Sensitization to HLA antigens is the main barrier to solid organ transplantation. Currently, HLA sensitization is monitored by testing patients' serum against a panel of HLA antigens (whether those will be presented on cell surface or on solid phase matrixes) and calculating the % of positive responses. Such result give indication of the relative breadth of sensitization but not on it "depth" - the relative strength of specific antibodies, nor does it provide any information regarding the memory B cells / plasma cells that can manufacture a specific HLA directed antibody.