Prospective iterative trial of proteasome inhibitor-based desensitization

Imlifidase in Highly Sensitized Kidney Transplant Recipients With a Positive Crossmatch Against a Deceased Donor

Introduction

Imlifidase is authorized for desensitization of highly sensitized adult kidney transplant candidates with a positive crossmatch (XM) against a deceased donor. Here, we report on the results for the first 9 patients transplanted in this context who had at least 3 months of follow-up.

Methods

The eligibility criteria were as follows: calculated panel reactive antibodies (cPRA) ³ 98%, ³ 3 years on the waiting list, immunodominant donor-specific antibodies (DSAs) with mean fluorescence intensity (MFI) > 6000 (and < 5000 at 1:10 dilution) and a negative post-imlifidase complement-dependent cytotoxic XM (CDCXM).

Results

All 9 patients had been on dialysis for an average of 123 ± 41 months, with cPRA at 99% (n = 2) or 100% (n = 7). At transplantation, the mean number of DSAs was 4.3 ± 1.4. The median immunodominant DSA MFI was 9153 (6430-16,980). Flow cytometry XM (FCXM) and CDCXM before imlifidase were positive in 9 and 2 patients, respectively. After 1 injection of imlifidase, all were negative. Patients received polyclonal antibodies, i.v. Igs (IVIg), rituximab, tacrolimus, and mycophenolate. Five patients had a DSA rebound within the first 14 days: 2 had concomitant clinical antibody-mediated rejection (ABMR), 2 had subclinical ABMR, and 1 had isolated positive C4d staining. No ABMR was observed in patients without rebound. Chronic Kidney Disease-Epidemiology Collaboration formula estimated glomerular filtration rate (eGFR) was 56 ± 22 ml/min per 1.73 m2 at the last follow-up (7 ± 2.8 months). No graft loss or death were observed. Four patients developed at least 1 infection.

Conclusion

These real-life data demonstrate that the use of imlifidase to desensitize highly sensitized patients can have an acceptable short-term efficacy and safety profile in selected patients.

Desensitization of Highly Immunized Kidney Transplant Recipients Awaiting Transplantation-Polish Single-Center Experience

INTRODUCTION

The increasing number of highly immunized patients waiting for kidney transplantation is a significant problem in Europe as the proportion of such patients has doubled in the last decade. Transplantation in this group is enabled by desensitization methods, i.e., intravenous pharmacotherapy with human immunoglobulin (IVIG), anti-CD20 monoclonal antibody (rituximab), and plasma exchange. The objective was to evaluate the efficacy and safety of this protocol.

MATERIAL AND METHODS

The inclusion criteria: presence of established anti-HLA antibodies with complement-binding capacity, i.e., anti-HLAC1q+ (>MFI 15,000 for the most common antigens), no renal transplantation within 1 year after activation on the waiting list. Thirteen patients were selected for the procedure. IVIG was administered twice (2 g/kg-maximum 140 g/dose). Between IVIG doses, patients received rituximab (375 mg/m2). Anti-HLA was tested after 1 and 2 months after completion of the procedure.

RESULTS

All patients have completed the protocol. No significant changes after desensitization in the amount/profile of alloantibodies were observed. However, with negative vCM for HLA-A/B/DR (no DSA against the reported donor) and negative CM-CDC, according to the allocation system, patients were given priority on the recipient list. Seven out of 13 patients received a transplant within 12 months after treatment (mean 11.5 weeks). Renal graft function was good (mean creatinine level after 1 month: 1.5 mg/dL). No incidents of acute rejection were reported. The most common complications were infections (especially pneumonia).

CONCLUSION

The desensitization protocol (IVIG + rituximab) allows highly immunized patients to undergo organ transplantation. In short-term analysis, no acute rejection was observed, graft function was satisfactory. Desensitization was associated with an increased risk of infection.

Management of the sensitized pediatric renal transplant candidate

Kidney transplantation is the treatment of choice for patients with ESRD as it is associated with improved patient survival and better quality of life, especially in children. There are several barriers to a successful transplant including organ shortage, anatomic barriers, and immunologic barriers. One of the biggest immunologic barriers that precludes transplantation is sensitization, when patients have antibodies prior to transplantation, resulting in positive crossmatches with donor. 30%-40% of adult patients on the wait list are sensitized. There is a growing number of pediatric patients on the wait list who are sensitized. This poses a unique challenge to the pediatric transplant community. Therefore, attempts to perform desensitization to remove or suppress pathogenic HLA antibodies resulting in acceptable crossmatches, and ultimately a successful transplant, while reducing the risk of acute rejection, are much needed in these children. This review article aims to address the management of such patients both prior to transplantation, with strategies to overcome sensitization, and after transplantation with monitoring for allograft rejection and other complications.

Imlifidase Desensitization in HLA-incompatible Kidney Transplantation: Finding the Sweet Spot

Imlifidase, derived from a Streptococcus pyogenes enzyme, cleaves the entire immunoglobulin G pool within hours after administration in fully cleaved antigen-binding and crystallizable fragments. These cleaved fragments can no longer exert their antibody-dependent cytotoxic functions, thereby creating a window to permit HLA-incompatible kidney transplantation. Imlifidase is labeled, in Europe only, for deceased donor kidney transplantation in highly sensitized patients, whose chances for an HLA-compatible transplant are negligible. This review discusses outcomes of preclinical and clinical studies on imlifidase and describes the phase III desensitization trials that are currently enrolling patients. A comparison is made with other desensitization methods. The review discusses the immunological work-up of imlifidase candidates and especially the "delisting strategy" of antigens that shift from unacceptable to acceptable with imlifidase desensitization. Other considerations for clinical implementation, such as adaptation of induction protocols, are also discussed. Imlifidase cleaves most of the currently used induction agents except for horse antithymocyte globulin, and rebound of donor-specific antibodies should be managed. Another consideration is the timing and interpretation of (virtual) crossmatches when bringing this novel desensitization agent into the clinic.

Does bortezomib influence pre-transplant desensitization therapy or benefit post-heart transplant outcomes for highly sensitized patients?

BACKGROUND

The use of bortezomib which is a proteasome inhibitor has been demonstrated to be efficacious in small number of patients as a desensitization strategy in heart transplant. We reviewed our single center's experience using Bortezomib along with plasmapheresis as desensitization therapy for highly sensitized patients to assess pre- and post-transplant outcomes.

METHOD

We assessed 43 highly sensitized patients awaiting HTx (defined as cPRA > 50%) between 2010 and 2021 who underwent desensitization therapy with bortezomib. Only those patients who subsequently underwent HTx were included in this study. Enrolled patients received up to four doses of bortezomib (1.3 mg/m2 ) over 2 weeks in conjunction with plasmapheresis. The efficacy of PP/BTZ was assessed by comparing the calculated panel reactive antibodies to HLA class I or class II antigens. Post-transplant outcomes including overall survival and incidence of rejection were compared to those of non-sensitized patients (PRA < 10%, n = 649) from the same center.

