Optimized Transduction of Canine Paediatric CD34+ Cells Using an MSCV-based Bicistronic Vector

We have used a murine MSCV-based bicistronic retroviral vector, containing the common gamma chain (γc) and enhanced green fluorescent protein (EGFP) cDNAs, to optimize retroviral transduction of canine cells, including an adherent canine thymus fibroblast cell line, Cf2Th, as well as normal canine CD34+ bone marrow (BM) cells. Both canine cell types were shown to express Ram-1 (the amphotropic retroviral receptor) mRNA. Supernatants containing infectious viruses were produced using both stable (PA317) and transient (Phoenix cells) amphotropic virus producer cell lines. Centrifugation (spinfection) combined with the addition of polybrene produced the highest transduction efficiencies, infecting ∼75% of Cf2Th cells. An average of 11% of highly enriched canine CD34+ cells could be transduced in a protocol that utilized spinfection and plates coated with the fibronectin fragment CH-296 (Retronectin). Indirect assays showed the vector-encoded canine γc cDNA produced a γc protein that was expressed on the cell surface of transduced cells. This strategy may result in the transduction of sufficient numbers of CD34+ BM cells to make the treatment of canine X-linked severe combined immunodeficiency and other canine genetic diseases feasible.