The in vivo development of human T cells from CD34(+) cells in the murine thymic environment

Genetically modified mouse models to help fight COVID-19

The research community is in a race to understand the molecular mechanisms of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, to repurpose currently available antiviral drugs and to develop new therapies and vaccines against coronavirus disease 2019 (COVID-19). One major challenge in achieving these goals is the paucity of suitable preclinical animal models. Mice constitute ~70% of all the laboratory animal species used in biomedical research. Unfortunately, SARS-CoV-2 infects mice only if they have been genetically modified to express human ACE2. The inherent resistance of wild-type mice to SARS-CoV-2, combined with a wealth of genetic tools that are available only for modifying mice, offers a unique opportunity to create a versatile set of genetically engineered mouse models useful for COVID-19 research. We propose three broad categories of these models and more than two dozen designs that may be useful for SARS-CoV-2 research and for fighting COVID-19.

Generation and Disease Model Relevance of a Manganese Enhanced Magnetic Resonance Imaging-Based NOD/scid-IL-2Rγc(null) Mouse Brain Atlas

Strain specific mouse brain magnetic resonance imaging (MRI) atlases provide coordinate space linked anatomical registration. This allows longitudinal quantitative analyses of neuroanatomical volumes and imaging metrics for assessing the role played by aging and disease to the central nervous system. As NOD/scid-IL-2Rγ(c)(null) (NSG) mice allow human cell transplantation to study human disease, these animals are used to assess brain morphology. Manganese enhanced MRI (MEMRI) improves contrasts amongst brain components and as such can greatly help identifying a broad number of structures on MRI. To this end, NSG adult mouse brains were imaged in vivo on a 7.0 Tesla MR scanner at an isotropic resolution of 100 μm. A population averaged brain of 19 mice was generated using an iterative alignment algorithm. MEMRI provided sufficient contrast permitting 41 brain structures to be manually labeled. Volumes of 7 humanized mice brain structures were measured by atlas-based segmentation and compared against non-humanized controls. The humanized NSG mice brain volumes were smaller than controls (p < 0.001). Many brain structures of humanized mice were significantly smaller than controls. We posit that the irradiation and cell grafting involved in the creation of humanized mice were responsible for the morphological differences. Six NSG mice without MnCl2 administration were scanned with high resolution T2-weighted MRI and segmented to test broad utility of the atlas.

Differentiation ability of multipotent hematopoietic stem/progenitor cells detected by a porcine specific anti-CD117 monoclonal antibody

CD117 is a cytokine receptor expressed on the surface of hematopoietic stem cells with a likely role in cell survival, proliferation and differentiation. In order to study the differentiation activity of porcine CD117 hematopoietic cells in vitro and in vivo we prepared an anti-swine CD117 Mab (2A1) with high specificity for flow-cytometrical analysis. The 2A1 Mab did not recognize mouse or human mast cells suggesting that 2A1 is species-specific. Swine bone marrow (BM) CD117+ cells differentiated in vitro mainly into erythroid and monocyte lineages in the methylcellulose-based colony assay. When the swine BM CD117+ cells were transplanted in vivo into immunodeficient NOG (NOD/SCID/IL-2gc-null) mice, a significant amount of swine CD45+ leukocytes, including CD3 positive T cells, were developed in the mice. These results revealed that the swine BM CD117+ cells possess hematopoietic stem/progenitor activity and when monitored in immunodeficient mice or in vitro they can develop into lymphoid, erythroid, and myeloid cells efficiently with the new monoclonal antibody.

