CpG oligodeoxynucleotides activate HIV replication in latently infected human T cells.

CpG oligodeoxynucleotides (CpG ODNs) stimulate immune cells via the Toll-like receptor 9 (TLR9). In this study, we have investigated the effects of CpG ODNs on latent human immunodeficiency virus (HIV) infection in human T cells. Treatment of the latently infected T cell line ACH-2 with CpG ODNs 2006 or 2040 stimulated HIV replication, whereas no effects were evident when ODNs without the CpG motif were used. CpG-induced virus reactivation was blocked by chloroquine, indicating the involvement of TLR9. In contrast to the responsiveness of ACH-2 cells, CpG ODNs failed to activate HIV provirus in the latently infected Jurkat clone J1.1. We also studied the effects of CpG ODNs on productive HIV infection and found enhancement of viral replication in A3.01 T cells, whereas again no stimulating effects were observed in Jurkat T cells. CpG ODN treatment activated NF-kappaB in ACH-2 cells, which was similarly triggered in uninfected A3.01 T cells following exposure to CpG ODNs, indicating that TLR9-induced signal transduction was not dependent on proviral infection. Our study demonstrates that CpG ODNs directly trigger the activation of NF-kappaB and reactivation of latent HIV in human T cells. Our results point to a novel role for CpG ODNs as stimulators of HIV replication and open new avenues to eradicate the latent viral reservoirs in HIV-infected patients treated with antiretroviral therapy.

Functional impairment of CD8(+) T cells by regulatory T cells during persistent retroviral infection.

The establishment of viral persistence generally requires evasion of the host CD8(+) T cell response. Here we describe a form of evasion wherein the CD8(+) T cells are fully capable of recognizing their cognate antigen but their effector functions are suppressed by regulatory T cells. Virus-specific CD8(+) T cells adoptively transferred into mice persistently infected with Friend virus proliferated and appeared activated, but failed to produce IFNgamma or reduce virus loads. Cotransfer experiments revealed that a subpopulation of CD4(+) T cells from persistently infected mice suppressed IFNgamma production by the CD8(+) T cells. Treatment of persistently infected mice with anti-GITR antibody to ameliorate suppression by regulatory T cells significantly improved IFNgamma production by transferred CD8(+) T cells and allowed a significant reduction in viral loads. The results indicate that CD4(+) regulatory T cells contribute to viral persistence and demonstrate an immunotherapy for treating chronic retroviral infections.

Treatment of infectious diseases with immunostimulatory oligodeoxynucleotides containing CpG motifs.

Bacterial DNA with CpG motifs can efficiently stimulate the vertebrate immune system. Thus, synthetic oligodeoxynucleotides that contain such CpG motifs (CpG-ODN) are currently used in preclinical and clinical studies to develop new allergy or cancer therapies and vaccine adjuvants. Recent animal studies indicate that CpG-ODN therapies can also be used for successful treatment of infections caused by bacteria, parasites or viruses. In these experiments, innate and adaptive immune responses against pathogens were augmented by CpG-ODN and subsequently induced resistance against infectious diseases. The stimulation of dendritic cells played a central role for the therapeutic effect of CpG-ODN. However, CpG-ODN can also have negative side effects, which accelerate disease progression in some viral infections. Clinical studies with CpG-ODN will determine their potential for the therapy of infectious diseases in humans.

Preinfection treatment of resistant mice with CpG oligodeoxynucleotides renders them susceptible to friend retrovirus-induced leukemia.

We recently reported that immunostimulatory oligodeoxynucleotides (CpG oligodeoxynucleotides [CpG-ODN]) were effective in postexposure treatment of retrovirus-induced disease (A. R. M. Olbrich et al., J. Virol. 76:11397-11404, 2002). We now show that the timing of treatment is a critical factor in treatment efficacy. In stark contrast to the success of postexposure treatments, we found that CpG treatment of susceptible mice prior to Friend retrovirus infection accelerated the development of virus-induced erythroleukemia. Furthermore, 70.8% of mice that were resistant to Friend virus-induced leukemia developed disease after inoculation of CpG-ODN before infection. The CpG pretreatment of these mice enhanced viral loads in their spleens and blood compared to controls that received ODN without CpG motifs. The main target cells of Friend virus, erythroid precursor cells and B cells, proliferated after CpG-ODN inoculation and provided an enlarged target cell population for viral infection. Our present findings together with our previous report demonstrate that CpG-ODN treatment of viral infections may be a double-edged sword that can result in an effective therapy but also in an acceleration of disease progression depending on the time point of treatment.

Effective postexposure treatment of retrovirus-induced disease with immunostimulatory DNA containing CpG motifs.

Therapeutic strategies for the treatment of acute retroviral infections have relied mainly on antiviral drugs. In this study we used the Friend virus model system to demonstrate that enhancement of the immune system can also have dramatic therapeutic effects. Since resistance to Friend virus-induced leukemia in mice is associated with T helper cell type 1 (Th1) immune responses, we enhanced these responses in susceptible mice by treatment with synthetic oligodeoxynucleotides containing unmethylated CpG motifs (CpG-ODN). Treatments begun at 4 days postinfection increased recovery from 6% in the control group to 74% in the CpG-treated group. CpG-mediated recovery was associated with a significant reduction of viral loads in the blood and spleens of treated mice compared to those of control animals. The treatment promoted Th1-type cytokine production by splenocytes of Friend virus-infected mice and augmented Friend virus-specific cytotoxic T-cell responses, but no influence on the virus-specific neutralizing antibody response was observed. Friend virus-specific CD8(+) T cells were critical for effective treatment with CpG-ODN, since in vivo depletion of these cells from treated mice prevented their recovery. Our results demonstrate that CpG-ODN therapy can significantly enhance virus-specific cellular immune responses and prevent retrovirus-induced disease. These findings may have implications for antiviral therapy in general.

The role of IL-5, IL-6 and IL-10 in primary and vaccine-primed immune responses to infection with Friend retrovirus (Murine leukaemia virus).

The defence of a host against viral infections is strongly influenced by cytokines. We investigated the role of the B-cell stimulating cytokines IL-5 and IL-6, and the immuno-suppressive cytokine IL-10, during primary and secondary immune responses in mice against infection with Friend retrovirus (FV) (Murine leukaemia virus). IL-5(-/-) mice were comparable to C57BL/6 wild-type mice in their ability to control acute FV infection. In contrast, IL-6(-/-) and IL-10(-/-) mice showed significantly enhanced virus loads in spleen cells. However, this impaired control of acute FV replication did not alter the long-term control over persistent FV in IL-6(-/-) and IL-10(-/-) mice. Immunization with a live attenuated vaccine virus prior to challenge protected all three types of cytokine-deficient mice from high levels of spleen virus, despite the finding that the vaccinated IL-5- and IL-6-deficient mice had significantly reduced titres of virus-neutralizing IgG class antibodies. The results indicate that IL-6 and IL-10 contribute to primary immune responses against FV, but are dispensable during persistent infection and vaccine-primed secondary responses.