K. Tinckam

Human T and Natural Killer Cells Possess a Functional Renin-Angiotensin System: Further Mechanisms of Angiotensin II–Induced Inflammation

The renin-angiotensin system (RAS) plays an important role in the regulation of inflammation and in the progression of chronic kidney disease. Accumulation of inflammatory cells into the renal parenchyma has been a hallmark of chronic kidney disease; however, little is known concerning the presence and the function of RAS elements in T and natural killer (NK) cells. Here is reported a co-stimulatory effect of angiotensin II (AngII) by showing an augmentation of mitogen and anti-CD3-stimulated T and NK cell proliferation with AngII treatment. Angiotensinogen and AngI also generated the same effect, suggesting that NK and T cells have functional renin and angiotensin-converting enzyme activity. Indeed, they express renin, the renin receptor, angiotensinogen, and angiotensin-converting enzyme by mRNA analysis. Flow cytometric analysis and Western blot revealed angiotensin receptor 2 (AT(2)) expression in T and NK cells, whereas AT(1) expression was found in T and NK cells and monocytes by Western blot. These receptors were shown to be functional in calcium signaling, chemotaxis, and proliferation. However, AT(1) and AT(2) antagonists alone or in combination were unable to abrogate completely the effects of AngII, suggesting that another AngII receptor may also be functional in leukocytes. This is the first study to show that T and NK cells are fully equipped with RAS elements and are potentially capable of producing and delivering AngII to sites of inflammation. Because their chemotaxis is enhanced by AngII, this creates a potential inflammatory amplification system.

Delayed Graft Function and the Risk for Death with a Functioning Graft

Delayed graft function (DGF) associates with an increased risk for graft failure, but its link with death with graft function (DWGF) is unknown. We used the US Renal Data System to assemble a cohort of all first, adult, deceased-donor kidney transplant recipients from January 1, 1998, through December 31, 2004. In total, 11,542 (23%) of 50,246 recipients required at least one dialysis session in the first week after transplantation. Compared with patients without DGF, patients with DGF were significantly more likely to die with a functioning graft (relative hazard 1.83 [95% confidence interval 1.73 to 1.93] and 1.53 [95% CI 1.45 to 1.63] for unadjusted and fully adjusted models, respectively). The risk for DWGF was slightly higher among women with DGF than among men. There was no significant heterogeneity among other subgroups, and the results were robust to sensitivity analyses. Acute rejection within the first year attenuated the DGF-DWGF association. Cardiovascular and infectious deaths were slightly more prevalent in the DGF group, but the relative hazards of cause-specific death were similar between DWGF and deaths during total follow-up. In summary, DGF associates with an increased risk for DWGF; the mechanisms underlying the negative impact of DGF require further study.

The role of donor-specific HLA alloantibodies in liver transplantation

The impact of donor‐specific HLA alloantibodies (DSA) on short‐ and long‐term liver transplant outcome is not clearly defined. While it is clear that not all levels of allosensitization produce overt clinical injury, and that liver allografts possess some degree of alloantibody resistance, alloantibody‐mediated adverse consequences are increasingly being recognized. To better define the current state of this topic, we assembled experts to provide insights, explore controversies and develop recommendations for future research on the consequences of DSA in liver transplantation. This article summarizes the proceedings of this inaugural meeting. Several insights emerged. Acute antibody‐mediated rejection (AMR), although rarely diagnosed, is increasingly understood to overlap with T cell–mediated rejection. Isolated liver allograft recipients are at increased risk of early allograft immunologic injury when preformed DSA are high titer and persist posttransplantation. Persons who undergo simultaneous liver–kidney transplantation are at risk of renal AMR when Class II DSA persist posttransplantation. Other under‐appreciated DSA associations include ductopenia and fibrosis, plasma cell hepatitis, biliary strictures and accelerated fibrosis associated with recurrent liver disease. Standardized DSA testing and diagnostic criteria for both acute and chronic AMR are needed to distil existing associations into etiological processes in order to develop responsive therapeutic strategies.