Influence of age, irradiation and humanization on NSG mouse phenotypes

Humanized mice are frequently utilized in bench to bedside therapeutic tests to combat human infectious, cancerous and degenerative diseases. For the fields of hematology-oncology, regenerative medicine, and infectious diseases, the immune deficient mice have been used commonly in basic research efforts. Obstacles in true translational efforts abound, as the relationship between mouse and human cells in disease pathogenesis and therapeutic studies requires lengthy investigations. The interplay between human immunity and mouse biology proves ever more complicated when aging, irradiation, and human immune reconstitution are considered. All can affect a range of biochemical and behavioral functions. To such ends, we show age- and irradiation-dependent influences for the development of macrocytic hyper chromic anemia, myelodysplasia, blood protein reductions and body composition changes. Humanization contributes to hematologic abnormalities. Home cage behavior revealed day and dark cycle locomotion also influenced by human cell reconstitutions. Significant age-related day-to-day variability in movement, feeding and drinking behaviors were observed. We posit that this data serves to enable researchers to better design translational studies in this rapidly emerging field of mouse humanization.

Establishment of a human allergy model using human IL-3/GM-CSF-transgenic NOG mice

The development of animal models that mimic human allergic responses is crucial to study the pathophysiology of disease and to generate new therapeutic methodologies. Humanized mice reconstituted with human immune systems are essential to study human immune reactions in vivo and are expected to be useful for studying human allergies. However, application of this technology to the study of human allergies has been limited, largely because of the poor development of human myeloid cells, especially granulocytes and mast cells, which are responsible for mediating allergic diseases, in conventional humanized mice. In this study, we developed a novel transgenic (Tg) strain, NOD/Shi-scid-IL2rγ(null) (NOG), bearing human IL-3 and GM-CSF genes (NOG IL-3/GM-Tg). In this strain, a large number of human myeloid cells of various lineages developed after transplantation of human CD34⁺ hematopoietic stem cells. Notably, mature basophils and mast cells expressing FcεRI were markedly increased. These humanized NOG IL-3/GM-Tg mice developed passive cutaneous anaphylaxis reactions when administered anti-4-hydroxy-3-nitrophenylacetyl IgE Abs and 4-hydroxy-3-nitrophenylacetyl. More importantly, a combination of serum from Japanese cedar pollinosis patients and cedar pollen extract also elicited strong passive cutaneous anaphylaxis responses in mice. Thus, to our knowledge, our NOG IL-3/GM-Tg mice are the first humanized mouse model to enable the study of human allergic responses in vivo and are excellent tools for preclinical studies of allergic diseases.

Regulation of in vitro human T cell development through interleukin-7 deprivation and anti-CD3 stimulation

BACKGROUND

The role of IL-7 and pre-TCR signaling during T cell development has been well characterized in murine but not in human system. We and others have reported that human BM hematopoietic progenitor cells (HPCs) display poor proliferation, inefficient double negative (DN) to double positive (DP) transition and no functional maturation in the in vitro OP9-Delta-like 1 (DL1) culture system.

RESULTS

In this study, we investigated the importance of optimal IL-7 and pre-TCR signaling during adult human T cell development. Using a modified OP9-DL1 culture ectopically expressing IL-7 and Fms-like tyrosine kinase 3 ligand (Flt3L), we demonstrated enhanced T cell precursor expansion. IL-7 removal at various time points during T cell development promoted a slight increase of DP cells; however, these cells did not differentiate further and underwent cell death. As pre-TCR signaling rescues DN cells from programmed cell death, we treated the culture with anti-CD3 antibody. Upon pre-TCR stimulation, the IL-7 deprived T precursors differentiated into CD3+TCRαβ+DP cells and further matured into functional CD4 T cells, albeit displayed a skewed TCR Vβ repertoire.

CONCLUSIONS

Our study establishes for the first time a critical control for differentiation and maturation of adult human T cells from HPCs by concomitant regulation of IL-7 and pre-TCR signaling.

