Imlifidase for the treatment of anti-HLA antibody-mediated processes in kidney transplantation

Escherichia coli in the production of biopharmaceuticals

Escherichia coli has shouldered a massive workload with the discovery of recombinant DNA technology. A new era began in the biopharmaceutical industry with the production of insulin, the first recombinant protein, in E. coli and its use in treating diabetes. After insulin, many biopharmaceuticals produced from E. coli have been approved by the US Food and Drug Administration and the European Medicines Agency to treat various human diseases. Although E. coli has some disadvantages, such as lack of post-translational modifications and toxicity, it is an important host with advantages such as being a well-known bacterium in recombinant protein production, cheap, simple production system, and high yield. This study examined biopharmaceuticals produced and approved in E. coli under the headings of peptides, hormones, enzymes, fusion proteins, antibody fragments, vaccines, and other pharmaceuticals. The topics on which these biopharmaceuticals were approved for treating human diseases, when and by which company they were produced, and their use and development in the field are included.

New Therapies for Highly Sensitized Patients on the Waiting List

Exposure to HLA alloantigens through pregnancy, blood products, and previous transplantations induce powerful immunologic responses that create an immunologic barrier to successful transplantation. This is commonly detected through screening for HLA antibodies using Luminex beads coated with HLA antigens at transplant evaluation. Currently accepted approaches to desensitization include plasmapheresis/low-dose or high-dose intravenous Ig plus anti-CD20. However, these approaches are often unsuccessful because of the inability to remove high titer circulating HLA antibodies and limit rebound responses by long-lived anti-HLA antibody secreting plasma cells (PCs) and memory B cells (B MEM ). This is especially significant for patients with a calculated panel reactive antibody of 99%-100%. Newer desensitization approaches, such as imlifidase (IgG endopeptidase), rapidly inactivate IgG molecules and create an antibody-free zone by cleaving IgG into F(ab'2) and Fc fragments, thus eliminating complement and cell-mediated injury to the graft. This represents an important advancement in desensitization. However, the efficacy of imlifidase is limited by pathogenic antibody rebound, increasing the potential for antibody-mediated rejection. Controlling antibody rebound requires new strategies that address the issues of antibody depletion and inhibition of B MEM and PC responses. This will likely require a combination of agents that effectively and rapidly deplete pathogenic antibodies and prevent immune cell activation pathways responsible for antibody rebound. Here, using anti-IL-6 receptor (tocilizumab) or anti-IL-6 (clazakizumab) could offer long-term control of B MEM and PC donor-specific HLA antibody responses. Agents aimed at eliminating long-lived PCs (anti-CD38 and anti-B-cell maturation antigen×CD3) are likely to benefit highly HLA sensitized patients. Complement inhibitors and novel agents aimed at inhibiting Fc neonatal receptor IgG recycling will be important in desensitization. Administering these agents alone or in combination will advance our ability to effectively desensitize patients and maintain durable suppression post-transplant. After many years of limited options, advanced therapeutics will likely improve efficacy of desensitization and improve access to kidney transplantation for highly HLA sensitized patients.

Roles of M1 and M2 macrophage infiltration in post-renal transplant antibody-mediated rejection

BACKGROUND

We aimed to analyze the roles of M1 and M2 macrophage infiltration in post-renal transplant antibody-mediated rejection (AMR).

METHODS

A total of 102 recipients who underwent renal allotransplant from January 2020 to February 2023 were divided into an immune tolerance group (n = 56) and a rejection group (n = 46). The transplant renal biopsy specimens were harvested by ultrasound-guided puncture. The M1 and M2 macrophages in renal tissues were counted, and the M1/M2 ratio was calculated. The numbers of M1 and M2 macrophages and M1/M2 ratios in patients with different severities of interstitial fibrosis/tubular atrophy (IF/TA) and different degrees of tubulointerstitial inflammatory cell infiltration were compared. The predictive values of M1 and M2 macrophages and M1/M2 ratio for post-renal transplant AMR were clarified.

