Overexpression of gibbon ape leukemia virus (GALV) receptor (GLVR1) on human CD34+ cells increases gene transfer mediated by GALV pseudotyped vectors

Retroviral transduction of CD34(+) cells on Retronectin using gibbon ape leukemia virus (GALV) pseudotyped vectors is inhibited by high concentrations of vector containing medium (VCM). Furthermore, this inhibitory activity is stable for at least 48 hours at 37degreesC and partially blocks a second hit with a GALV pseudotyped vector. We hypothesized that this inhibition was due to interference at the receptor level between infectious and noninfectious vector particles and that it might be possible to overcome it by increasing receptor expression on target cells. Activation of protein kinase C in CD34(+) cells with the phorbol ester PMA (phorbol 12-myristate 13-acetate) increased the mRNA level of the GALV receptor (GLVR1) and the transduction efficiency (TE), and fully reversed the inhibition of transduction seen with high-titer GALV VCM. A murine stem cell virus (MSCV) vector with the GLVR1 receptor and green fluorescent protein cDNAs (MGLIG) was used to transduce fibroblasts, and clones expressing different levels of GLVR1 were isolated. The TE of these cells using a GALV vector correlated with the level of GLVR1 expression. When CD34(+) cells or K562 cells were first transduced with MGLIG and then with high-titer GALV VCM, no inhibition of transduction was seen. The low level of GLVR1 expression limits gene transfer to K562 and CD34(+) cells using GALV pseudotyped vectors, especially in the presence of high-titer VCMs.