Eva Billerbeck

HIV therapy by a combination of broadly neutralizing antibodies in humanized mice

Human antibodies to human immunodeficiency virus-1 (HIV-1) can neutralize a broad range of viral isolates in vitro and protect non-human primates against infection. Previous work showed that antibodies exert selective pressure on the virus but escape variants emerge within a short period of time. However, these experiments were performed before the recent discovery of more potent anti-HIV-1 antibodies and their improvement by structure-based design. Here we re-examine passive antibody transfer as a therapeutic modality in HIV-1-infected humanized mice. Although HIV-1 can escape from antibody monotherapy, combinations of broadly neutralizing antibodies can effectively control HIV-1 infection and suppress viral load to levels below detection. Moreover, in contrast to antiretroviral therapy, the longer half-life of antibodies led to control of viraemia for an average of 60 days after cessation of therapy. Thus, combinations of potent monoclonal antibodies can effectively control HIV-1 replication in humanized mice, and should be re-examined as a therapeutic modality in HIV-1-infected individuals.

Analysis of CD161 expression on human CD8+ T cells defines a distinct functional subset with tissue-homing properties.

CD8+ T lymphocytes play a key role in host defense, in particular against important persistent viruses, although the critical functional properties of such cells in tissue are not fully defined. We have previously observed that CD8+ T cells specific for tissue-localized viruses such as hepatitis C virus express high levels of the C-type lectin CD161. To explore the significance of this, we examined CD8+CD161+ T cells in healthy donors and those with hepatitis C virus and defined a population of CD8+ T cells with distinct homing and functional properties. These cells express high levels of CD161 and a pattern of molecules consistent with type 17 differentiation, including cytokines (e.g., IL-17, IL-22), transcription factors (e.g., retinoic acid-related orphan receptor γ-t, P = 6 × 10−9; RUNX2, P = 0.004), cytokine receptors (e.g., IL-23R, P = 2 × 10−7; IL-18 receptor, P = 4 × 10−6), and chemokine receptors (e.g., CCR6, P = 3 × 10−8; CXCR6, P = 3 × 10−7; CCR2, P = 4 × 10−7). CD161+CD8+ T cells were markedly enriched in tissue samples and coexpressed IL-17 with high levels of IFN-γ and/or IL-22. The levels of polyfunctional cells in tissue was most marked in those with mild disease (P = 0.0006). These data define a T cell lineage that is present already in cord blood and represents as many as one in six circulating CD8+ T cells in normal humans and a substantial fraction of tissue-infiltrating CD8+ T cells in chronic inflammation. Such cells play a role in the pathogenesis of chronic hepatitis and arthritis and potentially in other infectious and inflammatory diseases of man.

HIV-1 suppression and durable control by combining single broadly neutralizing antibodies and antiretroviral drugs in humanized mice

Significance Treatment of HIV-1 infection in humans is achieved using combinations of highly effective antiretroviral therapy (ART) drugs to potently suppress viral replication and prevent the emergence of drug-resistant viruses. However, ART drugs must be taken indefinitely owing to rapid return of viremia upon termination of treatment. Highly potent broadly neutralizing antibodies (bNAbs) present a new potential therapeutic modality in the treatment of HIV-1 infection. Because of their comparatively longer half-lives relative to ART drugs and their ability to eliminate infected cells, bNAbs may alleviate some aspects of the lifelong treatment adherence burden of ART. Here we show that lowering the initial viral load with ART enables single bNAbs to effectively control an established HIV-1 infection in humanized mice. Effective control of HIV-1 infection in humans is achieved using combinations of antiretroviral therapy (ART) drugs. In humanized mice (hu-mice), control of viremia can be achieved using either ART or by immunotherapy using combinations of broadly neutralizing antibodies (bNAbs). Here we show that treatment of HIV-1–infected hu-mice with a combination of three highly potent bNAbs not only resulted in complete viremic control but also led to a reduction in cell-associated HIV-1 DNA. Moreover, lowering the initial viral load by coadministration of ART and immunotherapy enabled prolonged viremic control by a single bNAb after ART was withdrawn. Similarly, a single injection of adeno-associated virus directing expression of one bNAb produced durable viremic control after ART was terminated. We conclude that immunotherapy reduces plasma viral load and cell-associated HIV-1 DNA and that decreasing the initial viral load enables single bNAbs to control viremia in hu-mice.

