© 2013 Direct One Communications, Inc. All rights reserved. 1 Recognition and Management of Antibody-Mediated Rejection Malcolm P. MacConmara, MB, BCh,

© 2013 Direct One Communications, Inc. All rights reserved. 1

Recognition and Management of Antibody-Mediated Rejection

Malcolm P. MacConmara, MB, BCh, BAO

Emory University School of Medicine, Atlanta, Georgia

A REPORT FROM THE 2013 AMERICAN TRANSPLANT CONGRESS


Antibody-Mediated Rejection (AMR)

AMR is a major cause of acute and chronic allograft dysfunction1,2

» Acute AMR occurs in at least 5%–7% of all kidney transplant recipients and 25%–30% of presensitized crossmatch-positive patients.3

» Chronic AMR due to sensitization or de novo donor-reactive antigen contributes to long-term allograft loss.2,4

AMR may result from reactivation of antibody responses to preexisting antigens (type I) or de novo to donor-specific antibodies (DSAs) encountered late after transplant (type II), mostly as a result of nonadherence to immunosuppressive therapy.5


The Difficult Diagnosis of AMR

The current Banff classification of AMR relies upon three cardinal features: (1) positive C4d staining, (2) circulating DSA, and (3) tissue injury.

Histologic findings of injury vary.

Classification is based on clinical setting, underlying pathophysiology, and temporal relationship to transplantation (hyperacute, acute, and chronic).

Clinical manifestations range from immediate graft loss to chronic subclinical rejection with gradual loss of function.1–3


Outcomes Associated with AMR

AMR has a worse outcome than acute cellular rejection (ACR), likely because of diagnostic difficulty and less-effective therapeutic options.

Among renal transplant recipients with AMR, 15%–20% lose their grafts within 1 year.6

More than 40% of patients with AMR eventually develop transplant glomerulopathy, whether or not initial treatment can reverse acute renal functional impairment.

AMR-related glomerulopathy is associated with < 50% 5-year graft survival from the time of identification.6


Targets and Therapies

Development of antibody-mediated rejection1 MMF = mycophenolate mofetil; TH cell = T-helper cell; IVIg = immunoglobulin-


Targets and Therapies

Therapeutic options for AMR1,2,7 include: Inhibition or depletion of B-cell function with

rituximab or corticosteroids

Interference with antibody function using plasmapheresis, immunoadsorption, and/or intravenous immunoglobulin (IVIg)

Interruption of plasma-cell function with bortezomib

Prevention of complement cascade using eculizumab


The Population and the Risks

Over 96,000 patients currently are registered on the waiting list for kidney transplantation.

» Almost 16% are prior organ-transplant recipients.

» Approximately 30% are sensitized to human leukocyte antigen (HLA).8

» Highly sensitized patients with > 80% panel-reactive antibody (PRA) wait three times longer to undergo transplant surgery than do unsensitized renal transplant recipients and have an average wait time of almost 10 years.9

Desensitized patients continue to have an increased incidence of type I AMR and graft loss.10


Pathophysiology in Sensitized Patients

Type I AMR in desensitized patients apparently involves residual plasma cells and long-lived allospecific memory B cells.11

Approximately one fourth of desensitized recipients experience early AMR, usually within the first week after transplant.12

Two thirds of these patients respond to plasmapheresis.

The remainder may experience severe oliguric, plasmapheresis-resistant rejection, which often is accompanied by graft loss.


Pathophysiology in Sensitized Patients

The principal effector mechanism of antibody-mediated injury involves activation of the classic complement pathway by the antigen-antibody complex deposition.13

Ig = immunoglobulin; HLA = human leukocyte antigen; DAF = decay-accelerating factor; Y-CVF = Yunnan-cobra venom factor


Treatment of AMR: Plasmapheresis

Montgomery et al14 used plasmapheresis with IVIg to reduce DSA strength before transplantation.

Induction with antithymoglobulin and steroids with maintenance immunosuppression (tacrolimus and mycophenolate mofetil) prevented AMR in most desensitized patients.

» One third received anti-CD20 immediately before transplant.

» Desensitization improved patient survival to 90% and 80% at 1 and 5 years, respectively, as compared with 93% and 65% among those waiting for compatible donors.


Treatment of AMR: Plasmapheresis

Montgomery and colleagues12 reported a 22% incidence of early AMR that mostly responds to further treatment with plasmapheresis and IVIg.

Approximately 50% of treated patients lose grafts within 2 years.

Addition of complement inhibitor to splenectomy has increased the rescue rate and significantly reduced the development of tubular glomerulopathy.12


Phenotypes and Outcomes

Plasmapheresis better eliminates type I antibody generated to major histocompatibility complex (MHC) class I than it eradicates MHC class II antigen.