RESULTS

The average cPRA prior to PP/BTZ was 94.5%. Post-PP/BTZ there was no statistically significant decline in mean cPRA, class I cPRA, or class II cPRA, though the average percentage decrease in class I cPRA (8.7 ± 17.0%) was higher than the change in class II cPRA (4.4 ± 13.3%). Resulted were also replicated with C1q-binding antibodies showing more effect on I class compared to class II (15.0 ± 37.4% vs. 6.8 ± 33.6%) as well as with 1:8 dilutional assay (14.0 ± 23.0% vs. 9.1 ± 34.9%). Additionally, PP/BTZ treated patients and the control group of non-sensitized patients had similar overall 1 year survival (95.4 vs. 92.5%) but patients with PP/BTZ had increased incidence of AMR (79.1% vs. 97.1%, p = < .001), any treated rejection (62.8% vs. 86.7%, p = < .001) and de novo DSA development (81.4% vs. 92.5%, p = .007). Major side effects of PP/BTZ included thrombocytopenia (42%), infection requiring antibiotics (28%), and neuropathy (12%).

CONCLUSION

The use of bortezomib in highly sensitized patients does not significantly lower circulating antibodies prior to heart transplantation. However, its use may improve the chances of obtaining an immuno-compatible donor heart and contribute to acceptable post-transplant outcomes.

The Effect of Splenic Irradiation on Mean Fluorescence Intensity Values of HLA Antibody in Presensitized Patients Waiting for Kidney Transplantation

To explore the desensitization treatment of patients waiting for kidney transplantation, this article comparative analysis of the effect of splenic irradiation on mean fluorescence intensity (MFI) values of HLA antibodies of 4 presensitized patients. After splenic irradiation, the mean MFI values of HLA-I antibody in 4 patients all decreased (P ≤ .001, P ≤ .001, P ≤ .001, P ≤ .001), and 3 patients had a decrease in intensity level (P ≤ .001, P = .001, P ≤ .001); as for HLA-II antibody, the mean MFI values in 3 patients also decreased (P ≤ .001, P = .025, P = .016), 1 patient had a decrease in intensity level (P ≤ .001) and the other 2 cases had no significant changes (P = 1.000, P = .564). On the other hand, splenic irradiation reduces MFI values in different levels of HLA antibody. So, splenic irradiation can reduce the MFI values of HLA antibodies.

Carfilzomib-based antibody mediated rejection therapy in pediatric kidney transplant recipients

BACKGROUND

To date, the evidence for proteasome-inhibitor (PI) based antibody mediated rejection (AMR) therapy has been with the first-generation PI bortezomib. Results have demonstrated encouraging efficacy for early AMR with lesser efficacy for late AMR. Unfortunately, bortezomib is associated with dose-limiting adverse effects in some patients. We report use of the second generation proteosome inhibitor carfilzomib for AMR treatment in two pediatric patients with a kidney transplant.

METHODS

The clinical data on two patients who experienced dose limiting toxicities from bortezomib were collected along with their short- and long-term outcomes.

RESULTS

A two-year-old female with simultaneous AMR, multiple de novo DSAs (DR53 MFI 3900, DQ9 MFI 6600, DR15 2200, DR51 MFI 1900) and T-cell mediated rejection (TCMR) completed three carfilzomib cycles and experienced stage 1 acute kidney injury after the first two cycles. At 1 year follow up, all DSAs resolved, and her kidney function returned to baseline without recurrence. A 17-year-old female also developed AMR with multiple de novo DSAs (DQ5 MFI 9900, DQ6 MFI 9800, DQA*01 MFI 9900). She completed two carfilzomib cycles, which were associated with acute kidney injury. She had resolution of rejection on biopsy and decreased but persistent DSAs on follow-up.

CONCLUSIONS

Carfilzomib treatment for bortezomib-refractory rejection and/or bortezomib toxicity may provide DSA elimination or reduction, but also appears to be associated with nephrotoxicity. Clinical development of carfilzomib for AMR will require a better understanding of efficacy and development of approaches to mitigate nephrotoxicity.

Management of the sensitized heart transplant candidate

PURPOSE OF REVIEW

For sensitized heart transplant candidates who have antibodies to human leukocyte antigens (HLA), finding a suitable donor can be challenging and can lead to adverse waitlist outcomes. In recent years, the number of sensitized patients awaiting heart transplantation has increased likely due to the use of durable and mechanical circulatory support as well as increasing number of candidates with underlying congenital heart disease.

RECENT FINDINGS

Advances in the assessment of HLA antibodies allow for identification of heart transplant candidates who may benefit from desensitization strategies to widen the donor pool and mitigate the risk of adverse posttransplant outcomes.

SUMMARY

Antibody sensitization is a barrier to successful heart transplantation and strategies to identify sensitized patients, stratify their risk, and mitigate this risk through desensitization is crucial to optimize the quality of life and survival of HT recipients.

Chimeric HLA antibody receptor T cells for targeted therapy of antibody-mediated rejection in transplantation

The presence of donor-specific antibodies (DSA), mainly against HLA, increases the risk of allograft rejection. Moreover, antibody-mediated rejection (ABMR) remains an important barrier to optimal long-term outcomes after solid organ transplantation. The development of chimeric autoantibody receptor T lymphocytes has been postulated for targeted therapy of autoimmune diseases. We aimed to develop a targeted therapy for DSA desensitization and ABMR, generating T cells with a chimeric HLA antibody receptor (CHAR) that specifically eliminates DSA-producing B cells. We have genetically engineered an HLA-A2-specific CHAR (A2-CHAR) and transduced it into human T cells. Then, we have performed in vitro experiments such as cytokine measurement, effector cell activation, and cytotoxicity against anti-HLA-A2 antibody-expressing target cells. In addition, we have performed A2-CHAR-Tc cytotoxic assays in an immunodeficient mouse model. A2-CHAR expressing T cells could selectively eliminate HLA-A2 antibody-producing B cells in vitro. The cytotoxic capacity of A2-CHAR expressing T cells mainly depended on Granzyme B release. In the NSG mouse model, A2-CHAR-T cells could identify and eradicate HLA-A2 antibody-producing B cells even when those cells are localized in the bone marrow. This ability is effector:target ratio dependent. CHAR technology generates potent and functional human cytotoxic T cells to target alloreactive HLA class I antibody-producing B cells. Thus, we consider that CHAR technology may be used as a selective desensitization protocol or an ABMR therapy in transplantation.

