*Purpose: The benefit of class II HLA matching is primarily shown in deceased donor kidney transplantation. The objective of this study was to determine the association of DRB1 and DQB1 mismatches with kidney allograft loss in a contemporary cohort of patients receiving a living donor kidney transplant.

*Methods: Using 2020 SRTR data, we conducted a retrospective study of adult primary kidney recipients who received a living donor kidney-only transplant between Jan 1, 2010 and Dec 31, 2017 (n=38,699). Patients with missing HLA (n=1,267) or those with broad DRB1/DQB1 typing in the patient or donor (n= 2,164) were excluded. The final study cohort included n=35,268 patients (52% biologically related; 48% unrelated) with a median follow-up time of 6 years. Using the Kaplan-Meier methods, we analyzed the time to death censored graft loss, stratified by HLA mismatch and donor relationship.

*Results: Recipients of a 0-DRDQ mismatch living donor transplant had superior allograft survival compared to those with class II mismatches, but this was only observed in those receiving a living-related kidney transplant (Fig 1). When the analysis was further stratified to include an additional subgroup (0 ABDRDQ mm) to account for 2-haplotype matched donor-recipients who might have additional immune benefits beyond DRDQ matching, the inferior allograft survival with class II mismatches was no longer observed (Fig 2).

*Conclusions: Outside of 2-haplotype matched donor-recipient pairs, class II mismatches at DRB1 and DQB1 are not associated with kidney allograft loss in living donor kidney transplants with medium term follow-up.

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