HIV-1 Vpr Accelerates Viral Replication during Acute Infection by Exploitation of Proliferating CD4+ T Cells In Vivo

Kei Sato,Masao Matsuoka,Shingo Iwami,Kazuyuki Aihara,Naoko Misawa,Yorifumi Satou,Dong Sung An,Mamoru Ito,Yoshio Koyanagi,Yukihito Ishizaka,Jeremy Luban

doi:10.1371/journal.ppat.1003812

Abstract

The precise role of viral protein R (Vpr), an HIV-1-encoded protein, during HIV-1 infection and its contribution to the development of AIDS remain unclear. Previous reports have shown that Vpr has the ability to cause G2 cell cycle arrest and apoptosis in HIV-1-infected cells in vitro. In addition, vpr is highly conserved in transmitted/founder HIV-1s and in all primate lentiviruses, which are evolutionarily related to HIV-1. Although these findings suggest an important role of Vpr in HIV-1 pathogenesis, its direct evidence in vivo has not been shown. Here, by using a human hematopoietic stem cell-transplanted humanized mouse model, we demonstrated that Vpr causes G2 cell cycle arrest and apoptosis predominantly in proliferating CCR5+ CD4+ T cells, which mainly consist of regulatory CD4+ T cells (Tregs), resulting in Treg depletion and enhanced virus production during acute infection. The Vpr-dependent enhancement of virus replication and Treg depletion is observed in CCR5-tropic but not CXCR4-tropic HIV-1-infected mice, suggesting that these effects are dependent on the coreceptor usage by HIV-1. Immune activation was observed in CCR5-tropic wild-type but not in vpr-deficient HIV-1-infected humanized mice. When humanized mice were treated with denileukin diftitox (DD), to deplete Tregs, DD-treated humanized mice showed massive activation/proliferation of memory T cells compared to the untreated group. This activation/proliferation enhanced CCR5 expression in memory CD4+ T cells and rendered them more susceptible to CCR5-tropic wild-type HIV-1 infection than to vpr-deficient virus. Taken together, these results suggest that Vpr takes advantage of proliferating CCR5+ CD4+ T cells for enhancing viremia of CCR5-tropic HIV-1. Because Tregs exist in a higher cycling state than other T cell subsets, Tregs appear to be more vulnerable to exploitation by Vpr during acute HIV-1 infection.

Highlights

Human immunodeficiency virus type 1 (HIV-1), the causative agent of acquired immunodeficiency syndrome (AIDS), encodes four viral accessory proteins: Vif, Vpu, Nef, and viral protein R (Vpr)
By using a humanized mouse model, we demonstrate that Vpr enhances CCR5-tropic but not CXCR4-tropic HIV-1 replication in vivo by exploiting Tregs during acute infection
In CCR5-tropic HIV-1-infected humanized mice, Vpr-dependent G2 cell cycle arrest and apoptosis are predominantly observed in infected Tregs, and wild-type but not vprdeficient HIV-1-infected mice displayed acute Treg depletion

Summary

Introduction

Human immunodeficiency virus type 1 (HIV-1), the causative agent of acquired immunodeficiency syndrome (AIDS), encodes four viral accessory proteins: Vif, Vpu, Nef, and Vpr. Previous in vitro studies have reported that vpr-deficient HIV-1 is less replicative in CD4+ T cell lines [2] and cycling primary CD4+ T cells [3]. Vpr deficiency modestly affects viral replication kinetics in tonsil histocultures in which resting CD4+ T cells dominantly reside [4]. The main target of HIV-1 in vivo is CD4+ T cells. Based on their function and phenotype, primary CD4+ T cells are classified into three subsets: naive CD4+ T cells (Tns), memory CD4+ T cells (Tms), and regulatory CD4+ T cells (Tregs). It is speculated that such phenotypic and functional differences among these subsets

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