As the limitations of antiretroviral drug therapy, such as toxicity and resistance, become evident, interest in alternative therapeutic approaches for human immunodeficiency virus (HIV) infection is growing. We developed the first gene therapeutic strategy targeting entry of a broad range of HIV type 1 (HIV-1) variants. Infection was inhibited at the level of membrane fusion by retroviral expression of a membrane-anchored peptide derived from the second heptad repeat of the HIV-1 gp41 transmembrane glycoprotein. To achieve maximal expression and antiviral activity, the peptide itself, the scaffold for presentation of the peptide on the cell surface, and the retroviral vector backbone were optimized. This optimized construct effectively inhibited virus replication in cell lines and primary blood lymphocytes. The membrane-anchored C-peptide was also shown to bind to free gp41 N peptides, suggesting that membrane-anchored antiviral C peptides have a mode of action similar to that of free gp41 C peptides. Preclinical toxicity and efficacy studies of this antiviral vector have been completed, and clinical trials are in preparation.

OKT3, a mouse anti-human CD3 monoclonal antibody (mAb), is a potent immunosuppres-sive agent used in clinical transplantation to treat allograft rejection. Two major drawbacks of this therapy are the systemic release of several cytokines due to cross-linking mediated by the mAb between T cells and Fc + R-bearing cells and the human anti-mouse antibody (HAMA) response. To overcome these side effects, three chimeric OKT3 single chain variable fragment (scFv) IgM antibodies, scOKT3-+ ¿ IgM wt, scOKT3-+ ¿ IgM C575S and scOKT3-+ ¿ IgM VAEVD, were generated. They consist of the light and heavy variable binding domains of OKT3 mAb as well as the CH3 and CH4 domains of different human IgM variants linked with a human IgG3 hinge region to provide more flexibility and stability. Like the native IgM, scOKT3-+ ¿ IgM antibodies are able to form polymeric structures, which lead to an increase in binding affinity and immunosuppressive potential compared with the parental OKT3 mAb. However, independently of their polymerization, all scOKT3-+ ¿ IgM constructs do not induce any significant T cell proliferation or cytokine release (IL-2, TNF-§ and IFN-+) in in vitro assays, while their CD3-modulating properties are retained. These results suggest that the use of scOKT3-+ ¿ IgM antibodies may offer significant advantages over the OKT3 mAb in improving clinical immunosuppressive treatment.

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