Achieving incompatible transplantation through desensitization: current perspectives and future directions

Inhibition of spleen tyrosine kinase decreases donor specific antibody levels in a rat model of sensitization

Antibody mediated rejection is a major cause of renal allograft loss. Circulating preformed donor specific antibodies (DSA) can result as a consequence of blood transfusion, pregnancy or prior transplantation. Current treatment strategies are limited due to partial or transient efficacy, adverse side-effects or patient unsuitability. Previous in vivo studies exploring autoimmune diseases have shown that spleen tyrosine kinase (SYK) signalling is involved in the development of pathogenic autoantibody. The role of SYK in allogenic antibody production is unknown, and we investigated this in a rodent model of sensitization, established by the transfusion of F344 whole blood into LEW rats. Two-week treatment of sensitized rats with selective SYK inhibitor fostamatinib strongly blocked circulating DSA production without affecting overall total immunoglobulin levels, and inhibition was sustained up to 5 weeks post-completion of the treatment regimen. Fostamatinib treatment did not affect mature B cell subset or plasma cell levels, which remained similar between non-treated controls, vehicle treated and fostamatinib treated animals. Our data indicate fostamatinib may provide an alternative therapeutic option for patients who are at risk of sensitization following blood transfusion while awaiting renal transplant.

Emerging New Approaches in Desensitization: Targeted Therapies for HLA Sensitization

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

Phenotypic and Transcriptomic Lymphocytes Changes in Allograft Recipients After Intravenous Immunoglobulin Therapy in Kidney Transplant Recipients

High dose intravenous immunoglobulin (IVIG) are widely used after kidney transplantation and its biological effect on T and B cell phenotype in the context of maintenance immunosuppression was not documented yet. We designed a monocentric prospective cohort study of kidney allograft recipients with anti-HLA donor specific antibodies (DSA) without acute rejection on screening biopsies treated with prophylactic high-dose IVIG (2 g/kg) monthly for 2 months. Any previous treatment with Rituximab was an exclusion criterion. We performed an extensive analysis of phenotypic and transcriptomic T and B lymphocytes changes and serum cytokines after treatment (day 60). Twelve kidney transplant recipients who completed at least two courses of high-dose IVIG (2 g/kg) were included in a median time of 45 (12–132) months after transplant. Anti-HLA DSA characteristics were similar before and after treatment. At D60, PBMC population distribution was similar to the day before the first infusion. CD8⁺ CD45RA⁺ T cells and naïve B-cells (Bm2⁺) decreased (P = 0.03 and P = 0.012, respectively) whereas Bm1 (mature B-cells) increased (P = 0.004). RORγt serum mRNA transcription factor and CD3 serum mRNA increased 60 days after IVIG (P = 0.02 for both). Among the 25 cytokines tested, only IL-18 serum concentration significantly decreased at D60 (P = 0.03). In conclusion, high dose IVIG induced limited B cell and T cell phenotype modifications that could lead to anti-HLA DSA decrease. However, no clinical effect has been isolated and the real benefit of prophylactic use of IVIG after kidney transplantation merits to be questioned.

The Incremental Cost of Incompatible Living Donor Kidney Transplantation: A National Cohort Analysis

Incompatible living donor kidney transplantation (ILDKT) has been established as an effective option for end-stage renal disease patients with willing but HLA-incompatible living donors, reducing mortality and improving quality of life. Depending on antibody titer, ILDKT can require highly resource-intensive procedures, including intravenous immunoglobulin, plasma exchange, and/or cell-depleting antibody treatment, as well as protocol biopsies and donor-specific antibody testing. This study sought to compare the cost and Medicare reimbursement, exclusive of organ acquisition payment, for ILDKT (n = 926) with varying antibody titers to matched compatible transplants (n = 2762) performed between 2002 and 2011. Data were assembled from a national cohort study of ILDKT and a unique data set linking hospital cost accounting data and Medicare claims. ILDKT was more expensive than matched compatible transplantation, ranging from 20% higher adjusted costs for positive on Luminex assay but negative flow cytometric crossmatch, 26% higher for positive flow cytometric crossmatch but negative cytotoxic crossmatch, and 39% higher for positive cytotoxic crossmatch (p < 0.0001 for all). ILDKT was associated with longer median length of stay (12.9 vs. 7.8 days), higher Medicare payments ($91 330 vs. $63 782 p < 0.0001), and greater outlier payments. In conclusion, ILDKT increases the cost of and payments for kidney transplantation.