Adverse Outcomes of Tacrolimus Withdrawal in Immune–Quiescent Kidney Transplant Recipients

Concerns about adverse effects of calcineurin inhibitors (CNIs) have prompted development of protocols that minimize their use. Whereas previous CNI withdrawal trials in heterogeneous cohorts showed unacceptable rates of acute rejection (AR), we hypothesized that we could identify individuals capable of tolerating CNI withdrawal by targeting immunologically quiescent kidney transplant recipients. The Clinical Trials in Organ Transplantation-09 Trial was a randomized, prospective study of nonsensitized primary recipients of living donor kidney transplants. Subjects received rabbit antithymocyte globulin, tacrolimus, mycophenolate mofetil, and prednisone. Six months post-transplantation, subjects without de novo donor-specific antibodies (DSAs), AR, or inflammation at protocol biopsy were randomized to wean off or remain on tacrolimus. The intended primary end point was the change in interstitial fibrosis/tubular atrophy score between implantation and 24-month protocol biopsies. Serially collected urine CXCL9 ELISA results were correlated with outcomes. The study was terminated prematurely because of unacceptable rates of AR (4 of 14) and/or de novo DSAs (5 of 14) in the tacrolimus withdrawal arm. Positive urinary CXCL9 predated clinical detection of AR by a median of 15 days. Analyses showed that >16 HLA-DQ epitope mismatches and pretransplant, peripheral blood, donor-reactive IFN-γ ELISPOT assay results correlated with development of DSAs and/or AR on tacrolimus withdrawal. Although data indicate that urinary CXCL9 monitoring, epitope mismatches, and ELISPOT assays are potentially informative, complete CNI withdrawal must be strongly discouraged in kidney transplant recipients who are receiving standard-of-care immunosuppression, including those who are deemed to be immunologically quiescent on the basis of current clinical and laboratory criteria.

Utility of HLA Antibody Testing in Kidney Transplantation

HLA antigens are polymorphic proteins expressed on donor kidney allograft endothelium and are critical targets for recipient immune recognition. HLA antibodies are risk factors for acute and chronic rejection and allograft loss. Solid-phase immunoassays for HLA antibody detection represent a major advance in sensitivity and specificity over cell-based methods and are widely used in organ allocation and pretransplant risk assessment. Post-transplant, development of de novo donor-specific HLA antibodies and/or increase in donor-specific antibodies from pretransplant levels are associated with adverse outcomes. Although single antigen bead assays have allowed sensitive detection of recipient HLA antibodies and their specificities, a number of interpretive considerations must be appreciated to understand test results in clinical and research contexts. This review, which is especially relevant for clinicians caring for transplant patients, discusses the technical aspects of single antigen bead assays, emphasizes their quantitative limitations, and explores the utility of HLA antibody testing in identifying and managing important pre- and post-transplant clinical outcomes.

Antibody Mediated Rejection Associated With Complement Factor H–Related Protein 3/1 Deficiency Successfully Treated With Eculizumab

Antibody mediated rejection (AMR) activates the classical complement pathway and can be detrimental to graft survival. AMR can be accompanied by thrombotic microangiopathy (TMA). Eculizumab, a monoclonal C5 antibody prevents induction of the terminal complement cascade (TCC) and has recently emerged as a therapeutic option for AMR. We present a highly sensitized 13‐year‐old female with end‐stage kidney disease secondary to spina bifida‐associated reflux nephropathy, who developed severe steroid‐, ATG‐ and plasmapheresis‐resistant AMR with TMA 1 week post second kidney transplant despite previous desensitization therapy with immunoglobulin infusions. Eculizumab rescue therapy resulted in a dramatic improvement in biochemical (C3; creatinine) and hematological (platelets) parameters within 6 days. The patient was proven to be deficient in complement Factor H‐related protein 3/1 (CFHR3/1), a plasma protein that regulates the complement cascade at the level of C5 conversion and has been involved in the pathogenesis of atypical hemolytic uremic syndrome caused by CFH autoantibodies (DEAP‐HUS). CFHR1 deficiency may have worsened the severe clinical progression of AMR and possibly contributed to the development of donor‐specific antibodies. Thus, screening for CFHR3/1 deficiency should be considered in patients with severe AMR associated with TMA.

