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

Humoral immune responses in humanized BLT mice immunized with West Nile virus and HIV-1 envelope proteins are largely mediated via human CD5+ B cells

BLT mice, constructed by surgical implantation of human fetal thymus-liver tissues and intravenous delivery of autologous CD34+ haematopoietic stem cells into adult non-obese diabetic/severe combined immunodeficiency mice, were evaluated for vaccine-induced humoral immune responses. Following engraftment, these mice developed a human lymphoid system; however, the majority of the peripheral human B lymphocytes displayed an immature phenotype as evidenced by surface CD10 expression. Over 50% of the human B cells in the periphery but not in the bone marrow also expressed the CD5 antigen, which is found only infrequently on mature follicular B cells in humans. A single intramuscular immunization with recombinant viral envelope antigens, e.g., HIVgp140 and West Nile Virus envelope proteins, together with the immune stimulatory KLK/ODN1a composition) [corrected] adjuvant resulted in seroconversion characterized by antigen-specific human antibodies predominantly of the IgM isotype. However, repeated booster immunizations did not induce secondary immune responses as evidenced by the lack of class switching and specific IgM levels remaining relatively unchanged. Interestingly, the peripheral CD19+  CD5+ but not the CD19+  CD5- human B lymphocytes displayed a late developing CD27+  IgM+ memory phenotype, suggesting that the CD5+ B-cell subset, previously implicated in 'natural antibody' production, may play a role in the vaccine-induced antibody response. Furthermore, human T lymphocytes from these mice demonstrated suboptimal proliferative responses and loss of co-stimulatory surface proteins ex vivo that could be partially reversed with human interleukin-2 and interleukin-7. Therefore, vaccine-induced immune responses in BLT mice resemble a T-cell-independent pathway that can potentially be modulated in vivo by the exogenous delivery of human cytokines/growth factors.

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.

Expression of HLA class II molecules in humanized NOD.Rag1KO.IL2RgcKO mice is critical for development and function of human T and B cells

BACKGROUND

Humanized mice able to reconstitute a surrogate human immune system (HIS) can be used for studies on human immunology and may provide a predictive preclinical model for human vaccines prior to clinical trials. However, current humanized mouse models show sub-optimal human T cell reconstitution and limited ability to support immunoglobulin class switching by human B cells. This limitation has been attributed to the lack of expression of Human Leukocyte Antigens (HLA) molecules in mouse lymphoid organs. Recently, humanized mice expressing HLA class I molecules have been generated but showed little improvement in human T cell reconstitution and function of T and B cells.

METHODS

We have generated NOD.Rag1KO.IL2RγcKO mice expressing HLA class II (HLA-DR4) molecules under the I-E(d) promoter that were infused as adults with HLA-DR-matched human hematopoietic stem cells (HSC). Littermates lacking expression of HLA-DR4 molecules were used as control.

RESULTS

HSC-infused HLA-DR4.NOD.Rag1KO.IL-2RγcKO mice developed a very high reconstitution rate (>90%) with long-lived and functional human T and B cells. Unlike previous humanized mouse models reported in the literature and our control mice, the HLA-DR4 expressing mice reconstituted serum levels (natural antibodies) of human IgM, IgG (all four subclasses), IgA, and IgE comparable to humans, and elicited high titers of specific human IgG antibodies upon tetanus toxoid vaccination.

CONCLUSIONS

Our study demonstrates the critical role of HLA class II molecules for development of functional human T cells able to support immunoglobulin class switching and efficiently respond to vaccination.

Co-transplantation of fetal bone tissue facilitates the development and reconstitution in human B cells in humanized NOD/SCID/IL-2Rγnull (NSG) mice

BACKGROUND

In terms of the function and reconstitution efficacy of human immune cells, co-transplantation of human fetal tissues, such as thymus and liver, with CD34(+) hematopoietic stem cells (HSCs) has potential advantages in the generation of humanized mice.

