Recent studies of PBSC expansion by SCF, G-CSF and TPO in new medium formulations have shown retention of long-term reconstituting HSC activity in vitro[39], and as well as abrogating neutropenia when used as an adjunct to unmanipulated PBSC these have demonstrated durable clinical haematopoietic reconstitution by expanded cells alone, not as an adjunct to unmanipulated PBSC[11]. This evidence concerns the gene KITLG and neutropenia.