Alloantibody levels and acute humoral rejection early after positive crossmatch kidney transplantation

We examined the course of donor-specific alloantibody (DSA) levels early after transplant and their relationship with acute humoral rejection (AHR) in two groups of positive crossmatch (+XM) kidney transplant recipients: High DSA group-41 recipients with a baseline T- or B-cell flow crossmatch (TFXM, BFXM) channel shift >or=300 (molecules of equivalent soluble fluorochrome units (MESF) of approximately 19 300) who underwent pretransplant plasmapheresis (PP), and Low DSA group-29 recipients with a baseline channel shift <300 who did not undergo PP. The incidence of AHR was 39% (16/41) in the High DSA group and 31% (9/29) in the Low DSA group. Overall, mean DSA levels decreased by day 4 posttransplant and remained low in patients who did not develop AHR. By day 10, DSA levels increased in patients developing AHR with 92% (23/25) of patients with a BFXM >359 (MESF of approximately 34 000) developing AHR. The BFXM and the total DSA measured by single antigen beads correlated well across a wide spectrum suggesting that either could be used for monitoring. We conclude that AHR is associated with the development of High DSA levels posttransplant and protocols aimed at maintaining DSA at lower levels may decrease the incidence of AHR.

Survival of patients on the kidney transplant wait list: relationship to cardiac troponin T

Patients waiting for a kidney transplant have high mortality despite careful preselection. Herein, we assessed whether cardiac troponin T (cTnT) can help stratify risk in patients selected for kidney transplantation. cTnT levels were measured in all kidney transplant candidates but the results were not used for patient selection. Among 644 patients placed on the kidney waiting list from 9/2004 to 12/2006, 61% had elevated cTnT levels (>0.01 ng/mL). Higher levels related to diabetes, longer time on dialysis, history of cardiovascular disease and low serum albumin. High cTnT also related to cardiac anomalies, including left ventricular hypertrophy (LVH), wall motion abnormalities and stress-inducible ischemia by dobutamine echo (DSE). However, 54% of patients without these cardiac findings had elevated cTnT. Increasing cTnT levels were associated with reduced survival (HR = 1.729, CI (1.25-2.39), p = 0.01) independently of low serum albumin (0.449 (0.24-0.83), p = 0.011) and history of stroke (3.368 (1.47-7.73), p = 0.0004). The results of the DSE and/or coronary angiography did not relate significantly to survival. However, high cTnT identified patients with abnormal echo findings and poor survival. Wait listed patients with normal cTnT have excellent survival irrespective of other factors. In contrast, high cTnT levels are strongly predictive of poor survival in the kidney transplant waiting list.

Survival of patients on the kidney transplant wait list: relationship to cardiac troponin T

Patients waiting for a kidney transplant have high mortality despite careful preselection. Herein, we assessed whether cardiac troponin T (cTnT) can help stratify risk in patients selected for kidney transplantation. cTnT levels were measured in all kidney transplant candidates but the results were not used for patient selection. Among 644 patients placed on the kidney waiting list from 9/2004 to 12/2006, 61% had elevated cTnT levels (>0.01 ng/mL). Higher levels related to diabetes, longer time on dialysis, history of cardiovascular disease and low serum albumin. High cTnT also related to cardiac anomalies, including left ventricular hypertrophy (LVH), wall motion abnormalities and stress-inducible ischemia by dobutamine echo (DSE). However, 54% of patients without these cardiac findings had elevated cTnT. Increasing cTnT levels were associated with reduced survival (HR = 1.729, CI (1.25-2.39), p = 0.01) independently of low serum albumin (0.449 (0.24-0.83), p = 0.011) and history of stroke (3.368 (1.47-7.73), p = 0.0004). The results of the DSE and/or coronary angiography did not relate significantly to survival. However, high cTnT identified patients with abnormal echo findings and poor survival. Wait listed patients with normal cTnT have excellent survival irrespective of other factors. In contrast, high cTnT levels are strongly predictive of poor survival in the kidney transplant waiting list.

