Allograft Glomerulopathy Research Articles

Association of c4d deposition in renal allograft biopsy with morphologic features in Banff diagnosis

Association of c4d deposition in renal allograft biopsy with morphologic features in Banff diagnosis - IJPO- Print ISSN No: - 2394-6784 Online ISSN No:- 2394-6792 Article DOI No:- 10.18231/j.ijpo.2019.033, Indian Journal of Pathology and Oncology-Indian J Pathol Oncol

Histological picture of antibody-mediated rejection without donor-specific anti-HLA antibodies: Clinical presentation and implications for outcome.

In this cohort study (n=935 transplantations), we investigated the phenotype and risk of graft failure in patients with histological criteria for antibody-mediated rejection (ABMR) in the absence of circulating donor-specific anti-human leukocyte antigen (HLA) antibodies (DSA), and compared this to patients with definite ABMR and HLA-DSA-positivity. The histological picture did not differ between HLA-DSA-positive (n=85) and HLA-DSA-negative (n=123) cases of ABMR histology, apart from increased complement split product 4d (C4d) deposition in the peritubular capillaries in HLA-DSA-positive cases. Histology of ABMR without HLA-DSA was more transient than DSA-positive ABMR, and patients with ABMR histology without HLA-DSA had graft survival superior to that of HLA-DSA-positive patients, independent of concomitant T cell-mediated rejection (38.2%) or borderline changes (17.9%). Multivariate analysis showed that the risk of graft failure was not higher in patients with histological picture of ABMR (ABMRh ) in the absence of HLA-DSA, compared to patients without ABMRh . Despite an association between C4d deposition and HLA-DSA-positivity, using C4d deposition as alternative for the DSA criterion in the diagnosis of ABMR, as proposed in Banff 2017, did not contribute to the prognosis of graft function and graft failure. We concluded that biopsies with ABMRh but without detectable HLA-DSA represent a distinct, often transient phenotype with superior allograft survival.

Rituximab and Monitoring Strategies for Late Antibody-Mediated Rejection After Kidney Transplantation.

BackgroundThere is limited information on treatment strategies and monitoring strategies for late antibody-mediated rejection (ABMR) after kidney transplantation.MethodsIn this observational and nonrandomized study, we compared 78 patients diagnosed with late ABMR (>3 months after transplant) who were treated with standard of care steroids/IVIG (n = 38) ± rituximab (n = 40) at our center between March 1, 2013 and December 31, 2016. All patients had follow-up biopsy and donor-specific antibodies (DSA) monitoring within 3 to 12 weeks.ResultsPatients had biopsy 7.3 ± 7 years after transplant and were followed for 15.9 ± 9.6 months after ABMR was diagnosed. Both treatment strategies were associated with a significant decline in DSA, microvascular inflammation (peritubular capillaritis + glomerulitis), and C4d Banff scores. In univariate regression analyses, rituximab, estimated glomerular filtration rate (eGFR), Banff i, t, v, chronicity (interstitial fibrosis + tubular atrophy + fibrous intimal thickening + allograft glomerulopathy) scores on the first biopsy, and eGFR and Banff v score on follow-up biopsy were associated with graft loss. Multivariate analyses retained only rituximab (hazard ratio, 0.23; 95% confidence interval, 0.06-0.84; P = 0.03) and eGFR at follow-up biopsy (0.84; 95% confidence interval, 0.76-0.92; P < 0.001) as significant predictors of graft loss. Kaplan-Meier analyses demonstrated that the benefit associated with rituximab was apparent after 1 year (15% vs 32% graft loss, P = 0.02).ConclusionTreatment of late ABMR with steroids/IVIG ± rituximab was effective in reducing DSA and microcirculation inflammation. The addition of rituximab was associated with better graft survival. Follow-up biopsies could be considered in the management of acute rejection to monitor the effect of therapy. Randomized studies on the best therapeutic options for ABMR are needed.

