A personal perspective: 100-year history of the humoral theory of transplantation. Transplantation. 2012;93:751-756. [PMID: 22453870 DOI: 10.1097/tp.0b013e3182483713]

De Novo Donor-Specific Antibodies after Heart Transplantation: A Comprehensive Guide for Clinicians

Antibodies directed against donor-specific human leukocyte antigens (HLAs) can be detected de novo after heart transplantation and play a key role in long-term survival. De novo donor-specific antibodies (dnDSAs) have been associated with cardiac allograft vasculopathy, antibody-mediated rejection, and mortality. Advances in detection methods and international guideline recommendations have encouraged the adoption of screening protocols among heart transplant units. However, there is still a lack of consensus about the correct course of action after dnDSA detection. Treatment is usually started when antibody-mediated rejection is present; however, some dnDSAs appear years before graft failure is detected, and at this point, damage may be irreversible. In particular, class II, anti-HLA-DQ, complement binding, and persistent dnDSAs have been associated with worse outcomes. Growing evidence points towards a more aggressive management of dnDSA. For that purpose, better diagnostic tools are needed in order to identify subclinical graft injury. Cardiac magnetic resonance, strain techniques, or coronary physiology parameters could provide valuable information to identify patients at risk. Treatment of dnDSA usually involves plasmapheresis, intravenous immunoglobulin, immunoadsorption, and ritxumab, but the benefit of these therapies is still controversial. Future efforts should focus on establishing effective treatment protocols in order to improve long-term survival of heart transplant recipients.

Antibody Therapeutics as Interfering Agents in Flow Cytometry Crossmatch for Organ Transplantation

Donor-recipient matching is a highly individualized and complex component of solid organ transplantation. Flowcytometry crossmatching (FC-XM) is an integral step in the matching process that is used to detect pre-formed deleterious anti-donor immunoglobulin. Despite high sensitivity in detecting cell-bound immunoglobulin, FC-XM is not able to determine the source or function of immunoglobulins detected. Monoclonal antibody therapeutic agents used in a clinic can interfere with the interpretation of FC-XM. We combined data from the prospectively maintained Antibody Society database and Human Protein Atlas with a comprehensive literature review of PubMed to summarize known FC-XM-interfering antibody therapeutics and identify potential interferers. We identified eight unique FC-XM-interfering antibody therapeutics. Rituximab (anti-CD20) was the most-cited agent. Daratumuab (anti-CD38) was the newest reported agent. We identified 43 unreported antibody therapeutics that may interfere with FC-XM. As antibody therapeutic agents become more common, identifying and mitigating FC-XM interference will likely become an increased focus for transplant centers.

Can We Use Eplets (or Molecular) Mismatch Load Analysis to Improve Organ Allocation? The Hope and the Hype

In recent years, there have been calls for implementation of "epitope matching" in deceased-donor organ allocation policies (later changed to "eplet matching"). Emerging data indeed support the use of molecular mismatch load analysis in specific patient groups, with the objective of posttransplant stratification into different treatment arms. For this purpose, the expectation is to statistically categorize patients as low- or high-immune-risk. Importantly, these patients will continue to be monitored' and their risk category, as well as their management, can be adjusted according to on-going findings. However, when discussing deceased donor organ allocation and matching algorithms, where the decision is not modifiable and has lasting impact on outcomes, the situation is fundamentally different. The goal of changing allocation schemes is to achieve the best possible HLA compatibility between donor and recipient. Immunologically speaking, this is a very different objective. For this purpose, the specific interplay of immunogenicity between the donor and any potential recipient must be understood. In seeking compatibility, the aim is not to redefine matching but to identify those mismatches that are "permissible" or' in other words, less immunogenic. In our eagerness to improve transplant outcome, unfortunately, we have conflated the hype with the hope. Terminology is used improperly, and new terms are created in the process with no sufficient support. Here, we call for a cautious evaluation of baseline assumptions and a critical review of the evidence to minimize unintended consequences.

Efficacy of Combined Desensitization Therapy Based on Protein A Immunoadsorption on Anti-human Leukocyte Antigen Antibodies in Sensitized Kidney Transplant Recipients: A Retrospective Study

Background and objectives

Protein A immunoadsorption (PA-IA) therapy is an immunoglobulin selective apheresis for pre-transplantation desensitization therapy and treatment of post-transplantation antibody-mediated rejection. There is no unified protocol for the timing of PA-IA therapy or its combination with other drug therapy. This study aimed to investigate and analyze the clearance effects of desensitization therapy on human leukocyte antigen (HLA) antibodies to provide a reference for the formulation of clinical desensitization therapy regimens.

Materials and methods

Overall, 27 kidney transplant recipients who received preoperative/postoperative desensitization therapy based on PA-IA therapy in combination with drug therapy were enrolled. The pre-treatment mean fluorescence intensity (MFI) of 1324 human leukocyte antigen (HLA) antibody specificities (MFI >2000) and the post-treatment MFI of the corresponding antibody specificities (after one, four, seven, and 10 sessions) were recorded to analyze the changes in antibody level reduction for the different antibody classes and MFI ranges.

Results

After 10 sessions of PA-IA therapy, the MFI of class I antibodies decreased from 8298.56 to 3196.15 (reduction of 66.80%), while the MFI of class II antibodies decreased from 13,521.09 to 2773.29 (reduction of 71.14%). The pre-treatment level of class II antibodies was significantly higher than that of class I antibodies (p<0.001), whereas the post-treatment levels of class I and II antibodies were comparable (p>0.05). The clearance effects of PA-IA therapy were greater for strongly positive (MFI>10,000) class II antibodies than for strongly positive class I antibodies, showing a reduction of 62.59% (25.17% to 91.04%) and 45.13% (32.70% to 73.94%), respectively (p=0.015).

Conclusions

We confirmed the removal efficacy of PA-IA for HLA antibodies. The removal efficacy of class II antibodies on PA-IA is not inferior to that of class I. Under an adequate number of treatment sessions, the clearance effect of PA-IA therapy for strongly positive class II antibodies may be greater than that for strongly positive class I antibodies.

Imlifidase-generated Single-cleaved IgG: Implications for Transplantation

BACKGROUND

Imlifidase is an immunoglobulin G (IgG)-specific protease conditionally approved in the EU for desensitization in highly sensitized crossmatch positive kidney transplant patients. Imlifidase efficiently cleaves both heavy chains of IgG in a 2-step process. However, low levels of the intermediate cleavage product, single-cleaved IgG (scIgG), may persist in the circulation. The study objective was to investigate Fc-mediated effector functions of scIgG and its potential impact on common clinical immunologic assays used to assess transplant eligibility.

