IgG4 donor-specific HLA antibody profile is associated with subclinical rejection in stable pediatric liver recipients

The impact of donor-specific HLA antibody (DSA) following liver transplantation remains controversial. We hypothesized DSA IgG subclass characteristics, compared to total DSA IgG, might correlate with specific histopathological phenotype(s) of subclinical graft injury. We therefore studied 129 stable, arguably "clinically ideal," pediatric liver recipients at the time of a screening biopsy to enter an immunosuppression withdrawal trial. Sixty-five (50%) subjects tested positive for class II DSA. IgG subclass profile was characterized by mean fluorescence intensity (MFI) and normalized subclass composition (>5%). A prominent IgG4 DSA profile was strongly correlated with greater HLA mismatch, a histopathological phenotype characterized by the presence of interface activity (with variable degrees of fibrosis), and a transcriptional profile of attenuated T cell-mediated rejection. Specifically, compared to those without class II DSA, those with IgG4 class II DSA MFI sum >2000 exhibited an odds ratio (OR) of 20.79 (95% confidence interval [CI] 4.38-98.69) and IgG4 subclass composition >5% exhibited an OR of 8.99 (95% CI 2.70-29.9). Our data suggest that IgG4 DSA may serve as a useful biomarker to identify, among clinically and biochemically stable liver transplant recipients, a subset with histological and transcriptional features indicative of an active, suboptimally controlled alloimmune response.

A prospective, iterative, adaptive trial of carfilzomib-based desensitization

Proteasome inhibitor-based strategies hold promise in transplant but have yielded varying results. Carfilzomib, a second-generation proteasome inhibitor, may possess advantages over bortezomib, the first-generation proteasome inhibitors. The purpose of this study was to evaluate the safety, toxicity, and preliminary efficacy of carfilzomib in highly HLA-sensitized kidney transplant candidates. Renal transplant candidates received escalating doses of carfilzomib followed by plasmapheresis (group A) or an identical regimen with additional plasmapheresis once weekly before carfilzomib dosing. Thirteen participants received carfilzomib, which was well tolerated with most adverse events classified as low grade. The safety profile was similar to bortezomib desensitization; however, neurotoxicity was not observed with carfilzomib. Toxicity resulted in permanent dose reduction in 1 participant but caused no withdrawals or deaths. HLA antibodies were substantially reduced with carfilzomib alone, and median maximal immunodominant antibody reduction was 72.8% (69.8% for group A, P = .031, 80.1% for group B, P = .938). After depletion, rebound occurred rapidly and antibody levels returned to baseline between days 81 and 141. Bone marrow studies revealed that approximately 69.2% of plasma cells were depleted after carfilzomib monotherapy. Carfilzomib monotherapy-based desensitization provides an acceptable safety and toxicity profile while leading to significant bone marrow plasma cell depletion and anti-HLA antibody reduction.

Specificity, strength, and evolution of pretransplant donor-specific HLA antibodies determine outcome after kidney transplantation

In this cohort study (N = 924), we investigated the evolution and clinical significance of pretransplant donor-specific HLA antibodies (preDSA), detected in the single-antigen beads assay but complement-dependent cytotoxicity crossmatch-negative. Donor specificity of the preDSA (N = 107) was determined by high-resolution genotyping of donor-recipient pairs. We found that in 52% of the patients with preDSA, preDSA spontaneously resolved within the first 3 months posttransplant. PreDSA that persisted posttransplant had higher pretransplant median fluorescence intensity values and more specificity against DQ. Patients with both resolved and persistent DSA had a high incidence of histological picture of antibody-mediated rejection (ABMR_h ; 54% and 59% respectively). Patients with preDSA that persisted posttransplant had worse 10-year graft survival compared to resolved DSA and preDSA-negative patients. Compared to cases without preDSA, Cox modeling revealed an increased risk of graft failure only in the patients with persistent DSA, in the presence (hazard ratio [HR] = 8.3) but also in the absence (HR = 4.3) of ABMR_h . In contrast, no increased risk of graft failure was seen in patients with resolved DSA. We conclude that persistence of preDSA posttransplant has a negative impact on graft survival, beyond ABMR_h . Even in the absence of antibody-targeting therapy, low median fluorescence intensity DSA and non-DQ preDSA often disappear early posttransplantation and are not deleterious for graft outcome.

