B-cell immunotherapeutics: emerging roles in solid organ transplantation

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.

Cationic nanoparticles-based approaches for immune tolerance induction in vivo

The development of autoimmune diseases and the rejection of transplanted organs are primarily caused by an exaggerated immune response to autoantigens or graft antigens. Achieving immune tolerance is crucial for the effective treatment of these conditions. However, traditional therapies often have limited therapeutic efficacy and can result in systemic toxic effects. The emergence of nanomedicine offers a promising avenue for addressing immune-related diseases. Among the various nanoparticle formulations, cationic nanoparticles have demonstrated significant potential in inducing immune tolerance. In this review, we provide an overview of the underlying mechanism of autoimmune disease and organ transplantation rejection. We then highlight the recent advancements and advantages of utilizing cationic nanoparticles for inducing immune tolerance in the treatment of autoimmune diseases and the prevention of transplant rejection.

Approach to Highly Sensitized Kidney Transplant Candidates and a Positive Crossmatch

Human leukocyte antigen (HLA)-incompatible kidney transplantation offers survival benefit compared with ongoing dialysis. There have been considerable advances in the last decade to allow for increased access to transplant for the HLA-sensitized kidney transplant candidates. These include increased priority in the kidney allocation system, kidney paired donation, and novel desensitization strategies. A better understanding of the role of B cells, plasma cells, and complement and inflammatory cytokines in the pathophysiology of HLA antibody-mediated allograft injury has led to the use of novel therapeutics for desensitization and treatment of antibody-mediated rejection. Here we discuss current approaches to kidney transplantation in HLA-sensitized kidney transplant candidates.

Impact of Tocilizumab (Anti-IL-6R) Treatment on Immunoglobulins and Anti-HLA Antibodies in Kidney Transplant Patients With Chronic Antibody-mediated Rejection

BACKGROUND

Chronic antibody-mediated rejection (cAMR) results in the majority of renal allograft losses. Currently, there are no approved therapies. We recently reported on clinical use of tocilizumab (TCZ) for treatment of cAMR in HLA-sensitized kidney transplant patients. IgG1 and IgG3 subclasses of IgG are potent effectors of complement- and antibody-dependent cellular cytotoxicity, which are critical mediators of AMR. Here, we examined the impact of TCZ treatment for cAMR on total IgG, IgG1-4 subclasses, and anti-HLA-IgG (total and subclasses).

METHODS

Archived plasma obtained pre- and post-TCZ treatment (8 mg/kg, 6×, monthly) from 12 cAMR patients who failed standard of care treatment with intravenous immune globulin + rituximab with or without plasma exchange were tested for total IgG and IgG1-4 by ELISA, anti-HLA-total IgG, IgG3 and IgG4, and donor-specific antibody by Luminex assay. Archived plasma from 14 cAMR patients treated with the standard of care were included as controls.

RESULTS

Total IgG and IgG1-3 were significantly reduced post-TCZ, whereas no reduction was seen post-treatment in the control group. Of 11 patients, 8 (73%) showed reduction of anti-HLA-total IgG and IgG3 post-TCZ, but this was not statistically significant.

CONCLUSIONS

TCZ reduced total IgG and IgG1-3 and anti-HLA-total IgG and IgG3 levels, suggesting that TCZ suppresses Ig production in B cells nonspecifically, likely through inhibition of interleukin 6-mediated signaling to B cells and plasma cells. This may be a contributing factor for the beneficial effect of TCZ on cAMR observed in this patient population.

Outcomes of Canakinumab Treatment in Recipients of Kidney Transplant With Familial Mediterranean Fever: A Case Series

Familial Mediterranean fever (FMF) is an important and preventable cause of chronic kidney disease due to secondary amyloidosis. Although colchicine is the first-line therapy in patients with FMF with 60% to 65% complete remission rates, 5% to 10% of patients are colchicine-resistant and 5% to 10% of them are intolerant to the therapy. Anti-interleukin-1 agents, such as anakinra and canakinumab, are safe and efficient therapeutic options in patients with colchicine resistance or intolerance. However, the data on management of these targeted agents is limited in recipients of kidney transplant (RKT). In this case series, we aim to share our experience on canakinumab therapy of 4 RKTs with FMF-related amyloidosis, who were followed up in our clinic between 2010 and 2017. All of the 4 patients with end-stage renal disease were colchicine- resistant and on other alternative therapies, which provided poor disease control. For efficient control of secondary amyloidosis, canakinumab therapy was initiated in 1 of the patients before the renal transplant, and for the remaining patients after renal transplant. Any serious adverse effect, development of proteinuria, or graft dysfunction has not been observed in any of the patients. Under the canakinumab treatment, complete clinical responses, prevent typical familial Mediterranean fever attacks with fever and arthritis and abdominal pain, normalized serum amyloid A and C-reactive protein levels were achieved in all patients. Canakinumab treatment is a safe and effective therapeutic option for RKTs with FMF who are resistant or intolerant to colchicine and anakinra.

