The FBMD-1 stroma cell line secretes a unique moiety which can increase retroviral transduction of lineage-committed and primitive human peripheral blood progenitor cells

Peripheral blood progenitor cells are a prime target for gene therapy appro aches. As recent data point to the relevance of soluble stroma factors for the efficient transduction of progenitor ce I Is, we tested the stroma-cond itioned medium (SCM) of the two ce I I I in es FBMD-1 and L88/5 as well as desulfated and O-sulfated heparin (HS dS and HS OS) for their effect on tra nsduction of peripheral blood progenitor ce I Is. We transduced CD34(+) ce I Is of nine tumor patients with the retroviral SF-MDR vector containing th e human multidrug resistance I (MDR1) gene under serum-free conditions on t he fibronectin fragment CH-296 with or without SCM. Provirus-specific polym erase chain reaction showed a median 1.6-fold higher integration rate of th e transgene into committed progenitor cells for the group with added FBMD-1 SCM (P=.008). This was maintained after 2 (P=.02) and, as a trend, after 5 weeks of stroma-dependent long-term culture. We found a median 1.5-fold in crease in rhodamine-123 (Rh-123) exclusion in myeloid lineage-committed pro geny cel Is following transduction in the presence of FBMD-1 SCM(P=.0004). After 2 or 5 weeks of long-term culture, a significantly higher proportion of Rh-123(dull) cells could still be detected in the FBMD-1 SCM transductio n group (P=.003 and P=.04, respectively). L88/5 SCM or HS OS or HS dS was n ot effective as supplement for improving gene transfer. The FBMD-1 stroma c ell line appears to secrete a unique moiety, which can increase retroviral transduction of lineage-committed and primitive progenitor cells. The FBMD- 1 stroma activity is not attributable to heparan sulfate.