OR18 Identification of Anti-Endothelial Non–hla Antibodies in Kidney Allograft Rejection

The endothelium is the initial point of contact between the donor allograft and the transplant recipient’s immune system and therefore is a likely source for the identification of novel non-HLA Ab associated with rejection. The goal of this study was to identify novel anti-endothelial non-HLA Ab associated with kidney allograft rejection. Endothelial cell cross matches (ECXM) of three renal allograft recipient cohorts (adult living donor recipients n = 105, adult deceased donor recipients n = 109, and pediatric allograft recipients n = 65) consisting of 69/279 recipients with renal allograft rejection identified 16 renal allograft recipients with ECXM+ sera at the time of rejection. 35 patient sera (pre-transplant sera n = 3, neat sera n = 16, and EC eluted sera n = 16) were analyzed by protein microarrays (ProtoArray, Thermo Fisher Scientific) to screen 9,000 human proteins and identify antigens that bind non-HLA Ab (Prospector software, z-score ⩾3 and CV < 0.5). Protein microarray analysis identified 391 proteins recognized by the pre-transplant sera and 1252 proteins in the neat post-transplant sera and 388 proteins bound by the eluted post-transplant sera. 135/388 EC-specific, non-HLA Ab were present in post-transplant sera. Gene ontology analysis of the 135 endothelial antigens identified biological processes enriched for response to stimulus and signal transduction, as well as other biological processes shown in the figure below. 12 Ab were prioritized to select for ligands with membrane localization, kidney expression and an increased Ab binding frequency and will be assessed in future validation studies by multiplex bead array. Protein microarray analysis identified 135 novel anti-endothelial non–HLA Ab associated with kidney allograft rejection. These Ab bind endothelial antigens that are enriched for biological processes involving signal transduction and response to stimulus.