Summary Human antibodies to HIV-1 can neutralize a broad range of viral isolates in vitro and protect non-human primates against infection1,2. Previous work showed that antibodies exert selective pressure on the virus but escape variants emerge within a short period of time3,4. However, these experiments were performed before the recent discovery of more potent anti-HIV-1 antibodies and their improvement by structure-based design5-9. Here we re-examine passive antibody transfer as a therapeutic modality in HIV-1-infected humanized mice (hu-mice). Although HIV-1 can escape from antibody monotherapy, combinations of broadly neutralizing antibodies (bNAbs) can effectively control HIV-1 infection and suppress viral load to levels below detection. Moreover, in contrast to antiretroviral therapy (ART)10-12, the longer half-life of antibodies led to viremic control for an average of 60 days after cessation of therapy. Thus, combinations of potent monoclonal antibodies can effectively control HIV-1 replication in hu-mice, and should be re-examined as a therapeutic modality in HIV-1-infected individuals.

Hepatitis C virus (HCV) infects ∼2% of the world's population. It is estimated that there are more than 500,000 new infections annually in Egypt, the country with the highest HCV prevalence. An effective vaccine would help control this expanding global health burden. HCV is highly variable, and an effective vaccine should target conserved T- and B-cell epitopes of the virus. Conserved B-cell epitopes overlapping the CD81 receptor-binding site (CD81bs) on the E2 viral envelope glycoprotein have been reported previously and provide promising vaccine targets. In this study, we isolated 73 human mAbs recognizing five distinct antigenic regions on the virus envelope glycoprotein complex E1E2 from an HCV-immune phage-display antibody library by using an exhaustive-panning strategy. Many of these mAbs were broadly neutralizing. In particular, the mAb AR4A, recognizing a discontinuous epitope outside the CD81bs on the E1E2 complex, has an exceptionally broad neutralizing activity toward diverse HCV genotypes and protects against heterologous HCV challenge in a small animal model. The mAb panel will be useful for the design and development of vaccine candidates to elicit broadly neutralizing antibodies to HCV.

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.CD4bs | glycan | gp160

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 longterm 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-␥-null (NOD-SCID IL2R␥ null ) mouse strain that expressed human stem cell factor, granulocyte-macrophage colonystimulating 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. (Blood. 2011;117(11): 3076-3086) IntroductionHumanized mice are amenable small-animal models that have been transplanted with human cells or tissues (and/or equipped with human transgenes). In particular, animals conditioned to support engraftment of human immune cells have emerged as powerful tools for analysis of human hematopoiesis and the study of pathogens with unique human tropism. From the earliest attempts to engraftment of human immune cells in mice in the late 1980s, the field has progressed substantially, and improved, highly immunocompromised xenorecipient strains now allow for high-level engraftment of human immune cells. Currently, the most advanced strains are the nonobese diabetic, severe combined immunodeficiency (NOD-SCID) mouse with either truncated (NOG) or complete (NSG) disruptions in the interleukin-2 (IL-2) receptor common ␥-chain (IL2R␥ null ) and BALB/c Rag2 Ϫ/Ϫ IL2R␥ null (BRG) mice. 1 Injection of human hematopoietic stem cells (HSCs) isolated from human cord blood 2-5 or fetal liver tissue [5][6][7] results in robust engraftment of a human hematolymphoid system. Such human immune system (HIS) mice have opened new opportunities to analyze human immunity in vivo and to study pathogens with unique human tropism, including Epstein-Barr virus, HIV, and dengue virus. 8 However, current humanized mouse models have several shortcomings that must be overcome to advance toward a robust and predictive model for human immune responses. Specifically, the total amount of h...

Hepatitis C virus (HCV) establishes a chronic infection in the majority of exposed individuals and can cause cirrhosis and hepatocellular carcinoma. The role of antibodies directed against HCV in disease progression is poorly understood. Neutralizing antibodies (nAbs) can prevent HCV infection in vitro and in animal models. However, the effects of nAbs on an established HCV infection are unclear. Here, we demonstrate that three broadly nAbs, AR3A, AR3B and AR4A, delivered with adeno-associated viral (AAV) vectors can confer protection against viral challenge in humanized mice. Furthermore, we provide evidence that nAbs can abrogate an ongoing HCV infection in primary hepatocyte cultures and in a human liver chimeric mouse model. These results showcase a novel therapeutic approach to interfere with HCV infection exploiting a previously unappreciated need for HCV to continuously infect new hepatocytes in order to sustain chronicity.