Risk factors associated with the development of histocompatibility leukocyte antigen sensitization

PURPOSE OF REVIEW

Despite excellent short-term kidney allograft survival rates, long-term outcomes have not improved. For years, the focus on improving these outcomes revolved around minimization or elimination of calcineurin toxicity. Despite our best efforts, approximately 5000 allografts are lost each year in the United States and results in a significant emotional burden for patients and financial burden for the healthcare system.

RECENT FINDINGS

Advancements in detection of donor-specific histocompatibility leukocyte antigen antibodies (DSAs) and improved assessment of allograft biopsy tissue have shown that the most common cause for graft failures is DSA-related antibody-mediated rejection. Sensitization is directly related to human tissue exposure prior to transplant. We now know that sensitization can occur in patients who are non compliant or poorly compliant with their calcineurin inhibitors. They develop de-novo DSAs, which are responsible for numerous allograft losses around the world.

SUMMARY

Given the current evidence, it is imperative that all transplant physicians recognize the importance of encouraging medication adherence to prevent the consequences of DSA-induced graft failure. However, little progress has been made in this area. Other potential therapeutic approaches based on B-cell depletion or modulation early posttransplant may help to reduce the risk for de-novo DSA development.

Intravenous immunoglobulin therapy in kidney transplant recipients with de novo DSA: Results of an observational study

Background

Approximately 25% of kidney transplant recipients develop de novo anti-HLA donor-specific antibodies (dnDSA) leading to acute antibody-mediated rejection (ABMR) in 30% of patients. Preemptive therapeutic strategies are not available.

Methods

We conducted a prospective observational study including 11 kidney transplant recipients. Inclusion criteria were dnDSA occurring within the first year after transplant and normal allograft biopsy. All patients were treated with high-dose IVIG (2 g/kg 0, 1 and 2 months post-dnDSA). The primary efficacy outcome was incidence of clinical and subclinical acute ABMR within 12 months after dnDSA detection as compared to a historical control group (IVIG-).

Results

Acute ABMR occurred in 2 or 11 patients in the IVIG+ group and in 1 of 9 patients in the IVIG- group. IVIG treatment did not affect either class I or class II DSA, as observed at the end of the follow-up. IVIG treatment significantly decreased FcγRIIA mRNA expression in circulating leukocytes, but did not affect the expression of any other markers of B cell activation.

Conclusions

In this first pilot study including kidney allograft recipients with early dnDSA, preemptive treatment with high-dose IVIG alone did not prevent acute ABMR and had minimal effects on DSA outcome and B cell phenotype.

Interleukin-6, A Cytokine Critical to Mediation of Inflammation, Autoimmunity and Allograft Rejection: Therapeutic Implications of IL-6 Receptor Blockade

The success of kidney transplants is limited by the lack of robust improvements in long-term survival. It is now recognized that alloimmune responses are responsible for the majority of allograft failures. Development of novel therapies to decrease allosensitization is critical. The lack of new drug development in kidney transplantation necessitated repurposing drugs initially developed in oncology and autoimmunity. Among these is tocilizumab (anti-IL-6 receptor [IL-6R]) which holds promise for modulating multiple immune pathways responsible for allograft injury and loss. Interleukin-6 is a cytokine critical to proinflammatory and immune regulatory cascades. Emerging data have identified important roles for IL-6 in innate immune responses and adaptive immunity. Excessive IL-6 production is associated with activation of T-helper 17 cell and inhibition of regulatory T cell with attendant inflammation. Plasmablast production of IL-6 is critical for initiation of T follicular helper cells and production of high-affinity IgG. Tocilizumab is the first-in-class drug developed to treat diseases mediated by IL-6. Data are emerging from animal and human studies indicating a critical role for IL-6 in mediation of cell-mediated rejection, antibody-mediated rejection, and chronic allograft vasculopathy. This suggests that anti-IL-6/IL-6R blockade could be effective in modifying T- and B-cell responses to allografts. Initial data from our group suggest anti-IL-6R therapy is of value in desensitization and prevention and treatment of antibody-mediated rejection. In addition, human trials have shown benefits in treatment of graft versus host disease in matched or mismatched stem cell transplants. Here, we explore the biology of IL-6/IL-6R interactions and the evidence for an important role of IL-6 in mediating allograft rejection.

