A novel humanized mouse model with significant improvement of class-switched, antigen-specific antibody production.

Humanized mice are a powerful tool for the study of human hematopoiesis and immune function in vivo. However, the existing models cannot support robust adaptive immune responses, especially the generation of class-switched, antigen-specific antibody responses. Here we describe a new mouse strain, in which human interleukin 6 (IL-6) gene encoding the cytokine that is important for B- and T-cell differentiation was knocked into its respective mouse locus. The provision of human IL-6 not only enhanced thymopoiesis and periphery T-cell engraftment, but also significantly increased class switched memory B cells and serum immunoglobulin G (IgG). In addition, immunization with ovalbumin (OVA) induced OVA-specific B cells only in human IL-6 knock-in mice. These OVA-specific antibodies displayed the highest frequency of somatic mutation, further suggesting that human IL-6 is important for efficient B-cell activation and selection. We conclude that human IL-6 knock-in mice represent a novel and improved model for human adaptive immunity without relying on complex surgery to transplant human fetal thymus and liver. These mice can therefore be used to exploit or evaluate immunization regimes that would be unethical or untenable in humans.

AMCase is a crucial regulator of type 2 immune responses to inhaled house dust mites.

Chitinases are enzymes that cleave chitin, a component of the exoskeleton of many organisms including the house dust mite (HDM). Here we show that knockin mice expressing an enzymatically inactive acidic mammalian chitinase (AMCase), the dominant true chitinase in mouse lung, showed enhanced type 2 immune responses to inhaled HDM. We found that uncleaved chitin promoted the release of IL-33, whereas cleaved chitin could be phagocytosed and could induce the activation of caspase-1 and subsequent activation of caspase-7; this results in the resolution of type 2 immune responses, probably by promoting the inactivation of IL-33. These data suggest that AMCase is a crucial regulator of type 2 immune responses to inhaled chitin-containing aeroallergens.

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.

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.

Transgenic expression of human signal regulatory protein alpha in Rag2-/-gamma(c)-/- 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/γ(c)(-/-) (NSG) and BALB/c Rag2(-/-)γ(c)(-/-) 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(-/-)γ(c)(-/-) 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(-/-)γ(c)(-/-) mice represent a unique mouse strain supporting high levels of human cell engraftment, which can easily be genetically manipulated.

In vivo diabetogenic action of CD4+ T lymphocytes requires Fas expression and is independent of IL-1 and IL-18.

CD4(+) T lymphocytes are required to induce spontaneous autoimmune diabetes in the NOD mouse. Since pancreatic ß cells upregulate Fas expression upon exposure to pro-inflammatory cytokines, we studied whether the diabetogenic action of CD4(+) T lymphocytes depends on Fas expression on target cells. We assayed the diabetogenic capacity of NOD spleen CD4(+) T lymphocytes when adoptively transferred into a NOD mouse model combining: (i) Fas-deficiency, (ii) FasL-deficiency, and (iii) SCID mutation. We found that CD4(+) T lymphocytes require Fas expression in the recipients' target cells to induce diabetes. IL-1ß has been described as a key cytokine involved in Fas upregulation on mouse ß cells. We addressed whether CD4(+) T cells require IL-1ß to induce diabetes. We also studied spontaneous diabetes onset in NOD/IL-1 converting enzyme-deficient mice, in NOD/IL-1ß-deficient mice, and CD4(+) T-cell adoptively transferred diabetes into NOD/SCID IL-1ß-deficient mice. Neither IL-1ß nor IL-18 are required for either spontaneous or CD4(+) T-cell adoptively transferred diabetes. We conclude that CD4(+) T-cell-mediated ß-cell damage in autoimmune diabetes depends on Fas expression, but not on IL-1ß unveiling the existing redundancy regarding the cytokines involved in Fas upregulation on NOD ß cells in vivo.

Human IL-3/GM-CSF knock-in mice support human alveolar macrophage development and human immune responses in the lung.

Mice with a functional human immune system have the potential to allow in vivo studies of human infectious diseases and to enable vaccine testing. To this end, mice need to fully support the development of human immune cells, allow infection with human pathogens, and be capable of mounting effective human immune responses. A major limitation of humanized mice is the poor development and function of human myeloid cells and the absence of human immune responses at mucosal surfaces, such as the lung. To overcome this, we generated human IL-3/GM-CSF knock-in (hIL-3/GM-CSF KI) mice. These mice faithfully expressed human GM-CSF and IL-3 and developed pulmonary alveolar proteinosis because of elimination of mouse GM-CSF. We demonstrate that hIL-3/GM-CSF KI mice engrafted with human CD34(+) hematopoietic cells had improved human myeloid cell reconstitution in the lung. In particular, hIL-3/GM-CSF KI mice supported the development of human alveolar macrophages that partially rescued the pulmonary alveolar proteinosis syndrome. Moreover, human alveolar macrophages mounted correlates of a human innate immune response against influenza virus. The hIL-3/GM-CSF KI mice represent a unique mouse model that permits the study of human mucosal immune responses to lung pathogens.

