Polyethylenimine coating to produce serum-resistant baculoviral vectors for in vivo gene delivery Yi Yang a, b,1 , Seong-Loong Lo a, 1 , Jingye Yang a, b , Jing Yang b , Sally S.L. Goh b , Chunxiao Wu a , Si-Shen Feng c , Shu Wang a, b, * a Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, The Nanos, #04-01, Singapore 138669, Singapore b Department of Biological Sciences, National University of Singapore, Singapore 117543, Singapore c Division of Bioengineering, National University of Singapore, Singapore 117574, Singapore article info Article history: Received 19 May 2009 Accepted 9 June 2009 Available online 3 July 2009 Keywords: Gene therapy Gene transfer Nanoparticle Surface modification abstract Recombinant baculoviral vectors efficiently transduce many types of mammalian cells. However, their in vivo applications are hampered by the sensitivity of the virus to complement-mediated inactivation. Based on our observation that the surface charge of baculovirus is negative at neutral pH, we developed a procedure to coat baculoviral vectors with positively charged polyethylenimine 25 kDa, a commonly tested non-viral gene delivery vector, through electrostatic interaction. This coating was effective in protecting baculoviral vectors against human and rat serum-mediated inactivation in vitro, providing transduction efficiencies comparable with that generated by the control virus used under a serum-free condition. Enhanced in vivo gene expression in the liver and spleen was observed after tail vein injection of the coated viruses into mice. When injected directly into human tumor xenografts in nude mice, the coated viruses suppressed tumor development more effectively than uncoated viral vectors. These findings demonstrated the usefulness of using a simple coating method to circumvent a major obstacle to in vivo application of baculoviral vectors. The method may also serve as a flexible platform technology for improved use of the vectors, for example introducing a targeting ligand and minimizing immune responses. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Being capable of efficiently transducing diverse mammalian cell types, the insect baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) has been introduced as a prom- ising gene delivery vector [1–3]. One of the attractive advantages of using baculovirus AcMNPV as a gene delivery vector is the large cloning capacity conferred by its 130 kb viral genome, which may be favorable in delivering a large functional gene or multiple genes from a single vector. Baculoviral transduction results in transient gene expression. Although stable CHO cells expressing GFP could be isolated following baculoviral transduction and antibiotic selection, it is not clear at what frequency chromosomal integration of deliv- ered DNA sequences without antibiotic selection may occur in transduced cells [4]. Thus, the virus appears to be a vector suitable for applications requiring short-term gene expression. Different from many human viruses, baculovirus is incapable of replicating in mammalian cells due to transcriptional silence of its major regula- tory genes in these cells, thus significantly reducing the chance of vector neutralization caused by pre-existing antiviral immunity during in vivo gene delivery. Other empirical advantages of bacu- loviral vectors include easy construction of recombinant viral vectors and simple procedure of purifying large quantities of viruses with high titers. It would be possible to scale up the less labor- intensive process to pharmaceutical levels. Together, these features have made baculovirus a promising new vector to deliver specific genes of interest for the purposes of gene therapy, regenerative medicine and vaccination [5–11]. Despite the effective transduction of many types of proliferating and non-proliferating mammalian cells by baculovirus in vitro, in vivo gene delivery using baculoviral vectors is impeded by the susceptibility of the viruses to complement-mediated inactivation [12]. The complement system includes serum and membrane- bound proteins that function in a variety of specific and nonspecific immune defense mechanisms. Upon interaction with activators, for example viruses, the complement system initiates a series of enzymatic reactions which in some manner modify the activating * Corresponding author. Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, The Nanos, #04-01, Singapore 138669, Singapore. Tel.: þ65 6824 7105; fax: þ65 6478 9083. E-mail address: swang@ibn.a-star.edu.sg (S. Wang). 1 These authors have contributed equally to the work. Contents lists available at ScienceDirect Biomaterials journal homepage: www.elsevier.com/locate/biomaterials 0142-9612/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biomaterials.2009.06.020 Biomaterials 30 (2009) 5767–5774