Role of TLRs in HIV-1 Infection and Potential of TLR Agonists in HIV-1 Vaccine Development and Treatment Strategies

Toll-like receptors (TLRs), as a family of pattern recognition receptors, play an important role in the recognition of HIV-1 molecular structures by various cells of the innate immune system, but also provide a functional association with subsequent mechanisms of adaptive immunity. TLR7 and TLR8 play a particularly important role in the innate immune response to RNA viruses due to their ability to recognise GU-rich single-stranded RNA molecules and subsequently activate intracellular signalling pathways resulting in expression of genes coding for various biological response modifiers (interferons, proinflammatory cytokines, chemokines). The aim of this review is to summarise the most recent knowledge on the role of TLRs in the innate immune response to HIV-1 and the role of TLR gene polymorphisms in the biology and in the clinical aspects of HIV infections. In addition, the role of TLR agonists as latency reversing agents in research to treat HIV infections and as immunomodulators in HIV vaccine research will be discussed.

Changes to the Simian Immunodeficiency Virus (SIV) Reservoir and Enhanced SIV-Specific Responses in a Rhesus Macaque Model of Functional Cure after Serial Rounds of Romidepsin Administrations

HIV persistence requires lifelong antiretroviral therapy (ART), calling for a cure. The histone deacetylase inhibitor, romidepsin, is used in the "shock and kill" approach with the goal of reactivating virus and subsequently clearing infected cells through cell-mediated immune responses. We tested serial and double infusions of romidepsin in a rhesus macaque (RM) model of SIV functional cure, which controls virus without ART. Off ART, romidepsin reactivated SIV in all RMs. Subsequent infusions resulted in diminished reactivation, and two RMs did not reactivate the virus after the second or third infusions. Therefore, those two RMs received CD8-depleting antibody to assess the replication competence of the residual reservoir. The remaining RMs received double infusions, i.e., two doses separated by 48-h. Double infusions were well tolerated, induced immune activation, and effectively reactivated SIV. Although reactivation was gradually diminished, cell-associated viral DNA was minimally changed, and viral outgrowth occurred in 4/5 RMs. In the RM which did not reactivate after CD8 depletion, viral outgrowth was not detected in peripheral blood mononuclear cells (PBMC)-derived CD4+ cells. The frequency of SIV-specific CD8+ T cells increased after romidepsin administration, and the increased SIV-specific immune responses were associated, although not statistically, with the diminished reactivation. Thus, our data showing sequential decreases in viral reactivation with repeated romidepsin administrations with all RMs and absence of viral reactivation after CD8+ T-cell depletion in one animal suggest that, in the context of healthy immune responses, romidepsin affected the inducible viral reservoir and gradually increased immune-mediated viral control. Given the disparities between the results of romidepsin administration to ART-suppressed SIVmac239-infected RMs and HIV-infected normal progressors compared to our immune-healthy model, our data suggest that improving immune function for greater SIV-specific responses should be the starting point of HIV cure strategies. IMPORTANCE HIV cure is sought after due to the prevalence of comorbidities that occur in persons with HIV. One of the most investigated HIV cure strategies is the "shock and kill" approach. Our study investigated the use of romidepsin, a histone deacetylase (HDAC) inhibitor, in our rhesus macaque model of functional cure, which allows for better resolution of viral reactivation due to the lack of antiretroviral therapy. We found that repeated rounds of romidepsin resulted in gradually diminished viral reactivation. One animal inevitably lacked replication-competent virus in the blood. With the accompanying enhancement of the SIV-specific immune response, our data suggest that there is a reduction of the viral reservoir in one animal by the cell-mediated immune response. With the differences observed between our model and persons living with HIV (PWH) treated with romidepsin, specifically in the context of a healthy immune system in our model, our data thereby indicate the importance of restoring the immune system for cure strategies.

So Pathogenic or So What?-A Brief Overview of SIV Pathogenesis with an Emphasis on Cure Research

HIV infection requires lifelong antiretroviral therapy (ART) to control disease progression. Although ART has greatly extended the life expectancy of persons living with HIV (PWH), PWH nonetheless suffer from an increase in AIDS-related and non-AIDS related comorbidities resulting from HIV pathogenesis. Thus, an HIV cure is imperative to improve the quality of life of PWH. In this review, we discuss the origins of various SIV strains utilized in cure and comorbidity research as well as their respective animal species used. We briefly detail the life cycle of HIV and describe the pathogenesis of HIV/SIV and the integral role of chronic immune activation and inflammation on disease progression and comorbidities, with comparisons between pathogenic infections and nonpathogenic infections that occur in natural hosts of SIVs. We further discuss the various HIV cure strategies being explored with an emphasis on immunological therapies and "shock and kill".