Interim Results from an Ongoing Phase 1/2 Study of Lentiviral-mediated Ex-vivo Gene Therapy for Pediatric Patients with Severe Leukocyte Adhesion Deficiency-I (LAD-I)

Intensive chemotherapy with autologous stem cell transplantation is a therapeutic tool used in paediatric oncology. In adult patients, a peripheral blood CD34+ cell count superior to 20/μL enables an adequate collection of peripheral blood stem cells. There are no recommendations for children. This study aimed to determine whether the count of circulating CD34+ cells on the day before cytapheresis predicts successful collection in paediatric patients.We retrospectively studied all paediatric patients who underwent apheresis for stem cell autotransplantation in the CHU of Rennes between 2010 and 2019. Successful apheresis was defined as a collection superior to 3 × 106 CD34+/kg. “Success” and “failure” groups were compared.In total, 122 apheresis procedures were performed in 105 patients. It was a successful procedure in 81% of patients and a failure in 19% of patients. A minimal cut-off of circulating CD34+ count superior to 13/μL on D-1 allowed us to predict a collection of at least 3 × 106 CD34+/kg (PPV 94,8%, NPV 51,4%). For children aged < 6 years, the association with leucocyte increase during the 5 days before the procedure improved the prediction of success.The peripheral blood CD34+ cell count is a predictive factor for successful collection in paediatric patients. The minimal cut-off that allows an adequate collection of peripheral blood stem cells is inferior to the minimal cut-off in adult patients. Nevertheless, this minimal number of circulating CD34+ cells is insufficient to predict the success or failure of apheresis in patients younger than 6 years of age.