Desensitization strategies in adult heart transplantation-Will persistence pay off?

Strategies are needed to enable successful heart transplantation in highly sensitized patients. Immunologic challenges from sensitization to human leukocyte antigen (HLA) reduce access to compatible donors, extend waiting times to transplant, and increase the risks of antibody-mediated rejection and cardiac allograft vasculopathy after transplant. The prime goal of desensitization is to increase access to transplantation through expansion of the donor organ pool. Existing therapies are directed at key components of the humoral immune response with newer biologically based regimens able to target plasma cells as the source of antibody production, as well as complement activation that has a central role in antibody-mediated injury. Despite the emergence of early promising results for these agents, a significant knowledge gap remains with the current data for desensitization, extrapolated mostly from non-heart solid-organ transplants and small observational studies. Notably, no approach has demonstrated significant and sustainable reductions in HLA antibody pre-transplant, and the ideal desensitization strategy remains elusive. In addition, clinical tools to evaluate the humoral response and efficacy of therapy are limited, focusing almost exclusively on HLA antibody detection. Importantly, desensitization is associated with significant costs and potential risks, and overall long-term outcomes and cost-effectiveness have not been sufficiently evaluated. Investigation is ongoing into the development of a clinically effective desensitization strategy in heart transplantation.

Preclinical safety, pharmacokinetics, pharmacodynamics, and biodistribution studies with Ad35K++ protein: a novel rituximab cotherapeutic

Rituximab is a mouse/human chimeric monoclonal antibody targeted toward CD20. It is efficient as first-line therapy of CD20-positive B-cell malignancies. However, a large fraction of treated patients relapse with rituximab-resistant disease. So far, only modest progress has been made in treatment options for rituximab refractory patients. One of the mechanisms for rituximab resistance involves the upregulation of CD46, which is a key cell surface protein that blocks the activation of complement. We have recently developed a technology that depletes CD46 from the cell surface and thereby sensitizes tumor cells to complement-dependent cytotoxicity. This technology is based on a small recombinant protein, Ad35K++ that binds with high affinity to CD46. In preliminary studies using a 6 × histidinyl tagged protein, we had demonstrated that intravenous Ad35K++ injection in combination with rituximab was safe and increased rituximab-mediated killing of CD20-positive target cells in mice and nonhuman primates (NHPs). The presence of the tag, while allowing for easy purification by Ni-NTA chromatography, has the potential to increase the immunogenicity of the recombinant protein. For clinical application, we therefore developed an Ad35K++ protein without His-tag. In the present study, we performed preclinical studies in two animal species (mice and NHPs) with this protein demonstrating its safety and efficacy. These studies estimated the Ad35K++ dose range and treatment regimen to be used in patients. Furthermore, we showed that intravenous Ad35K++ injection triggers the shedding of the CD46 extracellular domain in xenograft mouse tumor models and in macaques. Shed serum CD46 can be measured in the serum and can potentially be used as a pharmacodynamic marker for monitoring Ad35K++ activity in patient undergoing treatment with this agent. These studies create the basis for an investigational new drug application for the use of Ad35K++ in combination with rituximab in the treatment of patients with B-cell malignancies.

Kidney transplantation in highly sensitized patients

BACKGROUND

Desensitization, a term loosely referring to a collection of antibody reduction and B-cell depletional therapies aimed at improving rates of transplantation in highly HLA and ABO-incompatible transplant recipients, has seen significant growth in the last decade. Advancements relate to an increasing unmet medical need for FDA-approved therapies, advancements in antibody detection methodologies and improved renal pathological assessments of antibody-mediated rejection (ABMR).

