Improved Allograft Survival Research Articles

Islet Allograft Rejection Is Independent of Toll-Like Receptor Signaling in Mice

Islet transplantation is a promising therapy for type 1 diabetes; however, most islet grafts fail within 5 years. Innate immunity has been suggested to play a role in islet allograft rejection, potentially mediated by toll-like receptors (TLRs), a class of innate immune receptors. Lack of TLR4, in particular, has been reported to improve allograft survival. Therefore, we hypothesized that TLRs may be involved in islet allograft rejection, and that deletion of TLR4 may improve islet graft survival. Islets were isolated from C57BL/10ScNJ (Tlr4(-/-)) and C57BL/10 (wild-type [WT]) animals and transplanted into Balb/cJ recipients with streptozotocin-induced diabetes. Blood glucose levels were used to determine graft viability and immunostaining to assess graft morphology and immune cell infiltration. The roles of the TLR4 adaptor molecules MyD88 and TLR adaptor molecule 1 (Ticam-1) were assessed using islets isolated from mice lacking MyD88 (MyD88(-/-)), Ticam-1 (Ticam-1(-/-)), or the combined double knockout (MyD88(-/-)/Ticam-1(-/-)). Contrary to our hypothesis, Tlr4(-/-) and WT islet allografts had similar failure rates; grafts failed at 23.2+/-1.2 and 24.5+/-1.5 days posttransplant, respectively (P=NS). Syngeneic grafts of Tlr4(-/-) and WT islets maintained normoglycemia for up to 10 weeks posttransplant, indicating that failure of Tlr4(-/-) islet allografts could not be attributed to an intrinsic defect in Tlr4(-/-) islets. Similarly, islet allotransplants from MyD88(-/-), Ticam-1(-/-), and MyD88(-/-)/Ticam-1(-/-) donors did not have improved allograft survival compared with WT controls. These findings indicate that islet allograft rejection in mice is independent of TLR4 and the TLR adaptor molecules MyD88 and Ticam-1, speaking against an essential role for TLR signaling in islet allograft rejection.

The relationship of donor source and age on short‐ and long‐term allograft survival in pediatric renal transplantation

Limited pediatric data on allograft survival from advanced aged kidney donors exist. To determine the influence of donor source and age on allograft survival in pediatric renal transplant recipients, we analyzed the OPTN database. Allograft survival for 7291 pediatric renal transplants was evaluated. Up to five yr post-transplantation, graft survival was higher for LD vs. DD recipients. At seven yr, allograft survival was 71% in 18-54 yr-old LD recipients, 59.1% in >or=55 yr-old LD, and 45.1% in >or=50 yr-old DD recipients. An approximate 35% improvement in allograft survival in 18-54 yr-old LD recipients was observed. Multivariate results showed that recipients of LD 35-49 (aRR 0.66, 95% CI 0.55-0.80) and LD 50-54 (aRR 0.65, 95% CI 0.45-0.94) have a graft survival advantage over the ideal DD. In LD >or=55 yr, no improvement in graft survival was observed when compared with the 18-34 yr-old DD. In summary, we observed in a pediatric population, <55 yr-old LD kidneys afford improved long-term allograft survival when compared with DD kidney recipients. Increasing awareness of the long-term graft survival advantage for children receiving an LD kidney, even from older donors, should be a priority.

Trough Tacrolimus Concentrations in the First Week After Kidney Transplantation Are Related to Acute Rejection