Current outcomes of chronic active antibody mediated rejection – A large single center retrospective review using the updated BANFF 2013 criteria

BackgroundThe updated BANFF 2013 criteria has enabled a more standardized and complete serologic and histopathologic diagnosis of chronic active antibody mediated rejection (cAMR). Little data exists on the outcomes of cAMR since the initiation of this updated criteria. Methods123 consecutive patients with biopsy proven cAMR (BANFF 2013) between 2006 and 2012 were identified. ResultsPatients identified with cAMR were followed for a median of 9.5 (2.7–20.3) years after transplant and 4.3 (0–8.8) years after cAMR. Ninety-four (76%) recipients lost their grafts with a median survival of 1.9years after diagnosis with cAMR. Mean C4d and allograft glomerulopathy scores were 2.6±0.7 and 2.2±0.8, respectively. 53.2% had class II DSA, 32.2% had both class I and II, and 14.5% had class I DSA only. Chronicity score >8 (HR 2.9, 95% CI 1–8.4, p=0.05), DSA >2500 MFI (HR 2.8, 95% CI 1.1–6.8, p=0.03), Scr >3mg/dL (HR 3.2, 95% CI 1.6–6.3, p=0.001) and UPC >1g/g (HR 2.5, 95% CI 1.4–4.5, p=0.003) were associated with a higher risk of graft loss. ConclusionscAMR was associated with poor graft survival after diagnosis. Improved therapies and earlier detection strategies are likely needed to improve outcomes of cAMR in kidney transplant recipients.

IgG Donor-Specific Anti-Human HLA Antibody Subclasses and Kidney Allograft Antibody-Mediated Injury.

Antibodies may have different pathogenicities according to IgG subclass. We investigated the association between IgG subclasses of circulating anti-human HLA antibodies and antibody-mediated kidney allograft injury. Among 635 consecutive kidney transplantations performed between 2008 and 2010, we enrolled 125 patients with donor-specific anti-human HLA antibodies (DSA) detected in the first year post-transplant. We assessed DSA characteristics, including specificity, HLA class specificity, mean fluorescence intensity (MFI), C1q-binding, and IgG subclass, and graft injury phenotype at the time of sera evaluation. Overall, 51 (40.8%) patients had acute antibody-mediated rejection (aABMR), 36 (28.8%) patients had subclinical ABMR (sABMR), and 38 (30.4%) patients were ABMR-free. The MFI of the immunodominant DSA (iDSA, the DSA with the highest MFI level) was 6724±464, and 41.6% of patients had iDSA showing C1q positivity. The distribution of iDSA IgG1-4 subclasses among the population was 75.2%, 44.0%, 28.0%, and 26.4%, respectively. An unsupervised principal component analysis integrating iDSA IgG subclasses revealed aABMR was mainly driven by IgG3 iDSA, whereas sABMR was driven by IgG4 iDSA. IgG3 iDSA was associated with a shorter time to rejection (P<0.001), increased microcirculation injury (P=0.002), and C4d capillary deposition (P<0.001). IgG4 iDSA was associated with later allograft injury with increased allograft glomerulopathy and interstitial fibrosis/tubular atrophy lesions (P<0.001 for all comparisons). Integrating iDSA HLA class specificity, MFI level, C1q-binding status, and IgG subclasses in a Cox survival model revealed IgG3 iDSA and C1q-binding iDSA were strongly and independently associated with allograft failure. These results suggest IgG iDSA subclasses identify distinct phenotypes of kidney allograft antibody-mediated injury.