SOURCES OF DATA, AREAS OF AGREEMENT AND CONTROVERSY

Data reviewed include collective summaries of experience with high-dose intravenous immunoglobulin (IVIG), B-cell depletion with rituximab and the use of plasma exchange with low-dose IVIG. Consensus suggests that these protocols are the most commonly used while experiences with other agents (i.e. bortezomib) are evolving. Controversy exists as to the extent of resources required, expense and outcomes of desensitization protocols.

GROWING POINTS OR AREAS TIMELY FOR DEVELOPING RESEARCH

Here we review and synthesize data from evolving protocols and summarize developments of novel biologics aimed at modification of B-cells, antibodies and complement activation which will likely improve desensitization and treatment of ABMR.

Avoiding immunological rejection in regenerative medicine

One of the major goals of regenerative medicine is repair or replacement of diseased and damaged tissues by transfer of differentiated stem cells or stem cell-derived tissues. The possibility that these tissues will be destroyed by immunological rejection remains a challenge that can only be overcome through a better understanding of the nature and expression of potentially immunogenic molecules associated with cell replacement therapy and the mechanisms and pathways resulting in their immunologic rejection. This review draws on clinical experience of organ and tissue transplantation, and on transplantation immunology research to consider practical approaches for avoiding and overcoming the possibility of rejection of stem cell-derived tissues.

Donor-specific antibodies in allograft recipients: etiology, impact and therapeutic approaches

PURPOSE OF REVIEW

Kidney transplantation remains the treatment of choice for patients with end-stage renal failure. However, despite significant advancements in detection of donor-specific human leukocyte antigen antibodies, improved immunosuppression and patient management, the durability of this life-saving therapy has not improved. This results in increased morbidity and mortality as well as increased cost to the healthcare system.

RECENT FINDINGS

The identification of immune-pathogenic pathways responsible for allograft failure coupled with targeted interventions will represent one of the most important future objectives of transplant immunologist and physicians. The development of sensitive donor-specific antibody (DSA) detection techniques and advancements in renal allograft pathology assessments have revealed the importance of humoral immunity in mediating allograft failure. This is especially true for complement activating DSAs (C1q+).

SUMMARY

Our current understanding suggests that reduction of immunosuppressive medications or medication nonadherence is now the major causes of DSA development and attendant pathology. Other important factors in initiation of de-novo DSA production include viral infections, human leukocyte antigen-DR/DQ mismatches and autoimmune diseases. Therapies aimed at antibody reduction, B-cell depletion and modification of the complement system will likely usher in new therapeutic approaches for prevention and treatment of DSA-mediated allograft dysfunction.

Achieving incompatible transplantation through desensitization: current perspectives and future directions

The application of life-saving transplantation is severely limited by the shortage of organs, and histoincompatibility. To increase transplant rates in sensitized patients, new protocols for HLA and blood type incompatible (ABOi) desensitization have emerged. These approaches require significant desensitization using intravenous immunoglobulin, rituximab and plasma exchange. In addition, the development of donor-specific antibody responses post transplant is the major cause of allograft failure with return to dialysis. This increases patient morbidity/mortality and cost. Immunotherapeutic agents used for desensitization evolved from drug development in oncology and autoimmune diseases. Currently, there is a renaissance in development of novel drugs likely to improve antibody reduction in transplantation. These include agents that inactivate IgG molecules, anticytokine antibodies, costimulatory molecule blockade, anticomplement agents and therapies aimed at the plasma cell.

Longitudinal analysis of T and B cell phenotype and function in renal transplant recipients with or without rituximab induction therapy

Background

Prevention of rejection after renal transplantation requires treatment with immunosuppressive drugs. Data on their in vivo effects on T- and B-cell phenotype and function are limited.

Methods

In a randomized double-blind placebo-controlled study to prevent renal allograft rejection, patients were treated with tacrolimus, mycophenolate mofetil (MMF), steroids, and a single dose of rituximab or placebo during transplant surgery. In a subset of patients, we analyzed the number and phenotype of peripheral T and B cells by multiparameter flow cytometry before transplantation, and at 3, 6, 12, and 24 months after transplantation.