Other phenotypes associated with poor outcome include C4d-positive staining with glomerulitis, peritubular capillaritis, and microcirculatory inflammation.

» These differ from results seen in the setting of type II AMR.

» Further studies must incorporate immunologic and histopathologic parameters into treatment algorithms that balance risk with degree of therapeutic aggression.


Complement Inhibition

Stegall and others15 compared 26 patients desensitized to levels of low-to-moderate antibody strength given eculizumab post transplant with 51 matched controls.

Within the first 3 months after transplant, AMR occurred in 7.7% of patients given eculizumab and 41% of matched controls.

Protocol-required biopsies examined up to 1 year after treatment showed no evidence of transplant glomerulopathy.


Risk of Rejection and DSA Titer and Type

DSAs are most commonly directed against HLA class I (on all nucleated cells) or class II (on antigen-presenting cells and endothelial cells).

» DSAs may develop against non-HLA antigens, including MHC class I–related chain A and B (MICA, MICB), molecules of the renin-angiotensin pathway, and platelet-specific antigens2

DSA level, expressed as mean fluorescent intensity (MFI), is proportional to the risk of rejection.

» Complement inhibition did not alter the DSA level but reduced AMR in patients with a high DSA concentration (control group, 100%; study group, 15%).15


Eculizumab-Resistant AMR

Treatment of late AMR with findings suggesting acute cellular rejection and AMR may involve thymoglobulin, plasma exchange, and eculizumab.

Chronic AMR accompanied by negative C4d staining may be a form of complement-independent rejection and eculizumab-resistant rejection.

The best treatment of chronic AMR appears to be a combination of therapeutic approaches, such as combining bortezomib therapy with plasma exchange and IVIg.16


C4d-Negative AMR

Traditionally, detection of C4d has been required for AMR diagnosis. However:

» Many C4d-negative cases have clinical and histologic findings similar to those of rejection and exhibit DSAs.

» A substantial fraction of cases of chronic graft failure previously labeled as calcineurin-inhibitor nephrotoxicity may result from C4d-negative AMR.4

Sis et al17 examined 329 biopsy samples from patients with graft dysfunction.

» Peritubular capillaritis and glomerulitis often were not associated with DSA (27%) during year 1 post transplant.


Molecular Scoring

Predictive molecular scoring systems based upon levels of gene expression increasingly are being used to augment standard diagnostic histopathology, which fails to improve risk stratification.

The Banff Working Group5 is addressing a number of approaches related to deficiencies, including:

» IgG subtyping

» MFI levels of DSA

» C1q-fixing DSA


Molecular Scoring

Sellarés et al18 used Affymetrix microarray technology to identify type II AMR in study biopsies obtained 1 year post-transplant.

For many patients, biopsy results were related to medication nonadherence.4

Survival was linked to timing of the biopsy and the disease process identified.

The risk of graft loss was greatest during the initial 3 years following indication biopsy.


Genetic Predisposition

A cohort of 30 human genes strongly associated with AMR have been identified and validated.18

The genes include cadherin 13 (CDH13), chemokine (C-X-C motif) ligands 10 and 11 (CXCL10 and CXCL11), and fibroblast growth factor binding protein 2 (FGFBP2), all of which are associated with endothelial injury and cellular trafficking.

This molecular fingerprint, applied to all samples, may be used to discriminate between AMR and other causes of acute deterioration in graft function.18


Subclinical AMR

Subclinical AMR is defined as graft changes that meet established pathologic and serologic criteria for AMR without graft dysfunction or concurrent ACR:

Serum creatinine level remains unchanged.

DSAs have low MFI values in the absence of proteinuria.

Patients repeatedly undergo biopsy without exhibiting clear evidence of rejection before developing clinical and pathologic changes.

Quiescent disease may erupt later as a result of an immunologic trigger.


Subclinical AMR

Risk of graft loss is 77% higher among patients with DSAs.

Some DSAs are more likely than others to result in graft rejection.

Non-HLA and non-complement fixing antibody may be responsible for subclinical AMR.


Accommodation vs Subclinical Rejection

Accommodation is defined as the presence of inhibitory mechanisms to the distal complement cascade downstream of C4d cleavage.

Accommodation is often is seen in protocol-required biopsies after ABO-incompatible transplantation.

Aside from ABO incompatibility, desensitized patients with C4d-positive staining typically experience tissue injury.

There is no way to differentiate C4d-positive biopsies that represent accommodation from subclinical AMR-mediated rejection.19


C4d-Negative AMR

Approximately 10% of biopsies with features of acute AMR are C4d negative.

Rejection may occur through complement-independent mechanisms.

Sis et al20 used microarray analysis to demonstrate increased endothelial cell gene expression in biopsies having histopathologic findings of AMR and DSA but negative C4d staining.

This approach may represent a novel method of AMR detection.


