Faculty Bibliography

Kidneys from donors with blood type A2 can be successfully transplanted into blood type B and O recipients without the need for desensitization if the recipient's starting anti-A hemagglutinin titer is within an acceptable range. National kidney allocation policy now offers priority for eligible B recipients to receive A2 or A2B deceased donor kidneys, and therefore, the frequency with which A2 or A2B to B transplants will occur is expected to increase. The precise mechanisms by which antibody-mediated rejection is averted in these cases despite the presence of both circulating anti-A antibody and expression of the A2 antigen on the graft endothelium are not known. Whether this process mirrors proposed mechanisms of accommodation, which can occur in recipients of ABO incompatible transplants, is also not known. Repeated exposure to mismatched antigens after retransplantation could elicit memory responses resulting in antibody rebound and accelerated antibody-mediated rejection. Whether this would occur in the setting of repeated A2 donor exposure was uncertain. Here we report the case of a patient with history of a prior A2 to B transplant which failed owing to nonimmunologic reasons; the patient successfully underwent a repeat A2 to B transplant. Neither rebound in anti-A2 antibody nor clinical evidence of antibody-mediated rejection were observed after the transplant. Current kidney allocation will likely enable more such transplants in the future, and this may provide a unique patient population in whom the molecular mechanisms of incompatible graft accommodation may be investigated.

OBJECTIVES/OBJECTIVE:The presence of a donor-specific positive crossmatch has been considered to be a contraindication to kidney transplantation because of the risk of hyperacute rejection. Desensitization is the process of removing hazardous preformed donor-specific antibody (DSA) in order to safely proceed with transplant. Traditionally, this involves plasmapheresis and intravenous immune globulin treatments that occur over days to weeks, and has been feasible when there is a living donor and the date of the transplant is known, allowing time for pre-emptive treatments. For sensitized patients without a living donor, transplantation has been historically difficult. SUMMARY OF BACKGROUND DATA/BACKGROUND:IdeS (imlifidase) is an endopeptidase derived from Streptococcus pyogenes which has specificity for human IgG, and when infused intravenously results in rapid cleavage of IgG. METHODS:Here we present our single-center's experience with 7 highly sensitized (cPRA98-100%) kidney transplant candidates who had DSA resulting in positive crossmatches with their donors (5 deceased, 2 living) who received IdeS within 24 hours prior to transplant. RESULTS:All pre-IdeS crossmatches were positive and would have been prohibitive for transplantation. All crossmatches became negative post-IdeS and the patients underwent successful transplantation. Three patients had DSA rebound and antibody-mediated rejection, which responded to standard of care therapies. Three patients had delayed graft function, which ultimately resolved. No serious adverse events were associated with IdeS. All patients have functioning renal allografts at a median follow-up of 235 days. CONCLUSION/CONCLUSIONS:IdeS may represent a groundbreaking new method of desensitization for patients who otherwise might have no hope for receiving a lifesaving transplant.

The human major histocompatibility complex is a family of genes that encodes HLAs, which have a crucial role in defence against foreign pathogens and immune surveillance of tumours. In the context of transplantation, HLA molecules are polymorphic antigens that comprise an immunodominant alloreactive trigger for the immune response, resulting in rejection. Remarkable advances in knowledge and technology in the field of immunogenetics have considerably enhanced the safety of transplantation. However, access to transplantation among individuals who have become sensitized as a result of previous exposure to alloantigens is reduced proportional to the breadth of their sensitization. New approaches for crossing the HLA barrier in transplantation using plasmapheresis, intravenous immunoglobulin and kidney paired donation have been made possible by the relative ease with which even low levels of anti-HLA antibodies can now be detected and tracked. The development of novel protocols for the induction of tolerance and new approaches to immunomodulation was also facilitated by advances in HLA technology. Here, we review the progress made in understanding HLAs that has enabled organ transplantation to become a life-saving endeavour that is accessible even for sensitized patients. We also discuss novel approaches to desensitization, immunomodulation and tolerance induction that have the potential to further improve transplantation access and outcomes.

