Author: Mohammad Ali Rafique, Transplant Technical Sales Specialist
The accuracy of HLA antibody results forms the cornerstone of effective patient care and transplant success in the H&I field. Single Antigen bead (SAB) assays, with their superior sensitivity and sensitivity, represent the gold standard for HLA antibody detection. Coupled with improvements in HLA typing resolution, the routine use of SAB assays has widened patient access to virtual crossmatch (VXM) methods, where HLA antibody and typing results are compared to assess immunological compatibility without the need for a physical (wet) crossmatch. VXMs have been widely acknowledged for reducing organ cold ischaemic times as well as providing numerous logistical benefits to laboratories.
However, non-specific serum interferences (which are infrequently present in a minority of patients) may potentially hinder analysing scientists from accurate interpretation of SAB results. These interferences can arise through different factors (such as cross-reactivity with unrelated antibodies or the presence of substances that mimic or interfere with the target HLA antigens) but result in high Negative Control (NC)/background values or spurious reactivity patterns, all serving to complicate SAB interpretation and potentially jeopardise the precision of HLA analyses. An example of this is pan-DR reactivity which may be handled differently between laboratories; some choose to list numerous DRB1 (and allele-specific) specificities while, in contrast, others require a wet crossmatch to risk-assess donor-recipient compatibility (since SAB reactivity against patient self-DR antigens indicates the reactivity may not be HLA in origin).
What is undisputed is that the correct interpretation of SAB results is crucial for making informed decisions in transplantation, emphasising the need for solutions to address these challenges head-on and ensure that the accuracy of HLA antibody detection remains uncompromised. Existing reagents such as Adsorb Out are adept at addressing specific issues but, while they still have a place in the laboratory toolkit, patients are not identical therefore no single solution is likely to work across the board. Extensive R&D from One Lambda has led to the release of PreSorb: a serum treatment reagent capable of tackling high NC bead reactivity like Adsorb Out. Unlike Adsorb Out however, PreSorb goes a step further by mitigating several known serum interferences. Polyhistidine antibodies (which can arise naturally in patients) are a major target of the reagent since histidine is used as a linker molecule between some beads and recombinant HLA molecules. One Lambda determined that anti-histidine antibodies are the cause of certain patterns of reactivity many of you will be familiar with (Cw1/12/15, pan-DR and anomalous DQ reactivity).
Table 1. Laboratory examples showing PreSorb reduction of high NC bead values.
Table 2. Laboratory example showing PreSorb efficacy on a sample with only minimal response to Adsorb Out.
There are numerous examples, both anecdotally and published*, demonstrating mitigation of several non-specific patterns of reactivity (including Cw1/12/15 and pan-DR) following PreSorb treatment. At the same time, it is important to note that PreSorb has undergone rigorous validation and exhibits minimal impact on overall MFI values, ensuring accurate calling of genuine HLA reactivity.
The PreSorb workflow is streamlined and efficient, taking approximately 20 minutes to complete, and is designed to fit around the laboratory’s existing process. When faced with troublesome sera, a laboratory should be considering all tools in its arsenal to achieve accurate SAB results and aid clearer interpretation through the reduction of non-specific reactivity. At a similar price point to Adsorb Out, this reagent represents excellent value for money.
Watch: Treating Sera with Non-Specific Interference in SAB assays
Get in touch with VH Bio to learn more about PreSorb from One Lambda.
*Reference available on request.