Imlifidase for Kidney Transplantation of Highly Sensitized Patients With a Positive Crossmatch: The French Consensus Guidelines

Imlifidase recently received early access authorization for highly sensitized adult kidney transplant candidates with a positive crossmatch against an ABO-compatible deceased donor. These French consensus guidelines have been generated by an expert working group, in order to homogenize patient selection, associated treatments and follow-up. This initiative is part of an international effort to analyze properly the benefits and tolerance of this new costly treatment in real-life. Eligible patients must meet the following screening criteria: cPRA ≥ 98%, ≤ 65-year of age, ≥ 3 years on the waiting list, and a low risk of biopsy-related complications. The final decision to use Imlifidase will be based on the two following criteria. First, the results of a virtual crossmatch on recent serum, which shall show a MFI for the immunodominant donor-specific antibodies (DSA) > 6,000 but the value of which does not exceed 5,000 after 1:10 dilution. Second, the post-Imlifidase complement-dependent cytotoxicity crossmatch must be negative. Patients treated with Imlifidase will receive an immunosuppressive regimen based on steroids, rATG, high dose IVIg, rituximab, tacrolimus and mycophenolic acid. Frequent post-transplant testing for DSA and systematic surveillance kidney biopsies are highly recommended to monitor post-transplant DSA rebound and subclinical rejection.

Ixazomib for Desensitization (IXADES) in Highly Sensitized Kidney Transplant Candidates: A Phase II Clinical Trial

Key Points

Ixazomib treatment resulted in decreases in B-cell subsets and bone marrow lymphocytes. Ixazomib treatment resulted in modest decreases in certain anti-HLA antibody specificities. Ixazomib treatment was tolerated, with modest adverse events.

Background

Ixazomib is a second-generation oral proteasome inhibitor approved for treatment of refractory multiple myeloma. We conducted an open-label phase II trial, IXAzomib for DESensitization (IXADES), testing the safety of ixazomib treatment as an approach to decreasing the level and diversity of specificities of anti-HLA antibodies in subjects awaiting kidney transplantation. The trial (NCT03213158 ) enrolled highly sensitized kidney transplant candidates, defined as subjects with calculated panel reactive antibodies (cPRA) >80%, awaiting kidney transplantation >24 months. The subjects were treated with 12 monthly cycles of ixazomib 3 mg+dexamethasone 20 mg. Efficacy was defined as a decrease of cPRA >20% or kidney transplantation. The safety end point was tolerability.

Methods

In ten enrolled subjects, no grade IV, five grade III, 11 grade II, and 43 grade I adverse events were noted. The adverse events included infection, transient paresthesia, nausea, vomiting, and diarrhea. The IXADES regimen was not associated with significant change in levels or diversity of anti-HLA antibodies (cPRA).

Results

Although the IXADES regimen did not exhibit a clear impact on levels and diversity of anti-HLA antibodies in this small cohort, the prolonged half-life of IgG could necessitate a longer duration of treatment for accurate evaluation of efficacy.

Conclusions

In conclusion, treatment with ixazomib/dexamethasone engendered mild-to-moderate toxicity. The impact on anti-HLA was modest and paradoxical in the case of anti-HLA-DR. Clinical trials combining ixazomib with other immunosuppressive agents may be more effective in addressing antibody-mediated processes in kidney transplantation.

Detection and management of HLA sensitization in candidates for adult heart transplantation

Heart transplantation (HT) remains the preferred therapy for patients with advanced heart failure. However, for sensitized HT candidates who have antibodies to human leukocyte antigens , finding a suitable donor can be challenging and can lead to adverse waitlist outcomes. In recent years, the number of sensitized patients awaiting HT has increased likely due to the use of durable and mechanical circulatory support as well as increasing number of candidates with underlying congenital heart disease. This State-of-the-Art review discusses the assessment of human leukocyte antigens antibodies, potential desensitization strategies including mechanisms of action and specific protocols, the approach to a potential donor including the use of complement-dependent cytotoxicity, flow cytometry, and virtual crossmatches, and peritransplant induction management.

Effects of invivo CXCR4 Blockade and Proteasome Inhibition on Bone Marrow Plasma Cells in HLA-Sensitized Kidney Transplant Candidates

To date, plasma cell (PC)-targeted therapies have been limited by suboptimal PC depletion and antibody rebound. We hypothesized this is partly because of PC residence in protective bone marrow (BM) microenvironments. The purpose of this proof-of-concept study was to examine the effects of the CXCR4 antagonist, plerixafor, on PC BM residence; its safety profile (alone and in combination with a proteasome inhibitor, bortezomib); and the transcriptional effect on BMPCs in HLA-sensitized kidney transplant candidates. Participants were enrolled into 3 groups: group A (n = 4), plerixafor monotherapy; and groups B (n = 4) and C (n = 4), plerixafor and bortezomib combinations. CD34⁺ stem cell and PC levels increased in the blood after plerixafor treatment. PC recovery from BM aspirates varied depending on the dose of plerixafor and bortezomib. Single-cell RNA sequencing on BMPCs from 3 group C participants pretreatment and posttreatment revealed multiple populations of PCs, with a posttreatment enrichment of oxidative phosphorylation, proteasome assembly, cytoplasmic translation, and autophagy-related genes. Murine studies demonstrated dually inhibiting the proteasome and autophagy resulted in greater BMPC death than did monotherapies. In conclusion, this pilot study revealed anticipated effects of combined plerixafor and bortezomib on BMPCs, an acceptable safety profile, and suggests the potential for autophagy inhibitors in desensitization regimens.

Desensitization in Crossmatch-positive Kidney Transplant Candidates

Access to kidney transplantation is limited by HLA-specific sensitization. Desensitization strategies enable crossmatch-positive kidney transplantation. In this review, we describe clinical experience gained over the last 20 y using desensitization strategies before kidney transplantation and describe the different tools used (both drugs and apheresis options), including IVIg, rituximab, apheresis techniques, interleukin-6 interference, proteasome inhibition, enzymatic degradation of HLA antibodies, complement inhibition, and B cytokine interference. Although access to transplantation for highly sensitized kidney transplantation candidates has been vastly improved by desensitization strategies, it remains, however, limited by the recurrence of HLA antibodies after transplantation and the occurrence of antibody-mediated rejection.