The spectrum of antibody-mediated renal allograft injury: implications for treatment

Improvements in anti-HLA antibody detection and diagnostic criteria have increased recognition of antibody-mediated rejection (AMR) following renal transplantation. Therapy of acute AMR is directed toward rapidly lowering circulating donor-specific antibody (DSA) activity. Despite reversal of acute renal dysfunction, however, antibody-secreting plasma cells in spleen and bone marrow are not depleted by treatment and circulating DSA commonly remains detectable in peripheral blood. Sequential ultrastructural studies of renal allografts during acute AMR show progression of microvascular endothelial abnormalities from necrosis and apoptosis to glomerular and peritubular capillary basement membrane duplication, termed transplant glomerulopathy (TG), a manifestation of chronic AMR. Additionally, long-term exposure to anti-HLA antibodies (particularly against class II antigens) is associated with shortened allograft survival and TG even in the absence of documented acute AMR. The association of TG with prior acute AMR and with circulating DSA provides evidence that antibody-mediated allograft injury exists as a spectrum of renal injury. Although effective therapy is available for acute AMR, allografts remain at risk for chronic AMR and shortened survival. The optimum approach to treatment for chronic AMR remains to be determined.

Calculating life years from transplant (LYFT): methods for kidney and kidney-pancreas candidates

The Organ Procurement and Transplantation Network (OPTN) Kidney Committee is considering a proposal for a new deceased donor kidney allocation system. Among the components under consideration is a strategy to rank candidates in part by the estimated incremental years of life that are expected to be achieved with a transplant from a specific available deceased donor, computed as the difference in expected median lifespan with that transplant compared with remaining on dialysis. This concept has been termed life years from transplant or LYFT. Median lifespans could be calculated, based on objective medical criteria, for each candidate when a deceased donor kidney becomes available, based on Cox regression models using current candidate and donor medical information. The distribution of the calculated LYFT scores for an average nonexpanded criteria donor kidney is similar across candidate sex, race/ethnicity, insurance status and, with the exception of diabetes, diagnosis. LYFT scores tend to be higher for younger candidates and lower for diabetics receiving a kidney-alone rather than a simultaneous kidney-pancreas transplant. Prioritizing candidates with higher LYFT scores for each available kidney could substantially increase total years of life among both transplant candidates and recipients. LYFT is also a powerful metric for assessing trends in allocation outcomes and for comparing alternative allocation systems.

Determinants of discard of expanded criteria donor kidneys: impact of biopsy and machine perfusion

We examined factors associated with expanded criteria donor (ECD) kidney discard. Scientific Registry of Transplant Recipients (SRTR)/Organ Procurement and Transplantation Network (OPTN) data were examined for donor factors using logistic regression to determine the adjusted odds ratio (AOR) of discard of kidneys recovered between October 1999 and June 2005. Logistic and Cox regression models were used to determine associations with delayed graft function (DGF) and graft failure. Of the 12,536 recovered ECD kidneys, 5139 (41%) were discarded. Both the performance of a biopsy (AOR = 1.21, p = 0.02) and the degree of glomerulosclerosis (GS) on biopsy were significantly associated with increased odds of discard. GS was not consistently associated with DGF or graft failure. The discard rate of pumped ECD kidneys was 29.7% versus 43.6% for unpumped (AOR = 0.52, p < 0.0001). Among pumped kidneys, those with resistances of 0.26-0.38 and >0.38 mmHg/mL/min were discarded more than those with resistances of 0.18-0.25 mmHg/mL/min (AOR = 2.5 and 7.9, respectively). Among ECD kidneys, pumped kidneys were less likely to have DGF (AOR = 0.59, p < 0.0001) but not graft failure (RR = 0.9, p = 0.27). Biopsy findings and machine perfusion are important correlates of ECD kidney discard; corresponding associations with graft failure require further study.

Transplant glomerulopathy

Transplant glomerulopathy (TG) is a histologic entity described more than four decades ago. In the last few years, our understanding of TG has improved significantly. Current evidence supports the postulate that TG is a unique pathologic and pathogenic entity distinct from other forms of chronic allograft injury. Detailed electron microscopic studies have shown basement membrane abnormalities in glomerular and peritubular capillaries, indicating that this is a disease of the entire renal capillary network. Staining biopsies for the complement fragment, C4d, showed positivity in subgroups of TG, suggesting the participation of antidonor antibodies. Consistent with this postulate, the incidence of TG is increased in patients with antidonor HLA antibodies prior to the transplant. The use of surveillance biopsies has demonstrated that TG can develop during the first few months after transplantation, although it may remain clinically quiescent for several years. However, TG is progressive, leading to reduced graft survival. Recent studies demonstrated a close association between TG and anti-HLA class II antibodies. Current therapies for TG are likely of limited value. However, it is also likely that an improved understanding of TG pathogenesis will result in the development of effective therapies for this form of progressive kidney allograft damage.