Challenges and strategies for generating therapeutic patient-specific hemangioblasts and hematopoietic stem cells from human pluripotent stem cells

Recent characterization of hemangioblasts differentiated from human embryonic stem cells (hESC) has further confirmed evidence from murine, zebrafish and avian experimental systems that hematopoietic and endothelial lineages arise from a common progenitor. Such progenitors may provide a valuable resource for delineating the initial developmental steps of human hemato-endotheliogenesis, which is a process normally difficult to study due to the very limited accessibility of early human embryonic/fetal tissues. Moreover, efficient hemangioblast and hematopoietic stem cell (HSC) generation from patient-specific pluripotent stem cells has enormous potential for regenerative medicine, since it could lead to strategies for treating a multitude of hematologic and vascular disorders. However, significant scientific challenges remain in achieving these goals, and the generation of transplantable hemangioblasts and HSC derived from hESC currently remains elusive. Our previous work has suggested that the failure to derive engraftable HSC from hESC is due to the fact that current methodologies for differentiating hESC produce hematopoietic progenitors developmentally similar to those found in the human yolk sac, and are therefore too immature to provide adult-type hematopoietic reconstitution. Herein, we outline the nature of this challenge and propose targeted strategies for generating engraftable human pluripotent stem cell-derived HSC from primitive hemangioblasts using a developmental approach. We also focus on methods by which reprogrammed somatic cells could be used to derive autologous pluripotent stem cells, which in turn could provide unlimited sources of patient-specific hemangioblasts and HSC.

Induction and maintenance of IL-4 expression are regulated differently by the 3' enhancer in CD4 T cells

IL-4 expression is known to be activated in CD4 T cells when they are differentiated to Th2 but not Th1 cells. However, CD4 T cells selected by MH class II-expressing thymocytes, named thymocyte-selected CD4 T cells (T-CD4 T cells), express IL-4 under both Th1 and Th2 conditions. In this study, we investigated molecular mechanisms by which IL-4 gene expression is regulated in T-CD4 T cells. We found that T-CD4 T cells express IL-4 soon after selection in the thymus. Deficiency of DNase I hypersensitive (HS) sites HS5a and HS5 at the 3'-enhancer region in the IL-4 gene decreased IL-4 production, but T-CD4 T cells were able to make IL-4 under the Th1-inducing condition. Consistent with this, IL-4 was expressed in Th1 differentiated T-CD4 T cells in the absence of recombination signal binding protein-J that interacts with HS5. When HS5 was examined separately from other endogenous regulatory elements using a reporter system, CD4 T cells that are selected by thymic epithelial cells cannot transcribe the IL-4 reporter gene with HS5 alone. However, HS5 was able to induce the expression of the IL-4 reporter gene in T-CD4 T cells. Interestingly, the Th1 differentiating signal led to deacetylation at HS5 of the IL-4 endogenous gene, whereas the Th2-inducing environment had no effect. Therefore, in T-CD4 T cells, HS5 plays an essential role during the induction phase of IL-4 expression, but the maintenance of IL-4 expression in Th1 cells requires additional regulatory elements.

The analysis of the functions of human B and T cells in humanized NOD/shi-scid/gammac(null) (NOG) mice (hu-HSC NOG mice)

'Humanized mice' are anticipated to be a valuable tool for studying the human immune system, but the reconstituted human immune cells have not yet been well characterized. Here, we extensively investigated the differentiation and functions of human B and T cells in a supra-immunodeficient mouse strain, NOD/shi-scid/gammac(null) (NOG) reconstituted with CD34(+) hematopoietic stem cells obtained from umbilical cord blood. In these hu-HSC NOG mice, the development of human B cells was partially blocked, and a significant number of B-cell progenitors accumulated in the spleen. The mature CD19(+)IgM(+)IgD(+) human B cells of the hu-HSC NOG mice could produce IgG in vivo and in vitro by antigenic stimulation. In contrast, although human T cells with an apparently normal phenotype developed, most of them could neither proliferate nor produce IL-2 in response to antigenic stimulation by anti-CD3 and anti-CD28 antibodies in vitro. The positive selection of human T cells in the thymus was sufficiently functional, if not complete, and mainly mediated by mouse class II, suggesting that the human T cells lost their function in the periphery. We found that multiple mechanisms were involved in the T-cell abnormalities. Collectively, our results demonstrate that further improvements are necessary before humanized mice with a functional human immune system are achieved.

