P244 False positive (self) antibodies in a haploidentical SCT case

Abstract

Case History: We evaluated a recipient for potential haploidentical stem cell transplantation for AML. The recipient, a 70 year old Asian man had an HLA typing of A∗02:03,24:02 B∗39:05,55:02 C∗07:02,12:03 DRB1∗09:01,16:02 DQB1∗03:03,05:02 DPB1∗04:01,05:01. No HLA matched related or unrelated donor was identified. Haploidentical transplantation was recommended. The recipient had two children; a son (HLA typing ∗11:01,24:02 B∗15:02,55:02 C∗08:01,12:03 DRB1∗12:02,16:02 DQB1∗03:01,05:02 DQA1∗02:02,04:01 DPB1∗02:02,04:01) and a daughter (HLA typing A∗02:03,24:02 B∗39:05,55:02 C∗01:02,07:02 DRB1∗09:01,12:02 DQB1∗03:01,03:03 DQA1∗03:03,06:01 DPB1∗05:01,05:01). Methods: The recipient had been heavily transfused and was testing for allo-sensitization by screening and single antigen bead assay in August 2016. Anti-HLA-B75 (15:02) was detected with a mean fluorescence intensity (MFI) of 1139 and was considered as a potential donor specific antibody (DSA). As such the son was not considered to be a suitable donor due to the potential presence of DSA in the recipient. His daughter was also evaluated at the same time and no DSA were detected. Later in October 2016 repeat testing demonstrated further sensitization with anti-DRB4 and -DPB1∗05 being detected, at 1494 MFI and 4272 MFI respectively. With these findings one would predict a positive flow cross-match (FCXM) between recipient and his daughter. We performed flow crossmatch to examine the validity of the DPB1∗05:01 and DRB4∗01:01 specificities. Results: Crossmatch with the daughter and a DPB1∗05:01 positive surrogate donor resulted in negative FCXM while crossmatch with the son was positive. FlowPRA phenotype beads were used to assay patient serum and no anti-HLA-class II antibodies were detected. Conclusion: All results considered we conclude that these are non-HLA antibodies that bind to single antigen beads, that appear as potential DSA but are not relevant when assessed by surrogate crossmatch. Flow crossmatch is important to rule out the possibility of a false positive antibody. Phenotype beads assay plays an important role to differentiate non-HLA from HLA antibodies especially those of class II. Relevant low level MFI alloantibodies can co-exist with non-HLA (auto) antibodies that have a significant MFI. Download high-res image (225KB) Download full-size image