Kidney paired donation: principles, protocols and programs

Due to the ongoing shortage of deceased-donor organs, novel strategies to augment kidney transplantation rates through expanded living donation strategies have become essential. These include desensitization in antibody-incompatible transplants and kidney paired donation (KPD) programs. KPD enables kidney transplant candidates with willing but incompatible living donors to join a registry of other incompatible pairs in order to find potentially compatible transplant solutions. Given the significant immunologic barriers with fewer donor options, single-center or small KPD programs may be less successful in transplanting the more sensitized patients; the optimal solution for the difficult-to-match patient is access to more potential donors and large multicenter or national registries are essential. Multicenter KPD programs have become common in the last decade, and now represent one of the most promising opportunities to improve transplant rates. To maximize donor-recipient matching, and minimize immunologic risk, these multicenter KPD programs use sophisticated algorithms to identify optimal match potential, with simultaneous two-, three- or more complex multiway exchanges. The article focuses on the recent progresses in KPD and it also reviews some of the differences and commonalities across four different national KPD programs.

A Survey of Current Practice for Antibody-Mediated Rejection in Heart Transplantation

No evidence based management guidelines exist for antibody mediated rejection (AMR) in heart transplantation. The International Society for Heart and Lung Transplantation (ISHLT) recently introduced standardized pathologic based diagnostic criteria for AMR (pAMR 0–3). We evaluated international practice for the management of AMR focusing on pAMR grade, donor specific antibody (DSA) and allograft function. On‐line survey data were analyzed from 184 ISHLT members (physicians‐78%, surgeons‐20%). The majority were from adult‐transplant (84%), medium‐large volume centres (transplants/year: 10–25, 61%; 25–50, 19%) across North America (60%) and Europe (26%). Irrespective of pAMR grade and DSA, 83–90% treated a drop in ejection fraction (EF ≤45% or >25% decrease). In the presence of stable EF, an increasing number elected treatment for progressively severe pAMR grade (p < 0.001) and for accompanying DSA (p < 0.05, pAMR 1–3). Intravenous steroid was the most commonly used therapy followed by intravenous immunoglobulin (IVIG) or plasmapheresis, rituximab and thymoglobulin. Plasmapheresis and rituximab were favored for positive versus negative DSA (p < 0.05). Using a threshold of ≥70% consensus among respondents, treatment for AMR may be considered for a drop in EF, asymptomatic pAMR 3 or asymptomatic pAMR 2 with DSA. Combination steroid, IVIG and plasmapheresis are suggested as initial therapies.

HLA-DR and -DQ Eplet Mismatches and Transplant Glomerulopathy: A Nested Case–Control Study

We conducted a nested case–control study from a cohort of adult kidney transplant recipients to assess the risk of transplant glomerulopathy (TG) as a function of donor and recipient HLA‐DR and ‐DQ incompatibility at the eplet level. Cases (n = 52) were defined as patients diagnosed with transplant glomerulopathy based on biopsies showing glomerular basement membrane duplication without immune complex deposition. Controls (n = 104) with a similar follow‐up from transplantation were randomly selected from the remaining cohort. HLAMatchmaker was used to ascertain the number of DRB1/3/4/5, DQA1 and DQB1 related eplet mismatches (eplet load). Multivariable conditional logistic regression models demonstrated an increase in the odds of TG (odds ratios [OR] of 2.84 [95% confidence interval (CI): 1.03, 7.84] and 4.62 [95% CI: 1.51, 14.14]) in the presence of 27–43 and >43 HLA‐DR + DQ related eplet mismatches versus <27 eplet mismatches, respectively. When the eplet load was modeled as a continuous variable, the OR for TG was 1.25 (95% CI: 1.04, 1.50) for every 10 additional HLA‐DR + DQ eplet mismatches. Our study suggests that minimization of HLA‐DR + DQ eplet mismatches may decrease the incidence of transplant glomerulopathy diagnosed by indication biopsies. The role of eplet immunogenicity/antigenicity as determinants of allograft outcomes requires further study.

Should HLA Mismatch Acceptability for Sensitized Transplant Candidates Be Determined at the High‐Resolution Rather Than the Antigen Level?

Defining HLA mismatch acceptability of organ transplant donors for sensitized recipients has traditionally been based on serologically defined HLA antigens. Now, however, it is well accepted that HLA antibodies specifically recognize a wide range of epitopes present on HLA antigens and that molecularly defined high resolution alleles corresponding to the same low resolution antigen can possess different epitope repertoires. Hence, determination of HLA compatibility at the allele level represents a more accurate approach to identify suitable donors for sensitized patients. This approach would offer opportunities for increased transplant rates and improved long term graft survivals.