RESULTS

The rejection group had significantly more M1 and M2 macrophages and higher M1/M2 ratio than those of the immune tolerance group (P < 0.05). In the rejection group, infiltrating macrophages were mainly distributed in the glomerular and interstitial capillaries, with M1 macrophages being the predominant type. With increasing severity of IF/TA, the numbers of M1 and M2 macrophages and M1/M2 ratio rose in patients with post-renal transplant AMR (P < 0.05). The numbers and ratio had significant positive correlations with the levels of blood urea nitrogen and serum creatinine (P < 0.05). The areas under the curves (AUCs) of numbers and M1 and M2 macrophages and M1/M2 ratio for predicting post-renal transplant AMR were 0.856, 0.839 and 0.887, respectively. The combined detection had AUC of 0.911 (95% CI: 0.802-0.986), sensitivity of 90.43% and specificity of 83.42%.

CONCLUSIONS

Significant macrophage infiltration is present in the case of post-renal transplant AMR, and closely related to the severity of IF/TA and the degree of tubulointerstitial inflammatory cell infiltration.

Engineered IgM and IgG cleaving enzymes for mitigating antibody neutralization and complement activation in AAV gene transfer

Systemic dosing of adeno-associated viral (AAV) vectors poses potential risk of adverse side effects including complement activation triggered by anti-capsid immunity. Due to the multifactorial nature of toxicities observed in this setting, a wide spectrum of immune modulatory regimens are being investigated in the clinic. Here, we discover an IgM cleaving enzyme (IceM) that degrades human IgM, a key trigger in the anti-AAV immune cascade. We then engineer a fusion enzyme (IceMG) with dual proteolytic activity against human IgM and IgG. IceMG cleaves B cell surface antigen receptors and inactivates phospholipase gamma signaling in vitro. Importantly, IceMG is more effective at inhibiting complement activation compared with an IgG cleaving enzyme alone. Upon IV dosing, IceMG rapidly and reversibly clears circulating IgM and IgG in macaques. Antisera from these animals treated with IceMG shows decreased ability to neutralize AAV and activate complement. Consistently, pre-conditioning with IceMG restores AAV transduction in mice passively immunized with human antisera. Thus, IgM cleaving enzymes show promise in simultaneously addressing multiple aspects of anti-AAV immunity mediated by B cells, circulating antibodies and complement. These studies have implications for improving safety of AAV gene therapies and possibly broader applications including organ transplantation and autoimmune diseases.

Imlifidase: Is it the Magic Wand in Renal Transplantation?

Potential kidney transplant patients with HLA-specific antibodies have reduced access to transplantation. Their harmful effects are mediated by the Fc portion of IgG, including activation of the complement system and Fc receptor-initiated cytotoxic processes by circulating leucocytes. Avoiding antibody incompatibility is the conventional approach, but for some patients this can mean extended waiting times, or even no chance of a transplant if there are no alternative, compatible donors. For these cases, pretransplant antibody removal may provide access to transplantation. Plasmapheresis is currently used to achieve this, with acceptable outcome results, but the process can take days to reduce the antibody levels to a safe level, so has limited use for deceased donors. There is now an alternative, in the form of an IgG-digesting enzyme, Imlifidase, which can be administered for in vivo IgG inactivation. Imlifidase cleaves human IgG, separating the antigen-binding part, F(ab')2 from Fc. Typically, within six hours of dosing, most, if not all, of the circulating IgG has been inactivated, allowing safe transplantation from a previously incompatible donor. For deceased donor transplantation, where minimizing cold ischaemia is critical, this six-hour delay before implantation should be manageable, with the compatibility testing processes adjusted to accommodate the treatment. This agent has been used successfully in phase 2 clinical trials, with good short to medium term outcomes. While a donation rate that matches demand may be one essential answer to providing universal access to kidney transplantation, this is currently unrealistic. IgG inactivation, using Imlifidase, is, however, a realistic and proven alternative.

