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

Aggregates in blood filter chambers used from the plasma donations of anti-D donors: evaluation for monoclonal antibody discovery using phage display

BACKGROUND

RhD-immunoglobulin (RhIg) prevents anti-D alloimmunisation in D-negative pregnant women when the fetus is D-positive, reducing the incidence of haemolytic disease of the fetus and newborn. Manufacturing RhIg is reliant on the limited supply of plasma donations with anti-D antibodies. Monoclonal antibody (mAb) development platforms such as phage display, require blood samples to be collected from anti-D donors, which may be a complicated process. The blood filter chamber (BFC) discarded after an anti-D donor's donation might provide a source of Ig-encoding RNA. This study aims to evaluate whether used BFCs are a suitable source of Ig-encoding RNA for phage display.

MATERIAL AND METHODS

Haemonetics PCS2 BFCs were obtained from 10 anti-D donors for total RNA extraction, cDNA synthesis and amplification of VH and VL IgG sequences for assembly of single-chain variable fragments (scFvs). A scFv-phage display library was constructed and 3 rounds of biopanning were performed using D-positive and D-negative red blood cells (RBCs). Positive phage clones were isolated, Sanger sequenced and, where possible, reformatted into full-length human IgGs to define specificity. The BFC aggregates from 2 anti-D donors underwent a Wright-Giemsa stain and hematological cell count.

RESULTS

Of 10 BFCs, a sufficient yield of total RNA for library construction was obtained from BFCs containing cellular aggregates (n=5). Aggregate analysis showed lymphocytes were the cellular source of Ig-encoding RNA. From the 5 samples with aggregates, scFvs were assembled from amplified IgG variable regions. The library constructed from 1 of these samples resulted in the isolation of clones binding to D-positive RBCs with IGHV3 gene usage. Of the 4 reformatted IgG, 3 were anti-D and 1 had undefined specificity.

DISCUSSION

BFC aggregates are a new and convenient source of Ig-encoding RNA which can be used to construct Ig gene libraries for mAb isolation and discovery via antibody phage display.

The restricted use of IGHV3 superspecies genes in anti-Rh is not limited to hyperimmunized anti-D donors

BACKGROUND

Antibodies produced against the D antigen make use of IGHV genes restricted to the IGHV3 superfamily. These findings are based on the IGHV gene analysis in anti-D-producing B cells from hyperimmunized donors, however, and therefore the restriction might be due to the hyperimmunization. In this study the IGHV gene usage of anti-Rh-producing B cells in a woman who was immunized in the last trimester of her pregnancy was analyzed.

STUDY DESIGN AND METHODS

Serologic analysis was performed by absorption and elution. Antibody-dependent cellular cytotoxicity (ADCC) of the different anti-Rh was determined. A phage display library was constructed from 2.2 x 10(6) isolated B cells and pannings were performed with red cells of the r'r, R1R1, and R2R2 phenotype.

RESULTS

A plasma sample of the immunized person showed high levels of both anti-D and anti-G and low levels of anti-C. Anti-D and anti-G contributed equally strong to the ADCC whereas anti-C did not. Eighteen anti-D-, 5 anti-G-, and 1 anti-C-specific phage clones were found, of which 16, 2, and 1 used the IGHV3s genes, respectively.

CONCLUSION

For the first time a restriction to the IGHV3s genes in anti-D in a naturally immunized pregnant woman is shown. Moreover, the use of IGHV3s genes appears to be present in anti-C and anti-G as well. Therefore, it is concluded that restricted IGHV3s gene usage in anti-D is not due to hyperimmunization but due to characteristics of the Rh antigens and the intrinsic binding capacities of IGHV3s genes, supporting the common Rh footprint hypothesis.