METHODS

Imlifidase-generated scIgG, obtained by in vitro cleavage of HLA-sensitized patient serum or selected antibodies, was investigated in different complement- and FcγR-dependent assays and models, including clinical tests used to evaluate HLA-specific antibodies.

RESULTS

ScIgG had significantly reduced Fc-mediated effector function compared with intact IgG, although some degree of activity in complement- and FcγR-dependent models was still detectable. A preparation of concentrated scIgG generated from a highly HLA-sensitized individual gave rise to a positive signal in the anti-HLA IgG LABScreen, which uses anti-Fc detection, but was entirely negative in the C1qScreen. The same high-concentration HLA-binding scIgG preparation also generated positive complement-dependent cytotoxicity responses against 80%-100% of donor T and B cells, although follow-up titrations demonstrated a much lower intrinsic activity than for intact anti-HLA IgG.

CONCLUSIONS

ScIgG has a significantly reduced capacity to mediate Fc-dependent effector functions. However, remaining HLA-reactive scIgG in plasma after imlifidase treatment can cause positive assay results equivalent to intact IgG in clinical assays. Therefore, complete IgG cleavage after imlifidase treatment is essential to allow correct decision-making in relation to transplant eligibility.

The role of endothelin II type A receptor (ETAR) in transplant injury

PURPOSE OF REVIEW

Antibody-mediated rejection is the leading cause of deterioration of graft function and graft loss after kidney transplantation. Recent studies have reported an increasing role of non-HLA antibodies in the humoral injury after kidney transplantation. We decided to present the influence of non-HLA antibodies - anti-endothelin II type A receptor (ETAR) on a transplanted kidney and characterize the significance of their receptor.

RECENT FINDINGS

The role of non-HLA antibodies is still uncertain. Many studies suggest that the presence of non-HLA antibodies, including anti-ETAR antibodies, is among the risk factors for antibody-mediated rejection, graft injury, and graft loss. The discovery of new antigen targets and antibodies, which participate in the humoral response, has provided a significantly better understanding of the mechanism of antibody-mediated rejection after organ transplantation.

SUMMARY

Endothelin and its receptors play an important role in physiology and pathophysiology after solid organ transplantation. ETAR and antibodies against ETAR may participate in humoral rejection and graft damage. The measurement of anti-ETAR antibodies may identify patients with an increased risk of rejection and even loss of a transplanted organ. Expression of ETAR detected in biopsy of transplant could become an additional tool used to better understand humoral activity. More research is needed to address many questions about non-HLA directed rejection and graft damage.

Significance of HLA-DQ in kidney transplantation: time to reevaluate human leukocyte antigen matching priorities to improve transplant outcomes? An expert review and recommendations

The weight of human leukocyte antigen (HLA) matching in kidney allocation algorithms, especially in the United States, has been devalued in a stepwise manner, supported by the introduction of modern immunosuppression. The intent was further to reduce the observed ethnic/racial disparity, as data emerged associating HLA matching with decreased access to transplantation for African American patients. In recent years, it has been increasingly recognized that a leading cause of graft loss is chronic antibody-mediated rejection, attributed to the development of de novo antibodies against mismatched donor HLA expressed on the graft. These antibodies are most frequently against donor HLA-DQ molecules. Beyond their impact on graft survival, generation of de novo donor-specific HLA antibodies also leads to increased sensitization, as measured by panel-reactive antibody metrics. Consequently, access to transplantation for patients returning to the waitlist in need of a second transplant is compromised. Herein, we address the implications of reduced HLA matching policies in kidney allocation. We highlight the observed diminished outcome data, the significant financial burden, the long-term health consequences, and, more important, the unintended consequences. We further provide recommendations to examine the impact of donor-recipient HLA class II and specifically HLA-DQα₁β₁ mismatching, focusing on collection of appropriate data, application of creative simulation approaches, and reconsideration of best practices to reduce inequalities while optimizing patient outcomes.

Measuring human leukocyte antigen alloantibodies: beyond a binary decision

PURPOSE OF REVIEW

Accurate measurement of human leukocyte antigen antibodies is critical for making clinical decisions treating patients awaiting transplantation or monitoring them post transplantation. Single antigen bead assay results are given as Mean Fluorescence Intensity, falling short of providing the required quantitative measure.

RECENT FINDINGS

Titration studies were shown to circumvent the limitation of target-saturation that affect interpretation of single antigen bead assays especially in highly sensitized patients with strong antibodies. In fact, titration information can serve to measure efficacy of antibody removal during pretransplant desensitization using plasmapheresis/intravenous immunoglobulin (PP/IVIg) approaches. Moreover, recent studies indicate that knowing the donor-specific antibody titer has prognostic value that can guide PP/IVIg desensitization treatments. Newer data demonstrates an additional layer of information obtained by titration studies allowing to stratify patients with very high cPRA (>99%) based on the strength of the antibodies present, rather than the breadth. This data can thereby identify patients that are more likely to benefit from desensitization approaches on the transplant wait-list.

SUMMARY

Titration studies have a prognostic value with regards to quantifying antibody strength. Obtaining this information does not require performing the complete set of dilutions. In fact, performing two to three specific dilutions can provide relevant information while maintaining practical cost.

Histopathology of Human Donor Spleen Utilized as a Desensitization Tool Before Intestinal Transplantation

OBJECTIVES

To describe the histopathologic and immunophenotypic features of a temporary splenic allograft exposed to massive donor-specific antibody (DSA) insult.

METHODS

A human cadaveric donor splenic allograft was temporarily transplanted in a highly sensitized patient with the intention of removing DSA before intestinal transplantation from the same donor. Before splenic transplant, the patient had several preformed cytotoxic DSAs that resulted in positive flow cytometric and complement-dependent cytotoxicity crossmatch. The splenic allograft was removed before intestinal transplantation and evaluated by H&E and immunohistochemical stains.

RESULTS

Explanted donor splenic allograft showed several histopathologic changes: expanded red pulp secondary to congestion and marked neutrophilic and macrophage infiltration in the sinusoids, numerous neutrophilic microabscesses, and focal capillaritis. The C4d and IgG immunohistochemical stains were diffusely positive in the endothelial lining of the capillaries and sinusoidal lining, indicating diffuse IgG deposition and complement activation.

CONCLUSIONS

We propose that the noted changes are features of splenic acute antibody-mediated rejection (AMR). Additional cases are required to determine all the features of splenic AMR. To our knowledge, this is the first report of histopathologic changes in donor spleen after exposure to DSA for a short duration.

