Current viral gene delivery vectors for gene therapy are inefficient due to 
short-lived transgene expression attributed to the cytosine-phosphate-guanine 
(CpG) motifs in the transgene. Here we assessed the effects of CpG motif 
reduction in lentiviral (LV) gene delivery context on the level and duration of 
reporter gene expression in Chinese Hamster Ovary (CHO) cells, Human 
Immortalized Myelogenous Leukemia (K562) cells and hematopoietic stem cells 
(HSCs). The cells were transduced with LV carrying Zero-CpG green fluorescent 
protein (ZGFP) reporter gene, LV/CMV/ZGFP. The GFP expression was compared to 
its non CpG-depleted GFP reporter gene LV (LV/CMV/GFP) counterpart. The 
LV/CMV/ZGFP exhibited prolonged transgene expression in CHO cells and HSCs up to 
10 days and 14 days, in the respective cells. This effect was not seen in the 
transduced K562 cells, which may be due to the DNA hypomethylation status of the 
cancer cell line. Transgene copy number analysis verified that the GFP 
expression was not from pseudo-transduction and the transgene remained in the 
genome of the cells throughout the period of the study. The modest positive 
effects from the LV/CMV/ZGFP suggest that the reduction of CpG in the LV 
construct was not substantial to generate higher and more prolonged transgene 
expression.