Novel Therapies for the Treatment of Antibody Mediated Rejection in Solid Organ Transplantation: A Systematic Review

Antibody-mediated rejection of the liver allograft: An update and a clinico-pathological perspective

Antibody-mediated rejection: analyzing the risk, proposing solutions.

Intravenous immunoglobulin significantly reduces exposure of concomitantly administered anti-C5 monoclonal antibody tesidolumab.

The efficacy of rituximab treatment for antibody-mediated rejection in liver transplantation: A retrospective Japanese nationwide study.

We sought to clarify the controversial issue of whether detecting low-level anti-donor-specific HLA antibody (HLA-DSA) by single-antigen flow-bead assay (SAFB) may have a potential role in reducing acute and chronic antibody-mediated rejection (AMR). We retrospectively studied the preoperative serum of ABO-compatible living kidney transplantation recipients transplanted between 2001 and 2004 by SAFB using a Luminex platform. HLA-DSA was detected only by SAFB in 24 patients, although all of them showed negative T-cell and B-cell complement-dependent cytotoxicity (CDC) crossmatches. The HLA-DSA patients went on to have surprisingly high levels of acute and chronic AMR despite being only weakly sensitized (acute AMR, 33.3%; chronic AMR, 41.7%). After 2005, we implemented SAFB routinely and any patient having a positive HLA-DSA was considered to be a desensitization candidate. The 52 patients found to have HLA-DSA underwent kidney transplantation after prior treatment with a single dose of rituximab (RIT) and three or four sessions of double-filtration plasmapheresis (DFPP) in addition to regimens commonly used between 2001 and 2004. After 2005, there was a significant reduction in the occurrence of acute and chronic AMR (acute AMR, 4.7%, P < 0.001; chronic AMR, 4.7%, P < 0.001). The 5-year graft survival rate also improved after implementing SAFB (83.3-98.1%, P = 0.032). The RIT/DFPP-induction protocol may improve graft survival even in patients with low-level DSA.

Background: Antibody mediated rejection (AMR) remains a major cause of graft failure post-renal transplantation, as current therapies are suboptimal. A potential new therapeutic strategy is the blockade of the intracytoplasmic tyrosine kinase, Syk (Spleen Tyrosine Kinase) which is involved in the signalling of Fcγ receptors, B cell receptors, integrins and GPVI collagen receptors on leukocytes and platelets. Aims: I explored the effect of Syk blockade in experimental renal allograft rejection. First a mixed model of rejection in non-sensitized rats was used. A selective Syk inhibitor was the only treatment administered from time of transplantation until the day of kill. We then created a pure model of AMR in sensitized rats in which endogenous production of anti- MHC (major histocompatibility complex) antibodies was induced pre transplantation by immunization. Cellular rejection was minimized by tacrolimus therapy pre- and post- surgery. A Syk inhibitor was administered from time of transplantation until animals were killed. Lastly, I looked at leukocytic infiltration in acute and chronic human AMR and the effect of commonly used drugs on the infiltrates. Results: In both the non-sensitized model of mixed rejection and the sensitized model of acute AMR, Syk inhibition improved renal allograft function. In the mixed model, macrophage and neutrophil numbers were reduced, as was extent of thrombosis but no effect was seen on T cell infiltration and activation due to the lack of Syk in mature T cells. In the sensitized model, there was a large decrease in macrophage numbers and activation as well as a reduction in neutrophil and NK cell activation and extent of thrombosis. DSA levels were unchanged by Syk inhibition in the sensitized model, as high levels of DSAs were present pre-transplantation. DSA deposition within the allograft was not significantly changed by Syk inhibition. In the human studies, macrophage and T cell rich glomerulitis was shown to be a bad prognostic sign. High dose intravenous immunoglobulins (IVIG) and plasma exchange (PEX) caused an increase in macrophage numbers in chronic and acute AMR respectively. Conclusion: The intracytoplasmic tyrosine kinase, Syk, plays a role in the pathogenesis of AMR and thus Syk may represent a new therapeutic target in AMR. High numbers on T cells and macrophages in glomeruli are bad prognostic signs in AMR and IVIG and current therapies in AMR cause an increase in macrophage numbers.

