We have utilized highly purified hematopoietic progenitor and stem cells (HPCs, HSCs) from normal peripheral blood to develop methodology for: (a) efficient transfer into HPCs of a non-hematopoietic membrane reporter, i.e., the nerve growth factor receptor complementary DNA; and (b) effective gene transduction of putative HSCs, i.e., cells initiating Dexter-type long-term culture (LTC-ICs).
Purified HPCs induced into cycling by growth factors (interleukin 3, interleukin 6, c-kit ligand) were transduced with the N2 retroviral vector containing the neomycin resistance (neor) gene. More than 80% of transduced HPCs were resistant to the toxic G418 level. Thereafter, the HPCs were effectively transduced with the LNSN retroviral vector containing a nerve growth factor receptor complementary DNA; the nerve growth factor receptor was detected on ≥18% of the transduced HPCs. These experiments provide a new tool from which (a) to monitor expression of a transduced membrane reporter on hematopoietic cells, particularly at the level of HPCs/HSCs, and (b) to characterize the transduced cells by double- and triple-labeling membrane antigen analysis.
Purified HPCs/HSCs grown in Dexter-type LTC were transduced at 1 week by exposure to supernatant N2 retroviral particles in the absence of exogenous hematopoietic growth factors. The procedure, devoid of toxic effects, allowed an efficient neor transduction into LTC-ICs. Thus, we consistently detected neomycin-resistant mRNA in the clonal progeny of HPCs produced in LTC at 5–8 weeks in both the nonadherent and adherent fractions; this timing of expression coincides with that of HPC production by LTC-ICs, thereby indicating the effective transduction of the LTC-ICs. These experiments represent a first step toward development of preclinical models for gene transfer into human peripheral blood HSCs by complex retroviral vectors.
This study was supported in part by Thomas Jefferson University, Philadelphia, PA; Fondazione Tettamanti, CNR (P.F. ACRO), Rome; Progetto Terapia dei Tumori, Istituto Superiore di Sanità, Rome.