Increasing Rate of Fatal Streptococcus pyogenes Bacteriemia-A Challenge for Prompt Diagnosis and Appropriate Therapy in Real Praxis

Streptococcus pyogenes, group A streptococci (GAS) bacteriaemia, is a life-threatening infection with high mortality, requiring fast diagnosis together with the use of appropriate antibiotic therapy as soon as possible. Our study analysed data from 93 patients with GAS bacteraemia at the General University Hospital in Prague between January 2006 and March 2024. In the years 2016-2019 there was an increase in GAS bacteraemia. Mortality in the period 2006-2019 was 21.9%; in the period 2020-2024, the mortality increased to 41.4%, p = 0.08. At the same time, in the post-2020 period, the time from hospital admission to death was reduced from 9.5 days to 3 days. A significant predictor of worse outcome in this period was high levels of procalcitonin, >35.1 µg/L (100% sensitivity and 82.35% specificity), and lactate, >5 mmol/L (90.91% sensitivity and 91.67% specificity). Myoglobin was a significant predictor in both compared periods, the AUC was 0.771, p = 0.044, and the AUC was an even 0.889, p ≤ 0.001, respectively. All isolates of S. pyogenes were susceptible to penicillin, and resistance to clindamycin was 20.3% from 2006-2019 and 10.3% in 2020-2024. Appropriate therapy was initiated in 89.1%. and 96.6%, respectively. We hypothesise that the increase in mortality after 2020 might be due to a decrease in the immune status of the population.

Improving Kidney Disease Care: One Giant Leap for Nephrology

Nephrology is an ever-evolving field of medicine. The importance of such a discipline is related to the high clinical impact of kidney disease. In fact, abnormalities of kidney function and/or structure are common in the general population, reaching an overall prevalence of about 10%. More importantly, the onset of kidney damage is related to a strikingly high risk of cardiovascular events, mortality, and progression to kidney failure which, in turn, compromises quality and duration of life. Attempts to comprehend the pathogenesis and molecular mechanisms involved in kidney disease occurrence have prompted the development and implementation of novel drugs in clinical practice with the aim of treating the 'specific cause' of kidney disease (including chronic kidney disease, glomerular disease, and genetic kidney disorders) and the main immunological complications following kidney transplantation. Herein, we provide an overview of the principal emerging drug classes with proved efficacy in the context of the aforementioned clinical conditions. This can represent a simplified guide for clinical nephrologists to remind them of the vast and heterogeneous armamentarium of drugs that should be used in the present and the future to improve the management of patients suffering from kidney disease.

Adeno-associated virus as a delivery vector for gene therapy of human diseases

Adeno-associated virus (AAV) has emerged as a pivotal delivery tool in clinical gene therapy owing to its minimal pathogenicity and ability to establish long-term gene expression in different tissues. Recombinant AAV (rAAV) has been engineered for enhanced specificity and developed as a tool for treating various diseases. However, as rAAV is being more widely used as a therapy, the increased demand has created challenges for the existing manufacturing methods. Seven rAAV-based gene therapy products have received regulatory approval, but there continue to be concerns about safely using high-dose viral therapies in humans, including immune responses and adverse effects such as genotoxicity, hepatotoxicity, thrombotic microangiopathy, and neurotoxicity. In this review, we explore AAV biology with an emphasis on current vector engineering strategies and manufacturing technologies. We discuss how rAAVs are being employed in ongoing clinical trials for ocular, neurological, metabolic, hematological, neuromuscular, and cardiovascular diseases as well as cancers. We outline immune responses triggered by rAAV, address associated side effects, and discuss strategies to mitigate these reactions. We hope that discussing recent advancements and current challenges in the field will be a helpful guide for researchers and clinicians navigating the ever-evolving landscape of rAAV-based gene therapy.

Advances in desensitization for human leukocyte antigen incompatible kidney transplantation

PURPOSE OF REVIEW

Human leukocyte antigen (HLA) sensitization is a major barrier to kidney transplantation induced by exposure to alloantigens through pregnancy, blood product exposure and previous transplantations. Desensitization strategies are undertaken to improve the chances of finding compatible organ offers. Standard approaches to desensitization include the use of plasmapheresis/low dose intravenous immunoglobulin (IVIG) or high dose IVIG plus anti-CD20. However, current methods to reduce HLA antibodies are not always successful, especially in those with calculated panel reactive antibody 99-100%.