Effects of liposome-encapsulated hemoglobin on human immune system: evaluation in immunodeficient mice reconstituted with human cord blood stem cells

As preclinical evaluation in animals does not necessarily portray human responses, liposome-encapsulated hemoglobin (LEH), an artificial oxygen carrier, was tested in immunodeficient mice reconstituted with human hematopoietic stem cells (cord blood-transfused NOD/SCID/IL-2R(gammanull)[CB-NOG] mice). Changes in immunocompetent T-cell and B-cell composition in peripheral blood, spleen, and bone marrow were examined 2 and 7 days after 10 mL/kg of intravenous administration of LEH, empty liposome (EL), or saline using immunohistochemical and flow cytometrical techniques in wild-type mice and CB-NOG mice. Responses to intraperitoneal administration of toxic shock syndrome toxin-1 (TSST-1) under the absence or presence of LEH (10 mL/kg) were also determined 4 h and 3 days later in terms of lymphocyte composition and IL-2 plasma level in wild-type as well as CB-NOG mice. When liposome (LEH or EL) was administered to wild-type or CB-NOG mice, the composition of B-cells and T-cells in the spleen or peripheral blood failed to show any consistent or significant changes. The responses to a bacterial antigen (TSST-1) measured by IL-2 production were comparable regardless of the presence or absence of LEH in wild-type as well as in CB-NOG mice. Cellularity, distribution, and maturation of these human cells in peripheral blood, spleen, and bone marrow were comparable among the groups. The results suggest that simple LEH administration may not change immune cellularity, and LEH presence may not largely affect the early T-cell response to bacterial enterotoxins in murine as well as in reconstituted human immune systems.

Establishment and characterization of in vivo human tumor models in the NOD/SCID/gamma(c)(null) mouse

Immunodeficient mice are widely used for xenografts of human cells and tissue. The purpose of the present study was to investigate the characteristics of xenograft human tumor models using engraftment of various non-hematopoietic tumors in the NOD/SCID/gamma(c) (null) mouse. For tumor models, human solid tumor tissues were serially passaged three or more times to establish tissue lines. A total of 326 fresh tumor specimens, mainly gastrointestinal and female genital tissue, were engrafted with 54 established tissue lines. The types of tissue lines varied and included tumor tissue of both epithelial and mesenchymal origin. In some cases the original surgical specimen was replaced with large mononuclear cells. In the established tumor tissue lines, differentiation and tumor structure were similar to that of the original surgical specimen. The interstitium of the xenograft tissue in the tissue lines was relatively well preserved although slightly decreased and replaced by host tissue. These results indicate that human solid tumors can be successfully engrafted into the NOD/SCID/gamma(c) (null) mouse and that tissue lines with the characteristics of the original tumors can be established. Investigators in the field of tumor research will benefit from the availability of tissue lines that allow the establishment of more relevant in vivo human tissue models.

Human intrathymic development: a selective approach

Human T lymphocytes can be generated from CD34 progenitor cells from different sources. This can be obtained in an in vivo model wherein human thymic tissue and fetal liver is transplanted in an immunodeficient mouse. However, human T cells are also generated in immunodeficient mice without co-transplantation of human thymus or in in vitro hybrid human-mouse fetal thymus organ culture. This shows that xenogeneic mouse thymus tissue supports human T cell differentiation. Finally, human T cells are generated on co-culture with murine stromal cells that express the Delta-like1 ligand for the Notch receptor. How these different environments influence the human T cell repertoire is reviewed and discussed.

