Marginal Impact of Tocilizumab Monotherapy on Anti-HLA Alloantibodies in Highly Sensitized Kidney Transplant Candidates

Targeting inerleukin-6 for renoprotection

Sterile inflammation has been increasingly recognized as a hallmark of non-infectious kidney diseases. Induction of pro-inflammatory cytokines in injured kidney tissue promotes infiltration of immune cells serving to clear cell debris and facilitate tissue repair. However, excessive or prolonged inflammatory response has been associated with immune-mediated tissue damage, nephron loss, and development of renal fibrosis. Interleukin 6 (IL-6) is a cytokine with pleiotropic effects including a major role in inflammation. IL-6 signals either via membrane-bound (classic signaling) or soluble receptor forms (trans-signaling) thus affecting distinct cell types and eliciting various metabolic, cytoprotective, or pro-inflammatory reactions. Antibodies neutralizing IL-6 or its receptor have been developed for therapy of autoimmune and chronic non-renal inflammatory diseases. Small molecule inhibitors of Janus kinases acting downstream of the IL-6 receptor, as well as recombinant soluble glycoprotein 130 variants suppressing the IL-6 trans-signaling add to the available therapeutic options. Animal data and accumulating clinical experience strongly suggest that suppression of IL-6 signaling pathways bears therapeutic potential in acute and chronic kidney diseases. The present work analyses the renoprotective potential of clinically relevant IL-6 signaling inhibitors in acute kidney injury, chronic kidney disease, and kidney transplantation with focus on current achievements and future prospects.

Interchain disulfide engineering enables the efficient production of functional HLA-DQ-Fc fusion proteins

HLA-DQ molecules drive unwanted alloimmune responses after solid-organ transplants and several autoimmune diseases, including type 1 diabetes and celiac disease. Biologics with HLA molecules as part of the design are emerging therapeutic options for these allo- and autoimmune conditions. However, the soluble α and β chains of class II HLA molecules do not dimerize efficiently without their transmembrane domains, which hinders their production. In this study, we examined the feasibility of interchain disulfide engineering by introducing paired cysteines to juxtaposed positions in the α and β chains of HLA-DQ7, encoded by HLA-DQA1∗05:01 and HLA-DQB1∗03:01 respectively. We identified three variant peptide-HLA-DQ7-Fc fusion proteins (DQ7Fc) with increased expression and production yield, namely Y19C-D6C (YCDC), A83C-E5C (ACEC), and A84C-N33C (ACNC). The mutated residues were conserved across all HLA-DQ proteins and had limited solvent exposure. Further characterizations of the YCDC variant showed that the expression of the fusion protein is peptide-dependent; inclusion of a higher-affinity peptide correlated with increased protein expression. However, high-affinity peptide alone was insufficient for stabilizing the DQ7 complex without the engineered disulfide bond. Multiple DQ7Fc variants demonstrated expected binding characteristics with commercial anti-DQ antibodies in two immunoassays and by a cell-based assay. Lastly, DQ7Fc variants demonstrated dose-dependent killing of DQ7-specific B cell hybridomas in a flow cytometric, complement-dependent cytotoxicity assay. These data support inter-chain disulfide engineering as a novel approach to efficiently producing functional HLA-DQ molecules and potentially other class II HLA molecules as candidate therapeutic agents.

Anti-HLA Class II Antibodies Are the Most Resistant to Desensitization in Crossmatch-positive Living-donor Kidney Transplantations: A Patient Series

Background

In HLA-incompatible kidney transplantation, the efficacy of desensitization in terms of anti-HLA antibody kinetics is not well characterized. We present an overview of the course of anti-HLA antibodies throughout plasma exchange (PE) desensitization in a series of crossmatch-positive patients.

Methods

All consecutive candidates in the Dutch HLA-incompatible kidney transplantation program between November 2012 and January 2022 were included. The eligibility criteria were a positive crossmatch with a living kidney donor and no options for compatible transplantation. Desensitization consisted of 5-10 PE with low-dose IVIg.