P120 : SIMULTANEOUS POLYOMA VIRUS (BKV) NEPHROPATHY, C4d POSITIVE ANTIBODY MEDIATED REJECTION (AMR) IN A RENAL TRANSPLANT CASE

To describe the case of a renal transplant with concurrent pathological evidence of C4d positive AMR and BK virus nephropathy. Several cases of BK virus nephropathy diagnosed based on BK viral DNA in blood/urine by PCR, and by the immunostaining of SV40 viral antigen in renal allograft biopsy were reviewed. Donor specific HLA Class I and Class II antibodies (HLA-DSA) were estimated by solid phase assay. The antibody mediated rejection was diagnosed based on C4d staining in the peritubular capillaries (PTC) and histopathological features based on Banff’2007 Classification. At the time of transplant the recipient had no detectable HLA-DSA. The recipient was followed up for serum creatinine (Scr) post transplant. The pre-transplant Scr level was 3.4 ± 0.69, and it remained between 1.3 and 1.16 until 3 years post transplant when BK virus was detected in urine (85,000 copies/ml) and Scr remained >1.3 since then. The immunosuppression was reduced and the BK virus load came down to 4200 copies/ml. A biopsy indicated interstitial fibrosis and tubular atrophy with no apparent etiology. At this time the patient had DSAs towards B8, DQ2, DR4, DR17, and DR53, and DR4. Another biopsy 6 months later showed Polyomavirus nephropathy , interstitial fibrosis and tubular atrophy involving 40% of the cortex, mild chronic allograft (transplant) glomerulopathy with global (6/16) and segmental (3/16) glomerulosclerosis along with C4d positivity in peritubular capillaries suggestive of AMR and had circulating DSAs mentioned above. We have described a case where BK virus nephropathy was co-existent with C4d positive AMR. It is possible that the reduced immunosuppression regimen after detecting BK virus in the urine lead to revived alloimmune response and AMR based on circumstantial evidence. Molecular mechanisms of BK virus nephropathy and ways to treat it without compromising the level of immunosuppression to avoid alloimmune immune response will be the key in dealing with these types of scenarios.

Increased Intragraft Endothelial Cell and Interferon-gamma Associated Transcripts and Banff Chronic Allograft Glomerulopathy (cg) Score Predict the Graft Loss in Transplant Glomerulopathy.

Increased Intragraft Endothelial Cell and Interferon-gamma Associated Transcripts and Banff Chronic Allograft Glomerulopathy (cg) Score Predict the Graft Loss in Transplant Glomerulopathy.

A8.31 Characterisation of human transitional B-cells though their regulatory functions

Transitional B cells represent a cortical link between the initial B cell compartment in bone marrow and the mature peripheral B cell repertoire. The prior characterisation of human transitional B-cells...

A8.32 Regulatory B-cell supress T-cell proliferation through a TGFβ/IDO axis and are deficient in chronic humoral rejection

In kidney transplantation, B cell is increasingly identified as an important determinant for graft outcome. Chronic antibody mediated rejection (cABMR) represent today the major complication in clinic. Patients with cABMR...

The chemokine receptor CXCR7 is expressed on lymphatic endothelial cells during renal allograft rejection

CXCR7 is an atypical receptor for the chemokines CXCL11 and CXCL12, which were found to be involved in animal models of allograft injury. We studied the expression of CXCR7 and its ligands in human kidneys by first quantifying the mRNA in 53 renal allograft biopsies. Receptor and ligand mRNAs were expressed in renal allografts, with a significant induction of CXCL11 and CXCL12 in biopsies showing borderline lesions and acute rejection. Immunohistochemical analysis for CXCR7 was performed in a series of 64 indication and 24 protocol biopsies. The indication biopsies included 46 acute rejections, 6 with interstitial fibrosis and tubular atrophy, and 12 pretransplant biopsies as controls. In control biopsies, CXCR7 protein was found on smooth muscle and on endothelial cells of a small number of peritubular vessels. The number of CXCR7-positive vessels was increased in acute rejection and, using double immunofluorescence labeling, a subset of these CXCR7-positive endothelial cells were identified as lymphatic vessels. Both CXCR7-positive blood and lymphatic vessels increased during allograft rejection. We found that CXCR7 is present in both blood and lymphatic endothelial cells in human renal allografts. Whether its presence modulates the formation of chemokine gradients and the recruitment of inflammatory cells will require further experimental studies.

