Recipient Human Leukocyte Antigen-DR Homozygosity and Access to Quality Kidneys

A primary objective of transplantation is equitable access to quality deceased donor kidney transplantation (DDKT), which includes highly-matched human leukocyte antigen (HLA)-DR DDKT. Little research has been conducted on DDKT access among HLA-DR homozygous candidates, who have 2 serologically equivalent HLA-DR alleles and have low frequency in general populations. Our aim was to investigate DDKT access by HLA-DR mismatches across HLA-DR homozygosity and race/ethnicity.

Our Scientific Registry of Transplant Recipients (SRTR) sample included 262,815 adult, primary, kidney-only transplant candidates from January 1, 2015 to May 31, 2024. We used 2021 Organ Procurement and Transplantation Network (OPTN) equivalency tables to identify serologically equivalent HLA-DR antigens for defining HLA-DR homozygosity and mismatches. We conducted Fine and Gray's competing risk analysis to estimate subdistribution hazard ratios (sHRs) for receiving all DDKT and DDKT with 0, 1, and 2 HLA-DR mismatches by HLA-DR homozygosity alone and interacted with race/ethnicity.

HLA-DR homozygosity was associated with a 0.95 sHR (95% confidence interval [CI]: 0.93-0.97) of receiving all DDKT, 0.46 sHR (95% CI: 0.43-0.49) of receiving DDKT with 0 HLA-DR mismatches, 0.83 sHR (95% CI: 0.81-0.86) of receiving DDKT with 1 HLA-DR mismatches, and conversely, 1.40 sHR (95% CI: 1.36-1.44) of receiving DDKT with 2 HLA-DR mismatches. Models interacting HLA-DR homozygosity and race/ethnicity showed that HLA-DR homozygosity was associated with a lower likelihood of receiving DDKT with 0 HLA-DR mismatches for all races/ethnicities.

HLA-DR homozygosity was associated with lower access to DDKT, particularly highly-matched DDKT, irrespective of race/ethnicity. Prioritization for access to transplantation should incorporate HLA-DR homozygosity to promote equity.