Results

A total of 16 patient-donor pairs were included. Patients had median virtual panel-reactive antibody of 99.58%. Cumulative donor-specific anti-HLA antibody (cumDSA) mean fluorescence intensity (MFI) was 31 399 median, and immunodominant DSA (iDSA) MFI was 18 677 for class I and 21 893 for class II. Median anti-HLA antibody MFI response to desensitization was worse in class II as compared with class I (P < 0.001), particularly for HLA-DQ. Class I cumDSA MFI decreased 68% after 4 PE versus 53% in class II. The decrease between the fifth and the 10th PE sessions was modest with 21% in class I versus 9% in class II. Antibody-mediated rejection occurred in 85% of patients, with the iDSA directed to the same mismatched HLA as before desensitization, except for 3 patients, of whom 2 had vigorous rebound of antibodies to repeated mismatches (RMMs). Rebound was highest (86%) in RMM-DSA with prior grafts removed (transplantectomy n = 7), lower (39%) in non-RMM-DSA (n = 30), and lowest (11%) for RMM-DSA with in situ grafts (n = 5; P = 0.018 for RMM-DSA transplantectomy versus RMM-DSA graft in situ). With a median follow-up of 59 mo, 1 patient had died resulting in a death-censored graft survival of 73%.

Conclusions

Patients with class II DSA, and particularly those directed against HLA-DQ locus, were difficult to desensitize.

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.

Granulomatous Tubulointerstitial Nephritis in a Kidney Allograft: Treatment with Interleukin-6 Receptor Antagonist Stabilises Kidney Function

Granulomatous tubulointerstitial nephritis (GTIN) attributed to early onset sarcoidosis is an ultrarare finding in an allograft kidney biopsy. We present the case of a young man with allograft dysfunction who had GTIN upon biopsy. We performed a thorough case review based on recovered records from early childhood and reassessed genetic testing results. We revised his underlying diagnosis from cryopyrin-associated periodic syndrome to early-onset sarcoidosis with wild-type NOD2 and established a rationale to use the interleukin-6 (IL-6) receptor blocker tocilizumab (TCZ). This suppressed his inflammatory disease and stabilised kidney function. We performed a literature review related to the emerging role of IL-6 pathway blockade in kidney transplantation. We identified 18 reports with 417 unique patients treated with TCZ for indications including HLA-desensitisation, transplant immunosuppression induction, treatment of chronic antibody-mediated rejection, and treatment of subclinical rejection. Both TCZ and the direct IL-6 inhibitor clazakizumab are being studied in ongoing randomised control trials.

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.

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.

Management of the sensitized heart transplant candidate

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Preventing Rejection of the Kidney Transplant

With increasing knowledge of immunologic factors and with the advent of potent immunosuppressive agents, the last several decades have seen significantly improved kidney allograft survival. However, despite overall improved short to medium-term allograft survival, long-term allograft outcomes remain unsatisfactory. A large body of literature implicates acute and chronic rejection as independent risk factors for graft loss. In this article, we review measures taken at various stages in the kidney transplant process to minimize the risk of rejection. In the pre-transplant phase, it is imperative to minimize the risk of sensitization, aim for better HLA matching including eplet matching and use desensitization in carefully selected high-risk patients. The peri-transplant phase involves strategies to minimize cold ischemia times, individualize induction immunosuppression and make all efforts for better HLA matching. In the post-transplant phase, the focus should move towards individualizing maintenance immunosuppression and using innovative strategies to increase compliance. Acute rejection episodes are risk factors for significant graft injury and development of chronic rejection thus one should strive for early detection and aggressive treatment. Monitoring for DSA development, especially in high-risk populations, should be made part of transplant follow-up protocols. A host of new biomarkers are now commercially available, and these should be used for early detection of rejection, immunosuppression modulation, prevention of unnecessary biopsies and monitoring response to rejection treatment. There is a strong push needed for the development of new drugs, especially for the management of chronic or resistant rejections, to prolong graft survival. Prevention of rejection is key for the longevity of kidney allografts. This requires a multipronged approach and significant effort on the part of the recipients and transplant centers.