RECENT FINDINGS

Newer desensitization strategies such as imlifidase [immunoglobulin G (IgG) endopeptidase] rapidly inactivates IgG molecules and creates an "antibody-free zone", representing an important advancement in desensitization. However, pathogenic antibodies rebound, increasing allograft injury that is not addressed by imlifidase. Here, use of anti-IL-6R (tocilizumab) or anti-interleukin-6 (clazakizumab) could offer long-term control of B-memory and plasma cell DSA responses to limit graft injury. Agents aimed at long-lived plasma cells (anti-CD38 and anti-BCMAxCD3) could reduce or eliminate HLA-producing plasma cells from marrow niches. Other agents such as complement inhibitors and novel agents inhibiting the Fc neonatal receptor (FcRn) mediated IgG recycling will likely find important roles in desensitization.

SUMMARY

Use of these agents alone or in combination will likely improve the efficacy and durability of desensitization therapies, improving access to kidney transplantation for immunologically disadvantaged patients.

Translating B cell immunology to the treatment of antibody-mediated allograft rejection

Antibody-mediated rejection (AMR), including chronic AMR (cAMR), causes ~50% of kidney allograft losses each year. Despite attempts to develop well-tolerated and effective therapeutics for the management of AMR, to date, none has obtained FDA approval, thereby highlighting an urgent unmet medical need. Discoveries over the past decade from basic, translational and clinical studies of transplant recipients have provided a foundation for developing novel therapeutic approaches to preventing and treating AMR and cAMR. These interventions are aimed at reducing donor-specific antibody levels, decreasing graft injury and fibrosis, and preserving kidney function. Innovative approaches emerging from basic science findings include targeting interactions between alloreactive T cells and B cells, and depleting alloreactive memory B cells, as well as donor-specific antibody-producing plasmablasts and plasma cells. Therapies aimed at reducing the cytotoxic antibody effector functions mediated by natural killer cells and the complement system, and their associated pro-inflammatory cytokines, are also undergoing evaluation. The complexity of the pathogenesis of AMR and cAMR suggest that multiple approaches will probably be required to treat these disease processes effectively. Definitive answers await results from large, double-blind, multicentre, randomized controlled clinical trials.

Imlifidase in kidney transplantation

Kidney transplantation, the gold-standard therapeutic approach for patients with end-stage kidney disease, offers improvement in patient survival and quality of life. However, broad sensitization against human leukocyte antigens often resulting in a positive crossmatch against the patient's living donor or the majority of potential deceased donors in the allocation system represents a major obstacle due to a high risk for antibody-mediated rejection, delayed graft function and allograft loss. Kidney-paired donation and desensitization protocols have been established to overcome this obstacle, with limited success. Imlifidase, a novel immunoglobulin G (IgG)-degrading enzyme derived from Streptococcus pyogenes and recombinantly produced in Escherichia coli, is a promising agent for recipients with a positive crossmatch against their organ donor with high specificity towards IgG, rapid action and high efficacy in early pre-clinical and clinical studies. However, the rebound of IgG after a few days can lead to antibody-mediated rejection, making the administration of potent immunosuppressive regimens in the early post-transplant phase necessary. There is currently no comparative study evaluating the efficiency of imlifidase therapy compared with conventional desensitization protocols along with the lack of randomized control trials, indicating the clear need for future large-scale clinical studies in this field. Besides providing a practical framework for the clinical use of the agent, our aim in this article is to evaluate the underlying mechanism of action, efficiency and safety of imlifidase therapy in immunologically high-risk kidney transplant recipients.

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.

Immunomodulating Enzymes from Streptococcus pyogenes-In Pathogenesis, as Biotechnological Tools, and as Biological Drugs

Streptococcus pyogenes, or Group A Streptococcus, is an exclusively human pathogen that causes a wide variety of diseases ranging from mild throat and skin infections to severe invasive disease. The pathogenesis of S. pyogenes infection has been extensively studied, but the pathophysiology, especially of the more severe infections, is still somewhat elusive. One key feature of S. pyogenes is the expression of secreted, surface-associated, and intracellular enzymes that directly or indirectly affect both the innate and adaptive host immune systems. Undoubtedly, S. pyogenes is one of the major bacterial sources for immunomodulating enzymes. Major targets for these enzymes are immunoglobulins that are destroyed or modified through proteolysis or glycan hydrolysis. Furthermore, several enzymes degrade components of the complement system and a group of DNAses degrade host DNA in neutrophil extracellular traps. Additional types of enzymes interfere with cellular inflammatory and innate immunity responses. In this review, we attempt to give a broad overview of the functions of these enzymes and their roles in pathogenesis. For those enzymes where experimentally determined structures exist, the structural aspects of the enzymatic activity are further discussed. Lastly, we also discuss the emerging use of some of the enzymes as biotechnological tools as well as biological drugs and vaccines.