Phasing out the pre-transplant cytotoxicity crossmatch: Are we missing something?

Introduction:

The anti-human globulin-enhanced complement-dependent cytotoxicity crossmatch (AHG-CDCXM) assay has been used to assess the presence of donor-specific antibodies (DSA) in recipient’s serum before kidney transplantation. The flow cytometric crossmatch (FCXM) assay was first introduced as an additional test. The aim of this study was to clinically validate the single use of the FCXM assay.

Methods:

This study compared the outcomes of a cohort of kidney transplant patients that underwent FCXM only (FCXM group) versus a cohort of kidney transplant patients that underwent AHG-CDCXM (control group).

Results:

Ninety-seven patients in the FCXM group and 98 controls were included. All crossmatches in the control group were negative. One patient in the FCXM group had a positive B cell crossmatch. One year after transplantation, there were no significant differences in patient survival (p = 0.591) and graft survival (p = 0.692) between the groups. Also, no significant difference was found in the incidence of Banff ≥ 1A acute cellular rejection episodes (p = 0.289). However, acute antibody-mediated rejections occurred in 3 controls (p = 0.028).

Conclusion:

The results showed that discontinuing the AHG-CDCXM assay does not modify the clinical outcomes in a 1-year follow-up.

Does a Useful Test Exist to Properly Evaluate the Pathogenicity of Donor-specific Antibodies? Lessons From a Comprehensive Analysis in a Well-studied Single-center Kidney Transplant Cohort

BACKGROUND

Donor-specific antibodies (DSA) play a major role in antibody-mediated rejection (AMR) and graft dysfunction. However, the clinical relevance of complement-binding anti-HLA antibodies remains unclear.

METHODS

Here, we analyzed DSA detected in the serum (sDSA) using single antigen bead, C1q, and C3d assays combined with the study of intragraft DSA (gDSA) in 86 patients who had DSA and underwent a kidney biopsy for cause (n = 58) or without evidence of kidney dysfunction (n = 28). DSA characteristics were collected and related to the presence of AMR, graft histological features, and allograft survival.

RESULTS

Forty-five patients (52%) had C1q DSA, and 42 (51%) had C3d DSA. Allograft biopsies revealed AMR in 63 cases (73%), regardless of kidney function. gDSA were identified in 74% of biopsies. We observed a strong correlation among single antigen bead mean fluorescence intensity and complement assays positivity, presence of gDSA, and AMR occurrence.

CONCLUSIONS

Complement-binding DSA per se were not significantly associated with allograft survival in the entire study sample. Finally, gDSA predicted subsequent graft loss in patients who showed a stable renal function at the day of biopsy. Our data suggest that DSA mean fluorescence intensity and presence of gDSA might provide prognostic information during posttransplant monitoring.

Endothelin A Receptors Expressed in Glomeruli of Renal Transplant Patients May Be Associated with Antibody-Mediated Rejection

BACKGROUND

Non-human leukocyte antigen (HLA) anti-endothelin A receptor antibodies are presented as being potentially important, but the expression of the endothelin A receptor in glomeruli (ETA receptor (g+)) has not yet been described. We decided to evaluate the presence and relevance of the ETA receptor in for-cause renal transplant biopsies. The aim of our study was to evaluate the immunoreactivity of the ETA receptor and its significance in patients who underwent a renal transplant biopsy due to the deterioration of transplant function, with detailed characterization of staining in glomeruli.

METHODS

The immunohistochemical expression of ETA receptor (ETAR) was analyzed in renal transplant biopsies. Microscopic evaluation was performed on paraffin sections in glomeruli. The analysis was performed using a two-step scale (0: lack of ETAR expression; 1: the presence of ETAR expression-mild to moderate immunoreactivity).

RESULTS

We analyzed 149 patients who underwent renal allograft biopsy after renal transplantation. Positive staining of ETA receptors in glomeruli (ETA receptor (g+)) was noticed in 13/149 (8.7%) patients. Five of these 13 (38.5%) patients with ETA receptor (g+) developed antibody-mediated rejection (AMR), while 13 of the remaining 136 (9.5%) ETA receptor (g-) patients developed AMR (p = 0.0022). Graft loss was noticed in all but one ETA receptor (g+) patient with AMR (4/5; 80%), but only in 2/13 (15%) ETA receptor (g-) patients with AMR (p = 0.009) during the first year after biopsy.

CONCLUSIONS

The expression of endothelin A receptors in glomeruli seems to be a potentially important feature in the diagnosis of damage during antibody-mediated rejection. It may help to identify patients at a higher risk of allograft rejection and injury.

HLA antibodies are associated with deterioration of kidney allograft function irrespective of donor specificity

BACKGROUND

Donor-specific antibodies are associated with high immunological risk and poor allograft outcome. Risk and clinical relevance of non-donor-specific HLA antibodies is less clear.

METHODS

A retrospective single-center study was conducted in all patients receiving a first kidney transplant at the University hospital of Zürich between 01/2006 and 02/2015. Patients were stratified into 3 groups having either no HLA antibodies at all (NoAB), HLA antibodies with donor specificity (DSA) and HLA antibodies without donor specificity (NonDSA). Allograft outcome was assessed using the slope of the estimated glomerular filtration rate (eGFR slope) starting at 12 months after transplantation.

RESULTS

During a median follow-up of 1808 days HLA antibodies were detected in 106 of 238 eligible patients (44%). Out of these, 73 patients (69%) had DSA and 33 patients (31%) had NonDSA only. Medium-term allograft function, as determined by eGFR slope over three years, improved in patients with NoAB (months 12-48: +0.7 ml/min/1.73 m²) but deteriorated significantly in patients with both DSA (months 12-48: -1.5 ml/min per1.73 m²/year, p = 0.015) and NonDSA (months 12-48: -1.8 ml/min per1.73 m²/year, p = 0.03) as compared to the group with NoAB.

CONCLUSION

Both, donor-specific and non-donor-specific HLA antibodies are associated with medium-term kidney allograft dysfunction as compared to patients with no HLA antibodies.

