Mitigation of therapeutic anti-CD38 antibody interference with fab fragments: How well does it perform?

BACKGROUND: Administration of anti-CD38 antibodies is a state-of-the-art therapy for patients diagnosed with multiple myeloma (MM). However, this treatment frequently leads to pan-agglutination of red blood cells (RBCs) in patients' serological testing making accurate blood typing and timely transfusion of compatible blood a challenging effort. The antigen masking indirect antiglobulin test (AMIAT) is an approach to address this diagnostic challenge. STUDY DESIGN AND METHODS: A new reagent, called DaraEx plus, uses anti-CD38 Fab fragments to mitigate the anti-CD38 antibody interference in serological assays by masking CD38 on the cell surface. Its performance is extensively examined with commercial sera as well as with patient samples, and compared to the current standard method using dithiothreitol (DTT), which denatures the CD38 antigens on test panel erythrocytes. RESULTS: In the Bio-Rad ID System, DaraEx plus effectively mitigated the interference caused by anti-CD38 antibodies in 86% of patient samples tested while DTT was successful in only 68%. Moreover, there was no negative influence on DTT-sensitive blood group systems such as KEL upon DaraEx plus treatment. The agglutination reactions of all tested anti-CD38 antibodies (Daratumumab, Felzartamab, and Isatuximab) were inhibited by DaraEx plus. The treatment was successful only if DaraEx plus was added to the test cells before the sample. Some of the other gel card systems tested showed background reactions with DaraEx plus-treated cells. CONCLUSION: DaraEx plus treatment is straightforward and quick to perform. In the Bio-Rad ID System, it is superior to DTT treatment in the prevention of anti-CD38 antibody interference.

Two novel antithetical KN blood group antigens may contribute to more than a quarter of all KN antisera in Europe.

BACKGROUND: All antigens described in the KN blood group system are located in the long homologous repeat D (LHR-D) of complement receptor 1 (CR1). While there have been reports that some sera react only with the long homologous repeat C (LHR-C), the antigens in LHR-C are unknown. STUDY DESIGN AND METHODS: Recombinant LHR-C and LHR-D were used to identify antibodies directed against LHR-C of CR1, into which a point mutation was introduced to characterize the underlying blood group antigens. In addition, database studies to define haplotypes of CR1 were performed. RESULTS: Several antisera were identified that were specific against CR1 p.1208His and against CR1 p.1208Arg, located in LHR-C. Fifteen KN haplotypes were found in the Ensembl genome browser. It was shown that due to a linkage disequilibrium anti-CR1 p.1208His may be mistaken for anti-KCAM. CONCLUSION: A novel antithetical KN blood group antigen pair was found at position p.1208 of CR1, for which the names DACY and YCAD are proposed. Antibodies against these two novel antigens seem to contribute to more than a quarter of all KN sera in Europe.