Development of human CD4+FoxP3+ regulatory T cells in human stem cell factor–, granulocyte-macrophage colony-stimulating factor–, and interleukin-3–expressing NOD-SCID IL2Rγnull humanized mice

Human hematolymphoid mice have become valuable tools for the study of human hematopoiesis and uniquely human pathogens in vivo. Recent improvements in xenorecipient strains allow for long-term reconstitution with a human immune system. However, certain hematopoietic lineages, for example, the myeloid lineage, are underrepresented, possibly because of the limited cross-reactivity of murine and human cytokines. Therefore, we created a nonobese diabetic/severe combined immunodeficiency/interleukin-2 receptor-γ-null (NOD-SCID IL2Rγ(null)) mouse strain that expressed human stem cell factor, granulocyte-macrophage colony-stimulating factor, and interleukin-3, termed NSG-SGM3. Transplantation of CD34(+) human hematopoietic stem cells into NSG-SGM3 mice led to robust human hematopoietic reconstitution in blood, spleen, bone marrow, and liver. Human myeloid cell frequencies, specifically, myeloid dendritic cells, were elevated in the bone marrow of humanized NSG-SGM3 mice compared with nontransgenic NSG recipients. Most significant, however, was the increase in the CD4(+)FoxP3(+) regulatory T-cell population in all compartments analyzed. These CD4(+)FoxP3(+) regulatory T cells were functional, as evidenced by their ability to suppress T-cell proliferation. In conclusion, humanized NSG-SGM3 mice might serve as a useful model to study human regulatory T-cell development in vivo, but this unexpected lineage skewing also highlights the importance of adequate spatiotemporal expression of human cytokines for future xenorecipient strain development.

Inflammatory Flt3l is essential to mobilize dendritic cells and for T cell responses during Plasmodium infection

Innate sensing mechanisms trigger a variety of humoral and cellular events that are essential to adaptive immune responses. Here we describe an innate sensing pathway triggered by Plasmodium infection that regulates dendritic cell homeostasis and adaptive immunity through Flt3 ligand (Flt3l) release. Plasmodium-induced Flt3l release in mice requires Toll-like receptor (TLR) activation and type I interferon (IFN) production. We found that type I IFN supports the upregulation of xanthine dehydrogenase, which metabolizes the xanthine accumulating in infected erythrocytes to uric acid. Uric acid crystals trigger mast cells to release soluble Flt3l from a pre-synthesized membrane-associated precursor. During infection, Flt3l preferentially stimulates expansion of the CD8-α+ dendritic cell subset or its BDCA3+ human dendritic cell equivalent and has a substantial impact on the magnitude of T cell activation, mostly in the CD8+ compartment. Our findings highlight a new mechanism that regulates dendritic cell homeostasis and T cell responses to infection.

Parallel Expansion of Human Virus-Specific FoxP3− Effector Memory and De Novo-Generated FoxP3+ Regulatory CD8+ T Cells upon Antigen Recognition In Vitro

Although FoxP3 has been shown to be the most specific marker for regulatory CD4+ T cells, its significance in the CD8+ T cell population is not well understood. In this study, we show that the in vitro stimulation of human PBMC with hepatitis C virus or Flu virus-specific peptides gives rise to two distinct Ag-specific T cell populations: FoxP3− and FoxP3+CD8+ T cells. The FoxP3+ virus-specific CD8+ T cells share phenotypical markers of regulatory T cells, such as CTLA-4 and glucocorticoid-induced TNFR family-related gene, and do produce moderate amounts of IFN-γ but not IL-2 or IL-10. IL-2 and IL-10 are critical cytokines, however, because the expansion of virus-specific FoxP3+CD8+ T cells is blocked by IL-2- or IL-10-neutralizing mAbs. The virus-specific FoxP3+CD8+ T cells have a reduced proliferative capacity, indicating anergy, and display a cell-cell contact-dependent suppressive activity. Taken together, our results indicate that stimulation with a defined viral Ag leads to the expansion of two different cell populations: FoxP3− memory/effector as well as FoxP3+ regulatory virus-specific CD8+ T cells.

Characterization of Human Antiviral Adaptive Immune Responses during Hepatotropic Virus Infection in HLA-Transgenic Human Immune System Mice

Humanized mice have emerged as a promising model to study human immunity in vivo. Although they are susceptible to many pathogens exhibiting an almost exclusive human tropism, human immune responses to infection remain functionally impaired. It has recently been demonstrated that the expression of HLA molecules improves human immunity to lymphotropic virus infections in humanized mice. However, little is known about the extent of functional human immune responses in nonlymphoid tissues, such as in the liver, and the role of HLA expression in this context. Therefore, we analyzed human antiviral immunity in humanized mice during a hepatotropic adenovirus infection. We compared immune responses of conventional humanized NOD SCID IL-2Rγ–deficient (NSG) mice to those of a novel NOD SCID IL-2Rγ–deficient strain transgenic for both HLA-A*0201 and a chimeric HLA-DR*0101 molecule. Using a firefly luciferase–expressing adenovirus and in vivo bioluminescence imaging, we demonstrate a human T cell–dependent partial clearance of adenovirus-infected cells from the liver of HLA-transgenic humanized mice. This correlated with liver infiltration and activation of T cells, as well as the detection of Ag-specific humoral and cellular immune responses. When infected with a hepatitis C virus NS3–expressing adenovirus, HLA-transgenic humanized mice mounted an HLA-A*0201–restricted hepatitis C virus NS3-specific CD8+ T cell response. In conclusion, our study provides evidence for the generation of partial functional antiviral immune responses against a hepatotropic pathogen in humanized HLA-transgenic mice. The adenovirus reporter system used in our study may serve as simple in vivo method to evaluate future strategies for improving human intrahepatic immune responses in humanized mice.

