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* Department of Medicine,
Department of Surgery, and
Department of Pathology, Beth Israel Deaconess Medical Center and Harvard Medical School;
Department of Pediatrics, Childrens Hospital and Harvard Medical School; and || Childrens Hospital Informatics Program, Childrens Hospital Boston
Address correspondence to: Dr. Terry B. Strom, Transplant Research Center, Beth Israel Deaconess Medical Center, Harvard Institutes of Medicine-1; Room 1026, 77 Avenue Louis Pasteur, Boston MA 02115. Phone: 617-667-0850; Fax: 617-667-0923; E-mail: tstrom{at}bidmc.harvard.edu
| Abstract |
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| Introduction |
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| Materials and Methods |
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Immunosuppressive Regimen
The intraoperative immunosuppressive regimen consisted of 1.5 mg/kg of thymoglobulin (Sangstat, Fremont, CA) given in a slow infusion begun before the transplant procedure or 20 mg of anti-CD25 mAb (Simulect; Novartis, East Hanover, NJ) and solumedrol 500 mg intravenously. Maintenance immunosuppressive regimens consisted of the calcineurin inhibitors tacrolimus (Fujisawa, Deerfield, IL) or cyclosporine (Novartis), prednisone, and mycophenolate mofetil (Roche, Nutley, NJ). Five patients received sirolimus (Wyeth-Ayerst, St. Davids, PA), prednisone, and mycophenolate mofetil.
Renal Biopsy
An intraoperative allograft wedge biopsy was performed 15 minutes after vascular reperfusion. One half of the biopsy was subjected to standard histopathologic analysis, and the rest was immediately snap-frozen in liquid nitrogen and stored in a 80°C refrigerator before RNA isolation.
Isolation of RNA
Total RNA was isolated from tissue homogenate samples with a commercial kit (RNeasy kit; Qiagen Inc, Chatworth, CA) (17). Reverse transcription of 1 mg of RNA was performed using multiscribed reverse transcriptase enzyme (PE Applied Biosystems, CA).
Quantification of Gene Expression by Real-Time Quantitative PCR
Real-time PCR was performed using the ABI 7700 sequence detector system (Applied Biosystems, Foster City, CA). PCR amplification was performed in a total volume of 25 ml containing 5 ml of cDNA sample, 0.6 mM of forward and reverse primer, 0.2 mM of TaqMan probe and 12.5 ml of TaqMan Universal PCR mastermix (Applied Biosystems). Amplification was performed using primer and hybridization probe sets of the listed targeted mRNAs (Table 1). To quantify the levels of mRNA, we normalized expression of the target genes to 18s ribosomal RNA (1).
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2 mg/dl at 6 mo posttransplantation.
Statistical Analyses
RNA expression data were first normalized (1). Next, simple logistic regression was performed for each variable on each of the three clinical outcomes of interest. For each outcome, each variable that demonstrated a P value <0.05 is listed in Table 2, along with the variables R value (18). Multiple logistic regression was then performed to determine combinations of time-zero intragraft gene expression patterns and clinical variables that correlate with each outcome of interest, using only those genes and clinical variables that demonstrated individual P values <0.05, as described above. For the purposes of training artificial neural nets (ANN), missing data points were imputed from the five nearest neighbors (19), as measured by Euclidean distance. Of 2700 data points, only 260 (9.6%) were missing. Missing data points were evenly distributed within each outcome (AR versus no rejection, DGF versus no DGF, and poor 6-mo outcome versus good 6-mo outcome). ANN were trained for each outcome (18), and cross-validation was performed. The area under the receiver-operator characteristic curve (ROC AUC) was then calculated to determine each ANN's performance for each outcome.
| Results |
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Zero-Hour Intragraft Gene Expression, Clinical Variables, and Prediction of DGF
Cadaver donor type, prolonged WIT and CIT, an abundance of transcripts for each of select pro-inflammatory cytokines (TNF-
, TGF-
, IL-10), the early T cell immune activation marker CD25, the pro-inflammatory cytokine-induced intercellular adhesion molecule (ICAM)-1 adhesion (e.g., TNF-
), and A20 molecules detected in zero-hour renal allograft biopsies were individually predictive for DGF (Table 2). In particular, TNF-
gene expression was highly predictive for DGF (R2 = 0.68, P < 0.001). Overall, these data support the hypothesis that evidence of intragraft inflammatory cytokines plus expression of inflammation-induced ICAM-1 and A20 molecules and early T cell immunity at the zero-hour are linked to DGF. The multiple logistic regression model that includes transcriptional events and pertinent clinical variables identified patients at very high risk for DGF (R2 = 0.98). Overall gene expression for TNF-
and other pro-inflammatory cytokines was far more abundant in cadaver than in living donor grafts at the zero-hour (data not shown). Only one recipient of a living donor graft, with a prolonged, intraoperative, warm ischemia experienced DGF. The zero-hour graft biopsy did reveal amplified gene expression of TNF-
and other pro-inflammatory cytokines that exceeded gene expression for these cytokines noted in any other recipient of a living donor graft. The presence of a cytomegalovirus carrier state or infusion of induction therapy, either thymoglobulin or anti-CD25 mAb, during the intraoperative period did not alter the pattern of gene expression in the zero-hour biopsy.
The ROC-AUC values for the ANN for DGF, including all significant molecular and clinical variables, the significant clinical variables alone, and the significant gene expression variables only were 1.0, 1.0, and 0.87, respectively, demonstrating that either clinical variables or transcriptional profiling can predict the occurrence of DGF with very high sensitivity and specificity (Figure 1, A, D, and G). The incidence of DGF was 14.5% during the study period. Analysis of the eight variables reported here therefore precisely identifies patients at risk for DGF.
