Identifying Correlates of Immune-Mediated Elimination of Productively and Latently HIV-Infected T Cells

Abstract

Persistent latent HIV-infected cells capable of producing infectious virus are the primary obstacle to curing HIV infection. They are rare and difficult to target, making their elimination challenging. Elimination of this latent reservoir (LR) is crucial for the success of HIV cure efforts and will likely require the development of new approaches to activate latently infected cells with latency reversing agents (LRA) to enable them to be identified and eliminated by an enhanced immune response. A strategy proposed to reduce the LR has been termed ``shock and kill" and uses various pharmacological treatments to function as LRAs to "shock" latently infected cells to produce virus, which either directly kills the cells or enables the immune system to eliminate the cells. Here, I describe two projects, each addressing some aspect of the "shock and kill" strategy. First, we developed an in vivo model to study the activation and eradication of the latent reservoir. Second, we investigated a possible therapeutic to eliminate HIV-infected, and potentially reactivated latent, cells by TCR gene therapy.

The development of treatments to cure HIV is hampered by the lack of latency models which recapitulate the in vivo activation and elimination of latent infected cells from patients. There are several humanized mouse models that have been used to study HIV infection and latency. Most of these studies use humanized mice populated with human CD4- T cells derived from transplanted human hematopoietic stem cells. These acutely infected humanized mice likely do not accurately recapitulate latent infection because continued replication may still be occurring as reported for patients in the first 6 months after ART initiation. We hypothesized that we could study in vivo reactivation of latently HIV-infected cells from the natural latent reservoir the efficacy of therapeutics to reactivate and eliminate the reactivated latent cells by developing a novel humanized mouse model consisting of PBMCs from virally suppressed patients intrasplenically injected into immunodeficientNOD-SCID-IL2γr -/- (NSG) mice. We used this mouse model to study the reactivation of the LR of several donors with different sizes of the reservoir as determined by the quantitative viral outgrowth assay (QVOA). We used this model to demonstrate the in vivo capacity of antibody dependent cellular cytotoxicity (ADCC) to eliminate reactivated latent cells and identified unique populations of latently infected cells activated in vivo that were not activated during in vitro activation assays.

The second part of my thesis investigated the role of T cell receptor (TCR) clonotypes in controlling HIV infection and using these findings to develop a potential therapy to control and eliminate HIV infected cells, thereby contributing to the goal of a functional cure. The CTL response controls viremia, which declines as the levels of HIV specific CTLs rise and CD4+ T cell counts recover. Lentiviral vectors expressing effective HIV specific TCR clonotypes can transform naïve CD8 T cells into potent HIV-specific CTLs, a possible gene therapy approach to increase HIV-specific immunity. To optimize this approach, it is crucial to identify TCR clonotypes which confer the most potent anti-HIV activity. However, the contributory role of the HIV-specific TCR clonotype on the potency of its antiviral activity is unclear. To specifically evaluate the contribution of TCR clonotypes to CTL function, we cloned the TCR α and TCR β chain genes from an effective and two ineffective CTL clones from an HLA*B2705 elite controller into TCR-expressing lentivectors. We used these lentivectors to transduce Jurkat/MA cells as well as primary CD8+ T cells to delineate the capacity of cells expressing these TCRs to recognize target cells presenting their cognate HIV peptide and elicit a TCR response upon activation of the TCR signal transduction pathway.

Overall, we developed a novel pre-clinical humanized model for the study of HIV latency reactivation and eradication. This model enabled us to demonstrate antibody-mediated in vivo elimination of reactivated latent HIV-infected cells from an HIV-1- infected patient and can be used to evaluate the efficacy of other HIV treatments. Additionally, we investigated the contribution of TCR clonotypes on the potency of the CTLs' ability to eliminate HIV infected cells. Our data suggests that the potent antiviral capacity in some HIV specific CTL clones is a consequence of factors other than TCR structure likely contribute to the ineffective phenotype of some CD8+ T cell clones. Determining these factors may enable the development of in vivo therapeutics converting naïve CD8+T cells into HIV speciffic CTLs capable of recognizing and eliminating HIV infected cells, including reactivated latent cells.