Novel insights in the clinical management of hyperimmune patients before and after transplantation

Despite improvements in anti-Human Leucocyte Antigens antibody detection, identification, and characterization offer a better in peri-operative management techniques, antibodies remain a serious cause of morbidity and mortality for patients both before and after organ transplantation. Hyperimmune patients are disadvantaged by having to wait longer to receive an organ from a suitably matched donor. They could benefit from desensitization protocols in both pre- and post-transplantation period. Clinical studies are underway to highlight which best desensitization strategies could be assure the best outcome in both heart and kidney transplantation. Although most clinical evidence about desensitization strategies by using anti-CD20 monoclonal antibodies, proteasome inhibitors, anti-CD38 monoclonal antibodies, interleukin-6 blockade, cysteine protease and complement inhibitors, comes from kidney transplantation studies, many of the debated novel concepts can be easily applied to desensitization also in heart transplantation. Here, we discuss the candidates and recipients' management by using most common standard of care and novel therapeutics, desensitization endpoints, and strategies for future studies.

Sensitization in transplantation: Assessment of Risk 2022 Working Group Meeting Report

The Sensitization in Transplantation: Assessment of Risk workgroup is a collaborative effort of the American Society of Transplantation and the American Society of Histocompatibility and Immunogenetics that aims at providing recommendations for clinical testing, highlights gaps in current knowledge, and proposes areas for further research to enhance histocompatibility testing in support of solid organ transplantation. This report provides updates on topics discussed by the previous Sensitization in Transplantation: Assessment of Risk working groups and introduces 2 areas of exploration: non-human leukocyte antigen antibodies and utilization of human leukocyte antigen antibody testing measurement to evaluate the efficacy of antibody-removal therapies.

Assessment and management of allosensitization following heart transplant in adults

Immunological injury to the allograft, specifically by antibodies to de novo donor specific human leukocyte antigen (dnDSA) and antibody mediated injury and rejection are the major limitations to graft survival after heart transplantation (HT). As such, our approach to allosensitization remains limited by the inability of contemporaneous immunoassays to unravel pathogenic potential of dnDSA. Additionally, the role of dnDSA is continuously evaluated with emerging methods to detect rejection. Moreover, the timing and frequency of dnDSA monitoring for early detection and risk mitigation as well as management of dnDSA remain challenging. A strategic approach to dnDSA employs diagnostic assays to determine relevant antibodies in conjunction with clinical presentation and injury/rejection of allograft to tailor therapeutics. In this review, we aim to outline contemporary knowledge involving detection, monitoring and management of dnDSA after HT. Subsequently, we propose a diagnostic and therapeutic approach that may mitigate morbidity and mortality while balancing adverse reactions from pharmacotherapy.

Recommendations for living donor kidney transplantation

This Guide for Living Donor Kidney Transplantation (LDKT) has been prepared with the sponsorship of the Spanish Society of Nephrology (SEN), the Spanish Transplant Society (SET), and the Spanish National Transplant Organization (ONT). It updates evidence to offer the best chronic renal failure treatment when a potential living donor is available. The core aim of this Guide is to supply clinicians who evaluate living donors and transplant recipients with the best decision-making tools, to optimise their outcomes. Moreover, the role of living donors in the current KT context should recover the level of importance it had until recently. To this end the new forms of incompatible HLA and/or ABO donation, as well as the paired donation which is possible in several hospitals with experience in LDKT, offer additional ways to treat renal patients with an incompatible donor. Good results in terms of patient and graft survival have expanded the range of circumstances under which living renal donors are accepted. Older donors are now accepted, as are others with factors that affect the decision, such as a borderline clinical history or alterations, which when evaluated may lead to an additional number of transplantations. This Guide does not forget that LDKT may lead to risk for the donor. Pre-donation evaluation has to centre on the problems which may arise over the short or long-term, and these have to be described to the potential donor so that they are able take them into account. Experience over recent years has led to progress in risk analysis, to protect donors' health. This aspect always has to be taken into account by LDKT programmes when evaluating potential donors. Finally, this Guide has been designed to aid decision-making, with recommendations and suggestions when uncertainties arise in pre-donation studies. Its overarching aim is to ensure that informed consent is based on high quality studies and information supplied to donors and recipients, offering the strongest possible guarantees.

Belatacept-Based Maintenance Immunosuppression Controls the Post-Transplant Humoral Immune Response in Highly Sensitized Nonhuman Primates

Preexisting donor-specific antibodies (DSA) to MHC antigens increase the risk of antibody-mediated rejection (AMR) in sensitized transplant recipients and reduces graft survival. Pretransplant desensitization with costimulation blockade and proteasome inhibition has facilitated transplantation in our preclinical nonhuman primate (NHP) model. However, long-term graft survival is limited by rebound of DSA after transplantation. In this study, we performed kidney transplants between highly sensitized, maximally MHC-mismatched NHPs (n=14). At kidney transplantation, primates received T cell depletion with rhesus-specific anti-thymocyte globulin (rhATG; n=10) or monoclonal anti-CD4 and anti-CD8 antibodies (n=4). Maintenance immunosuppression consisted of belatacept and tacrolimus (n=5) or belatacept and rapamycin (n=9) with steroids. Rebound of DSA post-kidney transplantation was significantly reduced compared with maintenance immunosuppression with tacrolimus, mycophenolate, and steroids. Protocol lymph node biopsy specimens showed a decrease in germinal center activity, with low frequencies of T follicular helper cells and class-switched B cells after kidney transplantation. Combined belatacept and rapamycin was superior in controlling viral reactivation, enabling weaning of ganciclovir prophylaxis. Tacrolimus was associated with increased morbidity that included cytomegalovirus and parvovirus viremia and post-transplant lymphoproliferative disorder. All primates in the tacrolimus/belatacept group failed discontinuation of antiviral therapy. Overall, belatacept-based immunosuppression increased AMR-free graft survival by controlling post-transplant humoral responses in highly sensitized NHP recipients and should be further investigated in a human clinical trial.

From bench to bedside: reversing established antibody responses and desensitization

PURPOSE OF REVIEW

Basic transplant immunology has primarily focused on the definition of mechanisms, but an often-stated aspirational goal is to translate basic mechanistic research into future therapy. Pretransplant donor-specific antibodies (DSA) mediate hyperacute as well as early antibody-mediated rejection (AMR), whereas DSA developing late posttransplantation may additionally mediate chronic rejection. Although contemporary immunosuppression effectively prevents early cellular rejection after transplant in nonsensitized patients, it is less effective at controlling preexisting HLA antibody responses or reversing DSA once established, thus underscoring a need for better therapies.

RECENT FINDINGS

We here review the development of a bench-to-bedside approach involving transient proteasome inhibition to deplete plasma cells, combined with maintenance co-stimulation blockade, with CTLA-4Ig or belatacept, to prevent the generation of new antibody-secreting cells (ASCs).

SUMMARY

This review discusses how this treatment regimen, which was rationally designed and validated to reverse established DSA responses in mouse models, translated into reversing active AMR in the clinic, as well as desensitizing highly sensitized patients on the transplant waitlist.

