Exploring biomarkers of the viral reservoir and anti-viral CD8+ T cell responses - towards a functional cure of HIV-1. (Doctoral thesis)
- HIV Clinical and Translational Research
Antiretroviral therapy (ART) halts progression to AIDS but is not curative due to persisting viral reservoirs in CD4 + T cells. Therefore patients depend on lifelong drug intake accompanied with potential side effects, drug resistance and heightened chronic inflammation. Besides the high economic costs, reach out to patients is especially challenging in low and middle income countries, which are most, affected from HIV-1. In addition to the need for increase of ART coverage in parts of the world, we face a growing number of a chronically infected and aging patient population worldwide. Consequently, new curative approaches to end HIV-1 infection are needed.
The total removal of HIV-1 reservoirs from the body (“sterile cure”) has proven impractical to date due do its high diversity and early seedings in tissues. However, ART free remission while HIV-1 remains detectable, termed a functional cure, might be in closer reach. In any of both cases, the search for exclusive markers of the replication competent viral reservoirs remains valuable with the ultimate objective of targeted depletion.
Most studies in humans are limited to the reservoir in the peripheral blood. HIV-1 infected humanized mice can help to gain insight into the tissue reservoirs. In this context, elite controllers, characterized by a very low viral reservoir, represent a rare and unique profile of natural control with opportunities to study immune-mediated containment of HIV-1 replication. Under the current consensus that a combination of interventions depleting the reservoir and improving host mediated clearance would most likely lead to viral control, the objectives of this PhD project were divided in two interrelated thematics: The characterization of tissue HIV-1 reservoirs in humanized mice and the identification of CD8+ T cell subsets associated with improved in vivo control of HIV-1.
Viral reservoirs are diverse entities with regard to which tissues and CD4 + T cell compartment they reside in. Therefore we sought to investigate reservoir dynamics in a well-controlled setting of early and late ART initiation in HIV-1 infected humanized mice. A particular focus point was the role of CD32, a recently proposed marker for the replication-competent reservoir in human blood CD4 + T cells, which we now wanted to investigate in peripheral tissues of virally suppressed animals. Clearly, early treatment significantly reduced total HIV-1 DNA whereas we observed no initial changes in viral rebound between early and late treated animals. However, over 25 % of early treated (and none of the late treated) animals went back to undetectable viral load after a short period of viral rebound. Interestingly CD32+CD4+ memory T cells were enriched for total HIV-1 DNA but not for cell-associated early RNA transcript levels. Importantly CD32+CD4+ memory T cells showed also a relative enrichment in productive infection upon latency reversal but constituted a negligible compartment for the total replication competent reservoir.
The viral suppressive capacity (VSC) of CD8+ T cells from patients under ART is generally found to be low. In order to test approaches of therapeutic vaccination we investigated HIV-1 consensus Gag peptide stimulation to increase viral suppression in vitro. Interestingly about 60% of ART patients indeed showed a considerably higher peptide induced VSC, which was associated with an expanded CD8 + memory T cell subsets co-expressing the immune checkpoint molecules, PD1 and CD160. Furthermore, upregulation of CD57 and HLA-DR expression were associated with increased in vitro suppression. These findings indicate a potential role of terminally differentiated CD8+ memory T cells with regard to efficient HIV-1 suppression in ART patients.
Spontaneous controllers of HIV-1 infection are recognized for their highly functional CD8+ T cell responses. However the exact subsets most effective in viral suppression have not been defined yet. To this end, the last part of this project intended to define immune correlates of natural control mediated by HIV-1 specific CD8+ T cells. Upon stimulation with potential T cell epitope (PTE) Gag peptides, viral suppressive capacity was strongly upregulated in controllers and this correlated with increased CXC5 expression, pointing to the capacity of these cells to home in germinal centers of the lymphoid organs, which are known as “sanctuar” HIV reservoirs. Furthermore, several distinct multifunctional cytotoxic subsets which correlated well with viral suppression were identified. These findings underline the probable role of distinct multifunctional CD8+ T cell subset with tissue homing abilities during natural control of HIV-1.
In conclusion, our studies contribute to mapping the HIV reservoir distribution under antiviral therapy. Moreover, we also show that antigenic stimulation with Gag induces multifunctional CD8 T cell responses with the potential ability to suppress HIV replication in the lymphoid tissues. These new insights will need to be translated into therapeutic strategies for functional cure of HIV-1.