BACKGROUND:Antibody-mediated rejection (AMR) is a major barrier to the long-term function of renal allografts. White blood cells, which may be present in red blood cell (RBC) units, and platelets (PLTs) express HLA antigens that may increase the risk of AMR by inducing or increasing humoral sensitization to HLA. STUDY DESIGN AND METHODS/METHODS:A retrospective cohort study of HLA-incompatible (HLAi) renal transplant recipients between 2004 and 2015 was conducted. Data on apheresis PLT and leukoreduced RBC transfusions within 4 weeks of transplantation, demographic information, and biopsy-proven AMR were collected from medical records and the Scientific Registry of Transplant Recipients. Patients were evaluated until they showed evidence of AMR or until 1 year posttransplant, whichever came first. Multivariable analysis with Cox modeling was performed. RESULTS:Of 244 individuals, 182 (74.6%) received RBCs and 20 (8.2%) of those also received PLTs. During the first year posttransplant, 97 (39.8%) had AMR. RBC-alone or RBC and PLT transfusions were not associated with increased risk of AMR after adjustment for panel-reactive antibody, years on dialysis, HLA antibody strength, and number of therapeutic plasma exchange treatments (adjusted hazard ratio [adjHR] 1.00, 95% confidence interval [95% CI] 0.59-1.69; and adjHR 0.68, 95% CI 0.28-1.68, respectively). For each 1-unit increase in RBC transfusions, there was no association with AMR (adjHR 0.94, 95% CI 0.85-1.05). Only HLA antibody strength before transplantation was associated with AMR (adjHR 2.23, 95% CI 1.10-4.52; cytotoxic crossmatch compared to crossmatch negative but detectable donor-specific HLA antibodies). CONCLUSIONS:Patients who receive an HLAi transplant who are transfused with leukoreduced RBCs or PLTs in the peritransplant period are at no higher risk of AMR than nontransfused patients.

BACKGROUND:Anti-human leukocyte antigen donor-specific antibodies (anti-HLA DSAs) are recognized as a major barrier to patients' access to organ transplantation and the major cause of graft failure. The capacity of circulating anti-HLA DSAs to activate complement has been suggested as a potential biomarker for optimizing graft allocation and improving the rate of successful transplantations. METHODS AND FINDINGS/RESULTS:To address the clinical relevance of complement-activating anti-HLA DSAs across all solid organ transplant patients, we performed a meta-analysis of their association with transplant outcome through a systematic review, from inception to January 31, 2018. The primary outcome was allograft loss, and the secondary outcome was allograft rejection. A comprehensive search strategy was conducted through several databases (Medline, Embase, Cochrane, and Scopus). A total of 5,861 eligible citations were identified. A total of 37 studies were included in the meta-analysis. Studies reported on 7,936 patients, including kidney (n = 5,991), liver (n = 1,459), heart (n = 370), and lung recipients (n = 116). Solid organ transplant recipients with circulating complement-activating anti-HLA DSAs experienced an increased risk of allograft loss (pooled HR 3.09; 95% CI 2.55-3.74, P = 0.001; I2 = 29.3%), and allograft rejection (pooled HR 3.75; 95% CI: 2.05-6.87, P = 0.001; I2 = 69.8%) compared to patients without complement-activating anti-HLA DSAs. The association between circulating complement-activating anti-HLA DSAs and allograft failure was consistent across all subgroups and sensitivity analyses. Limitations of the study are the observational and retrospective design of almost all included studies, the higher proportion of kidney recipients compared to other solid organ transplant recipients, and the inclusion of fewer studies investigating allograft rejection. CONCLUSIONS:In this study, we found that circulating complement-activating anti-HLA DSAs had a significant deleterious impact on solid organ transplant survival and risk of rejection. The detection of complement-activating anti-HLA DSAs may add value at an individual patient level for noninvasive biomarker-guided risk stratification. TRIAL REGISTRATION/BACKGROUND:National Clinical Trial protocol ID: NCT03438058.

Retrospective studies of angiotensin II type 1 receptor antibodies (AT1R-Ab) and anti-endothelial cell antibodies (AECA) have linked these antibodies to allograft injury. Because rising healthcare costs dictate judicious use of laboratory testing, we sought to define characteristics of kidney transplant recipients who may benefit from screening for non-HLA antibodies. Kidney recipients transplanted between 2011 and 2016 at Johns Hopkins, were evaluated for AT1R-Ab and AECA. Pre-transplant antibody levels were compared to clinical and biopsy indications of graft dysfunction. Biopsies were graded using the Banff' 2009-2013 criteria. AT1R-Ab and AECA were detected using ELISA and endothelial cell crossmatches, respectively. AT1R-Ab levels were higher in patients who were positive for AECAs. Re-transplanted patients (p < 0.0001), males (p = 0.008) and those with FSGS (p = 0.04) and younger (p = 0.04) at time of transplantation were more likely to be positive for AT1R-Ab prior to transplantation. Recipients who were positive for AT1R-Ab prior to transplantation had increases in serum creatinine within 3 months post-transplantation (p < 0.0001) and developed abnormal biopsies earlier than did AT1R-Ab negative patients (126 days versus 368 days respectively; p = 0.02). Defining a clinical protocol to identify and preemptively treat patients at risk for acute rejection with detectable non-HLA antibodies is an important objective for the transplant community.