There is evidence showing the importance of reaching immunosuppressant target concentrations as soon as possible. The aim of this study was to evaluate the relationship between tacrolimus trough concentrations within the first week after transplantation and the rate of acute rejection. In this descriptive-analytic study, we included 57 renal transplant patients receiving tacrolimus as the primary immunosuppressive drug. After univariate analysis, donor age, duration of hospital stay, and creatinine clearance (third month) showed significant differences between rejecters and nonrejecters. In addition, mean tacrolimus trough concentrations on day 5, day 7, mean of days 1-7, and mean of days 5-7 were found to be significantly lower in rejecters (P = 0.009, P = 0.012, P = 0.006, and P = 0.035, respectively). Receiver operating characteristic curve analysis with tacrolimus trough concentrations measured on days 5 and 7 was able to discriminate between patients with and without acute rejection (P = 0.028 and P = 0.048 after Bonferroni correction). The tacrolimus trough concentration with the best sensitivity-specificity balance was 9.3 ng/mL on day 5 and 8.7 ng/mL on day 7. In the Kaplan-Meier analysis, patients with tacrolimus trough concentrations below 9.3 mg/mL on day 5 showed a lower survival time without acute rejection (P = 0.048 after correction) in comparison with patients with tacrolimus trough concentrations above this concentration. After logistic regression, we obtained a model relating rejection with sex, donor age, and tacrolimus trough concentrations on day 5 (P = 0.004). No significant relationship between tacrolimus trough concentrations and delta creatinine clearance from week 1 to month 3 was obtained. These results confirm that tacrolimus trough concentrations during the first week are an important predictor of acute rejection. Therefore, it is critical to reach target blood concentrations of tacrolimus as soon as possible to improve allograft survival.

Transferable Cardiac Allograft Acceptance Induced by Transfusion of Donor B Cells With Impaired Inducible Costimulator/B7h Allorecognition

Objective Donor-specific transfusion (DST) of leukocytes with an impaired costimulatory signal has been proven to be an effective way to improve allograft survival. Inducible costimulator (ICOS) has been shown to play a crucial role in acute and chronic allograft rejection. To test the role of ICOS signaling during DST, we employed ICOS-Fc-targeted B cells as antigen of DST to challenge the allogeneic engraftment in vivo. Materials and Methods A murine cardiac allograft model was employed using BALB/c donors and C57BL/6 recipients, while various transfusions were performed according to treatment protocols. Results Allograft survival was prolonged by infusion of ICOS-Fc-targeted B cells; however, allograft acceptance could not be achieved unless additional systemic injections of ICOS-Fc were given. Adoptive transfer of splenic CD4 + but not CD4 +CD25 − subsets from long-term allograft survival (LTAS) mice to lightly irradiated naive recipients resulted in subsequent BALB/c allograft acceptance without additional immunosuppression. Conclusions ICOS/B7h signaling during direct allorecognition played an important role in prolonging allograft survival, and an allograft acceptance can be established by DST with complete blockade of ICOS/B7h in both direct and indirect allorecognition. Interestingly, this allograft acceptance was transferable and maintained at least partly by the immune regulation of CD4 +CD25 + T cells. These findings may help to design a potential therapeutic treatment to prevent allograft rejection by DST in combination with ICOS/B7h blockade.

Reducing De Novo Donor-Specific Antibody Levels during Acute Rejection Diminishes Renal Allograft Loss

The effect of de novo DSA detected at the time of acute cellular rejection (ACR) and the response of DSA levels to rejection therapy on renal allograft survival were analyzed. Kidney transplant patients with acute rejection underwent DSA testing at rejection diagnosis with DSA levels quantified using Luminex single-antigen beads. Fifty-two patients experienced acute rejection with 16 (31%) testing positive for de novo DSA. Median follow-up was 27.0 +/- 17.4 months postacute rejection. Univariate analysis of factors influencing allograft survival demonstrated significance for African American race, DGF, cytotoxic PRA >20% (current) and/or >50% (peak), de novo DSA, C4d and repeat transplantation. Multivariate analysis showed only de novo DSA (6.6-fold increased allograft loss risk, p = 0.017) to be significant. Four-year allograft survival was higher with ACR (without DSA) (100%) than mixed acute rejection (ACR with DSA/C4d) (65%) or antibody-mediated rejection (35%) (p < 0.001). Patients with >50% reduction in DSA within 14 days experienced higher allograft survival (p = 0.039). De novo DSAs detected at rejection are associated with reduced allograft survival, but prompt DSA reduction was associated with improved allograft survival. DSA should be considered a potential new end point for rejection therapy.

