Saturday, February 23, 2013

Antiperlecan Antibodies Are Novel Accelerators of Immune-Mediated Vascular Injury

Acute vascular rejection (AVR) is characterized by immune-mediated vascular injury and heightened endothelial cell (EC) apoptosis. We reported previously that apoptotic ECs release a bioactive C-terminal fragment of perlecan referred to as LG3. Here, we tested the possibility that LG3 behaves as a neoantigen, fuelling the production of anti-LG3 antibodies of potential importance in regulating allograft vascular injury. We performed a case–control study in which we compared anti-LG3 IgG titers in kidney transplant recipients with AVR (n = 15) versus those with acute tubulo-interstitial rejection (ATIR) (n = 15) or stable graft function (n = 30). Patients who experienced AVR had elevated anti-LG3 titers pre and posttransplantation compared to subjects with ATIR or stable graft function (p < 0.05 for both mediators). Elevated pretransplant anti-LG3 titers (OR: 4.62, 95% CI: 1.08–19.72) and pretransplant donor-specific antibodies (DSA) (OR 4.79, 95% CI: 1.03–22.19) were both independently associated with AVR. To address the functional role of anti-LG3 antibodies in AVR, we turned to passive transfer of anti-LG3 antibodies in an animal model of vascular rejection based on orthotopic aortic transplantation between fully MHC-mismatched mice. Neointima formation, C4d deposition and allograft inflammation were significantly increased in recipients of an ischemic aortic allograft passively transferred with anti-LG3 antibodies. Collectively, these data identify anti-LG3 antibodies as novel accelerators of immune-mediated vascular injury and obliterative remodeling (read more)

Acute Pancreas Allograft Rejection Is Associated With Increased Risk of Graft Failure in Pancreas Transplantation

The effect of acute allograft rejection (AR) on long-term pancreas allograft function is unclear. We retrospectively studied 227 consecutive pancreas transplants performed at our institution between January 1, 998 and December 31, 2009 including: 56 simultaneous pancreas and kidney (SPK), 69 pancreas transplantation alone (PTA); and 102 pancreas after kidney (PAK) transplants. With a median follow-up of 6.1 (IQR 3–9) years, 57 patients developed 79 episodes of AR, and 19 experienced more than one episode. The cumulative incidence for AR was 14.7%, 19.7%, 26.6% and 29.1% at 1, 2, 5 and 10 years. PTA transplant (hazards ratio [HR] = 2.28, p = 0.001) and donor age (per 10 years) (HR = 1.34, p = 0.006) were associated with higher risk for AR. The first AR episode after 3 months post PT was associated with increased risk for complete loss (CL) (HR 3.79, p < 0.001), and the first AR episode occurring during 3- to 12-month and 12- to 24-month periods after PT were associated with significantly increased risk for at least partial loss (PL) (HR 2.84, p = 0.014; and HR 6.25, p < 0.001, respectively). We conclude that AR is associated with increased risk for CL and at least PL. The time that the first AR is observed may influence subsequent graft failure (read more)

Class II Alloantibody and Mortality in Simultaneous Liver-Kidney Transplantation

Hyperacute kidney rejection is unusual in crossmatch positive recipients of simultaneous liver–kidney transplants (SLKT). However, recent data suggest that these patients remain at risk for antibody-mediated kidney rejection. To further investigate the risk associated with donor-specific alloantibodies (DSA) in SLKT, we studied 86 consecutive SLKT patients with an available pre-SLKT serum sample. Serum samples were analyzed in a blinded fashion for HLA DSA using single antigen beads (median florescence intensity ≥ 2,000 = positive). Post-SLKT samples were analyzed when available (76%). Thirty patients had preformed DSA, and nine developed de novo DSA. Preformed class I DSA did not change the risk of rejection, patient or allograft survival. In contrast, preformed class II DSA was associated with a markedly increased risk of renal antibody mediated rejection (AMR) (p = 0.006), liver allograft rejection (p = 0.002), patient death (p = 0.02), liver allograft loss (p = 0.02) and renal allograft loss (p = 0.045). Multivariable modeling showed class II DSA (preformed or de novo) to be an independent predictor of patient death (HR = 2.2; p = 0.043) and liver allograft loss (HR = 2.2; p = 0.044). These data warrant reconsideration of the approach to DSA in SLKT (read more)