Kidney transplant outcomes in patients with antibodies to human neutrophil antigen 3a

BACKGROUND

Antibody mediated rejection (ABMR) of kidney transplants has been shown to occur in the absence of a known donor specific antibody to human leucocyte antigen (HLA). Antibodies to the human neutrophil antigen (HNA) system have been detected in kidney transplant recipients and linked to ABMR in the absence of an HLA donor specific antibody (DSA), but there remains limited literature regarding this.

METHODS

Case series analysis was carried out examining three cases of HNA-3a antibody positive flow cytometry cross match (FC-XM) from two transplant centres in Scotland.

RESULTS

All patients included were female and had been sensitised as a result of pregnancy. One live donor recipient with HNA-3a antibodies identified prior to transplant received ATG induction and has had a good outcome. The remaining two patients received deceased donor transplants. HNA-3a antibodies were indicated following a retrospective flow cytometry crossmatch. Both patients received Basiliximab induction and both have experienced ABMR requiring supplementary immunosuppression.

CONCLUSIONS

The predicted rate of HNA-3a antibodies amongst patients awaiting kidney transplant in the UK is <1%. However, with increasing evidence to support a role for HNA-3a antibodies in the development of ABMR there may be value in screening at risk groups to allow for augmented immunosuppression to be considered at the time of kidney transplant.

Drug delivery systems for CRISPR-based genome editors

CRISPR-based drugs can theoretically manipulate any genetic target. In practice, however, these drugs must enter the desired cell without eliciting an unwanted immune response, so a delivery system is often required. Here, we review drug delivery systems for CRISPR-based genome editors, focusing on adeno-associated viruses and lipid nanoparticles. After describing how these systems are engineered and their subsequent characterization in preclinical animal models, we highlight data from recent clinical trials. Preclinical targeting mediated by polymers, proteins, including virus-like particles, and other vehicles that may deliver CRISPR systems in the future is also discussed.

Belatacept and carfilzomib-based treatment for antibody-mediated rejection in a sensitized nonhuman primate kidney transplantation model

Introduction

One-third of HLA-incompatible kidney transplant recipients experience antibody mediated rejection (AMR) with limited treatment options. This study describes a novel treatment strategy for AMR consisting of proteasome inhibition and costimulation blockade with or without complement inhibition in a nonhuman primate model of kidney transplantation.

Methods

All rhesus macaques in the present study were sensitized to maximally MHC-mismatched donors by two sequential skin transplants prior to kidney transplant from the same donor. All primates received induction therapy with rhesus-specific ATG (rhATG) and were maintained on various immunosuppressive regimens. Primates were monitored postoperatively for signs of acute AMR, which was defined as worsening kidney function resistant to high dose steroid rescue therapy, and a rise in serum donor-specific antibody (DSA) levels. Kidney biopsies were performed to confirm AMR using Banff criteria. AMR treatment consisted of carfilzomib and belatacept for a maximum of four weeks with or without complement inhibitor.

Results

Treatment with carfilzomib and belatacept was well tolerated and no treatment-specific side effects were observed. After initiation of treatment, we observed a reduction of class I and class II DSA in all primates. Most importantly, primates had improved kidney function evident by reduced serum creatinine and BUN as well as increased urine output. A four-week treatment was able to extend graft survival by up to two months.

Discussion

In summary, combined carfilzomib and belatacept effectively treated AMR in our highly sensitized nonhuman primate model, resulting in normalization of renal function and prolonged allograft survival. This regimen may translate into clinical practice to improve outcomes of patients experiencing AMR.