Association of CCR5-59029 A/G and CCR2-V64I variants with renal allograft survival.

Despite advances in the medical care of renal transplant recipients which have led to an improvement in allograft survival, renal allograft rejection is still a major obstacle to successful organ transplantation. Understanding the mechanisms contributing to allograft rejection will be of great importance for the development of efficient antirejection strategies. The aim of current investigation was to study the impact of polymorphisms of CCR5Delta32, CCR5- 59029 A/G and CCR2-V64I on renal allograft survival. Using PCR and PCR-RFLP methods in 84 renal transplant recipients, the influence of CCR5Delta32, CCR5- 59029 A/G and CCR2-V64I polymorphisms on renal allograft survival in two rejector and non-rejector groups were examined. Rejector group was defined as having rejection before 1 year and non-rejector group had stable graft function at least for 5 years. Significant reductions were found in the risk of renal transplant rejection in recipients possessing the CCR2-64I (A) allele (p=0.03) or 59029-A allele (p=0.03) compared to non-rejector group. There were no significant differences in the frequency of CCR5Delta32 polymorphism in rejector group compared to non-rejector group (p>0.05). It was possible to conclude that the chemokine receptors CCR2-V64I (A) and CCR5- 59029 A alleles may influence renal allograft survival.

Income-Related Disparities in Kidney Transplant Graft Failures Are Eliminated by Medicare’s Immunosuppression Coverage

Beginning January 1, 2000, Medicare extended coverage of immunosuppression medications from 3 years to lifetime based on age >65 years or disability. Using United States Renal Data System (USRDS) data for Medicare-insured recipients of kidney transplants between July 1995 and December 2000, we identified four cohorts of Medicare-insured kidney transplant recipients. Patients in cohort 1 were individuals who were both eligible and received lifetime coverage. Patients in cohort 2 would have been eligible, but their 3-year coverage expired before lifetime coverage was available. Patients in cohort 3 were ineligible for lifetime coverage because of youth or lack of disability. Patients in cohort 4 were transplanted between 1995 and 1996 and were ineligible for lifetime coverage. Incomes were categorized by ZIP code median household income from census data. Lifetime extension of Medicare immunosuppression was associated with improved allograft survival among low-income transplant recipients in the sense that the previously existing income-related disparities in graft survival in cohort 2 were not apparent in cohort 1. Ineligible individuals served as a control group; the income-related disparities in graft survival observed in the early cohort 4 persisted in more recent cohort 3. Multivariate proportional hazards models confirmed these findings. Future work should evaluate the cost effectiveness of these coverage increases, as well as that of benefits extensions to broader patient groups.

KIM-1 expression in kidney allograft biopsies: Improving the gold standard

Long-term outcomes of kidney allografts have shown only marginal improvement over the last three decades, despite the remarkable improvement in acute rejection and one-year graft survival. Novel biomarkers of tubular injury may prevent irreversible damage to the tubulointerstitial compartment and improve allograft survival.

The Role of Angiogenic and Wound Repair Factors During CMV-Accelerated Transplant Vascular Sclerosis in Rat Cardiac Transplants

Human cytomegalovirus (HCMV) accelerates transplant vascular sclerosis (TVS), a consequence of angiogenesis (AG) and wound repair (WR). While HCMV can be localized to TVS lesions, the low number of infected cells suggests a global effect on target tissues. We used microarray analysis followed by real-time-polymerase chain reaction (RT-PCR) in an RCMV-accelerated TVS rat cardiac transplant model to determine whether CMV activates host WR and AG factors. Dysregulated cellular genes in allografts from RCMV-infected recipients were compared to those from uninfected recipients and native hearts. We demonstrated that RCMV upregulates the genes involved in WR and AG, which was highest during the critical time of TVS acceleration (21-28 days). Using a standard in vitro AG assay, virus and serum-free supernatants collected at 48 h postinfection significantly induced endothelial cell (EC) migration, branching and tubule formation compared to supernatants from mock-infected cells. Supernatants from ultraviolet (UV)-inactivated RCMV-infected cells failed to induce AG, indicating that virus replication is required. Upregulation of WR and AG genes occurs during the critical period of CMV-accelerated TVS. Targeting these genes may prevent this process and improve allograft survival.