Out with the old, in with the new: Virtual versus physical crossmatching in the modern era

The virtual crossmatch (VXM) is gaining acceptance as an alternative approach to assess donor:recipient compatibility prior to transplantation. In contrast to a physical crossmatch, the virtual crossmatch does not require viable donor cells but rather relies on complete HLA typing of the donor and current antibody assessment of the recipient. Thus, the VXM can be performed in minutes which allows for faster transplant decisions thereby increasing the likelihood that organs can be shipped across significant distances yet safely transplanted. Here, we present a brief review of the past 50 years of histocompatibility testing; from the original complement-dependent cytotoxicity crossmatch in 1969 to the new era of molecular HLA typing, solid-phase antibody testing and virtual crossmatching. These advancements have shaped a paradigm shift in our approach to transplantation. That is, foregoing a prospective physical crossmatch in favor of a VXM. In this review, we undertake an in-depth analysis of the pros- and cons- of physical and virtual crossmatching.Finally, we provide objective data on the selected use of the VXM which demonstrate the value of a VXM in lieu of the traditional physical crossmatch for safe and efficient organ transplantation.

HLA-B*15:47:01 allele with undefined serological equivalent considered as B Blank

We report a discordance between complement-dependent cytotoxicity and next-generation sequencing molecular typing revealing HLA-B*15:47:01 allele with undefined serological equivalent confirmed by high-level immunization against the B15 serotype. Due to the high-level immunization against HLA-B15 and B70 antigens, we considered the HLA-B*15:47:01 allele to be B Blank and not as B15 or B70 serological specificity.

The quest to decipher HLA immunogenicity: Telling friend from foe

Molecular mismatch load analysis was recently introduced as a means for performing risk stratification following organ transplantation. However, although good correlation was demonstrated between molecular mismatch load and generation of de novo donor-specific HLA antibody (DSA), quite a few exceptions exist, and the underlying factors that define HLA immunogenicity remain unclear. Herein, we present a new paradigm to interrogate differences between molecular mismatches that lead to the generation of de novo DSA and those that do not (the 2MM1DSA cohort). Specifically, patients transplanted across 2 HLA-DQ mismatches, who formed de novo DSA only to one mismatch (foe) but not the other (friend), provide a unique environment in which patient-specific factors that affect the immune response other than immunogenicity, such as infection and immunosuppression, can be controlled for. It further permits focusing on mismatches uniquely exhibited by the de novo DSA allele, rather than mismatches shared by both DSA and non-DSA alleles. This concept paper illustrates several examples, highlights the need for center-specific or population-specific cutoff values for posttransplant risk stratification, and mostly argues that if there is no direct correlation between molecular mismatch load and immunogenicity, then molecular mismatch load must not be adopted as an approach for equitable organ allocation.

Allocation to highly sensitized patients based on acceptable mismatches results in low rejection rates comparable to nonsensitized patients

Whereas regular allocation avoids unacceptable mismatches on the donor organ, allocation to highly sensitized patients within the Eurotransplant Acceptable Mismatch (AM) program is based on the patient's HLA phenotype plus acceptable antigens. These are HLA antigens to which the patient never made antibodies, as determined by extensive laboratory testing. AM patients have superior long-term graft survival compared with highly sensitized patients in regular allocation. Here, we questioned whether the AM program also results in lower rejection rates. From the PROCARE cohort, consisting of all Dutch kidney transplants in 1995-2005, we selected deceased donor single transplants with a minimum of 1 HLA mismatch and determined the cumulative 6-month rejection incidence for patients in AM or regular allocation. Additionally, we determined the effect of minimal matching criteria of 1 HLA-B plus 1 HLA-DR, or 2 HLA-DR antigens on rejection incidence. AM patients showed significantly lower rejection rates than highly immunized patients in regular allocation, comparable to nonsensitized patients, independent of other risk factors for rejection. In contrast to highly sensitized patients in regular allocation, minimal matching criteria did not affect rejection rates in AM patients. Allocation based on acceptable antigens leads to relatively low-risk transplants for highly sensitized patients with rejection rates similar to those of nonimmunized individuals.