Improvements in prevention and management of cellular rejection of solid organ transplants, coupled with increasing numbers of sensitized patients, have focused attention on antibody-mediated rejection (AbMR). Complement is a critical component of AbMR, in addition to interfacing between innate and adaptive immunity and the coagulation cascade. This article reviews complement biology and strategies to overcome complement in AbMR, cognisant that antibody can act independently of complement. The past decade has witnessed an improvement in the prevention and treatment of AbMR as a result of solid-phase assays to determine antibody specificity, definition of histopathological criteria, and use of plasmapheresis and/or intravenous immunoglobulin (IVIG). Nonetheless, AbMR continues to impact adversely on short- and long-term graft survival. Use of B and/or T-lymphocyte-depleting therapies has not shown measurable benefit, and the need remains for therapies that deplete antibody, or provide better protection from complement-mediated damage. Disordered complement activity in human diseases such as paroxysmal nocturnal haemoglobinuria, has provided additional impetus to pursuing therapeutic complement inhibition. Preliminary data from C5 inhibition with eculizumab in the treatment and prevention of AbMR have shown promise. Trials with recombinant human inhibitors of C1 (effective in angioedema) to prevent or treat AbMR are beginning. Despite current limitations, 'protection' of the transplant through plasmapheresis and/or IVIG enables many allografts to survive in sensitized recipients. Elucidating the pathways mediating graft acceptance, by constitutive antibody deletion, or 'accommodation' (wherein donor organ remains uninjured despite antibody binding), or other local protective mechanism(s), is an equally important challenge in the quest to overcome AbMR.

Antibody-mediated rejection (AMR) is a major risk for renal allograft survival. Throughout decades, cyclophosphamide treatment has been proven to be effective in patients with antibody-associated autoimmune diseases. We investigated whether cyclophosphamide combined with plasmapheresis and intravenous immunoglobulins is an option for patients with AMR. Between March 2013 and November 2015, we initiated treatment of 13 consecutive patients with biopsy-proven acute AMR with intravenous cyclophosphamide pulses (15 mg/kg adapted to age and renal function) at 3-week intervals, PPH (6×), and high-dose intravenous immunoglobulin (1.5 g/kg). Treatment was completed after 6 cyclophosphamide pulses or in case of return to baseline serum creatinine together with reduction of donor-specific HLA antibodies (DSA) below 500 mean fluorescence intensity. Eleven of 13 patients completed treatment. Median follow-up was 18 (12-44) months. At the end of follow-up, graft survival was 77% (10/13). The 3 graft losses were caused at least in part by nonadherence and premature termination of treatment. Serum creatinine increased from 1.7±0.4 mg/dL at 3 months before diagnosis to 3.7±2.4 mg/dL at diagnosis (P = 0.01), and decreased to 2.1 ± 0.7 mg/dL at 3 months after diagnosis (P = 0.01). In 7 (64%) of 11 patients, who completed treatment, DSA decreased, in 4 (36%) of 11 DSA were below 500 mean fluorescence intensity after treatment. Dose reductions had to be performed in 3 of 13 patients for leukopenia. We observed 14 hospitalizations in 9 of 13 patients. To our knowledge, this is the first systematic report on cyclophosphamide-based treatment of acute AMR based on modern diagnostics. Treatment was effective and relatively safe. Future studies will show, whether cyclophosphamide proves to be a valuable alternative for the treatment of AMR.

