Recombinant blood group proteins in clinical practice – from puzzling to binary antibody testing

Abstract

The main drawback of red blood cell (RBC)-based antibody detection assays is that a positive reaction between serum and test cells does not identify the specificity of a given red blood cell antibody. When antibody mixtures or rare RBC antibodies are present, this indirect method reaches its limits. Recently, CEmarked recombinant blood group proteins (rBGPs) have become available in sufficient quantity and quality. The advantage of rBGPs over RBCs is that proteins carrying a single antigen can be used in the antibody identification assay, so a positive test directly indicates the presence and specificity of the target antibody. The use of soluble rBGPs in addition to RBCs has been shown to increase the sensitivity and specificity of antibody detection and identification in cases with difficult-to-identify antibodies, resulting in increased efficiency in providing blood to immunized patients. The rBGPs have been successfully used in a wide range of solid-phase assays (ELISA, microspheres, microarrays). Although all relevant antigen specificities have not yet been established, rBGPs have a diagnostic potential that could already be useful in antibody detection assays combining RBC-derived antigens and recombinantly expressed antigens. Such combined assays would benefit from the potential of rBGPs for single-step, direct antibody detection and identification, which could greatly facilitate and accelerate the identification of common and rare RBC antibodies. The clinical use of rBGPs in pretransfusion antibody screening would introduce a paradigm shift that could help to reduce the risk of haemolytic transfusion reaction, one of the leading causes of transfusion-related death.

When recombinant proteins can replace rare red cells in immunohematology workups

“…This approach has recently been accepted by the ISBT Working Party on Red Cell Immunogenetics and Blood Group Terminology. Panels of commercially available rBGPs could be developed, which in different combinations would provide handy sets of reagents for use in routine blood group serology, antibody screening, and antibody identification 39 …”

“…Because these red cells are lacking or scarce, many studies began utilizing rBGPs. [27][28][29][30][31][32][33][34][35][36][37][38][39][40] Also, rBGPs are easy to store frozen or lyophilized, quite different from the complex shipping and freezing requirements of red cells. 41 The expression of rBGP in eukaryotic systems is often preferred over expression vectors in prokaryotic systems, although they are easier and cheaper, 42 because appropriate posttranslational modifications are required for the formation of three-dimensional epitope structure.…”

“…No Immunohematology Reference Laboratory (IRL) may have all of them available. Because these red cells are lacking or scarce, many studies began utilizing rBGPs 27–40 . Also, rBGPs are easy to store frozen or lyophilized, quite different from the complex shipping and freezing requirements of red cells 41 .…”

An update on the Scianna blood group system

“…The high-prevalence Scianna system antigens Sc1, Sc3, Sc4 (STAR), Sc5 (SCER), and Sc6 (SCAN) can now be detected using CE-marked recombinant proteins. 14 Particularly in specimens containing mixtures of antibodies that include antibodies to a high-prevalence antigen, these reagents can be useful tools to remove the highprevalence antibody and permit alloantibody identification by standard methods. 15,16…”

Inhibition of blood group antibodies by soluble substances

“…If one wants to use specific rBGPs, they are commercially available if the molecular and genetic basis are known. 20 It may not always be possible to inhibit high-titer antibodies, particularly monoclonal antibody drug formulations, because the required high concentration of the soluble substance cannot be achieved.…”