Antibodies to human fetal erythroid cells from a nonimmune phage antibody library

The ability to isolate fetal nucleated red blood cells (NRBCs) from the mat ernal circulation makes possible prenatal genetic analysis without the need for diagnostic procedures that are invasive for the fetus. Such isolation requires antibodies specific to fetal NRBCs, To generate a panel of antibod ies to antigens present on fetal NRBCs, a new type of nonimmune phage antib ody library was generated in which multiple copies of antibody fragments ar e displayed on each phage. Antibody fragments specific for fetal NRBCs were isolated by extensive predepletion of the phage library on adult RBCs and white blood cells (WBCs) followed by positive selection and amplification o n fetal liver erythroid cells. After two rounds of selection, 44% of the an tibodies analyzed bound fetal NRBCs, with two-thirds of these showing no bi nding of WBCs. DNA fingerprint analysis revealed the presence of at least 1 6 unique antibodies. Antibody specificity was confirmed by flow cytometry, immunohistochemistry, and immunofluorescence of total fetal liver and adult RBCs and WBCs. Antibody profiling suggested the generation of antibodies t o previously unknown fetal RBC antigens. We conclude that multivalent displ ay of antibodies on phage leads to efficient selection of panels of specifi c antibodies to cell surface antigens, The antibodies generated to fetal RB C antigens may have clinical utility for isolating fetal NRBCs from materna l circulation for noninvasive prenatal genetic diagnosis. Some of the antib odies may also have possible therapeutic utility for erythroleukemia.