Pronase independent flow cytometry crossmatching of rituximab treated patients

Role of Complement-dependent Cytotoxicity Crossmatch and HLA Typing in Solid Organ Transplant

BACKGROUND

Solid organ transplantation is a life-saving medical operation that has progressed greatly because of developments in diagnostic tools and histocompatibility tests. Crossmatching for complement-dependent cytotoxicity (CDC) and human leukocyte antigen (HLA) typing are two important methods for checking graft compatibility and reducing the risk of graft rejection. HLA typing and CDC crossmatching are critical in kidney, heart, lung, liver, pancreas, intestine, and multi-organ transplantation.

METHODS

A systematic literature search was conducted on the internet, using PubMed, Scopus, and Google Scholar databases, to identify peer-reviewed publications about solid organ transplants, HLA typing, and CDC crossmatching.

CONCLUSION

Recent advances in HLA typing have allowed for high-resolution evaluation, epitope matching, and personalized therapy methods. Genomic profiling, next-generation sequencing, and artificial intelligence have improved HLA typing precision, resulting in better patient outcomes. Artificial intelligence (AI) driven virtual crossmatching and predictive algorithms have eliminated the requirement for physical crossmatching in the context of CDC crossmatching, boosting organ allocation and transplant efficiency. This review elaborates on the importance of HLA typing and CDC crossmatching in solid organ transplantation.

Antibody Therapeutics as Interfering Agents in Flow Cytometry Crossmatch for Organ Transplantation

Donor-recipient matching is a highly individualized and complex component of solid organ transplantation. Flowcytometry crossmatching (FC-XM) is an integral step in the matching process that is used to detect pre-formed deleterious anti-donor immunoglobulin. Despite high sensitivity in detecting cell-bound immunoglobulin, FC-XM is not able to determine the source or function of immunoglobulins detected. Monoclonal antibody therapeutic agents used in a clinic can interfere with the interpretation of FC-XM. We combined data from the prospectively maintained Antibody Society database and Human Protein Atlas with a comprehensive literature review of PubMed to summarize known FC-XM-interfering antibody therapeutics and identify potential interferers. We identified eight unique FC-XM-interfering antibody therapeutics. Rituximab (anti-CD20) was the most-cited agent. Daratumuab (anti-CD38) was the newest reported agent. We identified 43 unreported antibody therapeutics that may interfere with FC-XM. As antibody therapeutic agents become more common, identifying and mitigating FC-XM interference will likely become an increased focus for transplant centers.

Abrogating biologics interference in flow cytometric crossmatching

The flow cytometric crossmatch is currently the gold standard for evaluating donor and recipient histocompatibility. The assay however does have limitations and is sensitive to false positive reactions resulting from the presence of non-HLA antibodies or therapy related immune biologics. Such false positive reactions can lead to the inappropriate decline of an acceptable donor organ or unnecessary therapeutic intervention. Here we describe the successful validation of anti-idiotype blocking antibodies in prevention of false positive flow crossmatch results caused by biologic therapy. Blocking antibodies specific for the Fab portion of Rituximab and/or Alemtuzumab were incubated with biologic containing patient serum prior to use in flow cytometric crossmatching. Biologic blocking successfully negated false positive crossmatch results with Rituximab (B cell ave. % change = -97%) or Alemtuzumab (T cell ave. % change = -99%, B cell ave. % change = -95%) infused sera respectively. Simultaneous blocking of these biologics was also successful. A complex case is presented to demonstrate the application of this procedure.

