Chronic antibody-mediated rejection is the predo-minant cause for late renal allograft loss for which there is, as yet, no treatment approved by the US Food and Drug Administration, although there are clinical trials in progress to evaluate novel treatment strategies. The current standard of care treatment is based on expert consensus, rather than scientific evidence, and includes glucocorticoids, plasma exchange, and intravenous immunoglobulin, with or without rituximab or bortezomib. The low success rate with presently established management protocols represents a conspicuous exigency in the field of kidney transplantation. This review focuses on the biologic basis for interleukin 6 inhibitors, specifically tocilizumab and clazakizumab, and the safety and efficacy profiles of these agents for treatment of chronic antibody-mediated rejection in kidney transplant recipients.
Key words : Tocilizumab, Clazakizumab, IL-6
Chronic (active and inactive) antibody-mediated rejection (CAMR) is the predominant cause for late renal allograft loss. As yet, no treatment for CAMR has received approval from the US Food and Drug Administration (FDA); however, clinical trials are in progress to evaluate novel treatment strategies. Most cases of CAMR are attributed to allograft damage caused by donor-specific antibodies (DSA) that were either present before transplant or developed after transplant. Donor-specific antibodies form after transplant as a result of immunosuppression reduction, either physician directed or as a result of patient nonadherence.1
The Banff Classification forms the basis of diagnosing and reporting antibody-mediated rejection (AMR) and has undergone several updates based on improvements in our understanding of this disease, since it was first introduced in 1997. The most recent changes to the Banff Classification system were applied in 2019.2,3 These ongoing revisions reflect the progressive evolution of our understanding of this complex clinical condition, and many questions remain unanswered. The low rate of success of the presently accepted management protocols underscores the fact that our understanding of AMR is still evolving.
Antibody-mediated rejection, once considered an isolated incident occurring after transplant is now recognized to be a progressive condition that waxes and wanes over time and may ultimately lead to chronic allograft damage and allograft loss.4 The current standard of care treatment for AMR is based on expert consensus,5 rather than scientific evidence, and includes glucocorticoids, plasma exchange, and intravenous immunoglobulin (IVIG). Several therapeutic agents have been tested in randomized clinical trials, including anti-CD20 monoclonal antibody (mAb), rituximab, and the proteasome inhibitor, bortezomib, but these studies have failed to show a significant clinical benefit.6,7 A few randomized trials have tested the efficacy of the anti-C5 mAb, eculizumab, which inhibits terminal complement activation, but no clinical benefit has been demonstrated.8 A small pilot study has demonstrated the benefit of classical complement pathway blockade in late AMR with C1-esterase inhibitor.9
To address the urgent need for an effective treatment for AMR that could prolong renal allograft survival, the FDA has conducted open workshops with participation of industry, academia, and patient representatives to meet the challenges of clinical design for AMR-related clinical trials.10 This review focuses on the biologic basis for anti-interleukin 6 (anti-IL-6) therapeutic agents, specifically tocilizumab and clazakizumab, and the safety and efficacy of these agents for treatment of CAMR in kidney transplant recipients.
