Summary of FDA Antibody-Mediated Rejection Workshop

Authors

  • P. Archdeacon,

    1. Division of Special Pathogen and Transplant Products, Office of Antimicrobial Products, Center for Drug Evaluation and Research, FDA, Silver Spring, MD
    Search for more papers by this author
  • M. Chan,

    1. Division of Immunology and Hematology Devices, Office of In Vitro Diagnostic Devices Evaluation and Safety, Center for Devices and Radiologic Health, FDA, Silver Spring, MD
    Search for more papers by this author
  • C. Neuland,

    1. Gastroenterology and Renal Devices Branch, Division of Reproductive, Abdominal and Radiologic Devices, Office of Device Evaluation, Center for Devices and Radiologic Health, FDA, Silver Spring, MD
    Search for more papers by this author
  • E. Velidedeoglu,

    1. Division of Special Pathogen and Transplant Products, Office of Antimicrobial Products, Center for Drug Evaluation and Research, FDA, Silver Spring, MD
    Search for more papers by this author
  • J. Meyer,

    1. Division of Special Pathogen and Transplant Products, Office of Antimicrobial Products, Center for Drug Evaluation and Research, FDA, Silver Spring, MD
    Search for more papers by this author
  • L. Tracy,

    1. Division of Biometrics VII, Office of Biostatistics, Center for Drug Evaluation and Research, FDA, Silver Spring, MD
    Search for more papers by this author
  • M. Cavaille-Coll,

    1. Division of Special Pathogen and Transplant Products, Office of Antimicrobial Products, Center for Drug Evaluation and Research, FDA, Silver Spring, MD
    Search for more papers by this author
  • S. Bala,

    1. Division of Special Pathogen and Transplant Products, Office of Antimicrobial Products, Center for Drug Evaluation and Research, FDA, Silver Spring, MD
    Search for more papers by this author
  • A. Hernandez,

    1. Division of Special Pathogen and Transplant Products, Office of Antimicrobial Products, Center for Drug Evaluation and Research, FDA, Silver Spring, MD
    Search for more papers by this author
  • R. Albrecht

    1. Division of Special Pathogen and Transplant Products, Office of Antimicrobial Products, Center for Drug Evaluation and Research, FDA, Silver Spring, MD
    Search for more papers by this author

Corresponding author: Renata Albrecht, Renata.Albrecht@fda.hhs.gov

Abstract

The Food and Drug Administration (FDA) held an open public workshop in June 2010 to discuss the current state of science related to antibody-mediated rejection (AMR) in kidney transplantation. Desensitization, acute AMR and chronic AMR (CAMR) were considered in the context of clinical trial design. Participants discussed experiences with HLA antibody detection and quantitation and the utility of monitoring donor-specific antibodies (DSAs) to inform the management of patients with AMR. The role for animal models was discussed. Diagnostic and prognostic features of histology were presented, followed by discussion of sensitivity and specificity of various criteria. The published literature on treatment of acute AMR was summarized, which consisted of case series and limited data from controlled clinical trials. Considerations for future clinical trials were presented, including endpoints and statistical evaluations of outcome. Although many issues need further consideration, the meeting enabled an important exchange of ideas between experts in the field.

Abbreviations: 
FDA

Food and Drug Administration

AMR

antibody-mediated rejection

CAMR

chronic antibody-mediated rejection

DSA

donor-specific antibody

AST

American Society of Transplantation

ASTS

American Society of Transplant Surgeons

TTS

The Transplantation Society

PhRMA

Pharmaceutical Research and Manufacturers of America

CBER

Center for Biologics Evaluation and Research

CDC

complement-dependent lymphocytotoxicity

ELISA

enzyme-linked immunosorbent assay

MHC

major histocompatibility complex

PTC

peritubular capillary

PP

plasmapheresis

IVIG

intravenous immune globulin

RCT

randomized clinical trial

SOC

standard of care

CEP

clinical endpoint

SEP

surrogate endpoint

TG

transplant glomerulopathy

GFR

glomerular filtration rate

Introduction

Acute antibody-mediated rejection (AMR) events are relatively uncommon occurrences in patients following kidney transplantation (1,2). Among highly sensitized patients, however, the incidence of acute AMR exceeds 25% (3–5). Moreover, the contribution of antibody-mediated injury to late graft loss has been increasingly recognized (6,7). While various strategies have been used to manage AMR, few have been tested in controlled clinical trials and no therapies are currently approved by FDA for this use. Therefore, this represents an area of unmet medical need for transplant patients.

On June 28 and 29, 2010, at the recommendation of the transplant community, the Food and Drug Administration (FDA) held a public workshop to review the current state of knowledge and discuss clinical trial elements relevant to the treatment of acute AMR (8).

Desensitization, prevention of AMR, and chronic AMR (CAMR) were also discussed.