Results

In patients treated with tacrolimus/MMF/steroids the proportion of central memory CD4⁺ and CD8⁺ T cells was higher at 3 months post-transplant compared to pre-transplant levels. In addition, the ratio between the percentage of central memory CD4⁺ and CD4⁺ regulatory T cells was significantly higher up to 24 months post-transplant compared to pre-transplant levels. Interestingly, treatment with tacrolimus/MMF/steroids resulted in a shift toward a more memory-like B-cell phenotype post-transplant. Addition of a single dose of rituximab resulted in a long-lasting B-cell depletion. At 12 months post-transplant, the small fraction of repopulated B cells consisted of a high percentage of transitional B cells. Rituximab treatment had no effect on the T-cell phenotype and function post-transplant.

Conclusions

Renal transplant recipients treated with tacrolimus/MMF/steroids show an altered memory T and B-cell compartment post-transplant. Additional B-cell depletion by rituximab leads to a relative increase of transitional and memory-like B cells, without affecting T-cell phenotype and function.

Trial Registration

ClinicalTrials.gov NCT00565331

Clinical impact of H-Y alloimmunity

H-Y antigens are a group of minor histocompatibility antigens encoded on the Y-chromosome with homologous H-X antigens on the X-chromosome. The disparate regions of the H-Y antigens are highly immunogenic and play an important role in understanding human alloimmunity. In this review, we investigate the history of H-Y antigen discovery along with their critical contributions in transplantation and pregnancy. In hematopoietic cell transplantation, male recipients with female donors who become seropositive for B-cell responses as H-Y antibodies following transplantation have increased rates of chronic graft-versus-host disease and decreased rates of relapse. Conversely, female patients who receive male kidney allografts are more likely than other gender combinations to develop H-Y antibodies and reject their allografts. Finally, in the setting of pregnancy, mothers who initially gave birth to boys are more likely to have subsequent pregnancy complications, including miscarriages, in association with H-Y antibody development. H-Y antigens continue to serve as a model for alloimmunity in new clinical scenarios. Our development of more sensitive antibody detection and next-generation DNA sequencing promises to further advance our understanding and better predict the clinical consequences of alloimmunity.

Tocilizumab in the treatment of rheumatoid arthritis and beyond

Rheumatoid arthritis (RA) is a systemic inflammatory disease characterized by joint pain, swelling, stiffness, and progressive destruction of the small joints of the hands and feet. Treatment of RA has improved over the past decade. With multiple cytokines well-known now to play a role in the pathogenesis of RA, including tumor necrosis factor alpha, interleukin (IL)-1β, and IL-6, many targeted biological treatments against these cytokines have emerged, changing the treatment of this disease. Tocilizumab (TCZ) is a recombinant humanized monoclonal antibody against the IL-6 receptor and has been approved in many countries, including the United States, for the treatment of moderate to severe RA in patients who have not adequately responded to one or more disease-modifying antirheumatic drugs (DMARDs) or cannot tolerate other approved drug classes for RA. The aim of this review is to discuss the role of IL-6 in RA, and to provide an overview of the mode of action, pharmacokinetics, and safety of TCZ. Furthermore, efficacy studies of TCZ as both monotherapy and combination therapy will be evaluated. There have been several important clinical trials evaluating the efficacy and safety of TCZ in RA patients; this review summarizes this data from 14 key trials with emphasis on Phase III trials. Review of these trials provides strong evidence that its use, both as monotherapy and in combination with methotrexate or other DMARDs, is an effective treatment in reducing the signs and symptoms of RA. TCZ showed tolerable safety but care is required for its use since there are some important safety concerns including elevated liver enzymes, elevated low-density lipoprotein, infections, and gastrointestinal perforations. Additionally, given the efficacy of TCZ in the treatment of RA, this review discusses how TCZ may be beneficial in the treatment of other autoimmune diseases, spinal disease, cardiovascular disease, organ transplantation, and malignancies where elevated levels of IL-6 may play a role in the pathogenesis of these diseases.