Thursday, February 21, 2013

The DQ Barrier: Improving Organ Allocation Equity Using HLA-DQ Information

imageBackground: The United Network for Organ Sharing algorithm for deceased-donor kidney allocation considers only the human leukocyte antigen (HLA)-A, HLA-B, and HLA-DR loci. Although HLA-DQ serologic specificities can be entered as unacceptable antigens, they are assigned only by the identity of the DQβ chain, disregarding the role of the similarly polymorphic α chain. DQα/β combinations result in unique antigenic epitopes, which serve as targets to different antibodies. Therefore, the presence of HLA antibodies to one DQα/β combination should not preclude negative crossmatch (XM) against another combination. In this retrospective analysis, patients were allowed XM against a particular donor if they had antibodies to some, but not all, DQα/β allele combinations with the donor serologic HLA-DQ antigens.
Methods: HLA antibody signature was obtained using solid-phase Luminex-based antibody analysis. Results were captured at the high-resolution level (as provided by the positive beads). Potential donors were typed to include information on both HLA-DQA and HLA-DQB alleles.
Results: Of the 1130 flow XM assays performed, 147 patients had antibodies to donor serologic HLA-DQ antigens. Thirty-five of those patients had antibodies to an allelic DQα/β combination within the donor serologic DQ specificity that were different from the donor’s DQα/β, leading to negative flow XM results (24%). Virtual XM, accounting for donor DQα/β combinations, successfully predicts more than 98% of XM outcomes.
Conclusions: In patients with allelic DQα/β antibodies, denying the opportunity for XM based on serologically defined unacceptable antigens can disadvantage the patient. Larger cohort studies are required to substantiate our observation. Introducing DQα/β combination information may increase virtual XM accuracy and organ allocation equity (read more)

Anonymity and Live-Donor Transplantation: An ELPAT View

imageAnonymity of donors or recipients in living-donor transplantation is a complex issue and practice varies widely. There are compelling arguments for maintaining anonymity of both parties before unspecified donor transplantation and specified indirect transplantation. After transplantation, there are still good reasons to avoid disclosure of identities. Although anonymity could be lifted if both parties explicitly request it, there are significant, potentially negative consequences of such an approach. Both donor and recipient should be counseled regarding these, and transplant teams should consider the considerable financial and psychosocial costs if problems are encountered as a result of contact. Given the recent rise in the number of unspecified living-donor transplants and through paired exchange schemes, it is vital that data are collected regarding the effects of maintaining or revoking anonymity after transplantation (read more)

Monday, February 18, 2013

Rituximab in renal transplantation

Rituximab is a chimeric anti-CD20 monoclonal antibody that leads to B cell depletion. It is not licensed for use in renal transplantation but is in widespread use in ABO blood group incompatible transplantation. It is an effective treatment for post-transplant lymphoproliferative disorder, and is also used in both HLA antibody incompatible renal transplantation and the treatment of acute rejection. Recent evidence suggests rituximab may prevent the development of chronic antibody mediated rejection. The mechanisms underlying its effects are likely to relate both to long-term effects on plasma cell development and to the impact on B cell modulation of T cell responses. Rituximab (in multiple doses or in combination with other monoclonal antibodies and/or other immunosuppressants) may lead to an increase in infectious complications, although the evidence is not clear. Rarely, the drug can cause a cytokine release syndrome, thrombocytopenia and neutropenia. It has been related to an increased risk of progressive multifocal leucoencephalopathy and, recently, deaths from cardiovascular causes. Trials examining the effects of rituximab in induction therapy for compatible renal transplantation and the treatment of chronic antibody mediated rejection are ongoing. These trials should aid greater understanding of the role of B-cells in the alloresponse to renal transplantation (read more).

Tuesday, February 12, 2013

Transnational validation of the Australian algorithm for virtual crossmatch allocation in kidney paired donation.