The 2-day workshop was planned by a cross-center FDA steering committee and also by representatives from the American Society of Transplantation (AST), the American Society of Transplant Surgeons (ASTS), the Transplantation Society (TTS) and Pharmaceutical Research and Manufacturers of America (PhRMA). During the workshop, invited presentations were given by experts from academia, industry, government and a patient representative. The purpose of this summary is to highlight scientific, clinical and regulatory issues discussed during the course of the workshop.

Measurement of DSAs

The current state of knowledge of donor-specific antibody (DSA) tests and their potential use in drug therapy trials were discussed. HLA antibody tests are regulated by the Center for Biologics Evaluation and Research (CBER) and the Center for Devices and Radiological Health (CDRH). These tests are class II devices which require premarket clearance prior to commercial distribution. The HLA antibody tests are qualitative tests and are subdivided into cell-based and solid phase tests. Cell-based tests include complement-dependent lymphocytotoxity (CDC) and flow cytometric cross-match assays whereas solid phase tests include enzyme-linked immunosorbent assays (ELISAs) and multianalyte bead tests by flow cytometry or Luminex technology. While some CDC and solid phase assays for the detection of HLA antibodies have been cleared by FDA, no cell-based flow cytometric assay has been cleared for that intended use. The advantages of the solid phase tests include high sensitivity, specificity and high throughput. The cell-based flow cytometric and solid phase HLA antibody tests return results measured in arbitrary units (such as mean fluorescent intensity [MFI] for Luminex and mean channel shift [mcs] for the cell-based flow cytometry cross-matches). Although the cell-based flow cytometric assays and solid phase assays have either not been cleared by FDA or have been cleared as qualitative tests only, some investigators have attempted to determine whether additional information may be derived by considering the numeric values reported by the assays.

The participants reviewed various data regarding the clinical relevance of antibodies detected by the solid phase and cell-based flow cytometric tests. Some data indicate that those patients with detectable DSAs who do not experience AMR demonstrate similar graft survival as patients without DSAs who do not experience AMR (9). These findings imply that, with perhaps the exception of those DSAs detected by CDC cross-matching, detectable DSAs are not necessarily clinically relevant—the clinical relevance of such DSA remains uncertain until the patient experiences AMR. On the other hand, other data were also discussed which suggested a striking correlation between patients with higher levels of pre-existing DSAs detectable at time of transplantation and increased risk of AMR (4,10). While the optimal management strategy of a given transplant patient with detectable pretransplant DSAs is unclear, current approaches to quantifying DSAs appear to improve stratification of risk for AMR. Data were also discussed which suggested a correlation between detectable de novo DSA and increased late graft failure; those data regarding a risk associated with de novo DSA, however, did not demonstrate an increased risk for higher levels of de novo DSA compared to lower levels of de novo DSA (11,12).

The use of HLA antibody tests for quantitation purposes, a use for which they are not FDA cleared, is confounded by issues affecting assay reproducibility. For instance, data presented suggested that a lack of uniformity in the amount of antigen on the solid phase elements within an assay and between lots complicates the comparability of results (13). Other sources of variability include a lack of common laboratory protocols and differences in fluid handling. Some potential approaches to reducing the variability were discussed (including instituting common protocols, replacing manual fluid handling with a robotic system, and reducing of intertechnician variability with additional technical training).

With regard to future trials, participants discussed whether the HLA antibody tests currently available could be used to characterize patient populations as high risk or low risk. The participants suggested that a standardized test performed by a central laboratory could be used for enrolling patients and also recommended collection of data such that HLA antibody test kits could be FDA cleared for semiquantitative or quantitative use. Participants emphasized that it is essential to develop assays which generate reproducible results from site to site and over time both for identification of the patient population to be enrolled into clinical trials and also for identification of similar patients outside of the context of the clinical trials. There was discussion that the use of common protocols would significantly improve the consistency of test performance between laboratories and that establishing standards for interpreting and reporting data is essential.

Animal Models of Transplantation (Proof of Concept)

Animal models of transplantation may provide important evidence supporting proof of concept. The participants discussed the scientific value of animal models related to AMR and the role such models should play in developing related therapies. The merits and limitations of several models of acute and chronic AMR in rodents, α-gal knockout miniature pigs and nonhuman primates were discussed and are summarized in Table 1 (14–16). Small animals are often better suited for isolating biologic pathways as they are more amenable to genetic manipulation. In addition, one can more easily power small animal studies to generate statistically interpretable data. Large animals, however, have greater similarities to humans with regard to anatomy and major histocompatibility complex (MHC) biology. While imperfect, both small and large animal models provide opportunities to better understand the science underlying potential therapies directed against AMR.

Table 1.  Characteristics of small and large animal models of transplantation
Animal SpeciesAdvantagesDisadvantages
  1. NHP = nonhuman primates; AMR = antibody-mediated rejection.

