Collection of an adequate amount of autologous hematopoietic stem progenitor cells (HSPC) is required for ex vivo manipulation and successful engraftment for certain inherited disorders. Fifty-seven paediatric patients (age 0.5-11.4 years) underwent a bone marrow harvest for the purpose of HSPC gene therapy (GT), including adenosine deaminase severe combined immunodeficiency (ADA-SCID), Wiskott Aldrich syndrome (WAS) and metachromatic leukodystrophy (MLD) patients. Total nucleated cells and percentage and absolute counts of CD34+ cells were calculated at defined steps of the procedure (harvest, CD34+ cell purification, transduction with the gene transfer vector and infusion of the medicinal product). Minimum CD34+ cell dose for infusion was 2x106/kg, with optimal target at 5-10x106/kg.
Median volume of bone marrow harvested was 34.2 ml/kg (range 14.2-56.6). The number of CD34+ cells collected correlated inversely with weight and age in all patients and particularly in the MLD children group. All patients reached the minimum target dose for infusion: median dose of CD34+ cells/kg infused was 10.3 x106/kg (3.7-25.9), with no difference among the 3 groups. Bone marrow harvest of volumes >30 ml/kg in infants and children with ADA-SCID, WAS and MLD is well tolerated and allows obtaining an adequate dose of medicinal product for HSPC-GT.