Both early and committed haemopoietic progenitors are more frequent in peripheral blood than in bone marrow during mobilization induced by high-dose chemotherapy + G-CSF

Summary. Haemopoietic growth factor administration following high-dose chemotherapy markedly amplifies progenitor cell pool in the peripheral blood (PB). Collection and reinfusion of these cells enable rapid haemopoietic recon-stitution following autograft. Less is known on engraftment potentiality of bone marrow (BM) cells taken under analogous conditions. To investigate this tissue, PB and BM were evaluated simultaneously during maximal mobilization in a series of 14 patients undergoing the HDS chemotherapy programme. A significantly higher growth of committed progenitors was found from PB rather than from BM (663 ± 123 v 267±40CFU-GM/10⁵ MNC, respectively). Also, significantly more CFU-GM could be collected by a median of three leukaphereses, compared to those harvested from BM (158 ± 31 v 16 ± 4 ± 10⁴ CFU-GM/kg, respectively). Most mobilized CFU-GM were phenotypically immature (CD15⁻); in addition, circulating cells included primitive progenitors, as assessed by LTC-IC assay, or by evaluation of non-proliferating pre-CFU-GM, selected by an anti-CD71 immunotoxin. The amount of pre-CFU-GM determined by both techniques was consistently higher in PB than in BM. Moreover, a direct correlation could be established between circulating CFU-GM and primitive precursors. Thus, during optimally induced mobilization, PB contains many more haemopoietic progenitors, of both committed and primitive stages, than does BM. Under such conditions, PB is probably the best source of material for graft purposes.