Faculty Bibliography

OBJECTIVE: Animal organs engineered to be chimeric for human cells could contribute significantly to the field of transplantation, including studies of human-specific diseases such as hepatitis-C, as treatment for in-born errors of metabolism, and for development of a renewable source of transplantable organs via modified xenotransplantation. We sought to use human embryoid body-derived stem cells (EBDs) to populate livers in animals for applications in transplant surgery. METHODS: SCID mice and rats underwent liver injury with carbon tetrachloride exposure or partial hepatectomy. Animals received intrasplenic injection of fluorescently labeled human stem cells. Spleen and liver were assessed at 2, 7, 15, and 30 days after transplant for the presence of EBDs and markers of human hepatocyte differentiation. RESULTS: EBDs migrate to and engraft in animal liver after splenic injection under conditions of hepatic injury. EBDs are detectable at 2 days and are in abundance at 1 week after transplant. EBDs persist in rodent liver long term (>1 month), and once engrafted differentiate into functional human hepatocytes as assessed by production of human alpha-feto-protein (AFP) and human albumin. CONCLUSIONS: We developed a novel animal model in which hepatic injury and stem cell transplantation lead to the generation of humanized animal organs. We are currently using our model to study recurrent hepatitis-C after liver transplantation, and as an alternative to whole organ transplantation for treatment of in-born errors of metabolism.

BACKGROUND: Kidney paired donation (KPD) offers the best transplant option for patients with incompatible live kidney donors. Although studies suggest substantial expansion of the donor pool if fully used, few patients in the United States have undergone KPD. METHODS: We analyzed the 209 KPD and 89 list paired donation (LPD) transplants reported to United Network for Organ Sharing to better understand access to these modalities, clinical outcomes, and areas of potential expansion. RESULTS: Although many centers offer KPD/LPD, most centers have performed no more than a handful of transplants. As expected, outcomes with KPD/LPD were equivalent to direct donation matched controls. In analyzing current practice, we identified two limitations to KPD in its current use. First, KPD is likely limited now by benefiting mostly patients who are easy to identify and match (such as A donors with B recipients or B donors with A recipients). Second, although some expansion of local KPD availability has reduced travel requirements for patients in those areas, significant room for growth remains. CONCLUSIONS: Our results suggest that full utilization of KPD would encourage registration of and improve matching for patients who are more difficult to identify and match (such as highly sensitized recipients). Furthermore, expansion of KPD would likely reduce travel requirements and thereby improve access to this treatment modality.

PURPOSE OF REVIEW: Neither the concept nor the formal application of unacceptable antigens is new. However, identification of unacceptable antigens is now sufficiently accurate to be used as a virtual crossmatch, which can both prevent the unnecessary shipment of organs and increase the access for sensitized patients. RECENT FINDINGS: Desensitization protocols and an increasing array of cell-depleting agents can overcome the immunological barriers to transplantation for some patients, reducing the risk of graft rejection to an acceptable level. Increasingly sensitive and specific assays for identifying HLA antigens and antibodies are providing more accurate definition of incompatibilities. Additionally, tests of various biomarkers may permit characterization of responder types. SUMMARY: The definition of unacceptable antigens is determined by the clinical protocols and the physiological and immunological characteristics of the recipient and donor. These data should be integrated to maximize the opportunity for transplantation. The development of additional tests to assess a patient's capacity for recognizing and responding to a transplant will improve the identification of incompatible donor-recipient pairs.

When considering advocacy of split-liver transplantation, it is important to understand whether comparable outcomes can be achieved. The goal of this study was to identify donor and transplant characteristics predictive of comparable outcomes by risk factor analysis. Using the United Network for Organ Sharing/ Organ Procurement and Transplantation Network data base between January 1996 and May 2006, first time adult/child split cases (568 adults, 508 children) were examined. In multivariate analysis, recipient medical condition (hospitalization), status 1 assignment, ABO incompatibility, donor age (>40 years), donor body weight (< or = 40 kg), calculated whole graft volume to recipient body weight ratio (cGRWR < or = 1.5%) and no sharing between centers were significant risk factors in adult recipients. Recipient diagnosis of tumor, dialysis prior to transplant, recipient body weight (< or = 6 kg), donor age (>30 years), donor history of cardiac arrest after declaration of death and cold ischemia time (CIT > 6 h) increased the risk of graft failure in pediatric recipients. The livers from young donors showed comparable outcomes to whole deceased liver transplantation (LT) when other transplant-related risk factors were minimized in adult recipients. Reducing CIT is important to obtain comparable outcomes to living donor LT in pediatric recipients.

Use of live non-directed donors (LNDDs), or altruistic donors, has increased significantly over the past decade and has fueled debate regarding the ethics and allocation of this new source of live donor kidneys. Three allocation philosophies are currently in use, including donor-centric, recipient-centric and socio-centric models, and our group has also advocated the use of LNDDs in paired donation. However, no universally accepted allocation policy exists, nor does national oversight. To determine allocation patterns resulting from current practice models, we analyzed the 372 LNDD kidney transplants performed in the United States since 1998. Most LNDD transplants occurred at a minority of centers, with only five centers performing over 10, and over 28% of LNDDs traveled out-of-state to donate. Furthermore, a center's use of LNDD kidneys did not correlate with that center's organ shortage. Finally, African Americans were significantly under-represented among recipients who were allocated LNDD kidneys, even after accounting for differences in the racial makeup of the waiting list representing centers using LNDD kidneys. These disparities suggest the need for continued monitoring and discussion of LNDD at a national level. If non-directed donation continues to rise at its current rate, a national allocation policy may be reasonable.