Long-term benefits of pancreas transplantation

Pancreas transplantation has emerged as an effective treatment for patients with diabetes mellitus, especially those with established end-stage renal disease. Surgical and immunosuppressive advances have significantly improved allograft survival. With more recipients enjoying normoglycemia for longer periods of time, the opportunity to study more closely the effects of pancreas transplantation has arisen. This review will focus on these long-term benefits. The field of pancreas transplantation has been limited by a lack of randomized, controlled trials and relatively poor graft survival rates historically, however we can still glean many important points from the existing literature. The procedure reduces mortality compared with diabetic kidney transplant recipients and waitlisted patients. Improvements in diabetic nephropathy and retinopathy have also been demonstrated. Pancreas transplantation can improve cardiovascular risk profiles, improve cardiac function and decrease cardiovascular events. Lastly, improvements in diabetic neuropathy and quality of life can result from pancreas transplantation. Pancreas transplantation remains the most effective method to establish durable normoglycemia for patients with diabetes mellitus. Well designed clinical studies to assess outcomes and adverse events will be of paramount importance in providing optimal care to patients with diabetes mellitus.

Combined Coinhibitory and Costimulatory Modulation with Anti-BTLA and CTLA4Ig Facilitates Tolerance in Murine Islet Allografts

Complex interactions between positive and negative cosignaling receptors ultimately determine the fate of the immune response. The recently identified coinhibitory receptor, B and T lymphocyte attenuator (BTLA), contributes to regulation of autoimmune and potentially alloimmune responses. We investigated the role of BTLA in a fully major histocompatibility complex-mismatched mouse islet transplant model. We report that anti-BTLA mAb (6F7) alone does not accelerate graft rejection. Rather, while CTLA4Ig alone improved allograft survival, the addition of anti-BTLA mAb to CTLA4Ig led to indefinite (>100 days) allograft survival. Immediately after treatment with anti-BTLA mAb and CTLA4Ig, islet allografts showed intact islets and insulin production despite a host cellular response, with local accumulation of Foxp3+ cells. We clearly demonstrate that combined therapy with anti-BTLA mAb and CTLA4Ig mice induced donor-specific tolerance, since mice accepted a second donor-specific islet graft without further treatment and rejected third party grafts. CTLA4Ig and anti-BTLA mAb limited the initial in vivo proliferation of CFSE-labeled allogeneic lymphocytes, and anti-BTLA mAb enhanced the proportion of PD-1 expressing T cells while depleting pathogenic BTLA+ lymphocytes. We conclude that targeting the BTLA pathway in conjunction with CTLA4Ig costimulatory blockade may be a useful strategy for promoting immunological tolerance in murine islet allografts.

Type 1 IFN Mediates Cross-Talk between Innate and Adaptive Immunity That Abrogates Transplantation Tolerance

TLR activation of innate immunity prevents the induction of transplantation tolerance and shortens skin allograft survival in mice treated with costimulation blockade. The mechanism by which TLR signaling mediates this effect has not been clear. We now report that administration of the TLR agonists LPS (TLR4) or polyinosinic:polycytidylic acid (TLR3) to mice treated with costimulation blockade prevents alloreactive CD8(+) T cell deletion, primes alloreactive CTLs, and shortens allograft survival. The TLR4- and MyD88-dependent pathways are required for LPS to shorten allograft survival, whereas polyinosinic:polycytidylic acid mediates its effects through a TLR3-independent pathway. These effects are all mediated by signaling through the type 1 IFN (IFN-alphabeta) receptor. Administration of IFN-beta recapitulates the detrimental effects of TLR agonists on transplantation tolerance. We conclude that the type 1 IFN generated as part of an innate immune response to TLR activation can in turn activate adaptive immune responses that abrogate transplantation tolerance. Blocking of type 1 IFN-dependent pathways in patients may improve allograft survival in the presence of exogenous TLR ligands.