Drug-induced alloreactivity: A new paradigm for allorecognition

Abacavir administration is associated with drug-induced hypersensitivity reactions in HIV+ individuals expressing the HLA-B*57:01 allele. However, the immunological effects of abacavir administration in an HLA-B57 mismatched transplantation setting have not been studied. We hypothesized that abacavir exposure could induce de novo HLA-B57-specific allorecognition. HIV-specific CD8 T cell clones were generated from HIV+ individuals, using single cell sorting based on HIV peptide/HLA tetramer staining. The T cell clones were assayed for alloreactivity against a panel of single HLA-expressing cell lines, in the presence or absence of abacavir. Cytokine assay, CD137 upregulation, and cytotoxicity were used as readout. Abacavir exposure can induce de novo HLA-B57 allorecognition by HIV-specific T cells. A HIV Gag RK9/HLA-A3-specific T cell did exhibit interferon-γ production, CD137 upregulation, and cytolytic effector function against allogeneic HLA-B57, but only in the presence of abacavir. Allorecognition was specific to the virus specificity, HLA restriction, and T cell receptor TRBV use of the T cell. We provide proof-of-principle evidence that administration of a drug could induce specific allorecognition of mismatched HLA molecules in the transplant setting. We suggest that HIV-seropositive recipients of an HLA-B57 mismatched graft should not receive abacavir until further studies are completed.

Relating the number of human leucocytes antigen mismatches to pregnancy complications in oocyte donation pregnancies: study protocol for a prospective multicentre cohort study (DONOR study)

INTRODUCTION

Oocyte donation (OD) enables women with reproductive failure to conceive. Compared with naturally conceived (NC) and in vitrofertilisation (IVF) pregnancies, OD pregnancies are associated with a higher risk of pregnancy complications. The allogeneic nature of the fetus in OD pregnancies possibly plays a role in the development of these complications. The objective of the current study is therefore to study the number and nature of human leucocyte antigen (HLA) mismatches between fetus and mother and its association with the development of hypertensive pregnancy complications.

METHODS AND ANALYSIS

In this prospective multicentre cohort study, 200 patients visiting one of the 11 participating fertility centres in the Netherlands to perform OD or embryo donation or surrogacy will be invited to participate. These patients will be included as the exposed group. In addition, 146 patients with a NC pregnancy and 146 patients who applied for non-donor IVF are included as non-exposed subjects. These groups are frequency matched on age and ethnicity and only singleton pregnancies will be included. The primary clinical outcome of the study is the development of hypertensive disease during pregnancy. Secondary outcomes are the severity of the pre-eclampsia, time to development of pre-eclampsia and development of other pregnancy complications. The association of high number of HLA mismatches (>5) between mother and fetus will be determined and related to clinical outcome and pregnancy complication.

ETHICS AND DISSEMINATION

This study received ethical approval from the medical ethics committee in the Leiden University Medical Centre, the Netherlands (P16.048, ABR NL56308.058.16). Study findings will be presented at (inter) national conferences and published in peer-reviewed journals.

