We developed a model of controlled SIV infection by exposing rhesus macaques (RMs) to SIVagm. Our preliminary results showed that acute SIVagm infection in RMs is characterized by: high levels of viral replication, and dramatic acute mucosal CD4+ T-cell depletion, both similar to pathogenic SIV/HIV-1 infections. Surprisingly, a complete control of SIVagm replication was observed during chronic infection, resulting in the return to baseline of all the biological parameters during the follow-up. Experimental CD8 cell depletion in these elite controllers resulted in transient increases in VLs. Our hypothesis is that cellular immune responses are responsible for the control of SIVagm replication and lack of disease progression in RMs. Our overall objective is to establish the correlates of protection of elite SIV controllers and to expand this knowledge to pathogenic HIV-1 infection.
The specific aims are:
Specific Aim 1. To thoroughly study the pathogenesis of controlled SIVagm infection in RMs by: (a) defining the virological and immunological parameters of SIVagm infection of RMs, (b) characterizing the timing and extent of SIVagm infection in tissues of RMs, (c) studying """"""""sanctuary silencing"""""""" during controlled SIVagm infection of RMs, and (d) determining the stable reservoirs of integrated SIVagm. RMs will be inoculated with SIVagm and euthanized at sequential time points. VLs, CD4+ T-cell dynamics, immune activation, cell proliferation and apoptosis will be monitored. Tissue colonization with SIVagm during the primary infection as well as """"""""sanctuary silencing"""""""" at later time points will be determined by nested PCR, real-time PCR and in situ hybridization. Stable integrated SIVagm reservoirs in RMs will be detected by studying the replication-competent virus in resting CD4+ T- cells isolated from different tissues. Quantification of SIVagm DNA in purified resting CD4+ T-cells from tissues examined at necropsy will be done by real-time PCR. CD8 depletion of SIVagm-infected RMs controllers will complement the in vitro assays for the study of SIVagm reservoirs and will determine the order and timing of reactivation of tissue reservoirs responsible for the rebound of plasma viremia.
Specific Aim 2. To study the role of cellular immunity in control of SIVagm replication in RMs. We will: (i) Determine the dynamics, magnitude, breadth and quality of CD8+ and CD4+ T cell responses in blood and tissues by Elispot, polyfunctional intracellular cytokine staining (ICS), and assessment of granzyme and perforin expression. (ii) deplete immune responses in RMs during primary SIVagm- infection and maintain the CD8 ablation through elimination of B cells. (iii) Differentiate between the relative contribution of cellular immune responses versus immune activation as the mechanism of viral rebound after CD8 depletion, by using Ontak, a drug that induces immune activation in NHPs. Combined, these aims are designed to thoroughly characterize a long-term nonprogressive SIV infection and to determine the mechanisms responsible for this highly efficient control of virus.
This project is intended to develop an animal model for the control of SIV and HIV infections. Such a model is badly needed to understand the correlates of immune protection in elite controllers and it is not yet available. In our preliminary studies, we have shown that rhesus macaques (RMs) infected with SIV from African green monkeys have replicated the virus to high levels during acute infection but later have the ability to completely control the virus and consequently show complete restoration of immunity during the follow-up. However, in vivo depletion of CD8 cells in SIVagm-infected controller RMs resulted in the rebound of virus showing that strong cellular immune responses are responsible for viral control. Deciphering the mechanisms of viral control in this new model may significantly contribute to our understanding of HIV pathogenesis and design of new approaches for controlling HIV infection.
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