MOBILIZED PERIPHERAL-BLOOD CD34-MARROW CD34+ CELLS( CELLS EXPRESS MORE AMPHOTROPIC RETROVIRUS RECEPTOR THAN BONE)

Background and Objective. The increased susceptibility to gene transfe r by amphotropic retroviral vectors of mobilized peripheral blood (PB) CD34(+) cells compared to their bone marrow (BM) counterparts may dep end, among other factors, on the level of expression of the amphotropi c receptor on the progenitor cell. Using a previously described flow c ytometry strategy, we have studied retrovirus binding to mobilized CD3 4(+) cells, derived from cancer patients treated with high-dose chemot herapy and growth factor(s), that are efficiently transduced by N2 ret rovirus virus vector. Design and Methods. We measured the binding of t he retrovirus to the cells using a rat monoclonal antibody reactive wi th the gp70 envelope glycoprotein, common to all replication-defective amphotropic retroviruses. Antibody-virus-cell complexes were indirect ly labeled and analyzed by flow cytometry. We compared the binding of PA317-N2 vector to CD34(+) cells derived from steady-state BM, steady- state PB and mobilized PB from cancer patients treated with high-dose chemotherapy and cytokine. Results. The fluorescence intensity of mobi lized CD34(+) cells was approximately one log higher than that of stea dy-state BM or PB CD34(+) cells, indicating that the expression of the amphotropic receptor was increased. Moreover, the virus binding was p roportional to the gene transfer rate, as assessed by G418 resistance into mobilized PB-derived CFU-GM. The increase in fluorescence intensi ty appeared to be restricted to CD34(+) cell subset, neither CD2(+) no r CD14(+) cells bound the virus in an appreciable amount. Interpretati on and Conclusions. Virus binding, as assessed by indirect immunofluor escence assay, is increased in mobilized CD34(+) cells. The increased binding may contribute to their high susceptibility to retrovirus vect or infection. (C) 1998, Ferrata Storti Foundation.