Assessing the utilization of high-resolution 2-field HLA typing in solid organ transplantation

HLA typing in solid organ transplantation (SOT) is necessary for determining HLA-matching status between donor-recipient pairs and assessing patients' anti-HLA antibody profiles. Histocompatibility has traditionally been evaluated based on serologically defined HLA antigens. The evolution of HLA typing and antibody identification technologies, however, has revealed many limitations with using serologic equivalents for assessing compatibility in SOT. The significant improvements to HLA typing introduced by next-generation sequencing (NGS) require an assessment of the impact of this technology on SOT. We have assessed the role of high-resolution 2-field HLA typing (HR-2F) in SOT by retrospectively evaluating NGS-typed pre- and post-SOT cases. HR-2F typing was highly instructive or necessary in 41% (156/385) of the cases. Several pre- and posttransplant scenarios were identified as being better served by HR-2F typing. Five different categories are presented with specific case examples. The experience of another center (Temple University Hospital) is also included, whereby 21% of the cases required HR-2F typing by Sanger sequencing, as supported by other legacy methods, to properly address posttransplant anti-HLA antibody issues.

KIR specificity and avidity of standard and unusual C1, C2, Bw4, Bw6 and A3/11 amino acid motifs at entire HLA:KIR interface between NK and target cells, the functional and evolutionary classification of HLA class I molecules

Natural killer (NK) cells make vital contributions to the immune system and the reproductive system. Notably, NK cells of donor origin can recognize and kill residual leukaemic cells and cure malignant patients in hematopoietic stem cell (HSC) transplant setting. NK cell function is regulated by KIRs that recognize cognate HLA class I molecules on target cells, depending on their amino acid residues. In review, we addressed the question of binding capacity and avidity of HLA class I molecules to different killer cell immunoglobulin-like receptors (KIRs) depending on all interacting amino acid residues both on HLA and KIR side. We searched PubMed database and analysed available HLA:KIR crystallographic data for amino acid residues in HLA molecules, those physically involved in binding KIRs (termed here the "entire KIR interface"). Within entire KIR interface, we selected five functional sequence motifs (14-19, 66-76, 77-84, 88-92 and 142-151) and classified them according to the conservation of their amino acid sequences among 8,942 HLA class I molecules. Although some conserved amino acid motifs were shared by different groups of KIR ligands, the HLA motif combinations were exclusive for the ligand groups. In 135 common HLA class I molecules with known HLA:KIR recognition, we found 54 combinations of five motifs in each of the KIR-binding interfaces (C1, C2, Bw4, A3/11) and conserved non-KIR-binding interfaces. Based on the entire KIR interface, this analysis allowed to classify 8,942 HLA class I molecules into KIR specificity groups. This functional and evolutionary classification of entire KIR interfaces provides a tool for unambiguously predicting HLA:KIR interactions for common and those HLA molecules that have not yet been functionally tested. Considering the entire KIR interface in HLA class I molecules, functional interactions of HLA and KIR can be predicted in immune responses, reproduction and allotransplantation. Further functional studies are needed on the HLA:KIR interaction variations caused by the repertoires of peptides presented by HLA molecules and KIR polymorphisms at allelic level.

Bone Marrow Transplantation 1957-2019

Clinical bone marrow transplantation started in 1957 at a time when remarkably little was known about hematopoietic stems cells, immune responses to transplants or the identity of transplant antigens. This review will delineate the substantial increase in knowledge about these three areas gained between then and 1992 when the Ceppellini School course on Bone Marrow Transplantation was held, along with the progress made in clinical application, as well as the stumbling blocks that remained to be overcome by further research to advance knowledge. It will outline the significant progress made between 1992 and the present year, 2019, and the remaining problems.