European Guideline for the Management of Kidney Transplant Patients With HLA Antibodies: By the European Society for Organ Transplantation Working Group

This guideline, from a European Society of Organ Transplantation (ESOT) working group, concerns the management of kidney transplant patients with HLA antibodies. Sensitization should be defined using a virtual parameter such as calculated Reaction Frequency (cRF), which assesses HLA antibodies derived from the actual organ donor population. Highly sensitized patients should be prioritized in kidney allocation schemes and linking allocation schemes may increase opportunities. The use of the ENGAGE 5 ((Bestard et al., Transpl Int, 2021, 34: 1005–1018) system and online calculators for assessing risk is recommended. The Eurotransplant Acceptable Mismatch program should be extended. If strategies for finding a compatible kidney are very unlikely to yield a transplant, desensitization may be considered and should be performed with plasma exchange or immunoadsorption, supplemented with IViG and/or anti-CD20 antibody. Newer therapies, such as imlifidase, may offer alternatives. Few studies compare HLA incompatible transplantation with remaining on the waiting list, and comparisons of morbidity or quality of life do not exist. Kidney paired exchange programs (KEP) should be more widely used and should include unspecified and deceased donors, as well as compatible living donor pairs. The use of a KEP is preferred to desensitization, but highly sensitized patients should not be left on a KEP list indefinitely if the option of a direct incompatible transplant exists.

Donor specific HLA antibody in hematopoietic stem cell transplantation: Implications for donor selection

Advances in hematopoietic stem cell transplant (HSCT) have led to changes in the approach to donor selection. Many of these new approaches result in greater HLA loci mismatching, either through the selection of haploidentical donors or permissive HLA mismatches. Although these approaches increase the potential of transplant for many patients by expanding the number of acceptable donor HLA genotypes, they add the potential barrier of donor-specific HLA antibodies (DSA). DSA presents a unique challenge in HSCT, as it can limit engraftment and lead to graft failure. However, transient reduction of HLA antibodies through desensitization treatments can limit the risk of graft failure and facilitate engraftment. Thus, the consideration of DSA in donor selection and the management of DSA prior to transplant are playing an increasingly important role in HSCT. In this review, we will discuss studies addressing the role of HLA antibodies in HSCT, the reported impact of desensitization on DSA levels, and the implications for selecting donors for patients with DSA. We found that there is a clear consensus that moderate strength DSA should be avoided, while desensitization strategies are reported to be effective in most cases at reducing DSA to amenable levels. There is limited information regarding the impact of specific characteristics of DSA, such as HLA loci or overall level of sensitization, which could further aid in donor selection for sensitized HSCT candidates.

Approach to Highly Sensitized Kidney Transplant Candidates and a Positive Crossmatch

Human leukocyte antigen (HLA)-incompatible kidney transplantation offers survival benefit compared with ongoing dialysis. There have been considerable advances in the last decade to allow for increased access to transplant for the HLA-sensitized kidney transplant candidates. These include increased priority in the kidney allocation system, kidney paired donation, and novel desensitization strategies. A better understanding of the role of B cells, plasma cells, and complement and inflammatory cytokines in the pathophysiology of HLA antibody-mediated allograft injury has led to the use of novel therapeutics for desensitization and treatment of antibody-mediated rejection. Here we discuss current approaches to kidney transplantation in HLA-sensitized kidney transplant candidates.

Epitope-Level Matching—A Review of the Novel Concept of Eplets in Transplant Histocompatibility

The development of de novo donor-specific antibodies is related to the poor matching of the human leukocyte antigen (HLA) between donor and recipient, which leads to dismal clinical outcomes and graft loss. However, new approaches that stratify the risks of long-term graft failure in solid organ transplantation have emerged, changing the paradigm of HLA compatibility. In addition, advances in software development have given rise to a new structurally based algorithm known as HLA Matchmaker, which determines compatibility at the epitope rather than the antigen level. Although this technique still has limitations, plenty of research maintains that this assessment represents a more complete and detailed definition of HLA compatibility. This review summarizes recent aspects of eplet mismatches, highlighting the most recent advances and future research directions.

Current Desensitization Strategies in Heart Transplantation

Heart transplant candidates sensitized to HLA antigens wait longer for transplant, are at increased risk of dying while waiting, and may not be listed at all. The increasing prevalence of HLA sensitization and limitations of current desensitization strategies underscore the urgent need for a more effective approach. In addition to pregnancy, prior transplant, and transfusions, patients with end-stage heart failure are burdened with unique factors placing them at risk for HLA sensitization. These include homograft material used for congenital heart disease repair and left ventricular assist devices (LVADs). Moreover, these risks are often stacked, forming a seemingly insurmountable barrier in some cases. While desensitization protocols are typically implemented uniformly, irrespective of the mode of sensitization, the heterogeneity in success and post-transplant outcomes argues for a more tailored approach. Achieving this will require progress in our understanding of the immunobiology underlying the innate and adaptive immune response to these varied allosensitizing exposures. Further attention to B cell activation, memory, and plasma cell differentiation is required to establish methods that durably abrogate the anti-HLA antibody response before and after transplant. The contribution of non-HLA antibodies to the net state of sensitization and the potential implications for graft longevity also remain to be comprehensively defined. The aim of this review is to first bring forth select issues unique to the sensitized heart transplant candidate. The current literature on desensitization in heart transplantation will then be summarized providing context within the immune response. Building on this, newer approaches with therapeutic potential will be discussed emphasizing the importance of not only addressing the short-term pathogenic consequences of circulating HLA antibodies, but also the need to modulate alloimmune memory.

New Perspectives on Desensitization in the Current Era - An Overview

Blood group and tissue incompatibilities remain significant barriers to achieving transplantation. Although no patient should be labeled "un-transplantable" due to blood group or tissue incompatibility, all candidates should be provided with individualized and realistic counseling regarding their anticipated wait times for deceased donor or kidney paired donation matching, with early referral to expert centers for desensitization when needed. Vital is the careful selection of patients whose health status is such that desensitizing treatment is less likely to cause serious harm and whose anti-HLA antibody status is such that treatment is likely to accomplish the goal of increasing organ offers with an acceptable final crossmatch. Exciting new developments have re-energized the interest and scope of desensitization in the times ahead.

Plasma cell biology: Foundations for targeted therapeutic development in transplantation

Solid organ transplantation is a life-saving procedure for patients with end-stage organ disease. Over the past 70 years, tremendous progress has been made in solid organ transplantation, particularly in T-cell-targeted immunosuppression and organ allocation systems. However, humoral alloimmune responses remain a major challenge to progress. Patients with preexisting antibodies to human leukocyte antigen (HLA) are at significant disadvantages in regard to receiving a well-matched organ, moreover, those who develop anti-HLA antibodies after transplantation face a significant foreshortening of renal allograft survival. Historical therapies to desensitize patients prior to transplantation or to treat posttransplant AMR have had limited effectiveness, likely because they do not significantly reduce antibody levels, as plasma cells, the source of antibody production, remain largely unaffected. Herein, we will discuss the significance of plasma cells in transplantation, aspects of their biology as potential therapeutic targets, clinical challenges in developing strategies to target plasma cells in transplantation, and lastly, novel approaches that have potential to advance the field.

