Two novel assays of alloantibody-secreting cells demonstrating resistance to desensitization with IVIG and rATG.

Donor-specific alloantibody presents a major barrier to the successful transplantation of kidneys and hearts. However, the study of alloantibody production has been hampered by both an inadequate source of antibody-secreting cells (ASCs) and a paucity of assays to determine their function. We describe two new assays that allow for the determination of the frequency and specificities of allo-ASCs in humans using purified HLA as targets. These assays demonstrated allo-ASCs in the CD138(+) fraction of the bone marrow, but not in peripheral blood. Alloantibody specificities in these assays correlated well with those detected in the serum suggesting that bone marrow-derived ASCs are indeed a major source of alloantibody in vivo. However, ASCs for a specific HLA antigen were rare with an estimated frequency of only 1/2 x 10(6) marrow cells. Pretransplant treatment in vivo with multiple plasmaphereses and low-dose IVIG alone or in combination with rATG had no effect on ASC number or alloantibody production. These techniques allow for the study of allospecific ASCs and provide a method to test the potential efficacy of agents on alloantibody production in vivo.