HLA-DR/DQ molecular mismatch: A prognostic biomarker for primary alloimmunity

Alloimmune risk stratification in renal transplantation has lacked the necessary prognostic biomarkers to personalize recipient care or optimize clinical trials. HLA molecular mismatch improves precision compared to traditional antigen mismatch but has not been studied in detail at the individual molecule level. This study evaluated 664 renal transplant recipients and correlated HLA-DR/DQ single molecule eplet mismatch with serologic, histologic, and clinical outcomes. Compared to traditional HLA-DR/DQ whole antigen mismatch, HLA-DR/DQ single molecule eplet mismatch improved the correlation with de novo donor-specific antibody development (area under the curve 0.54 vs 0.84) and allowed recipients to be stratified into low, intermediate, and high alloimmune risk categories. These risk categories were significantly correlated with primary alloimmune events including Banff ≥1A T cell-mediated rejection (P = .0006), HLA-DR/DQ de novo donor-specific antibody development (P < .0001), antibody-mediated rejection (P < .0001), as well as all-cause graft loss (P = .0012) and each of these correlations persisted in multivariate models. Thus, HLA-DR/DQ single molecule eplet mismatch may represent a precise, reproducible, and widely available prognostic biomarker that can be applied to tailor immunosuppression or design clinical trials based on individual patient risk.

Shared alloimmune responses against blood and transplant donors result in adverse clinical outcomes following blood transfusion post-renal transplantation

De novo HLA donor-specific antibodies (DSA) following transplantation are associated with alloimmune injury and allograft failure. Blood transfusions are allogeneic, and when given posttransplant (PTBT) they may independently increase the risk of HLA antibody development. This study aims to analyze the development of HLA transfusion-specific antibodies (TSA) to blood donors of transfusions given posttransplant and examine the impact on clinical outcomes. A total of 244 blood donors of transfusions received by 86 transplant patients (46 who developed a DSA post transfusion and 40 who remained DSA negative) were HLA typed. De novo TSA developed against 150/244 (61.5%) blood donors. In 70/150 (46.7%) cases the TSA was of shared HLA antibody specificity with a DSA response in the recipient (DSA+ = TSA+). This occurred when there was a greater overall HLA match between the blood and transplant donor. DSA+ = TSA+ patients had increased risk of allograft failure (P = .0025) and AMR (P = .02) compared with the DSA+ ≠ TSA+ patients. To conclude, PTBT may elicit de novo HLA antibodies. Enhanced HLA matching between the blood and transplant donor is more likely to result in a DSA and TSA of shared antibody specificities. Transfusion avoidance or the use of HLA matched or selected blood may reduce this risk and improve outcomes.

Long-term outcomes of eculizumab-treated positive crossmatch recipients: Allograft survival, histologic findings, and natural history of the donor-specific antibodies

We aimed to determine the long-term outcomes of eculizumab-treated, positive crossmatch (+XM) kidney transplant recipients compared with +XM and age-matched negative crossmatch (-XM) controls. We performed an observational retrospective study and examined allograft survival, histologic findings, long-term B-cell flow cytometric XM (BFXM), and allograft-loss-associated factors. The mean (SD) posttransplant follow-up was 6.3 (2.5) years in the eculizumab group; 7.6 (3.5), +XM control group; 7.9 (2.5), -XM control group. The overall and death-censored allograft survival rates were similar in +XM groups (P = .73, P = .48) but reduced compared with -XM control patients (P < .001, P < .001). In the eculizumab-treated group, 57.9% (11/19) of the allografts had chronic antibody-mediated rejection, but death-censored allograft survival was 76.6%, 5 years; 75.4%, 7 years. Baseline IgG3 positivity and BFXM ≥300 were associated with allograft loss. C1q positivity was also associated with allograft loss but did not reach statistical significance. Donor-specific antibodies appeared to decrease in eculizumab-treated patients. After excluding patients with posttransplant plasmapheresis, 42.3% (9/21) had negative BFXMs; 31.8% (7/22), completely negative single-antigen beads 1 year posttransplant. Eculizumab-treated +XM patients had reduced allograft survival compared with -XM controls but similar survival to +XM controls. BFXM and complement-activating donor-specific antibodies (by IgG3 and C1q testing) may be used for risk stratification in +XM transplantation.

