James M. Gloor

Banff ’09 Meeting Report: Antibody Mediated Graft Deterioration and Implementation of Banff Working Groups

The 10th Banff Conference on Allograft Pathology was held in Banff, Canada from August 9 to 14, 2009. A total of 263 transplant clinicians, pathologists, surgeons, immunologists and researchers discussed several aspects of solid organ transplants with a special focus on antibody mediated graft injury. The willingness of the Banff process to adapt continuously in response to new research and improve potential weaknesses, led to the implementation of six working groups on the following areas: isolated v‐lesion, fibrosis scoring, glomerular lesions, molecular pathology, polyomavirus nephropathy and quality assurance. Banff working groups will conduct multicenter trials to evaluate the clinical relevance, practical feasibility and reproducibility of potential changes to the Banff classification. There were also sessions on quality improvement in biopsy reading and utilization of virtual microscopy for maintaining competence in transplant biopsy interpretation. In addition, compelling molecular research data led to the discussion of incorporation of omics‐technologies and discovery of new tissue markers with the goal of combining histopathology and molecular parameters within the Banff working classification in the near future.

Identifying Specific Causes of Kidney Allograft Loss

The causes of kidney allograft loss remain unclear. Herein we investigated these causes in 1317 conventional kidney recipients. The cause of graft loss was determined by reviewing clinical and histologic information the latter available in 98% of cases. During 50.3 ± 32.6 months of follow‐up, 330 grafts were lost (25.0%), 138 (10.4%) due to death with function, 39 (2.9%) due to primary nonfunction and 153 (11.6%) due to graft failure censored for death. The latter group was subdivided by cause into: glomerular diseases (n = 56, 36.6%); fibrosis/atrophy (n = 47, 30.7%); medical/surgical conditions (n = 25, 16.3%); acute rejection (n = 18, 11.8%); and unclassifiable (n = 7, 4.6%). Glomerular pathologies leading to failure included recurrent disease (n = 23), transplant glomerulopathy (n = 23) and presumed nonrecurrent disease (n = 10). In cases with fibrosis/atrophy a specific cause(s) was identified in 81% and it was rarely attributable to calcineurin inhibitor (CNI) toxicity alone (n = 1, 0.7%). Contrary to current concepts, most cases of kidney graft loss have an identifiable cause that is not idiopathic fibrosis/atrophy or CNI toxicity. Glomerular pathologies cause the largest proportion of graft loss and alloinmunity remains the most common mechanism leading to failure. This study identifies targets for investigation and intervention that may result in improved kidney transplantation outcomes.

Terminal complement inhibition decreases antibody-mediated rejection in sensitized renal transplant recipients.

Sensitized renal transplant recipients with high levels of donor‐specific alloantibody (DSA) commonly develop antibody‐mediated rejection (AMR), which may cause acute graft loss or shorten allograft survival. We examined the efficacy of terminal complement inhibition with the humanized anti‐C5 antibody, eculizumab, in the prevention AMR in renal transplant recipients with a positive crossmatch against their living donor. The incidence of biopsy‐proven AMR in the first 3 months posttransplant in 26 highly sensitized recipients of living donor renal transplants who received eculizumab posttransplant was compared to a historical control group of 51 sensitized patients treated with a similar plasma exchange (PE)‐based protocol without eculizumab. The incidence of AMR was 7.7% (2/26) in the eculizumab group compared to 41.2% (21/51) in the control group (p = 0.0031). Eculizumab also decreased AMR in patients who developed high levels of DSA early after transplantation that caused proximal complement activation. With eculizumab, AMR episodes were easily treated with PE reducing the need for splenectomy. On 1‐year protocol biopsy, transplant glomerulopathy was found to be present in 6.7% (1/15) eculizumab‐treated recipients and in 35.7% (15/42) of control patients (p = 0.044). Inhibition of terminal complement activation with eculizumab decreases the incidence of early AMR in sensitized renal transplant recipients (ClincalTrials.gov number NCT006707).

