Inability of Monoclonal Antibodies to Clear Red Blood Cells during Incompatible Transfusions is not a Property of the Whole Cell

Abstract During an incompatible transfusion (Tx), antibodies (Abs) against some blood group antigens (Ags) will lead to hemolysis while others will allow for continued red blood cell (RBC) circulation despite IgG binding. We tested the nature of RBC clearance using transgenic mice expressing well-defined RBC Ags and monoclonal Abs. Tx of RBCs, expressing human glycophorin A (hGPA), into mice treated with anti-hGPA IgG1 monoclonal Abs led to partial clearance of those RBCs. A population of RBCs persisted and continued to circulate in a 2nd animal also passively immunized against hGPA, indicating that survival was not due to splenic saturation or consumption of the monoclonal Abs. We therefore concluded that these hGPA RBCs were resistant to clearance as they were also positive for hGPA and bound Abs. These studies were also performed using RBCs expressing the Duffy Ag and anti-Duffy IgG2a monoclonal Abs. To test if resistance comprises a whole cell protection from Ab-induced lysis, we transfused blood expressing both hGPA and Duffy Ags into mice passively immunized against hGPA. The resistant RBCs were then transfused into mice passively immunized against Duffy. Although these RBCs were able to resist a 2nd Tx against the same anti-hGPA Ab as the one used during the 1st Tx, these did not resist a 2nd Tx during which anti-Duffy was used. We, therefore, conclude that resistance occurs with different Ags and is not a property of the cell but rather is at the Ag-Ab level.