The Pathology of Transplant Rejection

nephrologista · July 28, 2019, 11:11pm

In this GlomCon Nephropathology Essentials session, Dr. Ibrahim Batal discussed the pathology of transplant rejection. Our Moderator’s Notes are based on his live presentation, which you can watch here: https://glomcon.org/transplant/the-pathology-of-transplant-rejection/

Moderator’s Note
Author: Dr. Kate Robson
Editors: Dr. Pravir Baxi, Dr. Ali Poyan Mehr

Dr Batal reviewed the pathology of T-cell-mediated rejection (TCMR) and antibody-mediated rejection (AMR), emphasising that these are not two purely distinct entities: while one usually dominates the clinical picture, cell-mediated and antibody-mediated responses often coexist.

T-cell-mediated rejection (TCMR)

Recipient immune cells recognise donor MHC molecules either by direct presentation (donor-derived antigen-presenting cells (APCs) present alloantigens to recipient T cells) or indirect presentation (recipient APCs capture alloantigen and present them to T cells).
CD4+ helper T cells cause interstitial inflammation in the graft, and CD8+ cytotoxic T cells cause tubulitis and vasculitis.
Morphologic features of acute TCMR include interstitial inflammation, tubulitis, and intimal arteritis.
Evolution of induction and maintenance therapies has seen a decline in fulminant acute TCMR. TCMR remains important, however: it is associated with graft dysfunction and can be a predictor for subsequent de novo DSA formation.
Chronic-active TCMR now poses particular ongoing diagnostic and therapeutic challenges.
Inflammation in scarred areas of interstitial fibrosis and tubular atrophy (i-IFTA) is now recognised as a diagnostic feature of chronic-active TCMR in the 2017 (Revised) Banff Criteria, provided other causes of i-IFTA have been excluded (e.g. BK-virus nephropathy, pyelonephritis).

Antibody-mediated rejection (AMR)

Rejection resulting from antibodies against donor antigens
Stages of AMR (per Colvin J Am Soc Nephrol 2007)
I. Donor-specific antibody (DSA) in circulation
II. C4d staining in graft
III. Morphological injury in graft
IV. Graft dysfunction
Diagnosis depends on serologic, immunologic and morphologic evidence, the sensitivity and specificity of which can be influenced by several factors.
Serologic
DSA detection (usually by Luminex)
Complicating issues include:
• DSA absorption by the graft (‘sponge’ effect) ⇒ sensitivity
• Non-HLA antibodies (e.g. AT-1)
• IgG subclasses, mean fluorescence index (MFI) values, complement-activating vs. not, and pre-formed vs. de novo: all influence the course of AMR
Immunologic
C4d linear staining along peritubular +/- glomerular capillaries on kidney biopsy via immunofluorescence (IF) or immunohistochemistry (IHC) (C4d covalently binds to tissue, so is a more useful indicator of activation of the classical pathway of complement than e.g. C1 which has a very short half life)
Complicating issues include:
• C4d may be negative in the presence of DSA which do not activate complement
• C4d may be negative when severe injury causes endothelial sloughing
• C4d staining can be positive in the absence of AMR (e.g. with accommodation of anti-ABO Abs)
Morphologic
Acute tubular injury (ATI), peritubular capillaritis (ptc), glomerulitis (g), fibrinoid necrosis and thrombotic microangiopathy (TMA) are all morphologic features of AMR.
Complicating issues include:
• Inter-observer variability
• Features may be absent early in the course of AMR
• Features are non-specific, and can be observed in other diseases, possibly leading to overdiagnosis of AMR
The diagnostic use of endothelial-associated gene expression profiles (microarray on frozen kidney biopsy samples) in AMR has been a recent research focus. While currently used in some centres, it remains to be validated for wider use.
2017 (Revised) Banff Criteria for AMR
Morphologic evidence: 1 or more of: g>0 (in the absence of GN), ptc>0, v>0, acute TMA (in the absence of any known cause), ATI (in the absence of any known cause).
Antibody interaction with endothelium: 1 or more of: C4d staining, g+ptc≥2, expression of genetic transcripts (endothelial injury & NK cell-associated, if thoroughly validated).
Serologic evidence: DSA (HLA or other antigens). C4d staining or validated transcript expression may substitute for DSA.
Treatment of AMR can involve steroid therapy, plasmapheresis and/or intravenous immunoglobulin (IVIG). These are often insufficiently effective, resulting in chronic transplant glomerulopathy.

Selected References

ncbi.nlm.nih.gov

Dendritic Cells in Kidney Transplant Biopsy Samples Are Associated with T Cell Infiltration and Poor Allograft Survival.