Development and validation of a prognostic index for allograft outcome in kidney recipients with transplant glomerulopathy

Acute antibody-mediated rejection is a diagnostic challenge in renal transplantation medicine. However, it is an important diagnosis to make, since chronic antibody-mediated rejection (CAMR) is the main cause of long-term graft loss. Antibody-mediated rejection is diagnosed by detecting donor-specific antibodies (DSAs) in the blood in combination with observing typical histomorphological signs in kidney biopsy, as described in the Banff classification. Therapy is based on the removal of DSAs by administering intravenous immunoglobulins (IVIGs), plasmapheresis, or immunoadsorption. Reoccurrence of antibodies is diminished by the use of rituximab, increased immunosuppression, and in some cases additional experimental substances. A combination of these techniques has been shown to be successful in the majority of cases of acute and chronic antibody-mediated rejection. Routine DSA monitoring is warranted for early detection of antibody-mediated rejection.

Since the mid 1990s, incompatible kidney transplantation has become more widespread and available in the United States.1, 2 This trend has been driven in large part by a relative shortage of organs for transplantation, improvements in immunosuppressive regimens, a better understanding of the pathophysiology, histologic classification of antibody-mediated rejection (AMR), and major advances in the technology of antibody detection. Living donor transplants allow for the implementation of recipient preparative regimens to decrease antibody levels, preventing hyperacute rejection; many of these regimens include plasma exchange as a means of antibody reduction. Incompatible transplants may be HLA incompatible,3 ABO incompatible,4 or both HLA and ABO incompatible5 or due to non-HLA anti-endothelial antibodies. As these programs have been implemented in transplant centers across the country, a body of literature has been published documenting the breadth of experience with reports from clinical transplant services, immunogenetics laboratories, transfusion medicine laboratories, and apheresis services.6 AMR can arise de novo in the setting of seemingly compatible transplants or after known incompatible kidney transplantation. Subclinical AMR has been described in patients undergoing surveillance biopsies and in these cases both donor-specific antibody and the characteristic histologic features of AMR are found,7 without evidence of graft dysfunction.8 With some similarities to desensitization protocols for the prevention of hyperacute or acute accelerated rejection, protocols for the treatment of AMR are aimed at eliminating alloantibody to stop the rejection process and ultimately, preserve graft function and longevity. When our center first addressed the challenge of antibody reduction in the kidney transplant patient population, we began by treating AMR due to HLA antibody;9 after a successful experience treating AMR with effective reduction in HLA antibody that could now be accurately measured, we then decided to develop a similar protocol for desensitization of patients with donor-specific preformed HLA antibodies and, subsequently, desensitization for ABO incompatibility. Many centers have focused their efforts on incompatible transplant protocols, in part because these patients and their clinical conditions are more amenable to standardization of consistent treatment protocols. In contrast, AMR has a more variable phenotype with patients presenting at different time points in their clinical course with a range of severity. With experience and the passage of time, it has become clear that the treatment of AMR is a significant issue and a far greater challenge than the prevention of AMR with desensitization protocols. In recipients of incompatible transplants, differences between AMR related to HLA versus ABO antibodies have been well documented. The presence of donor-specific HLA antibody correlates well with AMR. In contrast, posttransplant increases in ABO antibodies directed against the kidney graft do not accurately and reliably predict AMR.10 Because of the strong correlation between donor-specific HLA antibody and rejection, patients with subclinical rejection should be treated when they are found to have antibody, even if they have no evidence of renal dysfunction.8 The significance of subclinical AMR is of concern, since many of these patients develop chronic AMR and transplant glomerulopathy despite successful reduction in donor-specific HLA antibody levels. Treatment protocols for AMR vary among transplant centers, but many of these protocols are based on plasma exchange followed by low-dose IVIG or CMV hyperimmune globulin. Additional, novel therapy has been shown to be effective in reducing antibody levels in patients with AMR which is severe or refractory to plasma exchange and IVIG; these therapies include splenectomy,11-13 rituximab (anti-CD20),14, 15 complement inhibitors such as eculizumab (anti-C5),13, 16 and proteasome inhibitors such as bortezomib.15 In this issue of TRANSFUSION, Yamada and colleagues17 report their experience treating AMR in 56 patients who received a course of plasma exchange (mean of 6 procedures, range of 2-11 procedures); each plasma exchange was followed by low-dose IVIG (100 mg/kg) and the last plasma exchange was followed by IVIG 500 mg/kg. There was variable use of other immunosuppressive therapies, such as methylprednisolone, antithymocyte globulin, and rituximab. Patients receiving more novel therapies, such as eculizumab and bortezomib, were not included in the study. The findings of this report confirm three important aspects of AMR, related to time of presentation, antibody characteristics, and graft function. Yamada and colleagues confirm the complexity and variability in timing of patient presentation including length of time since transplant (graft age) and length of time since last documented baseline creatinine (duration of kidney dysfunction).17 Their patients were diagnosed with AMR 2 to 6547 days (mean, 1286.2 days) after transplantation. Although not significant, they found a trend toward greater improvement in creatinine in patients who were treated sooner after transplantation. They also saw a trend toward greater creatinine improvement in patients who had evidence of more recent onset of AMR, as documented by fewer days of graft dysfunction with a shorter interval since having a baseline creatinine. These observations support the view that there are distinct differences in prognosis between early and late (6 months or more after transplantation) AMR, with early AMR being more treatable with