B-cell-mediated strategies to fight chronic allograft rejection

Solid organs have been transplanted for decades. Since the improvement in graft selection and in medical and surgical procedures, the likelihood of graft function after 1 year is now close to 90%. Nonetheless even well-matched recipients continue to need medications for the rest of their lives hence adverse side effects and enhanced morbidity. Understanding Immune rejection mechanisms, is of increasing importance since the greater use of living-unrelated donors and genetically unmatched individuals. Chronic rejection is devoted to T-cells, however the role of B-cells in rejection has been appreciated recently by the observation that B-cell depletion improve graft survival. By contrast however, B-cells can be beneficial to the grafted tissue. This protective effect is secondary to either the secretion of protective antibodies or the induction of B-cells that restrain excessive inflammatory responses, chiefly by local provision of IL-10, or inhibit effector T-cells by direct cellular interactions. As a proof of concept B-cell-mediated infectious transplantation tolerance could be achieved in animal models, and evidence emerged that the presence of such B-cells in transplanted patients correlate with a favorable outcome. Among these populations, regulatory B-cells constitute a recently described population. These cells may develop as a feedback mechanism to prevent uncontrolled reactivity to antigens and inflammatory stimuli. The difficult task for the clinician, is to quantify the respective ratios and functions of “tolerant” vs. effector B-cells within a transplanted organ, at a given time point in order to modulate B-cell-directed therapy. Several receptors at the B-cell membrane as well as signaling molecules, can now be targeted for this purpose. Understanding the temporal expansion of regulatory B-cells in grafted patients and the stimuli that activate them will help in the future to implement specific strategies aimed at fighting chronic allograft rejection.

Transplantation: rituximab induction only for sensitized kidney recipients?

In contrast to earlier studies that showed a beneficial influence of rituximab on HLA antibody production after kidney transplantation, a recent report by Ashimine et al. questions such an effect. That previous studies included presensitized patients who are more prone to antibody development, might explain this controversy.

AMP-activated protein kinase as a promoting factor, but complement and thrombin as limiting factors for acquisition of cytoprotection: implications for induction of accommodation

Accommodation has been termed as a condition without graft rejection even in the presence of antidonor antibody. We previously reported an in vitro accommodation model, which demonstrated that preincubation of A/B antigen-expressing endothelial cells with anti-A/B antibody resulted in ERK inactivation followed by resistance to complement-mediated cytotoxicity through the induction of complement regulatory genes. However, under the in vivo condition, the effects of complement and coagulation system cannot be ignored. The purpose of this study is to find effective ways to navigate accommodation by exploring the relevant signal transduction. Preincubation with a low level of complement or thrombin failed to induce resistance to complement-mediated cytotoxicity. AMP-activated protein kinase (AMPK) activators such as resveratrol, AICAR and metformin protected endothelial cells against complement-mediated cytotoxicity through the increase in CD55, CD59, haem oxygenase-1 (HO-1) and ferritin heavy chain (ferritin H) genes, all of which were attenuated by AMPKα knock-down. Resveratrol counteracted the inhibitory effect of pretreated complement and thrombin on acquisition of resistance to complement-mediated cytotoxicity through AMPKα. AMPK regulation in endothelial cells could become the potential strategy to induce accommodation in clinical pro-inflammation and pro-coagulation.

Neither pre-transplant rituximab nor splenectomy affects de novo HLA antibody production after renal transplantation

The long-term effect of rituximab and splenectomy on de novo HLA antibody production and chronic antibody-mediated rejection after renal transplantation is uncertain. In order to gain insight on this, we studied 92 ABO-incompatible and 228 ABO-identical/compatible consecutive renal transplant patients and determined their de novo HLA antibody production and graft outcome. Patients with pretransplant donor-specific antibodies had been excluded. ABO-incompatible transplants included 30 recipients treated with rituximab, 51 by splenectomy, or 11 with neither, due to low anti-A or -B antibody titer. Graft survival in ABO-identical/compatible patients (97.7% at 5 years) was significantly higher than in ABO-incompatible (87.0% at 5 years), rituximab (96.7% at 3 years), or splenectomy (85.7% at 5 years) patients. Only four patients had clinical chronic antibody-mediated rejection (two each identical/compatible and incompatible). There was no significant difference in prevalence of de novo HLA antibody, including donor-specific and nondonor-specific antibodies among ABO-identical/compatible patients (13.9%), patients receiving rituximab (14.3%) or splenectomy (13.2%), or among those receiving cyclosporine, tacrolimus, mycophenolate mofetil, mizoribine, and everolimus. Renal function remained stable in most recipients with de novo HLA antibody. Thus, neither pretransplant splenectomy nor rituximab treatment has an inhibitory effect on de novo HLA antibody production during medium-term follow-up. Further study on long-term effects is needed.

