Develop strategies that manipulate viral genes to interfere with viral replication.

Mid-Term Research Aims

• understand retroviral entry.
• understand retroviral assembly.
• develop and utilize avian leukosis virus susceptible mouse models for studying development and oncogenesis.

Approach

My research program studies the replication of several different retroviruses: avian leukosis virus (ALV), murine leukemia virus (MLV), and human immunodeficiency virus (HIV). A major tool of our experimental system is a series of retroviral vectors derived from ALV, that reliably deliver and express foreign genes in vitro and in vivo. ALV is unique among the simple retroviruses in that an additional gene (~2.5 kb) can be included in the genome of replication-competent viruses and vectors. The retroviral vectors can be used to express an experimental gene at a variety of levels either from the constitutive viral promoter or from an internal tissue-specific promoter. This experimental system has been extended to include both avian and murine animal model systems.

We are studying the protein interactions involved in retrovirus entry. We have been developing a receptor interference antiviral strategy that targets the initial step of the retroviral life cycle: the interaction of the retrovirus envelope glycoproteins with the host cell receptor. Receptor interference occurs when the retroviral envelope glycoproteins are expressed in the cell, block the specific receptor thereby preventing viral entry. We are currently developing a receptor interference strategy that uses secreted forms of the envelope glycoprotein or the cellular receptor to block infection.

We are also developing a second antiviral strategy, capsid-targeted viral inactivation (CTVI), that targets a late step in the retrovirus life-cycle: assembly of new virions. The structural proteins necessary for virion production self-assemble at the cell membrane for the majority of retroviruses. The CTVI strategy was designed to disable newly produced virions by inserting degradative nucleases fused to the viral structural proteins during assembly. We are currently using this strategy to study the protein interactions involved in retroviral assembly.

We have developed an experimental system that makes it possible to use the ALV retroviral vectors in a mouse model. Tissue-specific gene targeting can be achieved with the RCAS family of ALV retroviral vectors by expressing the receptor under the control of a tissue-specific promoter, thereby targeting the expression of the experimental gene to the appropriate tissue. It should be possible to further restrict the expression of the exogenous gene by including an internal tissue-specific promoter in the vector. This simple system for introducing retroviral vectors into mice and mouse embryos should prove useful for studying cell development, and oncogenesis, and for testing specific strategies for gene therapy.

Current Projects