The optimal dose of posttransplant cyclophosphamide (PTCy) for use in patients undergoing HLA-haploidentical hematopoietic cell transplantation with posttransplant cyclophosphamide (PTCy-haplo) has not been sufficiently examined. This study evaluates the safety and efficacy of HLA-haploidentical hematopoietic cell transplantation with a reduced dose of PTCy for patients with a poor prognosis or those with refractory hematological malignancies. We conducted a prospective clinical study of PTCy-haplo with peripheral blood stem cells (PBSCs) using a modified PTCy dosage regimen consisting of 50 mg/kg on day 3 posttransplantation and a reduced dose of 25 mg/kg on day 4. The cumulative incidences of grades II to III and IV acute graft-versus-host disease (GVHD) at day 100 posttransplantation were 30% and 0%, respectively. The cumulative incidence of moderate-to-severe chronic GVHD after transplantation was 7.0%. The cumulative incidence of nonrelapse mortality at 1 year posttransplantation was 6.1%. Overall survival (OS) at 1 year was 66%. In addition, the restricted cubic-spline Cox regression analysis showed nonlinear relationship between the number of infused CD34+ cells and CD3+ cells, and OS. A graft composition of >4.54 × 106/kg CD34+ cells and >1.85 × 108/kg but ≤3.70 × 108/kg CD3+ cells was significantly associated with better survival, irrespective of the disease status (hazard ratio, 0.13; 95% confidence interval, 0.04-0.41; P < 0.001). These results suggest that PTCy-haplo with PBSCs using a de-escalated dose of 50 mg/kg on day 3 and 25 mg/kg on day 4 posttransplantation is a feasible option.
Keywords: HLA-haploidentical hematopoietic cell transplantation; a reduced dose of posttransplant cyclophosphamide (PTCy); graft cellular composition; peripheral blood stem cells (PBSCs).