Immunoadsorption-Based HLA Desensitization in Patients Awaiting Deceased Donor Kidney Transplantation: An Interventional, Non-Randomised, Single Cohort Study

Whether immunoadsorption (IADS) as part of desensitization protocols could facilitate deceased donor kidney transplantation (KT) in highly sensitized (HS) patients remains to be proven. We retrospectively analyzed our IADS based desensitization protocol for deceased donor KTs between 2013 and 2018. Fifteen HS patients (age 52 years [40-56]) were included. Waiting time before IADS was 6 years [5-10] and the interval between IADS initiation and KT was 5 months [1-12] for the 14 transplanted patients. Nine patients had prior KT. Calculated panel reactive antibody decreased significantly during the protocol (99.3% [92.5-99.9] vs. 79.4% [56.7-81.9]; p = 0.004). Death-censored graft survival was 85.7% at 1 and 2 years post-transplantation. One-year median plasma creatinine level was 135 µmol/L [111-202]. Six developed active antibody mediated rejection (ABMR) at 1 year, with a median delay of 13 days [11-26]. Eight patients developed severe infections, including two fatal outcomes. Finally, compared to 93% of patients who received desensitization receiving a KT, only 43% of a control with similar characteristics underwent transplantation. However, no difference was found in overall probability of being alive with a functioning graft at the end of follow-up. The results indicate that our IADS-based desensitization strategy was not effective due to a high rate of ABMR and severe infectious complications which pose a challenge to its universalization.

Removal of natural anti-αGal antibodies elicits protective immunity against Gram-negative bacterial infections

Antibody-dependent enhancement (ADE) of bacterial infections occurs when blocking or inhibitory antibodies facilitate the infectivity of pathogens. In humans, antibodies involved in ADE of bacterial infections may include those naturally produced against Galα1-3Galβ1-4GlcNAcβ (αGal). Here, we investigate whether eliminating circulating anti-αGal antibodies using a soluble αGal glycopolymer confers protection against Gram-negative bacterial infections. We demonstrated that the in vivo intra-corporeal removal of anti-αGal antibodies in α1,3-galactosyltransferase knockout (GalT-KO) mice was associated with protection against mortality from Gram-negative sepsis after cecal ligation and puncture (CLP). The improved survival of GalT-KO mice was associated with an increased killing capacity of serum against Escherichia coli isolated after CLP and reduced binding of IgG1 and IgG3 to the bacteria. Additionally, inhibition of anti-αGal antibodies from human serum in vitro increases the bactericidal killing of E. coli O86:B7 and multidrug-resistant Klebsiella pneumoniae and Pseudomonas aeruginosa. In the case of E. coli O86:B7, there was also an improvement in bacteria opsonophagocytosis by macrophages. Both lytic mechanisms were related to a decreased binding of IgG2 to the bacteria. Our results show that protective immunity against Gram-negative bacterial pathogens can be elicited, and infectious diseases caused by these bacteria can be prevented by removing natural anti-αGal antibodies.

Emerging Therapies for Antibody-Mediated Rejection in Kidney Transplantation

Despite the advances in immunosuppressive medications, antibody-mediated rejection (AMR) continues to be a major cause of kidney allograft failure and remains a barrier to improving long-term allograft survival. Recently, there have been significant advances in the understanding of the pathophysiological process of AMR, along with the development of new therapeutic options. Additionally, surveillance protocols with donor-derived cell-free DNA and gene profile testing have been established, leading to the early detection of AMR. A multitude of clinical trials are ongoing, opening numerous opportunities for improving outcome in kidney transplant recipients. In this brief review, we discuss the emerging therapies for managing both active and chronic active AMR and highlight the ongoing clinical trials.

Antibody-mediated rejection in xenotransplantation: Can it be prevented or reversed?