Biologic Basis for Interleukin 6 Blockade in Chronic Antibody-Mediated Rejection in Kidney Transplant
Interleukin 6 is a pleiotropic inflammatory cytokine that can affect virtually all physiological systems, including bone marrow, hepatocytes, mesangial cells, and epithelial cells in the kidney, bone, and neurons. Abnormal production of IL-6 can result in chronic inflammation, immune stimulation, and neovascularization11 and is associated with various autoimmune diseases, such as rheumatoid arthritis (RA), Castleman disease, and cancers.12,13
Originally described as the B-cell stimulating factor 2 or hepatocyte growth factor,14 the IL-6 receptor (IL-6R) system consists of an 80-kDa IL-6R and a 130-kDa signal transducer (gp130). The 80-kDa receptor exists in a transmembrane form (mIL-6R) and a soluble form (sIL-6R). The mIL-6R has a short intracytoplasmic region and, upon stimulation by binding of the IL-6 molecule, triggers an association with gp130. The sIL-6R can form a stimulatory complex with IL-6 and thereby associate with gp130 to trigger cellular events in a process known as trans-signaling. The gp130 signal transducer has a transmembrane domain that facilitates signal transduction across the membrane.15 The IL-6 molecule binds to mIL-6R (also known as CD126) or sIL-6R, and the IL-6/mIL-6R or IL-6/sIL-6R complex then binds to the gp130 IL-6 transducer (CD130), which results in gp130 dimerization, phosphorylation, and subsequent activation of receptor-associated kinases (Janus kinases Jak1 and Jak2 and tyrosine kinase 2),16 followed by induction of tyrosine phosphorylation and recruitment of the signal transducer and activator of transcription 3 (STAT3), which dimerizes and translocates to the nucleus and leads to gene expression.15 The IL-6 signaling systems are regulated by negative feedback of the suppressors of cytokine signaling (SOCS) and the protein inhibitors of activated STAT. The IL-6/IL-6R interaction activates STAT3, which targets SOCS1. The SOCS1 molecule then binds to the Jak tyrosine kinase and acts as a negative regulator of gp130 signal transduction.15
Interleukin 6 stimulates B-cell differentiation and secretion of antibodies and prevents apoptosis of activated B cells,17-19 activates and induces proliferation of T cells, and, in the presence of interleukin 2, induces differentiation of mature and immature T cells into cytotoxic T cells.20,21 Interleukin 6 promotes the development and maturation of B cells to plasma cells, which in turn produce DSA that target the allograft. These DSA damage the allograft via complement-mediated and non-complement-mediated pathways and induce graft endothelial cells to produce inflammatory (eg, P selectin, vascular cell adhesion molecule 1) and prothrombotic (eg, von Willebrand factor) molecules. Interleukin 6 also shapes the T-cell immune response to promote long-lived proinflamma-tory helper T cells (eg, follicular helper T cells as well as Th17, Th1, and Th2 cells) and inhibit immune regulatory T cells that promote allograft tolerance.11 Classical IL-6/IL-6R signaling in hepatocytes induces the expression of acute-phase proteins that include C-reactive protein (CRP), serum amyloid A, fibrinogen, and hepcidin (contributes to anemia of chronic disease). Interleukin 6 inhibits other hepatic proteins including albumin, transferrin, and cytochrome P450 and also stimulates dermal and synovial fibroblasts, osteoclast differentiation, renal mesangial cell proliferation, megakaryocytes, and angiogenesis.11
Early clinical trials with anti-IL-6 murine mAb have demonstrated the safety of anti-IL-6 therapy, identified CRP as a surrogate marker, and shown that dosing must account for the high degree of variation in daily production of IL-6 with different disease states to achieve therapeutic inhibition.22 With murine anti-IL-6 mAb therapy, it was observed that the half-life of IL-6 increased from a few minutes in untreated patients to several days in treated patients.23 It was also observed that, at the end of anti-IL-6 mAb treatment, the ratio of the concentrations of free anti-IL-6 mAb to IL-6/anti-IL-6 mAb complexes decreased, allowing the sIL-6R or mIL-6R to disrupt the IL-6/anti-IL-6 mAb complexes. The resultant large amount of IL-6 released in circulation can trigger cell activation, resulting in quick recovery of CRP production, fever, and cancer cell progression at the end of anti-IL-6 treatment in some patients.24
Anti-IL-6R mAb therapy blocks the action of IL-6 without increasing the half-life of IL-6, as seen with anti-IL-6 cytokine mAb strategies.15,23 Anti-IL-6R mAb therapy also blocks the action of the sIL-6R, which mediates several actions of IL-6, including osteoclast formation, synovial fibroblast proliferation, and cartilage degradation.15 Hence, anti-IL-6 cytokine mAb therapy only partially blocks IL-6, allowing innate immune response to develop.25 In the context of antibody-mediated rejection, IL-6 blockade by anti-IL-6 mAb or anti-IL-6R mAb can cause significant reductions of alloantibodies, antibody production by splenic and bone marrow plasma cells, direct inhibition of plasma cell anti-HLA antibody production, and induction of T regulatory cells with inhibition of T follicular helper cells.11,26,27
Tocilizumab is a humanized monoclonal antibody directed against IL-6R and is approved for the treatment of RA and idiopathic juvenile arthritis.28,29 A number of clinical trials30-32 have shown efficacy and a favorable safety profile of tocilizumab to treat active RA (Table 1).
