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POST-TRANSPLANT PERSISTENCE OF PRE-FORMED DONOR SPECIFIC CLASS I AND CLASS II ANTIBODY DETECTED BY FLOWPRA IN PRIMARY RENAL ALLOGRAFTS TRANSPLANTED WITH A NEGATIVE ANTI-HUMAN GLOBULIN ENHANCED CROSSMATCH.
D. Pochinco , D. Kelm , K. Hacking , I. Dembinski , D. Rush , M. Karpinski and P. Nickerson . ¹ Faculty of Medicine, University of Manitoba, Winnipeg, MB, Canada .

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Pre-formed donor specific antibody (DSA) detectable by flow cytometry, but negative by cytotoxicity is generally only considered a risk factor for primary renal allograft transplantation. The purpose of this study was to determine the persistence of such pre-existing DSA monitored at serial time points post-transplant in patients with functioning grafts. We examined a group of 243 primary renal transplant recipients transplanted between 1992 and 2004 with undetectable Class I and II antibody by AHG-CDC T cell or extended CDC B cell crossmatch methodology. Of this group, 31 (13%) had DSA detectable in current pre-transplant sera proven by FlowPRA Single Antigen beads. Early humoral graft loss was experienced in 8/31 patients, while 23/31 maintained a functioning graft past 1 mo. out to a minimum of at least 1 yr. These 23 patients were selected for FlowPRA Single Antigen testing at 1 mo., 6 mo., and 1 yr post-transplant in order to confirm absence/presence of DSA. At 1 mo., 19/23 (83%) patients still had DSA present, while at 6 mo., DSA was detectable in only 5/23 (22%) patients. In contrast, at 1 yr, only 1/23 (4%) had persistent DSA remaining.

Persistence of DSA by Antibody Class

DSA pre-transplant (N = 23)	DSA at 1 mo.	DSA at 6 mo.	DSA at 1 yr
Class I (13)	9 (69%)	2 (15%)	0 (0%)
Class II (8)	8 (100%)	2 (25%)	0 (0%)
Class I II (2)	2 (100%)	1 (50%)	1 (50%)

In conclusion, although pre-existing low level DSA is still present at 1 mo. post-transplant, by 6 mo. it diminishes significantly and generally at 1 yr is no longer detectable in this group of transplant recipients.