Lymphatic endothelial cells promote productive and latent HIV infection in resting CD4+ T cells

Meghan Schilthuis,Bo Ram Kim,Derrick Kamp,Seth Verkaik,Mackenzie Walhof,Anding Shen,Andrew Philipose,Olivia Harlow

doi:10.1186/s12985-018-1068-6

Abstract

BackgroundAn HIV cure has not yet been achieved because latent viral reservoirs persist, particularly in resting CD4+ T lymphocytes. In vitro, it is difficult to infect resting CD4+ T cells with HIV-1, but infections readily occur in vivo. Endothelial cells (EC) line the lymphatic vessels in the lymphoid tissues and regularly interact with resting CD4+ T cells in vivo. Others and we have shown that EC promoted productive and latent HIV infection of resting CD4+ T cells. However, the EC used in previous studies were from human umbilical cords (HUVEC), which are macrovascular; whereas EC residing in the lymphoid tissues are microvascular.MethodsIn this study, we investigated the effects of microvascular EC stimulation of resting CD4+ T cells in establishing viral infection and latency. Human resting and activated CD4+ T cells were cultured alone or with endothelial cells and infected with a pseudotyped virus. Infection levels, indicated by green fluorescent protein expression, were measured with flow cytometry and data was analyzed using Flowing Software and Excel.ResultsWe confirmed that EC from lymphatic tissue (LEC) were able to promote HIV infection and latency formation in resting CD4+ T cells while keeping them in resting phenotype, and that IL-6 was involved in LEC stimulation of CD4+ T cells. However, there are some differences between stimulation by LEC and HUVEC. Unlike HUVEC stimulation, we demonstrated that LEC stimulation of resting memory T cells does not depend on major histocompatibility complex class II (MHC II) interactions with T cell receptors (TCR) and that CD2-CD58 interactions were not involved in LEC stimulation of resting T cells. LEC also secreted lower levels of IL-6 than HUVEC. We also found that LEC stimulation increases HIV infection rates in activated CD4+ T cells.ConclusionsWhile differences in T cell stimulation between lymphatic EC and HUVEC were observed, we confirmed that similar to macrovascular EC stimulation, microvascular EC stimulation promotes direct HIV infection and latency formation in resting CD4+ T cells without T cell activation. LEC stimulation also increased infection rates in activated CD4+ T cells. Additionally, the present study established a physiologically more relevant model of EC interactions with resting CD4+ T cells and further highlighted the importance of investigating the roles of EC in HIV infection and latency in both resting and activated CD4+ T cells.

Highlights

An Human immunodeficiency virus (HIV) cure has not yet been achieved because latent viral reservoirs persist, in resting Cluster of differentiation 4 (CD4)+ T lymphocytes
Kinetics of viral infection in resting CD4+ T cells co-cultured with lymphatic endothelial cells compared with Human umbilical vein endothelial cells (HUVEC) Infection in resting CD4+ T cells stimulated by endothelial cells (HUVEC) takes place much slower than in activated T cells [31]
Similar to HUVEC stimulation, lymphatic endothelial cells (LEC)- stimulation resulted in increased infection in resting T cells, at similar levels or slightly lower than those in T cells stimulated by LEC+

Summary

Introduction

An HIV cure has not yet been achieved because latent viral reservoirs persist, in resting CD4+ T lymphocytes. Much effort has been made to reactivate latent HIV in order to eliminate the reservoir, significant hurdles to this approach have been encountered because cell death did not ensue after latency reversal (reviewed in [6]). Recent innovations involve using latency strengthening agents or CRISPR based systems to further lock latent virus inside the infected cells in order to prevent reactivation [7]. This approach may be promising, but most of the work is still at the in vitro stage. Our understanding of how the latent reservoir is established is still very limited

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