Background: DSA is associated with increased risk for acute antibody mediated rejection (AMR). The optimal immunosuppression strategy for FCXM negative (-) DSA positive (+) renal transplant recipients has yet to be elucidated. The aim of this study is to examine the association between immunosuppression regimen and development of AMR among FCXM(-) DSA(+) renal transplant recipients.

Methods: We prospectively identified FCXM(-) DSA(+) renal transplant recipients between 2009-2011 (study group). All patients received antithymocyte globulin (rATG) induction and tacrolimus, mycophenolate and prednisone maintenance. No patients underwent desensitization although 2 gm/kg of IVIG was given peri-transplant for DSA MFI > 2500. The study group was compared to a cohort of 120 FCXM(-) DSA(-) kidney transplant recipients matched (in a 1:3 fashion) for age, sex, race and date of transplant.

Results: Forty (5%) of the 733 kidney transplant recipients were FCXM(-) DSA(+). 94% had a single DSA (MFI 900-6000). 67.5% had no detectable DSA at last follow up (f/u) with median f/u time of 16 months. Rate of acute AMR was 15% (6/40) in the study group vs. 1.5% (2/120) in the control group. There was 1 death and 3 graft losses in the control group but none in the study group and there were no differences in median MDRD GFR in between groups.

Conclusion: AMR risk in FCXM(-) DSA(+) renal transplant recipients is low and is not associated with increased graft loss with the use of standard immunosuppression with rATG induction and tacrolimus, mycophenolate and prednisone maintenance in the short to intermediate term f/u. Desensitization is not necessary. The fact that DSA disappeared in two thirds of patients, in the presence of excellent graft function, indicates some likelihood of good long-term outcomes. These findings have relevance in assigning unacceptable antigens and defining AMR risk.

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