Potential of new 250-nautical mile concentric circle allocation system for improving the donor/recipient HLA matching: Development of new matching algorithm.

Background: High-resolution typing of human leukocyte antigen (HLA) may revolutionize the field of kidney transplantation by selection of low immunogenic grafts. The new 250-nautical mile circle allocation system offers a unique opportunity to find low HLA immunogenic donors for eligible recipients.

Methods: 501 transplant candidates from the University of Toledo Medical Center (UTMC) between 2015 and 2019, registered at the Scientific Registry of Transplant Recipients (SRTR) were virtually matched to 4812 donors procured within 250-nautical miles using an in-house-developed simulation algorithm. Immunogenicity of HMS (hydrophobic mismatch score) ≤10 was measured based on imputed high-resolution HLAs. Simulated "optimal" matches with a KDPI≤50 % were compared with the transplant cohort between 2000 and 2010 with their kidney allograft survivals.

Results: Out of 501 recipients 500 (99.8 %) were matched with donors ≤10 HMS and KDPI ≤50 %. The average HMS value for simulated transplants was 1.4 (range 0-10) versus 6.3 (range 0-75) in the retrospective cohort (p < 0.001). The simulated model had a median mismatch number of 3/6, while the reference cohort 4/6 among HLA-A/B/DR antigens (p < 0.001). The estimated median graft survival was 18.2 years for the simulated cohort vs. 13.4 years in the real-life cohort (p < 0.001), gaining 4.9 years per transplant and 2450 survival years for all patients. For year 2014, out of 98 patients and 659 donors, each recipient had a median number of 141 donors (HMS < 10; range 8-378). Similar values were found for patients between 2015 and 2019.

Conclusion: Donors within 250-nautical miles proffers excellent and multiple options for finding well-matched low immunogenic HLA kidney donors for UTMC patients, thus significantly improving their chances for long-term allograft survival.