Abstract 760: Heme Oxygenase-1 expression in Dendritic Cells determines the Outcome of Transplantation Arteriosclerosis

Introduction: Although expression of heme oxygenase-1 (HO1) attenuates transplantation arteriosclerosis, the mechanism by which HO1 exerts its protective effect remains unclear. We studied the effect of HO1-deficient vs. wildtype (WT) dendritic cells (DCs) on the T-cell priming response and outcome in a murine transplant arteriosclerosis model. Methods: At day 0 C57bl6 mice received either WT (n=6) or HO1-knockout DCs (n=6) pre-sensitized with Balb/c splenocytes lysate to accelerate the development of arteriosclerosis. At day 10 an aorta segment from Balb/c mice was transplanted into the carotid artery position of C57Bl6 mice.14 days after transplantation allografts were excised and processed for immunohistochemical analysis. Results: HO1-deficient DCs significantly increased neointimal hyperplasia as compared to WT DCs (116995 vs. 46114μm 2 P&lt;0.05) and incidence of intima formation (83 vs. 50% in WT DC). HO1 deficient DCs also increased medial thickeness (15936 vs.12034 μm 2 P&lt;0.05) and intimal VSMCs content (76 vs. 46% P&lt;0.05) and resulted in more prominent medial cell infiltration (461μm 2 vs. 232μm 2 P&lt;0.05). Although HO1 deficient and WT DCs could be detected in allografts, HO1-nullizygous DCs induced an increase in CD4+ T-cell infiltration (9.5 vs. 0.1% in WT P&lt;0.05) concomitant to a decrease of CD8+ T cell infiltration (8 vs.14%, P&lt;0.05). In line with these observations Affymetrix microarray analysis confirmed that HO1 deletion in DCs was associated with a significant downregulation of MHCII-H2A expression (associated with CD4+T-cell activation) and induction of inhibitors of MHCII expression (including IK protein) whereas MHC I expression remained unchanged. Conclusions: HO1 expression in dendritic cells increases vascular cell infiltration with a higher CD8+/CD4+ T-cell ratio by stabilizing MHCII expression in vascular allografts resulting in inhibition of neointima formation and hence improved allograft survival.

The outcome of renal transplantation among systemic lupus erythematosus patients

Clinical outcome of renal transplantation among systemic lupus erythematosus (SLE) patients remains a topic of controversy. Most of the previous reports were based upon small single-centre studies that were not always well-designed. We conducted the retrospective analysis using data from USRDS and UNOS databases. Patients were divided into five groups based on the cause of end-stage renal disease (ESRD): diabetes mellitus (DM), SLE, glomerulonephritis, hypertension and other causes. Between 1990 and 1999, 2886 renal transplantation recipients with ESRD due to SLE were identified from a total of 92 844 patients. The mean follow-up period of this study was 4.7 +/- 2.4 years. While unadjusted analysis using Kaplan-Meier curves demonstrated an association between SLE and improved allograft survival compared with DM, in multivariate analysis the SLE group had worse allograft [hazard ratio (HR) 1.09, P < 0.05] and recipient (HR 1.19, P < 0.05) survival compared with the DM group. Subgroup analysis based on the type of donor showed that SLE patients who received deceased donor allograft had worse allograft and recipient survival (HR 1.14, P = 0.002 and HR 1.30, P = 0.001, respectively) compared with non-SLE deceased donor allograft recipients. Among living allograft recipients, there were no significant differences in either allograft or recipient survival compared with non-SLE recipients. SLE as a cause of ESRD in renal transplant recipients is associated with worse allograft and recipient survival compared with DM; this association is true for the entire population and for the recipients of deceased donor (but not living donor) transplant. Deceased donor allograft recipients have worse outcomes compared with living allograft recipients.

