P156 An unexpected discovery complicates an otherwise uneventful HLA identical hemapoetic stem cell transplant

Abstract

Oncology patients frequently require platelet transfusions during chemotherapy regimens. This case involves a 46 year old woman diagnosed with myelodysplastic syndrome, who developed HLA antibodies following platelet transfusions. The patient was then evaluated for a Hematopoietic Stem Cell Transplant (HSCT) with her sister. HLA typing was performed using rSSO, (One Lambda, Inc., Canoga Park, CA) and SBT with BigDye V1.1 Terminator reagents on a 3500 Genetic Analyzer (Applied Biosystems, Foster City, CA). HLA-specific antibody was assessed using phenotypes, LMID, (Lifecodes®, Immucor, Norcross, GA) and single antigen panels (One Lambda Inc., Canoga Park, CA). Flow cytometric crossmatch tests were performed on a BD FACSCanto II. Intermediate typing failed to identify the patient’s A-Locus antigen using peripheral blood and buccal samples. SBT typing revealed a novel HLA-A∗02 allele that differed from the HLA-A∗02:01 present in her otherwise HLA identical sibling. Sequence alignments showed an apparent HLA-A∗02:01/A∗03:XX gene conversion event involving exon 3. HLA antibody assessments of the patient’s serum showed low level sensitization toward HLA-A2, A9, A28, A25, A26 and A66. A negative flow cytometric crossmatch confirmed the low strength of the HLA-A2 antibody. The urgency for transplant and low likelihood of finding a donor for which the patient was not sensitized (CPRA = 77) precipitated her placement into our desensitization HSCT protocol. A non-myeloablative, HLA-A mismatched HSCT with her sibling occurred following desensitization using plasmapheresis and low dose IvIg. Identification of HLA antibodies is crucial for HSCT programs that support HLA mismatched transplantation. New or rare alleles can pose additional challenges in HSCT with regards to matching with potential donors and avoiding sensitization to common HLA antigens found in blood products.