Aspects on latency in HIV-1 infection

Abstract

The use of combination antiretroviral therapy (ART) has resulted in a substantial reduction in viremia, a rebound of CD4+ T-cells and increased survival for human immunodeficiency virus type 1 (HIV-1) infected individuals. Unfortunately, ART does not clear the infection or cure the individual from HIV-1. This is due to some unique characteristics of the virus, such as an ability to cause a latent infection in a subset of CD4+ T-cells, and a remarkable genetic variability. This allows HIV to become resistant to treatment under suboptimal conditions (i.e. adherence), and to escape the immune system. The mechanisms of latency needs to be better understood in order to achieve eradication of HIV-1 infection, and the general aim of this thesis was to study different aspects on HIV-1 latency, with a main focus on the circulating pool of HIV-1 infected resting memory CD4+ T-cells.

In paper I we set out to analyze whether resting memory CD4+ T-cells could serve as a reservoir of founder or resistant viral strains in patients with or without optimal suppressed viremia. Our results indicated a turn-over and replacement of the cell-pool in untreated and suboptimally treated patients. The memory CD4+ T-cell-pool forms an archive of the viral population, but former resistant viral variants are not always found in these circulating cells.

In paper II we wanted to investigate if treatment with high dose intraveneous immunoglobulin (IVIG) in combination with ART could reduce the pool of latently infected resting memory CD4+ T-cells in vivo. Our data suggested a reduction by an average of 68% of the HIV infected latent cell pool. The findings from this proof-ofconcept study suggest that the reservoir became accessible by IVIG treatment through activation of HIV-1 in the latently-infected resting CD4+ T-cells. IVIG will be further evaluated as an adjuvant to effective ART.

In paper III, we investigated the impact of DNA methylation inhibitors and NFkB activators on HIV-1 latency in resting memory CD4+ T-cells. Cytosine methylation may be an important component that controls HIV-1 latency. We found that a combination of the DNA methylation inhibitor Aza-CdR and the NFkB activator prostratin can reactivate latent HIV-1 in vitro. Our data indicate that clearance of HIV-1 from infected persons undergoing antiretroviral therapy may be enhanced by inclusion of these inhibitors.

In paper IV we wanted to investigate to what extent high mobility group box protein 1, HMGB1, alone or in complex with TLR ligands activate latent HIV-1 in vitro. HMGB1 is an abundant intracellular protein found in all cells in the body. It contributes to immune activation and has been suggested to have an important impact on HIV-1 pathogenesis. We found that recombinant HMGB1, or HMGB1 as part of necrotic extract, in complex with TLR stimulating ligands LPS, CpG ODN and flagellin, increased HIV-1 replication in vitro, as compared to HMGB1 or ligands alone, in a model of latent HIV-1 infection.

Our in vivo data suggest that a turn-over of the latent HIV-1 reservoir in resting memory CD4+ T-cells may appear in the natural course of HIV-1 infection in untreated and in suboptimally treated subjects. It is also possible to induce a decrease of the viral reservoirs by additional treatment, in our case IVIg, in patients with controlled viremia. Our in vitro data point at new possibilities to activate latent HIV-1 and further exploration of these mechanisms should be considered.