I Batal, SA De Serres, K Safa, V Bijol, T Ueno, ML Onozato, AJ Iafrate, JM Herter, AH Lichtman, TN Mayadas, I Guleria, HG Rennke, N Najafian and A Chandraker, Journal of the American Society of Nephrology : JASN, Dec 2015

Progress in long-term renal allograft survival continues to lag behind the progress in short-term transplant outcomes. Dendritic cells are the most efficient antigen-presenting cells, but surprisingly little attention has been paid to their presence in transplanted kidneys. We used dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin as a marker of dendritic cells in 105 allograft biopsy samples from 105 kidney transplant recipients. High dendritic cell density was associated with poor allograft survival independent of clinical variables. Moreover, high dendritic cell density correlated with greater T cell proliferation and poor outcomes in patients with high total inflammation scores, including inflammation in areas of tubular atrophy. We then explored the association between dendritic cells and histologic variables associated with poor prognosis. Multivariate analysis revealed an independent association between the densities of dendritic cells and T cells. In biopsy samples with high dendritic cell density, electron microscopy showed direct physical contact between infiltrating lymphocytes and cells that have the ultrastructural morphologic characteristics of dendritic cells. The origin of graft dendritic cells was sought in nine sex-mismatched recipients using XY fluorescence in situ hybridization. Whereas donor dendritic cells predominated initially, the majority of dendritic cells in late allograft biopsy samples were of recipient origin. Our data highlight the prognostic value of dendritic cell density in allograft biopsy samples, suggest a new role for these cells in shaping graft inflammation, and provide a rationale for targeting dendritic cell recruitment to promote long-term allograft survival.

ncbi.nlm.nih.gov

Complement activation in acute humoral renal allograft rejection: diagnostic significance of C4d deposits in peritubular capillaries.

AB Collins, EE Schneeberger, MA Pascual, SL Saidman, WW Williams, N Tolkoff-Rubin, AB Cosimi and RB Colvin, Journal of the American Society of Nephrology : JASN, Oct 1999

The distinction between acute humoral rejection (AHR) and acute cellular rejection (ACR) in renal allografts is therapeutically important, but pathologically difficult. Since AHR is probably mediated by antibodies to the donor endothelium that activate the classical complement pathway, it was hypothesized that peritubular capillary C4d deposition might distinguish this group. Renal biopsies (n = 16) from 10 patients with AHR who had acute graft dysfunction, neutrophils in peritubular capillaries, and a concurrent positive cross-match were stained for C4d by immunofluorescence. Control biopsies for comparison showed ACR (n = 14), cyclosporin A toxicity (n = 6), or no abnormality (n = 4). Peribiopsy sera were tested for anti-donor HLA antibody. C4d deposited prominently and diffusely in the peritubular capillaries in all AHR biopsies (16 of 16). IgM and/or C3 were also present in 19 and 44%, respectively. With two-color immunofluorescence, C4d was localized in basement membranes (type IV collagen+) and in the endothelium (Ulex europaeus agglutinin-I+). In ACR, no more than trace C4d was found in peritubular capillaries (P < 0.0001 versus AHR), and no patient had anti-donor HLA antibodies (0 of 8); 27% had neutrophils in peritubular capillaries. One of six biopsies with cyclosporin A toxicity had similar C4d deposits, and circulating anti-donor class I antibody was detected. Grafts with AHR were lost (40%) more often than those with ACR (0%; P < 0.02). C4d in peritubular capillary walls distinguishes AHR from ACR, is more specific and sensitive than traditional criteria, and is a potentially valuable adjunct in the diagnosis of graft dysfunction.

ncbi.nlm.nih.gov

Antibody-mediated renal allograft rejection: diagnosis and pathogenesis.

RB Colvin, Journal of the American Society of Nephrology : JASN, Apr 2007

Alloantibodies to HLA class I or II and other antigens expressed by endothelium cause a variety of effects on renal transplants, ranging from acute to chronic rejection, and even apparent graft acceptance (accommodation). Recognition of these conditions and appropriate therapy requires demonstration of C4d in biopsies, commonly confirmed by tests for circulating alloantibody. Substantial practical experience by pathologists in the interpretation and pitfalls of C4d stains are reviewed along with considerations of the clinical significance and pathologic mechanisms of the different effects of antibody on the endothelium of the renal allograft. Clinical trials will be needed to ascertain the optimal treatment for the newly appreciated conditions chronic humoral rejection and accommodation.

ncbi.nlm.nih.gov

The Banff 2017 Kidney Meeting Report: Revised diagnostic criteria for chronic active T cell-mediated rejection, antibody-mediated rejection, and prospects for integrative endpoints for next-generation clinical trials.