Small animals
 Rodents• Primarily vascularized grafts (kidneys and hearts) develop pathology consistent with AMR such as development of MHC-specific antibody, C4d deposition, endothelial damage, memory B cell and plasma cell differentiation
• MHC targets are defined, although endothelial MHC class II expression is different; this limitation is overcome by use of transgenic mice which express HLA class II antigens on their endothelium.
• Mechanisms of antibody formation, class switching, complement biology and coagulation are similar
• Multiple transgenic possibilities
• Useful to define the biological relevance of pathways and mechanisms due primarily to the ability to manipulate the animals genetically or use other means to isolate pathways, and the ability to repeat the experiment in a statistically meaningful way
• Inexpensive
• Too easy to induce tolerance in mice; Strain-specific spontaneous acceptance
• Lack of HLA class II antigen expression on the surface of vascular endothelial cells may be responsible for easy induction of tolerance in mice. This leads to the absence of capillaritis/microvascular disease, important component of AMR observed in humans.
• Naïve animals are insufficiently complex with regard to immune recruitment, repertoire breadth, and heterologous T cell help to anticipate human system responses.
• Graft function may be difficult to assess
• Difficult to model multidrug regimens, pheresis or other complex regimens.
Large animals
 Miniature pigs• Compatible anatomy and histology
• Antibody and complement biology similar
• Similar pattern of class II expression
• Similar biologic complexity
• MHC types defined in certain herds and gal knockout miniature swine model available
• Orthotopic transplantation and functional read-outs are available
• Availability of reagents for study of cell surface antigens
• Gal negative miniature pigs are available that allows gal+ve graft into gal negative animals
• PLHV 1 herpes virus behaves very similar to Epstein–Barr virus in that PTLD-type response can be generated
• Endothelium more reactive/vasospastic, particularly in lung transplantation model
• Express α-1,3-galactosyltransferase gene (gal) which is unlike humans
• Although reagents are available for studying cell surface antigens they are not as many as for mice or nonhuman primates
• Phylogenic differences lead to different responses to several common drugs e.g. very sensitive to calcineurin inhibitors
• Humanized molecules typically do not cross-react
 Nonhuman primates• Biological similarity to humans
• Major histocompatibility gene structure (rhesus>cynomolgus) including class II expression
• ABO biology
• Chronic rejection in heart and kidney associated with AMR that mimics human situation (rejection is histologically and temporally similar)
• Anatomical similarity of the major organs
• Cross reactivity and specificity of drugs especially humanized molecules such as monoclonal antibodies and fusion proteins
• Similar toxicity profiles to human drugs
• MHC definition and reagents (e.g. tetramers, beads) emerging
• Acute AMR has not been well modeled in NHPs
• Ethical and practical concerns limit size of studies

A stepwise evaluation of proof of concept in vitro to small and/or large animals was suggested by participants for new molecules. However, for products previously approved for nontransplant indications, participants had differing opinions on the role for proof of concept studies. Some emphasized the importance of establishing the likelihood of benefit in animal models prior to studying humans, while others suggested that such studies should not be considered necessary in all cases.

The pharmacology and toxicology of new drug and biologic products are always evaluated in animals prior to their study in humans. For products previously approved for use in other nontransplant indications, some participants proposed that existing human data may supersede the need for additional animal studies to evaluate safety.

Diagnostic Criteria

The three cardinal features for the diagnosis of acute AMR, as described by the Banff criteria, were reviewed and include (17)

  • • acute tubular injury with neutrophils and/or mononuclear cells in the peritubular capillaries (PTC) and/or glomeruli;
  • • interaction of antibody with tissue, (e.g. presence of C4d)
  • • serologic evidence of donor-specific antibodies (DSA)

The presence of graft dysfunction distinguishes clinical AMR from subclinical AMR.

Discussion ensued regarding the specificity and sensitivity of each component of the triad. In particular, the conversation focused on the utility and limitations of C4d staining in various contexts. Data were presented which showed that immunofluorescence on frozen tissue is more sensitive than immunohistochemistry on paraffin-processed tissue for C4d, which may have important practical implications when the definitive biopsy evaluation is performed locally versus centrally (18). In addition, while AMR events that occur early after transplantation (within the first 3 months) typically exhibit positive C4d staining, AMR events that occur thereafter often stain negative for C4d (6). Some participants felt that incorporating the C4d diagnostic criterion into clinical trial designs was important, while others suggested that newer diagnostic tools to indicate antibody interaction with the tissue, such as those based on transcript measurement may ultimately supersede the use of C4d (19).

Participants noted that early acute and late acute AMR events have important dissimilarities beyond differences in the presence of C4d staining. Perhaps because high-risk transplant recipients almost invariably receive lytic induction, early acute AMR events are typically pure antibody-mediated phenomena whereas late acute AMR events more commonly exhibit a significant cellular component (20). Differences may also exist in the underlying etiologies of early and late acute AMR (20). The majority of acute AMR events presenting in highly sensitized patients occur in the first month after transplantation; late acute AMR events, on the other hand, are commonly associated with medical nonadherence and/or formation of de novo antibodies (20). Some data presented suggested that the long-term prognoses of late acute AMR episodes are worse than those of early acute AMR episodes.1

The decision to employ a particular set of diagnostic criteria in a given trial design will have some ramifications on applicability of the results to the overall AMR population.

