Elizabeth E. Eynon

Humanized mice for modeling human infectious disease: challenges, progress, and outlook.

Over 800 million people worldwide are infected with hepatitis viruses, human immunodeficiency virus (HIV), and malaria, resulting in more than 5 million deaths annually. Here we discuss the potential and challenges of humanized mouse models for developing effective and affordable therapies and vaccines, which are desperately needed to combat these diseases.

Local Expression of TNFα in Neonatal NOD Mice Promotes Diabetes by Enhancing Presentation of Islet Antigens

The relationship of inflammation to autoimmunity has been long observed, but the underlying mechanisms are unclear. Here, we demonstrate that islet-specific expression of TNFalpha in neonatal nonobese diabetic mice accelerated diabetes. In neonatal transgenic mice, disease was preceded by apoptosis of some beta cells, upregulation of MHC class I molecules on residual islet cells, and influx and activation of both antigen-presenting cells bearing MHC-islet peptide complexes and T cells. Infiltrating dendritic cells/macrophages, but not B cells, from neonatal islets activated islet-specific T cells in vitro. Thus, inflammation can trigger autoimmunity by recruiting and activating dendritic cells/macrophages to present self-antigens to autoreactive T cells.

Human Hemato-Lymphoid System Mice: Current Use and Future Potential for Medicine

To directly study complex human hemato-lymphoid system physiology and respective system-associated diseases in vivo, human-to-mouse xenotransplantation models for human blood and blood-forming cells and organs have been developed over the past three decades. We here review the fundamental requirements and the remarkable progress made over the past few years in improving these systems, the current major achievements reached by use of these models, and the future challenges to more closely model and study human health and disease and to achieve predictive preclinical testing of both prevention measures and potential new therapies.

Human thrombopoietin knockin mice efficiently support human hematopoiesis in vivo

Hematopoietic stem cells (HSCs) both self-renew and give rise to all blood cells for the lifetime of an individual. Xenogeneic mouse models are broadly used to study human hematopoietic stem and progenitor cell biology in vivo. However, maintenance, differentiation, and function of human hematopoietic cells are suboptimal in these hosts. Thrombopoietin (TPO) has been demonstrated as a crucial cytokine supporting maintenance and self-renewal of HSCs. We generated RAG2−/−γc−/− mice in which we replaced the gene encoding mouse TPO by its human homolog. Homozygous humanization of TPO led to increased levels of human engraftment in the bone marrow of the hosts, and multilineage differentiation of hematopoietic cells was improved, with an increased ratio of myelomonocytic verus lymphoid lineages. Moreover, maintenance of human stem and progenitor cells was improved, as demonstrated by serial transplantation. Therefore, RAG2−/−γc−/− TPO-humanized mice represent a useful model to study human hematopoiesis in vivo.

Transgenic expression of human signal regulatory protein alpha in Rag2−/−γc−/− mice improves engraftment of human hematopoietic cells in humanized mice

Transplantation of human hematopoietic stem cells into severely immunocompromised newborn mice allows the development of a human hematopoietic and immune system in vivo. NOD/scid/γc−/− (NSG) and BALB/c Rag2−/−γc−/− mice are the most commonly used mouse strains for this purpose and a number of studies have demonstrated the high value of these model systems in areas spanning from basic to translational research. However, limited cross-reactivity of many murine cytokines on human cells and residual host immune function against the xenogeneic grafts results in defective development and maintenance of human cells in vivo. Whereas NSG mice have higher levels of absolute human engraftment than similar mice on a BALB/c background, they have a shorter lifespan and NOD ES cells are unsuitable for the complex genetic engineering that is required to improve human hematopoiesis and immune responses by transgenesis or knockin of human genes. We have generated mice that faithfully express a transgene of human signal regulatory protein alpha (SIRPa), a receptor that negatively regulates phagocytosis, in Rag2−/−γc−/− mice on a mixed 129/BALB/c background, which can easily be genetically engineered. These mice allow significantly increased engraftment and maintenance of human hematopoietic cells reaching levels comparable to NSG mice. Furthermore, we found improved functionality of the human immune system in these mice. In summary, hSIRPa-transgenic Rag2−/−γc−/− mice represent a unique mouse strain supporting high levels of human cell engraftment, which can easily be genetically manipulated.

A lupus-like syndrome develops in mice lacking the Ro 60-kDa protein, a major lupus autoantigen.

Antibodies against a conserved RNA-binding protein, the Ro 60-kDa autoantigen, occur in 24–60% of all patients with systemic lupus erythematosus. Anti-Ro antibodies are correlated with photosensitivity and cutaneous lesions in these patients and with neonatal lupus, a syndrome in which mothers with anti-Ro antibodies give birth to children with complete congenital heart block and photosensitive skin lesions. In higher eukaryotes, the Ro protein binds small RNAs of unknown function known as Y RNAs. Because the Ro protein also binds misfolded 5S rRNA precursors, it is proposed to function in a quality-control pathway for ribosome biogenesis. Consistent with a role in the recognition or repair of intracellular damage, an orthologue of Ro in the radiation-resistant eubacterium Deinococcus radiodurans contributes to survival of this bacterium after UV irradiation. Here, we show that mice lacking the Ro protein develop an autoimmune syndrome characterized by anti-ribosome antibodies, anti-chromatin antibodies, and glomerulonephritis. Moreover, in one strain background, Ro–/– mice display increased sensitivity to irradiation with UV light. Thus, one function of this major human autoantigen may be to protect against autoantibody development, possibly by sequestering defective ribonucleoproteins from immune surveillance. Furthermore, the finding that mice lacking the Ro protein are photosensitive suggests that loss of Ro function could contribute to the photosensitivity associated with anti-Ro antibodies in humans.