OBJECTIVE AND METHODS

To examine the effects of bone tissues in the reconstitution of human immune cells, particularly in B cells, we generated a new humanized mice co-transplanted with human fetal thymus (hFT)/fetal bone (hFB) tissues and human fetal liver-derived CD34(+) cells.

RESULTS

Humanized mice exhibited effective reconstitution of human immune cells earlier compared to control humanized mice. In terms of quantity, the number of immune cells, such as human T, B, and monocyte/macrophages was significantly increased. Furthermore, significant increase of B cell progenitors and immature/naïve B cells could be detected in the bone marrow and spleen of humanized mice.

CONCLUSION

Our results demonstrate that co-transplantation of hFB tissue may facilitate the reconstitution of human B and T cells, and therefore the humanized model may be used to develop therapeutic human antibodies for clinical use.

Generation of hematopoietic humanized mice in the newborn BALB/c-Rag2null Il2rγnull mouse model: a multivariable optimization approach

Hematopoietic humanized mice generated via transplantation of human hematopoietic stem cells (hHSCs) into immunodeficient mice are a valuable tool for studying development and function of the human immune system. This study was performed to generate a protocol that improves development and quality of humanized mice in the BALB/c-Rag2(null)Il2rγ(null) strain, testing route of injection, in vitro culture and freezing of hHSCs, types of cytokines in the culture, and co-injection of lineage-depleted CD34(-) cells. Specific hHSC culturing conditions and the addition of support cells were found to increase the frequency, and human hematopoietic chimerism, of humanized mice. The optimized protocol resulted in BALB/c-Rag2(null)Il2rγ(null) humanized mice displaying more consistent human hematopoietic and lymphoid engraftment. Thus, hematopoietic humanized mice generated on a BALB/c immunodeficient background represent a useful model to study the human immune system.

Development of B-lineage predominant lentiviral vectors for use in genetic therapies for B cell disorders

Sustained, targeted, high-level transgene expression in primary B lymphocytes may be useful for gene therapy in B cell disorders. We developed several candidate B-lineage predominant self-inactivating lentiviral vectors (LV) containing alternative enhancer/promoter elements including: the immunoglobulin β (Igβ) (B29) promoter combined with the immunoglobulin µ enhancer (EµB29); and the endogenous BTK promoter with or without Eµ (EµBtkp or Btkp). LV-driven enhanced green fluorescent protein (eGFP) reporter expression was evaluated in cell lines and primary cells derived from human or murine hematopoietic stem cells (HSC). In murine primary cells, EµB29 and EµBtkp LV-mediated high-level expression in immature and mature B cells compared with all other lineages. Expression increased with B cell maturation and was maintained in peripheral subsets. Expression in T and myeloid cells was much lower in percentage and intensity. Similarly, both EµB29 and EµBtkp LV exhibited high-level activity in human primary B cells. In contrast to EµB29, Btkp and EµBtkp LV also exhibited modest activity in myeloid cells, consistent with the expression profile of endogenous Bruton's tyrosine kinase (Btk). Notably, EµB29 and EµBtkp activity was superior in all expression models to an alternative, B-lineage targeted vector containing the EµS.CD19 enhancer/promoter. In summary, EµB29 and EµBtkp LV comprise efficient delivery platforms for gene expression in B-lineage cells.

Characterization of the epithelial cell adhesion molecule (EpCAM)+ cell population in hepatocellular carcinoma cell lines

