LAUSR

Aim Donor specific antibodies (DSA) directed to mismatched HLA-DQB antigens are the most prevalent DSA after transplantation. Such DSA have been implicated in the pathogenesis of chronic antibody mediated rejection and graft loss. Currently, patients listed for deceased donor kidney transplantation receive priority points for each HLA-DR, but not DQ, matched with their donor. We aimed to determine whether HLA-DR matching impacts the formation of DQB DSA. Methods Our study population included 567 patients without pre-transplant DSA who received kidney transplantation from Jan 1st 2009 to Dec 31st 2014. HLA typing of recipients and donors was performed by SSO/SSP. Pre- and post-transplant testing of anti-HLA antibodies was performed using solid phase assay (One Lambda). Prospective T and B cell crossmatches were performed in all cases by flow cytometry. Results Out of 567 patients, 72 (13%) had zero, 215 (38%) had one and 280 (49%) had two DR mismatches (mm) with their respective donor. Overall, during the follow-up interval (median 4.6 years), 92 (16%) patients developed DSA. Twenty-four patients (4%) developed class I DSA, 44 (8%) had cl II DSA and 24 (4%) had cl I and II DSA. Among patients with zero HLA-DR mismatches, only 9% developed DSA. These DSA were directed to the mismatched HLA class I antigens and, in only one case, to a mismatched DQB antigen. The percent of patients who developed DSA was significantly higher in the groups with 1 or 2 DR mm, namely 19% and 14%, respectively (p = 0.0002) The highest number of DQB DSA was observed in the group with 1 DR mm (Table 1). Conclusions Our results indicate that zero HLA-DR mm represents an acceptable surrogate for the absence of de novo DQB DSA. We suggest that the number of priority points received by patients with zero HLA-DR mm should be increased. This may limit the number of patients who develop de novo DQB DSA, resulting in improved transplant outcomes. No additional points are warranted for a single DR match, which does not appear to have any protective effect.