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

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

Desensitization in Crossmatch-positive Kidney Transplant Candidates

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

Tocilizumab Evaluation in HLA-Desensitization before Kidney Transplantation as an Add-On Therapy to Apheresis: The TETRA Study

BACKGROUND

Desensitization strategies improve access to transplantation in highly sensitized kidney transplant candidates. Tocilizumab could be a valuable addition to more traditional desensitization regimens. We investigated the effect of tocilizumab as an add-on therapy to our standard of care (SoC) desensitization strategy based on rituximab and apheresis.

METHODS

In this study, we prospectively included highly sensitized patients to receive monthly tocilizumab infusions for 6 months before our SoC regimen (Toci + SoC group). We compared the reductions in the mean fluorescent intensity (MFI) rebound at post-transplantation and kidney function at 1-year post-transplantation to patients treated by SoC (based on apheresis and two doses of rituximab).

RESULTS

Twenty-six patients were included in the SoC group; seven in the Toci + SoC group. Reductions in pre-transplantation MFI were similar between groups. At 1-year post-transplantation, there was no absolute difference in overall MFI rebounds, including donor-specific antibodies. Toci + SoC helped lower the rebound of antibodies with more elevated baseline MFIs. Graft function and survival rates were similar at one-year post-transplantation (median eGFR 62.8 vs. 65.6 mL/min/1.73 m² for SoC and Toci + SoC, respectively).

CONCLUSIONS

Tocilizumab as an add-on to SoC desensitization may help control the post-transplantation rebound of antibodies with elevated baseline MFIs. However, reductions in pre-transplantation MFIs were similar with or without tocilizumab. Further studies are needed to validate this pilot study.

Impact of interleukin-6 on T cells in kidney transplant recipients

Interleukin-6 (IL-6), a multifunctional proinflammatory cytokine, plays a key role in T cell activation, survival, and differentiation. Acting as a switch that induces the differentiation of naïve T cells into Th17 cells and inhibits their development into regulatory T cells, IL-6 promotes rejection and abrogates tolerance. Therapies that target IL-6 signaling include antibodies to IL-6 and the IL-6 receptor and inhibitors of janus kinases; several of these therapeutics have demonstrated robust clinical efficacy in autoimmune and inflammatory diseases. Clinical trials of IL-6 inhibition in kidney transplantation have focused primarily on its effects on B cells, plasma cells, and HLA antibodies. In this review, we summarize the impact of IL-6 on T cells in experimental models of transplant and describe the effects of IL-6 inhibition on the T cell compartment in kidney transplant recipients.

Addition of interleukin-6 receptor blockade to carfilzomib-based desensitization in a highly sensitized nonhuman primate model

Sensitized patients, those who had prior exposure to foreign human leukocyte antigens, are transplanted at lower rates due to challenges in finding suitable organs. Desensitization strategies have permitted highly sensitized patients to undergo kidney transplantation, albeit with higher rates of rejection. This study assesses targeting plasma cell and interleukin (IL)-6 receptor for desensitization in a sensitized nonhuman primate kidney transplantation model. All animals were sensitized using two sequential skin transplants from maximally major histocompatibility complex-mismatched donors. Carfilzomib (CFZ)/tocilizumab (TCZ) desensitization (N = 6) successfully decreased donor-specific antibody (DSA) titers and prevented the expansion of B cells compared to CFZ monotherapy (N = 3). Dual desensitization further delayed, but did not prevent humoral rebound, as evidenced by a delayed increase in post-kidney transplant DSA titers. Accordingly, CFZ/TCZ desensitization conferred a significant survival advantage over CFZ monotherapy. A trend toward increased T follicular helper cells was also observed in the dual therapy group along the same timeline as an increase in DSA and subsequent graft loss. Cytomegalovirus reactivation also occurred in the CFZ/TCZ group but was prevented with ganciclovir prophylaxis. In accordance with prior studies of CFZ-based dual desensitization strategies, the addition of IL-6 receptor blockade resulted in desensitization with further suppression of posttransplant humoral response compared to CFZ monotherapy.

[Improving access to kidney transplantation for highly sensitized patients: What place for IL-6 pathway blockade in desensitization protocols?]

