Kidney Intragraft Homing of De Novo Donor-Specific HLA Antibodies Is an Essential Step of Antibody-Mediated Damage but Not Per Se Predictive of Graft Loss

HLA (emphasis on DQ) compatibility for longer allograft survival in pediatric transplantation: Modern evidence and challenges

Kidney transplantation is the treatment of choice for children with end-stage kidney failure, yet suboptimal outcomes, the need for long-term immunosuppression, and the dependency on consecutive transplants pose significant barriers to success. Providing better HLA-matched organs to pediatric patients seems to be the most logical approach to improve graft and patient outcomes and to reduce risk of anti-HLA sensitization after graft failure. We here review recent literature on HLA matching in pediatric kidney transplantation. We further review newer approaches attempting to improve matching by using molecular mismatch load analysis. Our main focus is on the role of HLA-DQ compatibility between recipient and donor. We further emphasize the need to develop creative approaches that will support HLA (and DQ) matching utilization in organ allocation schemes, at least in those geared specifically for pediatric patients.

The human cytomegalovirus-specific and UL40-mediated imprint in the natural killer cell repertoire is associated with antibody-mediated rejection in lung transplant recipients

BACKGROUND

CD16⁺ natural killer (NK-) cells play, together with donor-specific antibodies (DSA) and via antibody-dependent cellular cytotoxicity (ADCC), an important role in the pathogenesis of antibody-mediated rejection (ABMR) in lung-transplant recipients (LTRs). Cytotoxic CD16⁺NKG2C⁺ NK cells proliferate in response to human Cytomegalovirus (HCMV) infections via the presentation of HCMV-encoded and highly polymorphic UL40 peptides. In our study, we aimed to clarify whether infections with HCMV-strains carrying different UL40 peptide variants are associated with the shift of the NK cell repertoire and the development of ABMR in LTRs.

METHODS

We included 30 DSA⁺ABMR⁺, 30 DSA⁺ABMR^- and 90 DSA^-ABMR^- LTRs. In all patients, 1 episode of high-level HCMV-replication occurred. In all DSA⁺ABMR⁺ LTRs, HCMV-replication occurred prior to ABMR diagnosis. The association of HCMV UL40 variants with the expansion of CD16⁺ NK cell subsets and ABMR was assessed in NK cell proliferation and ADCC assays.

RESULTS

Our study revealed that the VMAPRTLIL and VMTPRTLVL UL40 variants were significantly overrepresented in DSA⁺ABMR⁺ LTRs. Both peptides were associated with a pronounced proliferation of cytotoxic and proinflammatory CD16⁺NKG2C⁺ NK cells. The stimulation with both peptides led to a shift of the NK cell repertoire towards CD16⁺NKG2C⁺ NK cells, which was associated with strong ADCC responses after stimulation with endothelial cells and plasma from DSA⁺ABMR⁺ LTRs.

CONCLUSIONS

Distinct UL40 peptide variants of the infecting HCMV-strain are associated with the development of ABMR after lung transplantation, due to a shift towards a highly cytotoxic CD16⁺NKG2C⁺ NK cell population. These peptides are thus potential prognostic markers for ABMR.

Anti-glutathione S-transferase theta 1 antibodies correlate with graft loss in non-sensitized pediatric kidney recipients

Introduction

Immunity to Human leukocyte antigen (HLA) cannot explain all cases of ABMR, nor the differences observed in the outcome of kidney recipients with circulating DSAs endowed with similar biologic characteristics. Thus, increasing attention has recently been focused on the role of immunity to non-HLA antigenic targets.

Methods

We analyzed humoral auto- and alloimmune responses to the non-HLA antigen glutathione S-transferase theta 1 (GSTT1), along with development of de novo (dn)HLA-DSAs, in a cohort of 146 pediatric non-sensitized recipients of first kidney allograft, to analyze its role in ABMR and graft loss. A multiplex bead assay was employed to assess GSTT1 antibodies (Abs).