BACKGROUND: When the United Network for Organ Sharing changed its algorithm for liver allocation to the model for end-stage liver disease (MELD) system in 2002, highest priority shifted to patients with renal insufficiency as a major component of their end-stage liver disease. An unintended consequence of the new system was a rapid increase in the number of simultaneous liver-kidney transplants (SLK) being performed yearly. METHODS: Adult recipients of deceased donor liver transplants (LT, n=19,137), kidney transplants (n=33,712), and SLK transplants (n=1,032) between 1987 and 2006 were evaluated based on United Network for Organ Sharing data. Recipients were stratified by donor subgroup, MELD score, pre- versus post-MELD era, and length of time on dialysis. Matched-control analyses were performed, and graft and patient survival were analyzed by Kaplan-Meier and Cox proportional hazards analyses. RESULTS: MELD era outcomes demonstrate a decline in patient survival after SLK. Using matched-control analysis, we are unable to demonstrate a benefit in the SLK cohort compared with LT, despite the fact that higher quality allografts are being used for SLK. Subgroup analysis of the SLK cohort did demonstrate an increase in overall 1-year patient and liver graft survival only in those patients on long-term dialysis (> or =3 months) compared with LT (84.5% vs. 70.8%, P=0.008; hazards ratio 0.57 [95% CI 0.34, 0.95], P=0.03). CONCLUSION: These findings suggest that SLK may be overused in the MELD era and that current prioritization of kidney grafts to those liver failure patients results in wasting of limited resources.

Steroid use after liver transplantation (LT) has been associated with diabetes, hypertension, hyperlipidemia, obesity, and hepatitis C (HCV) recurrence. We performed meta-analysis and meta-regression of 30 publications representing 19 randomized trials that compared steroid-free with steroid-based immunosuppression (IS). There were no differences in death, graft loss, and infection. Steroid-free recipients demonstrated a trend toward reduced hypertension [relative risk (RR) 0.84, P = 0.08], and statistically significant decreases in cholesterol (standard mean difference -0.41, P < 0.001) and cytomegalovirus (RR 0.52, P = 0.001). In studies where steroids were replaced by another IS agent, the risks of diabetes (RR 0.29, P < 0.001), rejection (RR 0.68, P = 0.03), and severe rejection (RR 0.37, P = 0.001) were markedly lower in steroid-free arms. In studies in which steroids were not replaced, rejection rates were higher in steroid-free arms (RR 1.31, P = 0.02) and reduction of diabetes was attenuated (RR 0.74, P = 0.2). HCV recurrence was lower with steroid avoidance and, although no individual trial reached statistical significance, meta-analysis demonstrated this important effect (RR 0.90, P = 0.03). However, we emphasize the heterogeneity of trials performed to date and, as such, do not recommend basing clinical guidelines on our conclusions. We believe that a large, multicenter trial will better define the role of steroid-free regimens in LT.

Renal ischemia was induced in the rat by constriction of the renal artery for 45 min, and the ability of the ATP-sensitive K(+) (K(ATP)) channel opener diazoxide (DZ) to ameliorate renal ischemia-reperfusion (I/R) injury was evaluated. In this model, blood urea nitrogen and creatinine were elevated 2 days after I/R injury but returned closer to normal levels by 7 days after reperfusion. Histological staining for reactive oxygen species (ROS) was clearly positive and oxidized DNA, detected by the presence of the stable adduct 8-hydroxy-2'-deoxyguanosine, was clearly present in the cytoplasm of tubular cells after 1 h of reperfusion and declined 7 days after reperfusion. This finding was confirmed by ELISA, which detected 8-hydroxy-2'-deoxyguanosine in the mitochondrial fraction of kidney homogenates. Despite evidence of improved function measured by blood urea nitrogen and creatinine 7 days after reperfusion, the early changes in tubules were alarming. Mitochondrial DNA showed the common deletion, and the number of TdT-mediated dUTP nick-end label-positive tubular cells increased. Activation of caspase-3 continued, and abnormal levels of ROS were found in the mitochondrial fraction of cellular homogenates. Treatment with DZ before ischemia reduced or prevented the acute and subacute deleterious effects associated with renal I/R injury. We conclude that excess production of ROS by mitochondria on reperfusion is a major upstream event in renal reperfusion injury and that DZ functioned by preventing ROS accumulation in the mitochondria after I/R injury, thereby reducing oxidative stress as measured by the presence of oxidized mitochondrial DNA and features of apoptosis.

Although prolonged cold ischemia time (PCIT) is generally associated with worse outcomes following liver transplantation, evidence suggests that some recipients and some donors might be more sensitive to PCIT than others. The purpose of this study was to identify factors that predict a higher risk of graft loss after a transplant with PCIT when compared with a similar transplant with average CIT (ACIT). 14 637 recipients reported to United Network for Organ Sharing (UNOS) in the model for end-stage liver disease (MELD) era were studied by interaction term analysis in proportional hazards models. Recipient diabetes, obesity and donor African American (AA) ethnicity were found to significantly amplify the adverse effects of PCIT. Graft loss was 1.85-fold higher in diabetic or obese PCIT recipients compared with diabetic or obese ACIT recipients, (vs. 1.17 for the same comparison in non-diabetic non-obese recipients). Similarly, graft loss was 1.80-fold higher in AA PCIT donors compared with AA ACIT donors, (vs. 1.31 for the same comparison in non-AA donors). Other factors may also exist, but current clinical practices might already mitigate the risks from those factors. As such, we recommend expanding clinical practice to include our findings, but not abandoning current judgment based on factors already perceived to amplify the adverse effects of PCIT.