M Haas, A Loupy, C Lefaucheur, C Roufosse, D Glotz, D Seron, BJ Nankivell, PF Halloran, RB Colvin, E Akalin, N Alachkar, S Bagnasco, Y Bouatou, JU Becker, LD Cornell, JPD van Huyen, IW Gibson, ES Kraus, RB Mannon, M Naesens, V Nickeleit, P Nickerson, DL Segev, HK Singh, M Stegall, P Randhawa, L Racusen, K Solez and M Mengel, American journal of transplantation : official journal of the American Society of Transplantation and the American Society of Transplant Surgeons, 2018 02

The kidney sessions of the 2017 Banff Conference focused on 2 areas: clinical implications of inflammation in areas of interstitial fibrosis and tubular atrophy (i-IFTA) and its relationship to T cell-mediated rejection (TCMR), and the continued evolution of molecular diagnostics, particularly in the diagnosis of antibody-mediated rejection (ABMR). In confirmation of previous studies, it was independently demonstrated by 2 groups that i-IFTA is associated with reduced graft survival. Furthermore, these groups presented that i-IFTA, particularly when involving >25% of sclerotic cortex in association with tubulitis, is often a sequela of acute TCMR in association with underimmunosuppression. The classification was thus revised to include moderate i-IFTA plus moderate or severe tubulitis as diagnostic of chronic active TCMR. Other studies demonstrated that certain molecular classifiers improve diagnosis of ABMR beyond what is possible with histology, C4d, and detection of donor-specific antibodies (DSAs) and that both C4d and validated molecular assays can serve as potential alternatives and/or complements to DSAs in the diagnosis of ABMR. The Banff ABMR criteria are thus updated to include these alternatives. Finally, the present report paves the way for the Banff scheme to be part of an integrative approach for defining surrogate endpoints in next-generation clinical trials.

ncbi.nlm.nih.gov

Molecular diagnosis of antibody-mediated rejection in human kidney transplants.

J Sellarés, J Reeve, A Loupy, M Mengel, B Sis, A Skene, DG de Freitas, C Kreepala, LG Hidalgo, KS Famulski and PF Halloran, American journal of transplantation : official journal of the American Society of Transplantation and the American Society of Transplant Surgeons, Apr 2013

Antibody-mediated rejection is the major cause of kidney transplant failure, but the histology-based diagnostic system misses most cases due to its requirement for C4d positivity. We hypothesized that gene expression data could be used to test biopsies for the presence of antibody-mediated rejection. To develop a molecular test, we prospectively assigned diagnoses, including C4d-negative antibody-mediated rejection, to 403 indication biopsies from 315 patients, based on histology (microcirculation lesions) and donor-specific HLA antibody. We then used microarray data to develop classifiers that assigned antibody-mediated rejection scores to each biopsy. The transcripts distinguishing antibody-mediated rejection from other conditions were mostly expressed in endothelial cells or NK cells, or were IFNG-inducible. The scores correlated with the presence of microcirculation lesions and donor-specific antibody. Of 45 biopsies with scores>0.5, 39 had been diagnosed as antibody-mediated rejection on the basis of histology and donor-specific antibody. High scores were also associated with unanimity among pathologists that antibody-mediated rejection was present. The molecular score also strongly predicted future graft loss in Cox regression analysis. We conclude that microarray assessment of gene expression can assign a probability of ABMR to transplant biopsies without knowledge of HLA antibody status, histology, or C4d staining, and predicts future failure.

ncbi.nlm.nih.gov

Evolution and clinical pathologic correlations of de novo donor-specific HLA antibody post kidney transplant.

C Wiebe, IW Gibson, TD Blydt-Hansen, M Karpinski, J Ho, LJ Storsley, A Goldberg, PE Birk, DN Rush and PW Nickerson, American journal of transplantation : official journal of the American Society of Transplantation and the American Society of Transplant Surgeons, May 2012

The natural history for patients with de novo donor-specific antibodies (dnDSA) and the risk factors for its development have not been well defined. Furthermore, clinical and histologic correlation with serologic data is limited. We studied 315 consecutive renal transplants without pretransplant DSA, with a mean follow-up of 6.2 ± 2.9 years. Protocol (n = 215) and for cause (n = 163) biopsies were analyzed. Solid phase assays were used to screen for dnDSA posttransplant. A total of 47 out of 315 (15%) patients developed dnDSA at a mean of 4.6 ± 3.0 years posttransplant. Independent predictors of dnDSA were HLA-DRβ1 MM > 0 (OR 5.66, p < 0.006); and nonadherence (OR 8.75, p < 0.001); with a strong trend toward clinical rejection episodes preceding dnDSA (OR 1.57 per rejection episode, p = 0.061). The median 10-year graft survival for those with dnDSA was lower than the No dnDSA group (57% vs. 96%, p < 0.0001). Pathology consistent with antibody-mediated injury can occur and progress in patients with dnDSA in the absence of graft dysfunction and furthermore, nonadherence and cellular rejection contribute to dnDSA development and progression to graft loss.