The omission of the "wet" pre-transplant crossmatch in renal transplant centres in Scotland

The methods used for assessment of immunological risk for a patient receiving a kidney from a deceased donor have undergone significant change in the last few years. Many centres now proceed to transplant without any additional laboratory-based HLA testing for patients who are well defined as HLA antibody negative. Using rapid HLA antibody tests at the time of donor offer, such as Luminex, it is also possible to omit wet crossmatches in many sensitised patients. This virtual crossmatch (vXM) approach provides benefits in reducing cold ischaemia time (CIT), but also carries risks such as missing clinically relevant non-HLA reactivity or allelic HLA antibody reactivity. A number of factors need to be in place in a laboratory to enable a vXM policy to be extended to both sensitised and non-sensitised patients including access to complete donor HLA typing, ability to undertake Luminex-based HLA antibody testing out of working hours, and access to senior H&I Scientist expertise to assess and interpret results. Other approaches, such as using peripheral blood lymphocytes for crossmatching, may also enable a reduction in CIT and transplant units need to assess the risks of extending vXM processes for their patients against potential benefits.

Transfer of donor anti-HLA antibody expression to multiple transplant recipients: A potential variant of the passenger lymphocyte syndrome?

Antibody-mediated rejection, whereby transplant recipient B cells and/or plasma cells produce alloreactive anti-human leukocyte antigen (HLA) antibodies, negatively influences transplant outcomes and is a major contributor to graft loss. An early humoral immune response is suggested by the production of anti-HLA donor-specific antibodies (DSA) that can be measured using solid phase assays. We report the early posttransplant coexistence of a shared anti-HLA antibody profile in 5 solid organ transplant recipients who received organs from the same donor. Retrospective analysis of the donor's serum confirmed the presence of the same anti-HLA profile, suggesting the transfer of donor-derived anti-HLA antibodies, or the cells that produce them, to multiple solid organ transplant recipients. The time frame and extent of transfer suggest a novel variant of the passenger lymphocyte syndrome. These findings have important implications for the consideration of all posttransplant antibody measurements, particularly the interpretation of non-DSAs in the sera of transplant recipients.

[Fabrication of hydrophilic medical catheter with hydrogel grafting and the in vivo evaluation of its histo-compatibility]

The biocompatible hydrogel was fabricated under suitable conditions with natural dextran and polyethylene glycol (PEG) as the reaction materials. The oligomer (Dex-AI) was firstly synthesized with dextran and allylisocyanate (AI). This Dex-AI was then reacted with poly (ethyleneglycoldiacrylate) (PEGDA) under the mass ratio of 4∶6 to get hydrogel (DP) with the maximum water absorption of 810%. This hydrogel was grafted onto the surface of medical catheter via diphenyl ketone treatment under ultraviolet (UV) initiator. The surface contact angle became lower from (97 ± 6.1)° to (25 ± 4.2)° after the catheter surface was grafted with hydrogel DP, which suggests that the catheter possesses super hydrophilicity with hydrogel grafting. The in vivo evaluation after they were implanted into ICR rats subcutaneously verified that this catheter had less serious inflammation and possessed better histocompatibility comparing with the untreated medical catheter. Therefore, it could be concluded that hydrogel grafting is a good technology for patients to reduce inflammation due to catheter implantation, esp. for the case of retention in body for a relative long time.

Histological analysis of biocompatibility of different surgical adhesives in subcutaneous tissue

The focus of this study was to test the hypothesis that there would be no difference between the biocompatibility of cyanoacrylate-based adhesives in rat subcutaneous tissues. In total, 60 male Wistar rats were used, and divided into four groups (n = 15): Group C (control, PVA-polyvinyl alcohol sponge), Group NO (N-butyl-2-octylcyanoacrylate), Group NH (n-hexyl-cyanoacrylate), and Group EC (Ethyl-cyanoacrylate). The animals were sacrificed after time intervals of 7, 15, and 30 days and tissues were analyzed under optical microscope as regards the events of inflammatory infiltrate, edema, necrosis, granulation tissue, giant cells, young fibroblasts, and collagen formation. The results were statistically analyzed by the Kruskal-Wallis and Dunn tests (p < .05). Significant inflammatory infiltrate was shown for all the adhesives in the time intervals of 7 (p = .004) and 15 days (p = .003). In the time interval of 30 days, moderate inflammatory infiltrate was observed in Groups NH and EC, with significant difference from Control (p = .001). The quantity of collagen fibers in all the experimental groups showed significant difference compared with Control in the time intervals of 7 (p = .002) and 15 days (p = .001), at 30 days only Group EC showed a smaller quantity of collagen fibers in comparison with Control (p = .001). The hypothesis was rejected. The adhesive N-butyl-2-octylcyanoacrylate had less influence on the inflammatory intensity of multinucleated giant cells. Ethyl-cyanoacrylate demonstrated the lowest level of biocompatibility among the adhesives, but its use in clinical practice may be promising for coaptation of smaller edges of superficial tissue. Surgical adhesives were shown to be feasible for clinical use in substitution of conventional suturing. Ethyl-cyanoacrylate should be used with caution due to its greater influence on tissues.

