Objectives: In the Eurotransplant zone, the crossmatch serum exchange program was established to reduce unnecessary organ shipment, using the complement-dependent cytotoxicity crossmatch as the reference to make the decision. Crossmatching at the donor center dictates whether the transplant should be shipped to the recipient center where a decisive crossmatch would then be done. However, in recent years, the target cell used for the crossmatching has changed from spleen cells to peripheral blood lymphocytes. In this study, we assess the impact of this change on the outcome of complement-dependent cytotoxicity crossmatches for patients immunized against HLA-class II.
Materials and methods: The influence of the donor cell type was analyzed by crossmatching unseparated peripheral blood lymphocytes, separated T and B lymphocytes, as well as spleen cells from 12 organ donors with sera from 40 immunized kidney retransplant candidates. Negative sera and sera harboring only anti-HLA class-II antibodies were used as additional controls. We did more than 1200 complement-dependent cytotoxicity crossmatches.
Results: Crossmatches with sera containing anti-HLA class-I plus class-II alloantibodies (n=113 per cell type) were positive in 42% of peripheral blood lymphocytes, 72% of spleen cells, and 81% of B cells. Crossmatches with sera containing exclusively anti- HLA class-II antibodies (n=89 per cell type) were positive in 1% of peripheral blood lymphocytes, 30% of spleen cells, and in 31% of B cells. Overall, spleen or separated B cells identified approximately 30% more positive donor-recipient pairs.
Conclusions: The data show that the change from spleen cells to peripheral blood lymphocytes as donor target cells for complement-dependent cytotoxicity crossmatching increased risk of false negative results for patients harboring anti-HLA class-II antibodies.