*Purpose: Graft survivals are inferior for African American (AA) patients in comparison to Caucasian (CAU) patients in the United States. We examined how donor and recipient race may impact kidney transplant survivals evaluated by the physiochemically-calculated HLA immunogenicity (IM).

*Methods: Four patient cohorts of deceased donor transplants from 1987-2016 (SRTR database) included: 1) 60,544 CAU donors to CAU recipients (CAU-CAU); 2) 9,858 AA to AA (AA-AA); 3) 30,438 Cau to AA (CAU-AA); and, 4) 6,450 AA to CAU (AA-CAU). The HLA-A/B/DR for all these patients were converted from 2- to 4-digit HLAs using the HaploStats algorithm. The Oxford algorithm calculated the donor/recipient HLA IM based on physiochemical properties of their hydrophobic mismatch score (HMS): the death-censored graft survival was the endpoint

*Results: Chi-square test showed that AA patients were younger (AA=50.2 years vs. CAU=54.2 years; p < 0.0001), more sensitized (AA cPRA=17.7% vs. CAU=13.6%; p < 0.0001) and AA waited longer for transplants (p < 0.0001). While CAU-CAU group had the best 15-year graft survivals (Fig. 1A) followed by AA-CAU group (Fig. 1B), the donor race (CAU or AA) had a significant impact on the graft (p<0.0001) but not the patient (p=0.24) survival. In contrast, both AA-AA (Fig. 1C; p=0.0001) and CAU-AA (Fig. 1D; p=0.0001) groups had inferior 15-year graft survivals in comparison to CAU recipients regardless of their donor race. All transplanted AA recipients had an average HMS score of 8.3 that was higher than HMS score of 7.2 for all CAU recipients (p<0.001). The same pattern was confirmed by the higher MM score of 4.4 for AA group compared to the MM of 3.4 for CAU recipients (p<0.001). Interestingly, low IM transplants (HMS<6.8) significantly improved graft survival in CAU-CAU group (15.7 years) in comparison to high IM transplants (13.7 years; p<0.0001). This benefit disappeared for AA-CAU au group (p=0.8). Similarly, low IM transplants (HMS<7.3) improved graft survival in AA-AA group (9.4 years vs. 8.4 years; p=0.0002) but was less pronounced in CAU-AA group (9.9 years vs. 9.6 years; p=0.001).

*Conclusions: Overall, AA recipients had higher IM and MM scores than CAU recipients. The selection of donors with low IM values benefits more inter-racial that intra-racial transplants

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