Four Stages and Lack of Stable Accommodation in Chronic Alloantibody-Mediated Renal Allograft Rejection in Cynomolgus Monkeys

The etiology of immunologically mediated chronic renal allograft failure is unclear. One cause is thought to be alloantibodies. Previously in Cynomolgus monkeys, we observed a relationship among donor-specific alloantibodies (DSA), C4d staining, allograft glomerulopathy, allograft arteriopathy and progressive renal failure. To define the natural history of chronic antibody-mediated rejection and its effect on renal allograft survival, we now extend this report to include 417 specimens from 143 Cynomolgus monkeys with renal allografts. A subset of animals with long-term renal allografts made DSA (48%), were C4d positive (29%), developed transplant glomerulopathy (TG) (22%) and chronic allograft arteriopathy (CAA) (19%). These four features were highly correlated and associated with statistically significant shortened allograft survival. Acute cellular rejection, either Banff type 1 or 2, did not correlate with alloantibodies, C4d deposition or TG. However, endarteritis (Banff type 2) correlated with later CAA. Sequential analysis identified four progressive stages of chronic antibody-mediated rejection: (1) DSA, (2) deposition of C4d, (3) TG and (4) rising creatinine/renal failure. These new findings provide strong evidence that chronic antibody-mediated rejection develops without enduring stable accommodation, progresses through four defined clinical pathological stages and shortens renal allograft survival.

Two Rare Forms of Renal Allograft Glomerulopathy During Cytomegalovirus Infection and Treatment

Improvements in induction and maintenance immunosuppression have resulted in infections being the most common cause of hospitalization in renal transplant recipients. Although viremia with or without symptoms is the most common manifestation of cytomegalovirus (CMV) infection in renal transplant recipients, CMV occasionally can directly cause renal allograft infection and dysfunction. 1 Birk P.E. Chavers B.M. Does cytomegalovirus cause glomerular injury in renal allograft recipients?. J Am Soc Nephrol. 1997; 8: 1801-1808 PubMed Google Scholar Acute tubular dysfunction was described in patients with CMV-induced interstitial nephritis, with CMV detected in tubular epithelial cells. 2 Cameron J. Rigby R.J. van Deth A.G. Petrie J.J. Severe tubulo-interstitial disease in a renal allograft due to cytomegalovirus infection. Clin Nephrol. 1982; 18: 321-325 PubMed Google Scholar , 3 Ozdemir B.H. Sar A. Uyar P. Suren D. Demirhan B. Haberal M. Posttransplant tubulointerstitial nephritis: Clinicopathological correlation. Transplant Proc. 2006; 38: 466-469 Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar Interstitial infiltrates fulfilling the diagnosis of acute rejection typically were observed in these patients and attributed to upregulation of major histocompatibility molecules on tubular cells infected with CMV. 4 Hosenpud J.D. Chou S.W. Wagner C.R. Cytomegalovirus-induced regulation of major histocompatibility complex class I antigen expression in human aortic smooth muscle cells. Transplantation. 1991; 52: 896-903 Crossref PubMed Scopus (60) Google Scholar , 5 van Dorp W.T. van Wieringen P.A. Marselis-Jonges E. et al. Cytomegalovirus directly enhances MHC class I and intercellular adhesion molecule-1 expression on cultured proximal tubular epithelial cells. Transplantation. 1993; 55: 1367-1371 Crossref PubMed Scopus (56) Google Scholar , 6 Ustinov J. Loginov R. Bruggeman C. Suni J. Hayry P. Lautenschlager I. CMV-induced class II antigen expression in various rat organs. Transpl Int. 1994; 7: 302-308 Crossref PubMed Google Scholar In addition, CMV-induced acute glomerulopathy was described with characteristic lesions involving glomerular capillary endothelial cells and accumulation of mononuclear cells in glomerular capillaries. 1 Birk P.E. Chavers B.M. Does cytomegalovirus cause glomerular injury in renal allograft recipients?. J Am Soc Nephrol. 1997; 8: 1801-1808 PubMed Google Scholar , 7 Richardson W.P. Colvin R.B. Cheeseman S.H. et al. Glomerulopathy associated with cytomegalovirus viremia in renal allografts. N Engl J Med. 1981; 305: 57-63 Crossref PubMed Scopus (250) Google Scholar , 8 Herrera G.A. Alexander R.W. Cooley C.F. et al. Cytomegalovirus glomerulopathy: A controversial lesion. Kidney Int. 1986; 29: 725-733 Crossref PubMed Scopus (70) Google Scholar , 9 Onuigbo M. Haririan A. Ramos E. Klassen D. Wali R. Drachenberg C. Cytomegalovirus-induced glomerular vasculopathy in renal allografts: A report of two cases. Am J Transplant. 2002; 2: 684-688 Crossref PubMed Scopus (25) Google Scholar Such endothelial cell viral lesions were associated with acute necrotizing and crescentic glomerulonephritis 10 Detwiler R.K. Singh H.K. Bolin Jr, P. Jennette J.C. Cytomegalovirus-induced necrotizing and crescentic glomerulonephritis in a renal transplant patient. Am J Kidney Dis. 1998; 32: 820-824 Abstract Full Text PDF PubMed Scopus (28) Google Scholar and, in some cases, an acquired hypercoagulable state caused by endothelial cell dysfunction. 11 Kazory A. Ducloux D. Acquired hypercoagulable state in renal transplant recipients. Thromb Haemost. 2004; 91: 646-654 PubMed Google Scholar