BACKGROUND:Candidates for vascularized composite allotransplantation (VCA) are frequently sensitized, putting them at risk for antibody-mediated rejection (AMR). Current desensitization strategies are imperfect and require a living-donor setting. Here we investigated the impact of sensitization on and the efficacy of a desensitization protocol utilizing syngeneic hematopoietic stem cell transplantation (HSCT) to prevent AMR in VCA. METHODS:Skin transplants from Dark Agouti (DA) to Lewis rats were performed for sensitization. Orthotopic hind-limb transplants from DA donors were performed to sensitized and non-sensitized recipients, and the animals were treated with either daily tacrolimus or no immunosuppression. A desensitization protocol consisting of total body irradiation (TBI), fludarabine and syngeneic HSCT was applied to sensitized animals. Graft rejection was monitored by clinical assessment and histological analysis. Serum levels of donor-specific antibodies (DSA IgG) were measured using flow-cytometry. RESULTS:Sensitized recipients exhibited accelerated rejection by 5.5±1.2 days without immunosuppression and 10.2±3.6 days with daily tacrolimus, compared to 8.7±1.2 days and >30 days in non-sensitized recipients, respectively. Serum levels of DSA IgG were markedly elevated (37.3±3.34-fold from baseline) in sensitized recipients after VCA and correlated with histologic evidence of rejection and C4d deposition. Desensitization significantly reduced DSA compared to sensitized-controls (2.6±0.5-fold vs 6.0±1.2-fold, p<0.01) and along with daily tacrolimus led to improved VCA survival of >30 days without evidence of C4d deposition (n=6). CONCLUSIONS:In summary, sensitization leads to accelerated rejection of VCA, and syngeneic HSCT combined with conventional immunosuppression effectively reduces DSA and improves allograft survival in sensitized rats.

30% of kidney transplant recipients are readmitted in the first month post-transplant. Those with donor-specific antibody requiring desensitization and incompatible live donor kidney transplantation (ILDKT) constitute a unique subpopulation that might be at higher readmission risk. Drawing on a 22-center cohort, 379 ILDKTs with Medicare primary insurance were matched to compatible transplant matched controls and to waitlist-only matched controls on panel reactive antibody, age, blood group, renal replacement time, prior kidney transplantation, race, gender, diabetes, and transplant date/waitlisting date. Readmission risk was determined using multilevel, mixed-effects Poisson regression. In the first month, ILDKTs had a 1.28-fold higher readmission risk than compatible controls (95%CI: 1.13-1.46; P<0.001). Risk peaked at 6-12 months (RR 1.67; 95%CI: 1.49-1.87; P<0.001), attenuating by 24-36 months (RR 1.24; 95%CI: 1.10-1.40; P<0.001). ILDKTs had a 5.86-fold higher readmission risk (95%CI: 4.96-6.92; P<0.001) in the first month compared to waitlist-only controls. At 12-24 (RR 0.85; 95%CI: 0.77-0.95; P=0.002) and 24-36 months (RR 0.74; 95% CI: 0.66-0.84; P<0.001), ILDKTs had a lower risk than waitlist-only controls. These findings of ILDKTs having a higher readmission risk than compatible controls, but a lower readmission risk after the first year than waitlist-only controls should be considered in regulatory/payment schemas and planning clinical care.

Complement-activating anti-HLA donor-specific antibodies (DSAs) are associated with impaired kidney transplant outcome; however, whether these antibodies induce a specific rejection phenotype and influence response to therapy remains undetermined. We prospectively screened 931 kidney recipients for complement-activating DSAs and used histopathology, immunostaining, and allograft gene expression to assess rejection phenotypes. Effector cells were evaluated using in vitro human cell cultures. Additionally, we assessed the effect of complement inhibition on kidney allograft rejection phenotype and the clinical response to complement inhibition in 116 independent kidney recipients with DSAs at transplant receiving rejection prophylaxis with eculizumab or standard of care (plasma exchange and intravenous Ig) at ten international centers. The histomolecular rejection phenotype associated with complement-activating DSA was characterized by complement deposition and accumulation of natural killer cells and monocytes/macrophages in capillaries and increased expression of five biologically relevant genes (CXCL11, CCL4, MS4A7, MS4A6A, and FCGR3A) indicative of endothelial activation, IFNgamma response, CD16-mediated natural killer cell activation, and monocyte/macrophage activation. Compared with standard of care, eculizumab specifically abrogated this histomolecular rejection phenotype and associated with a decreased 3-month rejection incidence rate in patients with complement-activating DSAs (56%; 95% confidence interval [95% CI], 38% to 74% versus 19%; 95% CI, 8% to 35%; P=0.001) but not in those with noncomplement-activating DSAs (9%; 95% CI, 2% to 25% versus 13%; 95% CI, 2% to 40%; P=0.65). In conclusion, circulating complement-activating anti-HLA DSAs are associated with a specific histomolecular kidney allograft rejection phenotype that can be abrogated by complement inhibition.