SUMMARY Primary infection with the human oncogenic Epstein Barr virus (EBV) can result in infectious mononucleosis (IM), a self-limiting disease caused by massive lymphocyte expansion, which predisposes for the development of distinct EBV-associated lymphomas. It remains unclear why some individuals experience this symptomatic primary EBV infection, while the majority acquires the virus asymptomatically. Using a mouse model with reconstituted human immune system components, we show here that depletion of human natural killer (NK) cells enhances IM symptoms and promotes EBV-associated tumorigenesis, mainly due to loss of immune control over lytic EBV infection. These data suggest that failure of innate immune control by human NK cells augments symptomatic lytic EBV infection, which drives lymphocyte expansion and predisposes for EBV-associated malignancies.

Chemokines and adhesion molecules upregulated in lymphatic endothelial cells (LECs) during tissue inflammation are thought to enhance dendritic cell (DC) migration to draining lymph nodes, but the in vivo control of this process is not well understood. We performed a transcriptional profiling analysis of LECs isolated from murine skin and found that inflammation induced by a contact hypersensitivity (

Epstein Barr virus (EBV) infection expands CD8+ T cells specific for lytic antigens to high frequencies during symptomatic primary infection, and maintains these at significant numbers during persistence. Despite this, the protective function of these lytic EBV antigen-specific cytotoxic CD8+ T cells remains unclear. Here we demonstrate that lytic EBV replication does not significantly contribute to virus-induced B cell proliferation in vitro and in vivo in a mouse model with reconstituted human immune system components (huNSG mice). However, we report a trend to reduction of EBV-induced lymphoproliferation outside of lymphoid organs upon diminished lytic replication. Moreover, we could demonstrate that CD8+ T cells against the lytic EBV antigen BMLF1 can eliminate lytically replicating EBV-transformed B cells from lymphoblastoid cell lines (LCLs) and in vivo, thereby transiently controlling high viremia after adoptive transfer into EBV infected huNSG mice. These findings suggest a protective function for lytic EBV antigen-specific CD8+ T cells against EBV infection and against virus-associated tumors in extra-lymphoid organs. These specificities should be explored for EBV-specific vaccine development.

Epstein Barr virus (EBV) is one of the most ubiquitous human pathogens in the world, persistently infecting more than 90% of the adult human population. It drives some of the strongest human CD8 + T cell responses, which can be observed during symptomatic primary infection known as infectious mononucleosis (IM). Despite high viral loads and prolonged CD8 + T cell stimulation during IM, EBV enters latency and is under lifelong immune control in most individuals that experience this disease. We investigated whether changes in T cell function, as frequently characterized by PD-1 up-regulation, occur during IM due to the prolonged exposure to high antigen levels. We readily detected the expansion of PD-1 positive CD8 + T cells together with high frequencies of Tim-3, 2B4, and KLRG1 expression during IM and in mice with reconstituted human immune system components (huNSG mice) that had been infected with a high dose of EBV. These PD-1 positive CD8 + T cells, however, retained proliferation, cytokine production, and cytotoxic abilities. Multiple subsets of CD8 + T cells expanded during EBV infection, including PD-1 + Tim-3 + KLRG1 + cells that express CXCR5 and TCF-1 germinal center homing and memory markers, and may also contain BATF3. Moreover, blocking the PD-1 axis compromised EBV specific immune control and resulted in virus-associated lymphomagenesis. Finally, PD-1 + , Tim-3 + , and KLRG1 + CD8 + T cell expansion coincided with declining viral loads during low dose EBV infection. These findings suggest that EBV infection primes PD-1 positive CD8 + T cell populations that rely on this receptor axis for the efficient immune control of this ubiquitous human tumor virus.

Despite many theoretical incompatibilities between mouse and human cells, mice with reconstituted human immune system components contain nearly all human leukocyte populations. Accordingly, several human-tropic pathogens have been investigated in these in vivo models of the human immune system, including viruses such as human immunodeficiency virus (HIV) and Epstein-Barr virus (EBV), as well as bacteria such as Mycobacterium tuberculosis and Salmonella enterica Typhi. While these studies initially aimed to establish similarities in the pathogenesis of infections between these models and the pathobiology in patients, recent investigations have provided new and interesting functional insights into the protective value of certain immune compartments and altered pathology upon mutant pathogen infections. As more tools and methodologies are developed to make these models more versatile to study human immune responses in vivo, such improvements build toward small animal models with human immune components, which could predict immune responses to therapies and vaccination in human patients. Keywords:Dengue virus r EBV r HIV r Mycobacterium tuberculosis r Salmonella enterica typhi IntroductionThe complexity of infections and the corresponding elicited immune responses are best investigated in animal models that allow the manipulation of the timing and dose of infection, as well as of the responding immune compartments. Small animal models, such as the mouse, are preferred for these types of investigations due to low costs and ease of handling. However, divergent evolution between these small mammals and humans in the past 65 million years has rendered the immune system the third most different organ system between the two species, after olfaction and reproduction [1]. Many of these differences are found in the innate immune system, which ensures the initial survival of the infected host and also recognizes pathogens by their molecular patterns [2]. This divergence probably results from the different Correspondence: Prof. Christian Münz e-mail: christian.muenz@uzh.ch infectious disease challenges associated with the respective ecological niches that these two species inhabit. Unfortunately, these differences between the mouse and human immune systems also result in dissimilar inflammatory responses to burns, trauma, and endotoxemia at the gene expression level, such as integrin, ICOS-ICOSL, CD28, and PKC signaling [3]. Therefore, alternatives to classical mouse models, which more closely model human immune system behavior during infection in vivo, would be of significant benefit for the development of immunomodulatory treatments.The category of new models, which comes closest to achieving this goal, is mice with reconstituted human immune system components. These mice are mainly generated by neonatal injection of human hematopoietic progenitor cells in mice that lack murine innate and adaptive lymphocytes, namely NOD-scid γ c −/− (NSG), (Fig. 1). For some studies, a fetal organoid of liver and thymic tissue is implanted ...

The potential contribution of plasmacytoid dendritic cells (pDCs) in the presentation of tumor cell Ags remains unclear, and some controversies exist with regard to the ability of pDCs to phagocytose cell-derived particulate Ags and cross-present them to MHC class I–restricted T lymphocytes. In this study, we show that human pDCs, although inefficient in the internalization of cell membrane fragments by phagocytosis, can efficiently acquire membrane patches and associated molecules from cancer cells of different histotypes. The transfer of membrane patches to pDCs occurred in a very short time and required cell-to-cell contact. Membrane transfer also included intact HLA complexes, and the acquired Ags could be efficiently recognized on pDCs by tumor-specific CD8+ T cells. Remarkably, pDCs isolated from human colon cancer tissues displayed a strong surface expression of epithelial cell adhesion molecule, indicating that the exchange of exogenous Ags between pDCs and tumor cells also can occur in vivo. These data demonstrate that pDCs are well suited to acquire membrane patches from contiguous tumor cells by a cell-to-cell contact–dependent mechanism that closely resembles “trogocytosis.” This phenomenon may allow pDCs to proficiently present tumor cell–derived Ags, despite limited properties of endophagocytosis.

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