Patient survival and cardiovascular risk after kidney transplantation: the challenge of diabetes

An increasing proportion of kidney recipients have diabetes mellitus (DM). Herein, we assessed the impact of DM on morbidity and mortality. The study included 933 recipients of first transplants. DM was present in 212 (23%). Compared to non-diabetics (NoDM), DM were older, heavier and had more pretransplant cardiovascular (CV) disease (16% vs. 48%, p < 0.0001). DM had reduced survival (5 years, 93% vs. 70%, p < 0.0001) and higher incidence of CV events (9% vs. 37%, p < 0.0001). CV disease was the most common cause of death in DM (61%) but not in NoDM (26%). Mortality from infections was also higher in DM (p = 0.001). In NoDM, survival related to recipient age (hazard ratio (HR) = 1.07, p < 0.0001) and dialysis pretransplant HR = 2.21, p = 0.01, while in DM, survival related to dialysis (HR = 2.89, p = 0.01) and pretransplant CV disease (HR = 2.79, p = 0.007). In NoDM, the incidence of posttransplant CV events was related to traditional CV risk factors, while in DM only the pretransplant CV history related to this outcome. In conclusion, survival differs between NoDM and DM recipients quantitatively, by cause of death and by risk factors. In NoDM, survival is excellent, and the main threat to survival relates to immunosuppression. In DM, survival is inferior primarily due to CV disease generally present prior to transplantation.

Posttransplant diabetes mellitus after pancreas transplantation

Some patients do not achieve normoglycemia after an otherwise successful pancreas transplant. The aim of this study was to define the incidence and risk factors for the development of persistent diabetes mellitus after pancreas transplantation. We studied the outcomes of 144 pancreas transplants performed at our institution between January 2001 and December 2005. Diabetes mellitus was defined as the persistent need for pharmacologic treatment of diabetes mellitus despite evidence of allograft function. Data are expressed as median (25-75% inter-quartile range). Median follow-up was 39 months (IQR 26-55 months). During the follow-up period, 28 patients (19%) developed diabetes mellitus with a functioning allograft. Factors predicting hyperglycemia included: pretransplant insulin dose, BMI and acute rejection episodes (p < 0.0001, p = 0.0002 and p < 0.02, respectively). The median pretransplant hemoglobin A1c for patients developing diabetes was 8.3% (IQR 7.0-9.4%) compared to 6.2% (IQR 5.8-7.4%) at 2 years after transplant (p = 0.0069). In conclusion, persistent diabetes mellitus can occur despite the presence of a functioning pancreas allograft and is due to increased pretransplant BMI, high pretransplant insulin requirements and episodes of acute rejection.

Two novel assays of alloantibody-secreting cells demonstrating resistance to desensitization with IVIG and rATG

Donor-specific alloantibody presents a major barrier to the successful transplantation of kidneys and hearts. However, the study of alloantibody production has been hampered by both an inadequate source of antibody-secreting cells (ASCs) and a paucity of assays to determine their function. We describe two new assays that allow for the determination of the frequency and specificities of allo-ASCs in humans using purified HLA as targets. These assays demonstrated allo-ASCs in the CD138(+) fraction of the bone marrow, but not in peripheral blood. Alloantibody specificities in these assays correlated well with those detected in the serum suggesting that bone marrow-derived ASCs are indeed a major source of alloantibody in vivo. However, ASCs for a specific HLA antigen were rare with an estimated frequency of only 1/2 x 10(6) marrow cells. Pretransplant treatment in vivo with multiple plasmaphereses and low-dose IVIG alone or in combination with rATG had no effect on ASC number or alloantibody production. These techniques allow for the study of allospecific ASCs and provide a method to test the potential efficacy of agents on alloantibody production in vivo.