BACKGROUND

Desensitization allows kidney transplantation for HLA highly sensitized subjects. Due to the central role of IL-6 in immunological response, tocilizumab (monoclonal antibody directed against IL-6 receptor) could probably improve desensitization efficacy.

METHODS

Pubmed systematic review by using MeSH terms: tocilizumab, clazakizumab, interleukin-6 blockade, kidney transplantation, kidney graft and desensitization.

STUDIES

IL-6 plays a role in humoral response (plasmocyte differentiation induced by lymphocyte T, IL-21 secretion) as well as in cellular response (differentiation of LT Th17 rather than T reg). In desensitization field, tocilizumab was first studied as second-line treatment after failing of standard-of-care (apheresis, rituximab ± IgIV). Recent study showed that tocilizumab as a monotherapy attenuated anti-HLA antibodies rates but was not sufficient to allow transplantation. However, lymphocyte immunophenotyping showed that tocilizumab hindered B cells maturation. Thereby, tocilizumab could improve long-term efficacy of desensitization, by limiting the anti-HLA rebound and so avoiding antibody-mediated rejection. This hypothesis is supported by a recent study which used clazakizumab (monoclonal antibody directed against IL-6) in association with standard-of-care. In that study, clazakizumab was continued after kidney transplantation. Results were encouraging because 9/10 patients were transplanted and there was no donor-specific antibody at 6 months post-transplantation.

CONCLUSION

IL-6 pathway blockade as a monotherapy fails to desensitize HLA highly sensitized kidney transplant candidates. In association with standard-of-care, it does not seem to significatively improve kidney allograft access (short-term efficacy) vs. standard-of-care only. However, it could improve long-term prognosis of HLA incompatible transplantation by orienting the response towards a tolerogenic profile, by hindering B-cell maturation and, thereby, avoiding DSA rebounds after transplantation. This hypothesis needs to be proven by further studies.

Heart transplantation across preformed donor-specific antibody barriers using a perioperative desensitization protocol

Heart transplantation across preformed donor-specific HLA-antibody barriers is associated with impaired short- and long-term survival. Therefore, in recipients with preformed anti-HLA antibodies, waiting for crossmatch-negative donors is standard practice. As an alternative strategy, recipients with preformed anti-HLA donor specific antibodies have been managed at our institutions with a perioperative desensitization regimen. A retrospective analysis was performed comparing heart transplant recipients with preformed donor-specific HLA-antibodies to recipients without donor-specific antibodies. Recipients with a positive virtual crossmatch received a perioperative desensitization protocol including tocilizumab intraoperatively, plasma exchange and rituximab followed by a six-month course of IgGAM. Among the 117 heart-transplanted patients, 19 (16%) patients underwent perioperative desensitization, and the remaining 98 (84%) patients did not. Cold ischemic time, posttransplant extracorporeal life support for primary graft dysfunction, and intensive care unit stay time did not differ between groups. At 1-year follow-up, freedom from pulsed steroid therapy for presumed rejection and biopsy-confirmed acute cellular or humoral rejection did not differ between groups. One-year survival amounted to 94.7% in the treated patients and 81.4% in the control group. Therefore, heart transplantation in sensitized recipients undergoing a perioperative desensitization appears safe with comparable postoperative outcomes as patients with a negative crossmatch.

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.

Immune responses following tocilizumab therapy to desensitize HLA-sensitized kidney transplant candidates