Antibody-mediated rejection (AMR) is the commonest cause of failure of a pig graft after transplantation into an immunosuppressed nonhuman primate (NHP). The incidence of AMR compared to acute cellular rejection is much higher in xenotransplantation (46% vs. 7%) than in allotransplantation (3% vs. 63%) in NHPs. Although AMR in an allograft can often be reversed, to our knowledge there is no report of its successful reversal in a pig xenograft. As there is less experience in preventing or reversing AMR in models of xenotransplantation, the results of studies in patients with allografts provide more information. These include (i) depletion or neutralization of serum anti-donor antibodies, (ii) inhibition of complement activation, (iii) therapies targeting B or plasma cells, and (iv) anti-inflammatory therapy. Depletion or neutralization of anti-pig antibody, for example, by plasmapheresis, is effective in depleting antibodies, but they recover within days. IgG-degrading enzymes do not deplete IgM. Despite the expression of human complement-regulatory proteins on the pig graft, inhibition of systemic complement activation may be necessary, particularly if AMR is to be reversed. Potential therapies include (i) inhibition of complement activation (e.g., by IVIg, C1 INH, or an anti-C5 antibody), but some complement inhibitors are not effective in NHPs, for example, eculizumab. Possible B cell-targeted therapies include (i) B cell depletion, (ii) plasma cell depletion, (iii) modulation of B cell activation, and (iv) enhancing the generation of regulatory B and/or T cells. Among anti-inflammatory agents, anti-IL6R mAb and TNF blockers are increasingly being tested in xenotransplantation models, but with no definitive evidence that they reverse AMR. Increasing attention should be directed toward testing combinations of the above therapies. We suggest that treatment with a systemic complement inhibitor is likely to be most effective, possibly combined with anti-inflammatory agents (if these are not already being administered). Ultimately, it may require further genetic engineering of the organ-source pig to resolve the problem entirely, for example, knockout or knockdown of SLA, and/or expression of PD-L1, HLA E, and/or HLA-G.

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.

First use of imlifidase desensitization in a highly sensitized lung transplant candidate: a case report

Lung transplant candidates who are highly sensitized against human leucocyte antigen present an ongoing challenge with regards to finding immunologically acceptable donors. Desensitization strategies aimed at reducing preformed donor-specific antibodies have a number of limitations. Imlifidase, an IgG-degrading enzyme derived from Streptococcus pyogenes, is a novel agent that has been used to convert positive crossmatches to negative in kidney transplant candidates, allowing transplantation to occur. We present the first case of imlifidase use for antibody depletion in a highly sensitized lung transplant candidate who went on to undergo a successful bilateral lung transplant.

Updated management for antibody-mediated rejection: opportunity to prolong kidney allograft survival

PURPOSE OF REVIEW

Antibody-mediated rejection (ABMR) is an important barrier to achieve long-term kidney allograft survival. Human leukocyte antibody (HLA)-incompatibility and ABO-incompatibility are the two main mechanisms of ABMR. Nevertheless, the advances in managing ABMR have changed the paradigm for kidney transplantation. This review aimed to emphasize the HLA-incompatibility and ABO-incompatibility kidney transplant and update the management of ABMR.

RECENT FINDINGS

HLA-incompatibility kidney transplantation is a strong risk factor for ABMR. Donor-specific antibody (DSA) is a surrogate biomarker that prevents long-term allograft survival. The standard treatment for ABMR has unfavorable results. New drugs that target the B cell are a promising approach to treat ABMR. In the past, ABO-incompatibility kidney donor was an absolute contraindication but now, it is widely accepted as an alternative organ resource. The advancement of ABO antibody removal and B-cell depletion therapy has been successfully developed. ABO isoagglutination remains the main biomarker for monitoring ABMR during the transplantation process. C4d staining without inflammation of the kidney allograft is the marker for the accommodation process.

SUMMARY

With the shortage of organ donors, transplant experts have expanded the organ resources and learned how to overcome the immunological barriers by using novel biomarkers and developing new treatments that support long-term graft survival.

Extensive substrate recognition by the streptococcal antibody-degrading enzymes IdeS and EndoS

Enzymatic cleavage of IgG antibodies is a common strategy used by pathogenic bacteria to ablate immune effector function. The Streptococcus pyogenes bacterium secretes the protease IdeS and the glycosidase EndoS, which specifically catalyse cleavage and deglycosylation of human IgG, respectively. IdeS has received clinical approval for kidney transplantation in hypersensitised individuals, while EndoS has found application in engineering antibody glycosylation. We present crystal structures of both enzymes in complex with their IgG1 Fc substrate, which was achieved using Fc engineering to disfavour preferential Fc crystallisation. The IdeS protease displays extensive Fc recognition and encases the antibody hinge. Conversely, the glycan hydrolase domain in EndoS traps the Fc glycan in a "flipped-out" conformation, while additional recognition of the Fc peptide is driven by the so-called carbohydrate binding module. In this work, we reveal the molecular basis of antibody recognition by bacterial enzymes, providing a template for the development of next-generation enzymes.