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(-/-)γ(c)(-/-) 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(-/-)γ(c)(-/-) TPO-humanized mice represent a useful model to study human hematopoiesis in vivo.

A mouse model for the human pathogen Salmonella typhi.

Salmonella enterica serovar Typhi (S. Typhi) causes typhoid fever, a life-threatening human disease. The lack of animal models due to S. Typhi's strict human host specificity has hindered its study and vaccine development. We find that immunodeficient Rag2(-/-) γc(-/-) mice engrafted with human fetal liver hematopoietic stem and progenitor cells are able to support S. Typhi replication and persistent infection. A S. Typhi mutant in a gene required for virulence in humans was unable to replicate in these mice. Another mutant unable to produce typhoid toxin exhibited increased replication, suggesting a role for this toxin in the establishment of persistent infection. Furthermore, infected animals mounted human innate and adaptive immune responses to S. Typhi, resulting in the production of cytokines and pathogen-specific antibodies. We expect that this mouse model will be a useful resource for understanding S. Typhi pathogenesis and for evaluating potential vaccine candidates against typhoid fever.

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

Induced regulatory T cells (iT(reg) 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 iT(reg) cells remain unknown. We report a critical role for the transcription cofactor homeodomain-only protein (Hop; also known as Hopx) in iT(reg) cells to mediate T cell unresponsiveness in vivo. Hopx-sufficient iT(reg) cells downregulated expression of the transcription factor AP-1 complex and suppressed other T cells. In the absence of Hopx, iT(reg) 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 T(reg) cells induced by DCs and the promotion of DC-mediated T cell unresponsiveness in vivo.

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.

Amino acid polymorphisms altering the glycosylation of IL-2 do not protect from type 1 diabetes in the NOD mouse.

Idd3 is one of many gene regions that affect the development of type 1 diabetes (T1D) in the nonobese diabetic (NOD) mouse. Idd3 has been localized to a 650-kb region on chromosome 3 containing the IL-2 gene. Exon 1 of the IL-2 gene is polymorphic between the susceptible NOD and the protective C57BL/6 (B6) alleles, causing multiple amino acid changes that have been proposed to be responsible for the differing glycosylation status. To address whether this coding polymorphism recapitulates the disease suppression mediated by the B6 Idd3 allele, we generated knockin mice in which exon 1 of the B6 IL-2 allele replaces the homologous region in the NOD allele. We generated these mice by targeting the NOD allele of NOD/129 F(1) ES cells. IL-2 protein from the knockin mice showed the glycosylation pattern of the B6 IL-2 isoform, confirming that the amino acid differences encoded within exon 1 affect the glycosylation of the IL-2 protein. However, unlike NOD.B6 Idd3 congenic mice, the knockin mice were not protected from T1D. Furthermore, the difference in amino acid sequence in the IL-2 protein did not affect the level of expression of IL-2. This approach provides a general method for the determination of a functional role of a given genomic sequence in a disease process. Further, our result demonstrates that the variants in exon 1 of the IL-2 gene are not responsible for T1D suppression in NOD.B6 Idd3 mice, thereby supporting the hypothesis that variants in the regulatory region affecting expression levels are causative.

IL9 leads to airway inflammation by inducing IL13 expression in airway epithelial cells.

Constitutive expression of IL9 in the lungs of transgenic (Tg) mice resulted in an asthma-like phenotype consisting of lymphocytic and eosinophilic lung inflammation, mucus hypersecretion and mast cell hyperplasia. Several T(h)2 cytokines including IL4, IL5 and IL13 were expressed in the lung in response to Tg IL9. IL13 was absolutely necessary for the development of lung pathology. To understand how IL9 induces IL13-dependent lung inflammation and mucus production, we sought the IL13-producing cells. Surprisingly, we found that the absence of T cells and B cells in recombinase-activating gene 1 (RAG1)-deficient IL9 Tg mice enhanced lung inflammation and dramatically enhanced IL13 production. In addition, the lack of mast cells or eosinophils in IL9 Tg mice did not affect IL13 levels in the lung. In situ hybridization for IL13 on lung sections from RAG1-/- IL9 Tg mice revealed that airway epithelial cells were the major IL13-producing cell type. Our results implicate the lung epithelium as a potentially important source of inflammatory cytokines in asthma.

Sugar-coated regulation of T cells.

The human gut is host to hundreds of different species of commensal bacteria that live in peaceful partnership with the host immune system. These commensal bacteria are far from neutral bystanders as they are intimately involved in the development of the immune system. Reporting in this issue of Cell, Kasper and colleagues (Mazmanian et al., 2005) reveal that a bacterial polysaccharide, PSA, produced by the commensal bacterium Bacteroides fragilis directs development of the immune system of the mouse host.