CT-037: The Impact of CD34+ Cell Dose on the Outcome of Allo-HSCT in Adult SAA Patients Conditioned with a Non-ATG-Based Regimen with Post-Transplantation Cyclophosphamide from Fully Matched-Sibling Donors

Abstract

<h3>Context and Objective</h3> Allo-HSCT is an established treatment for SAA. In this study, we aimed at investigating the correlations between the CD34+ dose and early TRM, 1-year OS, and GVHD incidence. In addition, we aimed at finding a cut-off for the optimal CD34+ dose. <h3>Design</h3> We retrospectively reviewed the records of SAA patients who underwent allo-HSCT between 2017 and 2020. The median follow-up time was 23 months. <h3>Setting</h3> Nasser's Institute Hospital BMT, Cairo, Egypt. <h3>Patients or Other Participants</h3> Twenty-three SAA patients aged 20 years and older underwent allo-HSCT. Patients were conditioned with fludarabine, cyclophosphamide, and post-transplantation cyclophosphamide (FLU/Cy/PTCy). <h3>Interventions</h3> Patients received fludarabine (40 mg/m²/d from d-3 to d-1), cyclophosphamide (25 mg/kg/d from d-5 to d-2), and PTCy (50 mg/kg/d from d+3 to d+4). All patients received PBSC. Cyclosporine (3 mg/kg/d) was started from d+5. <h3>Main Outcome Measures</h3> 6-months TRM and 1-year OS. <h3>Results</h3> The median age at transplantation was 31 years (range: 20–55 years), and the median CD34+ dose was 6.1 × 10⁶/kg (range: 2.9–7.0 × 10⁶/kg). Neutrophil engraftment occurred in 15 patients (65.2%) and platelet engraftment in 12 patients (52.2%). The median time to engraftment was 18 days for neutrophils (range: 15–26 days) and 15 days for platelets (range: 9–27 days). Within the specified follow-up period, 12 patients died, where 7 deaths (58.3%) occurred before d+15. The primary cause of death was septic shock, which occurred in 6 patients (50%). The median survival was 5.5 months. No patient had aGVHD, and only 2 patients (8.70%) had pulmonary cGVHD. Receiver operating characteristic analysis identified a CD34+ dose of 6 × 10⁶/kg as an optimal cut-off to predict 6-month mortality with 66.7% sensitivity and 81.8% specificity (AUC: 0.75). CD34+ doses higher than 6 × 10⁶/kg correlated with lower 6-months TRM (30.8% <i>vs</i> 80.0%, <i>P</i> = 0.036) and higher 1-year OS (69.2% <i>vs</i> 20.0%, <i>P</i> = 0.016). <h3>Conclusions</h3> CD34+ doses higher than 6 × 10⁶/kg correlated with a significantly lower TRM and a better OS in SAA patients undergoing allo-HSCT conditioned with FLU/Cy/PTCy. However, further research is mandatory to confirm the cut-off for the optimal CD34+ dose.