Solid phase-based cross-matching as solution for kidney allograft recipients pretreated with therapeutic antibodies

Approaches for the characterization of clinically relevant pre-transplant human leucocyte antigen (HLA) antibodies in solid organ transplant patients

The avoidance of antibody-mediated rejection (AMR) attributed to human leucocyte antigen (HLA) antibody incompatibility remains an essential function of clinical Histocompatibility and Immunogenetics (H&I) laboratories who are supporting solid organ transplantation. Developments in HLA antibody identification assays over the past thirty years have greatly reduced unexpected positive cellular crossmatches and improved solid organ transplant outcomes. For sensitized patients, the decision to register unacceptable HLA antigen mismatches is often heavily influenced by results from solid phase antibody assays, particularly the Luminex^® Single Antigen Bead (SAB) assays, although the clinical relevance of antibodies identified solely by these assays remains unclear. As such, the identification of non-clinically relevant antibodies may proportionally increase the number of unacceptable transplant mismatches registered, with an associated increase in waiting time for a compatible organ. We reflect on the clinical relevance of antibodies identified solely by the Luminex SAB^® assays and consider whether the application of additional assays and/or tools could further develop our ability to define the clinical relevance of antibodies identified in patient sera. Improvements in this area would assist equity of access to a compatible transplant for highly sensitized patients awaiting a solid organ transplant.

Solid phase-based cross-matching for solid organ transplantation: Currently out-of-stock but urgently required for improved allograft outcome

Transplant recipients who have undergone sensitizing events, such as pregnancy, blood transfusion or previous transplants, frequently develop antibodies directed against the highly polymorphous human leukocyte antigen (HLA)-molecules. These pre-formed, donor-specific antibodies (DSA) present a high risk of causing organ failure or even complete loss of the grafted organ as a consequence of antibody-mediated, hyper-acute or acute allograft rejection. In order to detect DSA, the so-called functional complement-dependent lymphocytotoxicity assay (CDC-XM) was established about 50 years ago. Although effective in improving the outcome of solid organ allo-grafting, for the last ten years this assay has been controversially discussed due to its low sensitivity and especially because of its high susceptibility to various artificial factors, which generally do not yield reliable results. As a consequence, novel immunochemical test systems have been developed using ELISA- or bead-based solid phase assays as replacements for the traditional CDC-based assays. Because these assays are independent of single or vital cells, which are frequently not available, they have provided an additional and alternative diagnostic approach compared with the traditional CDC-based and flow-cytometric analyses. Unfortunately, however, the AMS-ELISA (Antibody Monitoring System), which was the first system to become commercially available, was recently discontinued by the manufacturer after seven years of successful use. Alternative procedures, such as the AbCross-ELISA, had to be either considerably modified, or did not yield reliable results, as in the case of the Luminex-based assay termed DSA. We draw the conclusion that due to the unique features and fields of application reviewed here, the implementation of solid phase cross-matching still represents an urgent requirement for any HLA-laboratory's routine tasks.

Unexpected Positive Prospective Crossmatches in Organ Transplant

Preformed donor-specific antibodies against human leukocyte antigen can induce antibody-mediated rejection after organ transplant. Hence, future transplant recipients undergo pretransplant screening for preformed antibodies (ie, virtual crossmatch). Subsequently, prospective (analytic) crossmatching is performed using conventional, complement-dependent cytotoxicity assays and/or flow cytometry-based methods. The present article reviews factors that must be considered when unexpected, positive, prospective crossmatches are observed. First, the prozone effect caused by the interference of complement or immunoglobulin M must be abrogated by treating the serum with moderate heat, dilution, hypotonic dialysis, EDTA, or dithiothreitol. Second, the physician must check for the presence of potentially interfering autoantibodies (in a context of autoimmune disease or human immunodeficiency virus infection) or therapeutic antibodies (such as rituximab and antithymocyte globulin). In conclusion, knowledge of each assay's technical characteristics will enable the physician to reliably interpret any discrepancies. The reasons for an unexpected, positive, prospective crossmatch must be elucidated before transplant to ensure efficient organ allocation and optimize patient outcomes.

Theranostic of biopharmaceuticals

Monoclonal antibodies (mAbs) and fusion proteins with an Fc portion of immunoglobulin G (IgG) are emblematic of the remarkable expansion of biopharmaceuticals. Despite their biological origin, these products display an interindividual variability in their efficacy and/or side effects, which must be taken into consideration. Biological monitoring allowing for adapted prescription and dose adjustments may lead to therapeutic optimization and limitation of the high costs of these drugs. Herein, we review the biological theranostic of mAbs and Fc fusion proteins, including pre-treatment analyses, monitoring of efficacy, therapeutic drug monitoring, and monitoring of side effects. Supported by concrete evidence, a specific interest is given to individualised therapeutic monitoring that combines intention to treat, biomarkers of efficacy and adaptation of serum concentrations.

ELISA-Based Crossmatching Allowing the Detection of Emerging Donor-Specific Anti-HLA Antibodies through the Use of Stored Donors' Cell Lysates

About forty years ago the complement-dependent crossmatch assay (CDC-CM) was developed as standard procedure in order to select recipients without donor-specific antibodies directed against human leukocyte antigens of their given donors since the negative outcome of pretransplant crossmatching represents one of the most important requirements for a successful kidney graft survival. However, as a functional assay the CDC-CM strongly depends on the availability of donors' isolated lymphocytes and in particular on their vitality highly limiting its applicability for recipients treated with special drugs and therapeutic antibodies or suffering from underlying autoimmune diseases. In the great majority of these cases ELISA-based crossmatching has been demonstrated to be an adequate alternative procedure nevertheless leading to valid results. With these case reports we show for the first time that ELISA-based crossmatching is suitable to demonstrate the upcoming donor-specific anti-HLA antibodies as a consequence of allografting using deep-frozen deceased donor's material such as blood or spleen detergent lysate. Thus, this ELISA-based procedure first provides the option to routinely perform crossmatching using stored material of deceased donors in order to substitute or at least to complement virtual crossmatching, that is, the comparison of the recipients' anti-HLA antibody specificities with the donors' historically identified HLA types.