Results

We observed development of GSTT1 Abs in 71 recipients after transplantation, 16 with MFI > 8031 (4th quartile: Q4 group). In univariate analyses, we found an association between Q4-GSTT1Abs and ABMR and graft loss, suggesting a potential role in inducing graft damage, as GSTT1 Abs were identified within ABMR biopsies of patients with graft function deterioration in the absence of concomitant intragraft HLA-DSAs. HLA-DSAs and GSTT1 Abs were independent predictors of graft loss in our cohort. As GSTT1 Ab development preceded or coincided with the appearance of dnHLA-DSAs, we tested and found that a model with the two combined parameters proved more fit to classify patients at risk of graft loss.

Discussion

Our observations on the harmful effects of GSTT1Abs, alone or in combination with HLA-DSAs, add to the evidence pointing to a negative role of allo- and auto-non-HLA Abs on kidney graft outcome.

The Presence of Donor-specific Antibodies Around the Time of Pancreas Graft Biopsy With Rejection Is Associated With an Increased Risk of Graft Failure

BACKGROUND

Donor-specific antibodies (DSA) against HLA are an important biomarker predicting graft injury, rejection (Rej), and failure in various solid-organ transplant recipients. However, the impact of DSA with or without histopathological evidence of rejection among pancreas transplant recipients (PTRs) is unknown.

METHODS

In this study, we included all PTRs at our center between 2005 and 2020, with pancreas allograft biopsy before March 31, 2021, and with DSA checked within 15 d of the biopsy. PTRs were divided into 4 groups based on the biopsy findings on the index biopsy and DSA status as Rej-/DSA-, Rej+/DSA-, Rej-/DSA+, and Rej+/DSA+.

RESULTS

Two hundred two PTRs had a pancreas allograft biopsy during the study period. Thirty-nine were in Rej-/DSA-, 84 Rej+/DSA-, 24 Rej-/DSA+, and 55 Rej+/DSA+. The mean interval from transplant to index biopsy was not statistically different between the 4 groups. The most common type of rejection was T cell-mediated rejection; however, antibody-mediated rejection was more prevalent in the Rej+/DSA+ group. At 5 y postbiopsy, the rate of death-censored graft failure (DCGF) for Rej-/DSA- was 18%, 24% in Rej+/DSA-; 17% in Rej-/DSA+ and 36% in Rej+/DSA+ (P = 0.14). In univariate analysis, mixed rejection (hazard ratio [HR], 3.0; 95% confidence intervals [CI], 1.22-7.39; P = 0.02) along with solitary pancreas transplantation and Rej+/DSA+ were associated with DCGF. In multivariate analysis, compared with Rej-/DSA-, Rej+/DSA+ was significantly associated with DCGF (HR, 2.32; 95% CI, 1.03-5.20; P = 0.04); however, Rej+/DSA- was not (HR, 1.06; 95% CI, 0.32-3.56; P = 0.92).

CONCLUSIONS

PTRs with pancreas allograft rejection and concomitant DSA have an increased risk of DCGF.

Allorecognition and the spectrum of kidney transplant rejection

Detection of mismatched human leukocyte antigens by adaptive immune cells is considered as the main cause of transplant rejection, leading to either T-cell mediated rejection or antibody-mediated rejection. This canonical view guided the successful development of immunosuppressive therapies and shaped the diagnostic Banff classification for kidney transplant rejection that is used in clinics worldwide. However, several observations have recently emerged that question this dichotomization between T-cell mediated rejection and antibody-mediated rejection, related to heterogeneity in the serology, histology, and prognosis of the rejection phenotypes. In parallel, novel insights were obtained concerning the dynamics of donor-specific anti-human leukocyte antigen antibodies, the immunogenicity of donor-recipient non-human leukocyte antigen mismatches, and the autoreactivity against self-antigens. Moreover, the potential of innate allorecognition was uncovered, as exemplified by natural killer cell-mediated microvascular inflammation through missing self, and by the emerging evidence on monocyte-driven allorecognition. In this review, we highlight the gaps in the current classification of rejection, provide an overview of the expanding insights into the mechanisms of allorecognition, and critically appraise how these could improve our understanding and clinical approach to kidney transplant rejection. We argue that consideration of the complex interplay of various allorecognition mechanisms can foster a more integrated view of kidney transplant rejection and can lead to improved risk stratification, targeted therapies, and better outcome after kidney transplantation.

