Background: De novo DSA formation is emerging as an important risk factor for adverse graft outcomes following renal transplantation. Specific pretransplant risk factors for DSA formation within one year have not been fully elucidated. Methods: 443 consecutive kidney-only recipients (without pre-existing DSA), managed with a standardized Tac/MMF/pred regimen and transplanted between Jan.2008 and Jan. 2013 , were prospectively monitored (at 1,3,6 and 12 months) for appearance of de novo DSA within one year of transplant. Of these, 401 had at least 4 DSA measurements and graft survival >1 year. Risk factors assessed were: age, race, gender, ESRD cause, diabetes, BMI, pretransplant dialysis, ABO type, donor source (LD vs DD), repeat transplant, induction (thymoglobulin vs IL-2R), pretransplant HLA sensitization, HLA mismatches, crossmatch status (T and B cell) and posttransplant dialysis. Statistical methods included Kaplan-Meier and Cox Regression. Results: 55/401(14%), developed DSA within one year of transplant (median time 39 days). However, 18/55 (33%) of DSA was transient (resolving without treatment). Therefore only 9% developed persistent DSA. All DSA with initial sumMFI > 4000 were persistent (23/23) whereas 16/28 with sumMFI < 4000 were transient. Class II DSA were more common than class I (69% vs 51%), with DQ the single most common (45%). DSA impacted overall graft and death-censored graft survival at 4 years (96% vs 86%; p=0.03 and 98% vs 92%; p=0.04 respectively). Of all pretransplant risk factors analyzed, only pretransplant sensitization appears to be a strong predictor for DSA within one year (Class I sens: 22%, Class II sens: 26%, Class I and II sens: 29%; p < 0.01 for all). Sensitized recipients developed DSA earlier than nonsensitized, (33 days vs 91 days; p=0.03). Patterns of pretransplant HLA antibody: strength (MFI's) and breadth (number of HLA antibodies) did not correlate with posttransplant DSA. Recipient age, race, gender, diabetes, transplant type (DD vs LD), HLA mismatches, crossmatch results, DGF and induction regimen (adjusted for sensitization) were not significant risk factors. Conclusion: Although de novo DSA within the first year after kidney transplant may be harmful, the incidence is low. Aside from pre-existing HLA sensitization, reliable pretransplant predictors for DSA are lacking; thus it remains difficult to identify a target population for preventative measures.

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