Antigen-specific antibody production of human B cells in NOG mice reconstituted with the human immune system

Passive antibody administration shows strong potential as a new therapeutic method. In clinical applications, human-derived antibodies with antigen specificity are more useful without putting individuals at risk. Production of human-derived antibodies against given antigens can be obtained from animal models if the human immune system is established in the animals. In fact, past reports revealed that human T and B cells develop from hematopoietic progenitor cells in immunodeficient mice. However, there have been few reports on sufficient induction of antigen-specific antibodies, particularly IgG, in immunodeficient mice reconstituted with human immune cells. In this chapter, we discuss a major shortcoming of induction of antigen-specific IgG antibodies in human immune cells developed in the murine environment based on our data. We demonstrated that human T cell development is restricted by the murine MHC and consequently T cells may not achieve cognate interaction with human B cells. Human B cells developed in the mouse are mainly CD5+B1 cells that preferentially produce IgM. At the same time, human LN transplantation on the spleen enabled NOG mice to produce antigen-specific IgG antibody. These results suggest that if efficient cognate interaction mediated by a certain antigen on MHC class II between human T and B-2 cells occurs, human B cells can produce IgG antibody against a given antigen in the murine environment.

Functional characterization of CD4+CD25+ regulatory T cells differentiated in vitro from bone marrow-derived haematopoietic cells of psoriasis patients with a family history of the disorder

BACKGROUND

In psoriasis CD4+CD25+ regulatory T cells are functionally deficient. The imbalance between regulatory and effector T-cell functions is important for inducing psoriasis. It is reasonable to speculate that the dysfunctional activity of CD4+CD25+ regulatory cells may originate partly from the abnormal haematopoietic cells determined mainly by genetic background.

OBJECTIVES

To test the hypothesis that haematopoietic stem cells are responsible for dysfunctional CD4+CD25+ regulatory cells in psoriasis.

METHODS

Bone marrow-derived CD34+ haematopoietic cells from patients with psoriasis (with a family history of psoriasis) and from normal controls were differentiated into T cells in vitro. CD4+CD25+ T cells were isolated by an immunomagnetic bead method, and proliferation activity and capacity for cytokine secretion were determined. Furthermore, the ability of CD4+CD25+ T cells to suppress the proliferative responses of allogeneous peripheral blood CD4+CD25- effector T cells was assessed in vitro.

RESULTS

The differentiated CD4+CD25+ T cells of psoriatic origin showed similar characteristics to those of normal volunteers, including proliferation activity and secretion profile of the cytokines interleukin (IL)-2, IL-4, IL-8, IL-10 and interferon (IFN)-gamma. However, proliferation and secretion levels of the cytokines IL-2 and IL-10 for CD4+CD25+ cells of psoriatic CD34+ cell origin were significantly lower than those of normal controls in response to streptococcal superantigen (Strep-A). In particular, CD4+CD25+ T cells differentiated from psoriatic CD34+ cells were functionally insufficient to restrain effector T-cell proliferation.

CONCLUSIONS

CD4+CD25+ T cells differentiated in vitro from haematopoietic cells of patients with psoriasis are impaired in regulatory function. The dysfunction of psoriatic CD4+CD25+ T cells may be due to inherent genetic programming passed down from bone marrow-derived haematopoietic cells.

Thymic selection pathway regulates the effector function of CD4 T cells

Recently, a new developmental pathway for CD4 T cells that is mediated by major histocompatibility complex class II-positive thymocytes was identified (Choi, E.Y., K.C. Jung, H.J. Park, D.H. Chung, J.S. Song, S.D. Yang, E. Simpson, and S.H. Park. 2005. Immunity. 23:387-396; Li, W., M.G. Kim, T.S. Gourley, B.P. McCarthy, D.B. Sant'angelo, and C.H. Chang. 2005. Immunity. 23:375-386). We demonstrate that thymocyte-selected CD4 (T-CD4) T cells can rapidly produce interferon gamma and interleukin (IL) 4 upon in vivo and in vitro T cell receptor stimulation. These T-CD4 T cells appear to be effector cells producing both T helper type 1 (Th1) and Th2 cytokines, and they maintain a potential to produce Th2 cytokines under Th1-skewing conditions in a signal transducer and activator of transcription 6-independent manner. The IL-4 mRNA level is high in CD4 single-positive thymocytes if they are selected on thymocytes, which is at least partly caused by enhanced histone acetylation of the IL-4 locus. However, mice that can generate T-CD4 T cells showed attenuated immune responses in an allergen-induced airway inflammation model, suggesting a protective role for T-CD4 T cells during an airway challenge. Our results imply that this thymic selection pathway plays an important role in determining the effector function of the resulting CD4 cells and in regulating immune response.