B cells in transplant tolerance and rejection: friends or foes?

Our understanding of the role of B cells in organ transplantation remains incomplete and continues to grow. The majority of research has focused on the detrimental role of antibodies that drive the development of pathogenesis of the transplanted organ. However, it has been shown that not all donor-specific antibodies are harmful and in some circumstances can even promote tolerance through the mechanism of accommodation. Furthermore, B cells can have effects on transplanted organs through their interaction with T cells, namely antigen presentation, cytokine production, and costimulation. More recently, the role and importance of Bregs was introduced to the field of transplantation. Due to this functional and ontogenetic heterogeneity, targeting B cells in transplantation may bring undesired immunologic side effects including increased rejection. Therefore, the selective control of B cells that contribute to the humoral response against donor antigens will continue to be an important and challenging area of research and potentially lead to improved long-term transplant outcomes.

Challenges of Diagnosing Antibody-Mediated Rejection: The Role of Invasive and Non-Invasive Biomarkers

Kidney transplantation is the best treatment modality for end-stage kidney disease, leading to improvement in a patient’s quality and quantity of life. With significant improvements in short-term outcomes, prolonging long-term allograft and patient survival remain ongoing challenges. The ability to monitor allograft function, immune tolerance and predict rejection accurately would enable personalization and better prognostication during post-transplant care. Though kidney biopsy remains the backbone of transplant diagnostics, emerging biomarkers can help detecting kidney allograft injury early enough to prevent permanent damage and detect injury before it is clinically apparent. In this review, we summarize the recent biomarkers that have shown promise in the prediction of acute rejection with a focus on antibody-mediated rejection in kidney transplantation.

Histologic Antibody-Mediated Kidney Allograft Rejection in the Absence of Donor Specific HLA Antibodies

Histologic antibody-mediated rejection (hAMR) is defined as a kidney allograft biopsy satisfying the first 2 Banff criteria for diagnosing antibody-mediated rejection (AMR): tissue injury and evidence of current/recent antibody interaction with the endothelium. In approximately one-half of such cases, circulating HLA donor specific antibodies (DSA) are not detectable by current methodology at the time of biopsy. Some studies indicated a better prognosis for HLA-DSA-negative cases of hAMR compared to those with detectable HLA-DSA, whereas others found equally poor survival compared to hAMR-negative cases. We reviewed the literature regarding the pathophysiology of HLA-DSA-negative hAMR. We find 3 nonmutually exclusive possibilities: 1) HLA-DSA are involved, but just not detected; 2) non-HLA DSA (allo- or autoantibodies) are pathogenically involved; and/or 3) antibody-independent NK cell activation is mediating the process through "missing self" or other activating mechanisms. These possibilities are discussed in detail. Recommendations regarding the approach to such patients are made. Clearly, more research is necessary regarding the measurement of non-HLA antibodies, recipient/donor NK cell genotyping, and the use of antibody reduction therapy or other immunosuppression in any subset of patients with HLA-DSA-negative hAMR.