Image cytometry as an alternative to flow cytometry for the transplant histocompatibility crossmatch assay

The lymphocyte crossmatch is currently the only cell-based compatibility assay performed by histocompatibility laboratories for transplant purposes. While in many transplant programs the complement-dependent cytotoxicity crossmatch (CDCXM) remains in use, when available, the flow cytometry crossmatch (FCXM) is the method of choice because of its superior sensitivity and specificity. Unfortunately, the maintenance and cost of a flow cytometer is a considerable limitation for small histocompatibility laboratories. Therefore, in this study, we evaluated the use of the Cellometer Vision CBA image cytometer (Nexcelom Bioscience LLC, Lawrence, Massachusetts) as an alternative instrument to perform the crossmatch assay. The 3-color FCXM protocol was modified into two separate 2-color panel image cytometry crossmatches (IXMs), one for T cells and one for B cells. After initial serum and cell incubation, a cocktail consisting of PE/Cy5-conjugated anti-human CD3 or CD19 and PE-conjugated anti-human IgG F(ab')₂ was added to the T cell and B cell panels, respectively. The final cell preparation was added to a separate counting chamber. Images were captured using the Cellometer Vision CBA, an image cytometer designed for cell counting, size analysis and fluorescence intensity measurement. Thirty-nine IXMs were performed and compared with the FCXM. We obtained a concordance sensitivity of 94.1% and 100% and specificity of 100% and 88.9% for T cells and B cells, respectively. The linearity of the system was verified using dilutions of a sample containing known donor-specific anti-HLA antibodies (DSA) against the target cells. This feasibility study demonstrates that the FCXM test could be easily adapted to the Cellometer Vision CBA image cytometer without compromising specificity and sensitivity. The low instrumentation cost, minimal maintenance, and simple operation allow for efficient implementation or transition from the FCXM to the IXM method.

Histological picture of antibody-mediated rejection without donor-specific anti-HLA antibodies: Clinical presentation and implications for outcome

In this cohort study (n = 935 transplantations), we investigated the phenotype and risk of graft failure in patients with histological criteria for antibody-mediated rejection (ABMR) in the absence of circulating donor-specific anti-human leukocyte antigen (HLA) antibodies (DSA), and compared this to patients with definite ABMR and HLA-DSA-positivity. The histological picture did not differ between HLA-DSA-positive (n = 85) and HLA-DSA-negative (n = 123) cases of ABMR histology, apart from increased complement split product 4d (C4d) deposition in the peritubular capillaries in HLA-DSA-positive cases. Histology of ABMR without HLA-DSA was more transient than DSA-positive ABMR, and patients with ABMR histology without HLA-DSA had graft survival superior to that of HLA-DSA-positive patients, independent of concomitant T cell-mediated rejection (38.2%) or borderline changes (17.9%). Multivariate analysis showed that the risk of graft failure was not higher in patients with histological picture of ABMR (ABMR_h ) in the absence of HLA-DSA, compared to patients without ABMR_h . Despite an association between C4d deposition and HLA-DSA-positivity, using C4d deposition as alternative for the DSA criterion in the diagnosis of ABMR, as proposed in Banff 2017, did not contribute to the prognosis of graft function and graft failure. We concluded that biopsies with ABMR_h but without detectable HLA-DSA represent a distinct, often transient phenotype with superior allograft survival.