Posttransplant Prophylactic Intravenous Immunoglobulin in Kidney Transplant Patients at High Immunological Risk: A Pilot Study

The effects of posttransplant prophylactic intravenous immunoglobulin (IVIg) were investigated in renal transplant recipients at high immunological risk. Thirty-eight deceased-donor kidney transplant recipients with previous positive complement-dependent cytotoxicity crossmatch (n=30), and/or donor-specific anti-HLA antibodies (n=14) were recruited. IVIg (2 g/kg) was administrated on days 0, 21, 42 and 63 with quadruple immunosuppression. Biopsy-proven acute cellular and humoral rejection rates at month 12 were 18% and 10%, respectively. Glomerulitis was observed in 31% and 60% of patients at months 3 and 12, respectively, while allograft glomerulopathy rose from 3% at month 3 to 28% at 12 months. Interstitial fibrosis/tubular atrophy increased from 18% at day 0 to 51% and 72% at months 3 and 12 (p<0.0001). GFR was 50 +/- 17 mL/min/1.73 m(2) and 48 +/- 17 mL/min/1.73 m(2) at 3 and 12 months. PRA decreased significantly after IVIg (class I: from 18 +/- 27% to 5 +/- 12%, p<0.01; class II: from 25 +/- 30% to 7 +/- 16%, p<0.001). Patient and graft survival were 97% and 95%, respectively and no graft was lost due to rejection (mean follow-up 25 months). In conclusion, prophylactic IVIg in high-immunological risk patients is associated with good one-year outcomes, with adequate GFR and a profound decrease in PRA level, but a significant increase in allograft nephropathy.

