The influence of patient-related factors on ex vivo retroviral-mediated gene transfer into mobilized peripheral blood myeloid progenitors.

Mobilized human peripheral blood progenitor cells are potential alternatives to bone marrow cells as targets for ex vivo gene transfer. We report the transduction efficiency of retroviral-mediated gene transfer into myeloid progenitors of peripheral blood progenitor cell (PBPC) harvests, mobilized by high-dose cyclophosphamide and GM-CSF, compared with nonmobilized bone marrow (BM). Eleven PBPC samples were enriched for CD34+ cells, preincubated with IL-3 (10 ng/ml), IL-6 (50 ng/ml), and 10% autologous plasma for 42 hr, and transduced over a 6-hr incubation with IL-3 + IL-6 and a retroviral vector carrying the NeoR gene. NeoR-specific sequences were detected by polymerase chain reaction in 10 cell pellets (91%). Gene expression in CFU-GM colonies was found in nine transduced samples (82%), with a mean transduction efficiency of 5.2% (95% CI, 1.3-11.8%) CFU-GM per PBPC sample. In univariate analysis, a higher transduction efficiency into CFU-GM correlated significantly with a higher CFU-GM concentration in the CD34+-enriched sample (p = 0.009), a shorter interval from diagnosis (p < 0.001), and fewer months of prior cytotoxic treatment (p = 0.001); correlation with younger age was of borderline statistical significance (p = 0.077). In multivariate analysis a shorter interval from diagnosis and, to a lesser degree, a higher CFU-GM concentration in the CD34+-enriched sample were independent predictors of higher transduction efficiency. Twelve BM samples were similarly transduced; 11 pellets were PCR positive. CFU-GM NeoR gene expression was 4.2% (95% CI, 2.0-7.2%) CFU-GM per BM sample, which was not significantly different from the transduction efficiency into PBPC cells. No correlation was found between the transduction efficiency of CFU-GM in BM samples and CFU-GM concentration in the CD34+-enriched sample, time from diagnosis, months of prior cytotoxic treatment, and/or patient age. Our data suggest that the transduction efficiency ex vivo may be influenced by time from diagnosis, CFU-GM concentration in the sample, and possibly by the extent of prior cytotoxic administration.