To accomplish this, we must understand the interactions of injected virus particles with proteins both on the surface of target cells and in the circulation. We will study the interaction of the retroviral envelope protein with its receptor, and characterize the specific regions of this protein involved in this interaction. Segments of the protein sequence which are likely to be responsible for these functions have been identified, and the amino acid sequence of these regions is being modified by site-specific mutagenesis. The resulting mutant viruses are assayed for their ability to bind and infect target cells. By modifying regions of the protein involved in binding, while retaining segments which allow fusion, we can design retrovirus-based vectors capable of targeting specific tissues.
Injected virus is inactivated by binding to complement.
The segment of the envelope protein bound by complement has been localized, and this region is being mutagenized. We hope to use these findings to construct delivery vehicles with an extended half-life in the circulation, which will optimally bind and infect their targets. We will study gene regulation in target tissues, initially liver and T-cells, in order to optimize the expression of transferred genes. Sequences from viral and cellular transcription units will be adapted in order to express genes as desired. Ultimately, we would like to engineer vectors that in addition to targeting the correct tissue, would integrate into a safe chromosomal location and be expressed in response to normal physiological signals.