Background: Historically, poorer outcome has been reported in kidney re-transplant patients with repeat HLA mismatch antigens. Transplant practice has evolved. Risk of repeat mismatch antigen was re-evaluated.

Methods: Retrospective review of patients who received ABO-compatible kidney transplant with negative T/B lymphocyte crossmatch (AHG-CDC or flow cytometry) between 2003-2013 was performed. Excluded were patients with less than one year follow-up or patients who received zero-antigen mismatch kidney for HLA-A, B, C, DR, and DQ. Donor specific antibody (DSA by LABScreen), T cell mediated (TCM) rejection (biopsy), and graft loss (death-censored) were evaluated as patient outcome. Outcomes of re-transplant patients with repeat mismatch antigens (Group 1; N=21) was compared to re-transplant patients without repeat mismatch antigens (Group 2; N=36) and to patients with no previous transplant (Group 3; N=261).

Results: There was no significant difference in the three groups in follow-up period (overall 5.3 ± 3.0 years) or number of mismatch antigens (overall 6.9 ± 2.4). In Group 1, repeat mismatch antigens were HLA-class I (N=14, 66.7%), class II (N=3, 14.3%), or both class I and II (N=4, 19.0%). There were more sensitized patients (as evaluated by PRA>20%) in Group 1 (33.3%) and 2 (50%) than Group 3 (6.1%, p<0.001). Group 1 was not significantly different from the other two groups in developing de novo DSA, TCM rejection, and graft loss (all p-values >0.05 between any groups). Regardless of patient groups, higher relative risk (RR) of graft failure was seen in patients with DSA (RR=3.19, 95% CI: 1.81-5.64, p=0.0003) or DSA with TCM rejection (RR=4.61; 95% CI: 2.66-7.97, p<0.0001), indicating importance of patient monitoring in all groups.

Conclusion: Repeat mismatch antigen in kidney re-transplantation is not significantly associated with adverse outcome. Post-transplant monitoring is important regardless of repeat mismatch antigens.

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