Novel Improvement of Haploidentical Hematopoietic Stem Cell Transplantation for Advanced Refractory/Relapsed Acute Leukemia

▪ Introduction The advanced refractory/relapsed acute leukemia has a very dismal prognosis even with the salvage allogeneic hematopoietic stem cell transplantation (allo-HSCT). To develop a novel transplant protocol to achieve a rapid engraftment and quick graft-versus leukemia (GVL) effect is crucial. Based on previous observation, the G-CSF primed bone marrow (BM) plus peripheral blood mononuclear cells (PBMNCs) could not only increase mononuclear cells and CD34 cells, but also change T-cell biology by down-regulating the expression of adhesion and CD28/B7 molecules and increase the absolute number of D2APCS, which promotes a T-cell shift from T1 to T2 subset to secrete a higher anti-inflammatory cytokines of IL-4 and IL-10. After going through a rigorous conditioning, the recipients' T-cells are incapable to attack host. We propose that reinfusion of G-CSF primed donor PBMNCs to recipient on transplant day + 6 may cross mismatched MHC barrier thus accelerating engraftment. Patients and Methods From April 2018 to June 2019, 30 advanced-stage patients with refractory/relapsed acute leukemia were enrolled and underwent a salvage haploidentical (haplo)-HSCT. The median age was 12 (2-63) years with M/F ratio of 17/13. There were 21 patients with acute myelocytic leukemia (AML, 70%), 4 -cell acute lymphoblastic leukemia (B-ALL, 13%), 2 biphenotypic acute leukemia (BAL, 7%), 1 juvenile myelomonocytic leukemia (JMML, 3%), and 2 T-lymphoblast leukemia (T-LBL, 7%). The median BM blasts were 40% (5%-90%). Twenty-eight patients received a conditioning regimen including fludarabine 30mg/m2/d×4 day, cytarabine 2.0g/m2/d×4 days, busulfan 3.2mg/kg/d Q6h×4days, cyclophosphamide 1.5g/m2/d×2 days and melphalan 110mg/m2/d×1 day. Two patients with T-LBL received BCNU+Etoposide+Cytarabine+Melphalan (BEAM) regimen. Graft-versus-host disease (GVHD) prophylaxis contained methotrexate (MTX), cyclosporine A (CsA) and mycophenolate mofetil (MMF), plus ATG (Rabbit anti-human thymocyte immunoglobulin, Sangstat) 1.5mg/kg/d iv daily from day -4 to -1 and additional 1.5mg/kg on day +7 (total dose of 7.5 mg/kg). In addition, anti-CD25 monoclonal antibody (basiliximab) 20 mg on day+1 and +4 was given iv. Donors were primed with G-CSF at 3-4 ug/kg/d sq d1-5. On day 4 of G-CSF, donor BM cells were harvested and were infused unmanipulated on the same day to patient on transplant day 01. On day 5 of G-CSF injection, donor primed PBMNCs were harvested, part of which were immediately infused u