Introduction: Technological advancements in high-resolution human leukocyte antigen (HLA) typing has revolutionized the field of transplantation, potentially enabling selection of optimally compatible, low immunogenic kidney grafts. The recent introduction of a policy delineating a 250 nautical mile concentric allocation circle rule may offer a unique opportunity finding low immunogenic donors for eligible recipients. Our preliminary analysis explored the potential for transplant candidates in our transplant center to assess the feasibility of identifying ideal HLA-matched donors for our candidates from the collective donor pool within the specified 250 nautical mile radius.
Methods: We performed a simulation of donor-recipient matching using active 672 transplant candidates listed at the University of Toledo Medical Center (UTMC) with all potential 6558 donors procured within 250 nautical miles radius between January 2014 and December 2019. We  leveraged our newly developed allocation algorithm that optimizes the number of transplants under the immunogenicity threshold score of 10, and then compared these simulated “optimal” matches with “real life” retrospective cohort with various levels of hydrophobic mismatch score, HMS .
Results: 492 recipients out of all 672 patients (73%) were matched with “optimal” immunogenicity donors under the low immunogenicity HMS threshold of 10. Furthermore, the matching efficiency out of available 6558 donors was extremely high as the average HMS immunogenicity value of selected “theoretical” transplants was 1.4 in a simulated cohort compared to 5.8 in the real-life reference cohort (p>0.05). This simulated model showed that selected transplants out of 6558 donors had a median HLA-A/B/DR mismatch score of 2 with 4 perfectly HLA-A/B/DR matched alleles. In contrast, the real-life cohort had a 4-mismatch score with only 2 matched HLA-A/B/DR alleles (p>0.05). The estimated median graft survival was 14.5 years for the optimally matched cohort, which was much better than only 10.4 years in the real-life cohort (p>0.05).
Conclusion: Our analysis showed that an increased number of available donors within 250 nautical miles proffered much better options for finding low HLA immunogenic kidney donors for the majority of patients at UTMC, thus significantly improving chances for kidney allograft survivals.