Emerging New Approaches in Desensitization: Targeted Therapies for HLA Sensitization

There is an urgent need for therapeutic interventions for desensitization and antibody-mediated rejection (AMR) in sensitized patients with preformed or de novo donor-specific HLA antibodies (DSA). The risk of AMR and allograft loss in sensitized patients is increased due to preformed DSA detected at time of transplant or the reactivation of HLA memory after transplantation, causing acute and chronic AMR. Alternatively, de novo DSA that develops post-transplant due to inadequate immunosuppression and again may lead to acute and chronic AMR or even allograft loss. Circulating antibody, the final product of the humoral immune response, has been the primary target of desensitization and AMR treatment. However, in many cases these protocols fail to achieve efficient removal of all DSA and long-term outcomes of patients with persistent DSA are far worse when compared to non-sensitized patients. We believe that targeting multiple components of humoral immunity will lead to improved outcomes for such patients. In this review, we will briefly discuss conventional desensitization methods targeting antibody or B cell removal and then present a mechanistically designed desensitization regimen targeting plasma cells and the humoral response.

HLA Desensitization in Solid Organ Transplantation: Anti-CD38 to Across the Immunological Barriers

The presence of anti-human leucocyte antigen (HLA) antibodies in the potential solid organ transplant recipient's blood is one of the main barriers to access to a transplantation. The HLA sensitization is associated with longer waitlist time, antibody mediated rejection and transplant lost leading to increased recipient's morbidity and mortality. However, solid organ transplantation across the HLA immunological barriers have been reported in recipients who were highly sensitized to HLA using desensitization protocols. These desensitization regimens are focused on the reduction of circulating HLA antibodies. Despite those strategies improve rates of transplantation, it remains several limitations including persistent high rejection rate and worse long-term outcomes when compare with non-sensitized recipient population. Currently, interest is growing in the development of new desensitization approaches which, beyond targeting antibodies, would be based on the modulation of alloimmune pathways. Plasma cells appears as an interesting target given their critical role in antibody production. In the last decade, CD38-targeting immunotherapies, such as daratumumab, have been recognized as a key component in the treatment of myeloma by inducing an important plasma cell depletion. This review focuses on an emerging concept based on targeting CD38 to desensitize in the field of transplantation.

Current Approaches to Desensitization in Solid Organ Transplantation

Major advancements in the development of HLA antibody detection techniques and our understanding of the outcomes of solid organ transplant in the context of HLA antibody have occurred since the relevance of sensitization was first recognized nearly 50 years ago. Additionally, kidney paired donation programs (KPD) have become widespread, deceased donor allocation policies have changed, and several new therapeutic options have become available with promise to reduce HLA antibody. In this overview we aim to provide thoughtful guidance about when desensitization in kidney transplantation should be considered taking into account the outcomes of HLA incompatible transplantation. Novel therapeutics, desensitization endpoints, and strategies for future study will also be discussed. While most of our understanding about desensitization comes from studying kidney transplant candidates and recipients, many of the concepts discussed can be easily applied to desensitization in all of solid organ transplantation.

Bortezomib treatment for refractory nontuberculous mycobacterial infection in the setting of interferon gamma autoantibodies

Interferon-γ autoantibodies increase the risk of disseminated nontuberculous mycobacterial infections. Addition of rituximab to antibiotics accelerates and improves outcomes, but refractory infections can occur due to persistent production of autoantibodies. We combined bortezomib with rituximab to reduce autoantibodies leading to clinical and radiographic improvement in infection.

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IFNγ autoantibodies increase the risk of disseminated infections with intracellular pathogens.

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Rituximab combined with antibiotics improves outcomes, but infections can become refractory.

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The addition of bortezomib is safe with close monitoring and can improve clinical outcomes.

Impact of carfilzomib-based desensitization on heart transplantation of sensitized candidates

BACKGROUND

Allosensitization in heart transplant candidates is associated with longer transplant wait times and post-transplant complications. We summarize our experience with desensitization using carfilzomib, an irreversible proteasome inhibitor that causes plasma cell apoptosis.

METHODS

One cycle of desensitization consisted of plasmapheresis and carfilzomib 20 mg/m² on days 1, 2, 8, 9, 15, and 16 with intravenous immune globulin 2 g/kg after carfilzomib on day 16. Patients underwent repeat cycles as indicated. We compare calculated panel-reactive antibody (cPRA) for neat combined Class I and II IgG and C1q pre- and post-treatment using a cutoff for cPRA entry of ≥ 4000 and 500 MFI, respectively.

RESULTS

From June 2013 to October 2019, 9 patients underwent 20 cycles of carfilzomib-based desensitization. Each cycle resulted in an average cPRA decrease of 24% (95% CI: 6-42) for IgG and 36% (95% CI: 17-55) for C1q. From treatment start to finish, mean cPRA fell from 76% to 40% (p = 0.01) for IgG and 56% to 4% (p = 0.017) for C1q. Six of 9 patients have been transplanted with 5 of the transplanted hearts crossing preoperative donor-specific antibodies. During a median follow-up of 35.1 months, all transplanted patients have survived with only 1 occurrence of treated rejection. Side effects of desensitization included acute kidney injury (67%) and thrombocytopenia (33%) with all episodes self-resolving.

CONCLUSIONS

A carfilzomib-based desensitization strategy among heart transplant candidates reduces the level of HLA antibodies and complement binding, facilitates successful transplantation, and is associated with excellent outcomes at 3 years.

Estimating alloantibody levels in highly sensitized renal allograft candidates: Using serial dilutions to demonstrate a treatment effect in clinical trials

Small reductions in calculated panel-reactive antibody (cPRA) are associated with increased kidney transplantation in 100% cPRA patients. However, the high level of antibody in these patients is such that desensitization may reduce antibody but not cPRA, thus the cPRA change on undiluted serum with desensitization is an insensitive measure of effectiveness. We evaluated cPRA reduction, calculated per antibody titer, as a desensitization trial endpoint. To accomplish this, two serum samples from 20 kidney transplant candidates with cPRA ≥99.9% (100%) were obtained and serially diluted in triplicate to determine the titer of individual human leukocyte antigen (HLA) antibody specificities. CPRA was computed per dilution to identify the titer at which cPRA drops below 98%. Inter- and intra-assay variability and changes overtime were determined. The dilution needed to reach a cPRA <98% was within 1 titer for replicates from the same sample, with 90% (36/40) concordance. This indicates that only changes >2 titers can be deemed clinically meaningful. The median (IQR) titer difference was 0 (0-1) from baseline to follow-up within 12 months. The cPRA per titer also risk-stratified candidates for trial inclusion. In conclusion, determining the cPRA per titer is a reliable approach to simplify complex antibody data and an ideal endpoint for desensitization trials.