Proteinuria after kidney transplantation, relationship to allograft histology and survival

Proteinuria is associated with reduced kidney allograft survival. Herein we assessed the association between proteinuria, graft histology and survival. The cohort included 613 kidney allograft recipients who had proteinuria (measured) and surveillance biopsies at 1-year posttransplant. Proteinuria >150 mg/day was detected in 276 patients (45%) and in 182 of these, proteinuria was below 500. In >84% of patients even low levels of proteinuria were associated with albuminuria. Proteinuria was associated with the presence of graft glomerular pathology and the use of sirolimus. Eighty percent of patients with proteinuria >1500 mg/day had glomerular pathology on biopsy. However, lower levels of proteinuria were not associated with specific pathologies at 1 year. Compared to no sirolimus, sirolimus use was associated with higher prevalence of proteinuria (40% vs. 76%, p < 0.0001) and higher protein excretion (378 + 997 vs. 955 + 1986 mg/day, p < 0.0001). Proteinuria was associated with reduced graft survival (HR = 1.40, p = 0.001) independent of other risk factors including, glomerular pathology, graft function, recipient age and acute rejection. The predominant pathology in lost allografts (n = 57) was glomerular, particularly in patients with 1-year proteinuria >500. Thus, proteinuria, usually at low levels (<500 mg/day), is present in 45% of recipients at 1 year. However, and even low levels of proteinuria relate to poor graft survival. Proteinuria and glomerular pathology relate independently to survival.

Decreased incidence of acute rejection in adolescent kidney transplant recipients using antithymocyte induction and triple immunosuppression

BACKGROUND

Acute rejection is a frequent event in pediatric renal transplantation; it can diminish allograft function and affect long-term outcome. Recent data from the North American Pediatric Renal Transplant Cooperative Study indicates that the rate of acute rejection remains high despite current immunosuppressive regimens.

METHODS

In this retrospective series, we examined 37 pediatric renal transplant recipients who received induction doses of antithymocyte globulin combined with maintenance immunotherapy using tacrolimus, mycophenolate mofetil, and prednisone. The postoperative course was reviewed for initial and total hospital stay, number of rehospitalizations, evidence of posttransplant complications, graft fibrosis, and overall patient and graft survival.

RESULTS

Three episodes of acute rejection (8.1%) were recorded in the first year posttransplant. The median initial hospital stay for patients receiving a kidney transplant was 8 days. Patient and graft survival were 100% and 91.9% at 1 year, respectively. The incidence of viral infection (cytomegalovirus, BK virus, and Epstein-Barr virus) and posttransplant lymphoproliferative disease remained low. Urinary tract infection and fluid and electrolyte complications were the main causes of posttransplant hospitalization.

CONCLUSIONS

We conclude that induction with antithymocyte globulin and maintenance immunosuppression with tacrolimus, mycophenolate, and prednisone should be considered a valuable tool in the management of children undergoing renal transplantation.

What can be learned using microarrays?

Whole-genome microarrays identify large numbers of gene expression changes that appear specifically related to disease states such as antineutrophil cytoplasmic autoantibody (ANCA) and systemic lupus erythematosus. Although understanding this enormous volume of esoteric data is difficult, a few basic concepts regarding microarray studies can significantly improve the general reader's comprehension.

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.

Molecular evidence of injury and inflammation in normal and fibrotic renal allografts one year posttransplant

INTRODUCTION

Factors contributing to kidney transplant fibrosis remain incompletely understood, particularly in the absence of acute complications.

METHODS

Baseline and 1-year surveillance biopsies from 15 uncomplicated living donor kidney transplants were subjected to microarray and quantitative reverse transcription polymerase chain reaction (qRT-PCR) analyses to examine changes in gene expression patterns over time. Biopsy pairs were purposefully selected from allografts with no history of acute complications and were divided into those that were histologically normal (n=7) and those that had developed subclinical interstitial fibrosis (n=8) at 1 year.