CD8+ regulatory T cells in persistent human viral infections

Regulatory T cells (T(reg) cells) play an important role in the regulation and suppression of immune responses to self- and foreign antigens. Suppressed and impaired host immune responses are a major characteristic of many persistent human virus infections, such as those caused by human immunodeficiency virus (HIV), hepatitis C virus (HCV), and herpes virus. It has recently become evident that immune regulation mediated by T(reg) cells may comprise one mechanism that contributes to the impairment of virus-specific immune responses. Indeed, during viral infection, the generation of distinct subsets of CD4+ as well as CD8+ T(reg) cells has been reported. The phenotypic and functional heterogeneity of T(reg) cell subsets involved in the suppression of virus-specific immune responses suggests that different mechanisms and factors contribute to the generation of those cells during viral infection. This review focuses on the CD8+ T(reg) cell subset and summarizes current knowledge about the induction and function of CD8+ T(reg) cells in persistent human virus infections.

Utility of Humanized BLT Mice for Analysis of Dengue Virus Infection and Antiviral Drug Testing

ABSTRACT Dengue virus (DENV) is the cause of a potentially life-threatening disease that affects millions of people worldwide. The lack of a small animal model that mimics the symptoms of DENV infection in humans has slowed the understanding of viral pathogenesis and the development of therapies and vaccines. Here, we investigated the use of humanized “bone marrow liver thymus” (BLT) mice as a model for immunological studies and assayed their applicability for preclinical testing of antiviral compounds. Human immune system (HIS) BLT-NOD/SCID mice were inoculated intravenously with a low-passage, clinical isolate of DENV-2, and this resulted in sustained viremia and infection of leukocytes in lymphoid and nonlymphoid organs. In addition, DENV infection increased serum cytokine levels and elicited DENV-2-neutralizing human IgM antibodies. Following restimulation with DENV-infected dendritic cells, in vivo-primed T cells became activated and acquired effector function. An adenosine nucleoside inhibitor of DENV decreased the circulating viral RNA when administered simultaneously or 2 days postinfection, simulating a potential treatment protocol for DENV infection in humans. In summary, we demonstrate that BLT mice are susceptible to infection with clinical DENV isolates, mount virus-specific adaptive immune responses, and respond to antiviral drug treatment. Although additional refinements to the model are required, BLT mice are a suitable platform to study aspects of DENV infection and pathogenesis and for preclinical testing of drug and vaccine candidates. IMPORTANCE Infection with dengue virus remains a major medical problem. Progress in our understanding of the disease and development of therapeutics has been hampered by the scarcity of small animal models. Here, we show that humanized mice, i.e., animals engrafted with components of a human immune system, that were infected with a patient-derived dengue virus strain developed clinical symptoms of the disease and mounted virus-specific immune responses. We further show that this mouse model can be used to test preclinically the efficacy of antiviral drugs.

CD161(+)CD4(+) T cells are enriched in the liver during chronic hepatitis and associated with co-secretion of IL-22 and IFN-γ.

Hepatitis C virus infection is a major cause of chronic liver disease. CD4+ T cells play a key role in disease outcome. However, the critical functions and associated phenotypes of intrahepatic CD4+ T cells are not well defined. We have previously shown that CD8+ T cells expressing the C type lectin CD161 are highly enriched in the human liver, especially during chronic hepatitis. These cells are associated with a type 17 differentiation pattern and express cytokines including IL-17A, IL-22, and IFN-γ. We therefore analyzed expression of CD161 on CD4+ T cells in blood and liver and addressed the relevant phenotype and functional capacity of these populations. We observed marked enrichment of CD161+CD4+ T cells in the liver during chronic hepatitis such that they are the dominant subtype (mean 55% of CD4+ T cells). IL-22 and IL-17 secreting CD4+ T cells were readily found in the livers of HCV+ and NASH donors, although not enriched compared to blood. There was, however, specific enrichment of a novel subset of IL-22/IFN-γ dual secretors (p = 0.02) compared to blood, a result reconfirmed with direct ex vivo analyses. These data indicate the dominance of CD161+ expressing lymphocyte populations within the hepatic infiltrate, associated with a distinct cytokine profile. Given their documented roles as antiviral and hepatoprotective cytokines respectively, the impact of co-secretion of IFN-γ and IL-22 in the liver may be particularly significant.