Unique Reduced-Intensity Conditioning Haploidentical Peripheral Blood Stem Cell Transplantation Protocol for Patients with Hematologic Malignancy

Abstract

Reduced-intensity conditioning (RIC) haploidentical (haplo-) hematopoietic stem cell transplantation (HSCT) requires more hematopoietic progenitor and stem cells (HPSCs) to promote engraftment and immune reconstitution and needs a stronger graft-versus-leukemia effect. Peripheral blood stem cells (PBSCs) offer advantages over bone marrow; however, the use of higher-dose non-T cell-depleted (non-TCD) in vitro PBSCs may increase the occurrence of severe graft-versus-host disease (GVHD). This prospective, single-arm clinical study was performed to investigate using high-dose non-TCD in vitro PBSCs as the graft source, using fludarabine/Ara-C/busulfan (FAB) as the conditioning regimen, using rabbit antithymocyte globulin to remove T cells in vivo, and enhancing GVHD prophylaxis with an IL-2 receptor antagonist in RIC-haplo-HSCT in patients with hematologic malignancies age 50 to 70 years or <50 years with comorbidities (Hematopoietic Cell Transplantation Comorbidity Index score ≥2) classified as intermediate to high risk. The primary endpoint was day 100 acute GVHD (aGVHD). A total of 47 patients were enrolled; the median age was 52 years (range, 30 to 68 years), the median duration of follow-up was 34 months (range, 2 to 99 months), and the medium-infused doses of mononuclear cells, CD34⁺ cells, and CD3⁺ cells were 15.93 × 10⁸/kg, 8.68 × 10⁶/kg, and 5.57 × 10⁸/kg, respectively. The cumulative incidence of grade II-IV aGVHD at day 100 was 30.3% (95% confidence interval [CI], 15.9% to 44.8%), and that of grade III-IV aGVHD was 10.2% (95% CI, .6% to 19.8%). The 2-year cumulative incidence of chronic GVHD (cGVHD) was 34.9% (95% CI, 19.0% to 50.8%). The 2-year cumulative incidences of localized and extensive cGVHD were 26.1% (95% CI, 11.80% to 40.40%) and 8.7% (95% CI, 3.26% to 20.65%), respectively. The 2-year cumulative incidence of relapse was 17.3% (95% CI, 5.1% to 29.5%), the 2-year overall survival rate was 71.2% (95% CI, 57.9% to 84.5%), and the 2-year disease-free survival rate was 66.2% (95% CI, 52.1% to 80.3%). The incidence of aGVHD was not high, and the overall efficacy was good. This study demonstrates that this unique RIC-haplo-PBSC transplantation protocol was effective in treating hematologic malignancies. Nonetheless, larger prospective multicenter clinical trials and experimental studies should be performed to further confirm our findings.

Keywords: Antithymocyte globulin; Haploidentical peripheral blood stem cell transplantation; Hematologic malignancy; IL-2 receptor antagonist; Reduced-intensity conditioning.