Post-transplant de novo non donor-specific HLA antibodies are not associated with poor graft outcome in non-sensitized pediatric recipients of kidney transplantation

While de novo donor-specific HLA antibodies (dnDSAs) have a detrimental impact on kidney graft outcome, the clinical significance of de novo non donor-specific antibodies (dnNDSAs) is more controversial. We retrospectively evaluated for Ab development and characteristics of dnNDSAs serially collected post-transplant sera and, when available, graft biopsy eluates, from 144 non-sensitized, primary pediatric kidney recipients, consecutively transplanted at a single center between 2003 and 2017, using HLA class I and class II single-antigen flow-bead assays (SAB). The results were compared with clinical-pathologic data from HLA antibody negative and HLA dnDSA-positive patients. Forty-five out of 144 patients developed dnNDSAs (31%). Among the dnNDSA-positive patients, 86% displayed one or more class I/II antibodies recognizing antigens included in the CREG/shared epitope groups that also comprise the mismatched donor HLA antigens. Despite potential pathogenicity, as suggested by their occasional presence within the graft, dnNDSAs displayed significantly lower MFI, and limited complement binding and graft homing properties, when compared with dnDSAs. In parallel, the graft survival probability was significantly lower in patients with dnDSA than in those with dnNDSA or without HLA antibodies (p < 0.005). Indeed, the dnNDSA-positive patients remaining dnDSA-negative throughout the posttransplant period did not develop clinical antibody mediated rejection and graft loss, and maintained good graft function at a median follow-up of 9 years. The biological characteristics of dnNDSAs may account for the low graft damaging capability when compared to dnDSAs.

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.

Does HLA matching matter in the modern era of renal transplantation?

Children with end-stage kidney disease should be offered the best chance for future survival which ideally would be a well-matched pre-emptive kidney transplant. Paediatric and adult practice varies around the world depending on geography, transplant allocation schemes and different emphases on living (versus deceased) donor renal transplantation. Internationally, paediatric patients often have priority in allocation schemes and younger donors are preferentially allocated to paediatric recipients. HLA matching can be difficult and may result in longer waiting times. Additionally, with improved surgical techniques and modern immunosuppressive regimens, how important is the contribution of HLA matching to graft longevity? In this review, we discuss the relative importance of HLA matching compared with donor quality; and long-term patient outcomes including re-transplantation rates. We share empirical evidence that will be useful for clinicians and families to make decisions about best donor options. We discuss why living donation still provides the best allograft survival outcomes and what to do in the scenario of a highly mismatched living donor.

Clinical relevance of donor-specific antibodies directed at HLA-C: A long road to acceptance

In solid organ transplantation (SOT), the clinical relevance of donor-specific antibodies (DSA) directed at anti-HLA-A, -B, -DR and -DQ antigens is largely recognized while it is still a matter of debate for DSA directed at HLA-C. In this review, we summarize the peculiarities of HLA-C among class I HLA antigens as well as their immunogenicity, which underlie the clinical relevance of HLA-C locus and anti-HLA-C DSA in SOT. Many factors, both intrinsic and extrinsic to the HLA-C gene and HLA-C protein, explain its lower expression in comparison with HLA-A and -B. This lower expression can explain the apparent lower immunogenicity of HLA-C leading to a lower prevalence and strength of anti-HLA-C antibodies. Nevertheless, HLA-C antigens are truly immunogenic and preformed anti-HLA-C DSA are clinically relevant. Indeed, anti-HLA-C DSA are able to bind donor cells and to activate the complement pathway both ex vivo and in vivo. In line with this, numerous clinical studies now show that preformed DSA directed at native HLA-C molecules induce poorer graft outcomes. We then plead for the inclusion of HLA-C in all transplant allocation systems and we propose a strategy to cope with anti-HLA-C DSA in SOT. Beyond SOT, anti-HLA-C antibodies generate a growing interest in the allo-HCT, transfusion and obstetrics fields, while new concepts such as the role of the "missing-self" in solid organ rejection places HLA-C as an inescapable actor in transplant tolerance.