A Comparison of Plasmapheresis Versus High-Dose IVIG Desensitization in Renal Allograft Recipients with High Levels of Donor Specific Alloantibody

Several protocols allow for the successful transplantation of sensitized renal allograft recipients, yet no one best method has emerged. The aim of the current study was to compare the efficacy of high‐dose IVIG with two different plasmapheresis (PP)‐based regimens in kidney transplant recipients with high levels of donor specific alloantibody (DSA) defined as a positive T‐cell cytotoxicity crossmatch. With the primary goal of achieving a negative crossmatch, we employed three protocols sequentially between April 2000 and May 2005: (i) PP, low‐dose IVIG, anti‐CD20 antibody (n = 32); (ii) high‐dose IVIG (n = 13); and (iii) PP, low‐dose IVIG, anti‐CD20 antibody and pre‐transplant Thymoglobulin combined with post‐transplant DSA monitoring (n = 16). IVIG decreased DSA activity in all treated patient, yet only 38% (5/13) achieved a negative crossmatch. In contrast, a negative crossmatch was achieved in 84% in PP group and 88% in the PP/monitoring group (p < 0.01 vs. IVIG). Even with a negative crossmatch, the rejection rates were 80% (IVIG), 37% (PP) and 29% (PP/monitoring), respectively, (p < 0.05 IVIG vs. PP). We conclude that multiple PP treatments leads to more reproducible desensitization and lower humoral rejection rates than a single high‐dose of IVIG, but that no regimen was completely effective in preventing humoral rejection.

Complete avoidance of calcineurin inhibitors in renal transplantation : A randomized trial comparing sirolimus and tacrolimus

Calcineurin inhibitors have decreased acute rejection and improved early renal allograft survival, but their use has been implicated in the development of chronic nephrotoxicity. We performed a prospective, randomized trial in kidney transplantation comparing sirolimus‐MMF‐prednisone to tacrolimus‐MMF‐prednisone. Eighty‐one patients in the sirolimus group and 84 patients in the tacrolimus group were enrolled (mean follow‐up = 33 months; range 13–47 months). At 1 year, patient survival was similar in the groups (98% with sirolimus, 96% with tacrolimus; p = 0.42) as was graft survival (94% sirolimus vs. 92% tacrolimus, p = 0.95). The incidence of clinical acute rejection was 10% in the tacrolimus group and 13% in the sirolimus group (p = 0.58). There was no difference in mean GFR measured by iothalamate clearance between the tacrolimus and sirolimus groups at 1 year (61 ± 19 mL/min vs. 63 ± 18 mL/min, p = 0.57) or 2 years (61 ± 17 mL/min vs. 61 ± 19 mL/min, p = 0.84). At 1 year, chronicity using the Banff schema showed no difference in interstitial, tubular or glomerular changes, but fewer chronic vascular changes in the sirolimus group. This study shows that a CNI‐free regimen using sirolimus‐MMF‐prednisone produces similar acute rejection rates, graft survival and renal function 1–2 years after transplantation compared to tacrolimus‐MMF‐prednisone.

Transplant Glomerulopathy: Subclinical Incidence and Association with Alloantibody

Transplant glomerulopathy (TG) usually has been described as part of a constellation of late chronic histologic abnormalities associated with proteinuria and declining function. The current study used both protocol and clinically‐indicated biopsies to investigate clinical and subclinical TG, their prognosis and possible association with alloantibody. We retrospectively studied 582 renal transplants with a negative pre‐transplant T‐cell complement dependent cytotoxicity crossmatch. TG was diagnosed in 55 patients, 27 (49%) based on protocol biopsy in well‐functioning grafts. The cumulative incidence of TG increased over time to 20% at 5 years. The prognosis of subclinical TG was equally as poor as TG diagnosed with graft dysfunction, with progressive worsening of histopathologic changes and function. Although TG was associated with both acute and chronic histologic abnormalities, 14.5% of TG biopsies showed no interstitial fibrosis or tubular atrophy, while 58% (7/12) of biopsies with severe TG showed only minimal abnormalities. TG was associated with acute rejection, pretransplant hepatitis C antibody positivity and anti‐HLA antibodies (especially anti‐Class II), with the risk increasing if the antibodies were donor specific. We suggest that subclinical TG is an under‐recognized cause of antibody‐mediated, chronic renal allograft injury which may be mechanistically distinct from other causes of nephropathy.