plasma exchange, IVIG, rituximab, and bortezomib.18-20 In distinction, late AMR is more difficult to successfully treat, carrying a worse prognosis.21, 22 The study by Yamada and colleagues found that HLA antibody decreased after the first three plasma exchange procedures and continued to decrease, although more gradually, after six plasma exchanges.17 Although HLA antibodies included those directed against Class I, Class II, or both, their patients had more antibodies with Class II specificity. Their results confirm that HLA antibody with Class II specificity are more persistent than antibodies with Class I specificity, especially antibodies against DRw51-53. With a median graft age of 1286.2 days since transplantation, this finding of Class II antibody specificity and persistence is not surprising, confirming both the finding of prevalent Class II specificity in patients with late AMR15 and the earlier finding of persistence of antibody with Class II specificity, particularly antibody directed against DRw51, -52, and -53.23 Many centers include bortezomib therapy in their treatment protocols for AMR. Unfortunately there is evidence showing that bortezomib more effectively reduces Class I HLA antibody with less efficacy in reducing Class II antibody,24 consistent with studies showing better efficacy of bortezomib containing regimens for the treatment of early AMR when more Class I antibody is typically found. It has been very difficult in the AMR treatment literature to tease out the individual contributions of the various components of these complex regimens to the overall success of the protocols. This challenge has been especially true for bortezomib and rituximab since both have been used in association with plasma exchange and IVIG. On the topic of improvement of renal function as evidenced by decreases in serum creatinine, again the study by Yamada and colleagues confirms that late AMR is a significant problem.17 They found that greater improvement in renal function as measured by decreases in serum creatinine was associated with younger grafts. Overall, creatinine improvement was minimal after treatment, although grafts transplanted more recently were more likely to have larger improvements in creatinine level. In light of these results in the context of other confirmatory publications, the importance of timely diagnosis emphasizes the significance of monitoring protocols. There is a need to develop and more widely implement better protocols to monitor these patients to facilitate the early identification of HLA AMR, such that therapy can be implemented as quickly as possible. Since late AMR has many features which are distinctly different from early AMR occurring within the first 6 months of transplantation, we should likely be taking a different, potentially more aggressive, approach to late AMR. There is emerging evidence suggesting that subclinical AMR with or without C4d staining can lead to transplant glomerulopathy and premature allograft loss.8 Plasma exchange is frequently the therapeutic foundation of treatment protocols for AMR. In light of the continuing difficulties in treating AMR, potential approaches to optimizing plasma exchange protocols should be considered. More intensive plasma exchange protocols, especially when therapy is being initiated, could reduce alloantibody more rapidly and decrease damage to the graft. The efficacy of daily procedures, instead of every other day procedures, should be investigated. Only a rigorous study could determine if there is benefit or improved efficacy using a protocol of daily exchanges versus every other day exchanges versus an initial course of daily exchanges followed by every other day. The downside of daily exchanges requiring plasma support can be mitigated by new pathogen-reduced plasma therapies. Potentially a more aggressive exchange protocol is only warranted for patients with late AMR or early severe AMR. It is clear that the treatment of AMR is complex and current treatment protocols may not have the necessary positive impact to successfully prevent graft injury. One must consider whether it would be a more effective approach to focus on prevention of AMR.25 With improvements in immunosuppressive medications, consideration of optimizing induction therapy at the time of transplant may be more effective. Rituximab has been considered for inclusion in induction regimens for HLA-incompatible kidney transplants; in this role, rituximab was associated with decreased HLA antibody rebound, but there was no positive effect on the incidence of AMR or long-term allograft survival.26 Another significant contributory factor to the diagnosis and treatment of AMR is the finding of non-HLA donor-specific antibodies. Of note, antibodies directed against endothelial cells have been associated with AMR and early transplant glomerulopathy.27 The identification of these antibodies may explain the presence of AMR in patients without donor-specific HLA antibodies. Testing for endothelial antibodies is not currently a standard part of routine posttransplant monitoring at all transplant centers and consequently, the testing is less available than testing for HLA antibodies. Although we now know about this type of donor-specific antibody, our awareness of endothelial antibodies highlights the potential that other unknown alloantibody specificities may cause or contribute to AMR. Consequently, it is important that the mechanism of AMR be thoroughly studied and elucidated. One final note to underscore the importance of studying both AMR and desensitization in kidney transplants relates to the field of transplantation as a whole. For other less frequently performed solid organ transplants and for progenitor cell transplants, issues related to incompatibility and the potential of AMR arise. Much of the knowledge gained in studying incompatible kidney transplantation and AMR of kidney grafts can be used as a starting point for consideration of the same issues and complications in other transplant settings. Although it would be unrealistic to think that all aspects of compatibility, incompatibility, and alloimmunization related to the kidney transplant experience would possibly be transferrable to every other organ transplant, our experience in kidney transplantation certainly provides a foundation for comparable challenges involving different types of organ transplants.28, 29 The authors have disclosed no conflicts of interest. Karen E. King, MD1 e-mail: [email protected] Robert A. Montgomery, MD, DPhil2 1Hemapheresis and Transfusion Support Service Department of Pathology 2Comprehensive Transplant Center Department of Surgery Johns Hopkins Medical Institutions Baltimore, MD