Current Approaches to the Treatment of AMR

The participants discussed the natural history of untreated acute AMR and the effectiveness of some reported interventions (see Table 2). The literature reviewed has several limitations: the studies predominately examined interventions aimed at early acute AMR events (those occurring within the first 3 months of transplant); the studies relied on different criteria to diagnose acute AMR; and the majority of the studies were retrospective, lacked control groups and/or examined interventions consisting of multiple agents instituted simultaneously with changes in maintenance immunosuppression, thereby complicating assessments of the contribution of each agent to overall efficacy. Finally, though these studies largely report positive early outcomes, they lack sufficient data regarding long-term follow-up. Despite the limitations, however, the available data informed discussions regarding possible future trial designs.

Table 2.  Published literature on the different treatment modalities of acute AMR in kidney transplantation and the outcomes
PublicationNTreatment regimenOutcomes
  1. PP = plasmapheresis; IVIG = intravenous immune globulin; rATG = rabbit antithymocyte globulin (Thymoglobulin®); ATG = antithymocyte globulin; OKT3 = muromonab; GFR = glomerular filtration rate.

  2. aOne patient was treated with PP alone and another with IVIG alone.

  3. bPatients not responding to initial treatment with high-dose corticosteroids or ATG and pheresis.

  4. cOne patient received five doses of rituximab and another received three doses.

  5. dIn addition to this regimen, four patients were treated with ATG and one other patient received IVIG.

  6. eInitially, recipients received immunoadsorption daily for 3 days followed by treatment at regular intervals (every 3 days; up to 6 weeks). All patients received either intravenous corticosteroids or ATG depending on the Banff score.

  7. fOption of immunoadsorption rescue after 3 weeks. Initially, recipients received daily treatment (3 days) followed by treatment at regular intervals (every 3 days; up to 6 weeks). All patients on cyclosporine A were converted to tacrolimus. Patients with borderline lesion or Banff type I cellular rejection received high-dose steroids, recipients with Banff II rejection antilymphocyte antibody.

  8. gOne patient with severe AMR uncontrolled by PP/IVIG/anti-CD20 therapy underwent splenectomy.

Jordan et al. (22)7IVIG 2g/kg × 1 dose (some patients received up to 3 doses, two patients received concomitant cyclophosphamide)Follow-up: up to 5 years
reversibility: 100% graft survival: 100% creatinine: 1.2–1.7 mg/dL
Pascual et al. (23)5PP once daily for 5 days (range 4–7 days), then every other day for 5 days, and IVIG 0.4 g/kg × 1 dose maintenance: tacrolimus + mycophenolate mofetil + corticosteroidsFollow-up: 20 months reversibility: 100% graft survival: 100% creatinine: 1.2 ± 0.3 mg/dL
Crespo et al. (36)19PP once daily × 5 days (range 4–7 days), IVIG 0.4 g/kg x× 1 dose, a d maintenance: tacrolimus + mycophenolate mofetil + corticosteroidsFollow-up: 29 months reversibility: 90% graft survival: 80% creatinine: 1.5 ± 0.4 mg/dL
Montgomery et al. (37)3PP every other day × 12 days (range 2–31 days), and IVIG or CMV IVIG 100 mg/kg × 1 dose maintenance: tacrolimus + mycophenolate mofetil + corticosteroidsFollow-up: 30 months Reversibility: 100% graft survival: 90% creatinine: 1.6 ± 0.5 mg/dL
Rocha et al. (38)16PP once daily × 4 days (range 3–6 days), and IVIG 2 g/kg × 3 dosesaReversibility: 94% follow-up: 569 days graft survival: 81% creatinine: 1.6 mg/dL
Shah et al. (39)5PP every other day × 7 days (± 6 days), and rATG 0.75–1 mg/kg/day × 6 doses maintenance: tacrolimus + mycophenolate mofetil + corticosteroidsFollow-up:12 months reversibility: 85% graft survival: 85% creatinine: 1.5 mg/dL
Becker et al. (40)27bRituximab 375 mg/m2× 1 dose methylprednisolone 500 mg once daily × unspecified duration, rATG 1.5 mg/kg/day × unspecified duration, and with or without apheresis maintenance: calcineurin-inhibitor + mycophenolate mofetil + corticosteroidsFollow-up: 605 days reversibility: not reported graft survival: 85%(excluding deaths) creatinine: 0.95 mg/dL
Faguer et al. (41)8PP once daily × 9 days (range 2–17 sessions), rituximab 375 mg/m2 once weekly × 4 weeks,c and methylprednisolone 10 mg/kg/day × 3 doses,d maintenance: tacrolimus + mycophenolate mofetil + corticosteroidsReversibility: 75% follow-up: 10 months graft survival: 75% creatinine: 1.7 mg/dL
Böhmig et al. (42)10 (group A: 5, group B: 5)Group A: tacrolimus + antilymphocyte antibody + immunoadsorption (9–14 sessions)ecompared to group B: tacrolimus + antilymphocyte antibodyfFollow-up: 24 months reversibility: group A = 100%, group B = 20% graft survival: group A = 80%, group B = 20% creatinine: group A = 2 mg/dL, group B = 1.6 mg/dL
Everly et al. (43)6PP unspecified regimen, rituximab 200–500 mg/m2× 1 dose, and bortezomib 1.3–1.5 mg/m2× 4 doses maintenance: tacrolimus + mycophenolate mofetil + corticosteroidsReversibility: 67%
Walsh et al. (44)2PP on days 1, 4, 8, 11, 14, 16 and 18, rituximab 375 mg/m2 on day 1, bortezomib 1.3 mg/m2 on days 1, 4, 8 and 11, methylprednisolone 100 mg on days 1 and 4 and 50 mg on days 8 and 11 maintenance: tacrolimus + mycophenolate mofetil + corticosteroidsReversibility: 100%
Lefaucheur et al. (45)24 (group A: 12 patients enrolled between January 2000 and December 2003, group B: 12 patients enrolled between January 2004 and December 2005)Group A: IVIG 2 g/kg × 4 doses, PP unspecified, rituximab 3.75 mg/m2× 2 doses and methylprednisolone 500 mg × 3 doses compared to
group B: PP once daily × 4 days and IVIG 100 mg/kg/day × 4 doses; followed by IVIG 2 gm/kg every 3 weeks × 4 doses and rituximab 3.75 mg/m2 weekly × 2 dosesg maintenance (both groups): calcineurin-inhibitor + mycophenolate mofetil + corticosteroids
Follow-up: 3 years Graft survival: group A = 50%, group B = 91% GFR: group A = 43 mL/min/1.7m2, group B = 45 mL/min/1.7m2
Brown et al. (46)18PP × 8 sessions (1–3 days apart) maintenance: calcineurin-inhibitor + mycophenolate mofetil + corticosteroidsFollow-up: 5 years graft survival: 78% in responders
mean creatinine: 1.5 mg/dL