Proteasome Inhibition Causes Apoptosis of Normal Human Plasma Cells Preventing Alloantibody Production

Antibody production by normal plasma cells (PCs) against human leukocyte antigens (HLA) can be a major barrier to successful transplantation. We tested four reagents with possible activity against PCs (rituximab, polyclonal rabbit antithymocyte globulin (rATG), intravenous immunoglobulin (IVIG) and the proteasome inhibitor, bortezomib) to determine their ability to cause apoptosis of human bone marrow‐derived PCs and subsequently block IgG secretion in vitro. IVIG, rituximab and rATG all failed to cause apoptosis of PCs and neither rituximab nor rATG blocked antibody production. In contrast, bortezomib treatment led to PC apoptosis and thereby blocked anti‐HLA and antitetanus IgG secretion in vitro. Two patients treated with bortezomib for humoral rejection after allogeneic kidney transplantation demonstrated a transient decrease in bone marrow PCs in vivo and persistent alterations in alloantibody specificities. Total IgG levels were unchanged. We conclude that proteasome activity is important for PC longevity and its inhibition may lead to new techniques of controlling antibody production in vivo.

Overcoming a Positive Crossmatch in Living‐Donor Kidney Transplantation

Many patients who have an otherwise acceptable living‐kidney donor do not undergo transplantation because of the presence of antibodies against the donor cells resulting in a positive crossmatch. In the current study, 14 patients with a positive cytotoxic crossmatch (titer ≤ 1 : 16) against their living donor underwent a regimen including pretransplant plasmapheresis, intravenous immunoglobulin, rituximab and splenectomy. Eleven of 14 grafts (79%) are functioning well 30–600 days after transplantation. Two grafts were lost to accelerated vasculopathy and one was lost to death with good function. No hyperacute or cellular rejections occurred. Antibody‐mediated rejection occurred in six patients [two clinical (14%) and four subclinical (29%)] and was reversible with plasmapheresis and steroids. Our results suggest that selected crossmatch‐positive patients can be transplanted successfully with living‐donor kidney allografts, using a protocol of pretransplant plasmapheresis, intravenous immunoglobulin, rituximab and splenectomy. Longer follow‐up will be needed, but the absence of anti‐donor antibody and good early outcomes are encouraging.

Baseline Donor‐Specific Antibody Levels and Outcomes in Positive Crossmatch Kidney Transplantation

Renal transplant candidates with donor‐specific alloantibody (DSA) have increased risk of antibody‐mediated allograft injury. The goal of this study was to correlate the risk of antibody‐mediated rejection (AMR), transplant glomerulopathy (TG) and graft survival with the baseline DSA level (prior to initiation of pretransplant conditioning). These analyses include 119 positive crossmatch (+XM) compared to 70 negative crossmatch (−XM) transplants performed between April 2000 and July 2007. Using a combination of cell‐based crossmatch tests, DSA level was stratified into very high +XM, high +XM, low +XM and −XM groups. In +XM transplants, increasing DSA level was associated with increased risk for AMR (HR = 1.76 [1.51, 2.07], p = 0.0001) but not TG (p = 0.18). We found an increased risk for both early and late allograft loss associated with very high DSA (HR = 7.71 [2.95, 20.1], p = 0.0001). Although lower DSA recipients commonly developed AMR and TG, allograft survival was similar to that of −XM patients (p = 0.31). We conclude that the baseline DSA level correlates with risk of early and late alloantibody‐mediated allograft injury. With current protocols, very high baseline DSA patients have high rates of AMR and poor long‐term allograft survival highlighting the need for improved therapy for these candidates.

Accommodation in ABO-incompatible kidney allografts, a novel mechanism of self-protection against antibody-mediated injury.

To elucidate the mechanism of self‐protection against anti‐donor blood‐group antibody known as accommodation, we studied 16 human ABO‐incompatible living‐donor kidney transplant recipients at 3 and 12 months post transplantation. Both circulating anti‐blood‐group antibody and the target blood‐group antigen in the graft were demonstrable in all patients after transplantation. Thirteen of 16 grafts had normal renal function and histology, while three grafts with prior humoral rejection demonstrated significant glomerulopathy and thus did not meet the criterion for accommodation. Using microarrays, we compared five 1‐year protocol ABO‐compatible renal graft biopsies to four accommodated ABO‐incompatible graft biopsies. Significant alterations in gene expression in 440 probe sets, including SMADs, protein tyrosine kinases, TNF‐α and Mucin 1 were identified. We verified these changes in gene expression using RT‐PCR and immunohistochemistry. Heme oxygenase‐1, Bcl‐2 and Bcl‐xl were not increased in ABO‐incompatible grafts at any time‐point. We conclude that accommodation is always present in well‐functioning, long‐surviving ABO‐incompatible kidney transplants. This self‐protection against antibody‐mediated damage may involve several novel mechanisms including the disruption of normal signal transduction, attenuation of cellular adhesion and the prevention of apoptosis.