Management of Subclinical AMR

Not all DSAs appear to pose the same risk.

Molecular phenotyping and electron microscopy may help in detecting and managing subclinical AMR.

Gloor et al21 reported that treating desensitized renal transplant recipients with subclinical AMR using corticosteroids, plasmapheresis, and IVIg resolved the histologic abnormalities; however, the long-term clinical outcome of this strategy is unclear.


Summary

Better understanding of acute AMR is the foundation for successful treatment of desensitized patients by blocking multiple points of the pathway.

Chronic AMR is a major cause of late graft loss and remains less understood than acute AMR.

New gene-based molecular approaches to the diagnosis of AMR offer hope of more timely and effective treatment.


References1. Levine MH, Abt PL. Treatment options and strategies for antibody mediated rejection after renal

transplantation. Semin Immunol. 2012;24:136–142.

2. Puttarajappa C, Shapiro R, Tan HP. Antibody-mediated rejection in kidney transplantation: a review. J Transplant. 2012;2012:193724.

3. Lucas JG, Co JP, Nwaogwugwu UT, Dosani I, Sureshkumar KK. Antibody-mediated rejection in kidney transplantation: an update. Expert Opin Pharmacother. 2011;12:579–592.

4. Sellarés J, de Freitas DG, Mengel M, et al. Understanding the causes of kidney transplant failure: the dominant role of antibody-mediated rejection and nonadherence. Am J Transplant. 2012;12:388–399.

5. Mengel M, Sis B, Haas M, et al. Banff 2011 meeting report: new concepts in antibody-mediated rejection. Am J Transplant. 2012;12:563–570.

6. Gloor JM, Cosio FG, Rea DJ, et al. Histologic findings one year after positive crossmatch or ABO blood group incompatible living donor kidney transplantation. Am J Transplant. 2006;6:1841–1847.

7. Fehr T, Gaspert A. Antibody-mediated kidney allograft rejection: therapeutic options and their experimental rationale. Transplant Int. 2012;25:623–632.

8. Organ Procurement and Transplantation Network (OPTN) Web site. http://optn.transplant.hrsa.gov. Accessed July 5, 2013.

9. Jordan SC, Reinsmoen N, Peng A, et al. Advances in diagnosing and managing antibody-mediated rejection. Pediatr Nephrol. 2010;25:2035–2045.

10. Paramesh AS, Zhang R, Baber J, et al. The effect of HLA mismatch on highly sensitized renal allograft recipients. Clin Transplant. 2010;24:E247–E252.

11. Stegall MD, Dean PG, Gloor J. Mechanisms of alloantibody production in sensitized renal allograft recipients. Am J Transplant. 2009;9:998–1005.


References12. Montgomery RA, Warren DS, Segev DL, Zachary AA. HLA incompatible renal transplantation.

Current Opin Organ Transplant. 2012;17:386–392.

13. Stegall MD, Chedid MF, Cornell LD. The role of complement in antibody-mediated rejection in kidney transplantation. Nat Rev Nephrol. 2012;8:670–678.

14. Montgomery RA, Lonze BE, King KE, et al. Desensitization in HLA-incompatible kidney recipients and survival. N Engl J Med. 2011;365:318–326.

15. Stegall MD, Diwan T, Raghavaiah S, et al. Terminal complement inhibition decreases antibody-mediated rejection in sensitized renal transplant recipients. Am J Transplant. 2011;11:2405–2413.

16. Trivedi HL, Terasaki PI, Feroz A, et al. Abrogation of anti-HLA antibodies via proteasome inhibition. Transplantation. 2009;87:1555–1561.

17. Sis B, Jhangri GS, Riopel J, et al. A new diagnostic algorithm for antibody-mediated microcirculation inflammation in kidney transplants. Am J Transplant. 2012;12:1168–1179.

18. Sellarés J, Reeve J, Loupy A, et al. Molecular diagnosis of antibody-mediated rejection in human kidney transplants. Am J Transplant. 2013;13:971–983.

19. Park WD, Grande JP, Ninova D, et al. Accommodation in ABO-incompatible kidney allografts, a novel mechanism of self-protection against antibody-mediated injury. Am J Transplant. 2003;3:952–960.

20. Sis B, Jhangri GS, Bunnag S, Allanach K, Kaplan B, Halloran PF. Endothelial gene expression in kidney transplants with alloantibody indicates antibody-mediated damage despite lack of C4d staining. Am J Transplant. 2009;9:2312–2323.

21. Gloor JM, DeGoey SR, Pineda AA, et al. Overcoming a positive crossmatch in living-donor kidney transplantation. Am J Transplant. 2003;3:1017–1023.

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© 2013 Direct One Communications, Inc. All rights reserved. 1 Recognition and Management of Antibody-Mediated Rejection Malcolm P. MacConmara, MB, BCh,