Understanding and using AlloSure donor derived cell-free DNA

Renal transplant is a lifesaving and cost-effective intervention for patients with End Stage Renal Failure. Yet it is often regarded as replacement therapy rather than a cure given the overall failure rate over time. With a shortage of organs, this global issue has been further compounded by increased incidences of obesity, hypertension and diabetes, such that the disease burden and need for transplantation continues to increase. Considering the lifetime of immunosupression in transplant patients, there will also be significant associated co-morbidities By leveraging the advances in innovation in Next Generation Sequencing, the field of transplant can now monitor patients with an optimized surveillance schedule, and change the care paradigm in the post-transplant landscape. Notably, low grade inflammation is an independent risk for mortality across different disease states. In transplantation, sub-clinical inflammation enhances acute and chronic rejection, as well as accelerates pathologies that leads to graft loss. Cell free DNA has been shown to be increased in inflammatory processes as we all as provide an independent predictor of all-cause mortality. This review considers the utility of AlloSure, a donor derived cell free DNA molecular surveillance tool, which has shown new clinical insights on how best to manage renal transplant patients, and how to improve patient outcomes.

Risk Factors of Antibody-Mediated Rejection and Predictors of Outcome in Kidney Transplant Recipients

OBJECTIVES

Kidney transplant is the treatment of choice for patients with end-stage renal disease. Antibody-mediated rejection is associated with higher rates of graft loss in kidney transplant recipients. Determining the risk factors of antibody-mediated rejection is vital for its prevention, early diagnosis, and appropriate treatment, as these factors may be important in maintaining long-term graft survival in transplant recipients. In our study, we analyzed the risk factors of antibody-mediated rejection in kidney transplant recipients and the negative impact of antibody-mediated rejection on graft function.

MATERIALS AND METHODS

We analyzed demographic and clinical data of 124 kidney transplant recipients (37 female [30%] and 87 male [70%] patients) who were diagnosed with antibody-mediated rejection at transplant biopsy. We compared graft outcomes of this patient cohort versus 75 kidney transplant recipients (24 female [32%] and 51 male [68%] patients) who were not diagnosed with antibody-mediated rejection.

RESULTS

Mean ages of patients with and without antibody-mediated rejection were 38.2 ± 13.6 and 34.4 ± 13.0 years, respectively. Mean ages of donors for patients with antibody-mediated rejection was significantly higher (48.0 ± 13.2 y) than for donors of patients without antibody-mediated rejection (47.1 ± 11.4 y; P < .05). Rate of graft loss was 15.3% in patients with antibody-mediated rejection; patients without antibody-mediated rejection had no graft loss (P < .05). Positive panel reactive antibody levels and blood transfusion before transplant were found to be risk factors of antibody-mediated rejection in kidney transplant recipients. However, recipients who received tacrolimus had less antibody-mediated rejection episodes than recipients who received sirolimus or cyclophosphamide.

CONCLUSIONS

Antibody-mediated rejection is associated with high rates of graft loss in kidney transplant recipients. Avoiding blood transfusion, lowering panel reactive antibody levels, choosing younger donors, and using tacrolimus in high-risk kidney transplant recipients may reduce antibody-mediated rejection rates and provide better graft survival.

Sex-Specific Differences in HLA Antibodies after Pneumococcal Vaccination in Kidney Transplant Recipients

In transplant recipients vaccination against Streptococcus pneumoniae is recommended to reduce mortality from invasive pneumococcal disease. It is still debated if vaccination in transplant recipients triggers alloresponses. Therefore, it was our aim to define if vaccination with Prevenar 13^®, a 13-valent, conjugated pneumococcal vaccine (Pfizer, New York, NY, USA) that acts T cell dependently, induces human leukocyte antigen (HLA) antibodies in clinically stable kidney transplant recipients. Forty-seven patients were vaccinated once with Prevenar 13^® and HLA antibodies were determined prior to vaccination and at month 1 and 12 thereafter. In parallel, pneumococcal IgG antibodies were measured. Using Luminex™ Mixed Beads technology (One Lambda/Thermo Fisher, Canoga Park, CA, USA) we observed overall no change in HLA antibodies after vaccination. Pneumococcal antibodies increased significantly at month 1 (p < 0.0001) and remained elevated at month 12 (p < 0.005). A more detailed analysis of HLA antibodies showed that in 18 females HLA class I and II antibodies increased significantly at month 1 and 12 (p < 0.05); whereas in 29 males HLA class I and II antibodies tended to decrease. Using Luminex™ Single Antigen Beads assay, no de novo donor-specific HLA antibodies were detected after vaccination. In conclusion, the current data indicate that females may be more susceptible to the induction of (non-specific) HLA antibodies after vaccination.

Antibodies against Angiotensin II Type 1 and Endothelin A Receptors: Relevance and pathogenicity

Antibodies against two G-protein coupled receptors (GPCRs), angiotensin II type 1 receptor (AT1R) and endothelin A receptor (ETAR) are among a growing number of autoantibodies that are found to be associated with allograft dysfunction. AT1R antibodies (AT1Rabs) and ETAR antibodies (ETARabs) have been shown to activate their target receptors and affect signaling pathways. Multiple single center reports have shown an association between presence of these antibodies and acute or chronic rejection and graft loss in kidney, heart, liver, lung and composite tissue transplantations. However, the characteristics of patients that are most likely to develop adverse outcomes, the phenotypes associated with graft damage solely due to these antibodies, and the antibody titer required to cause dysfunction are areas that remain controversial. This review compiles existing knowledge on the effect of antibodies against GPCRs in other diseases in order to bridge the gap in knowledge within transplantation biology. Future areas for research are highlighted and include the need for functional assays and treatment protocols for transplant patients who present with AT1Rabs and ETARabs. Understanding how antibodies that activate GPCRs influence transplantation outcome will have direct clinical implications for preemptive evaluation of transplant candidates as well as the post-transplant care of organ recipients.

Donor-specific Antibody Surveillance and Graft Outcomes in Pediatric Kidney Transplant Recipients

BACKGROUND

The development of de novo donor-specific antibodies (dnDSA) has been associated with rejection and graft loss in kidney transplantation, and DSA screening is now recommended in all kidney transplant recipients. However, the clinical significance of dnDSA detected by screening patients with a stable creatinine remains unclear.

METHODS

One hundred three patients younger than 18years receiving a first, kidney alone transplant between December 1, 2007, and December 31, 2013, underwent DSA screening every 3months for 2years posttransplant, with additional testing as clinically indicated. No treatment was given for DSAs in the absence of biopsy-proven rejection.

RESULTS

Twenty (19%) patients had dnDSA first detected on a screening test, and 13 (13%) patients had dnDSA first detected on a for-cause test. Mean follow-up time posttransplant was 4.4years. Screening-detected dnDSA was associated with an increased risk of rejection within 3years, microvascular inflammation, and C4d staining on a 2-year protocol biopsy. In a Cox proportional hazards regression, screening-detected dnDSA was not associated with time to 30% decline in estimated glomerular filtration rate (adjusted hazard ratio, 0.88; 95% confidence interval [CI], 0.30-2.00; P=0.598) or graft loss. dnDSA first detected on for-cause testing was associated with a 2.8 times increased risk of decline in graft function (95% CI, 1.08-7.27; P=0.034) and a 7.34 times increased risk of graft loss (95% CI, 1.37-39.23 P=0.020) compared with those who did not develop dnDSA.