Accumulating evidence suggests that cancer stem cells (CSC) play an important role in tumorigenicity. Epithelial cell adhesion molecule (EpCAM) is one of the markers that identifies tumor cells with high tumorigenicity. The expression of EpCAM in liver progenitor cells prompted us to investigate whether CSC could be identified in hepatocellular carcinoma (HCC) cell lines. The sorted EpCAM(+) subpopulation from HCC cell lines showed a greater colony formation rate than the sorted EpCAM(-) subpopulation from the same cell lines, although cell proliferation was comparable between the two subpopulations. The in vivo evaluation of tumorigenicity, using supra-immunodeficient NOD/scid/γc(null) (NOG) mice, revealed that a smaller number of EpCAM(+) cells (minimum 100) than EpCAM(-) cells was necessary for tumor formation. The bifurcated differentiation of EpCAM(+) cell clones into both EpCAM(+) and EpCAM(-) cells was obvious both in vitro and in vivo, but EpCAM(-) clones sustained their phenotype. These clonal analyses suggested that EpCAM(+) cells may contain a multipotent cell population. Interestingly, the introduction of exogenous EpCAM into EpCAM(+) clones, but not into EpCAM(-) clones, markedly enhanced their tumor-forming ability, even though both transfectants expressed a similar level of EpCAM. Therefore, the difference in the tumor-forming ability between EpCAM(+) and EpCAM(-) cells is probably due to the intrinsic biological differences between them. Collectively, our results suggest that the EpCAM(+) population is biologically quite different from the EpCAM(-) population in HCC cell lines, and preferentially contains a highly tumorigenic cell population with the characteristics of CSC.

Failure of effector function of human CD8+ T Cells in NOD/SCID/JAK3⁻/⁻ immunodeficient mice transplanted with human CD34+ hematopoietic stem cells

Humanized mice, which are generated by transplanting human CD34⁺ hematopoietic stem cells into immunodeficient mice, are expected to be useful for the research on human immune responses. It is reported that antigen-specific T cell responses occur in immunodeficient mice transplanted with both human fetal thymus/liver tissues and CD34⁺ fetal cells, but it remains unclear whether antigen-specific T cell responses occur in those transplanted with only human CD34⁺ hematopoietic stem cells (HSCs). Here we investigated the differentiation and function of human CD8⁺ T cells reconstituted in NOD/SCID/Jak3^−/− mice transplanted with human CD34⁺ HSCs (hNOK mice). Multicolor flow cytometric analysis demonstrated that human CD8⁺ T cells generated from the CD34⁺ HSCs comprised only 3 subtypes, i.e., CD27^highCD28⁺CD45RA⁺CCR7⁺, CD27⁺CD28⁺CD45RA⁻CCR7⁺, and CD27⁺CD28⁺CD45RA⁻CCR7⁻ and had 3 phenotypes for 3 lytic molecules, i.e., perforin(Per)⁻granzymeA(GraA)⁻granzymeB(GraB)⁻, Per⁻GraA⁺GraB⁻, and Per^lowGraA⁺GraB⁺. These CD8⁺ T cells failed to produce IFN-γ and to proliferate after stimulation with alloantigens. These results indicate that the antigen-specific T cell response cannot be elicited in mice transplanted with only human CD34⁺ HSCs, because the T cells fail to develop normally in such mice.

Progenitor cell dose determines the pace and completeness of engraftment in a xenograft model for cord blood transplantation

Two critical concerns in clinical cord blood transplantation are the initial time to engraftment and the subsequent restoration of immune function. These studies measured the impact of progenitor cell dose on both the pace and strength of hematopoietic reconstitution by transplanting nonobese diabetic/severe combined immunodeficiency/interleukin-2 receptor-gamma-null (NSγ) mice with lineage-depleted aldehyde dehydrogenase-bright CD34(+) human cord blood progenitors. The progress of each transplant was monitored over an extended time course by repeatedly analyzing the peripheral blood for human hematopoietic cells. In vivo human hematopoietic development was complete. After long-term transplantation assays (≥ 19 weeks), human T-cell development was documented within multiple tissues in 16 of 32 NSγ mice. Human T-cell differentiation was active within NSγ thymuses, as documented by the presence of CD4(+) CD8(+) T-cell progenitors as well as T-cell receptor excision circles. It is important to note that although myeloid and B-cell engraftment was detected as early as 4 weeks after transplantation, human T-cell development was exclusively late onset. High progenitor cell doses were associated with a robust human hematopoietic chimerism that accelerated both initial time to engraftment and subsequent T-cell development. At lower progenitor cell doses, the chimerism was weak and the human hematopoietic lineage development was frequently incomplete.