Proteasome inhibitor bortezomib has been used in the treatment of refractory cases of acute and chronic antibody-mediated rejection (AMR) in kidney transplant recipients. However, its efficacy and safety as a primary treatment for early AMR has been scarcely investigated. We herein present our preliminary experience with bortezomib- and plasmapheresis-based primary treatment for early AMR. Thirteen patients transplanted between October 2015 and September 2019 were treated (starting at median 19th post-transplant day) with bortezomib/plasmapheresis protocol for early biopsy-proven AMR. Twelve out of thirteen patients received 4 doses and one patient recieved 3 doses of bortezomib (1.3 mg/m2 per dose). In 11/13 patients, 4–7 concomitant plasmapheresis sessions were performed, with or without intravenous immunoglobulin (IVIG). Of note, rituximab was not used in all study patients. The kidney graft and patient survival were 100%. The mean 3-month estimated glomerular filtration rate (eGFR) was 55.3 (95%CI: 44.9–65.8) mL/min/1.73m2, 8/13 patients completed 12-month follow-up with mean eGFR 60.4 (45.4–75.4) mL/min/1.73m2, and 6/13 patients completed a 24-month follow-up period with mean eGFR 73.9 (56.7–91.1) mL/min/1.73m2. Neutropenia < 1 G/L was observed in one patient, third or fourth grade thrombocytopenia in two patients, and eleven patients needed a blood transfusion (median: 2 units/patient). The mid-term results of a primary bortezomib-based treatment for kidney AMR showed its non-inferiority as compared to preceding regimens and acceptable safety. However, our data should be validated in a multicenter randomized trial.