Everolimus for BKV nephropathy in kidney transplant recipients: a prospective, controlled study

There is no specific therapy for polyoma BK virus nephropathy (BKVN) in kidney transplant recipients, a condition associated with poor outcomes. Everolimus showed promising antiviral effects, but data from prospective studies are limited. Therefore, we converted ten consecutive kidney transplant recipients with biopsy-proven BKVN from standard exposure Calcineurin inhibitors and Mycophenolate to Everolimus and reduced exposure Calcineurin inhibitors. Ten patients not administered Everolimus, on reduced exposure Calcineurin inhibitor and halved MPA doses served as controls. All kidney transplant recipients continued steroid therapy. Each patient underwent kidney graft biopsy, BKV replication by PCR, and de novo DSA determination. During a 3-year follow-up no graft loss occurred in kidney transplant recipients on Everolimus but it was observed in 5/10 controls (P = 0.032). eGFR improved on Everolimus and worsened in controls (between group difference + 25.6 ml/min/1.73 m², 95% CI 10.5-40.7, P = 0.002). BKV replication declined in the Everolimus group alone (from 6.4 ± 0.8 to 3.6 ± 1.6 Log 10 genomic copies, P = 0.0001), and we found a significant inverse relationship between eGFR and BKV genomic copy changes (P = 0.022). Average Calcineurin inhibitors trough levels did not differ between the two study groups during follow-up. By multivariable Cox regression analysis, Everolimus treatment resulted the only significant predictor of survival free of a combined endpoint of graft loss and 57% eGFR reduction (P = 0.02). Kidney transplant recipients on Everolimus had a higher survival free of adverse graft outcome (log-rank test, P = 0.009). In conclusion an Everolimus-based immunosuppressive protocol with minimization of Calcineurin inhibitors and antimetabolite discontinuation effectively treated BKVN in kidney transplant recipients.

The Role of Major Histocompatibility Complex in Organ Transplantation- Donor Specific Anti-Major Histocompatibility Complex Antibodies Analysis Goes to the Next Stage

Organ transplantation has progressed with the comprehension of the major histocompatibility complex (MHC). It is true that the outcome of organ transplantation largely relies on how well rejection is managed. It is no exaggeration to say that to be well acquainted with MHC is a shortcut to control rejection. In human beings, MHC is generally recognized as human leukocyte antigens (HLA). Under the current circumstances, the number of alleles is still increasing, but the function is not completely understood. Their roles in organ transplantation are of vital importance, because mismatches of HLA alleles possibly evoke both cellular and antibody-mediated rejection. Even though the control of cellular rejection has improved by recent advances of immunosuppressants, there is no doubt that antibody-mediated rejection (AMR), which is strongly correlated with donor-specific anti-HLA antibodies (DSA), brings a poor outcome. Thus, to diagnose and treat AMR correctly is a clear proposition. In this review, we would like to focus on the detection of intra-graft DSA as a recent trend. Overall, here we will review the current knowledge regarding MHC, especially with intra-graft DSA, and future perspectives: HLA epitope matching; eplet risk stratification; predicted indirectly recognizable HLA epitopes etc. in the context of organ transplantation.

Early interstitial macrophage infiltration with mild dysfunction is associated with subsequent kidney graft loss

Macrophage infiltration is associated with unfavorable kidney graft outcome in protocol biopsies, but few studies have evaluated its impact on clinical practice. We therefore prospectively evaluated 37 kidney transplant recipients (KTRs) who underwent kidney biopsy due to slight increases in serum creatinine, or mild proteinuria (>0.3 g/24 hr), in the first post-transplant year. Banff score, CD68⁺ count (score 0-3) by immunohistochemistry, and 1-year DSA were assessed. DGF was reported in 10 (27%) patients, 6 (16%) had normal biopsy, 7 (19%) borderline lesions, 13 (35%) IFTA, and 11 (30%) other lesions. Fifteen KTRs had grade 3 CD68⁺ infiltration, and 47% developed de novo DSA. During a 6.2 ± 2.7 year follow-up, four patients (11%) suffered from biopsy-proven T-cell rejection, 17 KTRs (46%) lost their graft (12 in the grade 3 CD68⁺ group). Graft survival was lower in KTRs with grade 3 CD68⁺ infiltration (P = 0.0074; log-rank test). Grade 3 CD68⁺ infiltrate was an independent predictor of graft loss (HR 5.41, 95% CI 1.74-16.8; P = 0.003), together with more severe graft dysfunction at biopsy (HR 6.41, 95% CI 2.57-16; P < 0.001). We conclude that grade 3 CD68⁺ interstitial infiltration is associated with increased risk of subsequent graft loss independent of other factors.