RESULTS

Compared with the paired baseline specimens, expression levels of 3578 probesets were found altered in all the 1-year biopsies studied. A large proportion of the up-regulated genes in this transplant-associated profile were functionally linked with inflammation, immunity, or response to injury. These included components of inflammation-related signaling pathways (integrin, interferon, and Toll-like receptor) as well as individual mediators of inflammatory and immune responses. An additional 2884 probesets demonstrated altered expression in fibrotic grafts only at 1 year. The gene products in this fibrosis-associated profile also were predominantly linked with inflammation and immune function, suggesting exaggerated inflammatory activity within the fibrotic grafts. qRT-PCR analyses confirmed the predicted expression patterns for selected transcripts from the microarray profiles.

CONCLUSIONS

Transcriptional profiles of histologically normal living donor renal allografts indicate that there is ongoing injury response and inflammation at 1 year compared to the immediate posttransplant period. Subclinical development of interstitial fibrosis during the first posttransplant year is associated with additional up-regulation of inflammation-related genes.

The Effect of Antithymocyte Globulin on Anti–Human Leukocyte Antigen Antibody Detection Assays

BACKGROUND

We evaluated the effect of antithymocyte globulin (ATG) on anti-human leukocyte antigen (HLA) antibody assays.

METHODS

We tested sera from six in vivo ATG-treated kidney transplant patients after measuring serum concentrations, as well as six nonsensitized sera with ATG added in vitro. T- and B-cell complement-dependent cytotoxicity (CDC), flow cytometric (FXM), and solid-phase HLA class I and II assays based on antigen-coated microspheres and enzyme-linked immunosorbent assay (ELISA) were studied. Sera were then retested after treatment to remove ATG.

RESULTS

We found that ATG affects test results differently depending on whether sera is obtained from in vivo treated patients or added in vitro. In vitro treated sera produced ATG concentration-dependent positive results for T/B CDC, FXM, and flow bead testing for HLA I/II, while the ELISA-based assay was unaffected. In vivo treated sera from ATG-treated patients produced positive test results for T CDC and T/B FXM, while the B-cell CDC crossmatch remained negative. Solid phase assays were minimally affected using in vivo treated sera. After ATG extraction, all tests became negative.

CONCLUSION

We conclude that ATG produces positive results in anti-HLA antibody testing, and treatment to remove ATG abolishes this effect. This treatment allows ATG-treated patients to be monitored for anti-HLA antibodies.

The rationale for the new deceased donor pancreas allocation schema

BACKGROUND

To ensure the continued success of whole organ pancreas and islet transplantation, deceased donor pancreas allocation policy must continue to evolve.

METHODS

To assess the existing system, the Organ Procurement and Transplantation Network (OPTN)/United Network for Organ Sharing Kidney and Pancreas Transplant Committee retrospectively analyzed the disposition and outcomes of deceased donor pancreata in the United States between January 1, 2000 and December 31, 2003.

RESULTS

During the time period studied, consent was obtained but the pancreas was not recovered in 48% (11,820) of organ donors. The most common reasons given for nonrecovery were poor quality of the pancreas and difficulty in placement. Of whole organ pancreata that were transplanted, 90% were from donors with a body mass index (BMI) <or=30 kg/m and age <or=50 years. Pancreata from older and more obese donors were used more often for islet transplantation or research. For simultaneous pancreas-kidney transplants, the 1- and 3-year pancreas graft survival was lower when the donor was age >50 years (P=0.04), and there were trends toward lower graft survival with donor BMI >30 (P=0.06) and increasing cold-ischemia time.

CONCLUSIONS

Based on these data, the OPTN adopted a new allocation algorithm in which pancreata from donors >30 kg/m or >50 years of age are, unless accepted for a local whole organ pancreas transplant candidate, preferentially allocated for islet transplantation. These data also suggest that many good quality pancreata are not procured, emphasizing the need for improved communication and cooperation between organ procurement organizations and pancreas and islet transplant programs.