Chronic Antibody Mediated Rejection of Renal Allografts: Pathological, Serological and Immunologic Features in Nonhuman Primates

The pathogenesis of late renal allograft loss is heterogeneous and difficult to diagnose. We have analyzed renal allografts in nonhuman primates to determine the relationship between alloantibodies and the graft pathology of late graft loss. Seventeen Cynomolgus monkeys were chosen from among those on several protocols for renal allotransplantation with mixed chimerism induction so that animals with and without alloantibodies were included. All animals received transient CD154 blockade and short-term cyclosporine treatment until day 28. Serial blood samples were tested for alloantibodies. Protocol biopsies and autopsy kidneys were scored for pathology and C4d deposition. Group 1, defined by complete lack of C4d deposition (24 tissue samples; 8 recipients), had no detectable alloantibodies (33 serum samples; 1-7 samples per recipient) and no evidence of chronic rejection. Three survived greater than 2 years with normal function and histology. Group 2, defined as having C4d deposition in peritubular capillaries, all made alloantibodies (100%), and most grafts later showed chronic allograft glomerulopathy (89%), and/or arteriopathy (89%). All grafts in Group 2 failed (3-27 months). Pathologic lesions of typical of chronic rejection in humans develop in monkeys, correlate with antecedent alloantibodies/C4d deposition and predict chronic rejection rather than durable accommodation.

Ten‐year protocol biopsy findings of renal allografts in the calcineurin inhibitor era

Ten-year protocol biopsies were performed in 16 patients treated with calcineurin inhibitor (CNI) continuously. All kidney grafts were functioning well at the time of biopsy with the mean serum creatinine level of 1.6 +/- 0.8 mg/dL. The specimen of biopsy showed various degrees of tissue injury. According to the Banff grading, allograft glomerulopathy (cg) was observed in one case. Interstitial fibrosis (ci) and tubular atrophy (ct) were observed more frequently in 13 (81%) and 15 (93%) cases, respectively. Fibrous intimal thickening (cv) was seen in one (7%) case. Arteriolar hyaline thickening (ah) was seen in 14 (87%) cases. These findings were associated with chronic rejection in one case, recurrence of original disease in four (25%) cases, toxicity of CNI in 14 (87%) cases. Longer follow-up studies are needed to confirm whether CNI should be continued or not in the long-term period following kidney transplantation for better graft survival.

C4d Complement Split Product in Diagnosis of Immunological Activity of Chronic Allograft Nephropathy

Introduction Activation of the humoral branch of the immunological response is currently believed to play an important role in pathogenesis of chronic allograft nephropathy. The impact of humoral alloreactivity, indicated by the presence of C4d deposits in peritubular capillaries of a renal allograft, on the development of chronic allograft nephropathy is a significant problem in transplantation. The aim of the study was to assess and correlate C4d expression in patients with chronic allograft nephropathy, with clinical and morphological variables, as well as to assess the impact of a change in immunosuppression regimen on posttransplant course and renal allograft morphology. Patients and methods Twenty-six patients with chronic allograft nephropathy underwent biopsies to correlate C4d expression with clinical parameters and morphological findings. In all patients azathioprine was replaced with mycophenolate mofetil with additional CsA dose reduction in 12 patients. After 1 year, 14 protocol biopsies were performed. Results The frequency of C4d peritubular capillary deposition among patients with chronic allograft nephropathy was 30%. C4d expression appeared later after transplantation, was correlated with chronic allograft glomerulopathy and proteinuria but not other clinical or histological variables. C4d deposits displayed no independent impact on serum creatinine level. Proteinuria was significantly more reduced in the C4d(+) group. Progression of chronic morphological changes was significantly accelerated in the C4d(+) group. Conclusion C4d peritubular capillary expression did not differentiate patients after immunosuppression enhancement, but it predisposed to progression of chronic morphological findings during 1-year observation.

C4d deposition in allografts: current concepts and interpretation

Alloantibody responses are not prevented by the latest immunosuppressive regimens and contribute to increased early and late renal allograft graft loss. Numerous papers have set forth the clinical, pathological, and immunopathological features of acute humoral rejection, in particular the strong correlation between the presence of C4d deposition and circulating antidonor HLA class I and class II antibodies. Humoral rejection also occurs in a chronic setting, associated with chronic allograft glomerulopathy and arteriopathy. C4d deposition can also be found in stable grafts without concurrent graft pathology, a finding that may indicate accommodation. The central diagnostic criterion for humoral rejection is the demonstration of C4d in peritubular capillaries. The criteria for humoral rejection are not as widely accepted for other organs, such as the heart, lung, and pancreas, although humoral rejection, including C4d deposition, has been described. This review focuses on the practical aspects of this test, particularly as applied routinely in renal allografts since 1998 in our laboratory.