Smolen and colleagues have reported comprehensive safety data of IL-6 blockade with tocilizumab in patients with RA as a part of the OPTION study in which 419 patients received tocilizumab28 and experienced transient, mild, self-limited cutaneous adverse events such as localized skin rash or dermatitis, with or without pruritus, along with a transient rise in hepatic transaminases without any signs of hepatitis, as well as an increase in plasma concentration of high-density and low-density lipoprotein and total cholesterol was noted requiring treatment but was not associated with an increase in adverse cardiovascular events. Hypersensitivity reaction, transient neutropenia, and thrombocytopenia were also observed. Infectious events included pneumonia, Pneumocystis pneumonia, interstitial lung disease, cellulitis, and upper respiratory tract infection. A cerebrovascular accident occurred in 1 patient with cellulitis, and idiopathic pulmonary fibrosis was also reported. More serious adverse events included gastrointestinal perforation and peridiverticular abscess.28 In patients with RA who were treated with tocilizumab, there was a higher incidence of gastrointestinal perforation,28,33 which was likely related to chronic glucocorticoid and nonsteroidal anti-inflammatory drug use in this population.34
Sethi and colleagues recently presented robust data on infectious risks of tocilizumab in kidney transplant patients.35 A total of 57 infectious episodes were observed in 83 kidney transplant recipients treated with tocilizumab for desensitization or treatment of AMR, of which 31 episodes (54%) required hospitalization. There were no infection-related deaths, and there was a lower rate of infections associated with tocilizumab versus a contempo raneous group of 65 kidney transplant recipients who received IVIG and rituximab for similar indications. Urinary tract infections and pneumonia (2 episodes of Pneumocystis pneumonia) were the most common infections, whereas gastrointestinal complications (Clostridium difficile colitis, bacterial gastroenteritis), blood infections (primary or secondary bloodstream infections), skin/soft tissue infections, viral infections (mild cases of varicella-zoster, cytomegalovirus, and BK virus), and fungal infections were less common. In 1 patient with infectious colitis, a colonic stricture resulted in a perforation during a gastrointestinal procedure.35
In a previous publication from the same group of researchers, Choi and colleagues reported that, of the subset of 36 patients who received tocilizumab for CAMR, there were 7 patients with bacterial infections that resolved with treatment without the need to discontinue tocilizumab. Hypogammaglobulinemia was also noted and managed with IVIG. Three patients developed cardiovascular complications. One of the 3 patients experienced a stroke while on tocilizumab, but therapy was not discontinued, and this patient recovered with no residual deficits. The second of the 3 patients developed non-ST elevation myocardial infarction (NSTEMI), possibly related to hyperkalemia, after the ninth dose of tocilizumab. The third patient experienced NSTEMI at 2 years after therapy completion, but this was not related to tocilizumab. One case of trichodysplasia spinulosa (a benign skin condition related to polyomavirus) was also reported, but this patient recovered 1 month after the completion of tocilizumab therapy.27
Lavacca and colleagues used tocilizumab as a first-line therapy for 15 patients with CAMR and reported 4 patients with bacterial urinary tract infection and 1 patient with bacterial lower respiratory tract infection. These complications resolved with medical therapy without tocilizumab discontinuation. One patient developed idiopathic encephalitis and required temporary discontinuation of tocilizumab until recovery. Two patients developed interstitial lung disease, one related to adenovirus requiring temporary discontinuation of tocilizumab, and the other related to tocilizumab requiring therapy cessation. They also found a higher incidence of hypogammaglobulinemia requiring IVIG. A rise in liver function tests (LFTs), specifically hepatic transaminases, and pancreatic enzymes was also noted.36