Recurrence of ANCA-associated vasculitis following renal transplantation in the modern era of immunosupression

Progressive glomerulonephritis and attendant end-stage renal disease (ESRD) result from antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis. The optimum time of kidney transplantation in patients with ESRD due to ANCA-associated vasculitis (AAV) and the risk of renal or nonrenal recurrence of vasculitis after transplantation are unknown. To answer some of these questions, we followed 35 transplant recipients with diagnoses of microscopic polyangiitis (20 patients) and Wegener's granulomatosis (15 patients). The median time from diagnosis to transplantation was 25 months with all patients being in clinical remission. Fifteen patients were ANCA-positive at time of the transplant with 13 preemptive transplants. The most common immunosuppressive strategy included antibody induction, corticosteroid, mycophenolate mofetil, and tacrolimus with acute rejection occurring in eight cases. Overall and death-censored graft survivals were 94 and 100%, respectively, 5 years post-transplantation. Nonrenal relapse occurred in three patients with a satisfactory response to treatment. No clear risk factor to relapse emerged and no detrimental effect to renal function was found. We conclude that transplantation should be considered as the treatment of choice for ESRD due to AAV. Potent antirejection regimes are well tolerated in these patients, are associated with a low risk of recurrence and an absence of AAV-related graft dysfunction.

Diurnal blood pressure changes one year after kidney transplantation: relationship to allograft function, histology, and resistive index

Loss of circadian BP change has been linked to target organ damage and accelerated kidney function loss in hypertensive patients with and without chronic kidney disease. Ambulatory BP-derived data from 119 consecutive kidney transplant recipients who presented for the first annual evaluation were examined in relation to allograft function, histology, and ultrasound findings. A total of 101 (85%) patients were receiving antihypertensive medications (median 2), and 85 (71%) achieved target awake average systolic BP (SBP) of <135 mmHg. A day-night change in SBP by 10% or more (dippers) was detected in 29 (24%). Dipping status was associated with younger recipient age, lack of diabetes, low chronic vascular score, and low resistive index. Nondippers and reverse dippers had lower GFR compared with dippers (P = 0.04). For every 10% nocturnal drop in SBP, GFR increased by 4.6 ml/min per 1.73 m(2) (R = 0.3, P = 0.003). Nondippers and reverse dippers were equally common in recipients with normal histology and in those with pathologic findings on surveillance biopsy. On multivariate analysis, percentage of nocturnal fall in SBP and elevated resistive index independently correlated with GFR. This study indicates that lack of nocturnal fall in SBP is related to poor allograft function, high chronic vascular score, and high resistive index irrespective of allograft fibrosis. Further studies are needed to determine whether restoration of normal BP pattern will confer better allograft outcome.

Polyomavirus-associated nephropathy risk in kidney transplants: the influence of recipient age and donor gender

Polyomavirus-associated nephropathy (PVAN) is a frequent cause of kidney transplant failure. We determined the risk factors for biopsy-proven PVAN among 1027 recent kidney transplant recipients by univariate and multivariate analyses. The rate of PVAN was determined over an univariate and multivariate analysis over an average of 30 months of follow-up of patients receiving predominantly living donor grafts with antibody induction and sequential surveillance biopsies to detect subclinical graft disease. Seventy-four transplant recipients were diagnosed with PVAN with the finding made on surveillance biopsy in 40 patients. These 40 cases did not differ from the 34 non-surveillance cases with respect to baseline clinical characteristics or initial histological features. Older recipient age and female donor gender were independent risks associated with PVAN. Factors not linked to PVAN risk included the use and type of induction agent, use of tacrolimus vs sirolimus, the number of human lympocyte antigen (HLA) mismatches, or the frequency of acute rejection. We conclude that PVAN preferentially affects older age patients and allografts from female donors but is unrelated to immunological risk, choice of immunosuppression, or rejection history.

Assessment of changes in kidney allograft function using creatinine-based estimates of glomerular filtration rate

These analyses assessed whether creatinine based estimates of glomerular filtration rate (eGFR) accurately represent (1) graft function at different times post-transplant and (2) changes in function over time. These analyses compared iothalamate GFR to eGFR in 684 kidney allograft recipients. Changes in graft function over time (GFR slope) were measured in 360 of 459 recipients (78%) who were followed for at least 3 years. Ninety-five percent of the patients were Caucasians and 72% received kidneys from living donors. All eGFR calculations correlated significantly with GFR at all time points. However, eGFR were less precise and less accurate during the first-year post-transplant than thereafter. The average rate of GFR change (slope) was -2.93 +/- 11.3%/year (-1.06 +/- 5.3 mL/min/1.73 m(2)/year). Fifty-four percent of patients had stable or positive GFR slopes. The GFR and eGFR slopes were highly correlated. However, eGFR slope, particularly when calculated by MDRD, significantly underestimated the number of patients with declining graft function. For example, 165 out of 360 patients (46%) lost GFR faster than -1 mL/min/1.73 m(2)/year. eMDRD identified only 83 of these patients (50%) while the eMayo formula identified 134 (81%). In conclusion, eGFR correlate with GFR but they have relatively low precision and accuracy particularly early post-transplant. eGFR slopes underestimate graft functional loss although some formulas are significantly better than others for this calculation.

