*Purpose: Current US- based data suggests Black patients awaiting kidney re-transplantation are more likely to be highly sensitized compared to other races. Degree of HLA mismatching at first transplant has been suggested as a potential contributor. Herein we examine the association between race, number of HLA mismatches and death censored graft-failure in a contemporary era.

*Methods: Using the United Network for Organ Sharing data, we identified first deceased donor kidney transplants between1/1/2015, and 6/1/2019 with follow-up to 9/1/2020. Recipients were classified by their number of HLA mismatches and race [Non-Hispanic White(NHW) vs Black]. Analyses employed Cox multivariate regression including interaction terms for race and number of HLA mismatches and adjusting for age, gender, cause of renal failure, education level, insurance, working for income, BMI, KDRI and cold ischemia time

*Results: 33,234 adults met inclusion criteria. 16,400 (49%) were NHW, 16,834 (51%) were Black. Compared to NHW, Blacks had greater proportions of HLA mismatch Table 1. Kaplan Meier estimates of death censored graft failure was greater for Blacks. For NHW, graft failure at 1 year, 3 years and 5 years were 3%, 6% and 12% respectively. For Blacks, 3%, 9% and 18% respectively (p value 0.001) Figure 1. With Zero mismatches as reference, an increased risk of graft failure was observed for 5 mismatches [HR 1.41 (95% CI 1.08-1.85)]; 6 mismatches [HR 1.38 (95% CI 1.04-1.83)]; and Black race [HR 1.26 (95% CI 1.15-1.39)]. When effect modification was assessed, Black race did not modify the effect of HLA mismatches on graft failure [p values for interactions not significant].

*Conclusions: While an increasing number of HLA mismatches and Black race are associated with a higher risk of graft failure, for each number of HLA mismatches (zero to six), Blacks do not have poorer outcomes compared to NHW. The greater proportion of highly sensitized Black patients awaiting re-transplantation is more likely due to a greater proportion having been transplanted with greater mismatch than a unique effect specifically related to race.

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