P158 Selective antibody reactivity against HLA-DQA1 in transplant candidates is rare

Aim Single antigen bead (SAB) assay is used to test the presence of antibodies against HLA antigens including HLA-DQ. Each SAB DQ bead is comprised of an alpha and a beta chain representative of an HLA-DQ antigen. A positive result represents reactivity to either or both chains. The aim of this report is to evaluate the frequency of HLA-DQ alpha antibodies in transplant candidates known to have Class II antibody. Methods Class II SAB data (One Lambda Inc.) was collected from 2346 transplant candidates at Brigham and Women’s Hospital from 6/9/2012 to 1/15/2014. The reactivity to HLA-DQ alpha was considered positive (MFI >3000) if all the beads containing a specific HLA-DQ alpha were reactive but the beads with corresponding HLA-DQ beta chain were negative. For example, the sera which were considered positive for HLA DQA1*03:02, had positive reaction with two beads containing DQA1*03:02, [DQA1*03:02, DQB1*03:02] and [DQA1*03:02, DQB1*03:03], but negative reaction with five beads positive for either DQB1*03:02 or DQB1*03:03 combined with DQA1 chains other than DQA1*03:02. Results Of the 29 HLA-DQ assay beads, 12 different HLA-DQ alpha chains were combined with different HLA-DQ beta chains. Sixteen (16/2346, 0.69%) sera reacted with beads specific for DQA1*03:02. These sera reacted with the alpha chain in combination with either DQB1*03:02 or DQB1*03:03. A similar pattern could be observed with sera (17/2346, 0.72%) that had specific reactivity to DQA1*02:01. Interestingly, none of the sera appeared to react selectively with DQA1*01:01, DQA1*01:02, DQA1*03:01, or DQA1*05:01. Although reactions with beads coated with DQA1*01:03, DQA1*03:03, DQA1*04:01, DQA1*05:03, DQA1*05:05, or DQA1*06:01 were present, they could not be attributed to DQA1 as the number of reactions or beads were not sufficient to rule out reactivity to DQB1. Out of the 33 patients who showed reactivity to either DQA1*03:02 or DQA1*02:01, only three (9.1%) had reactivity exclusively to the HLA-DQ alpha chain with no reactivity to any other HLA class II antigen. Conclusions The frequency of antibodies which appear to have HLA-DQ alpha specificity in transplant candidates is low (1.4%). Our results imply that a large number of sensitized patients will have to be studied in order to determine the clinical significance of antibodies to DQAlpha.