Filgrastim post-chemotherapy mobilizes more CD34+ cells with a different antigenic profile compared with use during steady-state hematopoiesis.

For the mobilization of CD34+ peripheral blood progenitor cells (PBPC) filgrastim (R-metHuG-CSF) can be administered either during steady-state hematopoiesis or following cytotoxic chemotherapy. We compared both mobilization modalities intra-individually in seven patients with breast cancer. The number of circulating CD34+ cells was increased after filgrastim-supported chemotherapy compared with filgrastim administration during steady-state (on average, 129 vs. 19/microliters), resulting in a sevenfold higher yield of CD34+ cells per leukapheresis (5.73 vs. 0.79 x 10(6)/kg bodyweight). CD34+ PBPC harvested post-chemotherapy comprised a smaller proportion of early progenitor cells (CD34+/HLA-DR- or CD34+/CD38-) compared with filgrastim treatment alone. However, the absolute number of these early progenitor cells harvested was fivefold higher. The filgrastim-supported rebound after chemotherapy was characterized by a greater proportion of CD34+/CD33+ cells. Correspondingly, CD34+ PBPC mobilized post-chemotherapy contained a higher proportion of CFU-GM compared with filgrastim treatment during steady-state, while the cloning efficiency of CD34+ cells for BFU-E tended to be lower. Of note, the proportion of CD34+/CD19+ lymphoid progenitor and B cells was reduced after chemotherapy. In cancer patients, filgrastim mobilizes higher numbers of CD34+ cells when administered post-chemotherapy, compensating for the smaller proportion of early hematopoietic progenitors.