Kidney transplant candidates (KTCs) who are HLA highly sensitized (calculated panel-reactive alloantibodies >95%) have poor access to deceased kidney transplantation. In this single-center prospective study, 13 highly sensitized desensitization-naïve KTCs received IV tocilizumab (8 mg/kg) every 4 weeks. We evaluated tolerability as well as immune responses, that is, T cell, B cell, T follicular helper (Tfh) subsets, blood cytokines (IL-6, soluble IL-6 receptor-sIL-6R-, IL-21), blood chemokines (CXCL10, CXCL13), and anti-HLA alloantibodies. Tocilizumab treatment was well-tolerated except in one patient who presented spondylodiscitis, raising a note of caution. Regarding immune parameters, there were no significant changes of percentages of lymphocyte subsets, that is, CD3⁺ , CD3⁺ /CD4⁺ , CD3⁺ /CD8⁺ T cells, and NK cells. This was also the case for Tfh cell subsets, B cells, mature B cells, plasma cells, pre-germinal center (GC) B cells, and post-GC B cells, whereas we observed a significant increase in naïve B cells (p = .02) and a significant decrease in plasmablasts (p = .046) over the tocilizumab treatment course. CXCL10, CXCL13, IL-21, total IgG, IgA, and IgM levels did not significantly change during tocilizumab therapy; conversely, there was a significant increase in IL-6 levels (p = .03) and a huge increase in sIL-6R (p = .00004). There was a marginal effect on anti-HLA alloantibodies (class I and class II). To conclude in highly sensitized KTCs, tocilizumab as a monotherapy limited B cell maturation; however, it had almost no effect on anti-HLA alloantibodies.

Tocilizumab Trough Levels Variability in Kidney-Transplant Candidates Undergoing Desensitization

The presence of anti-HLA antibodies is an increasing challenge in kidney transplantation. Tocilizumab (TCZ), a monoclonal antibody targeting the interleukin-6 receptor (IL-6R), has been proposed to complement conventional desensitization therapy. We aimed to describe TCZ plasma trough concentrations and their variability and to investigate the link between TCZ concentration and the evolution of anti-HLA antibodies. Sensitized kidney-transplant candidates treated monthly with TCZ (8 mg/kg) for desensitization were retrospectively included. TCZ concentrations were determined by liquid chromatography-tandem mass spectrometry. Seventy-four TCZ concentrations from 10 patients were analyzed. The TCZ trough concentration ranged from <1.0 to 52.5 mg·L−1, with a median of 25.6 mg·L−1 [25th–75th percentiles: 13.2–35.3 mg·L−1). The inter- and intra-individual coefficients of variation were 55.0% and 33.0%, respectively. The TCZ trough concentration was not related to IL-6 (rho = −0.46, p = 0.792), soluble IL-6R (rho = −0.81, p = 0.65) concentrations or reduction of anti-HLA antibodies (mixed-effects model adjusting, effect of TCZ trough concentration: rho = −0.004, p = 0.26). The individual median TCZ concentration tended to be associated with the number of antibodies, with an initial MFI > 3000 that dropped to <3000 after TCZ treatment (rho = 0.397, p = 0.083). TCZ trough concentrations in kidney-transplant candidates treated for desensitization were highly variable. Further studies on larger cohorts are needed to study the possible link between TCZ concentrations and the reduction of anti-HLA antibodies.

Tocilizumab and Desensitization in Kidney Transplant Candidates: Personal Experience and Literature Review

Desensitization (DES) allows kidney transplantation for highly HLA-sensitized subjects. Due to the central role of IL-6 in the immunological response, tocilizumab may improve DES efficacy. Thus, we conducted a PubMed systematic review using the MeSH terms tocilizumab, interleukin-6, kidney transplantation, and desensitization. Tocilizumab (TCZ) was first studied for DES as the second-line treatment after failure of a standard DES protocol (SP) (apheresis, rituximab +/- IVIg). Although TCZ (as a monotherapy) attenuated anti-HLA antibody rates, it did not permit transplantation. However, lymphocyte immuno-phenotyping has shown that TCZ hinders B-cell maturation and thus could improve the long-term efficacy of DES by limiting anti-HLA rebound and so avoid antibody-mediated rejection. This hypothesis is supported by a recent study where clazakizumab, a monoclonal antibody directed against IL-6, was continued after kidney transplantation in association with an SP. Nine out of ten patients were then eligible for transplantation, and there were no donor-specific antibodies at 6 months post-transplantation. In association with an SP, tocilizumab does not seem to significantly improve kidney-allograft access (short-term efficacy) vs. a SP only. However, it could improve the long-term prognosis of HLA-incompatible transplantation by hindering B-cell maturation and, thereby, avoiding donor-specific antibody rebounds post-transplantation.