The Role Of Tat Polymorphisms In The HIV-1 Latent Reservoir

During HIV disease progression, most infected cells harbor HIV in a latent form undetectable by the immune system. This pattern of infection underlies HIV persistence during Highly Active Antiretroviral Therapy (HAART) regimens that effectively eliminate all viral replication; during HAART, short-lived productively infected cells are effectively targeted by a variety of immune clearance mechanisms while long-lived latently infected cells persist.  Therefore, the viral Tat protein may play a particularly important role in viral persistence since Tat functions as a master switch controlling the expression of all viral genes.  Polymorphisms attenuating Tat activity can have profound effects on viral persistence by allowing such variant quasispecies to escape immune detection. In our research, we have monitored the evolution of Tat quasispecies in patients at different points before and after initiation of HAART.  Peripheral blood mononuclear cells (PBMC’s) were obtained from HIV-1 infected patients and a nested PCR protocol was developed to amplify the Tat coding region from proviral DNA and cell-associated RNA.  Amplified products were then cloned and the distribution of Tat quasispecies was analyzed.  The accumulation of Tat-attenuating polymorphisms in the post-HAART reservoir indicates that Tat is the focus of strong selective pressure during HAART and, furthermore, that attenuation of Tat activity plays a role in the persistence of HIV.  Our experiments provide a higher resolution view of the latent reservoir, which may aid the development of more effective therapeutic strategies and may also indicate new approaches to HIV vaccine development.