Some data from the early 1990s, before the advent of highly sensitive assays to screen for DSAs, suggest that untreated AMR events have a poor prognosis. One study reported that patients who presented with acute rejection, newly detected IgG donor-specific lymphocytotoxins, and marked increases in panel reactive antibody (PRA) experienced 1 year graft survival of 16%, despite treatment for cell-mediated rejection with steroids and OKT3 (21). After the introduction of plasmapheresis (PP) and intravenous immune globulin (IVIG) for the treatment of acute AMR, other small retrospective studies from that era reported 1-year graft survival rates ranging from 67 to 100% (22,23). Participants noted that the mechanisms regarding how IVIG moderates AMR have not been established. In the context of these data, the participants discussed the ethics surrounding the conduct of trials for the treatment of acute AMR: it was suggested that future randomized clinical trials (RCT) should consist of a superiority design in which the investigational treatment is added to standard of care (SOC) and compared to SOC alone. Due to the limited data available to determine appropriate noninferiority (NI) margins, the participants noted that NI trials may not be appropriate for trials intended to support an indication for the treatment of AMR.

While the literature suggests that PP, with or without low dose IVIG, and high-dose IVIG alone have evidence of efficacy for the management of acute AMR, and could be considered as SOC, treatment regimens have not been standardized or optimized. Approaches vary with regard to the amount of replacement volume, types of replacement fluids, number of PP sessions, and dose, timing and formulation of IVIG used. The participants discussed the importance of using a standardized active comparator across centers in future clinical trials.

Other agents (including rituximab, bortezomib and eculizumab) have sometimes been used in conjunction with PP and/or IVIG for the treatment of acute AMR by individuals as part of their practice of medicine, though the contribution of these agents to any overall activity of the regimen has not been demonstrated (see Table 2). Splenectomy has been used as a last resort in cases refractory to medical treatment (24,25). The participants felt that future trial designs should also consider rescue treatments, which could potentially include the addition of these newer agents or interventions, for the management of patients refractory to initial treatment.

All treatment modalities are associated with specific toxicities. The most common complications of PP are related to vascular access and the procedure itself. Cardiovascular side effects have also been reported, but mortality appears low (26). Coagulopathy may be the limiting factor in determining the frequency of PP. IVIG has been associated with renal failure and, in some cases, death. Some events are related to the infusion, but others which are more severe include thromboembolic events. Rituximab has been associated with life-threatening viral, bacterial and fungal infections.

Endpoints for Phase 3 Treatment Trials of AMR

A clinical endpoint (CEP) is an outcome or variable representing a measure of how a patient feels, functions or survives. In renal transplantation, the current gold-standard CEP is patient and graft survival measured at an appropriate time point. A biomarker is an objectively measured characteristic that is evaluated as an indicator of normal biological or pathogenic processes or pharmacologic responses to an intervention. A biomarker may allow for faster, more efficient clinical trials but greatly depends on the quality of data supporting its use and the setting in which applied. A surrogate endpoint (SEP) is a biomarker intended to substitute for a CEP and expected to predict clinical benefit.