Development of human–human hybridoma from anti-Her-2 peptide–producing B cells in immunized NOG mouse

OBJECTIVE

Numerous monoclonal antibodies have been developed for the purpose of medical treatments, including cancer treatment. For clinical application, the most useful are human-derived antibodies. In this study, we tried to prepare designed antigen-specific antibodies of completely human origin using immunodeficient mouse.

METHODS

Nonobese diabetic/severe combined immunodeficient/IL-2 receptor gamma null mouse (NOG) mouse was used to reconstitute the human immune system with umbilical cord blood hematopoietic stem cells (CB-NOG mouse) and to prepare human-derived Her-2-epitope-specific antibodies. Hybridoma lines were prepared by fusing the human myeloma cell line Karpas707H.

RESULTS

Serum of immunized NOG mouse contained human-derived immunoglobulin M (IgM) antibodies specific for a short peptide sequence of 20 amino acids, including the epitope peptide of apoptotic Her-2 antibody CH401. Hybridoma lines were successfully prepared with spleen B cells obtained from the immunized CB-NOG mouse. One of these cell lines produced human IgM against the epitope peptide that can recognize surface Her-2 molecule.

CONCLUSION

We could produce human-derived IgM antibody against Her-2 epitope peptide in CB-NOG mouse, succeeding in generation of human hybridoma-secreting IgM against a given peptide.

An Alternate Pathway for CD4 T Cell Development: Thymocyte-Expressed MHC Class II Selects a Distinct T Cell Population

Conventional understanding of CD4 T cell development is that the MHC class II molecules on cortical thymic epithelial cell are necessary for positive selection, as demonstrated in mouse models. Clinical data, however, show that hematopoietic stem cells reconstitute CD4 T cells in patients devoid of MHC class II. Additionally, CD4 T cells generated from human stem cells in immunocompromised mice were restricted to human, but not mouse, MHC class II. These studies suggest an alternative pathway for CD4 T cell development that does not normally exist in mice. MHC class II is expressed on developing human thymocytes, indicating a possible role of MHC II on thymocytes for CD4 T cell generation. Therefore, we created mice in which MHC class II is expressed only on T lineage cells. Remarkably, the CD4 compartment in such mice is efficiently reconstituted with unique specificity, demonstrating a novel thymocyte-driven pathway of CD4 T cell selection.

Functional CD5+ B cells develop predominantly in the spleen of NOD/SCID/gammac(null) (NOG) mice transplanted either with human umbilical cord blood, bone marrow, or mobilized peripheral blood CD34+ cells

OBJECTIVE

Human CD5+ B cells are the major B cell subset in fetal spleen and umbilical cord blood (CB), and their number gradually diminishes in both spleen and peripheral blood from infancy through childhood while conventional B cells increase. In this study, we investigated whether CD5+ cells differentiate from adult hematopoietic stem cells (HSCs) as well as fetal ones in immunodeficient mice.

METHODS

In our system, NOD/SCID/gammac(null) (NOG) mice were transplanted with CD34+ cells from CB (hCB model), adult bone marrow (hBM model), and mobilized peripheral blood (hMPB model).

RESULTS

In these model mice, a high proportion of CD19+IgM+CD5+ mature B cells appeared in the spleen, regardless of the CD34+ cell origin, 4 to 8 weeks after transplantation, while the majority were CD19+IgM-CD5- immature B cells in BM. The CD19+CD5- BM cells showed to express CD5 after the coculture with NOG spleen cells. In the sera of immunized hCB model mice with DNP-KLH, antigen-specific IgM but not IgG was enhanced.

CONCLUSION

Our results show that adult CD34+ cells develop into functional CD5+ B cells in NOG spleen as much as fetal CD34+ cells do.