CONCLUSIONS

The clinical setting in which dnDSA is first detected impacts the association between dnDSA and graft function. Further research is needed to clarify the role of dnDSA screening in pediatric kidney transplantation.

Determination of HLA-A, -B, -C, -DRB1 and -DQB1 allele and haplotype frequencies in heart failure patients

Aims

Cell therapy can be used to repair functionally impaired organs and tissues in humans. Although autologous cells have an immunological advantage, it is difficult to obtain high cell numbers for therapy. Well‐characterized banks of cells with human leukocyte antigens (HLA) that are representative of a given population are thus needed. The present study investigates the HLA allele and haplotype frequencies in a cohort of heart failure (HF) patients.

Methods and results

We carried out the HLA typing and the allele and haplotype frequency analysis in 247 ambulatory HF patients. We determined HLA class I (A, B, and C) and class II (DRB1 and DQB1) using next‐generation sequencing technology. The allele frequencies were obtained using Python for Population Genomics (PyPop) software, and HLA haplotypes were estimated using HaploStats. A total of 30 HLA‐A, 56 HLA‐B, 23 HLA‐C, 36 HLA‐DRB1, and 15 HLA‐DQB1 distinct alleles were identified within the studied cohort. The genotype frequencies of all five HLA loci were in Hardy–Weinberg equilibrium. We detected differences in HLA allele frequencies among patients when the etiological cause of HF was considered. There were a total of 494 five‐loci haplotypes, five of which were present six or more times. Moreover, the most common estimated HLA haplotype was HLA‐A*01:01, HLA‐B*08:01, HLA‐C*07:01, HLA‐DRB1*03:01, and HLA‐DQB1*02:01 (6.07% haplotype frequency per patient). Remarkably, the 11 most frequent haplotypes would cover 31.17% of the patients of the cohort in need of allogeneic cell therapy.

Conclusions

Our findings could be useful for improving allogeneic cell administration outcomes without concomitant immunosuppression.

Human Leukocyte Antigen Epitope Matching in Solid Organ Transplantation

HLA epitope matching provides a better approach to stratify patients at risk of developing antibody-mediated rejection compared with counting HLA mismatches. However, several immunologic parameters are not incorporated into these algorithms used to assess HLA epitopes, raising questions about the predictive value of these programs. Therefore, it is imperative to obtain more 3D structural data of antibody-antigen binding to "train" these computer algorithms. Also, mechanistic studies should be performed to prove these theoretic "epitopes." Most important, more information is needed to ensure these predictive computer algorithms are equitable and safe to use in clinical diagnostics before wide-scale implementation.

Control of Humoral Response in Renal Transplantation by Belatacept Depends on a Direct Effect on B Cells and Impaired T Follicular Helper-B Cell Crosstalk

Generation of de novo donor-specific antibodies (dnDSAs) after renal transplant is recognized as the leading cause of late transplant failure. Hence, the optimal immunosuppressive strategies to limit dnDSA development need to be defined. Recent clinical trials using the novel costimulatory blockade agent CTLA4-Ig (Belatacept) have shown that kidney transplant recipients (KTRs) treated with Belatacept have better graft survival and function and a lower proportion of dnDSAs than control-treated KTRs. Mechanisms involved in the control of humoral responses by Belatacept remain to be investigated. Here, we analyzed the effect of Belatacept on different steps of the B cell-mediated response in humans. In vitro, Belatacept reduced plasmablast differentiation, Ig production, and the expression of the major transcription factor involved in plasma cell function, Blimp-1, in a T cell-independent manner. Moreover, Belatacept induced activation of the STAT3 transcription factor in stimulated B cells and reduced the expression of CD86. Additionally, Belatacept blocked CD28-mediated activation of T follicular helper cells (Tfhs) in an autologous Tfh-memory B cells model. We then validated these observations in KTRs treated with Belatacept, who had a reduced proportion of blood effector B cells and activated Tfh (PD1⁺ICOS⁺) compared with control-treated KTRs. Our in vitro and in vivo results suggest that Belatacept modulates B cell function directly and at the level of B cell-Tfh interaction. These mechanisms likely account for the optimal control of humoral responses observed in KTRs treated with Belatacept.

Evidence for an important role of both complement-binding and noncomplement-binding donor-specific antibodies in renal transplantation

PURPOSE OF REVIEW

The review describes the current clinical relevance of circulating anti-human leukocyte antigen (anti-HLA) antibodies in kidney transplantation and discusses recent improvements in their characterization that provide new insights into the identification and management of important clinical outcomes.

RECENT FINDINGS

Recent studies addressing the relationships between donor-specific anti-HLA antibody (HLA-DSA) properties (i.e., their strength, complement-binding capacity, and IgG subclass composition) and allograft injury and survival have highlighted their relevance in the prediction of antibody-mediated injury and allograft loss.

SUMMARY

Antibody-mediated rejection is the leading cause of kidney allograft loss. Although considerable experimental and clinical evidence suggests a causal effect of circulating HLA-DSAs in antibody-mediated rejection and allograft failure, HLA-DSAs induce a wide spectrum of injuries to the allograft that illustrate the need to delineate the characteristics of HLA-DSAs that confer pathogenesis. Current risk stratification is based on HLA-DSA characteristics, including antibody specificity, HLA class, and strength. Recently, the complement-binding capacity of HLA-DSAs has been recognized as a clinically relevant marker for predicting pathogenicity and allograft loss. Emerging data also support a role for HLA-DSA IgG subclass composition in discriminating distinct patterns of antibody-mediated injury. This progress in our understanding of HLA-DSA pathogenicity provides new tools to stratify individual immunological risks. However, specific prospective studies addressing immunological risk stratification in large and unselected populations are required to define the clinical benefit and cost-effectiveness of such a comprehensive assessment of HLA-DSAs before implementation in current clinical practice.

Complement-Activating Anti-HLA Antibodies in Kidney Transplantation: Allograft Gene Expression Profiling and Response to Treatment

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, IFNγ 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.