Prospective RCTs represent a means to evaluate regimens intended to treat AMR. An RCT designed to demonstrate superiority of a treatment on a CEP (such as patient and graft survival) would demand a large sample size and lengthy follow-up. While the scientific value of such a study would be significant, it would also be expensive and would take years to complete.

Given these challenges and the current treatment needs, the participants discussed the possibility of using an accelerated approval pathway. For products intended to treat severe or life-threatening illnesses, a SEP that is ‘reasonably likely’ to predict a clinical benefit can be used for initial approval (27). Approval under this regulation requires that the product be studied further after approval to confirm clinical benefit. Extending the pivotal trials which relied on a SEP into the postmarketing period to confirm that the intervention resulted in improved patient and/or graft life, for instance, could represent one possible approach.

Potential SEPs were discussed, including glomerular filtration rate (GFR), DSAs and histology. GFR is a potential SEP—the complete or near-complete recovery of GFR after treatment of rejection, for instance, may predict a positive long-term outcome (28). The estimation of GFR from measurements of serum creatinine, however, assumes steady-state renal function. Some kidney transplant patients may require several days or even weeks to achieve state–state renal function. Since AMR often occurs during this time, it may prove difficult to establish the baseline GFRs necessary to conduct a longitudinal analysis of GFR after treatment. Further, while the assay for serum creatinine is highly reproducible, interpatient variability in GFR complicates the use of mean GFRs at a fixed time after treatment as an endpoint when the baseline mean GFRs of the study groups are unknown.

DSAs may also deserve further evaluation as a possible SEP. In a large retrospective study, DSAs post-transplant were shown to have a detrimental impact on graft survival (29). A ‘dose–response’ curve between DSA levels, which correlated with pathology findings of C4d deposition, early after transplant and the potential for AMR has been published (30). DSA levels have also been shown to drop in response to treatment for AMR and patients without a sustained or significant improvement do significantly worse (31). Questions were raised regarding timing and change in DSA level, the meaning of rebound antibodies after treatment whether they are persistent or transient, and which DSA(s) should be measured.

Another potential SEP is histology information obtained from biopsies. Suggested biopsy endpoints included the presence or absence of inflammatory cells, C4d deposition, return to normal of the endothelium and presence or absence of transplant glomerulopathy (TG) along with exploratory endpoints of return to normal of signaling proteins and changes in gene expression. Biopsies which stain positive for C4d positive within the first year after transplant have been shown to be a predictor of graft loss and later TG (32,33). C4d deposition plus evidence of TG together have a worse prognosis in terms of survival than either one alone (34). Potential issues relating to use of biopsies include missing or incomplete data, sampling and technique errors, measures of quantification and subjective interpretation.

The discussion of these various potential SEPs suggested that each had its strengths and limitations. Given that reliance on a single SEP may not allow prediction of clinical outcome in every context, approaches to constructing a composite SEP comprised GFR, DSAs and histology were also discussed. The use of either a single or composite SEP to support the accelerated approval of a new product, however, is predicate on the review of data demonstrating that the proposed SEP is ‘reasonably likely’ to predict clinical benefit.

Experiences with Desensitization/Prevention of AMR

Considerations for clinical trials designed to evaluate therapies related to desensitization of highly sensitized transplant candidates and prevention of AMR among high-risk transplant recipients constituted another focus of discussion. Desensitization might be considered to represent those interventions aimed at changing measures of pretransplant DSA levels so that patients may proceed to transplant, while prevention might be considered to represent those interventions before, during and/or after transplant that are aimed at decreasing the incidence of AMR.

Some recent experiences with transplanting highly sensitized patient were presented. Preliminary data suggest that individual investigators have encountered some success at impacting pretransplant DSA levels and preventing acute early AMR.2,3 None of the data, however, were derived from RCTs. The participants agreed that well-designed RCTs are needed to evaluate the hypotheses raised by these small case series reports.

Possible approaches to desensitization trials were discussed. To the degree that the decision to transplant a patient is based on measurements of DSA levels, the participants noted that a primary endpoint based on increased rates of transplantation after desensitization would reflect a belief that a reduction in measured pretransplant DSA levels would necessarily confer a long-term benefit to the patients. Some participants, however, expressed concerns that insufficient evidence exists to justify such a conclusion at present. Therefore, determining any intervention successful should also require a demonstration of benefit in important clinical outcomes (e.g. acceptable graft survival, reduced incidence of AMR) after transplant. Challenges may exist in designing protocols to evaluate therapies aimed at desensitization as the treatment groups would presumably have disparate proportions of patients undergoing transplant. Such imbalances would complicate the rigorous statistical comparison of intermediate and long-term transplant outcomes across the groups. Interventions aimed at preventing AMR among trials patients who have all undergone transplant may therefore prove, in some instances, more straightforward to study in the context of RCTs.

