KSHV infection drives poorly cytotoxic CD56-negative natural killer cell differentiation in vivo upon KSHV/EBV dual infection.

Herpesvirus infections shape the human natural killer (NK) cell compartment. While Epstein-Barr virus (EBV) expands immature NKG2A+ NK cells, human cytomegalovirus (CMV) drives accumulation of adaptive NKG2C+ NK cells. Kaposi sarcoma-associated herpesvirus (KSHV) is a close relative of EBV, and both are associated with lymphomas, including primary effusion lymphoma (PEL), which nearly always harbors both viruses. In this study, KSHV dual infection of mice with reconstituted human immune system components leads to the accumulation of CD56-CD16+CD38+CXCR6+ NK cells. CD56-CD16+ NK cells were also more frequently found in KSHV-seropositive Kenyan children. This NK cell subset is poorly cytotoxic against otherwise-NK-cell-susceptible and antibody-opsonized targets. Accordingly, NK cell depletion does not significantly alter KSHV infection in humanized mice. These data suggest that KSHV might escape NK-cell-mediated immune control by driving CD56-CD16+ NK cell differentiation.

LIGHT/LTßR signaling regulates self-renewal and differentiation of hematopoietic and leukemia stem cells.

The production of blood cells during steady-state and increased demand depends on the regulation of hematopoietic stem cell (HSC) self-renewal and differentiation. Similarly, the balance between self-renewal and differentiation of leukemia stem cells (LSCs) is crucial in the pathogenesis of leukemia. Here, we document that the TNF receptor superfamily member lymphotoxin-ß receptor (LTßR) and its ligand LIGHT regulate quiescence and self-renewal of murine and human HSCs and LSCs. Cell-autonomous LIGHT/LTßR signaling on HSCs reduces cell cycling, promotes symmetric cell division and prevents primitive HSCs from exhaustion in serial re-transplantation experiments and genotoxic stress. LTßR deficiency reduces the numbers of LSCs and prolongs survival in a murine chronic myeloid leukemia (CML) model. Similarly, LIGHT/LTßR signaling in human G-CSF mobilized HSCs and human LSCs results in increased colony forming capacity in vitro. Thus, our results define LIGHT/LTßR signaling as an important pathway in the regulation of the self-renewal of HSCs and LSCs.

Attenuated immune control of Epstein-Barr virus in humanized mice is associated with the multiple sclerosis risk factor HLA-DR15.

Immune responses to Epstein-Barr virus (EBV) infection synergize with the main genetic risk factor HLA-DRB1*15:01 (HLA-DR15) to increase the likelihood to develop the autoimmune disease multiple sclerosis (MS) at least sevenfold. In order to gain insights into this synergy, we investigated HLA-DR15 positive human immune compartments after reconstitution in immune-compromised mice (humanized mice) with and without EBV infection. We detected elevated activation of both CD4+ and CD8+ T cells in HLA-DR15 donor-reconstituted humanized mice at steady state, even when compared to immune compartments carrying HLA-DRB1*04:01 (HLA-DR4), which is associated with other autoimmune diseases. Increased CD8+ T cell expansion and activation was also observed in HLA-DR15 donor-reconstituted humanized mice after EBV infection. Despite this higher immune activation, EBV viral loads were less well controlled in the context of HLA-DR15. Indeed, HLA-DR15-restricted CD4+ T cell clones recognized EBV-transformed B cell lines less efficiently and demonstrated cross-reactivity toward allogeneic target cells and one MS autoantigen. These findings suggest that EBV as one of the main environmental risk factors and HLA-DR15 as the main genetic risk factor for MS synergize by priming hyperreactive T-cell compartments, which then control the viral infection less efficiently and contain cross-reactive CD4+ T cell clones.

Correction: Immunosuppressive FK506 treatment leads to more frequent EBV-associated lymphoproliferative disease in humanized mice.

[This corrects the article DOI: 10.1371/journal.ppat.1008477.].