New approach to desensitization in solid organ transplantation-imlifidase

The IgG-degrading enzyme derived from Streptococcus pyogenes is a recombinant cysteine protease of S. pyogenes produced in Escherichia coli that cleaves all four human subclasses of IgG with strict specificity. The proteolytic activity on IgG molecules prevents the occurrence of IgG-mediated antibody-dependent, cellular cytotoxicity and complement-mediated cytotoxicity, two processes that are critical for antibody rejection. The results from phase II studies demonstrated that desensitization with imlifidase represents a therapeutic strategy that can operationalize desensitization, allowing life-saving transplants from deceased donors (DD) and living donors (LD) to proceed in highly sensitized kidney transplant candidates with low risk of hyperacute rejection. Its action onset is rapid, allowing kidney transplantation from a deceased donor. Disadvantages of imlifidase include a quick reappearance of DSAs, which poses a risk of antibody-mediated rejection, the quick development of anti-Ides antibodies, which rules out repeated use of imlifidase and its IgG-degrading potential, limiting the use of therapeutic antibodies. Imlifdase received conditional approval on 26 August 2020 in the EU for desensitization treatment of highly sensitized adult kidney transplant patients with positive crossmatch against an available deceased donor.

Pharmacotherapeutic options for the prevention of kidney transplant rejection: the evidence to date

INTRODUCTION

Although early rejection episodes are successfully controlled, the problem of unrecognized production of de novo anti HLA antibodies and associated chronic rejection still persists.

AREAS COVERED

In addition to the standard induction and maintenance therapy, we present a couple of new drugs as induction (Alemtuzumab), CNI free protocol (Belatacept, Sirolimus, Everolimus), maintenance treatment in transplant patients with various type of malignancies (T cell targeted immunomodulators blocking the immune checkpoints CTLA-4, PD1/PDL1) and TMA (aHUS) -eculizimab, and IL6 receptor antagonists in antibody mediated rejection (AMR).

EXPERT OPINION

There are couple of issues still preventing improvement in kidney transplant long-term outcomes with current and anticipated future immunosuppression: patient more susceptible to infection and CNI nephrotoxicity in kidneys obtained from elderly donors, highly sensitized patients with limited chances to get appropriate kidney and a higher risk for late AMR. A lower rate of CMV/BK virus infections has been observed in everolimus treated patients. Belatacept use has been justified only in EBV seropositive kidney transplants due to the increased risk of PTLD. Eculizumab upon recurrence of aHUS is a sole cost-effective option. A new IL-6 blocking drug (clazakizumab/tocilizumab) is promising option for prevention/treatment of AMR. Clinical experience in tailoring immunosuppression for as long as possible graft and patient survival is inevitable.

Emerging drugs for antibody-mediated rejection after kidney transplantation: a focus on phase II & III trials

INTRODUCTION

Antibody-mediated rejection (ABMR) is a leading cause of kidney allograft failure. Its therapy continues to be challenge, and no treatment has been approved for the market thus far.

AREAS COVERED

In this article, we discuss the pathophysiology and phenotypic presentation of ABMR, the current level of evidence to support the use of available therapeutic strategies, and the emergence of tailored drugs now being evaluated in systematic clinical trials. We searched PubMed, Clinicaltrials.gov and Citeline's Pharmaprojects for pertinent information on emerging anti-rejection strategies, laying a focus on phase II and III trials.

EXPERT OPINION

Currently, we rely on the use of apheresis for alloantibody depletion and intravenous immunoglobulin (referred to as standard of care), preferentially in early active ABMR. Recent systematic trials have questioned the benefits of using the CD20 antibody rituximab or the proteasome inhibitor bortezomib. However, there are now several promising treatment approaches in the pipeline, which are being trialed in phase II and III studies. These include interleukin-6 antagonism, CD38-targeting antibodies, and selective inhibitors of complement. On the basis of the information that has emerged so far, it seems that innovative treatment strategies for clinical use in ABMR may be available within the next 5-10 years.