P128 LOW MFI DP DONOR SPECIFIC ANTIBODY PRODUCES UNEXPECTED WEAK POSITIVE FLOW B CELL CROSSMATCH

The new Ontario provincial renal allocation algorithm utilizes virtual crossmatch (CXM) to indicate the presence of current and cumulative DP DSA. Deceased donor typing and corresponding DP antibodies as reported by the recipients HLA laboratory are used. Currently, the presence of DP DSA does not preclude allocation but notification of DP DSA is provided. The clinical significance of DP DSA has been debated in current literature and varying results may be reported depending on local thresholds for positivity. Given this, each local program determines how DP DSA will be handled on a cases by case basis. Data is being collected by the provincial resource center on the ability of the DP virtual CXM to predict positive flow CXM. Our center has adopted a policy to accept all allocations with the presence of DP DSA and rely on a negative flow CXM to proceed to transplant. When the likelihood of flow CXM being positive is high, the program will bring a backup recipient into hospital. When the likelihood is low, the lab will perform CXM on two backup recipients that will not be brought into hospital. Our first case of DP DSA was in a 58year old female with a cPRA of 98%, a potential DQ6 allele specific antibody and a DP3 DSA. The DQ6 allele specific antibody was ruled out and our local criteria indicated low likelihood of positive CXM due to low MFI (1000–2100) for the DP3 DSA. Other DP antibodies in the DED DEAV epitope pattern were present but with low MFI (1500–1900). We proceeded to flow CXM with this recipient and 2 backups that were not brought into hospital. Surprisingly, the B cell CXM testing performed on current monthly serum was positive. Unfortunately this DCD donor was not declared in the prescribed time frame and donation did not proceed. Single antigen bead testing was performed post call on the CXM serum to determine if new DSA was present. The antibody profile remained the same indicating the DP epitope group with the DP3 DSA all with low MFI. Further studies will be performed with surrogate DP3 positive and negative cells to lend more support to a determination of true DP DSA or some other non HLA reactivity.