anti-PLA2R, a new era in nephrology


In June the FDA approved the first commercial assay for anti-PLA2r antibodies.
On July first, our new fellows began their nephrology careers.

Taken together, this means that our brand new fellows will be the oldest nephrologists to never experience nephrology without a reliable blood test for membranous nephropathy. Sure, there still is a third of idiopathic membranous patients that are anti-PLA2R negative, but largely, one of the great mysteries of nephrology has fallen to science, we now know the targeted glomerular antigen in idiopathic membranous and we have a way to test for, and quantify, the pathogenic autoantibodies.

This month’s eJC focuses on this antibody and what the assay’s role in nephrology should be. #NephJC, the Nephrology Twitter Journal Club, will also be focusing on aPLA2r this month by examining a study of Acthar Gel in idiopathic membranous nephropathy.

cJASN eJC August, 2014

The nephrology fellowship at St. John Hospital & Medical Centre in Detroit Michigan has the honor of hosting August’s eJC. This summary has been prepared by Bilal Saleem, MD and Joel Topf, MD

Download supplementary information here (pdf)

Association of anti-PLA2R-antibodies with outcomes after immunosuppressive therapy in idiopathic membranous nephropathy

Anneke P. Bech, Julia M. Hofstra, Paul E. Brenchley, Jack F.M. Wetzels.

Idiopathic Membranous Nephropathy (iMN) is among the common non-diabetic cause of Nephrotic syndrome in Caucasians above the age of 60 years. Anti-Phospholipase A2 Receptor (aPLA2R) antibodies are found in 70-80 % of patients with iMN. The Phospholipase A2 receptor is found on podocytes, and the formation of autoantibodies against it appear to be central to the pathology of iMN.

From Changing Incidence of Glomerular Disease in Olmsted County, Minnesota: A 30-Year Renal Biopsy Study
by Swaminathan et al. Clin J Am Soc Nephrol 1: 483– 487, 2006

The discovery of a reliable serologic indicator of iMN is especially important because the natural history of membranous can be so maddeningly variable. The classic teaching is:

  • a third of patients spontaneously remit
  • a third smolder along with nephrotic syndrome but don’t progressively lose renal function
  • a third have an aggressive course with renal failure.

This variability has made patient selection for treatment regimens and research protocols, determination of optimal medications and duration, as well as when to abandon failing treatments, difficult to determine.

Spontaneous remission (SR) rates are reported to be as high as 30%, with higher rates in females and individuals exhibiting non-nephrotic range proteinuria at initial presentation. However 25-40% of patients with complete remission will relapse, some as late as 20 years after remission. The rates of relapse in individuals who experienced partial remission are slightly higher at 50%; however they still showed better long-term clinical outcomes when compared to patients who never went into remission. See Troyanov. KI 2004.

Since the initial discovery of aPLA2R ABs in 2008:

Serum samples from 26 of 37 patients (70%) with idiopathic but not secondary membranous nephropathy specifically identified a 185-kD glycoprotein in non-reduced glomerular extract. Mass spectrometry of the reactive protein band detected the M-type phospholipase A2 receptor (PLA2R). Reactive serum specimens recognized recombinant PLA2R and bound the same 185-kD glomerular protein as did the monospecific anti-PLA2R antibody. Anti-PLA2R autoantibodies in serum samples from patients with membranous nephropathy were mainly IgG4, the predominant immunoglobulin subclass in glomerular deposits. PLA2R was expressed in podocytes in normal human glomeruli and co-localized with IgG4 in immune deposits in glomeruli of patients with membranous nephropathy. IgG eluted from such deposits in patients with idiopathic membranous nephropathy, but not in those with lupus membranous or IgA nephropathy, recognized PLA2R.