Other adverse events associated with tocilizumab treatment of AMR in kidney transplant patients have been reported, including 1 patient with cytomegalovirus esophagitis for whom tocilizumab was discontinued but was successfully treated with valganciclovir.37 Fungal infections, including 1 patient with pulmonary aspergillosis and 1 patient with Microsporidia infection, have been reported by Massat and colleagues in 9 kidney transplant patients with AMR who were treated with tocilizumab.38 Discontinuation of tocilizumab in response to hypersensitivity has also been reported.37 Sharma and colleagues observed a transient rise in hepatic transaminases in a patient after the fifth dose of tocilizumab, but liver function test results recovered to normal levels after cessation of tocilizumab.39
The largest reported experience with tocilizumab therapy in kidney transplant recipients included 36 patients with CAMR refractory to standard of care therapy (including steroids and IVIG plus rituximab) from a single center who received tocilizumab therapy for 6 to 25 months. There was a significant reduction in immunodominant DSA (iDSA), along with a reduction in microcirculation inflammation (glomerulitis plus peritubular capillaritis scores). Graft loss was noted in 4 patients, for whom tocilizumab was discontinued for medical reasons in 1 patient and for insurance reasons in the other 3 patients. The results of this study showed an overall graft survival probability of 80% at 6 years after CAMR diagnosis; in addition, in patients with transplant glomerulopathy, a 77% graft survival probability was reported at 6 years after CAMR diagnosis.27 These results from Choi and colleagues are in stark contrast to results published by Redfield and colleagues (in 2016), who had reported a 55% rate of 2-year graft survival for CAMR patients treated with standard of care treatment, and a 20% rate of 2-year graft survival for CAMR patients without any treatment.40
Lavacca and colleagues used tocilizumab as a first-line therapy for 15 patients with CAMR with severe transplant glomerulopathy and severe microvascular inflammation. Allograft loss was reported for a single patient, at 25.3 months after discontinuation of tocilizumab. There was a significant decrease in iDSA, along with a significant reduction in microvascular inflammation, and an absence of progression in chronicity scores or C4d deposition.36 Pottebaum and colleagues treated 7 patients with tocilizumab. Of these 7 patients, only 1 had CAMR, and this patient completed 6 months of tocilizumab therapy and demonstrated stable serum creatinine, marked reduction of iDSA, reduction of microvascular inflammation, and stabilization of transplant glomerulopathy and proteinuria.37 In the study by Sharma and colleagues, their patient with refractory CAMR (without DSA) was removed from tocilizumab therapy after the fifth dose due to rise in serum transaminases, but the creatinine returned to baseline and remained stable at 1 year follow-up.39
In contrast to the previously mentioned studies, Massat and colleagues found no difference in graft survival or renal function in patients with AMR refractory to standard of care who were treated with tocilizumab versus patients in historical control groups who were treated with standard of care. This study included 9 patients, 6 of whom had CAMR and 4 had mixed AMR/T-cell rejection. Despite their stated conclusion, they did find a dramatic reduction in tubulitis and microvascular inflammation scores along with a reduction in iDSA as reported in other studies.38
Clazakizumab is a genetically engineered huma-nized immunoglobulin G1 (IgG1) monoclonal antibody that binds to human IL-6.41 Multiple assays for signaling and cellular functions in response to IL-6 alone (to measure classical signaling) and a combination of IL-6 and sIL-6R (to measure trans-signaling) have shown clazakizumab to be a potent and full antagonist of IL-6-induced signaling as measured by phosphorylation of STAT3, as well as cellular functions such as cell proliferation, differentiation, activation, B-cell production of immunoglobulins, and hepatocyte production of acute phase proteins (CRP and fibrinogen). In addition, clazakizumab is a competitive antagonist of IL-6-induced cell proliferation. A large ongoing phase 3 multicenter international trial is underway to study the effect of clazakizumab treatment in kidney transplant patients with CAMR (IMAGINE: Clazakizumab for the Treatment of Chronic Active Antibody Mediated Rejection in Kidney Transplant Recipients; ClinicalTrials.gov Identifier: NCT03744910).