Long-term human CD34+ stem cell-engrafted nonobese diabetic/SCID/IL-2R gamma(null) mice show impaired CD8+ T cell maintenance and a functional arrest of immature NK cells

Allogeneic hematopoietic stem cell transplantation represents the most effective form of immunotherapy for chemorefractory diseases. However, animal models have been missing that allow evaluation of donor-patient-specific graft-versus-leukemia effects. Thus, we sought to establish a patient-tailored humanized mouse model that would result in long-term engraftment of various lymphocytic lineages and would serve as a donor-specific surrogate. Following transfer of donor-derived peripheral blood stem cells into NOD/SCID/IL-2Rgamma(null) (NSG) mice with supplementation of human IL-7, we could demonstrate robust engraftment and multilineage differentiation comparable to earlier studies using cord blood stem cells. Phenotypical and functional analyses of lymphoid lineages revealed that >20 wk posthematopoietic stem cell transplantation, the majority of T lymphocytes consisted of memory-type CD4(+) T cells capable of inducing specific immune functions, whereas CD8(+) T cells were only present in low numbers. Analysis of NSG-derived NK cells revealed the expression of constitutively activated CD56(bright)CD16(-) killer Ig-like receptor(negative) NK cells that exhibited functional impairments. Thus, the data presented in this study demonstrate that humanized NSG mice can be successfully used to develop a xenotransplantation model that might allow patient-tailored treatment strategies in the future, but also highlight the need to improve this model, for example, by coadministration of differentiation-promoting cytokines and induction of human MHC molecules to complement existing deficiencies in NK and CD8(+) T cell development.

Analysis of innate defences against Plasmodium falciparum in immunodeficient mice

BACKGROUND

Mice with genetic deficiencies in adaptive immunity are used for the grafting of human cells or pathogens, to study human diseases, however, the innate immune responses to xenografts in these mice has received little attention. Using the NOD/SCID Plasmodium falciparum mouse model an analysis of innate defences responsible for the substantial control of P. falciparum which remains in such mice, was performed.

METHODS

NOD/SCID mice undergoing an immunomodulatory protocol that includes, clodronate-loaded liposomes to deplete macrophages and an anti-polymorphonuclear leukocytes antibody, were grafted with human red blood cells and P. falciparum. The systematic and kinetic analysis of the remaining innate immune responses included the number and phenotype of peripheral blood leukocytes as well as inflammatory cytokines/chemokines released in periphery. The innate responses towards the murine parasite Plasmodium yoelii were used as a control.

RESULTS

Results show that 1) P. falciparum induces a strong inflammation characterized by an increase in circulating leukocytes and the release of inflammatory cytokines; 2) in contrast, the rodent parasite P. yoelii, induces a far more moderate inflammation; 3) human red blood cells and the anti-inflammatory agents employed induce low-grade inflammation; and 4) macrophages seem to bear the most critical function in controlling P. falciparum survival in those mice, whereas polymorphonuclear and NK cells have only a minor role.

CONCLUSIONS

Despite the use of an immunomodulatory treatment, immunodeficient NOD/SCID mice are still able to mount substantial innate responses that seem to be correlated with parasite clearance. Those results bring new insights on the ability of innate immunity from immunodeficient mice to control xenografts of cells of human origin and human pathogens.

Humanized mouse models to study human diseases

PURPOSE OF REVIEW

Update on humanized mouse models and their use in biomedical research.

RECENT FINDINGS

The recent description of immunodeficient mice bearing a mutated IL-2 receptor gamma chain (IL2rgamma) facilitated greatly the engraftment and function of human hematolymphoid cells and other cells and tissues. These mice permit the development of human immune systems, including functional T and B cells, following engraftment of hematopoietic stem cells (HSCs). The engrafted functional human immune systems are capable of T and B cell-dependent immune responses, antibody production, antiviral responses, and allograft rejection. Immunodeficient IL2rgamma(null) mice also support heightened engraftment of primary human cancers and malignant progenitor cells, permitting in-vivo investigation of pathogenesis and function. In addition, human-specific infectious agents for which animal models were previously unavailable can now be studied in vivo using these new-generation humanized mice.