The extracellular matrix of the gastrointestinal tract: a regenerative medicine platform

The synthesis and secretion of components that constitute the extracellular matrix (ECM) by resident cell types occur at the earliest stages of embryonic development, and continue throughout life in both healthy and diseased physiological states. The ECM consists of a complex mixture of insoluble and soluble functional components that are arranged in a tissue-specific 3D ultrastructure, and it regulates numerous biological processes, including angiogenesis, innervation and stem cell differentiation. Owing to its composition and influence on embryonic development, as well as cellular and organ homeostasis, the ECM is an ideal therapeutic substrate for the repair of damaged or diseased tissues. Biologic scaffold materials that are composed of ECM have been used in various surgical and tissue-engineering applications. The gastrointestinal (GI) tract presents distinct challenges, such as diverse pH conditions and the requirement for motility and nutrient absorption. Despite these challenges, the use of homologous and heterologous ECM bioscaffolds for the focal or segmental reconstruction and regeneration of GI tissue has shown promise in early preclinical and clinical studies. This Review discusses the importance of tissue-specific ECM bioscaffolds and highlights the major advances that have been made in regenerative medicine strategies for the reconstruction of functional GI tissues.

Histocompatibility and management of the highly sensitized kidney transplant candidate

PURPOSE OF REVIEW

Increasing national participation in kidney paired donation and implementation of new sharing policies via the current kidney allocation system have brought about greater opportunities for the most highly sensitized patients awaiting a kidney transplant. The purpose of this review is to discuss the application of histocompatibility data in the context of the clinical practice of kidney transplantation as pertains to the sensitized candidate.

RECENT FINDINGS

With desensitization techniques, transplantation across virtually any antibody barrier is technically feasible, but long-term outcomes after transplantation are improved when the immunologic match between donor and recipient is optimized. Solid-phase immunoassays have changed the landscape of histocompatibility testing. These sensitive and specific assays for identifying donor-specific antibody not only help determine feasibility of transplantation but have enabled outcomes studies aimed at understanding the spectrum of risk posed by different antibody profiles. This, in turn, has helped guide decision-making in donor selection, in particular for sensitized patients.

SUMMARY

Careful evaluation of donor-specific antibody profiles with individualized, patient-specific determination of unacceptable antigens is necessary to ensure that highly sensitized patients receive every opportunity for transplantation.

From Humoral Theory to Performant Risk Stratification in Kidney Transplantation

The purpose of the present review is to describe how we improve the model for risk stratification of transplant outcomes in kidney transplantation by incorporating the novel insights of donor-specific anti-HLA antibody (DSA) characteristics. The detection of anti-HLA DSA is widely used for the assessment of pre- and posttransplant risks of rejection and allograft loss; however, not all anti-HLA DSA carry the same risk for transplant outcomes. These antibodies have been shown to cause a wide spectrum of effects on allografts, ranging from the absence of injury to indolent or full-blown acute antibody-mediated rejection. Consequently, the presence of circulating anti-HLA DSA does not provide a sufficient level of accuracy for the risk stratification of allograft outcomes. Enhancing the predictive performance of anti-HLA DSA is currently one of the most pressing unmet needs for facilitating individualized treatment choices that may improve outcomes. Recent advancements in the assessment of anti-HLA DSA properties, including their strength, complement-binding capacity, and IgG subclass composition, significantly improved the risk stratification model to predict allograft injury and failure. Although risk stratification based on anti-HLA DSA properties appears promising, further specific studies that address immunological risk stratification in large and unselected populations are required to define the benefits and cost-effectiveness of such comprehensive assessment prior to clinical implementation.

Antibody-Mediated Rejection: A Review

BACKGROUND

Chronic antibody injury is a serious threat to allograft outcomes and is therefore the center of active research. In the continuum of allograft rejection, the development of antibodies plays a critical role. In recent years, an increased recognition of molecular and histologic changes has provided a better understanding of antibody-mediated rejection (AMR), as well as potential therapeutic interventions. However, several pathways are still unknown, which accounts for the lack of efficacy of some of the currently available agents that are used to treat rejection.

METHODS

We review the current diagnostic criteria for AMR; AMR paradigms; and desensitization, treatment, and prevention strategies.

RESULTS

Chronic antibody-mediated endothelial injury results in transplant glomerulopathy, manifested as glomerular basement membrane duplication, double contouring, or splitting. Clinical manifestations of AMR include proteinuria and a rise in serum creatinine. Current strategies for the treatment of AMR include antibody depletion with plasmapheresis (PLEX), immunoadsorption (IA), immunomodulation with intravenous immunoglobulin (IVIG), and T cell- or B cell-depleting agents. Some treatment benefits have been found in using PLEX and IA, and some small nonrandomized trials have identified some benefits in using rituximab and the proteasome inhibitor-based therapy bortezomib. More recent histologic follow-ups of patients treated with bortezomib have not shown significant benefits in terms of allograft outcomes. Furthermore, no specific treatment approaches have been approved by the US Food and Drug Administration. Other agents used for more difficult rejections include bortezomib and eculizumab (an anti-C5 monoclonal antibody).

CONCLUSION

AMR is a fascinating field with ample opportunities for research and progress in the future. Despite the use of advanced techniques for the detection of human leukocyte antigen (HLA) or non-HLA donor-specific antibodies, alloimmune response remains an important barrier for successful long-term allograft function. Treatment of AMR with currently available therapies has produced a variety of results, some of them suboptimal, precluding the development of standardized protocols. New therapies are promising, but randomized controlled trials are needed to find surrogate markers and improve the efficacy of therapy.

Progress in Transplantation: Will It Be Achieved in Big Steps or by Marginal Gains?

A wish for progress in transplantation assumes that there are needs not met by the currently available therapy and that the barriers to resolving the problems can be surmounted. There are 5 major unmet needs: the potential to avoid transplantation either by prevention of disease or provision of an alternative to natural biological organ replacement; geographic heterogeneity of access to, and quality of, transplantation; availability of transplantation to those in need of it; survival of the patient and the transplant; and the avoidance of adverse effects of immunosuppression. During the past 50 years, there have been advances on at least 4 of these 5 fronts that illustrate the interplay of "big steps" and "marginal gains" in the following areas: surgical technique, testing the immunologic barriers, introduction of chemical and biological immunosuppression, and prophylaxis for microbial infections. The potential for further improvement comes in 5 major areas: blood biomarkers for monitoring of rejection, drug-free transplantation through the development of stable tolerance, eliminating the impact of ischemia-reperfusion injury, xenotransplantation of porcine kidneys, and finally, the possibility of autologous regeneration of functioning kidney tissue to treat advanced kidney disease.