Immunosuppressive FK506 treatment leads to more frequent EBV-associated lymphoproliferative disease in humanized mice.

Post-transplant lymphoproliferative disorder (PTLD) is a potentially fatal complication after organ transplantation frequently associated with the Epstein-Barr virus (EBV). Immunosuppressive treatment is thought to allow the expansion of EBV-infected B cells, which often express all eight oncogenic EBV latent proteins. Here, we assessed whether HLA-A2 transgenic humanized NSG mice treated with the immunosuppressant FK506 could be used to model EBV-PTLD. We found that FK506 treatment of EBV-infected mice led to an elevated viral burden, more frequent tumor formation and diminished EBV-induced T cell responses, indicative of reduced EBV-specific immune control. EBV latency III and lymphoproliferation-associated cellular transcripts were up-regulated in B cells from immunosuppressed animals, akin to the viral and host gene expression pattern found in EBV-PTLD. Utilizing an unbiased gene expression profiling approach, we identified genes differentially expressed in B cells of EBV-infected animals with and without FK506 treatment. Upon investigating the most promising candidates, we validated sCD30 as a marker of uncontrolled EBV proliferation in both humanized mice and in pediatric patients with EBV-PTLD. High levels of sCD30 have been previously associated with EBV-PTLD in patients. As such, we believe that humanized mice can indeed model aspects of EBV-PTLD development and may prove useful for the safety assessment of immunomodulatory therapies.

Persistent KSHV Infection Increases EBV-Associated Tumor Formation In Vivo via Enhanced EBV Lytic Gene Expression.

The human tumor viruses Epstein-Barr virus (EBV) and Kaposi sarcoma-associated herpesvirus (KSHV) establish persistent infections in B cells. KSHV is linked to primary effusion lymphoma (PEL), and 90% of PELs also contain EBV. Studies on persistent KSHV infection in vivo and the role of EBV co-infection in PEL development have been hampered by the absence of small animal models. We developed mice reconstituted with human immune system components as a model for KSHV infection and find that EBV/KSHV dual infection enhanced KSHV persistence and tumorigenesis. Dual-infected cells displayed a plasma cell-like gene expression pattern similar to PELs. KSHV persisted in EBV-transformed B cells and was associated with lytic EBV gene expression, resulting in increased tumor formation. Evidence of elevated lytic EBV replication was also found in EBV/KSHV dually infected lymphoproliferative disorders in humans. Our data suggest that KSHV augments EBV-associated tumorigenesis via stimulation of lytic EBV replication.

Interleukins 12 and 15 induce cytotoxicity and early NK-cell differentiation in type 3 innate lymphoid cells.

Type 3 innate lymphoid cells (ILC3s) fulfill protective functions at mucosal surfaces via cytokine production. Although their plasticity to become ILC1s, the innate counterparts of type 1 helper T cells, has been described previously, we report that they can differentiate into cytotoxic lymphocytes with many characteristics of early differentiated natural killer (NK) cells. This transition is promoted by the proinflammatory cytokines interleukin 12 (IL-12) and IL-15, and correlates with expression of the master transcription factor of cytotoxicity, eomesodermin (Eomes). As revealed by transcriptome analysis and flow cytometric profiling, differentiated ILC3s express CD94, NKG2A, NKG2C, CD56, and CD16 among other NK-cell receptors, and possess all components of the cytotoxic machinery. These characteristics allow them to recognize and kill leukemic cells with perforin and granzymes. Therefore, ILC3s can be harnessed for cytotoxic responses via differentiation under the influence of proinflammatory cytokines.

Cognate HLA absence in trans diminishes human NK cell education.