Multiple studies have confirmed the association of aPLA2R Abs and idiopathic membranous. Some studies have shown that the titers of these antibodies can be used to predict the natural history of the disease and to correlate with the degree of proteinuria:

It is clear that antiPLA2R will be an important tool in the treatment of iMN but we don’t know how to use it. We are like the apes at the beginning of 2001 A Space Odyssey, on the precipice of learning to use a new tool.

https://www.youtube.com/watch?v=mM6OIlreneA

This month’s eJC article by Bech et al. looks at the benefit of serial measurements of aPLA2R antibodies at the beginning and end of immunosuppressive therapy, and of using the aPLA2R titers to predict clinical outcomes.


Methods

The study looked at 48 patients with biopsy proven iMN, from 1997 to 2005. Treatment was provided for all patients with a creatinine greater than 1.5 or severe nephrotic syndrome. So this is an assessment of high risk membranous patients. The treatment protocol evolved over the 8 years under study. Initially patients were treated with oral steroids + oral cyclophosphamide (1997-2002) and later patients were giver steroids + mycophenolate mofetil (MMF). The duration of therapy in both cases was 12 months. Follow-up was 5 years. Frozen serum samples from the beginning and end of therapy were thawed and tested for aPLA2R antibody titers using an in-house ELISA assay.

Definitions:

  • Complete remission—Proteinuria less than 0.2 gm/day and stable renal function.
  • Partial remission — Proteinuria less than 3.5 gm/day, a 50% reduction in proteinuria, and stable renal function.
  • Relapse — Proteinuria more than 3.5 gm/24hr and an increase of more than 50% in proteinuria compared to the lowest point reached during remission.

Results

Out of a total of 48 patients, 34 were aPLA2R positive and 14 were aPLA2R negative at the initiation of treatment. The finding that 70% of idiopathic membranous patients are aPLA2R positive has been remarkably consistent across studies and assays. The baseline characteristics of the aPLA2R positive and negative patients were indistinguishable. Additionally they had the same response to treatment.

Modified Table 1. A whole mess of non-signifigant P values, except aPLA2R titers.

Of the 33 aPLA2R + patients that underwent treatment and had post-treatment data, 9 patients remained aPLA2R positive and 24 patients converted to aPLA2R negative. Unlike the baseline aPLA2R status, this conversion from positive to negative was highly illuminating.

First off, patients who cleared their antibody were much more likely to be in remission (33% for aPLA2R+, 92% for aPLA2R–, P=0.003)

After 5 years of follow-up:

  • 14/24 (58%) patients who seroconverted remained in remission
  • None of the 9 patients who were aPLA2R positive at the end of 1 year were in remission.

Additionally, 2 of the 9 were dead, 2 had begun additional treatment, 1 had persistent proteinuria and four relapsed.

The reason there is no blue on the left can be seen in the following Kaplan-Meier plot
https://twitter.com/kidney_boy/status/490683062523408384
Our data suggest that measurement of PLA2R-abs at the end of immunosuppressive therapy in PLA2R-ab–positive patients predicts the subsequent course during prolonged follow-up.

The authors were also able to provide some insight into the relative efficacies of the two treatment protocols used. In addition to aPLA2R titers at the beginning and end of treatment, some patients had titers measured at 2 and 6 months of treatment. Those samples show rapid aPLA2R conversion with cyclophosphamide and slower conversion with MMF.

The denominators change because not everyone had serum for testing at 2 and 4 months.
This study also suggests that antibodies disappeared more often in patients treated with CP than in patients treated with MMF. These observations are compatible with previously reported study results: MMF induced clinical remission in iMN, but there were more patients with a primary nonresponse and more patients with a relapse soon after the end of therapy.

Summary

The PLA2R antibody levels at the start of the study were not predictive of either the initial response to therapy or of the final outcome.

However, among patients who were PLA2R+ at the beginning of therapy, the antibody status at the end of 1 year of treatment was predictive of their long-term outcome. Converting to aPLA2R negative predicted a much better 5-year prognosis.