Unraveling the Role of Allo-Antibodies and Transplant Injury

Alloimmunity driving rejection in the context of solid organ transplantation can be grossly divided into mechanisms predominantly driven by either T cell-mediated rejection (TCMR) and antibody-mediated rejection (ABMR), though the co-existence of both types of rejections can be seen in a variable number of sampled grafts. Acute TCMR can generally be well controlled by the establishment of effective immunosuppression (1, 2). Acute ABMR is a low frequency finding in the current era of blood group and HLA donor/recipient matching and the avoidance of engraftment in the context of high-titer, preformed donor-specific antibodies. However, chronic ABMR remains a major complication resulting in the untimely loss of transplanted organs (3-10). The close relationship between donor-specific antibodies and ABMR has been revealed by the highly sensitive detection of human leukocyte antigen (HLA) antibodies (7, 11-15). Injury to transplanted organs by activation of humoral immune reaction in the context of HLA identical transplants and the absence of donor specific antibodies (17-24), strongly suggest the participation of non-HLA (nHLA) antibodies in ABMR (25). In this review, we discuss the genesis of ABMR in the context of HLA and nHLA antibodies and summarize strategies for ABMR management.

Delayed Cytotoxic T Lymphocyte-Associated Protein 4-Immunoglobulin Treatment Reverses Ongoing Alloantibody Responses and Rescues Allografts From Acute Rejection

Antibody-mediated rejection has emerged as the leading cause of late graft loss in kidney transplant recipients, and inhibition of donor-specific antibody production should lead to improved transplant outcomes. The fusion protein cytotoxic T lymphocyte-associated protein 4-immunoglobulin (CTLA4-Ig) blocks T cell activation and consequently inhibits T-dependent B cell antibody production, and the current paradigm is that CTLA4-Ig is effective with naïve T cells and less so with activated or memory T cells. In this study, we used a mouse model of allosensitization to investigate the efficacy of continuous CTLA4-Ig treatment, initiated 7 or 14 days after sensitization, for inhibiting ongoing allospecific B cell responses. Delayed treatment with CTLA4-Ig collapsed the allospecific germinal center B cell response and inhibited alloantibody production. Using adoptively transferred T cell receptor transgenic T cells and a novel approach to track endogenous graft-specific T cells, we demonstrate that delayed CTLA4-Ig minimally inhibited graft-specific CD4(+) and T follicular helper responses. Remarkably, delaying CTLA4-Ig until day 6 after transplantation in a fully mismatched heart transplant model inhibited alloantibody production and prevented acute rejection, whereas transferred hyperimmune sera reversed the effects of delayed CTLA4-Ig. Collectively, our studies revealed the unexpected efficacy of CTLA4-Ig for inhibiting ongoing B cell responses even when the graft-specific T cell response was robustly established.

HLA Matching Trumps Donor Age: Donor-Recipient Pairing Characteristics That Impact Long-Term Success in Living Donor Kidney Transplantation in the Era of Paired Kidney Exchange

BACKGROUND

We sought to identify donor characteristics influencing long-term graft survival, expressed by a novel measure, kidney life years (KLYs), in living donor kidney transplantation (LDKT).

METHODS

Cox and multiple regression analyses were applied to data from the Scientific Registry for Transplant Research from 1987 to 2015. Dependent variable was KLYs.

RESULTS

Living donor kidney transplantation (129 273) were performed from 1987 to 2013 in the United States. To allow sufficient time to assess long-term results, outcomes of LDKTs between 1987 and 2001 were analyzed. After excluding cases where a patient died with a functioning graft (8301) or those missing HLA data (9), 40 371 cases were analyzed. Of 18 independent variables, the focus became the 4 variables that were the most statistically and clinically significant in that they are potentially modifiable in donor selection (P <0.0001; ie, HLA match points, donor sex, donor biological sibling and donor age). HLA match points had the strongest relationship with KLYs, was associated with the greatest tendency toward graft longevity on Cox regression, and had the largest increase in KLYs (2.0 year increase per 50 antigen Match Points) based on multiple regression.

CONCLUSIONS

In cases when a patient has multiple potential donors, such as through paired exchange, graft life might be extended when a donor with favorable matching characteristics is selected.

A significant role for anti-human leukocyte antigen antibodies and antibody-mediated rejection in the biopsy-for-cause population

The role of anti-human leukocyte antigen (HLA) antibodies and antibody-mediated rejection is well known, but our comprehension and the preventive measures we take seem to be insufficient. One of the major causes of premature renal transplant loss is recepients' immunologic hyperactivity to donors' antigens. Monitoring of humoral alloreactivity gives hope for early diagnosis and adequate therapy. The goal of our analysis was the assessment of the influence of anti-HLA antibodies on the function and survival of transplants. In our study we included 60 consecutive renal transplant recipients who had a renal transplant biopsy-for-cause performed due to insufficiency. Transplant biopsies were performed between the 7th day and 12th year (median, 2 years) after transplantation. Anti-HLA antibodies were present in 20 patients (33%). The patients were divided into 2 groups according the presence of anti-HLA antibodies. In a 12-month observation, 10/20 (50%) patients in the anti-HLA(+) group returned to dialysis in contrast with 7/40 (17.5%; P = .014) in the anti-HLA(-) group. Also, 8/10 (80%) of the anti-HLA(+) patients who lost the transplant had anti-HLA Abs class II and only 2/10 (20%) had anti-HLA Abs class I. Anti-HLA antibodies were specific to a donor (donor-specific antibodies [DSA]) in 8/10 (80%) of the patients who lost the transplant. Anti-HLA antibodies appeared de novo in 50% of patients who lost the transplant. Nonadherence was suspected in 50% of patients. Acute humoral rejection occurred in 1 patient. Also, 8/10 (90%) developed chronic active humoral rejection. Our study revealed that graft loss in the renal transplant biopsy-for-cause population with the presence of anti-HLA Abs during a 12-month observation reached 50%. Nonadherence in these patients was very high and amounted to 50%. Monitoring of renal transplant recipients and individualization of therapy considering humoral activity should prolong renal graft survival.

MHC/Peptide-Specific Interaction of the Humoral Immune System: A New Category of Antibodies

Abs bind to unprocessed Ags, whereas cytotoxic CD8(+) T cells recognize peptides derived from endogenously processed Ags presented in the context of class I MHC complexes. We screened, by ELISA, human sera for Abs reacting specifically with the influenza matrix protein (IMP)-derived peptide(58-66) displayed by HLA-A*0201 complexes. Among 653 healthy volunteers, blood donors, and women on delivery, high-titered HLA-A*0201/IMP(58-66) complex-specific IgG Abs were detected in 11 females with a history of pregnancies and in 1 male, all HLA-A*0201(-). These Abs had the same specificity as HLA-A*0201/IMP(58-66)-specific cytotoxic T cells and bound neither to HLA-A*0201 nor the peptide alone. No such Abs were detected in HLA-A*0201(+) volunteers. These Abs were not cross-reactive to other self-MHC class I alleles displaying IMP(58-66), but bound to MHC class I complexes of an HLA nonidentical offspring. HLA-A*0201/IMP(58-66) Abs were also detected in the cord blood of newborns, indicating that HLA-A*0201/IMP(58-66) Abs are produced in HLA-A*0201(-) mothers and enter the fetal blood system. That Abs can bind to peptides derived from endogenous Ags presented by MHC complexes opens new perspectives on interactions between the cellular and humoral immune system.