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, TGF-
, IL-6), activated T cells (CD3 and CD25), and the inflammation-induced ICAM-1 adhesion and hemoxygenase (HO)-1 molecules detected in zero-hour individually predicted increased risk of AR (Table 2). The data may suggest that patients with heretofore undetected forms of T cell anti-donor immunity (gene expression of CD3 and CD25) present at the time of transplantation are at heightened risk for rejection.
It has been hypothesized that injury to the donor kidney present at the organ harvest and heightened injury during vascular reperfusion may serve as a stimulus for rejection (20,21). Indeed, DGF and AR are inter-related complications that can lead to impaired long-term graft function and survival (1,2,5,6,8). Ischemia/reperfusion injury in several settings initiates an inflammatory response leading to increased host immunologic reactivity (2024). It is notable that a near-identical pattern of intragraft gene expression events including amplified expression of pro-inflammatory cytokines (TNF-
, TGF-
, and either IL-10 or IL-6), T cell activation/T cell (CD25/CD3), and expression of inflammation-induced (ICAM-1, HO-1, or A20) molecules at the zero-hour is linked to both DGF and AR (Table 2).
The multiple logistic model that included the gene expression events cited above and clinical variables were highly predictive of AR during the first 3 mo (R2 = 0.88). The ROC AUC values for the ANN for AR, including all significant variables, the significant clinical variables only, and the significant gene variables alone were 0.73, 0.56, and 0.77, respectively. Thus, analysis of the abundance of select immune- and inflammation-related transcripts can predict the occurrence of AR with high sensitivity and specificity (Table 2; Figure 1, B, E, and H). By comparison, the incidence of AR was only 12% during the study period.
Zero-Hour Intragraft Gene Expression, Clinical Variables, and Prediction of 6-Month Graft Function
With respect to 6-mo graft function, African-American recipient race, cadaver organ donation, increased donor age, an episode of AR during the first three transplant months, the degree of HLA mismatching, increased CD25, and decreased Bcl-Xl gene expression individually predicted risk for poor graft function (serum creatinine >2.0 mg/ dl) 6 mo posttransplantation (Table 2). Because AR during the first 3 mo is not a "time-zero" event, multiple logistic regression analyses were performed with and without AR as a predictor. The multiple logistic model, which included all five clinical variables, increased expression of the T cell activation gene CD25, and decreased expression of the cytoprotective Bcl-Xl gene, an anti-apoptotic gene that unlike HO-1 and A20 is not triggered by pro-inflammatory cytokines, predicted with modest accuracy for poor graft function at 6 mo posttransplantation (R2 = 0.48). Evidence of early T cell active immunity unopposed by cytoprotective Bcl-Xl, anti-apoptotic, cytoprotective molecules that are not elicited by pro-inflammatory cytokines predicts for compromised graft function at 6 mo.
Removing AR, as AR is not a zero-hour event, from the multiple logistic regression model did not change the models performance for predicting graft function 6 mo posttransplantation (R2 = 0.48). The ROC-AUC values for the ANN for 6-mo graft function, including all significant variables except AR, the significant clinical variables only (except AR), and the two significant gene variables alone were 0.84, 0.73, and 0.78, respectively, demonstrating that gene expression values for only two genes can predict the quality of 6-mo function with high sensitivity and specificity (Figure 1C, 1F, 1I), exceeding the accuracy achieved with the clinical variable model.
Histologic Analysis of Zero-Hour Biopsies and Prediction of Clinical Outcomes
The histology of zero-hour biopsies was evaluated by standard histology without knowledge of clinical outcomes. At most, minor changes were noted. Rare focal infiltration of monocytes/macrophages was seen in five samples. Two of these five samples were from patients with DGF. Glomerulosclerosis involving less than 10% of glomeruli was found in three samples. One of these samples was obtained from a patient who ultimately had poor graft function at 6 mo.
| Discussion |
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For some clinical endpoints, the combined use of molecular analysis and established clinical indicators further enhances the quality of prognosis. In the absence of pretransplant clinical information, the transcriptional profiling data provide absolutely essential data to the predictive models, particularly with respect to AR and renal function 6 mo posttransplantation. The data also supports the hypothesis that evidence of concurrent intraoperative intragraft inflammation plus active T cell immunity leads to the early complications of DGF and AR.
In the future, identification of renal transplant recipients at high risk for DGF, AR, or chronic allograft nephropathy by molecular analysis of the zero-hour biopsy in combination with time-zero clinical variables may facilitate individualized, optimized care. Linkage between the molecular analysis of the allograft and ischemia-reperfusion, DGF, AR, and long-term graft function has been demonstrated through clinical studies. Our study may give some insight into the molecular nature and pathogenesis of these interactions and identify potential therapeutic targets. Because of the inability to use immunostaining or proteomic methods to readily and quantitatively analyze a wide range of protein expression events in each biopsy, we utilized a transcriptional profiling approach. Although the transcriptional profile associated with adverse clinical events may be for prognosis, as concluded herein, the data in the absence of protein expression data do not fully indicate that TNF-
and other pro-inflammatory cytokines can be considered important potential therapeutic targets.
| Acknowledgments |
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We would like to acknowledge Drs. David Shaffer and Marc Uknis for providing intraoperative biopsy specimens, Drs. Candace Wang and Christian Mix for helping in communicating with the patients and aiding the acquisition of clinical data, Dr. Takashi Maki for providing the HLA-typing data, Dr. S. Ananth Karumanchi for sharing his critical information, Prof. H.D. Volk and Dr. M. Suthanthiran for aid in probe design, and Christina Mottley for expert technical help with PCR analysis.
| Footnotes |
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| References |
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