Immunological Consequences of Apoptotic Cell Phagocytosis

Cells undergo apoptosis in development, tissue homeostasis, and disease and are subsequently cleared by professional and nonprofessional phagocytes. There is now overwhelming evidence that phagocyte function is profoundly altered following apoptotic cell uptake, with consequences for the ensuing innate and adaptive immune response. Pathogens and tumors exploit the changes in macrophage function following apoptotic cell uptake. Here, we will outline the consequences of apoptotic cell phagocytosis and illustrate how apoptotic cells could be used to manipulate the immune response for therapeutic gain.

BK Virus Nephropathy and Kidney Transplantation

Nephropathy from BK virus (BKV) infection is an evolving challenge in kidney transplant recipients. It is the consequence of modern potent immunosuppression aimed at reducing acute rejection and improving allograft survival. Untreated BKV infections lead to kidney allograft dysfunction or loss. Decreased immunosuppression is the principle treatment but predisposes to acute and chronic rejection. Screening protocols for early detection and prevention of symptomatic BKV nephropathy have improved outcomes. Although no approved antiviral drug is available, leflunomide, cidofovir, quinolones, and intravenous Ig have been used. Retransplantation after BKV nephropathy has been successful.

New insights into the pathophysiology of cyclosporine nephrotoxicity: a role of aldosterone

Cyclosporine A (CsA), a calcineurin inhibitor, has improved allograft survival in solid organ transplantation and has been increasingly applied in the management of autoimmune diseases. While marked progress has been made in patient and allograft survival rates, clinical use of CsA is often limited by its nephrotoxic effect, which can be presented as two distinct and well-characterized forms: acute and chronic nephrotoxicity. The acute form is characterized by renal vasoconstriction, induced by an imbalance of vasoactive substances release, which leads to renal dysfunction. This form is reversible. The chronic toxicity, in contrast, is characterized by the vasoconstriction plus the development of structural damage that includes arteriolopathy and tubulointerstitial fibrosis that are often not reversible. The exact mechanisms of these deleterious effects are not fully understood, but major advances have occurred over the last few years. Here we review the current literature regarding the pathogenesis and strategies that have been used to ameliorate renal injury in chronic CsA nephrotoxicity. Recent observations suggest that aldosterone plays a central role in the pathogenesis of CsA nephrotoxicity and that spironolactone could be a useful agent to prevent it. These studies and the use of mineralocorticoid receptor blockade are discussed.

Improved Renal Allograft Survival with Vitamin D Receptor Polymorphism

Background. Polymorphisms in genes, coding for proteins involved in immune response, or the pathogenesis of atherosclerosis may influence immunological and non-immunological mechanisms that lead to allograft loss. Vitamin D receptor (VDR) agonists reduce allograft rejection in animal models, and there are a number of functional polymorphisms in VDR. Methods. In all, 379 renal transplant recipients were genotyped for VDR (FokI & ApaI) polymorphisms, and the association of each genotype with renal allograft survival and acute rejection was determined. Results. There was significantly improved allograft survival for patients who were homozygous or heterozygous for the VDR FokI T allele (Hazard Ratio [HR] = 0.488, p < 0.001). Conclusion. The association of VDR FokI T allele with improved renal allograft survival is a unique observation. The finding is in keeping with data showing the prevention of chronic allograft rejection with the use of Vitamin D receptor agonists.

Induction of long-term liver allograft survival by delayed immunosuppression is dependent on interleukin-10