Complement Factor H Deficiency in Acute Allograft Glomerulopathy and Post-Transplant Hemolytic Uremic Syndrome

Acute allograft glomerulopathy (AAG) is a distinct form of allograft rejection characterized by cytotoxic T-cell-mediated injury to the renal glomerular and arteriolar endothelium. Acute allograft glomerulopathy is characterized by mononuclear cell infiltration of glomerular capillary tufts in association with endothelial cell hypertrophy and injury. Intra-glomerular thrombi have been described in AAG, suggesting that overlapping features of AAG and post-transplant thrombotic microangiopathy (TMA) may coexist. We present a case suggesting that complement factor H deficiency, a known hereditary risk factor for TMA, may also favor development of AAG. We discuss the potential implications of factor H deficiency in the pathophysiology of renal allograft microvascular injury, leukocyte infiltration and formation of intraglomerular platelet thrombi. We propose that unopposed complement activation is a risk factor for both immune and nonimmune forms of microvascular injuries in renal allografts.

Microangiopathies and malignant vascular injury in the kidney

Microangiopathies without vasculitis are a challenge to interpretation and diagnosis of renal biopsy. This review focuses on the thrombotic microangiopathies in native and allograft kidneys, with discussion of nomenclature, cause, pathogenesis, pathological features and lesions of differential diagnosis, including disseminated intravascular coagulation, pre-eclampsia, lupus vasculopathy and chronic allograft glomerulopathy.

Combination therapy of mycophenolate mofetil and rapamycin in prevention of chronic renal allograft rejection in the rat1

Chronic rejection is the leading cause of long-term allograft loss. Until now, no therapy has been recognized as being efficient in its prevention. In addition to their immunosuppressive activity, mycophenolate mofetil (MMF) and rapamycin (RAPA) show diverse properties against vascular smooth muscle cell activity, cell-adhesion molecule expression, and ischemia-reperfusion injury. The combination effect of MMF and RAPA was tested to prevent chronic renal allograft rejection in the rat in this study. Nephrectomized Lewis recipients underwent orthotopic transplantation with Fisher (F344) kidneys (allograft groups) or Lewis kidneys (isograft control). The initial episode of acute rejection was controlled with a short course of cyclosporine A (CsA) (1.5 mg/kg/day for 10 days). From weeks 4 to 20, animals were thereafter treated every other day either with vehicle, MMF (20 mg/kg), RAPA (0.8 mg/kg), or MMF (20 mg/kg) plus RAPA (0.8 mg/kg) in combination. Animals were sequentially killed at serial intervals over a follow-up of 50 weeks, and histologic study was performed on harvested kidneys according to the Banff working classification for allograft pathology. Animals treated with MMF or RAPA alone showed a Banff sum score similar to the allograft control group (6.31+/-1.01 and 7.27+/-1.14 vs. 7.21+/-1.14, respectively; P>0.05). When the recipient rats were treated with MMF and RAPA in combination, it resulted in a clinically and statistically significant reduction of Banff sum score (4.21+/-0.79, P<0.01), with specific inhibition of vascular fibrous intimal thickening, allograft glomerulopathy, and interstitial fibrosis. Over a 50-week study, concomitant therapy of MMF and RAPA prevents chronic renal allograft rejection, probably through reduction of ischemic and cytotoxic degenerative changes. These results warrant further investigation in the combination of MMF and RAPA as anti-chronic rejection therapy in clinical transplantation.