Blinatumomab As A Successful Bridge To Hematopoietic Stem Cell Transplant In A Down Syndrome Patient With Relapsed B-Precursor Acute Lymphoblastic Leukemia

Introduction Children with Down syndrome (DS) carry a 20-fold higher risk of developing acute lymphoblastic leukemia (ALL) than other children and have increased rates of treatment-related mortality (TRM) and relapse. The prognosis for relapsed DS-ALL patients is grim with long-term survival rates of 20%. Blinatumomab, a CD19/CD3 bispecific antibody, is FDA approved for relapsed pediatric pre-B ALL, and recently approved for patients with minimal residual disease (MRD). However there are few reports of the use of blinatumomab in DS-ALL patients, and no reports of blinatumomab as a bridge to stem cell transplant (SCT) in this population. Case Description A 19 year old male with DS presented with thrombocytopenia and was diagnosed with pre-B ALL. Upfront therapy included fractionated cyclophosphamide, vincristine, doxorubicin, dexamethasone, pegaspargase, and rituximab for 8 cycles, and he achieved complete remission (CR). Maintenance therapy included 26 months of 6-mercaptopurine, vincristine, methotrexate, and prednisone. He relapsed 5 months after completion of therapy and was found to have a P2RY8-CRLF2 fusion. IgH gene rearrangement analysis by next generation sequencing (LymphoTrack assay) demonstrated clonal rearrangement. Re-induction therapy included vincristine, pegaspargase, and prednisone. He completed 2 additional courses of chemotherapy but continued to have MRD both by flow cytometry and LymphoTrack. Given persistent MRD with CD19+ lymphoblasts, he was treated with blinatumomab at the FDA recommended dosing; he had no signs of toxicity. He achieved negative MRD by flow cytometry and LymphoTrack after 1 cycle. He then proceeded to a T-cell depleted peripheral blood SCT from a 10/10 matched sibling after conditioning with total body irradiation, thiotepa, and cyclophosphamide. Post-SCT course was uncomplicated and he is now 1 year post-SCT with no evidence of leukemia and 100% donor chimerism. Conclusion Blinatumomab is clinically effective and safe for patients with relapsed/refractory pre-B ALL, yet there is limited information on its use in DS-ALL patients. These patients have been largely excluded from blinatumomab trials given their altered immune system and unknown level of innate T cell dysfunction, potentially altering the efficacy of blinatumomab. We present here the case of a 22 year old male with relapsed DS-ALL who remained MRD positive after several cycles of re-induction chemotherapy, but achieved a CR following 1 cycle of blinatumomab with no toxicities, and safely proceeded to SCT. Although this is a single case, it demonstrates clinical efficacy of blinatumomab in relapsed DS-ALL, suggesting that these patients' T cells can be engaged to recognized CD19-positive leukemic blasts. Furthermore, blinatumomab represents a particularly attractive bridging therapy to SCT for DS-ALL patients who experience high rates of TRM with traditional agents.