An independent pool of 16 incompatible live donor-recipient pairs registered at the Vienna transplant unit was applied to test whether virtual crossmatch allocation used in the Australian kidney paired donation (KPD) program reliably predicts negative crossmatches. High resolution HLA data were entered into the computer-matching algorithm and allocation was performed excluding any DSA >2000MFI. CDC and flow crossmatch data of recipients against any of the donors were available for 112 crossmatch combinations. The computer program identified 19 possible pairings in 2-way or 3-way chains in multiple combinations. The top ranked combination included one 3-way and two 2-way ABO-compatible chains. Where crossmatches were available all recipients were CDC crossmatch negative with the computer-matched donor. Excluding allocation of KPD donors in the presence of DSA >2000MFI had a negative predictive of 99.9% for CDC and 96.4% for flow crossmatch. In the 12 pairings with 1 DSA against crossmatched donors there was a negative CDC and flow crossmatch. These results show excellent correlation between matching using virtual crossmatch and actual crossmatch results. Using the 2000MFI cut-off the number of potentially unacceptable CDC and flow crossmatch positive pairings identified by virtual crossmatching is low, but some potential crossmatch negative pairings are missed (read more)

Friday, February 8, 2013

Transplanted Human Pancreatic Islets After Long-Term Insulin Independence

Long-term insulin independence after islets of Langerhans transplantation is rarely achieved. The aims of this study were to identify the histological and immunological features of islets transplanted in a type 1 diabetic patient who died of a cerebral hemorrhage after >13 years insulin independence. Islets were pooled from two donors with respectively one and five HLA mismatches. Insulin-positive islets were found throughout the right and left liver, and absent in the pancreas. Two- and three-dimensional analysis showed that islets lost their initial rounded and compact morphology, had a mean diameter of 136 μm and were constituted of an unfolded epithelial band of 39.1 μm. Leukocyte phenotyping showed no evidence of a tolerogenic environment in the islet-containing portal spaces. Finally, HLA typing of microdissected islets showed HLA from the best matched donor in all 23 microdissection samples, compared to 1/23 for the least matched donor. This case report demonstrates that allogeneic islets can survive over 13 years while maintaining insulin independence. Allogeneic islets had unique morphologic features and implanted in the liver regardless of their size. Finally, our results suggest that, in this case, rejection had been prevalent over autoimmunity, although this hypothesis warrants further investigation (read more)

Dynamic Challenges Inhibiting Optimal Adoption of Kidney Paired Donation: Findings of a Consensus Conference

While kidney paired donation (KPD) enables the utilization of living donor kidneys from healthy and willing donors incompatible with their intended recipients, the strategy poses complex challenges that have limited its adoption in United States and Canada. A consensus conference was convened March 29–30, 2012 to address the dynamic challenges and complexities of KPD that inhibit optimal implementation. Stakeholders considered donor evaluation and care, histocompatibility testing, allocation algorithms, financing, geographic challenges and implementation strategies with the goal to safely maximize KPD at every transplant center. Best practices, knowledge gaps and research goals were identified and summarized in this document (read more)

No Impact of KIR-Ligand Mismatch on Allograft Outcome in HLA-Compatible Kidney Transplantation

Natural killer (NK) cell function can be modulated by the killer cell immunoglobulin-like receptors (KIR) which interact with human leukocyte antigen (HLA) class I molecules on target cells. KIR-ligand mismatching has recently been shown by van Bergen et al. (American Journal of Transplantation 2011; 11(9): 1959–1964) to be a significant risk factor for long-term graft loss in HLA-A, -B and -DR compatible kidney transplants. To verify this potentially important finding, we performed genotyping of 608 deceased-donor kidney graft recipients and their HLA-A, -B and -DR compatible donors for KIR and HLA, using samples and clinical data provided by the Collaborative Transplant Study. Graft survival of KIR-ligand-matched and -mismatched transplants was compared. We found no impact of KIR-ligand mismatching on 10-year graft survival in HLA-A, -B, -DR compatible kidney transplants. Further analysis did not reveal a significant effect of recipient activating/inhibitory KIR or KIR genotypes on graft survival. Our data do not support the concept that KIR-HLA matching might serve as a tool to improve long-term renal allograft survival (read more)