A single dose of rituximab does not deplete B cells in secondary lymphoid organs but alters phenotype and function

A single dose of the anti-CD20 monoclonal antibody rituximab induces a nearly complete B cell depletion in peripheral blood, but not in secondary lymphoid organs. Modulation of this remaining B cell population due to rituximab treatment may contribute to the therapeutic effects of rituximab. To assess the in vivo effects of rituximab we used lymph nodes (LNs) collected during renal transplant surgery in patients who had received rituximab 4 weeks earlier in preparation for an ABO-incompatible transplantation. Rituximab treatment resulted in a lower percentage of naïve (IgD(+)CD27(-)) and a higher percentage of switched memory (IgD(-)CD27(+)) B cells. Remarkably, transitional (CD24(++)CD38(++)) B cells were virtually lacking in the LNs of rituximab-treated patients. Moreover, LN-derived B cells from rituximab-treated patients produced different amounts of various Ig-subclasses after anti-CD40/IL-21 stimulation ex vivo. Finally, after stimulation of allogeneic T cells with LN-derived B cells from rituximab-treated patients, the proliferated T cells showed a decreased production of IL-17. In conclusion, after treatment with rituximab there remains a B cell population with different functional capacities. Consequently, the effect of rituximab on the immune response will not only be determined by the extent of B cell depletion, but also by the functional properties of the remaining B cells.

Incompatible kidney transplantation: a brief overview of the past, present and future

Live kidney donor transplantation across immunological barriers, either blood group or positive crossmatch [ABO- and human leucocyte antigens (HLA)-incompatible kidney transplantation, respectively], is now practised widely across many transplant centres. This provides transplantation opportunities to patients that hitherto would have been deemed contra-indicated and would subsequently have waited indefinitely for a suitably matched kidney. Protocols have evolved with time as experience has grown and now a variety of desensitization strategies are currently practised to overcome such immunological barriers. In addition, desensitization protocols are complemented by kidney paired donation exchange schemes and therefore incompatible patients now have strategies to either confront or bypass immunological barriers, respectively. As the field expands it is clear that non-transplant clinicians will be exposed to incompatible kidney transplant recipients outside of experienced centres. It is therefore timely to review the evolution of practice that have led to current desensitization modalities, contrast protocols and outcomes of current regimens and speculate on future direction of incompatible kidney transplantation.

Transient removal of CD46 is safe and increases B-cell depletion by rituximab in CD46 transgenic mice and macaques

We have developed a technology that depletes the complement regulatory protein (CRP) CD46 from the cell surface, and thereby sensitizes tumor cells to complement-dependent cytotoxicity triggered by therapeutic monoclonal antibodies (mAbs). This technology is based on a small recombinant protein, Ad35K++, which induces the internalization and subsequent degradation of CD46. In preliminary studies, we had demonstrated the utility of the combination of Ad35K++ and several commercially available mAbs such as rituximab, alemtuzumab, and trastuzumab in enhancing cell killing in vitro as well as in vivo in murine xenograft and syngeneic tumor models. We have completed scaled manufacturing of Ad35K++ protein in Escherichia coli for studies in nonhuman primates (NHPs). In macaques, we first defined a dose of the CD20-targeting mAb rituximab that did not deplete CD20-positive peripheral blood cells. Using this dose of rituximab, we then demonstrated that pretreatment with Ad35K++ reconstituted near complete elimination of B cells. Further studies demonstrated that the treatment was well tolerated and safe. These findings in a relevant large animal model provide the rationale for moving this therapy forward into clinical trials in patients with CD20-positive B-cell malignancies.

IVIG and rituximab for treatment of chronic antibody-mediated rejection: a prospective study in paediatric renal transplantation with a 2-year follow-up