Determining proper inclusion/exclusion criteria that will allow the selection of comparable patient populations was felt to constitute a critical challenge in studying indications related to desensitization and AMR prevention. As noted earlier, qualitative assays have been used clinically to perform semiquantitative measurements of pre-existing DSAs in an effort to define higher risk transplant candidates: the accumulated data suggest that the risk of AMR relates to the amount and/or type of DSA (4,10). Trials that enroll all patients with any detectable DSA may, therefore, fail to demonstrate the same risk-benefit as trials which include only patients whose DSAs have been characterized as high risk. In order to facilitate interpretation, however, future trials that define the target population using DSAs should rely on DSA testing methods that are supported by data either previously submitted to FDA or developed within the context of the trial.

Chronic AMR

The clinical significance of CAMR has been increasingly documented in recent years, with some data suggesting that it may represent the leading cause of late allograft loss (6). As opposed to acute AMR, CAMR is a long-term process which develops in sequential steps over months to years (35). Diagnostic features of CAMR can include the presence of DSA, TG, PTC basement membrane multilayering and the presence of C4d. In contrast to early acute AMR, however, CAMR is a heterogeneous entity; as a consequence, its study presents some considerable challenges. Data from case series on the management of CAMR with IVIG, PP, rituximab and/or splenectomy were presented (24,25). The results reported have been variable, such that no strategy has been widely implemented in clinical practice.

Participants felt RCTs designed to treat or prevent CAMR are needed. Some suggested that placebo-controlled trials demonstrating an effect on certain hallmark characteristics of CAMR (such as TG) could constitute as evidence of clinical benefit. Others stated that demonstrating differences in long-term outcomes such as graft survival might be necessary. As with acute AMR, the regulations regarding accelerated approval pathways, SEPs and CEPs could potentially be applicable here as well.

Summary/Conclusions

The workshop brought together experts in the field of transplantation and provided for a series of informative presentations and discussion on treatment and prevention of acute AMR, desensitization and CAMR. Topics included measurement of DSAs, diagnostic criteria, current approaches to management and potential trial endpoints. A session was devoted to animal models. The participants emphasized the need for greater refinement and standardization of tools intended to measure DSAs, diagnose AMR and/or otherwise instruct management of patients. While individual transplant centers have made significant contributions in the diagnosis and management various AMR-related conditions, RCTs are needed to elucidate treatment effect. Although further work is necessary, the presentations and discussions at the workshop will help inform future considerations regarding clinical trial design in this area and, thereby, help facilitate the development of new therapies.

Disclosure

The authors of this manuscript have no conflicts of interest to disclose as described by the American Journal of Transplantation.

Footnotes

  • 1

    Halloran PF. Transcript measurements in antibody-mediated rejection: mechanistic and diagnostic insights. Public Workshop on ‘Issues in the Development of Medical Products for the Prophylaxis and/or Treatment of Acute Antibody Mediated Rejection (AMR) in Kidney Transplant Recipients’. Sponsored by the Food and Drug Administration, Silver Spring, MD. 2010.

  • 2

    Woodle ES. Drug development and clinical trial design considerations for desensitization. Public Workshop on ‘Issues in the Development of Medical Products for the Prophylaxis and/or Treatment of Acute Antibody Mediated Rejection (AMR) in Kidney Transplant Recipients’. Sponsored by the Food and Drug Administration, Silver Spring, MD. 2010.

  • 3

    Stegall M. Public Workshop on ‘Issues in the Development of Medical Products for the Prophylaxis and/or Treatment of Acute Antibody Mediated Rejection (AMR) in Kidney Transplant Recipients’. Sponsored by the Food and Drug Administration, Silver Spring, MD. 2010.

Appendix

List of workshop participants

Renata Albrecht, MD

Director, Division of Special Pathogen and Transplant Products

Center for Drug Evaluation and Research (CDER), FDA

Michael Amos, PhD

Scientific Advisor, Chemical Science and Technology Laboratory

National Institute of Standards and Technology (NIST)

Patrick Archdeacon, MD

Medical Officer, Division of Special Pathogen and

Transplant Products

Center for Drug Evaluation and Research (CDER), FDA

Shukal Bala, PhD

Microbiology Team Leader, Division of Special Pathogen and Transplant Products

Center for Drug Evaluation and Research (CDER), FDA

Marcelo Cantarovich, MD

Professor of Medicine, McGill University

Medical Director, Kidney and Pancreas Transplant

Assoc. Director, Multi-Organ Transplant Program

Royal Victoria Hospital, McGill University Health Centre

Marc Cavaille-Coll, MD, PhD

Medical Officer, Division of Special Pathogen and Transplant Products

Center for Drug Evaluation and Research (CDER), FDA

Maria Chan, PhD

Director, Division of Immunology and Hematology Devices

Center for Devices and Radiological Health (CDRH), FDA

David Cohen, MD

Professor of Clinical Medicine

Columbia University

Robert Colvin, MD

Pathologist, Massachusetts General Hospital

Professor of Pathology, Emeritus, Harvard Medical School

Donna Cryer, JD

CEO, Cryer Health

Dixie Esseltine, MD, FRCPC

Vice President, Global Medical Affairs

Mellennium Pharmaceuticals, Inc.