Searching for Uremic Toxins

Treatment of uremia by hemodialysis has become widespread over the last 40 years and has improved substantially over that time. However, people treated with this modality continue to suffer from multiple disabilities. Retention of organic solutes, especially those poorly removed by hemodialysis, likely contributes to these disabilities. Certain classes of solutes are removed less well than urea by hemodialysis and by the normal kidney. These include protein-bound solutes, relatively large solutes, sequestered compounds, and substances removed at rates higher than urea by the normal kidney. Several strategies could be used to discover the solutes responsible for residual morbidities in standardly dialyzed people. Rather than continue to focus only on urea removal as an index for dialysis adequacy, finding additional approaches for removing toxic solutes with characteristics different from urea (and the similar small solutes it represents) is a desirable and feasible goal (read more)

Tuesday, February 5, 2013

Blood Group Antigen-Targeting Peptide Suppresses Anti-Blood Group Antibody Binding to Antigen in Renal Glomerular Capillaries After ABO-Incompatible Blood Reperfusion

imageBackground: Antibody-mediated rejection after ABO-incompatible kidney transplantation (ABO-I KTx) is a major barrier to transplantation success. The advent of immunosuppressive therapy has markedly improved graft survival in ABO-I KTx. However, compared with normal KTx, clinical conditions during ABO-I KTx are difficult to control because of overimmunosuppression. To reduce the need for immunosuppression, we aimed to develop a novel blood group antigen-neutralizing therapy.
Methods: We screened for an ABO blood group antigen-targeting peptide (BATP) by screening of T7 phage-displayed peptide library. After screening, hemagglutination inhibition assays, enzyme-linked immunosorbent assay, and cytotoxicity assay were used to analyze the blood group antigen-blocking effect and toxicity of BATP. We also tested the inhibitory effects on anti-blood group antibody binding in normal human kidney tissues blocked with BATP and excised kidneys perfused ex vivo with BATP.
Results: We identified six peptide sequences that efficiently suppressed hemagglutination of red blood cells by anti-ABO blood group antibodies and binding of these antibodies to ABO histo-blood group antigens in kidney tissues. Surprisingly, ex vivo perfusion of BATP in kidneys excised from renal cell carcinoma patients caused significant suppression of anti-blood group antibody binding to antigen and IgG and IgM deposition in renal glomerular capillaries after ABO-I blood reperfusion.
Conclusions: These data indicate that A/B blood group antigens on red blood cells and in kidney tissues may be neutralized by BATP. This approach may enable the development of a novel blood group antigen-neutralizing therapy to overcome the challenges of ABO-I KTx (read more)

Incidence and Impact of De Novo Donor-Specific Alloantibody in Primary Renal Allografts

imageBackground: To date, limited information is available describing the incidence and impact of de novo donor-specific anti–human leukocyte antigen (HLA) antibodies (dnDSA) in the primary renal transplant patient. This report details the dnDSA incidence and actual 3-year post-dnDSA graft outcomes.
Methods: The study includes 189 consecutive nonsensitized, non-HLA-identical patients who received a primary kidney transplant between March 1999 and March 2006. Protocol testing for DSA via LABScreen single antigen beads (One Lambda) was done before transplantation and at 1, 3, 6, 9, and 12 months after transplantation then annually and when clinically indicated.
Results: Of 189 patients, 47 (25%) developed dnDSA within 10 years. The 5-year posttransplantation cumulative incidence was 20%, with the largest proportion of patients developing dnDSA in the first posttransplantation year (11%). Young patients (18–35 years old at transplantation), deceased-donor transplant recipients, pretransplantation HLA (non-DSA)–positive patients, and patients with a DQ mismatch were the most likely to develop dnDSA. From DSA appearance, 9% of patients lost their graft at 1 year. Actual 3-year death-censored post-dnDSA graft loss was 24%.
Conclusion: We conclude that 11% of the patients without detectable DSA at transplantation will have detectable DSA at 1 year, and over the next 4 years, the incidence of dnDSA will increase to 20%. After dnDSA development, 24% of the patients will fail within 3 years. Given these findings, future trials are warranted to determine if treatment of dnDSA-positive patients can prevent allograft failure (read more)