Clearance of Intra-graft Donor Specific Anti-HLA Antibodies in the Early Stage of Antibody-Mediated Rejection Following Rituximab and Apheresis Therapy in Renal Transplantation

BACKGROUND

The management of acute or, in particular, chronic antibody-mediated rejection (AMR) resulting from donor-specific HLA antibodies (DSA) is a critical barrier to obtaining better long-term graft survival. To ascertain the efficacy of anti-AMR therapies, the transition of intra-graft DSA (g-DSA) was assessed.

METHODS

Allograft biopsy specimens were analyzed by graft immunocomplex capture fluorescence analysis, as previously described. One hundred recipients who underwent graft biopsies between April 2016 and December 2017 were enrolled for this study. Fifteen recipients diagnosed with g-DSA positive (+) received anti-humoral treatments and underwent follow-up biopsies. g-DSA levels were assessed again by a follow-up biopsy at 6-12 months following the treatments.

RESULTS

With anti-humoral treatments, 9 out of 15 recipients comprised a g-DSA negative (-) (3.59 ± 2.82-.58 ± .25): g-DSA6-12- group, while the remaining 6 recipients comprised a g-DSA +(20.6 ± 17.0-14.9 ± 14.1): g-DSA6-12+ group. The initial g-DSA scores were significantly higher in the g-DSA6-12+ group (P = .01). All samples were diagnosed as chronic AMR in the g-DSA+ groups, whereas there were 3 chronic AMR, 4 acute AMR, and 2 incomplete AMR samples in the g-DSA- group. Interestingly, the frequency of responsible DSA belonging to class II tended to be higher in the g-DSA6-12+ group (4/6) compared to the g-DSA6-12- group (2/9) (P = .14).

CONCLUSION

These results imply that chronic exposure to DSA causes significant and irreversible damage to the allograft. Timely and adequate anti-humoral intervention might reverse the early phase of AMR with complete clearance of g-DSA.

Donor-Specific Antibodies in the Absence of Rejection Are Not a Risk Factor for Allograft Failure

Introduction

Donor-specific antibodies (DSAs) are considered an important risk factor for graft injury and failure. However, there is limited information on long-term outcomes for kidney transplant recipients with positive DSAs in the absence of rejection on biopsy.

Methods

We evaluated all patients at the University of Wisconsin who underwent a kidney allograft biopsy between January 1, 2013, and December 31, 2016. All patients with clinical indication or protocol biopsies that were negative for acute rejection and lacked significant acute pathological features were included in the study and divided into 2 groups based on DSAs at the time of biopsy. There were a total of 1102 kidney biopsies during the study period of which 587 fulfilled our selection criteria (DSA+, n = 192, and DSA−, n = 395). The incidence of subsequent rejection and death-censored graft failure (DCGF) were outcomes of interest.

Results

There was no difference in acute (i + t + v + c4d + ptc + g = 0 in both groups) or chronic (ci + ct + cv + cg = 2.4 ± 2.2 vs. 2.7 ± 2.4; cg = 0.12 ± 0.48 vs. 0.13 ± 0.48) Banff scores in the index biopsy. Patients were followed for a mean of 33.1 ± 16.8 months. Kaplan-Meier analyses demonstrated a higher incidence of DCGF in DSA− group (n = 83) but this was not observed for subsequent rejection (n = 76). In multivariate Cox regression analyses, the interval from transplant to biopsy, de novo DSA, and younger age remained independently associated with increased risk of subsequent rejection. Notably, there was no association between subsequent rejection or DSA (pretransplant, de novo, persistant, Class I/II, MFI_sum, or MFI_max) and graft failure.