Chronic antibody-mediated rejection (AMR) is the major cause of late renal allograft loss. There is, however, no established treatment for this condition. We report the results of a prospective pilot study on an antihumoral therapy (AHT) consisting of high-dose intravenous immunoglobulin G (IVIG) and rituximab in 20 paediatric renal transplant recipients. Donor-specific HLA antibodies (HLA DSA) were quantified by Luminex-based bead array technology. Loss of eGFR decreased significantly from 7.6 ml/min/1.73 m² during 6 months prior to AHT to 2.1 ml/min/1.73 m² (P = 0.0013) during 6 months after AHT. Fourteen patients (70%) responded: nine of nine patients (100%) without and five of 11 (45%) with transplant glomerulopathy (P = 0.014). C4d positivity in PTC decreased from 40 ± 18.5% in the index biopsy to 11.6 ± 12.2% (P = 0.002) in the follow-up biopsy. In four of nine biopsies (44%) C4d staining turned negative. During 2 years of follow-up, the median loss of eGFR in each of the four 6-month periods remained significantly lower compared with prior to AHT. Class I DSA declined in response to AHT by 61% (p = 0.044), class II DSA by 63% (p = 0.033) 12 months after intervention. AHT with IVIG and rituximab significantly reduces or stabilizes the progressive loss of transplant function in paediatric patients with chronic AMR over an observation period of 2 years, apparently by lowering circulating DSA and reducing intrarenal complement activation.

Effects of sotrastaurin, mycophenolic acid and everolimus on human B-lymphocyte function and activation

Humoral rejection processes may lead to allograft injury and subsequent dysfunction. Today, only one B-cell-specific agent is in clinical use and the effects of standard and new immunosuppressant substances on B-cell activation and function are not fully clarified. The impact of sotrastaurin, mycophenolic acid and everolimus on human B-lymphocyte function was assessed by analysing proliferation, apoptosis, CD80/CD86 expression and immunoglobulin and IL-10 production in primary stimulated B cells. In addition, B-cell co-cultures with pre-activated T cells were performed to evaluate the effect of the different immunosuppressive agents on T-cell-dependent immunoglobulin production. Sotrastaurin did not inhibit B-cell proliferation, CD80/CD86 expression, and IgG production and had only minor effects on IgM levels at the highest concentration administered. In contrast, mycophenolic acid and everolimus had strong effects on all B-cell functions in a dose-dependent manner. All immunosuppressive agents caused decreased immunoglobulin levels in T-cell-dependent B-cell cultures. The data provided here suggest that mycophenolic acid and everolimus, but not sotrastaurin, are potent inhibitors of human B-lymphocyte function and activation.

HLA class I: an unexpected role in integrin β4 signaling in endothelial cells

The production of anti-donor antibodies to HLA class I and class II antigens following transplantation is associated with development of transplant vasculopathy and graft loss. Antibodies against HLA class I (HLA-I) molecules are thought to contribute to transplant vasculopathy by triggering signals that elicit the activation and proliferation of endothelial cells. The proximal molecular events that regulate HLA-I dependent signal transduction are not well understood. We demonstrated a mutual dependency between HLA-I and integrin β4 to stimulate signal transduction and cell proliferation. Similarly, we found that integrin β4-mediated cell migration was dependent upon its interactions with HLA-I molecules. Since integrin β4 has been implicated in angiogenesis and tumor formation, associations between integrin β4 and HLA-I may play an important role in cancer. Further characterization of interactions between HLA-I and integrin β4 may lead to the development of therapeutic strategies for the treatment and prevention of chronic allograft rejection and cancer.

The impact of donor-specific anti-HLA antibodies on late kidney allograft failure

Despite improvements in outcomes of renal transplantation, kidney allograft loss remains substantial, and is associated with increased morbidity, mortality and costs. Identifying the pathologic pathways responsible for allograft loss, and the attendant development of therapeutic interventions, will be one of the guiding future objectives of transplant medicine. One of the most important advances of the past decade has been the demonstration of the destructive power of anti-HLA alloantibodies and their association with antibody-mediated rejection (ABMR). Compelling evidence exists to show that donor-specific anti-HLA antibodies (DSAs) are largely responsible for the chronic deterioration of allografts, a condition previously attributed to calcineurin inhibitor toxicity and chronic allograft nephropathy. The emergence of sensitive techniques to detect DSAs, together with advances in the assessment of graft pathology, have expanded the spectrum of what constitutes ABMR. Today, subtler forms of rejection--such as indolent ABMR, C4d-negative ABMR, and transplant arteriopathy--are seen in which DSAs exert a marked pathological effect. In addition, arteriosclerosis, previously thought to be a bystander lesion related to the vicissitudes of aging, is accelerated in ABMR. Advances in our understanding of the pathological significance of DSAs and ABMR show their primacy in the mediation of chronic allograft destruction. Therapies aimed at B cells, plasma cells and antibodies will be important therapeutic options to improve the length and quality of kidney allograft survival.