Progress in Desensitization of the Highly HLA Sensitized Patient

The presence of HLA antibodies remains a significant and often impenetrable barrier to kidney transplantation, leading to increased morbidity and mortality for patients remaining on long-term dialysis. In recent years, a number of new approaches have been developed to overcome these barriers. Intravenous immunoglobulin (IVIG) remains the lynchpin of HLA desensitization therapy and has been shown in a prospective, randomized, placebo-controlled trial to improve transplantation rates. In addition, IVIG used in low doses with plasma exchange is a reliable protocol for desensitization. Another significant advancement was the addition of rituximab (anti-B-cell therapy) to IVIG and plasma exchange-based desensitization. This approach has significantly improved rates of transplantation and outcomes. There is limited experience with bortezomib (anti-plasma cell therapy) and eculizumab (complement inhibition) for desensitization. However, recent data from a completed trial of eculizumab failed to show a significant benefit for prevention of antibody-mediated rejection compared with standard therapy plus placebo, and bortezomib produced inconsistent results. There is a growing interest in developing new therapeutic agents for desensitization. Newer approaches that address antibody reduction with B-cell depletion are discussed.

Desensitization: Overcoming the Immunologic Barriers to Transplantation

HLA (Human Leucocyte Antigen) sensitization is a significant barrier to successful kidney transplantation. It often translates into difficult crossmatch before transplant and increased risk of acute and chronic antibody mediated rejection after transplant. Over the last decade, several immunomodulatory therapies have emerged allowing for increased access to kidney transplantation for the immunologically disadvantaged group of HLA sensitized end stage kidney disease patients. These include IgG inactivating agents, anti-cytokine antibodies, costimulatory molecule blockers, complement inhibitors, and agents targeting plasma cells. In this review, we discuss currently available agents for desensitization and provide a brief analysis of data on novel biologics, which will likely improve desensitization outcomes, and have potential implications in treatment of antibody mediated rejection.

Immune Tolerance for Autoimmune Disease and Cell Transplantation

The undesired destruction of healthy cells, either endogenous or transplanted, by the immune system results in the loss of tissue function or limits strategies to restore tissue function. Current therapies typically involve nonspecific immunosuppression that may prevent the appropriate response to an antigen, thereby decreasing humoral immunity and increasing the risks of patient susceptibility to opportunistic infections, viral reactivation, and neoplasia. The induction of antigen-specific immunological tolerance to block undesired immune responses to self- or allogeneic antigens, while maintaining the integrity of the remaining immune system, has the potential to transform the current treatment of autoimmune disease and serve as a key enabling technology for therapies based on cell transplantation.

Drug target molecules to guide immunosuppression

The individual and interindividual variability of response to immunosuppressants combined with the prevailing concept of lifelong immunosuppression following any organ transplantation motivates the search for methods to further individualize such therapy. Traditional therapeutic drug monitoring, adapting dose according to concentrations in blood, targets the pharmacokinetic variability. It has been increasingly recognized, however, that there is also a considerable variability in the response to a given concentration. Attempts to overcome this variability in response include the efforts to identify relevant targets and methods for pharmacodynamic monitoring. For several of the currently used immunosuppressants there is experimental data suggesting markers that are relevant as indicators for individual monitoring of the effects of these drugs. There are also some clinical data to support these approaches; however what is generally missing, are studies that in a prospective manner demonstrates the benefits and effects on outcome. The monitoring of antithymocyte globulin by lymphocyte subset counts is actually the only well established example of pharmacodynamic monitoring. For drugs such as MPA and mTOR inhibitors, there are candidates such as IMPDH activity expression and p70SK6 phosphorylation status, respectively. The monitoring of CNIs using assays for NFAT RGE, either alone or combined with concentration measurements, is already well documented. Even here, some further investigations relating to the categories of organ transplant, combination of immunosuppressants etc. will be requested. Although some further standardization of the assay is warranted and there is a need for specific recommendations of target levels and how to adjust dose, the NFAT RGE approach to pharmacodynamic monitoring of CNIs may be close to implementation in clinical routine.