KDIGO Clinical Practice Guideline on the Evaluation and Management of Candidates for Kidney Transplantation

The 2020 Kidney Disease: Improving Global Outcomes (KDIGO) Clinical Practice Guideline on the Evaluation and Management of Candidates for Kidney Transplantation is intended to assist health care professionals worldwide who evaluate and manage potential candidates for deceased or living donor kidney transplantation. This guideline addresses general candidacy issues such as access to transplantation, patient demographic and health status factors, and immunological and psychosocial assessment. The roles of various risk factors and comorbid conditions governing an individual's suitability for transplantation such as adherence, tobacco use, diabetes, obesity, perioperative issues, causes of kidney failure, infections, malignancy, pulmonary disease, cardiac and peripheral arterial disease, neurologic disease, gastrointestinal and liver disease, hematologic disease, and bone and mineral disorder are also addressed. This guideline provides recommendations for evaluation of individual aspects of a candidate's profile such that each risk factor and comorbidity are considered separately. The goal is to assist the clinical team to assimilate all data relevant to an individual, consider this within their local health context, and make an overall judgment on candidacy for transplantation. The guideline development process followed the Grades of Recommendation Assessment, Development, and Evaluation (GRADE) approach. Guideline recommendations are primarily based on systematic reviews of relevant studies and our assessment of the quality of that evidence, and the strengths of recommendations are provided. Limitations of the evidence are discussed with differences from previous guidelines noted and suggestions for future research are also provided.

Novel strategies to target the humoral alloimmune response

Antibody-mediated rejection (ABMR) represents a major cause of late allograft loss in solid organ transplantation worldwide. This process is driven by donor-specific antibodies (DSA), which develop either de-novo or, in sensitized patients, are preformed at the time of transplantation. Effective targeting of ABMR has been hampered by a lack of robust randomized controlled trials (RCT), required for the regulatory approval of new therapeutics. In this review, we discuss the evidence behind the present "standard" of care and recent progress in the development of novel strategies targeting different aspects of the alloimmune humoral response, including naïve and memory B-cell activation, the germinal centre reaction, plasma cell survival and antibody effector functions. In particular, we focus on co-stimulation blockade and its combination with next-generation proteasome inhibitors, new depleting monoclonal antibodies (anti-CD19, anti-BCMA, anti-CD38, anti-CD138), interleukin-6 blockade, complement inhibition and DSA degradation. These treatment modalities, when used in the appropriate clinical context and combination, have the potential to finally improve long-term allograft survival.

Canadian Cardiovascular Society/Canadian Cardiac Transplant Network Position Statement on Heart Transplantation: Patient Eligibility, Selection, and Post-Transplantation Care

Significant practice-changing developments have occurred in the care of heart transplantation candidates and recipients over the past decade. This Canadian Cardiovascular Society/Canadian Cardiac Transplant Network Position Statement provides evidence-based, expert panel recommendations with values and preferences, and practical tips on: (1) patient selection criteria; (2) selected patient populations; and (3) post transplantation surveillance. The recommendations were developed through systematic review of the literature and using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system. The evolving areas of importance addressed include transplant recipient age, frailty assessment, pulmonary hypertension evaluation, cannabis use, combined heart and other solid organ transplantation, adult congenital heart disease, cardiac amyloidosis, high sensitization, and post-transplantation management of antibodies to human leukocyte antigen, rejection, cardiac allograft vasculopathy, and long-term noncardiac care. Attention is also given to Canadian-specific management strategies including the prioritization of highly sensitized transplant candidates (status 4S) and heart organ allocation algorithms. The focus topics in this position statement highlight the increased complexity of patients who undergo evaluation for heart transplantation as well as improved patient selection, and advances in post-transplantation management and surveillance that have led to better long-term outcomes for heart transplant recipients.

Reversing donor-specific antibody responses and antibody-mediated rejection with bortezomib and belatacept in mice and kidney transplant recipients

Active antibody-mediated rejection (AMR) is a potentially devastating complication and consistently effective treatment remains elusive. We hypothesized that the reversal of acute AMR requires rapid elimination of antibody-secreting plasma cells (PC) with a proteasome inhibitor, bortezomib, followed by the sustained inhibition of PC generation with CTLA4-Ig or belatacept (B/B). We show in mice that B/B therapy selectively depleted mature PC producing donor-specific antibodies (DSA) and reduced DSA, when administered after primary and secondary DSA responses had been established. A pilot investigation was initiated to treat six consecutive patients with active AMR with B/B. Compassionate use of this regimen was initiated for the first patient who developed early, severe acute AMR that did not respond to steroids, plasmapheresis, and intravenous immunoglobulin after his third kidney transplant. B/B treatment resulted in a rapid reversal of AMR, leading us to treat five additional patients who also resolved their acute AMR episode and had sustained disappearance of circulating DSA for ≤30 months. This study provides a proof-of-principle demonstration that mouse models can identify mechanistically rational therapies for the clinic. Follow-up investigations with a more stringent clinical design are warranted to test whether B/B improves on the standard of care for the treatment of acute AMR.

Novel therapeutic opportunities afforded by plasma cell biology in transplantation

Despite new immunotherapies aimed at B and T cells, plasma cells and their lifelong antibody secretion constitute a major immune barrier to long-term graft survival. In this mini-review, we survey the recent advances that have been made in the biology and immunometabolism of long-lived plasma cells, and outline aspects of plasma cell function that can be exploited for clinical benefit in recipients of solid organ transplants. A handful of ongoing studies are already targeting plasma cells to achieve desensitization and reduce the alloantibody burden in individuals posttransplant. In reviewing the recent strides made in our understanding of the molecular basis of plasma cell survival, we will place our discussions in the context of existing preclinical and clinical studies.