Manish J. Gandhi, MD

Medical Director, Tissue Typing Laboratory

Mayo Clinic, Rochester, MN

Robert Gaston, MD

Professor of Medicine/Surgery

Medical Director, Kidney and Pancreas Transplantation

University of Alabama at Birmingham

Howard Gebel, PhD

Professor, Pathology & Laboratory Medicine

Emory University School of Medicine

Hal Gibson

Post-Transplant Monitoring Division Manager

One Lambda, Inc.

Denis Glotz, MD

Chief, Department of Nephrology and Kidney Transplantation

Hopital Saint-Louis

Arturo Hernandez, MD

Medical Officer, Division of Special Pathogen and

Transplant Products

Center for Drug Evaluation and Research (CDER), FDA

Philip Halloran, MD, PhD, OC, FRSC

Director, Alberta Transplant Applied Genomics Centre

Distinguished University Professor, University of Alberta

Editor-in-Chief, American Journal of Transplantation

Stanley Jordan, MD

Director, Kidney Transplantation and Transplant Immunology, Kidney and Pancreas Transplant Center

Director, Division of Pediatric and Adult Nephrology

Cedars-Sinai Medical Center

Robert Linke

Senior Director Sales

Transplant Diagnostics, Gen-Probe

Ronald Kerman, PhD

Professor of Surgery

Director, Histocompatibility and Immune Evaluation Laboratories

University of Texas Medical School Houston

Allan Kirk, MD, PhD

Professor of Surgery, Division of Transplantation, Department of Surgery

Emory University School of Medicine

Stuart Knechtle, MD

Professor of Surgery and Chief, Division of Transplantation, Department of Surgery

Emory University School of Medicine

John Magee, MD

Associate Professor, Section of General Surgery, Division of Transplantation

University of Michigan Health System

Kevin Maher, PhD

Reviewer, Division of Immunology and Hematology Devices

Center for Devices and Radiological Health (CDRH), FDA

Roslyn (Roz) Mannon, MD

Professor of Medicine, Division of Nephrology

Director of Research for the Transplant Nephrology Section

University of Alabama at Birmingham

Arthur Matas, MD

Professor of Surgery

Director, Renal Transplant Program

University of Minnesota

Herwig-Ulf Meier-Kriesche, MD

Professor of Medicine

Medical Director, Renal Transplant in the Department of Medicine

University of Florida

Joette Meyer, PharmD

Clinical Team Leader, Division of Special

Pathogen and Transplant Products

Center for Drug Evaluation and Research (CDER), FDA

Carolyn Neuland, PhD

Director, Gastroenterology and Renal Devices Branch

Center for Devices and Radiological Health (CDRH), FDA

Peter Nickerson, MD

Transplant Nephrologist and Professor of Internal Medicine and Immunology

University of Manitoba

Annette Ragosta, RAC, MT(ASCP)SBB

Team Leader and Senior Advisor for

Immunohematology, Division of Blood Applications, Devices Review Branch

Center for Biologics Evaluation & Research (CBER), FDA

Elaine Reed, PhD

Director, Immunogenetics Center

Department of Pathology, School of Medicine

University of California Los Angeles

Nancy Reinsmoen, PhD

Director, HLA Laboratory

Cedars-Sinai Medical Center

David Sachs, MD

Professor of Surgery (Immunology), Harvard Medical School

Director, Transplantation Biology Research Center

Massachusetts General Hospital

Milagros (Millie) Samaniego, MD

Medical Director of Kidney and Kidney Pancreas Transplantation

University of Michigan Health System

Dorry Segev, MD, PhD

Associate Professor of Surgery and Epidemiology

Director of Clinical Research, Division of Transplantation,

Director of Information Technology, Department of Surgery

Johns Hopkins Medical Institutions

Stephen Squinto, PhD

Executive Vice President

Head of Research and Development

Alexion Pharmaceuticals

Mark Stegall, MD

Chair of Surgery and Professor of Surgery, William J. von Liebig Transplant Center

Mayo Clinic

LaRee Tracy, MS, PhD

Statistical Team Leader

Division of Biometrics VII

Center for Drug Evaluation and Research (CDER), FDA

Kathleen (Cook) Uhl, MD

Deputy Director, Office of Medical Policy

Center for Drug Evaluation and Research (CDER), FDA

Marc Uknis, MD, FACS

Medical Director

ViroPharma Incorporated

Ergun Velidedeoglu, MD

Medical Officer, Division of Special Pathogen and

Transplant Products

Center for Drug Evaluation and Research (CDER), FDA

E. Steve Woodle, MD

Professor of Surgery

Director, Division of Transplantation in the Department of Surgery

University of Cincinnati

Andrea Zachary, PhD, D.ABHI

Professor of Medicine

Director, Immunogenetics Laboratory

Johns Hopkins University School of Medicine

Adriana Zeevi, PhD, D.ABHI

Division of Transplant Pathology, Department of Pathology

University of Pittsburg Medical Center

Thomas E. Starzl Transplantation Institute

Ancillary