Identification of infectious virions which are vesicular stomatitis virus pseudotypes of murine type C virus

Transgenic animals: current and alternative strategies

Transgenic animal technology is one of the most fascinating technologies developed in the last two decades. It allows us to address questions in life sciences that no other methods have achieved. The impact on biomedical and biological research, as well as commercial interests are overwhelming. The questions accompanying this fast growing technology and its diversified applications attract the attention from a variety of entities. Still, one of the most fundamental problems remaining is the search for an efficient and reliable gene delivery system for creating transgenic animals. The traditional method of pronuclear microinjection has displayed great variability in success among species. While an acceptable efficiency in the production of transgenic mice has been attained, the relative low efficiency (<1%) in creating transgenic livestock has become one of the barriers for its application. In the past decades, improvements in producing transgenic livestock have made a slow progression, however, the recent advancement in cloning technology and the ability to create transgenic livestock in a highly efficient manner, have opened the gate to a new era in transgenic technology. Discoveries of new gene delivery systems have created an enthusiastic atmosphere that has made this technology so unique. This review focuses on gene delivery strategies as well as various approaches that may assist the advancement of transgenic efficiency in large animals.

In vitro cell-free conversion of noninfectious Moloney retrovirus particles to an infectious form by the addition of the vesicular stomatitis virus surrogate envelope G protein

In the absence of envelope gene expression, retrovirus packaging cell lines expressing Moloney murine leukemia virus (MLV) gag and pol genes produce large amounts of noninfectious virus-like particles that contain reverse transcriptase, processed Gag protein, and viral RNA (gag-pol RNA particles). We demonstrate that these particles can be made infectious in an in vitro, cell-free system by the addition of a surrogate envelope protein, the G spike glycoprotein of vesicular stomatitis virus (VSV-G). The appearance of infectivity is accompanied by physical association of the G protein with the immature, noninfectious virus particles. Similarly, exposure in vitro of wild-type VSV-G to a fusion-defective pseudotyped virus containing a mutant VSV-G markedly increases the infectivity of the virus to titers similar to those of conventional VSV-G pseudotyped viruses. Furthermore, similar treatment of an amphotropic murine leukemia virus significantly allows infection of BHK cells not otherwise susceptible to infection with native amphotropic virus. The partially cell-free virus maturation system reported here should be useful for studies aimed at the preparation of tissue-targeted retrovirus vectors and will also aid in studies of nucleocapsid-envelope interactions during budding and of virus assembly and virus-receptor interactions during virus uptake into infected cells. It may also represent a potentially useful step toward the eventual development of a completely cell-free retrovirus assembly system.

Sensitization of rhabdo-, lenti-, and spumaviruses to human serum by galactosyl(alpha1-3)galactosylation

Vesicular stomatitis virus, human immunodeficiency virus type 2, and human foamy virus, which were produced by cell lines expressing galactosyl(alpha1-3)galactosyl (alphaGal) sugars, were found to be less stable in human serum than those from alphaGal-negative cells, indicating that galactosyl(alpha1-3)galactosylation sensitizes these viruses as well as mammalian type C oncoviruses (Rother et al., J. Exp. Med. 182:1345-1355, 1995; Takeuchi et al., Nature (London) 379:85-88, 1996) to complement killing via natural anti-alphaGal antibodies. Thus, virus killing mediated by anti-alphaGal antibodies may play a role as a barrier to animal-to-human infection of various enveloped viruses. Virus vectors for human in vivo gene therapy based on the viruses mentioned above should be produced from alphaGal-negative cells.

Retroviral pseudo-virus carrying the envelope proteins of neurotropic Friend murine leukemia virus effectively transferred retroviral vector into glial cells

We isolated the neurotropic Friend murine leukemia virus, FrC6 and its molecular clone A8, which proliferated in rat glial cell lines in vitro and in the rat brain in vivo. To investigate the contribution of viral envelope proteins to the neurotropism of A8 virus, the retroviral pseudo-virus carrying the envelope proteins of A8 virus and Moloney murine leukemia virus (MoMLV) was produced by transfecting the env gene of A8 virus (A8env) in the MoMLV based packaging cell, psi CRE. The phenotypically mixed pseudo-virus infected the rat glial cell lines as well as NIH 3T3 cells, whereas the psi CRE-produced pure pseudo-virus without A8env expression infected the glial cells at lower efficiency. Furthermore, the psi CRE cells with A8env expression produced pseudo-virus at a higher titer than normal psi CRE cells. The infectivity of the phenotypically mixed pseudo-virus to the glial cells was abolished by a neutralizing antibody against A8 virus, which did not reduce the ability of the psi CRE-produced pure pseudo-virus to infect NIH 3T3 cells. These results indicated that the envelope protein of A8 virus is assembled into the pseudo-viral particles and that it contributes to glial cell infection by the A8 virus.

Retroviral pseudotypes produced by rescue of a Moloney murine leukemia virus vector by C-type, but not D-type, retroviruses

Human HOS cells containing a Moloney murine leukemia virus (Mo-MLV) recombinant genome were infected by a panel of retroviruses. The C-type viruses simian sarcoma associated virus, feline leukemia virus subgroup B, and the feline endogenous virus RD114 were able to form pseudotypes with the Mo-MLV genome, which transferred a selectable marker gene to target cells; however, Human T cell leukemia virus-1 and the D-type viruses Mason-Pfizer monkey virus and simian retrovirus-1 failed to rescue the Mo-MLV vector. Further characterization of the RD114 pseudotype demonstrated that it retained the receptor specificity of RD114 and will therefore prove useful in receptor characterization.

Pseudotypes of human T-cell leukemia virus types 1 and 2: neutralization by patients' sera

Pseudotypes of vesicular stomatitis virus (VSV) bearing envelope antigens of human T-cell leukemia virus (HTLV) types 1 and 2 were prepared by propagating VSV in cells lines productively infected with HTLV. Plaque assays of VSV (HTLV) pseudotypes were employed to determine the presence of (i) HTLV receptors on cells and (ii) neutralizing antibodies in the serum of patients with adult T-cell leukemia-lymphoma (ATLL). Cell surface receptors for HTLV-1 and HTLV-2 were found on nonlymphoid cells of human and mammalian origin. Neutralizing antibodies specific to VSV(HTLV-1) were found in sera of ATLL patients in titers varying from 1:50 to 1:30,000 and did not correlate closely with antibody titers for internal viral antigens. Sera from ATLL patients in the United Kingdom (Caribbean immigrants), United States, and Japan completely neutralized VSV (HTLV-1), indicating that the HTLV isolates from these distinct geographic regions represent a single envelope serotype. Neutralization of VSV (HTLV-1) was more specific and more sensitive than assays of syncytium inhibition. No cross-neutralization was observed between bovine leukosis virus and HTLV, and only limited cross-reaction was found for envelope antigens of HTLV-1 and HTLV-2. These studies show that VSV (HTLV) pseudotypes can be readily used to screen for neutralizing antibodies in patients' sera and to distinguish HTLV envelope serotypes.