proteinuria. As a result, the excellent treatment efficacy was associated with a very good tolerability. Future studies are needed to establish whether even lower doses are enough to obtain disease remission.

Together, this case documents that combined B-cell and plasma-cell depletion can promote remission even in severe rFSGS cases. When present, anti-nephrin antibodies may provide an important biomarker of disease activity, especially when renal biopsy is not feasible or in the presence of anuria. Notably, in this case, anti-nephrin antibody assessment was performed retrospectively after transplantation and therefore did not influence the initial transplant decision. These findings highlight the need for prospective evaluation of anti-nephrin antibodies in pre-transplant risk stratification and raise the testable hypothesis that their identification before transplantation could inform tailored induction strategies in selected high-risk patients.

AUTHORS’ CONTRIBUTIONS

X.K., A.S. and G.C. performed the anti-nephrin antibody experiments, with overall supervision by X.K. K.M. performed immunofluorescence staining and contributed to data acquisition. G.V. performed the kidney transplantation as the primary surgeon. F.C.V., A.P., P.E., D.P., M.T.G., G.M., E.V., A.M. and C.B. were involved in the long-term clinical follow-up of the patient, including sample collection and processing, and contributed to the complex therapeutic management. A.A. and P.C. conceived the study, supervised the work, and wrote the manuscript. All authors critically revised the manuscript and approved the final version.

CONFLICT OF INTEREST STATEMENT

None declared.

FUNDING

G.C. and A.A. were supported by a grant provided by the Italian Ministry of Health in compliance with Mission 6/component 2/Investment: 2.1 “Strengthening and enhancement of biomedical research of the SSN,” funded by the European Union—NextGenerationEU—Progetto PNRR-MR1-2022-12375880.