#11-OR
COMPLEX HLA ANTIBODY RESPONSES: HLA-A2 SUBTYPE REACTIVE ANTIBODIES IN HIGH PRA SERA.
David Kahle MA 1, Van Cagahastian BS 1, Angela Michael BS 1, Paul Kawczak BS 1, Alan Smerglia BS 1, Daniel Cook Ph.D. 1 and Edward J. Ball Ph.D. 1. 1 Allogen Laboratories, Cleveland Clinic Foundation, Cleveland, OH, USA .
A significant portion of patients awaiting transplant are highly sensitized to HLA as measured by PRA. Such individuals commonly have multiple antibody populations specific for different HLA antigens and epitopes. The ability to identify individual specificities has been greatly facilitated by methods that use purified single antigen targets. Using single antigen flow beads, we previously found that most high PRA sera with HLA-A2 reactivity demonstrate reactivity against other A2-CREG antigens, confirming studies of others using traditional serologic methods. We have now further investigated anti-A2 antibodies in high PRA sera using beads coupled with A*0201, A*0203, A*0205, A*0206, A*0210 subtype products. The amount of antibody bound was estimated by comparison to reference beads and corrected for the level of binding by W6/32 monoclonal antibody. Relative binding greater than 20% of maximum was considered positive. Sera from A2-positive donors were selected based on known A*0201 reactivity or potential A*02 subtype reactivity based on generic level screening. Six of 26 such sera were found to have A*02 subtype specificity: A*0210 (n=4), A*0205 (n=1), A*0201/*0203/*0206*0210 (n=1). DNA typing of serum donors showed that those with A*0205 or A*0210 specificity were all A*0201, while the donor with anti-A*0201/03/06/10 specificity was A*0202. Comparison of sequence alignments of A*02 allele subtypes suggests particular residues are critical to these patterns. Knowledge of allele subtype epitope reactivity can be useful in predicting cross match results and may be particularly important in evaluating HLA 
antigen level matched prospective donors for transplantation.