Solutions to Avoid False Positives for Rituximab in Pre-Transplant Crossmatches

Rituximab (anti-CD20) is commonly used as immunotherapy against B cells, in the context of pre-transplant crossmatches, where the presence of rituximab in the tested sera with donor cells can alter their results both by flow cytometry (FCXM) as complement-dependent cytotoxicity (CDCXM) giving rise to false positives. In the present study, we tested the use of an anti-rituximab monoclonal antibody (10C5, Abnova) as a method to avoid false positives in FCXM and CDCXM. We used the serum from ten patients who received therapy with rituximab, and the cells were incubated with sera treated or untreated with the 10C5 clone. In previous studies, attempts have been made to control these false positives through the use of pronase, although in these cases the alteration of Human Leukocyte Antigen (HLA) molecules has been found to be a limitation. As an alternative, we performed an assay to exclude false positives by a pre-incubation with anti-rituximab antibody (10C5) in 1:5 proportion avoiding the misinterpretation of crossmatches, particularly in patients with specific donor antibodies (DSA) without affecting the HLA molecules.

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.

Excellent outcome after desensitization in high immunologic risk kidney transplantation

Introduction

HLA-incompatible (HLAi) and ABO-incompatible (ABOi) kidney transplantation (KT) has been on the increase over the last decade. However, there are wide variations in outcomes from these procedures. In this study we evaluated the graft and patient outcomes in incompatible KT and non-sensitized KT.

Methods

Patients who underwent KT between January 2012 and April 2018 were enrolled and reviewed. We divided kidney transplant recipients (KTRs) into five groups as follows: HLAi (n = 50); ABOi (n = 65); HLAi+ABOi (n = 5); control (n = 428); and living-donor control (LD control, n = 218). We compared the risk of rejection, graft function, graft survival, and patient survival between incompatible KTRs and control/LD control KTRs.

Results

Although the incidence of active antibody-mediated rejection in HLAi group tends to be higher than in control and LD control groups (6.0% vs. 2.8%, P = 0.20; 6.0% vs. 3.7%, P = 0.44, respectively), the rejection-free survival, graft survival, and patient survival were not significantly different from those of the control and LD control groups in all three incompatible KT groups (all P>0.05). Graft function during the study period was also not different between incompatible KTRs and control/LD control groups (both P>0.05). Using Cox regression analysis, neither HLAi nor ABOi were risk factors for graft failure. Some infectious diseases such as urinary tract infection and cytomegalovirus infection were more common in the HLAi group than in the control/LD control group (both P<0.05), but only one infection-related death occurred in HLAi KTRs. Infection risks were similar in the ABOi and HLAi+ABOi groups compared to controls.

Conclusion

Our results showed favorable outcomes for incompatible KT after desensitization. Although desensitization therapy for incompatible KT has improved access to transplantation for KT candidates with high immunological risk, more clinical data are clearly needed.

Implications of Monoclonal Antibody Therapeutics Use for Clinical Laboratory Testing

BACKGROUND

Monoclonal antibody therapeutics (MATs) represent a rapidly expanding class of biological drugs used to treat a variety of diseases. The widespread use of MATs increasingly affects clinical laboratory medicine.

CONTENT

This review provides an overview of MATs currently approved for clinical use in the US, starting from basic biology of antibodies to the engineering, pharmacokinetic and pharmacodynamic properties, nomenclature, and production of MATs. Immunogenicity and the production of antidrug antibodies (ADAs) play a major role in loss of therapeutic response and the development of treatment failure to certain MATs. Laboratory-based monitoring for MATs and detection of ADAs represent emerging needs for optimizing the use of MATs to achieve the best outcomes at affordable cost. In addition, the increased use of MATs affects clinical laboratory testing by interference of MATs with clinical laboratory tests across different areas of laboratory medicine, including histocompatibility, blood bank, and monoclonal protein testing.

SUMMARY

The number of MATs is rapidly growing each year to address previously unmet clinical needs. Laboratory monitoring of MATs and detecting ADAs represent expanding areas of laboratory testing. Test-based strategies allow for treatment optimization at the level of the individual patient, thus providing a personalized medicine approach. In addition, clinical laboratories must be aware that the increasing use of MATs affects laboratory testing and be ready to implement methods to eliminate or mitigate interference with clinical tests.