OR48 Haploidentical hematopoietic cell transplantation in a highly sensitized patient with donor-specific antibodies – A success story

A nine-year-old female with refractory Acute Myelomonocytic Leukemia (AML) was referred to our institute for Hematopoietic Cell Transplant (HCT) in 2015. While preparing for transplant, this patient became severely refractory to platelet transfusion. HLA antibody identification using single antigen bead technology revealed that she was highly sensitized to both HLA class I and class II antigens and had donor specific antibodies (DSA) to both parents (antibodies against HLA-B35 specific for her father; antibodies against A36 and DQ2 specific for her mother). Flow cytometric T cell allo-crossmatch of patient serum was positive with both parents. Unfortunately, this patient had no full siblings and an unfavorable matched unrelated donor search. The patient had few options other than haploidentical HCT from one of her parents and was therefore given a desensitization regimen of rituximab and plasmapheresis. Following two cycles of desensitization, overall class I PRA remained high (91%), but the patient’s DSA against her father (B35) became negative. The patient’s maternal DSA to DQ2 persisted. Patient/father T cell crossmatch after the desensitization treatment was diminished to borderline. The patient proceeded to HCT using her father as the donor, and was supported with HLA compatible platelets in the post-transplant period. She had neutrophil and platelet engraftment by days +13 and +19 respectively, following HCT. HLA antibody testing on the patient’s serum nine months post-transplant revealed greatly reduced antibody positivity with only two positive class I specificities and no antibodies to class II. This patient continues to remain in remission nearly three years post-transplant. This case study highlights the value of desensitization regimens for patients with donor specific antibodies and few donor options for HCT.