The review outlines the diagnosis, prevention strategies, and possible treatment options for acute and chronic antibody-mediated rejection (AMR). Although rare, severe acute AMR (aAMR) usually occurs in patients with high mean fluorescence intensity despite serial dilutions or high-titer preformed class I donor-specific alloantibodies (DSA). The diagnosis is suspected when allograft dysfunction occurs with DSA, diffuse C4d staining, and a microvascular injury, and may be aided by the aAMR score. However, the incidence of and treatment approach to combined T-cell-mediated rejection (TCMR) with DSA present and some but not all features of AMR is yet to be determined. Chronic liver allograft AMR is characterized by low-grade chronic inflammation and progressive fibrosis with DSA, the chronic AMR (cAMR) score may facilitate diagnosis. The 'two-hit' hypothesis, whereby a coexistent insult upregulates human leukocyte antigen class II target antigens on the microvascular endothelium, may explain why suboptimal donors with lower sensitization levels might suffer from acute AMR and those with chronic complications (e.g., recurrent original disease) might be more susceptible to chronic AMR. Although treatment algorithms are needed, prevention is preferable and at a minimum includes transfusion minimization, and medication adherence. Severe acute AMR is rare but diagnosable, and there is need to determine the incidence of and optimal therapy for less severe combined AMR and TCMR. Chronic AMR is likely more common and of significant relevance to long-term allograft survival improvement. The two-hit hypothesis may help to explain the rarity of both findings and shed insight onto future prevention and treatment strategies.

Antibody-mediated rejection: New approaches in prevention and management.

The aim of our study was to determine outcomes of standard treatment of antibody-mediated rejection (ABMR) of kidney grafts as compared to the addition of bortezomib or rituximab. The cohort of this retrospective study included patients treated for ABMR of kidney grafts at our national center in the period of 2005-2017, divided into two groups: standard (ST) group treated standardly with plasmapheresis or immunoadsorption, intravenous immunoglobulins, and corticosteroids, and BR group treated with the addition of bortezomib and/or rituximab. Patient and graft survival at 2years was analyzed by Kaplan-Meier method, and predictors of graft survival were analyzed by Cox regression. There were 78 patients with ABMR (48 in the ST group, 30 in the BR group), 41 (53%) were men, mean age 49.5±13.8 years. In ST and BR, respectively, mean serum creatinine was 267±164 and 208±112 µmol/L (p=0.088), donor-specific antibodies (DSA)<bold> </bold>were positive in 75% and 97% (p=0.022), and ABMR was acute in 50% and 33% (p=0.149). Patient survival at 2years was 89% in the ST and 100% in the BR group (p=0.125). Cumulative proportion of kidney graft survival at 1 and 2 years was 67% and 53% in the ST group and 73% and 48% in the BR group, respectively, (p=0.641). Chronic ABMR (HR 5.22, p=0.004) was significant, while dialysis dependency at biopsy (HR 3.28, p=0.072), serum creatinine at kidney biopsy (HR 1.003, p=0.082), and presence of DQ-DSA (HR 3.37, p=0.062) were borderline significant predictors of worse graft outcome. Infections were relatively common in both groups, with a trend towards more rehospitalizations due to infections in the first 6 months after treatment in the BR group (p=0.066). In 5 patients (17%), treatment with bortezomib was discontinued prematurely due to cytopenia. Bortezomib or rituximab, added to standard treatment, did not significantly improve kidney graft survival and was also not associated with significant side effects, except cytopenia in some cases. Treatment of acute ABMR resulted in better graft survival than chronic ABMR. .