SUMMARY

Immunodeficient mice bearing an IL2rgamma(null) mutated gene can be engrafted with functional human cells and tissues, including human immune systems, following engraftment with human hematolymphoid cells. These mice are now used as in-vivo models to study human hematopoiesis, immunity, regeneration, stem cell function, cancer, and human-specific infectious agents without putting patients at risk.

Current humanized mouse models for studying human immunology and HIV-1 immuno-pathogenesis

A robust animal model for "hypothesis-testing/mechanistic" research in human immunology and immuno-pathology should meet the following criteria. First, it has well-studied hemato-lymphoid organs and target cells similar to those of humans. Second, the human pathogens establish infection and lead to relevant diseases. Third, it is genetically inbred and can be manipulated via genetic, immunological and pharmacological means. Many human-tropic pathogens such as HIV-1 fail to infect murine cells due to the blocks at multiple steps of their life cycle. The mouse with a reconstituted human immune system and other human target organs is a good candidate. A number of human-mouse chimeric models with human immune cells have been developed in the past 20 years, but most with only limited success due to the selective engraftment of xeno-reactive human T cells in hu-PBL-SCID mice or the lack of significant human immune responses in the SCID-hu Thy/Liv mouse. This review summarizes the current understanding of HIV-1 immuno-pathogenesis in human patients and in SIV-infected primate models. It also reviews the recent progress in the development of humanized mouse models with a functional human immune system, especially the recent progress in the immunodeficient mice that carry a defective gammaC gene. NOD/SCID/gammaC(-/-) (NOG or NSG) or the Rag2(-/-)gammaC(-/-) double knockout (DKO) mice, which lack NK as well as T and B cells (NTB-null mice), have been used to reconstitute a functional human immune system in central and peripheral lymphoid organs with human CD34(+) HSC. These NTB-hu HSC humanized models have been used to investigate HIV-1 infection, immuno-pathogenesis and therapeutic interventions. Such models, with further improvements, will contribute to study human immunology, human-tropic pathogens as well as human stem cell biology in the tissue development and function in vivo.

A novel active mouse model for bullous pemphigoid targeting humanized pathogenic antigen

Bullous pemphigoid (BP), the most common autoimmune blistering disease, is caused by autoantibodies against type XVII collagen (COL17). To establish an active stable BP animal model that demonstrates the persistent inflammatory skin lesions initiated by the anti-human COL17 Abs, we used COL17-humanized (COL17(m-/-,h+)) mice that we recently produced. First, we generated immunodeficient Rag-2(-/-)/COL17-humanized mice by crossing Rag-2(-/-) mice with COL17-humanized mice. Then, splenocytes from wild-type mice that had been immunized by grafting of human COL17-transgenic mouse skin were transferred into Rag-2(-/-)/COL17-humanized mice. The recipient mice continuously produced anti-human COL17 IgG Abs in vivo and developed blisters and erosions corresponding to clinical, histological, and immunopathological features of BP, although eosinophil infiltration, one of the characteristic histological findings observed in BP patients, was not detected in the recipients. Although the depletion of CD8(+) T cells from the immunized splenocytes was found to produce no effects in the recipients, the depletion of CD4(+) T cells as well as CD45R(+) B cells was found to inhibit the production of anti-human COL17 IgG Abs in the recipients, resulting in no apparent clinical phenotype. Furthermore, we demonstrated that cyclosporin A significantly suppressed the production of anti-human COL17 IgG Abs and prevented the development of the BP phenotype in the treated recipients. Although this model in an immunodeficient mouse does not exactly reproduce the induction mechanism of BP in human patients, this unique experimental system targeting humanized pathogenic Ag allows us to investigate ongoing autoimmune responses to human molecules in experimental animal models.