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Human monoclonal Fab fragments recovered from a combinatorial library bind specifically to the platelet HPA-1a
1Canadian Red Cross Society, Québec Transfusion Centre-Montréal, Ste-Foy, Canada.
Background And Objectives:
Certain clinical conditions are related to the presence of platelet-specific alloantibodies in the patient's serum. We studied the molecular diversity of HPA-1a antibodies to analyze some peculiarities of this antibody response.
Materials And Methods:
Human antibody Fab fragments that bind to the platelet alloantigen HPA-1a on glycoprotein IIb-IIIa (GPIIbIIIa) were generated by using a recombinant phage display system. We established an immunoglobulin G1, kappa combinatorial library from the peripheral blood lymphocytes of a person undergoing a severe posttransfusion purpura.
Results:
Characterization of Fab clones selected from the fifth round of antigen-specific panning of this library demonstrates a highly specific reactivity to the HPA-1a alloantigen. The nucleotide sequence analysis of representative HPA-la-specific clones reveals at least 3 distinct V1 and 3VH gene segments that present an extensive degree of mutation as demonstrated by comparison of gene usage and homologies to the nearest germline genes.
Conclusions:
These human HPA-la-specific Fab reagents should allow us to better understand the molecular mechanism involved in HPA-la alloimmunization.