Value of monitoring circulating donor-reactive memory B cells to characterize antibody-mediated rejection after kidney transplantation

Antibody-mediated rejection (ABMR) is defined by specific histopathological lesions and evidence of circulating donor-specific antibodies (DSA). Although DSA are not always detectable, monitoring donor-reactive memory B cells (mBC) could identify patients at risk of developing ABMR. Peripheral donor-reactive mBC using a novel HLA B cell ELISpot assay, serum DSA, and numbers of different B cell subsets were assessed in 175 consecutive kidney transplants undergoing either for-cause or 6- and 24-month surveillance biopsies for their association with main histological lesions of ABMR and impact on allograft outcome. In 85 incident for-cause biopsies, high frequencies of donor-reactive mBC were detected in all 16 (100%) acute ABMR/DSA+ and most chronic ABMR, with or without DSA (24/30[80%] and 21/29[72.4%], respectively). In a longitudinal cohort of 90 nonsensitized patients, a progressively higher expansion of donor-reactive mBC than de novo DSA was observed at 6 and 24 months (8.8% vs 7.7% and 15.5% vs 11.1%, respectively) and accurately identified patients with ongoing subclinical ABMR (area under the curve = 0.917 and area under the curve = 0.809, respectively). An unsupervised hierarchical cluster analysis revealed a strong association between donor-reactive mBC with main fundamental allograft lesions associated with ABMR and conferred a significant deleterious impact on graft outcome. Monitoring donor-reactive mBC may be useful to further characterize humoral rejection after kidney transplantation.

Prognostic tools to assess candidacy for and efficacy of antibody-removal therapy

Currently, the ability to predict or monitor the efficacy of HLA antibody-removal therapies is deficient. We previously reported that titration studies are a consistent and accurate means of assessing antibody strength. To test whether titration studies can also predict which patients are better candidates for desensitization, we studied 38 patients from 3 centers (29 receiving plasmapheresis/low-dose intravenous immunoglobulin [IVIg]; 9 patients receiving high-dose IVIg). For patients undergoing plasmapheresis/low-dose IVIg, antibody titer reduction correlated with number of treatment cycles for both class I and II antibodies but only up to approximately 4 cycles. Reduction in titer slowed with additional cycles, suggesting a limit to the efficacy of this approach. Furthermore, initial titer (predesensitization) can guide the selection of candidates for successful antibody-removal treatment. In our experience, patients with antibodies at an initial titer >1:512 could not be reduced to the goal of a negative lymphocyte crossmatch, corresponding to a 1:16 titer, despite a significant increase in the number of treatment cycles. Change in mean fluorescence intensity (MFI) value did not correlate with success of treatment if initial MFI values were >10 000, likely due to single antigen bead saturation. Overall, we present a potential prognostic tool to predict candidacy and a monitoring tool to assess efficacy of desensitization treatment.

Banff Lung Report: Current knowledge and future research perspectives for diagnosis and treatment of pulmonary antibody-mediated rejection (AMR)

The Lung session of the 2017 14th Banff Foundation for Allograft Pathology Conference, Barcelona focused on the multiple aspects of antibody-mediated rejection (AMR) in lung transplantation. Multidimensional approaches for AMR diagnosis, including classification, histological and immunohistochemical analysis, and donor- specific antibody (DSA) characterization with their current strengths and limitations were reviewed in view of recent research. The group also discussed the role of tissue gene expression analysis in the context of unmet needs in lung transplantation. The current best practice for monitoring of AMR and the therapeutic approach are summarized and highlighted in this report. The working group reached consensus of the major gaps in current knowledge and focused on the unanswered questions regarding pulmonary AMR. An important outcome of the meeting was agreement on the need for future collaborative research projects to address these gaps in the field of lung transplantation.