We have previously demonstrated that baculovirus can efficiently transduce human mesenchymal stem cells (MSCs). In this study, we further demonstrated, for the first time, that baculovirus can transduce adipogenic, chondrogenic and osteogenic progenitors originating from MSCs. The transduction efficiency (21-90%), transgene expression level and duration (7-41 days) varied widely with the differentiation lineages and stages of the progenitors, as determined by flow cytometry. The variation stemmed from differential transgene transcription (as revealed by real-time reverse transcription-polymerase chain reaction), rather than from variability in virus entry or cell cycle (as determined by quantitative real-time PCR and flow cytometry). Nonetheless, the baculovirus-transduced cells remained capable of differentiating into adipogenic, osteogenic and chondrogenic pathways. The susceptibility to baculovirus transduction was higher for adipogenic and osteogenic progenitors, but was lower for chondrogenic progenitors. In particular, the duration of transgene expression was prolonged in the transduced adipogenic and osteogenic progenitors (as opposed to the MSCs), implicating the possibility of extending transgene expression via a proper transduction strategy design. Taken together, baculovirus may be an attractive alternative to genetically modify adipogenic and osteogenic progenitors in the ex vivo setting for cell therapy or tissue engineering.

Baculovirus has emerged as a novel vector for in vitro and in vivo gene delivery due to its low cytotoxicity and nonreplication nature in mammalian cells, but the applications of baculovirus in the genetic modification of human mesenchymal stem cells (hMSCs) and tissue engineering are yet to be reported. In this study, we genetically engineered hMSCs with a baculovirus (Bac-CB) expressing bone morphogenetic protein-2 (BMP-2). Bac-CB transduction of hMSCs at a multiplicity of infection of 40 triggered effective differentiation of hMSCs into osteoblasts. Supertransduction at day 6 after initial transduction enhanced the BMP-2 expression and further accelerated the in vitro osteogenesis, as confirmed by alkaline phosphatase assay, Alizarin red staining and reverse transcription-polymerase chain reaction analysis of osteoblastic genes. Implantation of the supertransduced cells at ectopic sites in the nude mice resulted in efficient cell differentiation into osteoblasts at week 2 and induced progressive mineralization and partial bone formation at week 6, as confirmed by hematoxylin and eosin, immunohistochemical and Alizarin red staining. These data collectively demonstrated, for the first time, the potential of baculovirus in hMSCs engineering and implicated its use in bone tissue engineering.

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