*Purpose: The prognostic value of low level preformed donor-specific antibodies (DSA) remains controversial for kidney transplantation. The aim of the present study was to investigate the impact of low level DSA on post-transplant renal outcomes in living donor – (LDKT) and deceased donor kidney transplantation (DDKT).

*Methods: This study included 1,034 cases of kidney transplantation (KT) (LDKT; 634 cases, DDKT; 400 cases) performed between Jan 2010 and Dec 2018 in Seoul St. Mary’s hospital. Low dose DSA was defined as the presence of pre-transplant DSA, which mean fluorescence intensity (MFI) level was less than 5000, regardless of cross-match results. Patients with DSA, which MFI level≥5000 were excluded. 53 of 634 LDKT cases and 17 of 400 DDKT cases had low dose DSA. Finally, there were 53 low dose DSA (+) LDKT, 581 DSA (-) LDKT, 17 low dose DSA (+) DDKT and 383 DSA (-) DDKT patients. We compared the impact of low dose DSA on post-transplant renal outcomes such as the biopsy-proven antibody-mediated rejection(ABMR), the change of allograft function, allograft or patient survival, and post-transplant infections in both LDKT and DDKT. Additionally, we investigated composite outcome, which was defined as (i) allograft rejection or (ii) allograft failure or (iii) post-transplant infection.

*Results: The incidence of biopsy-proven antibody-mediated rejection(ABMR) within 1 year was significantly higher in low dose DSA (+) group compared to DSA (-) group in LDKT (17.0%, 9/53 versus 2.8%, 16/581, P < 0.001), while there was no difference in DDKT (11.8%, 2/17 versus 2.6%, 10/383, P = 0.087). In LDKT, the allograft function after 24 months of KT was significantly inferior in low dose DSA (+) group compared to DSA (-) group (P < 0.05). In DDKT, the allograft function was significantly inferior in low dose DSA (+) group compared to DSA (-) group at 12 months of KT (P < 0.05). However, this difference disappeared after 12 months. There was no difference in the allograft or patient survival rate according to the presence of low dose DSA in both LDKT and DDKT. In LDKT, the infection-free survival rate was lower in low dose DSA (+) group compared to DSA (-) group (9-year survival of 39.6% versus 51.1%, P = 0.027). In DDKT, there was no difference in infection-free survival rate between DSA (+) group and DSA (-) group (9-year survival rate of 23.5% versus 36.6%, P = 0.235). In LDKT, the composite outcome-free survival rate was lower in low dose DSA (+) group compared to DSA (-) group (8-year survival of 32.1% versus 44.2%, P = 0.004). In DDKT, there was no difference in composite outcome-free survival rate between DSA (+) group and DSA (-) group (8-year survival rate of 17.6% versus 29.5%, P = 0.057).

*Conclusions: In conclusion, preformed low dose DSA has a distinct impact on post-transplant clinical outcomes in LDKT, whereas this impact is negligible in DDKT.

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