Conclusion

This study suggests that in the absence of biopsy-proven rejection and acute inflammation, human leukocyte antigen (HLA) DSAs are not associated with increased risk of graft failure.

Failure to remove de novo donor-specific HLA antibodies is influenced by antibody properties and identifies kidney recipients with late antibody-mediated rejection destined to graft loss - a retrospective study

Current research is focusing on identifying bioclinical parameters for risk stratification of renal allograft loss, largely due to antibody-mediated rejection (AMR). We retrospectively investigated graft outcome predictors in 24 unsensitized pediatric kidney recipients developing HLA de novo donor-specific antibodies (dnDSAs), and treated for late AMR with plasmapheresis + low-dose IVIG + Rituximab or high-dose IVIG + Rituximab. Renal function and DSA properties were assessed before and longitudinally post treatment. The estimated GFR (eGFR) decline after treatment was dependent on a negative % eGFR variation in the year preceding treatment (P = 0.021) but not on eGFR at treatment (P = 0.74). At a median follow-up of 36 months from AMR diagnosis, 10 patients lost their graft. Altered eGFR (P < 0.001) and presence of C3d-binding DSAs (P = 0.005) at treatment, and failure to remove DSAs (P = 0.01) were negatively associated with graft survival in the univariable analysis. Given the relevance of DSA removal for therapeutic success, we analyzed antibody properties dictating resistance to anti-humoral treatment. In the multivariable analysis, C3d-binding ability (P < 0.05), but not C1q-binding, and high mean fluorescence intensity (P < 0.05) were independent factors characterizing DSAs scarcely susceptible to removal. The poor prognosis of late AMR is related to deterioration of graft function prior to treatment and failure to remove C3d binding and/or high-MFI DSAs.

Utility of protocol kidney biopsies for de novo donor-specific antibodies

There is limited information about the role of protocol kidney biopsies for de novo donor-specific antibodies (dnDSA) in kidney transplant recipients, especially in those with stable graft function. We initiated a routine posttransplant DSA monitoring and surveillance biopsy program for dnDSA since 2014. We identified 45 kidney transplant recipients with dnDSA detected between January 2014 and February 2017 who underwent kidney biopsy within 60 days of detection of dnDSA. Twenty-nine (64%) had stable graft function and 16 (36%) had impaired graft function at the time of dnDSA detection. Even in the group with stable graft function, we found a high rate of rejection (53%) on biopsy. Eighty-eight percent of patients with impaired graft function had rejection. Those patients with impaired graft function had significantly lower estimated glomerular filtration rate at 12 months postbiopsy and at last follow-up. Those with impaired graft function had more graft failures; however, this result was not statistically significant. The high rate of asymptomatic rejection, and the fact that outcomes in asymptomatic patients are poor, is in support of the utility of surveillance biopsies in patients with dnDSA.

Application and interpretation of histocompatibility data in pediatric kidney transplantation

PURPOSE OF REVIEW

Advances in technology to assess immunologic risk in solid organ transplant offer an opportunity to optimize the approach to pediatric deceased donor kidney transplant in the setting of a new allocation system in the United States.

RECENT FINDINGS

Degree of human leukocyte antigen (HLA) mismatch, class II HLA mismatch, unacceptable antigens and donor-specific antibody (DSA) detected by solid-phase assays, and epitope matching pretransplant affect pediatric kidney transplant outcomes. Detection of de novo DSAs (dnDSAs) posttransplant has been associated with increased risk of acute rejection and worse allograft function. Development of dnDSA occurs in recipients with greater epitope mismatching.

SUMMARY

Improved long-term outcomes may be anticipated in pediatric kidney transplant recipients by incorporating extended HLA mismatch information and updating the clinical approach to donor kidney matching using available technology to identify clinically relevant immunologic risk.