Development of a suitable animal model of AIDS is much needed in AIDS research to study infection and pathogenesis as well as to evaluate methods of prevention and treatment of HIV infection. Small animals such as rodents are attractive candidates for AIDS research due to the availability of various inbred and genetically engineered strains, extensive knowledge or their immune system, especially in mice, and the relative ease of breeding and maintaining animal colonies. Transgenic small animal models carrying entire HIV genome or selected genes have been instrumental to understand functions of HIV genes in vivo and their role in HIV pathogenesis. The type of cells in which HIV genes are expressed seems to be an import prerequisite for the study of HIV gene functions in transgenic mice. Mice constitutively expressing the entire HIV-1 genome or HIV-1 nef gene in CD4 + T cells and in the cells of macrophage/dendritic lineage develop an AIDS-like disease very similar to AIDS disease in humans. Similarly, expression of Nef in adult mice, using inducible system, results in the AIDS-like disease. This disease is characterized by thymic atrophy, impaired thymocyte maturation, loss of CD4+ T cells, increased activation and turnover of T cells, which can occur in the absence of lymphypenia, and non-lymphoid organ disease involving the lungs and kidneys. Susceptibility of adult mice to the pathological effects of Nef suggests that the AIDS-like disease in the constitutively expressing Nef Tg mice is not due to developmental defects caused by early expression of Nef. This model highlights the important role of Nef in HIV-1 pathogenesis. The high similarity in the disease in these Tg mice with human AIDS strongly suggest that these mice are a relevant model to study AIDS. This study further evidence that mouse cells can support functions of Nef and these Tg mice represent a unique model to study Nef functions in vivo in the context of the primary immune system. Moreover, the inducible Nef Tg model has given us the ability to control the level and time of expression of Nef which was impossible to do in the previously reported constitutive Nef Tg mouse models. These mice will be useful to study immune reconstitution since Nef expression can be turned off after withdrawal from dox.

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