This study aims to investigate the potential role of endogenous interleukin (IL)-10 in long-term liver allograft survival induced by delayed immunosuppression (FK506 days 2-7). Liver transplantation was performed by using Dark Agouti and Lewis rats as donors and recipients, respectively. The delayed immunosuppression protocol induced indefinite allograft survival. A transient upregulation of plasma IL-10 levels was detected in the nontreatment and FK506 treatment groups. Macrophages were found to be one of the major sources of IL-10 produced from the liver allografts. Administration of IL-10-neutralizing antibody shortened the long-term isograft survival and FK506-induced indefinite allograft survival, particularly in the FK506 group. Damaged liver graft histology and increase of plasma alanine aminotransferase levels were detected in the groups with IL-10 antibody treatment. In an ex vivo setting, IL-10 recombinant protein augmented the expression of Foxp3, downregulated the expression of IL-2 and interferon gamma, and induced the generation of CD4(+)CD25(+)Foxp3(+) and CD8(+)CD25(+)Foxp3(+) cells, but this effect was blocked by the administration of IL-10 antibody. Finally, administration of IL-10 recombinant protein after the decline of endogenous IL-10 levels improved allograft survival, and a 100% long-term allograft survival was achieved by the combination of IL-10 with low-dose FK506. In conclusion, the delayed immunosuppression could induce long-term liver allograft survival in the presence of endogenous IL-10 produced by the tissue macrophages. Supplementary exogenous IL-10 administration combined with low-dose immunosuppressive drug may be a useful strategy to induce long-term liver allograft survival.

ABO-Incompatible Kidney Transplantation with and without Splenectomy

The letter to the editor from Dr. Mitsuhata et al. raises interesting points with regard to the role of splenectomy in ABO-incompatible (ABOI) kidney transplants. The authors contend that the classification of ABOI kidney transplant recipients as “high risk” should not be made on the basis of baseline antibody titer. The association of humoral rejection with baseline antidonor blood group antibody titer in splenectomized ABOI recipients not undergoing posttransplant plasmapheresis has been reported by Shimmura et al., who found a 70% humoral rejection rate in patients with baseline titer ≥128 and 20% in those with titers ≤1:64 (1). These findings are similar to those of our report in which rejection occurred in 12% of patients with titers <1:64, while 83% of those with titers exceeding 1:64 rejected (2). Interestingly, Shimmura et al. have recently reported that posttransplant plasmapheresis to maintain a low titer in conjunction with splenectomy is effective in preventing humoral rejection in ABOI recipients with very high baseline titers (3). In their letter, Mitsuhata et al. refer to their Brief Communication describing their use of mycophenolate mofetil during four weeks preceding ABOI transplantation in 18 patients compared to 18 patients who did not receive pretransplant mycophenolate mofetil (4). In their report, all patients underwent antibody lowering therapy with plasmapheresis or plasma exchange. No comment was made as to whether or not recipients underwent splenectomy, although their current letter to the editor implies that they did. They report improved allograft survival six months after transplant in the pretreated group, although the humoral rejection rate was comparable. The causes for allograft loss in the pretreatment group were not reported, nor were baseline antidonor blood group antibody titers. The authors indicate that on the day of transplantation antidonor blood group antibody titers ranging from 1–128, although not specifically reported. Given our admittedly smaller experience in ABOI kidney transplantation, we would be very reluctant to proceed to transplantation at the time the recipient's titer exceeded 1:16, and our practice is to continue to perform plasmapheresis until achieving a titer ≤1:8 on the day of transplantation. An important point is that the antibody titer depends strongly on the method used to measure it. It is possible that the antibody measurement technique used by Mitsuhata et al. differs from the technique reported in our investigation. The authors present their opinion that the benefits of transplantation without splenectomy are outweighed by the psychological, physical, and economic burden posed by posttransplant plasmapheresis and/or anti-CD20 antibody therapy. Our opinion is that with aggressive posttransplant antibody monitoring and therapy to maintain low titer during the first two weeks after transplantation, humoral rejection is an unusual complication in the large majority of ABOI kidney transplants. We also feel that the life long advantage of avoiding splenectomy exceeds the disadvantage of posttransplant therapy during the first one to two weeks after transplantation. Finally, the authors refer to the important fact that other potentially injurious antibodies with donor reactivity may also complicate ABOI transplantation, similar to ABO compatible transplants, and we agree. James Gloor Department of Internal Medicine and Nephrology Mayo Clinic Rochester, MN Mark Stegall Division of Transplantation Surgery Mayo Clinic Rochester, MN