Integration of humoral and cellular HLA-specific immune responses in cord blood allograft rejection

In allo-stem cell transplantation (SCT), it is unclear whether donor-specific anti-HLA Abs (DSAs) can actually mediate graft rejection or if they are simply surrogate markers for the cellular immunity that causes graft rejection. Here, we first analyzed a case of cord blood allograft rejection in which DSA and cytotoxic T lymphocyte (CTL) specific for donor HLA-B*54:01 were detected at the time of graft rejection. Both the DSA and CTL inhibited colony formation by unrelated bone marrow mononuclear cells sharing HLA-B*54:01, suggesting that the humoral and cellular immune responses were involved in the graft rejection. Interestingly, the DSA and CTL were also detected in cryopreserved pre-transplant patient blood, raising a hypothesis that the presence of anti-HLA Abs could be an indicator for corresponding HLA-specific T cells. We then evaluated the existence of HLA-specific CD8(+) T cells in other patient blood specimens having anti-HLA class I Abs. Interferon-γ enzyme-linked immunospot assays clearly confirmed the existence of corresponding HLA-specific T-cell precursors in three of seven patients with anti-HLA Abs. In conclusion, our data demonstrate that integrated humoral and cellular immunity recognizing the same alloantigen of the donor can mediate graft rejection in DSA-positive patients undergoing HLA-mismatched allo-SCT. Further studies generalizing our observation are warranted.

Bioengineered stem cells as an alternative for islet cell transplantation

Type 1 diabetes is an autoimmune and increasingly prevalent condition caused by immunological destruction of beta cells. Insulin remains the mainstay of therapy. Endeavours in islet transplantation have clearly demonstrated that type 1 diabetes is treatable by cellular replacement. Many challenges remain with this approach. The opportunity to use bioengineered embryonic or adult pluripotential stem cells, or islets derived from porcine xenograft sources could address future demands, but are still associated with considerable challenges. This detailed review outlines current progress in clinical islet transplantation, and places this in perspective for the remarkable scientific advances now occurring in stem cell and regenerative medicine approaches in the treatment of future curative treatment of diabetes.

Detection of C3d-binding donor-specific anti-HLA antibodies at diagnosis of humoral rejection predicts renal graft loss

Antibody-mediated rejection (AMR) is a major cause of kidney graft loss, yet assessment of individual risk at diagnosis is impeded by the lack of a reliable prognosis assay. Here, we tested whether the capacity of anti-HLA antibodies to bind complement components allows accurate risk stratification at the time of AMR diagnosis. Among 938 kidney transplant recipients for whom a graft biopsy was performed between 2004 and 2012 at the Lyon University Hospitals, 69 fulfilled the diagnosis criteria for AMR and were enrolled. Sera banked at the time of the biopsy were screened for the presence of donor-specific anti-HLA antibodies (DSAs) and their ability to bind C1q and C3d using flow bead assays. In contrast with C4d graft deposition, the presence of C3d-binding DSA was associated with a higher risk of graft loss (P<0.001). Despite similar trend, the difference did not reach significance with a C1q-binding assay (P=0.06). The prognostic value of a C3d-binding assay was further confirmed in an independent cohort of 39 patients with AMR (P=0.04). Patients with C3d-binding antibodies had worse eGFR and higher DSA mean fluorescence intensity. In a multivariate analysis, only eGFR <30 ml/min per 1.73 m(2) (hazard ratio [HR], 3.56; 95% confidence interval [CI], 1.46 to 8.70; P=0.005) and the presence of circulating C3d-binding DSA (HR, 2.80; 95% CI, 1.12 to 6.95; P=0.03) were independent predictors for allograft loss at AMR diagnosis. We conclude that assessment of the C3d-binding capacity of DSA at the time of AMR diagnosis allows for identification of patients at risk for allograft loss.

Immunology of liver transplantation

In comparison with other solid-organ transplants, liver allografts are immunologically privileged. Allografts are rejected by immune reactions of the host, and clinical therapy for liver allografts includes immunosuppression to prevent rejection. Orthotopic liver transplant causes systemic donor-specific T-cell tolerance. In addition, antigens introduced into hepatocytes or the portal vein cause tolerance. The basic mechanism in liver tolerance may include continuous exposure of diverse liver cell types to endotoxin derived from intestinal bacteria. This exposure promotes the expression of cytokines, antigen-presenting molecules, and costimulatory signals that inactivate T cells, partly by effects on liver antigen-presenting cells. A simple, reliable, noninvasive assay to evaluate antidonor alloreactivity may be important in implementing these approaches in the laboratory and clinic.

Costimulation blockade alters germinal center responses and prevents antibody-mediated rejection

De novo donor-specific antibody (DSA) after organ transplantation promotes antibody-mediated rejection (AMR) and causes late graft loss. Previously, we demonstrated that depletion using anti-CD3 immunotoxin combined with tacrolimus and alefacept (AMR regimen) reliably induced early DSA production with AMR in a nonhuman primate kidney transplant model. Five animals were assigned as positive AMR controls, four received additional belatacept and four received additional anti-CD40 mAb (2C10R4). Notably, production of early de novo DSA was completely attenuated with additional belatacept or 2C10R4 treatment. In accordance with this, while positive controls experienced a decrease in peripheral IgM(+) B cells, bela- and 2C10R4-added groups maintained a predominant population of IgM(+) B cells, potentially indicating decreased isotype switching. Central memory T cells (CD4(+) CD28(+) CD95(+)) as well as PD-1(hi) CD4(+) T cells were decreased in both bela-added and 2C10R4-added groups. In analyzing germinal center (GC) reactions in situ, lymph nodes further revealed a reduction of B cell clonal expansion, GC-follicular helper T (Tfh) cells, and IL-21 production inside GCs with additional belatacept or 2C10R4 treatment. Here we provide evidence that belatacept and 2C10R4 selectively suppresses the humoral response via regulating Tfh cells and prevents AMR in this nonhuman primate model.