Retroviruses have been extensively used in the development of gene transfer systems. Recently, there has been a great deal of interest in the use of lentiviruses for gene transfer because they infect nondividing cells. Human immunodeficiency virus (HIV) has been the lentivirus most often used for this purpose, but its genomic complexity and limited tropism present some challenges to the establishment of efficient gene transfer systems. In this paper we present data showing intrinsic differences between the infectivity of wild-type HIV and HIV particles pseudotyped with heterologous envelope glycoproteins. Interestingly, HIV pseudotypes with envelope glycoproteins from the amphotropic murine leukemia virus or the vesicular stomatitis virus (VSV) are 3 and 40 times more infectious than wild-type HIV, respectively. In addition, we show that the reliance on Nef expression for maximal infectivity of HIV particles is dependent on the path of virus entry. The dependence on Nef for higher infectivity is greater for amphotropic pseudotypes and wild- type HIV than for VSV-G pseudotypes. We conclude that VSV-G pseudotypes of HIV vectors are an excellent choice for gene transfer purposes and Nef- mediated vital infectivity enhancement is affected by virus entry pathway.
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