Safety data on IL-6 cytokine blockade have been reported from a phase 3 trial of sirukumab in patients with RA in which 1114 patients received the drug (SIRROUND-D: A Study of CNTO 136 [Sirukumab], Administered Subcutaneously, in Patients With Active Rheumatoid Arthritis Despite Disease-Modifying Antirheumatic Drug [DMARD] Therapy; ClinicalTrials.gov identifier NCT01604343). The most common adverse events were elevated liver enzymes, upper respiratory tract infection, bronchitis, nasopharyngitis, injection site erythema and pruritus, leukopenia, neutropenia, headache, and hypertension. The incidence of serious adverse events was 20.8%, which included 1 patient with a gastric perforation and 1 patient with perforated appendicitis.42
In the transplant literature, there is a single published report of a phase 2 study of anti-IL-6 blockade with clazakizumab in 20 kidney transplant patients with CAMR (Table 2). There was a 25% incidence of serious infectious events, including pneumonia, pyelonephritis, ovarian abscess, and coxsackievirus-associated meningitis. One patient developed recurrent pleural effusion requiring pleurodesis and, subsequently, permanent thoracic cavity drainage; 2 patients with diverticulosis developed diverticulitis, 1 of whom developed a colon perforation that required surgery, and the other patient with diverticulitis required percutaneous abscess drainage and antibiotics. Clazakizumab was also associated with mild injection site reactions, increases in lipid levels, and mild abnormalities of liver enzymes or blood cell count.43
There was a decrease in mean DSA within 12 weeks of clazakizumab treatment, with a further decrease in DSA after prolonged treatment. A significantly slower decline in the estimated glomerular filtration rate was observed in the patients who received clazakizumab. There was also a significant reduction in molecular AMR and all rejection scores after prolonged treatment at 51 weeks; 38.9% patients had a negative AMR score, 22.2% had resolution of AMR activity, and 27.8% demonstrated C4d disappearance. However, there was no significant change in microcirculation inflammation, and transplant glomerulopathy remained essentially unchanged. A significant increase was noted in interstitial fibrosis and tubular atrophy.43
The manufacturer’s prescribing information for tocilizumab contains a recommendation that, upon therapy initiation or discontinuation, therapeutic monitoring of effect (eg, warfarin) or drug concentration (eg, calcineurin inhibitors) should be performed and the individual dose of the cytochrome P450 enzyme substrate drugs should be adjusted as needed (Actemra [tocilizumab] injection, for intravenous or subcutaneous use; Prescribing information, Genentech, August 2017). Furthermore, caution is advised when coadministering with CYP 3A4 substrate drugs (eg, oral contraceptives, ?-hydroxy ?-methylglutaryl-coenzyme A reductase inhibitors) where a decrease in effectiveness is undesirable .
Sufficient safety data have been compiled for IL-6 inhibitors from reports on treatment in patients with RA; however, kidney transplant data is small, and caution is warranted when evaluating these scant data. In a phase 2 study, clazakizumab was associated with serious adverse events such as gastrointestinal perforation, diverticulitis, and peridiverticular abscess; therefore, in patients with diverticulosis, clazakizumab should be avoided entirely or used with caution. Given the high incidence of infectious adverse events, it is prudent to consider a reduction in the dose of mycophenolate mofetil by 50% during tocilizumab or clazakizumab therapy and to initiate prophylaxis for Pneumocystis pneumonia and cytomegalovirus as well; however, a paucity of reports precludes any conclusive recommendations.
Tocilizumab therapy has been shown to consistently and significantly reduce iDSA, C4d, and microvascular inflammation scores and stabilize transplant glomerulopathy, whereas clazakizumab has been shown to significantly slow the rate of decline in estimated glomerular filtration rate without any significant change in microvascular inflammation and transplant glomerulopathy, although there was an increase in interstitial fibrosis and tubular atrophy with clazakizumab. These effects could be related to the differences in the mechanisms of action of the 2 drugs, specifically, partial IL-6 blockade by anti-IL-6 cytokine mAb, clazakizumab.
Larger studies are needed to make sense of these observed effects, because there is only limited experience with these 2 drugs in the transplant setting. In conclusion, IL-6 blockade is a powerful tool to prolong renal allograft survival; however, given the high rate of allograft failure with standard of care treatment in CAMR, as well as the absence of an FDA-approved treatment, if IL-6 blockade is selected as rescue therapy for patients with CAMR when standard of care treatment has failed, then it must be used cautiously.
Volume : 20
Issue : 8
Pages : 709 - 716
DOI : 10.6002/ect.2021.0254
From the Michael and Marian Ilitch Department of Surgery, Wayne Health, Detroit, Michigan, USA
Acknowledgements: The author has not received any funding or grants in support of the presented research or for the preparation of this work and has no declarations of potential conflicts of interest.
Corresponding author: Rajeev Sharma, DMC-Harper Univ. Hospital, Michael and Marian Ilitch Dept. of Surgery, Wayne Health, 4160 John R Street, Professional Bldg., Suite 400, Detroit, MI 48201, USA
Phone: +1 313 745 8797
Table 1. Efficacy and Safety Data for Tocilizumab
Table 2. Efficacy and Safety Data for Clazakizumab