Kidney transplantation in patients with antibodies against donor HLA class II

The immunologic risk associated with donor-specific antibodies (DSA) against Class II human leukocyte antigens (HLA) in kidney transplant (KTx) recipients is unclear. The aim of this study was to determine the outcome of KTx when DSA was detected only against HLA Class II. To isolate the impact of anti-Class II DSA, we retrospectively analyzed 12 KTx recipients who at baseline had a positive B-cell flow cytometric crossmatch (FXM) and a negative T-cell FXM. Using alloantibody specification analysis, 58.3% (7/12) had DSA against donor Class II and 41.7% had no demonstrable DSA. Biopsy-proven AMR occurred in 57% (4/7) in the Class II(+) group and 0% in the Class II(-) group (p > 0.05). Peritubular capillaries stained positive for C4d in 86% (6/7) of the Class II(+) patients and in 40% (2/5) of the Class II(-) patients (p > 0.05). One patient in the Class II(+) group lost their graft at 3 months to accelerated transplant glomerulopathy, while all other grafts were functioning 3-37 months posttransplant despite the persistence of anti-Class II DSA. We conclude that KTx recipients with clearly defined anti-Class II DSA are at risk for humoral rejection suggesting that desensitization and/or close posttransplant monitoring may be needed to prevent AMR.

A meta-analysis of kidney microarray datasets: investigation of cytokine gene detection and correlation with rt-PCR and detection thresholds

Background

Microarrays provide a means to simultaneously examine the gene expression of the entire transcriptome in a single sample. Many studies have highlighted the need for novel software and statistical approaches to assess the measured gene expression. Less attention has been directed toward whether genes considered undetectable by microarray can be detected by other strategies or whether these genes can provide accurate gene expression determinations. In the kidney this is a concern for genes such as cytokines which dramatically influence the immune response but are often considered low abundance genes produced by a small number of cells.

Results

Using both publicly available and our own microarray datasets we analyzed the detection p-value and detection call values for 81 human kidney samples run on the U133A or U133Plus2.0 Affymetrix microarrays (Affymetrix, Santa Clara, CA). For the cytokine genes, the frequency of detection in each sample group (normal, transplant and renal cell carcinoma) was examined and revealed that a majority of cytokine related genes are not detectable in human kidney by microarray. Using a subset of 29 Mayo transplant samples, a group of seven transplant-related cytokines and eight non-cytokine genes were evaluated by real-time PCR (rt-PCR). For these 15 genes we compared the impact of decreasing microarray detection frequency with the changes in gene expression observed by both microarray and rt-PCR. We found that as microarray detection frequency decreased the correlation between microarray and rt-PCR data also decreased.

Conclusion

We conclude that, when analyzing microarray data from human kidney samples, genes generally expressed at low abundance (i.e. cytokines) should be evaluated with more sensitive approaches such as rt-PCR. In addition, our data suggest that the use of detection frequency cutoffs for inclusion or exclusion of microarray data may be appropriate when comparing microarray and rt-PCR gene expression data and p-value calculations.

Protocol biopsies in renal transplantation: insights into patient management and pathogenesis

A 1-day symposium on the application of protocol biopsies in renal transplantation was held in Boston, 21 July 2006. Representatives from centers with extensive experience in the use of protocol biopsies for routine patient care and research reported results on the pathological findings and their value in patient management. The consensus was that protocol biopsies, in experienced hands, are a safe and valuable means of detecting subclinical disease that can benefit from modification of therapy. Furthermore, molecular studies reveal evidence of activity or progression not readily appreciated by histological techniques. Wider application is expected in multicenter clinical trials to predict and validate outcomes. The principal barrier to wider use of protocol biopsies is knowledge of the benefits of intervention.