HLA-Haploidentical Hematopoietic Cell Transplantation after TCR-Αβ and CD45RA+ Depletion Following Reduced Intensity Conditioning in Adults and Children with Hematological Malignancies: Three-Year Follow-up of Multicenter Study in Singapore

Background: Haploidentical hematopoietic cell transplantation (HCT) provides an alternative option for patients without HLA-matched donor. Graft-versus-host disease (GVHD), engraftment failure, and infectious complications continue to be the main causes of non-relapse mortality (NRM). We hypothesized that selective depletion of TCRαβ+ and CD45RA+ naïve T-cells subset will permit hematopoietic engraftment, while effectively reducing GVHD, and provide improved donor immune reconstitution through adoptive transfer of donor’s mature NK-cells, γδ T-cells, and CD45RO+ memory T-cells. Methods: Mobilized PBSC products were divided into two fractions in 9:1 ratio and depleted using CliniMACS device after labeling with TCRαβ and CD45RA reagents (Miltenyi Biotec, Bergish-Gladbach, Germany), respectively. The conditioning regimen consisted of fludarabine 160mg/m2 divided daily over 4 days, thiotepa 10mg/kg divided twice daily for 1 day, and melphalan 70-140mg/m2 for 1 day, in combination with total lymphoid irradiation 6Gy (n=35) or 7.5Gy (n=12) over 3 equal fractions, total body irradiation of 2Gy (n=13) or antithymocyte globuline (n=2). Short term GVHD prophylaxis for 30 days was given to 1 patient using MMF, 50 patients using tacrolimus, and 2 patients using sirolimus. Results: We transplanted 62 patients, including 55 adults (median age, 47 years; range 20-69) and 7 children (median age, 13 years, range 7-17) with high risk AML (n=34), ALL (n=15), MDS (n=7), plasma cell neoplasm (n=2), mast cell leukemia (n=1), acute undifferentiated leukemia (n=1), and NK/T-cell lymphoma (n=1). The patients were infused with TCRαβ and CD45RA depleted graft containing a median of 6.79 x 106 (range 3.54-20.78) CD34+ cells/kg, 0.00 x 104 (range 0-0.97) CD45RA+CD3+ cells/kg, and 1.09 x 106 (range 0.15-11.67) CD45RO+CD3+ cells/kg. The TCRαβ depleted graft fraction contained a median of 0.20 x 104 (range 0-11.30) TCRαβ+ cells/kg, and 8.52 x 106 (range 0.62-30.00) TCRγδ+ cells/kg. Only 1 patient experienced primary graft failure. All others had engraftment of ANC > 500 cells/µL at a median of 10 days (range 8-22) and platelet > 20,000 cells/µL at a median of 12 days (range 8-22). There was no secondary graft failure. Six patients with high titers of donor-specific HLA antibodies (DSA) engrafted successfully after effective desensitisation with plasma exchange, rituximab, and immunoglobulin. Twenty-two patients (35%) developed acute GVHD of grade II - IV (Gd II, n=15; Gd III, n=5; Gd IV,