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Abstracts S47 51-W DETERMINING THE OPTIMAL INTERVAL BETWEEN CONSECUTIVE HIGH DOSE IVIG ADMINISTRATION PRE-TRANSPLANTATION FACILITATED SUCCESSFUL HE...

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Abstracts

S47

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DETERMINING THE OPTIMAL INTERVAL BETWEEN CONSECUTIVE HIGH DOSE IVIG ADMINISTRATION PRE-TRANSPLANTATION FACILITATED SUCCESSFUL HEART TRANSPLANTATION IN A HIGHLY SENSITIZED PATIENT Sandesh Dev,1 William Cotts,1 Edwin McGee,1 John Friedewald,2 Marguerite Buckingham,2 Anat R. Tambur.2 1Heart Failure and Cardiac Transplant Program, Northwestern University, Chicago, IL, USA; 2Division of Organ Transplantation, Northwestern University, Chicago, IL, USA Aim: Pre-sensitization in heart transplant (HT) recipients is associated with an increased risk of rejection and vasculopathy. High dose IVIg (2 g/Kg) administered monthly has been demonstrated to lower allosensitization, but the optimal interval between dosing is not yet known. Methods: A 57-yo multiparous female was listed for HT after a blood transfusion with 54% AHG-PRA. Solid-phase based flow cytometric (FC) screen PRA was 95% for class I; and 0% for class II. Crossmatch (XM) results with 7 potential deceased heart donors were positive by cytotoxic and FC testing. A desensitization protocol consisting of serial IVIG 2 g/kg and MMF 1g/d was initiated. Since high dose IVIg precludes the use of more sensitive antibody ID and XM testing using cell-based assays, changes in HLAdirected antibody strength were monitored using solid-phase based methods. The complete panel of class I single-antigen coated microparticles (total of 80 specificities, One Lambda) was used in order to maximize the scope of testing. HLA-directed antibody specificities and their strength were determined weekly following manufacturers recommendations. Scope: Sixty of the 80 tested class I antigens reacted with the patient’s serum. Seven percent of antibodies had a titer of 1:256 (HLA-B7, -B61, -B72, -Cw6), and 24% had a titer of 1:64. Maximal effect of IVIg was noted two weeks after the 1st infusion, with a reduction in high-titer antibodies. At 3 weeks, however, some of the higher-titer antibodies began to re-appear, and a 2nd dose of IVIg was given. A further decrement in antibody titers was noted three weeks after the 2nd IVIg dose. During that period additional six potential deceased heart donors were XM positive with the patient’s sera and a 3rd dose of IVIg was administered, leading to further decrease in detectable antibody specificities. Two weeks after the 3rd IVIg dose, a donor heart with a negative virtual XM was identified. Retrospective testing, using pronase to remove Fc receptors, confirmed a negative T and B-cell FC and a weak positive T-cell cytotoxic XM. The patient received pre-HT plasmapheresis and 0.4gm/kg IVIg, followed by thymoglobulin and tacrolimus-based immunosuppression. At 2 weeks post-HT there was a low titer (1:4) donor-specific antibody (DSA) to HLA-Cw5 but no other detectable DSA in the serum or the graft. The patient is currently doing well 4 months post-HT and has been free of cellular and antibody-mediated rejection on protocol biopsies. Conclusions: High dose IVIg reduced antibody titers maximally at 2 weeks, followed by a rebound effect in this particular patient. By dosing IVIg at 3-week intervals, we achieved an additive effect in decreasing antibody strength. These results suggest that antibody titers should be serially assessed in order to optimize the IVIg dosing interval for an individual patient. Furthermore, the use of the virtual XM can facilitated HT in the face of high dose IVIg.

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INTERPRETATION OF ONE LAMBDA FLOW BEAD SCREENING AND IDENTIFICATION RESULTS: THE ROLE OF DRB3 Derek Middleton, Jeanie Martin, Bernie Magee, Miceal Cole. Histocompatibility and Immunogenetics Laboratory, Belfast City Hospital, Belfast, Northern Ireland, United Kingdom Aim: The regular monitoring of the HLA antibody status of patients awaiting kidney transplantation is a vital part of the routine work of the Histocompatibility laboratory. A patient who had been previously transplanted with the only apparent HLA mismatches being HLA-A30, -Cw5 was found to have class II IgG antibodies by Flow PRA Bead screening. Methods: Screening for HLA antibody is performed in this laboratory on samples taken every two months and on samples taken 10 and 30 days post transfusion. Screening is performed using Flow PRA Screening Beads with both IgG and IgM FITC conjugates (One Lambda). If a sample is found to contain antibodies further investigations are performed to identify specificity using Flow PRA Single Antigen Beads. Scope: The use of single antigen beads revealed that the patient had antibodies to DRB3*0201. This is the only bead available for DRB3. HLA typing for DRB3 using Luminex found that the recipient had DRB3*01 (probably *0101) whereas the donor was DRB3*01, 02 (probably *0101, *0202). Difference in sequence between DRB3*0201 and 0202 is only 4 nucleotides whereas both these alleles differ from DRB3*0101 by 35 and 33 nucleotides respectively. Conclusions: Patients with antibodies which cannot be explained by testing with single antigen beads for DRB1 and DQ should be screened for antibodies against DRB3, DRB4, DRB5 and DP. In these patients previous transplants should be typed for alleles of these four genes. Having available single antigen beads for all loci, thus making identification of antibodies feasible, changes interpretation of crossmatch results from an art to a science.