The long-term outcome in patients who became aPLA2R negative was not dependent on the immunosuppressant regimen utilized, however, patients on cyclophosophamide were more likely to become aPLA2R negative.


Discussion and Comments

Based on the results of the study by Bech et al. and others one can begin to build a rational methodology to use aPLA2R antibody titers in the clinical management of idiopathic membranous nephropathy.

Richard Glassock builds a preliminary schema for the possible uses of aPLA2R in the editorial in the same issue of CJASN.

  1. “First, the results of aPLA2R in nephrotic patients indicates the likely finding of iMN on renal biopsy only if the test result is positive, regardless of the assay method.” In other words the test is highly specific. Its sensitivity, however, is insufficient to rule out idiopathic membranous with a blood test.
  2. Second, a high value for the quantification of circulating aPLA2R indicates a lower likelihood of a spontaneous remission (<10%) and therefore it might be used as a rationale for immediate therapy in patients with less severe disease (Hofstra CJASN 2011).
  3. Third, when a patient with clinical and pathobiological features suggestive of iMN but has a low or negative value for aPLA2R, a delay in initiating treatment might be appropriate because these findings may herald a subsequent partial or complete spontaneous remission.
  4. Fourth, the level of aPLA2R should probably not be used as a sole criterion for a decision to treat or not to treat. (KDIGO guidelines for GN | PDF).
  5. Fifth, whenever possible, secondary forms of MN should be excluded in aPLA2R-negative patients with MN on renal biopsy.
  6. Sixth, serial measurement of aPLA2R during (possibly monthly or bimonthly) and at the end of a scheduled treatment regimen should be routine. This could be used to limit exposure to dangerous chemotherapy for patients who rapidly convert or used to change therapy who are having a slow response.
  7. Lastly some attention should be paid to patients with ESRD who are about to receive a kidney transplant and remain aPLA2R positive.

Though not mentioned by Glassock, we feel that aPLA2R may be useful as a serologic test in patients with diabetes while trying to determine if this population of patients have proteinuria only due to diabetic nephropathy or have an occult glomerulonephritis. In a series of 567 patients with diabetes and proteinuria who went for a biopsy to determine if there was an occult glomerulonephritis, thirty percent were found to have diagnosis besides isolated diabetic nephropathy.

References

  1. Swaminathan S, Leung N, Lager DJ, et al. Changing incidence of glomerular disease in Olmsted County, Minnesota: a 30-year renal biopsy study. Clin J Am Soc Nephrol. 2006;1(3):483-7.
  2. Troyanov, S : Idiopathic membranous nephropathy: Definition and relevance of a partial remission. Kidney International (2004) 66, 1199–1205
  3. Beck LH, Bonegio RG, Lambeau G, et al. M-type phospholipase A2 receptor as target antigen in idiopathic membranous nephropathy. N Engl J Med. 2009;361(1):11-21.
  4. Hofstra, JM. : Anti-phospholipase A₂ receptor antibodies correlate with clinical status in idiopathic membranous nephropathy. Clin J Am Soc Nephrol. 2011 Jun;6(6):1286-91
  5. Hofstra JM. : Antiphospholipase A2 receptor antibody titer and subclass in idiopathic membranous nephropathy. J Am Soc Nephrol. 2012 Oct;23(10):1735-43
  6. Bech AP, Hofstra JM, Brenchley PE, Wetzels JF. Association of Anti-PLA2R Antibodies with Outcomes after Immunosuppressive Therapy in Idiopathic Membranous Nephropathy. Clin J Am Soc Nephrol. 2014;
  7. Beck, Jr . : Rituximab-Induced Depletion of Anti-PLA2R Autoantibodies Predicts Response in Membranous Nephropathy. JASN August 1, 2011 vol. 22 no. 8 1543-1550,2011
  8. Haider DG, Peric S, Friedl A, et al. Kidney biopsy in patients with diabetes mellitus. Clin Nephrol. 2011;76(3):180-5.

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