Regulating human Th17 cells via differential expression of IL-1 receptor.

In humans, interleukin-1beta (IL-1beta) has been suggested as an essential cytokine for developing IL-17- or IL-17A-producing CD4(+) T helper 17 (Th17) cells. However, little is known about the relationship of IL-1 receptor expression and Th17 cell differentiation. We report here the presence of 2 distinct CD4(+) T-cell populations with and without expression of IL-1RI that correlates with the capacity to produce IL-17 in naive and memory CD4(+) T cells of human peripheral blood. IL-1RI(+) memory CD4(+) T cells had increased gene expression of IL17, RORC, and IRF4 even before T-cell receptor triggering, indicating that the effect of IL-1beta is programmed in these cells via IL-1RI. Although CD4(+) T cells from umbilical cord blood did not express IL-1RI, the cytokines IL-7, IL-15, and transforming growth factor-beta (TGF-beta) up-regulated IL-1RI expression on naive CD4(+) T cells, suggesting that IL-1RI(+) naive CD4(+) T cells develop in periphery. Furthermore, IL-17 production from the cytokine-treated naive CD4(+) T cells was induced by IL-1beta and this induction was blocked by IL-1R antagonist. These results indicate that human Th17 cell differentiation is regulated via differential expression of IL-1RI, which is controlled by IL-7 and IL-15.

Efficient differentiation and function of human macrophages in humanized CSF-1 mice

Humanized mouse models are useful tools to understand pathophysiology and to develop therapies for human diseases. While significant progress has been made in generating immunocompromised mice with a human hematopoietic system, there are still several shortcomings, one of which is poor human myelopoiesis. Here, we report that human CSF-1 knockin mice show augmented frequencies and functions of human myeloid cells. Insertion of human CSF1 into the corresponding mouse locus of Balb/c Rag2(-/-) γc(-/-) mice through VELOCIGENE technology resulted in faithful expression of human CSF-1 in these mice both qualitatively and quantitatively. Intra-hepatic transfer of human fetal liver derived hematopoietic stem and progenitor cells (CD34(+)) in humanized CSF-1 (CSF1(h/h)) newborn mice resulted in more efficient differentiation and enhanced frequencies of human monocytes/macrophages in the bone marrow, spleens, peripheral blood, lungs, liver and peritoneal cavity. Human monocytes/macrophages obtained from the humanized CSF-1 mice show augmented functional properties including migration, phagocytosis, activation and responses to LPS. Thus, humanized mice engineered to express human cytokines will significantly help to overcome the current technical challenges in the field. In addition, humanized CSF-1 mice will be a valuable experimental model to study human myeloid cell biology.

FAT10/Diubiquitin-Like Protein-Deficient Mice Exhibit Minimal Phenotypic Differences

ABSTRACT The FAT10 gene encodes a diubiquitin-like protein containing two tandem head-to-tail ubiquitin-like domains. There is a high degree of similarity between murine and human FAT10 sequences at both the mRNA and protein levels. In various cell lines, FAT10 expression was shown to be induced by gamma interferon or by tumor necrosis factor alpha. In addition, FAT10 expression was found to be up-regulated in some Epstein-Barr virus-infected B-cell lines, in activated dendritic cells, and in several epithelial tumors. However, forced expression of FAT10 in cultured cells was also found to produce apoptotic cell death. Overall, these findings suggest that FAT10 may modulate cellular growth or cellular viability. Here we describe the steps to generate, by genetic targeting, a FAT10 gene knockout mouse model. The FAT10 knockout homozygous mice are viable and fertile. No gross lesions or obvious histological differences were found in these mutated mice. Examination of lymphocyte populations from spleen, thymus, and bone marrow did not reveal any abnormalities. However, flow cytometry analysis demonstrated that the lymphocytes of FAT10 knockout mice were, on average, more prone to spontaneous apoptotic death. Physiologically, these mice demonstrated a high level of sensitivity toward endotoxin challenge. These findings indicate that FAT10 may function as a survival factor.

The transcription cofactor Hopx is required for regulatory T cell function in dendritic cell-mediated peripheral T cell unresponsiveness

Induced T regulatory (iTreg) cells can be generated by peripheral dendritic cells (DCs) that mediate T cell-unresponsiveness to re-challenge with antigen. The molecular factors required for the function of such iTreg cells remain unknown. We report a critical role for the transcription co-factor Homeodomain only protein (Hop, also know as Hopx) in iTregs cells to mediate T cell unresponsiveness in vivo. Hopx-sufficient iTreg cells down-regulate the expression of the AP-1 complex and suppress other T cells. In the absence of Hopx, iTreg cells express high levels of the AP-1 complex, proliferate and fail to mediate T cell-unresponsiveness to re-challenge with antigen. Thus, Hopx is required for the function of Treg cells induced by DCs and the promotion of DC-mediated T cell unresponsiveness in vivo.Induced regulatory T cells (iTreg cells) can be generated by peripheral dendritic cells (DCs) that mediate T cell unresponsiveness to rechallenge with antigen. The molecular factors required for the function of such iTreg cells remain unknown. We report a critical role for the transcription cofactor homeodomain-only protein (Hop; also known as Hopx) in iTreg cells to mediate T cell unresponsiveness in vivo. Hopx-sufficient iTreg cells downregulated expression of the transcription factor AP-1 complex and suppressed other T cells. In the absence of Hopx, iTreg cells had high expression of the AP-1 complex, proliferated and failed to mediate T cell unresponsiveness to rechallenge with antigen. Thus, Hopx is required for the function of Treg cells induced by DCs and the promotion of DC-mediated T cell unresponsiveness in vivo.