NK cells are innate lymphocytes with protective functions against viral infections and tumor formation. Human NK cells carry inhibitory killer cell Ig-like receptors (KIRs), which recognize distinct HLAs. NK cells with KIRs for self-HLA molecules acquire superior cytotoxicity against HLA- tumor cells during education for improved missing-self recognition. Here, we reconstituted mice with human hematopoietic cells from donors with homozygous KIR ligands or with a mix of hematopoietic cells from these homozygous donors, allowing assessment of the resulting KIR repertoire and NK cell education. We found that co-reconstitution with 2 KIR ligand-mismatched compartments did not alter the frequency of KIR-expressing NK cells. However, NK cell education was diminished in mice reconstituted with parallel HLA compartments due to a lack of cognate HLA molecules on leukocytes for the corresponding KIRs. This change in NK cell education in mixed human donor-reconstituted mice improved NK cell-mediated immune control of EBV infection, indicating that mixed hematopoietic cell populations could be exploited to improve NK cell reactivity against leukotropic pathogens. Taken together, these findings indicate that leukocytes lacking cognate HLA ligands can disarm KIR+ NK cells in a manner that may decrease HLA- tumor cell recognition but allows for improved NK cell-mediated immune control of a human γ-herpesvirus.

Animal models of Epstein Barr virus infection.

Epstein Barr virus (EBV) was the first human tumor virus to be described. Despite its discovery now more than fifty years ago, immune control of this virus is still not very well understood and no vaccine is available. This knowledge gap is due in part to the lack of a preclinical small animal model which can faithfully recapitulate EBV infection and immune control, and would allow testing of EBV specific vaccine candidates. With the advent of mice with reconstituted human immune system compartments (HIS mice) during the past decade this is changing. We will discuss which aspects of EBV infection and its immune control can already be modeled in HIS mice, and which shortcomings still need to be overcome in order to recapitulate the immunobiology of oncogenic EBV infection.

Adoptive transfer of EBV specific CD8+ T cell clones can transiently control EBV infection in humanized mice.

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.

Dendritic cell-mediated immune humanization of mice: implications for allogeneic and xenogeneic stem cell transplantation.

De novo regeneration of immunity is a major problem after allogeneic hematopoietic stem cell transplantation (HCT). HCT modeling in severely compromised immune-deficient animals transplanted with human stem cells is currently limited because of incomplete maturation of lymphocytes and scarce adaptive responses. Dendritic cells (DC) are pivotal for the organization of lymph nodes and activation of naive T and B cells. Human DC function after HCT could be augmented with adoptively transferred donor-derived DC. In this study, we demonstrate that adoptive transfer of long-lived human DC coexpressing high levels of human IFN-α, human GM-CSF, and a clinically relevant Ag (CMV pp65 protein) promoted human lymphatic remodeling in immune-deficient NOD.Rag1(-/-).IL-2rγ(-/-) mice transplanted with human CD34(+) cells. After immunization, draining lymph nodes became replenished with terminally differentiated human follicular Th cells, plasma B cells, and memory helper and cytotoxic T cells. Human Igs against pp65 were detectable in plasma, demonstrating IgG class-switch recombination. Human T cells recovered from mice showed functional reactivity against pp65. Adoptive immunotherapy with engineered DC provides a novel strategy for de novo immune reconstitution after human HCT and a practical and effective tool for studying human lymphatic regeneration in vivo in immune deficient xenograft hosts.

Spontaneous lytic replication and epitheliotropism define an Epstein-Barr virus strain found in carcinomas.

The Epstein-Barr virus (EBV) is found in a variety of tumors whose incidence greatly varies around the world. A poorly explored hypothesis is that particular EBV strains account for this phenomenon. We report that M81, a virus isolated from a Chinese patient with nasopharyngeal carcinoma (NPC), shows remarkable similarity to other NPC viruses but is divergent from all other known strains. M81 exhibited a reversed tropism relative to common strains with a reduced ability to infect B cells and a high propensity to infect epithelial cells, which is in agreement with its isolation from carcinomas. M81 spontaneously replicated in B cells in vitro and in vivo at unusually high levels, in line with the enhanced viral replication observed in NPC patients. Spontaneous replication and epitheliotropism could be partly ascribed to polymorphisms within viral proteins. We suggest considering M81 and its closely related isolates as an EBV subtype with enhanced pathogenic potential.

Infectious diseases in humanized mice.

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.