The analysis and quantification of a clonal B cell response in a hyperimmunized anti‐D donor

Summary Healthy volunteers are hyperimmunized with RhD‐positive red cells in order to obtain plasma containing high titres of anti‐D immunoglobulin, which is used for the prevention of haemolytic disease of the fetus and newborn. We analysed the anti‐D immune response in a donor who had been hyperimmunized for 7 years and who showed declining anti‐D titres despite re‐immunization. A phage display library representing the complete immunorepertoire and a second library representing the IGHV3 superspecies family genes ( IGHV3 s) repertoire in the donor were constructed and analysed. A clonal Ig‐gene rearrangement was quantified in the peripheral blood by limiting dilution polymerase chain reaction (PCR) All RhD‐binding phages from both libraries, except one, had heavy chains with IGH–VDJ rearrangements of the same clonal origin, but with different patterns of somatic mutations and joined with different light chains. Limiting dilution PCR performed on mRNA and genomic DNA showed a frequency of 1 clonal B cell in 2000 IgG1/3‐positive B cells. We show the presence of clonally related RhD‐specific B cells in a hyperimmunized anti‐D donor who had declining anti‐D titres and who was unresponsive to re‐immunization. Furthermore, we found a high frequency of clonal B cells. These results contribute to the understanding of the immune response against RhD in hyperimmunized anti‐D donors.