Efficient Gene Transfer in Primitive CD34 + /CD38 lo Human Bone Marrow Cells Reselected after Long-Term Exposure to GALV-Pseudotyped Retroviral Vector

Abstract

Successful retroviral gene transfer into human hematopoietic stem cells was demonstrated in preliminary clinical trials at low efficiency. We have shown previously that gene transfer into committed hematopoietic progenitor cells is more efficient using a gibbon ape leukemia virus (GALV)-pseudotyped retroviral vector instead of an amphotropic retroviral vector. Here, we have conducted a systematic study of human hematopoietic progenitor cells after extended transduction with a GALV-pseudotyped retroviral vector. CD34⁺/CD38^lo Cells were transduced for 5 days and reselected according to phenotype after culture and analyzed for cell cycle status, long-term culture-initiating cell (LTC-IC) activity, and gene transfer. Reselection of rare, very primitive progenitor cells was successful. Equal to fresh CD34⁺/CD38^lo cells, >90% of reselected CD34⁺/CD38^locells were in G₀/G₁. CD34⁺/CD38^lo reselection enriched for LTC-IC (10-fold), as compared to freshly isolated CD34⁺/CD38^lo cells with excellent specificity (82.7% of total LTC-IC were recovered in the reselected CD34⁺/CD38^lo population) and recovery (62% of initial LTC-IC number in CD34⁺/CD38^lo cells were recovered in the reselected fraction after transduction). Gene transfer into primitive progenitor cells was efficient with 50.5% G418-resistant LTC-IC colonies and more than 40 copies of vector provirus detectable per 100 nuclei of CD34⁺/CD38^lo cells. To our knowledge, this is the first systematic analysis of phenotype, function, and cell cycle demonstrating retroviral gene transfer into rare, very primitive human hematopoietic progenitor cells. The chosen strategy should be of considerable value for analyzing and improving gene therapy of the hematopoietic system.

Overview summary

We have performed a systematic study of retroviral gene transfer in primitive human hematopoietic progenitor cells by analyzing the phenotype, function, cell cycle status, and retrovirus transduction after culture. Following extended exposure of CD34⁺/CD38^lo marrow cells to gibbon ape leukemia virus (GALV)-pseudotyped retroviral vector, cells were efficiently reisolated that had characteristics of very primitive progenitor cells, including a CD34⁺/CD38^lo phenotype, a very high content of long-term culture-initiating cells, and a low mitotic activity. In this population, functional and molecular analysis indicate a transduction efficiency of more than 40%. The presented strategy demonstrates the feasibility of efficiently transducing, isolating, and characterizing very primitive hematopoietic progenitor cells and should have interesting implications for hematopoietic gene therapy.