P122 : DR7 PEDIATRIC HEART TRANSPLANT PATIENTS CAN HAVE ANTIBODIES REACTIVE TO DR4, 7 AND 9 SINGLE ANTIGEN BEADS THAT ARE NON-REACTIVE TO CELLS

Abstract

We report three cases of DR7 pediatric heart transplant patients producing antibodies reactive to DR4, 7, and 9 single antigen beads that were non-reactive to cells. The first patient EH is a 4 year old male with congenital complete heart block related to maternal lupus and no history of sensitization. At the time of initial antibody testing DR4, 7 and 9 antibodies were detected by single antigen bead assay. To assess whether antibodies were reactive to cells, a series of pronase treated B cell flow cytometry crossmatches (XM) were set up using PBL from panel members (PM) who are DR4, 7 and/or 9. PM#1 is DRB1 ∗ 04:05, 09:01, PM#2 is DRB1 ∗ 04:01, 13:01, and PM#3 is DRB1 ∗ 07:01, –. Single antigen testing revealed DR0401 antibodies at 6162 MFI, DR0405 at 4678 MFI, DR0701 at 7227 MFI and DR0901 at 5098 MFI. All B cell XM were negative. EH was transplanted with a heart from a DR4 donor in the presence of antibodies reacting to single antigen beads but non-reactive to cells. XM with the donor was negative. The patient is currently 2 years post-transplant with no signs of rejection despite DR4 antibodies detectable by single antigen bead testing. The second patient JW is a 9 year old male with complete heart block with long QT and no history of sensitization. Initial antibody testing identified DR7 antibodies at 2555 MFI, DR4 antibodies at 2139 MFI and DR9 antibodies at 3333 MFI. B cell flow cytometry XM with DR7 and DR4 donors were negative. The third patient AD is a 9 year old male with complex congenital heart defect sensitized by blood products. The patient has DR7 antibodies at 3820 MFI, DR4 antibodies at 2403 MFI and DR9 antibodies at 2339 MFI. XM with DR4, 7 and 9 donors were negative. Taken together our data indicate that single antigen bead results for DR7 pediatric heart transplant patients should be carefully reviewed and antibodies to DR4, 7 and/or 9 specificities should be verified using mock donor XM. This will ensure only clinically relevant antibodies are listed as unacceptable antigens in UNOS and greater access to donors.