The suppressive effect on CD4 T cell alloresponse against endothelial HLA-DR via PD-L1 induced by anti-A/B ligation

While donor-specific human leukocyte antigen (HLA) antibodies are a frequent cause for chronic antibody-mediated rejection in organ transplantation, this is not the case for antibodies targeting blood group antigens, as ABO-incompatible (ABO-I) organ transplantation has been associated with a favorable graft outcome. Here, we explored the role of CD4 T cell-mediated alloresponses against endothelial HLA-D-related (DR) in the presence of anti-HLA class I or anti-A/B antibodies. CD4 T cells, notably CD45RA-memory CD4 T cells, undergo extensive proliferation in response to endothelial HLA-DR. The CD4 T cell proliferative response was enhanced in the presence of anti-HLA class I, but attenuated in the presence of anti-A/B antibodies. Microarray analysis and molecular profiling demonstrated that the expression of CD274 programmed cell death ligand 1 (PD-L1) increased in response to anti-A/B ligation-mediated extracellular signal-regulated kinase (ERK) inactivation in endothelial cells that were detected even in the presence of interferon-γ stimulation. Anti-PD-1 antibody enhanced CD4 T cell proliferation, and blocked the suppressive effect of the anti-A/B antibodies. Educated CD25⁺ CD127^- regulatory T cells (edu.T_regs ) were more effective at preventing CD4 T cell alloresponses to endothelial cells compared with naive T_reg ; anti-A/B antibodies were not involved in the T_reg -mediated events. Finally, amplified expression of transcript encoding PD-L1 was observed in biopsy samples from ABO-I renal transplants when compared with those from ABO-identical/compatible transplants. Taken together, our findings identified a possible factor that might prevent graft rejection and thus contribute to a favorable outcome in ABO-I renal transplantation.

Plasma cell targeting to prevent antibody-mediated rejection

Plasma cells (PCs) are the major source of pathogenic allo- and autoantibodies and have historically demonstrated resistance to therapeutic targeting. However, significant recent clinical progress has been made with the use of second-generation proteasome inhibitors (PIs). PIs provide efficient elimination of plasmablast-mediated humoral responses; however, long-lived bone marrow (BM) resident PCs (LLPCs) demonstrate therapeutic resistance, particularly to first-generation PIs. In addition, durability of antibody (Ab) reduction still requires improvement. More recent clinical trials have focused on conditions mediated by LLPCs and have included mechanistic studies of LLPCs from PI-treated patients. A recent clinical trial of carfilzomib (a second-generation irreversible PI) demonstrated improved efficacy in eliminating BM PCs and reducing anti-HLA Abs in chronically HLA-sensitized patients; however, Ab rebound was observed over several weeks to months following PI therapy. Importantly, recent murine studies have provided substantial insights into PC biology, thereby further enhancing our understanding of PC populations. It is now clear that BMPC populations, where LLPCs are thought to primarily reside, are heterogeneous and have distinct gene expression, metabolic, and survival signatures that enable identification and characterization of PC subsets. This review highlights recent advances in PC biology and clinical trials in transplant populations.

Experimental modeling of desensitization: What have we learned about preventing AMR?

During the past 5 decades, short-term outcomes in kidney transplant have significantly improved, in large part due to reduced rates and severity of acute rejection. Development of better immunosuppressive maintenance agents, as well as new induction therapies, helped make these advances. Nonhuman primate models provided a rigorous testing platform to evaluate candidate biologics during this process. However, antibody-mediated rejection remains a major cause of late failure of kidney allografts despite advances made in pharmacologic immunosuppression and strategies developed to facilitate improved donor-recipient matching. Our laboratory has been actively working to develop strategies to prevent and treat antibody-mediated rejection and immunologic sensitization in organ transplant, relying largely on a nonhuman primate model of kidney transplant. In this review, we will cover outcomes achieved by managing antibody-mediated rejection or sensitization in nonhuman primate models and discuss promises, limitations, and future directions for this model.

Desensitization strategies: is it worth it?

Preformed donor-specific antibodies (DSAs) limit access to transplantation for thousands of renal transplant patients. While kidney paired donation offers the best strategy for patients with a living donor, for very highly sensitized patients and those without living donors, a strategy of desensitization offers the best hope of transplantation. Removal of DSAs with plasmapheresis, intravenous immunoglobulin and anti-CD20 antibodies can permit successful transplantation. While the clinical outcomes remain inferior to compatible transplant and the costs are significantly greater, when compared with long-term dialysis treatment, these strategies are offer improved survival and are cost-effective given nationally accepted benchmarks.

Proteasomal adaptations underlying carfilzomib-resistance in human bone marrow plasma cells

Donor-specific antibodies (DSAs) have a deleterious effect on allografts and remain a major immunologic barrier in transplantation. Current therapies to eliminate DSAs are ineffective in highly HLA-sensitized patients. Proteasome inhibitors have been employed as a strategy to target bone marrow plasma cells (BMPCs), the source of long-term antibody production; however, their efficacy has been limited by poorly defined drug-resistance mechanisms. Here, we performed transcriptomic profiling of CD138⁺ BMPCs that survived in vivo desensitization therapy with the proteasome inhibitor carfilzomib to identify mechanisms of drug resistance. The results revealed a genomic signature that included increased expression of the immunoproteasome, a highly specialized proteasomal variant. Western blotting and functional studies demonstrated that catalytically active immunoproteasomes and the immunoproteasome activator PA28 were upregulated in carfilzomib-resistant BMPCs. Carfilzomib-resistant BMPCs displayed reduced sensitivity to the proteasome inhibitors carfilzomib, bortezomib, and ixazomib, but enhanced sensitivity to an immunoproteasome-specific inhibitor ONX-0914. Finally, in vitro carfilzomib treatment of BMPCs from HLA-sensitized patients increased levels of the immunoproteasome β5i (PSMB8) catalytic subunit suggesting that carfilzomib therapy directly induces an adaptive immunoproteasome response. Taken together, our results indicate that carfilzomib induces structural changes in proteasomes and immunoproteasome formation.

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

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

Successful treatment of early acute antibody-mediated rejection in an human leukocyte antigen-incompatible and ABO-incompatible living-donor kidney transplant patient

For successful human leukocyte antigen-incompatible (HLAi) or ABO-incompatible (ABOi) living-donor kidney transplantations (LDKTs), pretransplant desensitization is essential; however, early antibody-mediated rejection (ABMR) remains the most important complication after HLAi or ABOi transplantation. Here, we report a case of early acute ABMR in simultaneous HLAi and ABOi LDKT with preformed donor-specific antibody (DSA), despite desensitization. Dialysis-dependent, severe ABMR occurred with a rebound of pre-existing DSA and appearance of de novo DSA after initial normalization of renal function, 8 days postoperatively. However, a low anti-ABO antibody titer (1:8) was maintained after transplantation. Combination therapy of plasmapheresis, high-dose intravenous immunoglobulin, and bortezomib improved both ABMR and renal functions. Thus, an appropriate preventive and therapeutic management for early ABMR is important among high-risk LDKT patients. Furthermore, early AMBR can occur despite pretransplant desensitization as seen in this case, and close monitoring of the patient and prompt management are considered vital for better therapeutic outcomes.